Rename ra_hir_ty -> hir_ty

crates/hir_ty/src/autoderef.rs

@@ -0,0 +1,131 @@
+//! In certain situations, rust automatically inserts derefs as necessary: for
+//! example, field accesses `foo.bar` still work when `foo` is actually a
+//! reference to a type with the field `bar`. This is an approximation of the
+//! logic in rustc (which lives in librustc_typeck/check/autoderef.rs).
+
+use std::iter::successors;
+
+use base_db::CrateId;
+use hir_def::lang_item::LangItemTarget;
+use hir_expand::name::name;
+use log::{info, warn};
+
+use crate::{
+    db::HirDatabase,
+    traits::{InEnvironment, Solution},
+    utils::generics,
+    BoundVar, Canonical, DebruijnIndex, Obligation, Substs, TraitRef, Ty,
+};
+
+const AUTODEREF_RECURSION_LIMIT: usize = 10;
+
+pub fn autoderef<'a>(
+    db: &'a dyn HirDatabase,
+    krate: Option<CrateId>,
+    ty: InEnvironment<Canonical<Ty>>,
+) -> impl Iterator<Item = Canonical<Ty>> + 'a {
+    let InEnvironment { value: ty, environment } = ty;
+    successors(Some(ty), move |ty| {
+        deref(db, krate?, InEnvironment { value: ty, environment: environment.clone() })
+    })
+    .take(AUTODEREF_RECURSION_LIMIT)
+}
+
+pub(crate) fn deref(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    ty: InEnvironment<&Canonical<Ty>>,
+) -> Option<Canonical<Ty>> {
+    if let Some(derefed) = ty.value.value.builtin_deref() {
+        Some(Canonical { value: derefed, kinds: ty.value.kinds.clone() })
+    } else {
+        deref_by_trait(db, krate, ty)
+    }
+}
+
+fn deref_by_trait(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    ty: InEnvironment<&Canonical<Ty>>,
+) -> Option<Canonical<Ty>> {
+    let deref_trait = match db.lang_item(krate, "deref".into())? {
+        LangItemTarget::TraitId(it) => it,
+        _ => return None,
+    };
+    let target = db.trait_data(deref_trait).associated_type_by_name(&name![Target])?;
+
+    let generic_params = generics(db.upcast(), target.into());
+    if generic_params.len() != 1 {
+        // the Target type + Deref trait should only have one generic parameter,
+        // namely Deref's Self type
+        return None;
+    }
+
+    // FIXME make the Canonical / bound var handling nicer
+
+    let parameters =
+        Substs::build_for_generics(&generic_params).push(ty.value.value.clone()).build();
+
+    // Check that the type implements Deref at all
+    let trait_ref = TraitRef { trait_: deref_trait, substs: parameters.clone() };
+    let implements_goal = Canonical {
+        kinds: ty.value.kinds.clone(),
+        value: InEnvironment {
+            value: Obligation::Trait(trait_ref),
+            environment: ty.environment.clone(),
+        },
+    };
+    if db.trait_solve(krate, implements_goal).is_none() {
+        return None;
+    }
+
+    // Now do the assoc type projection
+    let projection = super::traits::ProjectionPredicate {
+        ty: Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, ty.value.kinds.len())),
+        projection_ty: super::ProjectionTy { associated_ty: target, parameters },
+    };
+
+    let obligation = super::Obligation::Projection(projection);
+
+    let in_env = InEnvironment { value: obligation, environment: ty.environment };
+
+    let canonical =
+        Canonical::new(in_env, ty.value.kinds.iter().copied().chain(Some(super::TyKind::General)));
+
+    let solution = db.trait_solve(krate, canonical)?;
+
+    match &solution {
+        Solution::Unique(vars) => {
+            // FIXME: vars may contain solutions for any inference variables
+            // that happened to be inside ty. To correctly handle these, we
+            // would have to pass the solution up to the inference context, but
+            // that requires a larger refactoring (especially if the deref
+            // happens during method resolution). So for the moment, we just
+            // check that we're not in the situation we're we would actually
+            // need to handle the values of the additional variables, i.e.
+            // they're just being 'passed through'. In the 'standard' case where
+            // we have `impl<T> Deref for Foo<T> { Target = T }`, that should be
+            // the case.
+
+            // FIXME: if the trait solver decides to truncate the type, these
+            // assumptions will be broken. We would need to properly introduce
+            // new variables in that case
+
+            for i in 1..vars.0.kinds.len() {
+                if vars.0.value[i - 1] != Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
+                {
+                    warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.value, solution);
+                    return None;
+                }
+            }
+            Some(Canonical {
+                value: vars.0.value[vars.0.value.len() - 1].clone(),
+                kinds: vars.0.kinds.clone(),
+            })
+        }
+        Solution::Ambig(_) => {
+            info!("Ambiguous solution for derefing {:?}: {:?}", ty.value, solution);
+            None
+        }
+    }
+}

crates/hir_ty/src/db.rs

@@ -0,0 +1,158 @@
+//! FIXME: write short doc here
+
+use std::sync::Arc;
+
+use arena::map::ArenaMap;
+use base_db::{impl_intern_key, salsa, CrateId, Upcast};
+use hir_def::{
+    db::DefDatabase, expr::ExprId, DefWithBodyId, FunctionId, GenericDefId, ImplId, LocalFieldId,
+    TypeParamId, VariantId,
+};
+
+use crate::{
+    method_resolution::{InherentImpls, TraitImpls},
+    traits::chalk,
+    Binders, CallableDefId, GenericPredicate, InferenceResult, OpaqueTyId, PolyFnSig,
+    ReturnTypeImplTraits, TraitRef, Ty, TyDefId, ValueTyDefId,
+};
+use hir_expand::name::Name;
+
+#[salsa::query_group(HirDatabaseStorage)]
+pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
+    #[salsa::invoke(infer_wait)]
+    #[salsa::transparent]
+    fn infer(&self, def: DefWithBodyId) -> Arc<InferenceResult>;
+
+    #[salsa::invoke(crate::infer::infer_query)]
+    fn infer_query(&self, def: DefWithBodyId) -> Arc<InferenceResult>;
+
+    #[salsa::invoke(crate::lower::ty_query)]
+    #[salsa::cycle(crate::lower::ty_recover)]
+    fn ty(&self, def: TyDefId) -> Binders<Ty>;
+
+    #[salsa::invoke(crate::lower::value_ty_query)]
+    fn value_ty(&self, def: ValueTyDefId) -> Binders<Ty>;
+
+    #[salsa::invoke(crate::lower::impl_self_ty_query)]
+    #[salsa::cycle(crate::lower::impl_self_ty_recover)]
+    fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
+
+    #[salsa::invoke(crate::lower::impl_trait_query)]
+    fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
+
+    #[salsa::invoke(crate::lower::field_types_query)]
+    fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>>;
+
+    #[salsa::invoke(crate::callable_item_sig)]
+    fn callable_item_signature(&self, def: CallableDefId) -> PolyFnSig;
+
+    #[salsa::invoke(crate::lower::return_type_impl_traits)]
+    fn return_type_impl_traits(
+        &self,
+        def: FunctionId,
+    ) -> Option<Arc<Binders<ReturnTypeImplTraits>>>;
+
+    #[salsa::invoke(crate::lower::generic_predicates_for_param_query)]
+    #[salsa::cycle(crate::lower::generic_predicates_for_param_recover)]
+    fn generic_predicates_for_param(
+        &self,
+        param_id: TypeParamId,
+    ) -> Arc<[Binders<GenericPredicate>]>;
+
+    #[salsa::invoke(crate::lower::generic_predicates_query)]
+    fn generic_predicates(&self, def: GenericDefId) -> Arc<[Binders<GenericPredicate>]>;
+
+    #[salsa::invoke(crate::lower::generic_defaults_query)]
+    fn generic_defaults(&self, def: GenericDefId) -> Arc<[Binders<Ty>]>;
+
+    #[salsa::invoke(InherentImpls::inherent_impls_in_crate_query)]
+    fn inherent_impls_in_crate(&self, krate: CrateId) -> Arc<InherentImpls>;
+
+    #[salsa::invoke(TraitImpls::trait_impls_in_crate_query)]
+    fn trait_impls_in_crate(&self, krate: CrateId) -> Arc<TraitImpls>;
+
+    #[salsa::invoke(TraitImpls::trait_impls_in_deps_query)]
+    fn trait_impls_in_deps(&self, krate: CrateId) -> Arc<TraitImpls>;
+
+    // Interned IDs for Chalk integration
+    #[salsa::interned]
+    fn intern_callable_def(&self, callable_def: CallableDefId) -> InternedCallableDefId;
+    #[salsa::interned]
+    fn intern_type_param_id(&self, param_id: TypeParamId) -> GlobalTypeParamId;
+    #[salsa::interned]
+    fn intern_impl_trait_id(&self, id: OpaqueTyId) -> InternedOpaqueTyId;
+    #[salsa::interned]
+    fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> ClosureId;
+
+    #[salsa::invoke(chalk::associated_ty_data_query)]
+    fn associated_ty_data(&self, id: chalk::AssocTypeId) -> Arc<chalk::AssociatedTyDatum>;
+
+    #[salsa::invoke(chalk::trait_datum_query)]
+    fn trait_datum(&self, krate: CrateId, trait_id: chalk::TraitId) -> Arc<chalk::TraitDatum>;
+
+    #[salsa::invoke(chalk::struct_datum_query)]
+    fn struct_datum(&self, krate: CrateId, struct_id: chalk::AdtId) -> Arc<chalk::StructDatum>;
+
+    #[salsa::invoke(crate::traits::chalk::impl_datum_query)]
+    fn impl_datum(&self, krate: CrateId, impl_id: chalk::ImplId) -> Arc<chalk::ImplDatum>;
+
+    #[salsa::invoke(crate::traits::chalk::fn_def_datum_query)]
+    fn fn_def_datum(&self, krate: CrateId, fn_def_id: chalk::FnDefId) -> Arc<chalk::FnDefDatum>;
+
+    #[salsa::invoke(crate::traits::chalk::associated_ty_value_query)]
+    fn associated_ty_value(
+        &self,
+        krate: CrateId,
+        id: chalk::AssociatedTyValueId,
+    ) -> Arc<chalk::AssociatedTyValue>;
+
+    #[salsa::invoke(crate::traits::trait_solve_query)]
+    fn trait_solve(
+        &self,
+        krate: CrateId,
+        goal: crate::Canonical<crate::InEnvironment<crate::Obligation>>,
+    ) -> Option<crate::traits::Solution>;
+
+    #[salsa::invoke(crate::traits::chalk::program_clauses_for_chalk_env_query)]
+    fn program_clauses_for_chalk_env(
+        &self,
+        krate: CrateId,
+        env: chalk_ir::Environment<chalk::Interner>,
+    ) -> chalk_ir::ProgramClauses<chalk::Interner>;
+}
+
+fn infer_wait(db: &impl HirDatabase, def: DefWithBodyId) -> Arc<InferenceResult> {
+    let _p = profile::span("infer:wait").detail(|| match def {
+        DefWithBodyId::FunctionId(it) => db.function_data(it).name.to_string(),
+        DefWithBodyId::StaticId(it) => {
+            db.static_data(it).name.clone().unwrap_or_else(Name::missing).to_string()
+        }
+        DefWithBodyId::ConstId(it) => {
+            db.const_data(it).name.clone().unwrap_or_else(Name::missing).to_string()
+        }
+    });
+    db.infer_query(def)
+}
+
+#[test]
+fn hir_database_is_object_safe() {
+    fn _assert_object_safe(_: &dyn HirDatabase) {}
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct GlobalTypeParamId(salsa::InternId);
+impl_intern_key!(GlobalTypeParamId);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct InternedOpaqueTyId(salsa::InternId);
+impl_intern_key!(InternedOpaqueTyId);
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct ClosureId(salsa::InternId);
+impl_intern_key!(ClosureId);
+
+/// This exists just for Chalk, because Chalk just has a single `FnDefId` where
+/// we have different IDs for struct and enum variant constructors.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Ord, PartialOrd)]
+pub struct InternedCallableDefId(salsa::InternId);
+impl_intern_key!(InternedCallableDefId);

crates/hir_ty/src/diagnostics.rs

@@ -0,0 +1,444 @@
+//! FIXME: write short doc here
+mod expr;
+mod match_check;
+mod unsafe_check;
+
+use std::any::Any;
+
+use hir_def::DefWithBodyId;
+use hir_expand::diagnostics::{Diagnostic, DiagnosticSink};
+use hir_expand::{name::Name, HirFileId, InFile};
+use stdx::format_to;
+use syntax::{ast, AstPtr, SyntaxNodePtr};
+
+use crate::db::HirDatabase;
+
+pub use crate::diagnostics::expr::{record_literal_missing_fields, record_pattern_missing_fields};
+
+pub fn validate_body(db: &dyn HirDatabase, owner: DefWithBodyId, sink: &mut DiagnosticSink<'_>) {
+    let _p = profile::span("validate_body");
+    let infer = db.infer(owner);
+    infer.add_diagnostics(db, owner, sink);
+    let mut validator = expr::ExprValidator::new(owner, infer.clone(), sink);
+    validator.validate_body(db);
+    let mut validator = unsafe_check::UnsafeValidator::new(owner, infer, sink);
+    validator.validate_body(db);
+}
+
+#[derive(Debug)]
+pub struct NoSuchField {
+    pub file: HirFileId,
+    pub field: AstPtr<ast::RecordExprField>,
+}
+
+impl Diagnostic for NoSuchField {
+    fn message(&self) -> String {
+        "no such field".to_string()
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.field.clone().into())
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MissingFields {
+    pub file: HirFileId,
+    pub field_list_parent: AstPtr<ast::RecordExpr>,
+    pub field_list_parent_path: Option<AstPtr<ast::Path>>,
+    pub missed_fields: Vec<Name>,
+}
+
+impl Diagnostic for MissingFields {
+    fn message(&self) -> String {
+        let mut buf = String::from("Missing structure fields:\n");
+        for field in &self.missed_fields {
+            format_to!(buf, "- {}\n", field);
+        }
+        buf
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile {
+            file_id: self.file,
+            value: self
+                .field_list_parent_path
+                .clone()
+                .map(SyntaxNodePtr::from)
+                .unwrap_or_else(|| self.field_list_parent.clone().into()),
+        }
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MissingPatFields {
+    pub file: HirFileId,
+    pub field_list_parent: AstPtr<ast::RecordPat>,
+    pub field_list_parent_path: Option<AstPtr<ast::Path>>,
+    pub missed_fields: Vec<Name>,
+}
+
+impl Diagnostic for MissingPatFields {
+    fn message(&self) -> String {
+        let mut buf = String::from("Missing structure fields:\n");
+        for field in &self.missed_fields {
+            format_to!(buf, "- {}\n", field);
+        }
+        buf
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile {
+            file_id: self.file,
+            value: self
+                .field_list_parent_path
+                .clone()
+                .map(SyntaxNodePtr::from)
+                .unwrap_or_else(|| self.field_list_parent.clone().into()),
+        }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MissingMatchArms {
+    pub file: HirFileId,
+    pub match_expr: AstPtr<ast::Expr>,
+    pub arms: AstPtr<ast::MatchArmList>,
+}
+
+impl Diagnostic for MissingMatchArms {
+    fn message(&self) -> String {
+        String::from("Missing match arm")
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.match_expr.clone().into() }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MissingOkInTailExpr {
+    pub file: HirFileId,
+    pub expr: AstPtr<ast::Expr>,
+}
+
+impl Diagnostic for MissingOkInTailExpr {
+    fn message(&self) -> String {
+        "wrap return expression in Ok".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.expr.clone().into() }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct BreakOutsideOfLoop {
+    pub file: HirFileId,
+    pub expr: AstPtr<ast::Expr>,
+}
+
+impl Diagnostic for BreakOutsideOfLoop {
+    fn message(&self) -> String {
+        "break outside of loop".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.expr.clone().into() }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MissingUnsafe {
+    pub file: HirFileId,
+    pub expr: AstPtr<ast::Expr>,
+}
+
+impl Diagnostic for MissingUnsafe {
+    fn message(&self) -> String {
+        format!("This operation is unsafe and requires an unsafe function or block")
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.expr.clone().into() }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
+#[derive(Debug)]
+pub struct MismatchedArgCount {
+    pub file: HirFileId,
+    pub call_expr: AstPtr<ast::Expr>,
+    pub expected: usize,
+    pub found: usize,
+}
+
+impl Diagnostic for MismatchedArgCount {
+    fn message(&self) -> String {
+        let s = if self.expected == 1 { "" } else { "s" };
+        format!("Expected {} argument{}, found {}", self.expected, s, self.found)
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.call_expr.clone().into() }
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+    fn is_experimental(&self) -> bool {
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use base_db::{fixture::WithFixture, FileId, SourceDatabase, SourceDatabaseExt};
+    use hir_def::{db::DefDatabase, AssocItemId, ModuleDefId};
+    use hir_expand::{
+        db::AstDatabase,
+        diagnostics::{Diagnostic, DiagnosticSinkBuilder},
+    };
+    use rustc_hash::FxHashMap;
+    use syntax::{TextRange, TextSize};
+
+    use crate::{diagnostics::validate_body, test_db::TestDB};
+
+    impl TestDB {
+        fn diagnostics<F: FnMut(&dyn Diagnostic)>(&self, mut cb: F) {
+            let crate_graph = self.crate_graph();
+            for krate in crate_graph.iter() {
+                let crate_def_map = self.crate_def_map(krate);
+
+                let mut fns = Vec::new();
+                for (module_id, _) in crate_def_map.modules.iter() {
+                    for decl in crate_def_map[module_id].scope.declarations() {
+                        if let ModuleDefId::FunctionId(f) = decl {
+                            fns.push(f)
+                        }
+                    }
+
+                    for impl_id in crate_def_map[module_id].scope.impls() {
+                        let impl_data = self.impl_data(impl_id);
+                        for item in impl_data.items.iter() {
+                            if let AssocItemId::FunctionId(f) = item {
+                                fns.push(*f)
+                            }
+                        }
+                    }
+                }
+
+                for f in fns {
+                    let mut sink = DiagnosticSinkBuilder::new().build(&mut cb);
+                    validate_body(self, f.into(), &mut sink);
+                }
+            }
+        }
+    }
+
+    pub(crate) fn check_diagnostics(ra_fixture: &str) {
+        let db = TestDB::with_files(ra_fixture);
+        let annotations = db.extract_annotations();
+
+        let mut actual: FxHashMap<FileId, Vec<(TextRange, String)>> = FxHashMap::default();
+        db.diagnostics(|d| {
+            let src = d.display_source();
+            let root = db.parse_or_expand(src.file_id).unwrap();
+            // FIXME: macros...
+            let file_id = src.file_id.original_file(&db);
+            let range = src.value.to_node(&root).text_range();
+            let message = d.message().to_owned();
+            actual.entry(file_id).or_default().push((range, message));
+        });
+
+        for (file_id, diags) in actual.iter_mut() {
+            diags.sort_by_key(|it| it.0.start());
+            let text = db.file_text(*file_id);
+            // For multiline spans, place them on line start
+            for (range, content) in diags {
+                if text[*range].contains('\n') {
+                    *range = TextRange::new(range.start(), range.start() + TextSize::from(1));
+                    *content = format!("... {}", content);
+                }
+            }
+        }
+
+        assert_eq!(annotations, actual);
+    }
+
+    #[test]
+    fn no_such_field_diagnostics() {
+        check_diagnostics(
+            r#"
+struct S { foo: i32, bar: () }
+impl S {
+    fn new() -> S {
+        S {
+      //^ Missing structure fields:
+      //|    - bar
+            foo: 92,
+            baz: 62,
+          //^^^^^^^ no such field
+        }
+    }
+}
+"#,
+        );
+    }
+    #[test]
+    fn no_such_field_with_feature_flag_diagnostics() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+struct MyStruct {
+    my_val: usize,
+    #[cfg(feature = "foo")]
+    bar: bool,
+}
+
+impl MyStruct {
+    #[cfg(feature = "foo")]
+    pub(crate) fn new(my_val: usize, bar: bool) -> Self {
+        Self { my_val, bar }
+    }
+    #[cfg(not(feature = "foo"))]
+    pub(crate) fn new(my_val: usize, _bar: bool) -> Self {
+        Self { my_val }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_enum_with_feature_flag_diagnostics() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+enum Foo {
+    #[cfg(not(feature = "foo"))]
+    Buz,
+    #[cfg(feature = "foo")]
+    Bar,
+    Baz
+}
+
+fn test_fn(f: Foo) {
+    match f {
+        Foo::Bar => {},
+        Foo::Baz => {},
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_with_feature_flag_diagnostics_on_struct_lit() {
+        check_diagnostics(
+            r#"
+//- /lib.rs crate:foo cfg:feature=foo
+struct S {
+    #[cfg(feature = "foo")]
+    foo: u32,
+    #[cfg(not(feature = "foo"))]
+    bar: u32,
+}
+
+impl S {
+    #[cfg(feature = "foo")]
+    fn new(foo: u32) -> Self {
+        Self { foo }
+    }
+    #[cfg(not(feature = "foo"))]
+    fn new(bar: u32) -> Self {
+        Self { bar }
+    }
+    fn new2(bar: u32) -> Self {
+        #[cfg(feature = "foo")]
+        { Self { foo: bar } }
+        #[cfg(not(feature = "foo"))]
+        { Self { bar } }
+    }
+    fn new2(val: u32) -> Self {
+        Self {
+            #[cfg(feature = "foo")]
+            foo: val,
+            #[cfg(not(feature = "foo"))]
+            bar: val,
+        }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_such_field_with_type_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! Type { () => { u32 }; }
+struct Foo { bar: Type![] }
+
+impl Foo {
+    fn new() -> Self {
+        Foo { bar: 0 }
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn missing_record_pat_field_diagnostic() {
+        check_diagnostics(
+            r#"
+struct S { foo: i32, bar: () }
+fn baz(s: S) {
+    let S { foo: _ } = s;
+      //^ Missing structure fields:
+      //| - bar
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn missing_record_pat_field_no_diagnostic_if_not_exhaustive() {
+        check_diagnostics(
+            r"
+struct S { foo: i32, bar: () }
+fn baz(s: S) -> i32 {
+    match s {
+        S { foo, .. } => foo,
+    }
+}
+",
+        )
+    }
+
+    #[test]
+    fn break_outside_of_loop() {
+        check_diagnostics(
+            r#"
+fn foo() { break; }
+         //^^^^^ break outside of loop
+"#,
+        );
+    }
+}

crates/hir_ty/src/diagnostics/expr.rs

@@ -0,0 +1,569 @@
+//! FIXME: write short doc here
+
+use std::sync::Arc;
+
+use hir_def::{path::path, resolver::HasResolver, AdtId, DefWithBodyId};
+use hir_expand::diagnostics::DiagnosticSink;
+use rustc_hash::FxHashSet;
+use syntax::{ast, AstPtr};
+
+use crate::{
+    db::HirDatabase,
+    diagnostics::{
+        match_check::{is_useful, MatchCheckCtx, Matrix, PatStack, Usefulness},
+        MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkInTailExpr, MissingPatFields,
+    },
+    utils::variant_data,
+    ApplicationTy, InferenceResult, Ty, TypeCtor,
+};
+
+pub use hir_def::{
+    body::{
+        scope::{ExprScopes, ScopeEntry, ScopeId},
+        Body, BodySourceMap, ExprPtr, ExprSource, PatPtr, PatSource,
+    },
+    expr::{
+        ArithOp, Array, BinaryOp, BindingAnnotation, CmpOp, Expr, ExprId, Literal, LogicOp,
+        MatchArm, Ordering, Pat, PatId, RecordFieldPat, RecordLitField, Statement, UnaryOp,
+    },
+    src::HasSource,
+    LocalFieldId, Lookup, VariantId,
+};
+
+pub(super) struct ExprValidator<'a, 'b: 'a> {
+    owner: DefWithBodyId,
+    infer: Arc<InferenceResult>,
+    sink: &'a mut DiagnosticSink<'b>,
+}
+
+impl<'a, 'b> ExprValidator<'a, 'b> {
+    pub(super) fn new(
+        owner: DefWithBodyId,
+        infer: Arc<InferenceResult>,
+        sink: &'a mut DiagnosticSink<'b>,
+    ) -> ExprValidator<'a, 'b> {
+        ExprValidator { owner, infer, sink }
+    }
+
+    pub(super) fn validate_body(&mut self, db: &dyn HirDatabase) {
+        let body = db.body(self.owner.into());
+
+        for (id, expr) in body.exprs.iter() {
+            if let Some((variant_def, missed_fields, true)) =
+                record_literal_missing_fields(db, &self.infer, id, expr)
+            {
+                self.create_record_literal_missing_fields_diagnostic(
+                    id,
+                    db,
+                    variant_def,
+                    missed_fields,
+                );
+            }
+
+            match expr {
+                Expr::Match { expr, arms } => {
+                    self.validate_match(id, *expr, arms, db, self.infer.clone());
+                }
+                Expr::Call { .. } | Expr::MethodCall { .. } => {
+                    self.validate_call(db, id, expr);
+                }
+                _ => {}
+            }
+        }
+        for (id, pat) in body.pats.iter() {
+            if let Some((variant_def, missed_fields, true)) =
+                record_pattern_missing_fields(db, &self.infer, id, pat)
+            {
+                self.create_record_pattern_missing_fields_diagnostic(
+                    id,
+                    db,
+                    variant_def,
+                    missed_fields,
+                );
+            }
+        }
+        let body_expr = &body[body.body_expr];
+        if let Expr::Block { tail: Some(t), .. } = body_expr {
+            self.validate_results_in_tail_expr(body.body_expr, *t, db);
+        }
+    }
+
+    fn create_record_literal_missing_fields_diagnostic(
+        &mut self,
+        id: ExprId,
+        db: &dyn HirDatabase,
+        variant_def: VariantId,
+        missed_fields: Vec<LocalFieldId>,
+    ) {
+        // XXX: only look at source_map if we do have missing fields
+        let (_, source_map) = db.body_with_source_map(self.owner.into());
+
+        if let Ok(source_ptr) = source_map.expr_syntax(id) {
+            let root = source_ptr.file_syntax(db.upcast());
+            if let ast::Expr::RecordExpr(record_expr) = &source_ptr.value.to_node(&root) {
+                if let Some(_) = record_expr.record_expr_field_list() {
+                    let variant_data = variant_data(db.upcast(), variant_def);
+                    let missed_fields = missed_fields
+                        .into_iter()
+                        .map(|idx| variant_data.fields()[idx].name.clone())
+                        .collect();
+                    self.sink.push(MissingFields {
+                        file: source_ptr.file_id,
+                        field_list_parent: AstPtr::new(&record_expr),
+                        field_list_parent_path: record_expr.path().map(|path| AstPtr::new(&path)),
+                        missed_fields,
+                    })
+                }
+            }
+        }
+    }
+
+    fn create_record_pattern_missing_fields_diagnostic(
+        &mut self,
+        id: PatId,
+        db: &dyn HirDatabase,
+        variant_def: VariantId,
+        missed_fields: Vec<LocalFieldId>,
+    ) {
+        // XXX: only look at source_map if we do have missing fields
+        let (_, source_map) = db.body_with_source_map(self.owner.into());
+
+        if let Ok(source_ptr) = source_map.pat_syntax(id) {
+            if let Some(expr) = source_ptr.value.as_ref().left() {
+                let root = source_ptr.file_syntax(db.upcast());
+                if let ast::Pat::RecordPat(record_pat) = expr.to_node(&root) {
+                    if let Some(_) = record_pat.record_pat_field_list() {
+                        let variant_data = variant_data(db.upcast(), variant_def);
+                        let missed_fields = missed_fields
+                            .into_iter()
+                            .map(|idx| variant_data.fields()[idx].name.clone())
+                            .collect();
+                        self.sink.push(MissingPatFields {
+                            file: source_ptr.file_id,
+                            field_list_parent: AstPtr::new(&record_pat),
+                            field_list_parent_path: record_pat
+                                .path()
+                                .map(|path| AstPtr::new(&path)),
+                            missed_fields,
+                        })
+                    }
+                }
+            }
+        }
+    }
+
+    fn validate_call(&mut self, db: &dyn HirDatabase, call_id: ExprId, expr: &Expr) -> Option<()> {
+        // Check that the number of arguments matches the number of parameters.
+
+        // FIXME: Due to shortcomings in the current type system implementation, only emit this
+        // diagnostic if there are no type mismatches in the containing function.
+        if self.infer.type_mismatches.iter().next().is_some() {
+            return Some(());
+        }
+
+        let is_method_call = matches!(expr, Expr::MethodCall { .. });
+        let (sig, args) = match expr {
+            Expr::Call { callee, args } => {
+                let callee = &self.infer.type_of_expr[*callee];
+                let sig = callee.callable_sig(db)?;
+                (sig, args.clone())
+            }
+            Expr::MethodCall { receiver, args, .. } => {
+                let mut args = args.clone();
+                args.insert(0, *receiver);
+
+                // FIXME: note that we erase information about substs here. This
+                // is not right, but, luckily, doesn't matter as we care only
+                // about the number of params
+                let callee = self.infer.method_resolution(call_id)?;
+                let sig = db.callable_item_signature(callee.into()).value;
+
+                (sig, args)
+            }
+            _ => return None,
+        };
+
+        if sig.is_varargs {
+            return None;
+        }
+
+        let params = sig.params();
+
+        let mut param_count = params.len();
+        let mut arg_count = args.len();
+
+        if arg_count != param_count {
+            let (_, source_map) = db.body_with_source_map(self.owner.into());
+            if let Ok(source_ptr) = source_map.expr_syntax(call_id) {
+                if is_method_call {
+                    param_count -= 1;
+                    arg_count -= 1;
+                }
+                self.sink.push(MismatchedArgCount {
+                    file: source_ptr.file_id,
+                    call_expr: source_ptr.value,
+                    expected: param_count,
+                    found: arg_count,
+                });
+            }
+        }
+
+        None
+    }
+
+    fn validate_match(
+        &mut self,
+        id: ExprId,
+        match_expr: ExprId,
+        arms: &[MatchArm],
+        db: &dyn HirDatabase,
+        infer: Arc<InferenceResult>,
+    ) {
+        let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
+            db.body_with_source_map(self.owner.into());
+
+        let match_expr_ty = match infer.type_of_expr.get(match_expr) {
+            Some(ty) => ty,
+            // If we can't resolve the type of the match expression
+            // we cannot perform exhaustiveness checks.
+            None => return,
+        };
+
+        let cx = MatchCheckCtx { match_expr, body, infer: infer.clone(), db };
+        let pats = arms.iter().map(|arm| arm.pat);
+
+        let mut seen = Matrix::empty();
+        for pat in pats {
+            if let Some(pat_ty) = infer.type_of_pat.get(pat) {
+                // We only include patterns whose type matches the type
+                // of the match expression. If we had a InvalidMatchArmPattern
+                // diagnostic or similar we could raise that in an else
+                // block here.
+                //
+                // When comparing the types, we also have to consider that rustc
+                // will automatically de-reference the match expression type if
+                // necessary.
+                //
+                // FIXME we should use the type checker for this.
+                if pat_ty == match_expr_ty
+                    || match_expr_ty
+                        .as_reference()
+                        .map(|(match_expr_ty, _)| match_expr_ty == pat_ty)
+                        .unwrap_or(false)
+                {
+                    // If we had a NotUsefulMatchArm diagnostic, we could
+                    // check the usefulness of each pattern as we added it
+                    // to the matrix here.
+                    let v = PatStack::from_pattern(pat);
+                    seen.push(&cx, v);
+                    continue;
+                }
+            }
+
+            // If we can't resolve the type of a pattern, or the pattern type doesn't
+            // fit the match expression, we skip this diagnostic. Skipping the entire
+            // diagnostic rather than just not including this match arm is preferred
+            // to avoid the chance of false positives.
+            return;
+        }
+
+        match is_useful(&cx, &seen, &PatStack::from_wild()) {
+            Ok(Usefulness::Useful) => (),
+            // if a wildcard pattern is not useful, then all patterns are covered
+            Ok(Usefulness::NotUseful) => return,
+            // this path is for unimplemented checks, so we err on the side of not
+            // reporting any errors
+            _ => return,
+        }
+
+        if let Ok(source_ptr) = source_map.expr_syntax(id) {
+            let root = source_ptr.file_syntax(db.upcast());
+            if let ast::Expr::MatchExpr(match_expr) = &source_ptr.value.to_node(&root) {
+                if let (Some(match_expr), Some(arms)) =
+                    (match_expr.expr(), match_expr.match_arm_list())
+                {
+                    self.sink.push(MissingMatchArms {
+                        file: source_ptr.file_id,
+                        match_expr: AstPtr::new(&match_expr),
+                        arms: AstPtr::new(&arms),
+                    })
+                }
+            }
+        }
+    }
+
+    fn validate_results_in_tail_expr(&mut self, body_id: ExprId, id: ExprId, db: &dyn HirDatabase) {
+        // the mismatch will be on the whole block currently
+        let mismatch = match self.infer.type_mismatch_for_expr(body_id) {
+            Some(m) => m,
+            None => return,
+        };
+
+        let core_result_path = path![core::result::Result];
+
+        let resolver = self.owner.resolver(db.upcast());
+        let core_result_enum = match resolver.resolve_known_enum(db.upcast(), &core_result_path) {
+            Some(it) => it,
+            _ => return,
+        };
+
+        let core_result_ctor = TypeCtor::Adt(AdtId::EnumId(core_result_enum));
+        let params = match &mismatch.expected {
+            Ty::Apply(ApplicationTy { ctor, parameters }) if ctor == &core_result_ctor => {
+                parameters
+            }
+            _ => return,
+        };
+
+        if params.len() == 2 && params[0] == mismatch.actual {
+            let (_, source_map) = db.body_with_source_map(self.owner.into());
+
+            if let Ok(source_ptr) = source_map.expr_syntax(id) {
+                self.sink
+                    .push(MissingOkInTailExpr { file: source_ptr.file_id, expr: source_ptr.value });
+            }
+        }
+    }
+}
+
+pub fn record_literal_missing_fields(
+    db: &dyn HirDatabase,
+    infer: &InferenceResult,
+    id: ExprId,
+    expr: &Expr,
+) -> Option<(VariantId, Vec<LocalFieldId>, /*exhaustive*/ bool)> {
+    let (fields, exhausitve) = match expr {
+        Expr::RecordLit { path: _, fields, spread } => (fields, spread.is_none()),
+        _ => return None,
+    };
+
+    let variant_def = infer.variant_resolution_for_expr(id)?;
+    if let VariantId::UnionId(_) = variant_def {
+        return None;
+    }
+
+    let variant_data = variant_data(db.upcast(), variant_def);
+
+    let specified_fields: FxHashSet<_> = fields.iter().map(|f| &f.name).collect();
+    let missed_fields: Vec<LocalFieldId> = variant_data
+        .fields()
+        .iter()
+        .filter_map(|(f, d)| if specified_fields.contains(&d.name) { None } else { Some(f) })
+        .collect();
+    if missed_fields.is_empty() {
+        return None;
+    }
+    Some((variant_def, missed_fields, exhausitve))
+}
+
+pub fn record_pattern_missing_fields(
+    db: &dyn HirDatabase,
+    infer: &InferenceResult,
+    id: PatId,
+    pat: &Pat,
+) -> Option<(VariantId, Vec<LocalFieldId>, /*exhaustive*/ bool)> {
+    let (fields, exhaustive) = match pat {
+        Pat::Record { path: _, args, ellipsis } => (args, !ellipsis),
+        _ => return None,
+    };
+
+    let variant_def = infer.variant_resolution_for_pat(id)?;
+    if let VariantId::UnionId(_) = variant_def {
+        return None;
+    }
+
+    let variant_data = variant_data(db.upcast(), variant_def);
+
+    let specified_fields: FxHashSet<_> = fields.iter().map(|f| &f.name).collect();
+    let missed_fields: Vec<LocalFieldId> = variant_data
+        .fields()
+        .iter()
+        .filter_map(|(f, d)| if specified_fields.contains(&d.name) { None } else { Some(f) })
+        .collect();
+    if missed_fields.is_empty() {
+        return None;
+    }
+    Some((variant_def, missed_fields, exhaustive))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostics::tests::check_diagnostics;
+
+    #[test]
+    fn simple_free_fn_zero() {
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(1); }
+       //^^^^^^^ Expected 0 arguments, found 1
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(); }
+"#,
+        );
+    }
+
+    #[test]
+    fn simple_free_fn_one() {
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(); }
+       //^^^^^ Expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(1); }
+"#,
+        );
+    }
+
+    #[test]
+    fn method_as_fn() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method();
+} //^^^^^^^^^^^ Expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method(&S);
+    S.method();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn method_with_arg() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+            fn f() {
+                S.method();
+            } //^^^^^^^^^^ Expected 1 argument, found 0
+            "#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+fn f() {
+    S::method(&S, 0);
+    S.method(1);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_struct() {
+        check_diagnostics(
+            r#"
+struct Tup(u8, u16);
+fn f() {
+    Tup(0);
+} //^^^^^^ Expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant() {
+        check_diagnostics(
+            r#"
+enum En { Variant(u8, u16), }
+fn f() {
+    En::Variant(0);
+} //^^^^^^^^^^^^^^ Expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant_type_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! Type {
+    () => { u32 };
+}
+enum Foo {
+    Bar(Type![])
+}
+impl Foo {
+    fn new() {
+        Foo::Bar(0);
+        Foo::Bar(0, 1);
+      //^^^^^^^^^^^^^^ Expected 1 argument, found 2
+        Foo::Bar();
+      //^^^^^^^^^^ Expected 1 argument, found 0
+    }
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn varargs() {
+        check_diagnostics(
+            r#"
+extern "C" {
+    fn fixed(fixed: u8);
+    fn varargs(fixed: u8, ...);
+    fn varargs2(...);
+}
+
+fn f() {
+    unsafe {
+        fixed(0);
+        fixed(0, 1);
+      //^^^^^^^^^^^ Expected 1 argument, found 2
+        varargs(0);
+        varargs(0, 1);
+        varargs2();
+        varargs2(0);
+        varargs2(0, 1);
+    }
+}
+        "#,
+        )
+    }
+
+    #[test]
+    fn arg_count_lambda() {
+        check_diagnostics(
+            r#"
+fn main() {
+    let f = |()| ();
+    f();
+  //^^^ Expected 1 argument, found 0
+    f(());
+    f((), ());
+  //^^^^^^^^^ Expected 1 argument, found 2
+}
+"#,
+        )
+    }
+}

crates/hir_ty/src/diagnostics/unsafe_check.rs

@@ -0,0 +1,205 @@
+//! Provides validations for unsafe code. Currently checks if unsafe functions are missing
+//! unsafe blocks.
+
+use std::sync::Arc;
+
+use hir_def::{
+    body::Body,
+    expr::{Expr, ExprId, UnaryOp},
+    resolver::{resolver_for_expr, ResolveValueResult, ValueNs},
+    DefWithBodyId,
+};
+use hir_expand::diagnostics::DiagnosticSink;
+
+use crate::{
+    db::HirDatabase, diagnostics::MissingUnsafe, lower::CallableDefId, ApplicationTy,
+    InferenceResult, Ty, TypeCtor,
+};
+
+pub(super) struct UnsafeValidator<'a, 'b: 'a> {
+    owner: DefWithBodyId,
+    infer: Arc<InferenceResult>,
+    sink: &'a mut DiagnosticSink<'b>,
+}
+
+impl<'a, 'b> UnsafeValidator<'a, 'b> {
+    pub(super) fn new(
+        owner: DefWithBodyId,
+        infer: Arc<InferenceResult>,
+        sink: &'a mut DiagnosticSink<'b>,
+    ) -> UnsafeValidator<'a, 'b> {
+        UnsafeValidator { owner, infer, sink }
+    }
+
+    pub(super) fn validate_body(&mut self, db: &dyn HirDatabase) {
+        let def = self.owner.into();
+        let unsafe_expressions = unsafe_expressions(db, self.infer.as_ref(), def);
+        let is_unsafe = match self.owner {
+            DefWithBodyId::FunctionId(it) => db.function_data(it).is_unsafe,
+            DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) => false,
+        };
+        if is_unsafe
+            || unsafe_expressions
+                .iter()
+                .filter(|unsafe_expr| !unsafe_expr.inside_unsafe_block)
+                .count()
+                == 0
+        {
+            return;
+        }
+
+        let (_, body_source) = db.body_with_source_map(def);
+        for unsafe_expr in unsafe_expressions {
+            if !unsafe_expr.inside_unsafe_block {
+                if let Ok(in_file) = body_source.as_ref().expr_syntax(unsafe_expr.expr) {
+                    self.sink.push(MissingUnsafe { file: in_file.file_id, expr: in_file.value })
+                }
+            }
+        }
+    }
+}
+
+pub struct UnsafeExpr {
+    pub expr: ExprId,
+    pub inside_unsafe_block: bool,
+}
+
+pub fn unsafe_expressions(
+    db: &dyn HirDatabase,
+    infer: &InferenceResult,
+    def: DefWithBodyId,
+) -> Vec<UnsafeExpr> {
+    let mut unsafe_exprs = vec![];
+    let body = db.body(def);
+    walk_unsafe(&mut unsafe_exprs, db, infer, def, &body, body.body_expr, false);
+
+    unsafe_exprs
+}
+
+fn walk_unsafe(
+    unsafe_exprs: &mut Vec<UnsafeExpr>,
+    db: &dyn HirDatabase,
+    infer: &InferenceResult,
+    def: DefWithBodyId,
+    body: &Body,
+    current: ExprId,
+    inside_unsafe_block: bool,
+) {
+    let expr = &body.exprs[current];
+    match expr {
+        Expr::Call { callee, .. } => {
+            let ty = &infer[*callee];
+            if let &Ty::Apply(ApplicationTy {
+                ctor: TypeCtor::FnDef(CallableDefId::FunctionId(func)),
+                ..
+            }) = ty
+            {
+                if db.function_data(func).is_unsafe {
+                    unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
+                }
+            }
+        }
+        Expr::Path(path) => {
+            let resolver = resolver_for_expr(db.upcast(), def, current);
+            let value_or_partial = resolver.resolve_path_in_value_ns(db.upcast(), path.mod_path());
+            if let Some(ResolveValueResult::ValueNs(ValueNs::StaticId(id))) = value_or_partial {
+                if db.static_data(id).mutable {
+                    unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
+                }
+            }
+        }
+        Expr::MethodCall { .. } => {
+            if infer
+                .method_resolution(current)
+                .map(|func| db.function_data(func).is_unsafe)
+                .unwrap_or(false)
+            {
+                unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
+            }
+        }
+        Expr::UnaryOp { expr, op: UnaryOp::Deref } => {
+            if let Ty::Apply(ApplicationTy { ctor: TypeCtor::RawPtr(..), .. }) = &infer[*expr] {
+                unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
+            }
+        }
+        Expr::Unsafe { body: child } => {
+            return walk_unsafe(unsafe_exprs, db, infer, def, body, *child, true);
+        }
+        _ => {}
+    }
+
+    expr.walk_child_exprs(|child| {
+        walk_unsafe(unsafe_exprs, db, infer, def, body, child, inside_unsafe_block);
+    });
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostics::tests::check_diagnostics;
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_raw_ptr() {
+        check_diagnostics(
+            r#"
+fn main() {
+    let x = &5 as *const usize;
+    unsafe { let y = *x; }
+    let z = *x;
+}         //^^ This operation is unsafe and requires an unsafe function or block
+"#,
+        )
+    }
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_unsafe_call() {
+        check_diagnostics(
+            r#"
+struct HasUnsafe;
+
+impl HasUnsafe {
+    unsafe fn unsafe_fn(&self) {
+        let x = &5 as *const usize;
+        let y = *x;
+    }
+}
+
+unsafe fn unsafe_fn() {
+    let x = &5 as *const usize;
+    let y = *x;
+}
+
+fn main() {
+    unsafe_fn();
+  //^^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
+    HasUnsafe.unsafe_fn();
+  //^^^^^^^^^^^^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
+    unsafe {
+        unsafe_fn();
+        HasUnsafe.unsafe_fn();
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn missing_unsafe_diagnostic_with_static_mut() {
+        check_diagnostics(
+            r#"
+struct Ty {
+    a: u8,
+}
+
+static mut static_mut: Ty = Ty { a: 0 };
+
+fn main() {
+    let x = static_mut.a;
+          //^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
+    unsafe {
+        let x = static_mut.a;
+    }
+}
+"#,
+        );
+    }
+}

crates/hir_ty/src/display.rs

@@ -0,0 +1,631 @@
+//! FIXME: write short doc here
+
+use std::fmt;
+
+use crate::{
+    db::HirDatabase, utils::generics, ApplicationTy, CallableDefId, FnSig, GenericPredicate,
+    Obligation, OpaqueTyId, ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
+};
+use hir_def::{
+    find_path, generics::TypeParamProvenance, item_scope::ItemInNs, AdtId, AssocContainerId,
+    Lookup, ModuleId,
+};
+use hir_expand::name::Name;
+
+pub struct HirFormatter<'a> {
+    pub db: &'a dyn HirDatabase,
+    fmt: &'a mut dyn fmt::Write,
+    buf: String,
+    curr_size: usize,
+    pub(crate) max_size: Option<usize>,
+    omit_verbose_types: bool,
+    display_target: DisplayTarget,
+}
+
+pub trait HirDisplay {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError>;
+
+    /// Returns a `Display`able type that is human-readable.
+    /// Use this for showing types to the user (e.g. diagnostics)
+    fn display<'a>(&'a self, db: &'a dyn HirDatabase) -> HirDisplayWrapper<'a, Self>
+    where
+        Self: Sized,
+    {
+        HirDisplayWrapper {
+            db,
+            t: self,
+            max_size: None,
+            omit_verbose_types: false,
+            display_target: DisplayTarget::Diagnostics,
+        }
+    }
+
+    /// Returns a `Display`able type that is human-readable and tries to be succinct.
+    /// Use this for showing types to the user where space is constrained (e.g. doc popups)
+    fn display_truncated<'a>(
+        &'a self,
+        db: &'a dyn HirDatabase,
+        max_size: Option<usize>,
+    ) -> HirDisplayWrapper<'a, Self>
+    where
+        Self: Sized,
+    {
+        HirDisplayWrapper {
+            db,
+            t: self,
+            max_size,
+            omit_verbose_types: true,
+            display_target: DisplayTarget::Diagnostics,
+        }
+    }
+
+    /// Returns a String representation of `self` that can be inserted into the given module.
+    /// Use this when generating code (e.g. assists)
+    fn display_source_code<'a>(
+        &'a self,
+        db: &'a dyn HirDatabase,
+        module_id: ModuleId,
+    ) -> Result<String, DisplaySourceCodeError> {
+        let mut result = String::new();
+        match self.hir_fmt(&mut HirFormatter {
+            db,
+            fmt: &mut result,
+            buf: String::with_capacity(20),
+            curr_size: 0,
+            max_size: None,
+            omit_verbose_types: false,
+            display_target: DisplayTarget::SourceCode { module_id },
+        }) {
+            Ok(()) => {}
+            Err(HirDisplayError::FmtError) => panic!("Writing to String can't fail!"),
+            Err(HirDisplayError::DisplaySourceCodeError(e)) => return Err(e),
+        };
+        Ok(result)
+    }
+}
+
+impl<'a> HirFormatter<'a> {
+    pub fn write_joined<T: HirDisplay>(
+        &mut self,
+        iter: impl IntoIterator<Item = T>,
+        sep: &str,
+    ) -> Result<(), HirDisplayError> {
+        let mut first = true;
+        for e in iter {
+            if !first {
+                write!(self, "{}", sep)?;
+            }
+            first = false;
+            e.hir_fmt(self)?;
+        }
+        Ok(())
+    }
+
+    /// This allows using the `write!` macro directly with a `HirFormatter`.
+    pub fn write_fmt(&mut self, args: fmt::Arguments) -> Result<(), HirDisplayError> {
+        // We write to a buffer first to track output size
+        self.buf.clear();
+        fmt::write(&mut self.buf, args)?;
+        self.curr_size += self.buf.len();
+
+        // Then we write to the internal formatter from the buffer
+        self.fmt.write_str(&self.buf).map_err(HirDisplayError::from)
+    }
+
+    pub fn should_truncate(&self) -> bool {
+        if let Some(max_size) = self.max_size {
+            self.curr_size >= max_size
+        } else {
+            false
+        }
+    }
+
+    pub fn omit_verbose_types(&self) -> bool {
+        self.omit_verbose_types
+    }
+}
+
+#[derive(Clone, Copy)]
+enum DisplayTarget {
+    /// Display types for inlays, doc popups, autocompletion, etc...
+    /// Showing `{unknown}` or not qualifying paths is fine here.
+    /// There's no reason for this to fail.
+    Diagnostics,
+    /// Display types for inserting them in source files.
+    /// The generated code should compile, so paths need to be qualified.
+    SourceCode { module_id: ModuleId },
+}
+
+impl DisplayTarget {
+    fn is_source_code(&self) -> bool {
+        matches!(self, Self::SourceCode {..})
+    }
+}
+
+#[derive(Debug)]
+pub enum DisplaySourceCodeError {
+    PathNotFound,
+}
+
+pub enum HirDisplayError {
+    /// Errors that can occur when generating source code
+    DisplaySourceCodeError(DisplaySourceCodeError),
+    /// `FmtError` is required to be compatible with std::fmt::Display
+    FmtError,
+}
+impl From<fmt::Error> for HirDisplayError {
+    fn from(_: fmt::Error) -> Self {
+        Self::FmtError
+    }
+}
+
+pub struct HirDisplayWrapper<'a, T> {
+    db: &'a dyn HirDatabase,
+    t: &'a T,
+    max_size: Option<usize>,
+    omit_verbose_types: bool,
+    display_target: DisplayTarget,
+}
+
+impl<'a, T> fmt::Display for HirDisplayWrapper<'a, T>
+where
+    T: HirDisplay,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self.t.hir_fmt(&mut HirFormatter {
+            db: self.db,
+            fmt: f,
+            buf: String::with_capacity(20),
+            curr_size: 0,
+            max_size: self.max_size,
+            omit_verbose_types: self.omit_verbose_types,
+            display_target: self.display_target,
+        }) {
+            Ok(()) => Ok(()),
+            Err(HirDisplayError::FmtError) => Err(fmt::Error),
+            Err(HirDisplayError::DisplaySourceCodeError(_)) => {
+                // This should never happen
+                panic!("HirDisplay failed when calling Display::fmt!")
+            }
+        }
+    }
+}
+
+const TYPE_HINT_TRUNCATION: &str = "…";
+
+impl HirDisplay for &Ty {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        HirDisplay::hir_fmt(*self, f)
+    }
+}
+
+impl HirDisplay for ApplicationTy {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        if f.should_truncate() {
+            return write!(f, "{}", TYPE_HINT_TRUNCATION);
+        }
+
+        match self.ctor {
+            TypeCtor::Bool => write!(f, "bool")?,
+            TypeCtor::Char => write!(f, "char")?,
+            TypeCtor::Int(t) => write!(f, "{}", t)?,
+            TypeCtor::Float(t) => write!(f, "{}", t)?,
+            TypeCtor::Str => write!(f, "str")?,
+            TypeCtor::Slice => {
+                let t = self.parameters.as_single();
+                write!(f, "[{}]", t.display(f.db))?;
+            }
+            TypeCtor::Array => {
+                let t = self.parameters.as_single();
+                write!(f, "[{}; _]", t.display(f.db))?;
+            }
+            TypeCtor::RawPtr(m) => {
+                let t = self.parameters.as_single();
+                write!(f, "*{}{}", m.as_keyword_for_ptr(), t.display(f.db))?;
+            }
+            TypeCtor::Ref(m) => {
+                let t = self.parameters.as_single();
+                let ty_display = if f.omit_verbose_types() {
+                    t.display_truncated(f.db, f.max_size)
+                } else {
+                    t.display(f.db)
+                };
+                write!(f, "&{}{}", m.as_keyword_for_ref(), ty_display)?;
+            }
+            TypeCtor::Never => write!(f, "!")?,
+            TypeCtor::Tuple { .. } => {
+                let ts = &self.parameters;
+                if ts.len() == 1 {
+                    write!(f, "({},)", ts[0].display(f.db))?;
+                } else {
+                    write!(f, "(")?;
+                    f.write_joined(&*ts.0, ", ")?;
+                    write!(f, ")")?;
+                }
+            }
+            TypeCtor::FnPtr { is_varargs, .. } => {
+                let sig = FnSig::from_fn_ptr_substs(&self.parameters, is_varargs);
+                write!(f, "fn(")?;
+                f.write_joined(sig.params(), ", ")?;
+                if is_varargs {
+                    if sig.params().is_empty() {
+                        write!(f, "...")?;
+                    } else {
+                        write!(f, ", ...")?;
+                    }
+                }
+                write!(f, ")")?;
+                let ret = sig.ret();
+                if *ret != Ty::unit() {
+                    let ret_display = if f.omit_verbose_types() {
+                        ret.display_truncated(f.db, f.max_size)
+                    } else {
+                        ret.display(f.db)
+                    };
+                    write!(f, " -> {}", ret_display)?;
+                }
+            }
+            TypeCtor::FnDef(def) => {
+                let sig = f.db.callable_item_signature(def).subst(&self.parameters);
+                match def {
+                    CallableDefId::FunctionId(ff) => {
+                        write!(f, "fn {}", f.db.function_data(ff).name)?
+                    }
+                    CallableDefId::StructId(s) => write!(f, "{}", f.db.struct_data(s).name)?,
+                    CallableDefId::EnumVariantId(e) => {
+                        write!(f, "{}", f.db.enum_data(e.parent).variants[e.local_id].name)?
+                    }
+                };
+                if self.parameters.len() > 0 {
+                    let generics = generics(f.db.upcast(), def.into());
+                    let (parent_params, self_param, type_params, _impl_trait_params) =
+                        generics.provenance_split();
+                    let total_len = parent_params + self_param + type_params;
+                    // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
+                    if total_len > 0 {
+                        write!(f, "<")?;
+                        f.write_joined(&self.parameters.0[..total_len], ", ")?;
+                        write!(f, ">")?;
+                    }
+                }
+                write!(f, "(")?;
+                f.write_joined(sig.params(), ", ")?;
+                write!(f, ")")?;
+                let ret = sig.ret();
+                if *ret != Ty::unit() {
+                    let ret_display = if f.omit_verbose_types() {
+                        ret.display_truncated(f.db, f.max_size)
+                    } else {
+                        ret.display(f.db)
+                    };
+                    write!(f, " -> {}", ret_display)?;
+                }
+            }
+            TypeCtor::Adt(def_id) => {
+                match f.display_target {
+                    DisplayTarget::Diagnostics => {
+                        let name = match def_id {
+                            AdtId::StructId(it) => f.db.struct_data(it).name.clone(),
+                            AdtId::UnionId(it) => f.db.union_data(it).name.clone(),
+                            AdtId::EnumId(it) => f.db.enum_data(it).name.clone(),
+                        };
+                        write!(f, "{}", name)?;
+                    }
+                    DisplayTarget::SourceCode { module_id } => {
+                        if let Some(path) = find_path::find_path(
+                            f.db.upcast(),
+                            ItemInNs::Types(def_id.into()),
+                            module_id,
+                        ) {
+                            write!(f, "{}", path)?;
+                        } else {
+                            return Err(HirDisplayError::DisplaySourceCodeError(
+                                DisplaySourceCodeError::PathNotFound,
+                            ));
+                        }
+                    }
+                }
+
+                if self.parameters.len() > 0 {
+                    let parameters_to_write =
+                        if f.display_target.is_source_code() || f.omit_verbose_types() {
+                            match self
+                                .ctor
+                                .as_generic_def()
+                                .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
+                                .filter(|defaults| !defaults.is_empty())
+                            {
+                                None => self.parameters.0.as_ref(),
+                                Some(default_parameters) => {
+                                    let mut default_from = 0;
+                                    for (i, parameter) in self.parameters.iter().enumerate() {
+                                        match (parameter, default_parameters.get(i)) {
+                                            (&Ty::Unknown, _) | (_, None) => {
+                                                default_from = i + 1;
+                                            }
+                                            (_, Some(default_parameter)) => {
+                                                let actual_default = default_parameter
+                                                    .clone()
+                                                    .subst(&self.parameters.prefix(i));
+                                                if parameter != &actual_default {
+                                                    default_from = i + 1;
+                                                }
+                                            }
+                                        }
+                                    }
+                                    &self.parameters.0[0..default_from]
+                                }
+                            }
+                        } else {
+                            self.parameters.0.as_ref()
+                        };
+                    if !parameters_to_write.is_empty() {
+                        write!(f, "<")?;
+                        f.write_joined(parameters_to_write, ", ")?;
+                        write!(f, ">")?;
+                    }
+                }
+            }
+            TypeCtor::AssociatedType(type_alias) => {
+                let trait_ = match type_alias.lookup(f.db.upcast()).container {
+                    AssocContainerId::TraitId(it) => it,
+                    _ => panic!("not an associated type"),
+                };
+                let trait_ = f.db.trait_data(trait_);
+                let type_alias = f.db.type_alias_data(type_alias);
+                write!(f, "{}::{}", trait_.name, type_alias.name)?;
+                if self.parameters.len() > 0 {
+                    write!(f, "<")?;
+                    f.write_joined(&*self.parameters.0, ", ")?;
+                    write!(f, ">")?;
+                }
+            }
+            TypeCtor::OpaqueType(opaque_ty_id) => {
+                let bounds = match opaque_ty_id {
+                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                        let datas =
+                            f.db.return_type_impl_traits(func).expect("impl trait id without data");
+                        let data = (*datas)
+                            .as_ref()
+                            .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
+                        data.subst(&self.parameters)
+                    }
+                };
+                write!(f, "impl ")?;
+                write_bounds_like_dyn_trait(&bounds.value, f)?;
+                // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
+            }
+            TypeCtor::Closure { .. } => {
+                let sig = self.parameters[0].callable_sig(f.db);
+                if let Some(sig) = sig {
+                    if sig.params().is_empty() {
+                        write!(f, "||")?;
+                    } else if f.omit_verbose_types() {
+                        write!(f, "|{}|", TYPE_HINT_TRUNCATION)?;
+                    } else {
+                        write!(f, "|")?;
+                        f.write_joined(sig.params(), ", ")?;
+                        write!(f, "|")?;
+                    };
+
+                    let ret_display = if f.omit_verbose_types() {
+                        sig.ret().display_truncated(f.db, f.max_size)
+                    } else {
+                        sig.ret().display(f.db)
+                    };
+                    write!(f, " -> {}", ret_display)?;
+                } else {
+                    write!(f, "{{closure}}")?;
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for ProjectionTy {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        if f.should_truncate() {
+            return write!(f, "{}", TYPE_HINT_TRUNCATION);
+        }
+
+        let trait_ = f.db.trait_data(self.trait_(f.db));
+        write!(f, "<{} as {}", self.parameters[0].display(f.db), trait_.name)?;
+        if self.parameters.len() > 1 {
+            write!(f, "<")?;
+            f.write_joined(&self.parameters[1..], ", ")?;
+            write!(f, ">")?;
+        }
+        write!(f, ">::{}", f.db.type_alias_data(self.associated_ty).name)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Ty {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        if f.should_truncate() {
+            return write!(f, "{}", TYPE_HINT_TRUNCATION);
+        }
+
+        match self {
+            Ty::Apply(a_ty) => a_ty.hir_fmt(f)?,
+            Ty::Projection(p_ty) => p_ty.hir_fmt(f)?,
+            Ty::Placeholder(id) => {
+                let generics = generics(f.db.upcast(), id.parent);
+                let param_data = &generics.params.types[id.local_id];
+                match param_data.provenance {
+                    TypeParamProvenance::TypeParamList | TypeParamProvenance::TraitSelf => {
+                        write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
+                    }
+                    TypeParamProvenance::ArgumentImplTrait => {
+                        write!(f, "impl ")?;
+                        let bounds = f.db.generic_predicates_for_param(*id);
+                        let substs = Substs::type_params_for_generics(&generics);
+                        write_bounds_like_dyn_trait(
+                            &bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(),
+                            f,
+                        )?;
+                    }
+                }
+            }
+            Ty::Bound(idx) => write!(f, "?{}.{}", idx.debruijn.depth(), idx.index)?,
+            Ty::Dyn(predicates) => {
+                write!(f, "dyn ")?;
+                write_bounds_like_dyn_trait(predicates, f)?;
+            }
+            Ty::Opaque(opaque_ty) => {
+                let bounds = match opaque_ty.opaque_ty_id {
+                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                        let datas =
+                            f.db.return_type_impl_traits(func).expect("impl trait id without data");
+                        let data = (*datas)
+                            .as_ref()
+                            .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
+                        data.subst(&opaque_ty.parameters)
+                    }
+                };
+                write!(f, "impl ")?;
+                write_bounds_like_dyn_trait(&bounds.value, f)?;
+            }
+            Ty::Unknown => write!(f, "{{unknown}}")?,
+            Ty::Infer(..) => write!(f, "_")?,
+        }
+        Ok(())
+    }
+}
+
+fn write_bounds_like_dyn_trait(
+    predicates: &[GenericPredicate],
+    f: &mut HirFormatter,
+) -> Result<(), HirDisplayError> {
+    // Note: This code is written to produce nice results (i.e.
+    // corresponding to surface Rust) for types that can occur in
+    // actual Rust. It will have weird results if the predicates
+    // aren't as expected (i.e. self types = $0, projection
+    // predicates for a certain trait come after the Implemented
+    // predicate for that trait).
+    let mut first = true;
+    let mut angle_open = false;
+    for p in predicates.iter() {
+        match p {
+            GenericPredicate::Implemented(trait_ref) => {
+                if angle_open {
+                    write!(f, ">")?;
+                }
+                if !first {
+                    write!(f, " + ")?;
+                }
+                // We assume that the self type is $0 (i.e. the
+                // existential) here, which is the only thing that's
+                // possible in actual Rust, and hence don't print it
+                write!(f, "{}", f.db.trait_data(trait_ref.trait_).name)?;
+                if trait_ref.substs.len() > 1 {
+                    write!(f, "<")?;
+                    f.write_joined(&trait_ref.substs[1..], ", ")?;
+                    // there might be assoc type bindings, so we leave the angle brackets open
+                    angle_open = true;
+                }
+            }
+            GenericPredicate::Projection(projection_pred) => {
+                // in types in actual Rust, these will always come
+                // after the corresponding Implemented predicate
+                if angle_open {
+                    write!(f, ", ")?;
+                } else {
+                    write!(f, "<")?;
+                    angle_open = true;
+                }
+                let type_alias = f.db.type_alias_data(projection_pred.projection_ty.associated_ty);
+                write!(f, "{} = ", type_alias.name)?;
+                projection_pred.ty.hir_fmt(f)?;
+            }
+            GenericPredicate::Error => {
+                if angle_open {
+                    // impl Trait<X, {error}>
+                    write!(f, ", ")?;
+                } else if !first {
+                    // impl Trait + {error}
+                    write!(f, " + ")?;
+                }
+                p.hir_fmt(f)?;
+            }
+        }
+        first = false;
+    }
+    if angle_open {
+        write!(f, ">")?;
+    }
+    Ok(())
+}
+
+impl TraitRef {
+    fn hir_fmt_ext(&self, f: &mut HirFormatter, use_as: bool) -> Result<(), HirDisplayError> {
+        if f.should_truncate() {
+            return write!(f, "{}", TYPE_HINT_TRUNCATION);
+        }
+
+        self.substs[0].hir_fmt(f)?;
+        if use_as {
+            write!(f, " as ")?;
+        } else {
+            write!(f, ": ")?;
+        }
+        write!(f, "{}", f.db.trait_data(self.trait_).name)?;
+        if self.substs.len() > 1 {
+            write!(f, "<")?;
+            f.write_joined(&self.substs[1..], ", ")?;
+            write!(f, ">")?;
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for TraitRef {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        self.hir_fmt_ext(f, false)
+    }
+}
+
+impl HirDisplay for &GenericPredicate {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        HirDisplay::hir_fmt(*self, f)
+    }
+}
+
+impl HirDisplay for GenericPredicate {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        if f.should_truncate() {
+            return write!(f, "{}", TYPE_HINT_TRUNCATION);
+        }
+
+        match self {
+            GenericPredicate::Implemented(trait_ref) => trait_ref.hir_fmt(f)?,
+            GenericPredicate::Projection(projection_pred) => {
+                write!(f, "<")?;
+                projection_pred.projection_ty.trait_ref(f.db).hir_fmt_ext(f, true)?;
+                write!(
+                    f,
+                    ">::{} = {}",
+                    f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name,
+                    projection_pred.ty.display(f.db)
+                )?;
+            }
+            GenericPredicate::Error => write!(f, "{{error}}")?,
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for Obligation {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        Ok(match self {
+            Obligation::Trait(tr) => write!(f, "Implements({})", tr.display(f.db))?,
+            Obligation::Projection(proj) => write!(
+                f,
+                "Normalize({} => {})",
+                proj.projection_ty.display(f.db),
+                proj.ty.display(f.db)
+            )?,
+        })
+    }
+}

crates/hir_ty/src/infer.rs

@@ -0,0 +1,802 @@
+//! Type inference, i.e. the process of walking through the code and determining
+//! the type of each expression and pattern.
+//!
+//! For type inference, compare the implementations in rustc (the various
+//! check_* methods in librustc_typeck/check/mod.rs are a good entry point) and
+//! IntelliJ-Rust (org.rust.lang.core.types.infer). Our entry point for
+//! inference here is the `infer` function, which infers the types of all
+//! expressions in a given function.
+//!
+//! During inference, types (i.e. the `Ty` struct) can contain type 'variables'
+//! which represent currently unknown types; as we walk through the expressions,
+//! we might determine that certain variables need to be equal to each other, or
+//! to certain types. To record this, we use the union-find implementation from
+//! the `ena` crate, which is extracted from rustc.
+
+use std::borrow::Cow;
+use std::mem;
+use std::ops::Index;
+use std::sync::Arc;
+
+use arena::map::ArenaMap;
+use hir_def::{
+    body::Body,
+    data::{ConstData, FunctionData, StaticData},
+    expr::{BindingAnnotation, ExprId, PatId},
+    lang_item::LangItemTarget,
+    path::{path, Path},
+    resolver::{HasResolver, Resolver, TypeNs},
+    type_ref::{Mutability, TypeRef},
+    AdtId, AssocItemId, DefWithBodyId, EnumVariantId, FieldId, FunctionId, Lookup, TraitId,
+    TypeAliasId, VariantId,
+};
+use hir_expand::{diagnostics::DiagnosticSink, name::name};
+use rustc_hash::FxHashMap;
+use stdx::impl_from;
+use syntax::SmolStr;
+
+use super::{
+    primitive::{FloatTy, IntTy},
+    traits::{Guidance, Obligation, ProjectionPredicate, Solution},
+    InEnvironment, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor, TypeWalk,
+};
+use crate::{
+    db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
+};
+
+pub(crate) use unify::unify;
+
+macro_rules! ty_app {
+    ($ctor:pat, $param:pat) => {
+        crate::Ty::Apply(crate::ApplicationTy { ctor: $ctor, parameters: $param })
+    };
+    ($ctor:pat) => {
+        ty_app!($ctor, _)
+    };
+}
+
+mod unify;
+mod path;
+mod expr;
+mod pat;
+mod coerce;
+
+/// The entry point of type inference.
+pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<InferenceResult> {
+    let _p = profile::span("infer_query");
+    let resolver = def.resolver(db.upcast());
+    let mut ctx = InferenceContext::new(db, def, resolver);
+
+    match def {
+        DefWithBodyId::ConstId(c) => ctx.collect_const(&db.const_data(c)),
+        DefWithBodyId::FunctionId(f) => ctx.collect_fn(&db.function_data(f)),
+        DefWithBodyId::StaticId(s) => ctx.collect_static(&db.static_data(s)),
+    }
+
+    ctx.infer_body();
+
+    Arc::new(ctx.resolve_all())
+}
+
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+enum ExprOrPatId {
+    ExprId(ExprId),
+    PatId(PatId),
+}
+impl_from!(ExprId, PatId for ExprOrPatId);
+
+/// Binding modes inferred for patterns.
+/// https://doc.rust-lang.org/reference/patterns.html#binding-modes
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+enum BindingMode {
+    Move,
+    Ref(Mutability),
+}
+
+impl BindingMode {
+    pub fn convert(annotation: BindingAnnotation) -> BindingMode {
+        match annotation {
+            BindingAnnotation::Unannotated | BindingAnnotation::Mutable => BindingMode::Move,
+            BindingAnnotation::Ref => BindingMode::Ref(Mutability::Shared),
+            BindingAnnotation::RefMut => BindingMode::Ref(Mutability::Mut),
+        }
+    }
+}
+
+impl Default for BindingMode {
+    fn default() -> Self {
+        BindingMode::Move
+    }
+}
+
+/// A mismatch between an expected and an inferred type.
+#[derive(Clone, PartialEq, Eq, Debug, Hash)]
+pub struct TypeMismatch {
+    pub expected: Ty,
+    pub actual: Ty,
+}
+
+/// The result of type inference: A mapping from expressions and patterns to types.
+#[derive(Clone, PartialEq, Eq, Debug, Default)]
+pub struct InferenceResult {
+    /// For each method call expr, records the function it resolves to.
+    method_resolutions: FxHashMap<ExprId, FunctionId>,
+    /// For each field access expr, records the field it resolves to.
+    field_resolutions: FxHashMap<ExprId, FieldId>,
+    /// For each field in record literal, records the field it resolves to.
+    record_field_resolutions: FxHashMap<ExprId, FieldId>,
+    record_field_pat_resolutions: FxHashMap<PatId, FieldId>,
+    /// For each struct literal, records the variant it resolves to.
+    variant_resolutions: FxHashMap<ExprOrPatId, VariantId>,
+    /// For each associated item record what it resolves to
+    assoc_resolutions: FxHashMap<ExprOrPatId, AssocItemId>,
+    diagnostics: Vec<InferenceDiagnostic>,
+    pub type_of_expr: ArenaMap<ExprId, Ty>,
+    pub type_of_pat: ArenaMap<PatId, Ty>,
+    pub(super) type_mismatches: ArenaMap<ExprId, TypeMismatch>,
+}
+
+impl InferenceResult {
+    pub fn method_resolution(&self, expr: ExprId) -> Option<FunctionId> {
+        self.method_resolutions.get(&expr).copied()
+    }
+    pub fn field_resolution(&self, expr: ExprId) -> Option<FieldId> {
+        self.field_resolutions.get(&expr).copied()
+    }
+    pub fn record_field_resolution(&self, expr: ExprId) -> Option<FieldId> {
+        self.record_field_resolutions.get(&expr).copied()
+    }
+    pub fn record_field_pat_resolution(&self, pat: PatId) -> Option<FieldId> {
+        self.record_field_pat_resolutions.get(&pat).copied()
+    }
+    pub fn variant_resolution_for_expr(&self, id: ExprId) -> Option<VariantId> {
+        self.variant_resolutions.get(&id.into()).copied()
+    }
+    pub fn variant_resolution_for_pat(&self, id: PatId) -> Option<VariantId> {
+        self.variant_resolutions.get(&id.into()).copied()
+    }
+    pub fn assoc_resolutions_for_expr(&self, id: ExprId) -> Option<AssocItemId> {
+        self.assoc_resolutions.get(&id.into()).copied()
+    }
+    pub fn assoc_resolutions_for_pat(&self, id: PatId) -> Option<AssocItemId> {
+        self.assoc_resolutions.get(&id.into()).copied()
+    }
+    pub fn type_mismatch_for_expr(&self, expr: ExprId) -> Option<&TypeMismatch> {
+        self.type_mismatches.get(expr)
+    }
+    pub fn add_diagnostics(
+        &self,
+        db: &dyn HirDatabase,
+        owner: DefWithBodyId,
+        sink: &mut DiagnosticSink,
+    ) {
+        self.diagnostics.iter().for_each(|it| it.add_to(db, owner, sink))
+    }
+}
+
+impl Index<ExprId> for InferenceResult {
+    type Output = Ty;
+
+    fn index(&self, expr: ExprId) -> &Ty {
+        self.type_of_expr.get(expr).unwrap_or(&Ty::Unknown)
+    }
+}
+
+impl Index<PatId> for InferenceResult {
+    type Output = Ty;
+
+    fn index(&self, pat: PatId) -> &Ty {
+        self.type_of_pat.get(pat).unwrap_or(&Ty::Unknown)
+    }
+}
+
+/// The inference context contains all information needed during type inference.
+#[derive(Clone, Debug)]
+struct InferenceContext<'a> {
+    db: &'a dyn HirDatabase,
+    owner: DefWithBodyId,
+    body: Arc<Body>,
+    resolver: Resolver,
+    table: unify::InferenceTable,
+    trait_env: Arc<TraitEnvironment>,
+    obligations: Vec<Obligation>,
+    result: InferenceResult,
+    /// The return type of the function being inferred, or the closure if we're
+    /// currently within one.
+    ///
+    /// We might consider using a nested inference context for checking
+    /// closures, but currently this is the only field that will change there,
+    /// so it doesn't make sense.
+    return_ty: Ty,
+    diverges: Diverges,
+    breakables: Vec<BreakableContext>,
+}
+
+#[derive(Clone, Debug)]
+struct BreakableContext {
+    pub may_break: bool,
+    pub break_ty: Ty,
+    pub label: Option<name::Name>,
+}
+
+fn find_breakable<'c>(
+    ctxs: &'c mut [BreakableContext],
+    label: Option<&name::Name>,
+) -> Option<&'c mut BreakableContext> {
+    match label {
+        Some(_) => ctxs.iter_mut().rev().find(|ctx| ctx.label.as_ref() == label),
+        None => ctxs.last_mut(),
+    }
+}
+
+impl<'a> InferenceContext<'a> {
+    fn new(db: &'a dyn HirDatabase, owner: DefWithBodyId, resolver: Resolver) -> Self {
+        InferenceContext {
+            result: InferenceResult::default(),
+            table: unify::InferenceTable::new(),
+            obligations: Vec::default(),
+            return_ty: Ty::Unknown, // set in collect_fn_signature
+            trait_env: TraitEnvironment::lower(db, &resolver),
+            db,
+            owner,
+            body: db.body(owner),
+            resolver,
+            diverges: Diverges::Maybe,
+            breakables: Vec::new(),
+        }
+    }
+
+    fn resolve_all(mut self) -> InferenceResult {
+        // FIXME resolve obligations as well (use Guidance if necessary)
+        let mut result = std::mem::take(&mut self.result);
+        for ty in result.type_of_expr.values_mut() {
+            let resolved = self.table.resolve_ty_completely(mem::replace(ty, Ty::Unknown));
+            *ty = resolved;
+        }
+        for ty in result.type_of_pat.values_mut() {
+            let resolved = self.table.resolve_ty_completely(mem::replace(ty, Ty::Unknown));
+            *ty = resolved;
+        }
+        result
+    }
+
+    fn write_expr_ty(&mut self, expr: ExprId, ty: Ty) {
+        self.result.type_of_expr.insert(expr, ty);
+    }
+
+    fn write_method_resolution(&mut self, expr: ExprId, func: FunctionId) {
+        self.result.method_resolutions.insert(expr, func);
+    }
+
+    fn write_field_resolution(&mut self, expr: ExprId, field: FieldId) {
+        self.result.field_resolutions.insert(expr, field);
+    }
+
+    fn write_variant_resolution(&mut self, id: ExprOrPatId, variant: VariantId) {
+        self.result.variant_resolutions.insert(id, variant);
+    }
+
+    fn write_assoc_resolution(&mut self, id: ExprOrPatId, item: AssocItemId) {
+        self.result.assoc_resolutions.insert(id, item);
+    }
+
+    fn write_pat_ty(&mut self, pat: PatId, ty: Ty) {
+        self.result.type_of_pat.insert(pat, ty);
+    }
+
+    fn push_diagnostic(&mut self, diagnostic: InferenceDiagnostic) {
+        self.result.diagnostics.push(diagnostic);
+    }
+
+    fn make_ty_with_mode(
+        &mut self,
+        type_ref: &TypeRef,
+        impl_trait_mode: ImplTraitLoweringMode,
+    ) -> Ty {
+        // FIXME use right resolver for block
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
+            .with_impl_trait_mode(impl_trait_mode);
+        let ty = Ty::from_hir(&ctx, type_ref);
+        let ty = self.insert_type_vars(ty);
+        self.normalize_associated_types_in(ty)
+    }
+
+    fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
+        self.make_ty_with_mode(type_ref, ImplTraitLoweringMode::Disallowed)
+    }
+
+    /// Replaces Ty::Unknown by a new type var, so we can maybe still infer it.
+    fn insert_type_vars_shallow(&mut self, ty: Ty) -> Ty {
+        match ty {
+            Ty::Unknown => self.table.new_type_var(),
+            _ => ty,
+        }
+    }
+
+    fn insert_type_vars(&mut self, ty: Ty) -> Ty {
+        ty.fold(&mut |ty| self.insert_type_vars_shallow(ty))
+    }
+
+    fn resolve_obligations_as_possible(&mut self) {
+        let obligations = mem::replace(&mut self.obligations, Vec::new());
+        for obligation in obligations {
+            let in_env = InEnvironment::new(self.trait_env.clone(), obligation.clone());
+            let canonicalized = self.canonicalizer().canonicalize_obligation(in_env);
+            let solution =
+                self.db.trait_solve(self.resolver.krate().unwrap(), canonicalized.value.clone());
+
+            match solution {
+                Some(Solution::Unique(substs)) => {
+                    canonicalized.apply_solution(self, substs.0);
+                }
+                Some(Solution::Ambig(Guidance::Definite(substs))) => {
+                    canonicalized.apply_solution(self, substs.0);
+                    self.obligations.push(obligation);
+                }
+                Some(_) => {
+                    // FIXME use this when trying to resolve everything at the end
+                    self.obligations.push(obligation);
+                }
+                None => {
+                    // FIXME obligation cannot be fulfilled => diagnostic
+                }
+            };
+        }
+    }
+
+    fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
+        self.table.unify(ty1, ty2)
+    }
+
+    /// Resolves the type as far as currently possible, replacing type variables
+    /// by their known types. All types returned by the infer_* functions should
+    /// be resolved as far as possible, i.e. contain no type variables with
+    /// known type.
+    fn resolve_ty_as_possible(&mut self, ty: Ty) -> Ty {
+        self.resolve_obligations_as_possible();
+
+        self.table.resolve_ty_as_possible(ty)
+    }
+
+    fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
+        self.table.resolve_ty_shallow(ty)
+    }
+
+    fn resolve_associated_type(&mut self, inner_ty: Ty, assoc_ty: Option<TypeAliasId>) -> Ty {
+        self.resolve_associated_type_with_params(inner_ty, assoc_ty, &[])
+    }
+
+    fn resolve_associated_type_with_params(
+        &mut self,
+        inner_ty: Ty,
+        assoc_ty: Option<TypeAliasId>,
+        params: &[Ty],
+    ) -> Ty {
+        match assoc_ty {
+            Some(res_assoc_ty) => {
+                let trait_ = match res_assoc_ty.lookup(self.db.upcast()).container {
+                    hir_def::AssocContainerId::TraitId(trait_) => trait_,
+                    _ => panic!("resolve_associated_type called with non-associated type"),
+                };
+                let ty = self.table.new_type_var();
+                let substs = Substs::build_for_def(self.db, res_assoc_ty)
+                    .push(inner_ty)
+                    .fill(params.iter().cloned())
+                    .build();
+                let trait_ref = TraitRef { trait_, substs: substs.clone() };
+                let projection = ProjectionPredicate {
+                    ty: ty.clone(),
+                    projection_ty: ProjectionTy { associated_ty: res_assoc_ty, parameters: substs },
+                };
+                self.obligations.push(Obligation::Trait(trait_ref));
+                self.obligations.push(Obligation::Projection(projection));
+                self.resolve_ty_as_possible(ty)
+            }
+            None => Ty::Unknown,
+        }
+    }
+
+    /// Recurses through the given type, normalizing associated types mentioned
+    /// in it by replacing them by type variables and registering obligations to
+    /// resolve later. This should be done once for every type we get from some
+    /// type annotation (e.g. from a let type annotation, field type or function
+    /// call). `make_ty` handles this already, but e.g. for field types we need
+    /// to do it as well.
+    fn normalize_associated_types_in(&mut self, ty: Ty) -> Ty {
+        let ty = self.resolve_ty_as_possible(ty);
+        ty.fold(&mut |ty| match ty {
+            Ty::Projection(proj_ty) => self.normalize_projection_ty(proj_ty),
+            _ => ty,
+        })
+    }
+
+    fn normalize_projection_ty(&mut self, proj_ty: ProjectionTy) -> Ty {
+        let var = self.table.new_type_var();
+        let predicate = ProjectionPredicate { projection_ty: proj_ty, ty: var.clone() };
+        let obligation = Obligation::Projection(predicate);
+        self.obligations.push(obligation);
+        var
+    }
+
+    fn resolve_variant(&mut self, path: Option<&Path>) -> (Ty, Option<VariantId>) {
+        let path = match path {
+            Some(path) => path,
+            None => return (Ty::Unknown, None),
+        };
+        let resolver = &self.resolver;
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+        // FIXME: this should resolve assoc items as well, see this example:
+        // https://play.rust-lang.org/?gist=087992e9e22495446c01c0d4e2d69521
+        let (resolution, unresolved) =
+            match resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
+                Some(it) => it,
+                None => return (Ty::Unknown, None),
+            };
+        return match resolution {
+            TypeNs::AdtId(AdtId::StructId(strukt)) => {
+                let substs = Ty::substs_from_path(&ctx, path, strukt.into(), true);
+                let ty = self.db.ty(strukt.into());
+                let ty = self.insert_type_vars(ty.subst(&substs));
+                forbid_unresolved_segments((ty, Some(strukt.into())), unresolved)
+            }
+            TypeNs::AdtId(AdtId::UnionId(u)) => {
+                let substs = Ty::substs_from_path(&ctx, path, u.into(), true);
+                let ty = self.db.ty(u.into());
+                let ty = self.insert_type_vars(ty.subst(&substs));
+                forbid_unresolved_segments((ty, Some(u.into())), unresolved)
+            }
+            TypeNs::EnumVariantId(var) => {
+                let substs = Ty::substs_from_path(&ctx, path, var.into(), true);
+                let ty = self.db.ty(var.parent.into());
+                let ty = self.insert_type_vars(ty.subst(&substs));
+                forbid_unresolved_segments((ty, Some(var.into())), unresolved)
+            }
+            TypeNs::SelfType(impl_id) => {
+                let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
+                let substs = Substs::type_params_for_generics(&generics);
+                let ty = self.db.impl_self_ty(impl_id).subst(&substs);
+                match unresolved {
+                    None => {
+                        let variant = ty_variant(&ty);
+                        (ty, variant)
+                    }
+                    Some(1) => {
+                        let segment = path.mod_path().segments.last().unwrap();
+                        // this could be an enum variant or associated type
+                        if let Some((AdtId::EnumId(enum_id), _)) = ty.as_adt() {
+                            let enum_data = self.db.enum_data(enum_id);
+                            if let Some(local_id) = enum_data.variant(segment) {
+                                let variant = EnumVariantId { parent: enum_id, local_id };
+                                return (ty, Some(variant.into()));
+                            }
+                        }
+                        // FIXME potentially resolve assoc type
+                        (Ty::Unknown, None)
+                    }
+                    Some(_) => {
+                        // FIXME diagnostic
+                        (Ty::Unknown, None)
+                    }
+                }
+            }
+            TypeNs::TypeAliasId(it) => {
+                let substs = Substs::build_for_def(self.db, it)
+                    .fill(std::iter::repeat_with(|| self.table.new_type_var()))
+                    .build();
+                let ty = self.db.ty(it.into()).subst(&substs);
+                let variant = ty_variant(&ty);
+                forbid_unresolved_segments((ty, variant), unresolved)
+            }
+            TypeNs::AdtSelfType(_) => {
+                // FIXME this could happen in array size expressions, once we're checking them
+                (Ty::Unknown, None)
+            }
+            TypeNs::GenericParam(_) => {
+                // FIXME potentially resolve assoc type
+                (Ty::Unknown, None)
+            }
+            TypeNs::AdtId(AdtId::EnumId(_)) | TypeNs::BuiltinType(_) | TypeNs::TraitId(_) => {
+                // FIXME diagnostic
+                (Ty::Unknown, None)
+            }
+        };
+
+        fn forbid_unresolved_segments(
+            result: (Ty, Option<VariantId>),
+            unresolved: Option<usize>,
+        ) -> (Ty, Option<VariantId>) {
+            if unresolved.is_none() {
+                result
+            } else {
+                // FIXME diagnostic
+                (Ty::Unknown, None)
+            }
+        }
+
+        fn ty_variant(ty: &Ty) -> Option<VariantId> {
+            ty.as_adt().and_then(|(adt_id, _)| match adt_id {
+                AdtId::StructId(s) => Some(VariantId::StructId(s)),
+                AdtId::UnionId(u) => Some(VariantId::UnionId(u)),
+                AdtId::EnumId(_) => {
+                    // FIXME Error E0071, expected struct, variant or union type, found enum `Foo`
+                    None
+                }
+            })
+        }
+    }
+
+    fn collect_const(&mut self, data: &ConstData) {
+        self.return_ty = self.make_ty(&data.type_ref);
+    }
+
+    fn collect_static(&mut self, data: &StaticData) {
+        self.return_ty = self.make_ty(&data.type_ref);
+    }
+
+    fn collect_fn(&mut self, data: &FunctionData) {
+        let body = Arc::clone(&self.body); // avoid borrow checker problem
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
+            .with_impl_trait_mode(ImplTraitLoweringMode::Param);
+        let param_tys =
+            data.params.iter().map(|type_ref| Ty::from_hir(&ctx, type_ref)).collect::<Vec<_>>();
+        for (ty, pat) in param_tys.into_iter().zip(body.params.iter()) {
+            let ty = self.insert_type_vars(ty);
+            let ty = self.normalize_associated_types_in(ty);
+
+            self.infer_pat(*pat, &ty, BindingMode::default());
+        }
+        let return_ty = self.make_ty_with_mode(&data.ret_type, ImplTraitLoweringMode::Disallowed); // FIXME implement RPIT
+        self.return_ty = return_ty;
+    }
+
+    fn infer_body(&mut self) {
+        self.infer_expr_coerce(self.body.body_expr, &Expectation::has_type(self.return_ty.clone()));
+    }
+
+    fn resolve_lang_item(&self, name: &str) -> Option<LangItemTarget> {
+        let krate = self.resolver.krate()?;
+        let name = SmolStr::new_inline_from_ascii(name.len(), name.as_bytes());
+        self.db.lang_item(krate, name)
+    }
+
+    fn resolve_into_iter_item(&self) -> Option<TypeAliasId> {
+        let path = path![core::iter::IntoIterator];
+        let trait_ = self.resolver.resolve_known_trait(self.db.upcast(), &path)?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Item])
+    }
+
+    fn resolve_ops_try_ok(&self) -> Option<TypeAliasId> {
+        let path = path![core::ops::Try];
+        let trait_ = self.resolver.resolve_known_trait(self.db.upcast(), &path)?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Ok])
+    }
+
+    fn resolve_ops_neg_output(&self) -> Option<TypeAliasId> {
+        let trait_ = self.resolve_lang_item("neg")?.as_trait()?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Output])
+    }
+
+    fn resolve_ops_not_output(&self) -> Option<TypeAliasId> {
+        let trait_ = self.resolve_lang_item("not")?.as_trait()?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Output])
+    }
+
+    fn resolve_future_future_output(&self) -> Option<TypeAliasId> {
+        let trait_ = self.resolve_lang_item("future_trait")?.as_trait()?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Output])
+    }
+
+    fn resolve_boxed_box(&self) -> Option<AdtId> {
+        let struct_ = self.resolve_lang_item("owned_box")?.as_struct()?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_full(&self) -> Option<AdtId> {
+        let path = path![core::ops::RangeFull];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range(&self) -> Option<AdtId> {
+        let path = path![core::ops::Range];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_inclusive(&self) -> Option<AdtId> {
+        let path = path![core::ops::RangeInclusive];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_from(&self) -> Option<AdtId> {
+        let path = path![core::ops::RangeFrom];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_to(&self) -> Option<AdtId> {
+        let path = path![core::ops::RangeTo];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_range_to_inclusive(&self) -> Option<AdtId> {
+        let path = path![core::ops::RangeToInclusive];
+        let struct_ = self.resolver.resolve_known_struct(self.db.upcast(), &path)?;
+        Some(struct_.into())
+    }
+
+    fn resolve_ops_index(&self) -> Option<TraitId> {
+        self.resolve_lang_item("index")?.as_trait()
+    }
+
+    fn resolve_ops_index_output(&self) -> Option<TypeAliasId> {
+        let trait_ = self.resolve_ops_index()?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Output])
+    }
+}
+
+/// The kinds of placeholders we need during type inference. There's separate
+/// values for general types, and for integer and float variables. The latter
+/// two are used for inference of literal values (e.g. `100` could be one of
+/// several integer types).
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub enum InferTy {
+    TypeVar(unify::TypeVarId),
+    IntVar(unify::TypeVarId),
+    FloatVar(unify::TypeVarId),
+    MaybeNeverTypeVar(unify::TypeVarId),
+}
+
+impl InferTy {
+    fn to_inner(self) -> unify::TypeVarId {
+        match self {
+            InferTy::TypeVar(ty)
+            | InferTy::IntVar(ty)
+            | InferTy::FloatVar(ty)
+            | InferTy::MaybeNeverTypeVar(ty) => ty,
+        }
+    }
+
+    fn fallback_value(self) -> Ty {
+        match self {
+            InferTy::TypeVar(..) => Ty::Unknown,
+            InferTy::IntVar(..) => Ty::simple(TypeCtor::Int(IntTy::i32())),
+            InferTy::FloatVar(..) => Ty::simple(TypeCtor::Float(FloatTy::f64())),
+            InferTy::MaybeNeverTypeVar(..) => Ty::simple(TypeCtor::Never),
+        }
+    }
+}
+
+/// When inferring an expression, we propagate downward whatever type hint we
+/// are able in the form of an `Expectation`.
+#[derive(Clone, PartialEq, Eq, Debug)]
+struct Expectation {
+    ty: Ty,
+    /// See the `rvalue_hint` method.
+    rvalue_hint: bool,
+}
+
+impl Expectation {
+    /// The expectation that the type of the expression needs to equal the given
+    /// type.
+    fn has_type(ty: Ty) -> Self {
+        Expectation { ty, rvalue_hint: false }
+    }
+
+    /// The following explanation is copied straight from rustc:
+    /// Provides an expectation for an rvalue expression given an *optional*
+    /// hint, which is not required for type safety (the resulting type might
+    /// be checked higher up, as is the case with `&expr` and `box expr`), but
+    /// is useful in determining the concrete type.
+    ///
+    /// The primary use case is where the expected type is a fat pointer,
+    /// like `&[isize]`. For example, consider the following statement:
+    ///
+    ///    let x: &[isize] = &[1, 2, 3];
+    ///
+    /// In this case, the expected type for the `&[1, 2, 3]` expression is
+    /// `&[isize]`. If however we were to say that `[1, 2, 3]` has the
+    /// expectation `ExpectHasType([isize])`, that would be too strong --
+    /// `[1, 2, 3]` does not have the type `[isize]` but rather `[isize; 3]`.
+    /// It is only the `&[1, 2, 3]` expression as a whole that can be coerced
+    /// to the type `&[isize]`. Therefore, we propagate this more limited hint,
+    /// which still is useful, because it informs integer literals and the like.
+    /// See the test case `test/ui/coerce-expect-unsized.rs` and #20169
+    /// for examples of where this comes up,.
+    fn rvalue_hint(ty: Ty) -> Self {
+        Expectation { ty, rvalue_hint: true }
+    }
+
+    /// This expresses no expectation on the type.
+    fn none() -> Self {
+        Expectation { ty: Ty::Unknown, rvalue_hint: false }
+    }
+
+    fn coercion_target(&self) -> &Ty {
+        if self.rvalue_hint {
+            &Ty::Unknown
+        } else {
+            &self.ty
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+enum Diverges {
+    Maybe,
+    Always,
+}
+
+impl Diverges {
+    fn is_always(self) -> bool {
+        self == Diverges::Always
+    }
+}
+
+impl std::ops::BitAnd for Diverges {
+    type Output = Self;
+    fn bitand(self, other: Self) -> Self {
+        std::cmp::min(self, other)
+    }
+}
+
+impl std::ops::BitOr for Diverges {
+    type Output = Self;
+    fn bitor(self, other: Self) -> Self {
+        std::cmp::max(self, other)
+    }
+}
+
+impl std::ops::BitAndAssign for Diverges {
+    fn bitand_assign(&mut self, other: Self) {
+        *self = *self & other;
+    }
+}
+
+impl std::ops::BitOrAssign for Diverges {
+    fn bitor_assign(&mut self, other: Self) {
+        *self = *self | other;
+    }
+}
+
+mod diagnostics {
+    use hir_def::{expr::ExprId, DefWithBodyId};
+    use hir_expand::diagnostics::DiagnosticSink;
+
+    use crate::{
+        db::HirDatabase,
+        diagnostics::{BreakOutsideOfLoop, NoSuchField},
+    };
+
+    #[derive(Debug, PartialEq, Eq, Clone)]
+    pub(super) enum InferenceDiagnostic {
+        NoSuchField { expr: ExprId, field: usize },
+        BreakOutsideOfLoop { expr: ExprId },
+    }
+
+    impl InferenceDiagnostic {
+        pub(super) fn add_to(
+            &self,
+            db: &dyn HirDatabase,
+            owner: DefWithBodyId,
+            sink: &mut DiagnosticSink,
+        ) {
+            match self {
+                InferenceDiagnostic::NoSuchField { expr, field } => {
+                    let (_, source_map) = db.body_with_source_map(owner);
+                    let field = source_map.field_syntax(*expr, *field);
+                    sink.push(NoSuchField { file: field.file_id, field: field.value })
+                }
+                InferenceDiagnostic::BreakOutsideOfLoop { expr } => {
+                    let (_, source_map) = db.body_with_source_map(owner);
+                    let ptr = source_map
+                        .expr_syntax(*expr)
+                        .expect("break outside of loop in synthetic syntax");
+                    sink.push(BreakOutsideOfLoop { file: ptr.file_id, expr: ptr.value })
+                }
+            }
+        }
+    }
+}

crates/hir_ty/src/infer/coerce.rs

@@ -0,0 +1,197 @@
+//! Coercion logic. Coercions are certain type conversions that can implicitly
+//! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions
+//! like going from `&Vec<T>` to `&[T]`.
+//!
+//! See: https://doc.rust-lang.org/nomicon/coercions.html
+
+use hir_def::{lang_item::LangItemTarget, type_ref::Mutability};
+use test_utils::mark;
+
+use crate::{autoderef, traits::Solution, Obligation, Substs, TraitRef, Ty, TypeCtor};
+
+use super::{unify::TypeVarValue, InEnvironment, InferTy, InferenceContext};
+
+impl<'a> InferenceContext<'a> {
+    /// Unify two types, but may coerce the first one to the second one
+    /// using "implicit coercion rules" if needed.
+    pub(super) fn coerce(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool {
+        let from_ty = self.resolve_ty_shallow(from_ty).into_owned();
+        let to_ty = self.resolve_ty_shallow(to_ty);
+        self.coerce_inner(from_ty, &to_ty)
+    }
+
+    /// Merge two types from different branches, with possible coercion.
+    ///
+    /// Mostly this means trying to coerce one to the other, but
+    ///  - if we have two function types for different functions, we need to
+    ///    coerce both to function pointers;
+    ///  - if we were concerned with lifetime subtyping, we'd need to look for a
+    ///    least upper bound.
+    pub(super) fn coerce_merge_branch(&mut self, ty1: &Ty, ty2: &Ty) -> Ty {
+        if self.coerce(ty1, ty2) {
+            ty2.clone()
+        } else if self.coerce(ty2, ty1) {
+            ty1.clone()
+        } else {
+            if let (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnDef(_))) = (ty1, ty2) {
+                mark::hit!(coerce_fn_reification);
+                // Special case: two function types. Try to coerce both to
+                // pointers to have a chance at getting a match. See
+                // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916
+                let sig1 = ty1.callable_sig(self.db).expect("FnDef without callable sig");
+                let sig2 = ty2.callable_sig(self.db).expect("FnDef without callable sig");
+                let ptr_ty1 = Ty::fn_ptr(sig1);
+                let ptr_ty2 = Ty::fn_ptr(sig2);
+                self.coerce_merge_branch(&ptr_ty1, &ptr_ty2)
+            } else {
+                mark::hit!(coerce_merge_fail_fallback);
+                ty1.clone()
+            }
+        }
+    }
+
+    fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool {
+        match (&from_ty, to_ty) {
+            // Never type will make type variable to fallback to Never Type instead of Unknown.
+            (ty_app!(TypeCtor::Never), Ty::Infer(InferTy::TypeVar(tv))) => {
+                let var = self.table.new_maybe_never_type_var();
+                self.table.var_unification_table.union_value(*tv, TypeVarValue::Known(var));
+                return true;
+            }
+            (ty_app!(TypeCtor::Never), _) => return true,
+
+            // Trivial cases, this should go after `never` check to
+            // avoid infer result type to be never
+            _ => {
+                if self.table.unify_inner_trivial(&from_ty, &to_ty, 0) {
+                    return true;
+                }
+            }
+        }
+
+        // Pointer weakening and function to pointer
+        match (&mut from_ty, to_ty) {
+            // `*mut T`, `&mut T, `&T`` -> `*const T`
+            // `&mut T` -> `&T`
+            // `&mut T` -> `*mut T`
+            (ty_app!(c1@TypeCtor::RawPtr(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::Ref(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(Mutability::Mut)), ty_app!(c2@TypeCtor::RawPtr(_))) => {
+                *c1 = *c2;
+            }
+
+            // Illegal mutablity conversion
+            (
+                ty_app!(TypeCtor::RawPtr(Mutability::Shared)),
+                ty_app!(TypeCtor::RawPtr(Mutability::Mut)),
+            )
+            | (
+                ty_app!(TypeCtor::Ref(Mutability::Shared)),
+                ty_app!(TypeCtor::Ref(Mutability::Mut)),
+            ) => return false,
+
+            // `{function_type}` -> `fn()`
+            (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnPtr { .. })) => {
+                match from_ty.callable_sig(self.db) {
+                    None => return false,
+                    Some(sig) => {
+                        from_ty = Ty::fn_ptr(sig);
+                    }
+                }
+            }
+
+            (ty_app!(TypeCtor::Closure { .. }, params), ty_app!(TypeCtor::FnPtr { .. })) => {
+                from_ty = params[0].clone();
+            }
+
+            _ => {}
+        }
+
+        if let Some(ret) = self.try_coerce_unsized(&from_ty, &to_ty) {
+            return ret;
+        }
+
+        // Auto Deref if cannot coerce
+        match (&from_ty, to_ty) {
+            // FIXME: DerefMut
+            (ty_app!(TypeCtor::Ref(_), st1), ty_app!(TypeCtor::Ref(_), st2)) => {
+                self.unify_autoderef_behind_ref(&st1[0], &st2[0])
+            }
+
+            // Otherwise, normal unify
+            _ => self.unify(&from_ty, to_ty),
+        }
+    }
+
+    /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>`
+    ///
+    /// See: https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html
+    fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> Option<bool> {
+        let krate = self.resolver.krate().unwrap();
+        let coerce_unsized_trait = match self.db.lang_item(krate, "coerce_unsized".into()) {
+            Some(LangItemTarget::TraitId(trait_)) => trait_,
+            _ => return None,
+        };
+
+        let generic_params = crate::utils::generics(self.db.upcast(), coerce_unsized_trait.into());
+        if generic_params.len() != 2 {
+            // The CoerceUnsized trait should have two generic params: Self and T.
+            return None;
+        }
+
+        let substs = Substs::build_for_generics(&generic_params)
+            .push(from_ty.clone())
+            .push(to_ty.clone())
+            .build();
+        let trait_ref = TraitRef { trait_: coerce_unsized_trait, substs };
+        let goal = InEnvironment::new(self.trait_env.clone(), Obligation::Trait(trait_ref));
+
+        let canonicalizer = self.canonicalizer();
+        let canonicalized = canonicalizer.canonicalize_obligation(goal);
+
+        let solution = self.db.trait_solve(krate, canonicalized.value.clone())?;
+
+        match solution {
+            Solution::Unique(v) => {
+                canonicalized.apply_solution(self, v.0);
+            }
+            _ => return None,
+        };
+
+        Some(true)
+    }
+
+    /// Unify `from_ty` to `to_ty` with optional auto Deref
+    ///
+    /// Note that the parameters are already stripped the outer reference.
+    fn unify_autoderef_behind_ref(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool {
+        let canonicalized = self.canonicalizer().canonicalize_ty(from_ty.clone());
+        let to_ty = self.resolve_ty_shallow(&to_ty);
+        // FIXME: Auto DerefMut
+        for derefed_ty in autoderef::autoderef(
+            self.db,
+            self.resolver.krate(),
+            InEnvironment {
+                value: canonicalized.value.clone(),
+                environment: self.trait_env.clone(),
+            },
+        ) {
+            let derefed_ty = canonicalized.decanonicalize_ty(derefed_ty.value);
+            match (&*self.resolve_ty_shallow(&derefed_ty), &*to_ty) {
+                // Stop when constructor matches.
+                (ty_app!(from_ctor, st1), ty_app!(to_ctor, st2)) if from_ctor == to_ctor => {
+                    // It will not recurse to `coerce`.
+                    return self.table.unify_substs(st1, st2, 0);
+                }
+                _ => {
+                    if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) {
+                        return true;
+                    }
+                }
+            }
+        }
+
+        false
+    }
+}

crates/hir_ty/src/infer/expr.rs

@@ -0,0 +1,873 @@
+//! Type inference for expressions.
+
+use std::iter::{repeat, repeat_with};
+use std::{mem, sync::Arc};
+
+use hir_def::{
+    builtin_type::Signedness,
+    expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
+    path::{GenericArg, GenericArgs},
+    resolver::resolver_for_expr,
+    AdtId, AssocContainerId, FieldId, Lookup,
+};
+use hir_expand::name::{name, Name};
+use syntax::ast::RangeOp;
+
+use crate::{
+    autoderef, method_resolution, op,
+    traits::{FnTrait, InEnvironment},
+    utils::{generics, variant_data, Generics},
+    ApplicationTy, Binders, CallableDefId, InferTy, IntTy, Mutability, Obligation, Rawness, Substs,
+    TraitRef, Ty, TypeCtor,
+};
+
+use super::{
+    find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
+    InferenceDiagnostic, TypeMismatch,
+};
+
+impl<'a> InferenceContext<'a> {
+    pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
+        let ty = self.infer_expr_inner(tgt_expr, expected);
+        if ty.is_never() {
+            // Any expression that produces a value of type `!` must have diverged
+            self.diverges = Diverges::Always;
+        }
+        let could_unify = self.unify(&ty, &expected.ty);
+        if !could_unify {
+            self.result.type_mismatches.insert(
+                tgt_expr,
+                TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
+            );
+        }
+        self.resolve_ty_as_possible(ty)
+    }
+
+    /// Infer type of expression with possibly implicit coerce to the expected type.
+    /// Return the type after possible coercion.
+    pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
+        let ty = self.infer_expr_inner(expr, &expected);
+        let ty = if !self.coerce(&ty, &expected.coercion_target()) {
+            self.result
+                .type_mismatches
+                .insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
+            // Return actual type when type mismatch.
+            // This is needed for diagnostic when return type mismatch.
+            ty
+        } else if expected.coercion_target() == &Ty::Unknown {
+            ty
+        } else {
+            expected.ty.clone()
+        };
+
+        self.resolve_ty_as_possible(ty)
+    }
+
+    fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
+        let krate = self.resolver.krate()?;
+        let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
+        let output_assoc_type =
+            self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
+        let generic_params = generics(self.db.upcast(), fn_once_trait.into());
+        if generic_params.len() != 2 {
+            return None;
+        }
+
+        let mut param_builder = Substs::builder(num_args);
+        let mut arg_tys = vec![];
+        for _ in 0..num_args {
+            let arg = self.table.new_type_var();
+            param_builder = param_builder.push(arg.clone());
+            arg_tys.push(arg);
+        }
+        let parameters = param_builder.build();
+        let arg_ty = Ty::Apply(ApplicationTy {
+            ctor: TypeCtor::Tuple { cardinality: num_args as u16 },
+            parameters,
+        });
+        let substs =
+            Substs::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
+
+        let trait_env = Arc::clone(&self.trait_env);
+        let implements_fn_trait =
+            Obligation::Trait(TraitRef { trait_: fn_once_trait, substs: substs.clone() });
+        let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
+            value: implements_fn_trait.clone(),
+            environment: trait_env,
+        });
+        if self.db.trait_solve(krate, goal.value).is_some() {
+            self.obligations.push(implements_fn_trait);
+            let output_proj_ty =
+                crate::ProjectionTy { associated_ty: output_assoc_type, parameters: substs };
+            let return_ty = self.normalize_projection_ty(output_proj_ty);
+            Some((arg_tys, return_ty))
+        } else {
+            None
+        }
+    }
+
+    pub fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
+        match ty.callable_sig(self.db) {
+            Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
+            None => self.callable_sig_from_fn_trait(ty, num_args),
+        }
+    }
+
+    fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
+        let body = Arc::clone(&self.body); // avoid borrow checker problem
+        let ty = match &body[tgt_expr] {
+            Expr::Missing => Ty::Unknown,
+            Expr::If { condition, then_branch, else_branch } => {
+                // if let is desugared to match, so this is always simple if
+                self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
+
+                let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
+                let mut both_arms_diverge = Diverges::Always;
+
+                let then_ty = self.infer_expr_inner(*then_branch, &expected);
+                both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
+                let else_ty = match else_branch {
+                    Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
+                    None => Ty::unit(),
+                };
+                both_arms_diverge &= self.diverges;
+
+                self.diverges = condition_diverges | both_arms_diverge;
+
+                self.coerce_merge_branch(&then_ty, &else_ty)
+            }
+            Expr::Block { statements, tail, .. } => {
+                // FIXME: Breakable block inference
+                self.infer_block(statements, *tail, expected)
+            }
+            Expr::Unsafe { body } => self.infer_expr(*body, expected),
+            Expr::TryBlock { body } => {
+                let _inner = self.infer_expr(*body, expected);
+                // FIXME should be std::result::Result<{inner}, _>
+                Ty::Unknown
+            }
+            Expr::Loop { body, label } => {
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    break_ty: self.table.new_type_var(),
+                    label: label.clone(),
+                });
+                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+
+                let ctxt = self.breakables.pop().expect("breakable stack broken");
+                if ctxt.may_break {
+                    self.diverges = Diverges::Maybe;
+                }
+
+                if ctxt.may_break {
+                    ctxt.break_ty
+                } else {
+                    Ty::simple(TypeCtor::Never)
+                }
+            }
+            Expr::While { condition, body, label } => {
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    break_ty: Ty::Unknown,
+                    label: label.clone(),
+                });
+                // while let is desugared to a match loop, so this is always simple while
+                self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
+                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                let _ctxt = self.breakables.pop().expect("breakable stack broken");
+                // the body may not run, so it diverging doesn't mean we diverge
+                self.diverges = Diverges::Maybe;
+                Ty::unit()
+            }
+            Expr::For { iterable, body, pat, label } => {
+                let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
+
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    break_ty: Ty::Unknown,
+                    label: label.clone(),
+                });
+                let pat_ty =
+                    self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
+
+                self.infer_pat(*pat, &pat_ty, BindingMode::default());
+
+                self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
+                let _ctxt = self.breakables.pop().expect("breakable stack broken");
+                // the body may not run, so it diverging doesn't mean we diverge
+                self.diverges = Diverges::Maybe;
+                Ty::unit()
+            }
+            Expr::Lambda { body, args, ret_type, arg_types } => {
+                assert_eq!(args.len(), arg_types.len());
+
+                let mut sig_tys = Vec::new();
+
+                // collect explicitly written argument types
+                for arg_type in arg_types.iter() {
+                    let arg_ty = if let Some(type_ref) = arg_type {
+                        self.make_ty(type_ref)
+                    } else {
+                        self.table.new_type_var()
+                    };
+                    sig_tys.push(arg_ty);
+                }
+
+                // add return type
+                let ret_ty = match ret_type {
+                    Some(type_ref) => self.make_ty(type_ref),
+                    None => self.table.new_type_var(),
+                };
+                sig_tys.push(ret_ty.clone());
+                let sig_ty = Ty::apply(
+                    TypeCtor::FnPtr { num_args: sig_tys.len() as u16 - 1, is_varargs: false },
+                    Substs(sig_tys.clone().into()),
+                );
+                let closure_ty =
+                    Ty::apply_one(TypeCtor::Closure { def: self.owner, expr: tgt_expr }, sig_ty);
+
+                // Eagerly try to relate the closure type with the expected
+                // type, otherwise we often won't have enough information to
+                // infer the body.
+                self.coerce(&closure_ty, &expected.ty);
+
+                // Now go through the argument patterns
+                for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
+                    let resolved = self.resolve_ty_as_possible(arg_ty);
+                    self.infer_pat(*arg_pat, &resolved, BindingMode::default());
+                }
+
+                let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
+                let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
+
+                self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
+
+                self.diverges = prev_diverges;
+                self.return_ty = prev_ret_ty;
+
+                closure_ty
+            }
+            Expr::Call { callee, args } => {
+                let callee_ty = self.infer_expr(*callee, &Expectation::none());
+                let canonicalized = self.canonicalizer().canonicalize_ty(callee_ty.clone());
+                let mut derefs = autoderef(
+                    self.db,
+                    self.resolver.krate(),
+                    InEnvironment {
+                        value: canonicalized.value.clone(),
+                        environment: self.trait_env.clone(),
+                    },
+                );
+                let (param_tys, ret_ty): (Vec<Ty>, Ty) = derefs
+                    .find_map(|callee_deref_ty| {
+                        self.callable_sig(
+                            &canonicalized.decanonicalize_ty(callee_deref_ty.value),
+                            args.len(),
+                        )
+                    })
+                    .unwrap_or((Vec::new(), Ty::Unknown));
+                self.register_obligations_for_call(&callee_ty);
+                self.check_call_arguments(args, &param_tys);
+                self.normalize_associated_types_in(ret_ty)
+            }
+            Expr::MethodCall { receiver, args, method_name, generic_args } => self
+                .infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
+            Expr::Match { expr, arms } => {
+                let input_ty = self.infer_expr(*expr, &Expectation::none());
+
+                let mut result_ty = if arms.is_empty() {
+                    Ty::simple(TypeCtor::Never)
+                } else {
+                    self.table.new_type_var()
+                };
+
+                let matchee_diverges = self.diverges;
+                let mut all_arms_diverge = Diverges::Always;
+
+                for arm in arms {
+                    self.diverges = Diverges::Maybe;
+                    let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
+                    if let Some(guard_expr) = arm.guard {
+                        self.infer_expr(
+                            guard_expr,
+                            &Expectation::has_type(Ty::simple(TypeCtor::Bool)),
+                        );
+                    }
+
+                    let arm_ty = self.infer_expr_inner(arm.expr, &expected);
+                    all_arms_diverge &= self.diverges;
+                    result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
+                }
+
+                self.diverges = matchee_diverges | all_arms_diverge;
+
+                result_ty
+            }
+            Expr::Path(p) => {
+                // FIXME this could be more efficient...
+                let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
+                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
+            }
+            Expr::Continue { .. } => Ty::simple(TypeCtor::Never),
+            Expr::Break { expr, label } => {
+                let val_ty = if let Some(expr) = expr {
+                    self.infer_expr(*expr, &Expectation::none())
+                } else {
+                    Ty::unit()
+                };
+
+                let last_ty =
+                    if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
+                        ctxt.break_ty.clone()
+                    } else {
+                        Ty::Unknown
+                    };
+
+                let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
+
+                if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
+                    ctxt.break_ty = merged_type;
+                    ctxt.may_break = true;
+                } else {
+                    self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
+                        expr: tgt_expr,
+                    });
+                }
+
+                Ty::simple(TypeCtor::Never)
+            }
+            Expr::Return { expr } => {
+                if let Some(expr) = expr {
+                    self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
+                } else {
+                    let unit = Ty::unit();
+                    self.coerce(&unit, &self.return_ty.clone());
+                }
+                Ty::simple(TypeCtor::Never)
+            }
+            Expr::RecordLit { path, fields, spread } => {
+                let (ty, def_id) = self.resolve_variant(path.as_ref());
+                if let Some(variant) = def_id {
+                    self.write_variant_resolution(tgt_expr.into(), variant);
+                }
+
+                self.unify(&ty, &expected.ty);
+
+                let substs = ty.substs().unwrap_or_else(Substs::empty);
+                let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
+                let variant_data = def_id.map(|it| variant_data(self.db.upcast(), it));
+                for (field_idx, field) in fields.iter().enumerate() {
+                    let field_def =
+                        variant_data.as_ref().and_then(|it| match it.field(&field.name) {
+                            Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
+                            None => {
+                                self.push_diagnostic(InferenceDiagnostic::NoSuchField {
+                                    expr: tgt_expr,
+                                    field: field_idx,
+                                });
+                                None
+                            }
+                        });
+                    if let Some(field_def) = field_def {
+                        self.result.record_field_resolutions.insert(field.expr, field_def);
+                    }
+                    let field_ty = field_def
+                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
+                    self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
+                }
+                if let Some(expr) = spread {
+                    self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
+                }
+                ty
+            }
+            Expr::Field { expr, name } => {
+                let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
+                let ty = autoderef::autoderef(
+                    self.db,
+                    self.resolver.krate(),
+                    InEnvironment {
+                        value: canonicalized.value.clone(),
+                        environment: self.trait_env.clone(),
+                    },
+                )
+                .find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
+                    Ty::Apply(a_ty) => match a_ty.ctor {
+                        TypeCtor::Tuple { .. } => name
+                            .as_tuple_index()
+                            .and_then(|idx| a_ty.parameters.0.get(idx).cloned()),
+                        TypeCtor::Adt(AdtId::StructId(s)) => {
+                            self.db.struct_data(s).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: s.into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types(s.into())[field.local_id]
+                                    .clone()
+                                    .subst(&a_ty.parameters)
+                            })
+                        }
+                        TypeCtor::Adt(AdtId::UnionId(u)) => {
+                            self.db.union_data(u).variant_data.field(name).map(|local_id| {
+                                let field = FieldId { parent: u.into(), local_id };
+                                self.write_field_resolution(tgt_expr, field);
+                                self.db.field_types(u.into())[field.local_id]
+                                    .clone()
+                                    .subst(&a_ty.parameters)
+                            })
+                        }
+                        _ => None,
+                    },
+                    _ => None,
+                })
+                .unwrap_or(Ty::Unknown);
+                let ty = self.insert_type_vars(ty);
+                self.normalize_associated_types_in(ty)
+            }
+            Expr::Await { expr } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
+            }
+            Expr::Try { expr } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
+            }
+            Expr::Cast { expr, type_ref } => {
+                let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                let cast_ty = self.make_ty(type_ref);
+                // FIXME check the cast...
+                cast_ty
+            }
+            Expr::Ref { expr, rawness, mutability } => {
+                let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) =
+                    &expected.ty.as_reference_or_ptr()
+                {
+                    if *exp_mutability == Mutability::Mut && *mutability == Mutability::Shared {
+                        // FIXME: throw type error - expected mut reference but found shared ref,
+                        // which cannot be coerced
+                    }
+                    if *exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
+                        // FIXME: throw type error - expected reference but found ptr,
+                        // which cannot be coerced
+                    }
+                    Expectation::rvalue_hint(Ty::clone(exp_inner))
+                } else {
+                    Expectation::none()
+                };
+                let inner_ty = self.infer_expr_inner(*expr, &expectation);
+                let ty = match rawness {
+                    Rawness::RawPtr => TypeCtor::RawPtr(*mutability),
+                    Rawness::Ref => TypeCtor::Ref(*mutability),
+                };
+                Ty::apply_one(ty, inner_ty)
+            }
+            Expr::Box { expr } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                if let Some(box_) = self.resolve_boxed_box() {
+                    Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
+                } else {
+                    Ty::Unknown
+                }
+            }
+            Expr::UnaryOp { expr, op } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                match op {
+                    UnaryOp::Deref => match self.resolver.krate() {
+                        Some(krate) => {
+                            let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
+                            match autoderef::deref(
+                                self.db,
+                                krate,
+                                InEnvironment {
+                                    value: &canonicalized.value,
+                                    environment: self.trait_env.clone(),
+                                },
+                            ) {
+                                Some(derefed_ty) => {
+                                    canonicalized.decanonicalize_ty(derefed_ty.value)
+                                }
+                                None => Ty::Unknown,
+                            }
+                        }
+                        None => Ty::Unknown,
+                    },
+                    UnaryOp::Neg => {
+                        match &inner_ty {
+                            // Fast path for builtins
+                            Ty::Apply(ApplicationTy {
+                                ctor: TypeCtor::Int(IntTy { signedness: Signedness::Signed, .. }),
+                                ..
+                            })
+                            | Ty::Apply(ApplicationTy { ctor: TypeCtor::Float(_), .. })
+                            | Ty::Infer(InferTy::IntVar(..))
+                            | Ty::Infer(InferTy::FloatVar(..)) => inner_ty,
+                            // Otherwise we resolve via the std::ops::Neg trait
+                            _ => self
+                                .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
+                        }
+                    }
+                    UnaryOp::Not => {
+                        match &inner_ty {
+                            // Fast path for builtins
+                            Ty::Apply(ApplicationTy { ctor: TypeCtor::Bool, .. })
+                            | Ty::Apply(ApplicationTy { ctor: TypeCtor::Int(_), .. })
+                            | Ty::Infer(InferTy::IntVar(..)) => inner_ty,
+                            // Otherwise we resolve via the std::ops::Not trait
+                            _ => self
+                                .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
+                        }
+                    }
+                }
+            }
+            Expr::BinaryOp { lhs, rhs, op } => match op {
+                Some(op) => {
+                    let lhs_expectation = match op {
+                        BinaryOp::LogicOp(..) => Expectation::has_type(Ty::simple(TypeCtor::Bool)),
+                        _ => Expectation::none(),
+                    };
+                    let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
+                    // FIXME: find implementation of trait corresponding to operation
+                    // symbol and resolve associated `Output` type
+                    let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty.clone());
+                    let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
+
+                    // FIXME: similar as above, return ty is often associated trait type
+                    op::binary_op_return_ty(*op, lhs_ty, rhs_ty)
+                }
+                _ => Ty::Unknown,
+            },
+            Expr::Range { lhs, rhs, range_type } => {
+                let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
+                let rhs_expect = lhs_ty
+                    .as_ref()
+                    .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
+                let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
+                match (range_type, lhs_ty, rhs_ty) {
+                    (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
+                        Some(adt) => Ty::simple(TypeCtor::Adt(adt)),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, None, Some(ty)) => {
+                        match self.resolve_range_to_inclusive() {
+                            Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                            None => Ty::Unknown,
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, Some(_), Some(ty)) => {
+                        match self.resolve_range_inclusive() {
+                            Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                            None => Ty::Unknown,
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
+                        Some(adt) => Ty::apply_one(TypeCtor::Adt(adt), ty),
+                        None => Ty::Unknown,
+                    },
+                    (RangeOp::Inclusive, _, None) => Ty::Unknown,
+                }
+            }
+            Expr::Index { base, index } => {
+                let base_ty = self.infer_expr_inner(*base, &Expectation::none());
+                let index_ty = self.infer_expr(*index, &Expectation::none());
+
+                if let (Some(index_trait), Some(krate)) =
+                    (self.resolve_ops_index(), self.resolver.krate())
+                {
+                    let canonicalized = self.canonicalizer().canonicalize_ty(base_ty);
+                    let self_ty = method_resolution::resolve_indexing_op(
+                        self.db,
+                        &canonicalized.value,
+                        self.trait_env.clone(),
+                        krate,
+                        index_trait,
+                    );
+                    let self_ty =
+                        self_ty.map_or(Ty::Unknown, |t| canonicalized.decanonicalize_ty(t.value));
+                    self.resolve_associated_type_with_params(
+                        self_ty,
+                        self.resolve_ops_index_output(),
+                        &[index_ty],
+                    )
+                } else {
+                    Ty::Unknown
+                }
+            }
+            Expr::Tuple { exprs } => {
+                let mut tys = match &expected.ty {
+                    ty_app!(TypeCtor::Tuple { .. }, st) => st
+                        .iter()
+                        .cloned()
+                        .chain(repeat_with(|| self.table.new_type_var()))
+                        .take(exprs.len())
+                        .collect::<Vec<_>>(),
+                    _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
+                };
+
+                for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
+                    self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
+                }
+
+                Ty::apply(TypeCtor::Tuple { cardinality: tys.len() as u16 }, Substs(tys.into()))
+            }
+            Expr::Array(array) => {
+                let elem_ty = match &expected.ty {
+                    ty_app!(TypeCtor::Array, st) | ty_app!(TypeCtor::Slice, st) => {
+                        st.as_single().clone()
+                    }
+                    _ => self.table.new_type_var(),
+                };
+
+                match array {
+                    Array::ElementList(items) => {
+                        for expr in items.iter() {
+                            self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
+                        }
+                    }
+                    Array::Repeat { initializer, repeat } => {
+                        self.infer_expr_coerce(
+                            *initializer,
+                            &Expectation::has_type(elem_ty.clone()),
+                        );
+                        self.infer_expr(
+                            *repeat,
+                            &Expectation::has_type(Ty::simple(TypeCtor::Int(IntTy::usize()))),
+                        );
+                    }
+                }
+
+                Ty::apply_one(TypeCtor::Array, elem_ty)
+            }
+            Expr::Literal(lit) => match lit {
+                Literal::Bool(..) => Ty::simple(TypeCtor::Bool),
+                Literal::String(..) => {
+                    Ty::apply_one(TypeCtor::Ref(Mutability::Shared), Ty::simple(TypeCtor::Str))
+                }
+                Literal::ByteString(..) => {
+                    let byte_type = Ty::simple(TypeCtor::Int(IntTy::u8()));
+                    let array_type = Ty::apply_one(TypeCtor::Array, byte_type);
+                    Ty::apply_one(TypeCtor::Ref(Mutability::Shared), array_type)
+                }
+                Literal::Char(..) => Ty::simple(TypeCtor::Char),
+                Literal::Int(_v, ty) => match ty {
+                    Some(int_ty) => Ty::simple(TypeCtor::Int((*int_ty).into())),
+                    None => self.table.new_integer_var(),
+                },
+                Literal::Float(_v, ty) => match ty {
+                    Some(float_ty) => Ty::simple(TypeCtor::Float((*float_ty).into())),
+                    None => self.table.new_float_var(),
+                },
+            },
+        };
+        // use a new type variable if we got Ty::Unknown here
+        let ty = self.insert_type_vars_shallow(ty);
+        let ty = self.resolve_ty_as_possible(ty);
+        self.write_expr_ty(tgt_expr, ty.clone());
+        ty
+    }
+
+    fn infer_block(
+        &mut self,
+        statements: &[Statement],
+        tail: Option<ExprId>,
+        expected: &Expectation,
+    ) -> Ty {
+        for stmt in statements {
+            match stmt {
+                Statement::Let { pat, type_ref, initializer } => {
+                    let decl_ty =
+                        type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
+
+                    // Always use the declared type when specified
+                    let mut ty = decl_ty.clone();
+
+                    if let Some(expr) = initializer {
+                        let actual_ty =
+                            self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
+                        if decl_ty == Ty::Unknown {
+                            ty = actual_ty;
+                        }
+                    }
+
+                    let ty = self.resolve_ty_as_possible(ty);
+                    self.infer_pat(*pat, &ty, BindingMode::default());
+                }
+                Statement::Expr(expr) => {
+                    self.infer_expr(*expr, &Expectation::none());
+                }
+            }
+        }
+
+        let ty = if let Some(expr) = tail {
+            self.infer_expr_coerce(expr, expected)
+        } else {
+            // Citing rustc: if there is no explicit tail expression,
+            // that is typically equivalent to a tail expression
+            // of `()` -- except if the block diverges. In that
+            // case, there is no value supplied from the tail
+            // expression (assuming there are no other breaks,
+            // this implies that the type of the block will be
+            // `!`).
+            if self.diverges.is_always() {
+                // we don't even make an attempt at coercion
+                self.table.new_maybe_never_type_var()
+            } else {
+                self.coerce(&Ty::unit(), expected.coercion_target());
+                Ty::unit()
+            }
+        };
+        ty
+    }
+
+    fn infer_method_call(
+        &mut self,
+        tgt_expr: ExprId,
+        receiver: ExprId,
+        args: &[ExprId],
+        method_name: &Name,
+        generic_args: Option<&GenericArgs>,
+    ) -> Ty {
+        let receiver_ty = self.infer_expr(receiver, &Expectation::none());
+        let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
+
+        let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
+
+        let resolved = self.resolver.krate().and_then(|krate| {
+            method_resolution::lookup_method(
+                &canonicalized_receiver.value,
+                self.db,
+                self.trait_env.clone(),
+                krate,
+                &traits_in_scope,
+                method_name,
+            )
+        });
+        let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
+            Some((ty, func)) => {
+                let ty = canonicalized_receiver.decanonicalize_ty(ty);
+                self.write_method_resolution(tgt_expr, func);
+                (ty, self.db.value_ty(func.into()), Some(generics(self.db.upcast(), func.into())))
+            }
+            None => (receiver_ty, Binders::new(0, Ty::Unknown), None),
+        };
+        let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
+        let method_ty = method_ty.subst(&substs);
+        let method_ty = self.insert_type_vars(method_ty);
+        self.register_obligations_for_call(&method_ty);
+        let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
+            Some(sig) => {
+                if !sig.params().is_empty() {
+                    (sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
+                } else {
+                    (Ty::Unknown, Vec::new(), sig.ret().clone())
+                }
+            }
+            None => (Ty::Unknown, Vec::new(), Ty::Unknown),
+        };
+        // Apply autoref so the below unification works correctly
+        // FIXME: return correct autorefs from lookup_method
+        let actual_receiver_ty = match expected_receiver_ty.as_reference() {
+            Some((_, mutability)) => Ty::apply_one(TypeCtor::Ref(mutability), derefed_receiver_ty),
+            _ => derefed_receiver_ty,
+        };
+        self.unify(&expected_receiver_ty, &actual_receiver_ty);
+
+        self.check_call_arguments(args, &param_tys);
+        self.normalize_associated_types_in(ret_ty)
+    }
+
+    fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
+        // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
+        // We do this in a pretty awful way: first we type-check any arguments
+        // that are not closures, then we type-check the closures. This is so
+        // that we have more information about the types of arguments when we
+        // type-check the functions. This isn't really the right way to do this.
+        for &check_closures in &[false, true] {
+            let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
+            for (&arg, param_ty) in args.iter().zip(param_iter) {
+                let is_closure = matches!(&self.body[arg], Expr::Lambda { .. });
+                if is_closure != check_closures {
+                    continue;
+                }
+
+                let param_ty = self.normalize_associated_types_in(param_ty);
+                self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
+            }
+        }
+    }
+
+    fn substs_for_method_call(
+        &mut self,
+        def_generics: Option<Generics>,
+        generic_args: Option<&GenericArgs>,
+        receiver_ty: &Ty,
+    ) -> Substs {
+        let (parent_params, self_params, type_params, impl_trait_params) =
+            def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
+        assert_eq!(self_params, 0); // method shouldn't have another Self param
+        let total_len = parent_params + type_params + impl_trait_params;
+        let mut substs = Vec::with_capacity(total_len);
+        // Parent arguments are unknown, except for the receiver type
+        if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
+            for (_id, param) in parent_generics {
+                if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
+                    substs.push(receiver_ty.clone());
+                } else {
+                    substs.push(Ty::Unknown);
+                }
+            }
+        }
+        // handle provided type arguments
+        if let Some(generic_args) = generic_args {
+            // if args are provided, it should be all of them, but we can't rely on that
+            for arg in generic_args.args.iter().take(type_params) {
+                match arg {
+                    GenericArg::Type(type_ref) => {
+                        let ty = self.make_ty(type_ref);
+                        substs.push(ty);
+                    }
+                }
+            }
+        };
+        let supplied_params = substs.len();
+        for _ in supplied_params..total_len {
+            substs.push(Ty::Unknown);
+        }
+        assert_eq!(substs.len(), total_len);
+        Substs(substs.into())
+    }
+
+    fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
+        if let Ty::Apply(a_ty) = callable_ty {
+            if let TypeCtor::FnDef(def) = a_ty.ctor {
+                let generic_predicates = self.db.generic_predicates(def.into());
+                for predicate in generic_predicates.iter() {
+                    let predicate = predicate.clone().subst(&a_ty.parameters);
+                    if let Some(obligation) = Obligation::from_predicate(predicate) {
+                        self.obligations.push(obligation);
+                    }
+                }
+                // add obligation for trait implementation, if this is a trait method
+                match def {
+                    CallableDefId::FunctionId(f) => {
+                        if let AssocContainerId::TraitId(trait_) =
+                            f.lookup(self.db.upcast()).container
+                        {
+                            // construct a TraitDef
+                            let substs = a_ty
+                                .parameters
+                                .prefix(generics(self.db.upcast(), trait_.into()).len());
+                            self.obligations.push(Obligation::Trait(TraitRef { trait_, substs }));
+                        }
+                    }
+                    CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
+                }
+            }
+        }
+    }
+}

crates/hir_ty/src/infer/pat.rs

@@ -0,0 +1,241 @@
+//! Type inference for patterns.
+
+use std::iter::repeat;
+use std::sync::Arc;
+
+use hir_def::{
+    expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
+    path::Path,
+    type_ref::Mutability,
+    FieldId,
+};
+use hir_expand::name::Name;
+use test_utils::mark;
+
+use super::{BindingMode, Expectation, InferenceContext};
+use crate::{utils::variant_data, Substs, Ty, TypeCtor};
+
+impl<'a> InferenceContext<'a> {
+    fn infer_tuple_struct_pat(
+        &mut self,
+        path: Option<&Path>,
+        subpats: &[PatId],
+        expected: &Ty,
+        default_bm: BindingMode,
+        id: PatId,
+    ) -> Ty {
+        let (ty, def) = self.resolve_variant(path);
+        let var_data = def.map(|it| variant_data(self.db.upcast(), it));
+        if let Some(variant) = def {
+            self.write_variant_resolution(id.into(), variant);
+        }
+        self.unify(&ty, expected);
+
+        let substs = ty.substs().unwrap_or_else(Substs::empty);
+
+        let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
+
+        for (i, &subpat) in subpats.iter().enumerate() {
+            let expected_ty = var_data
+                .as_ref()
+                .and_then(|d| d.field(&Name::new_tuple_field(i)))
+                .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+            self.infer_pat(subpat, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    fn infer_record_pat(
+        &mut self,
+        path: Option<&Path>,
+        subpats: &[RecordFieldPat],
+        expected: &Ty,
+        default_bm: BindingMode,
+        id: PatId,
+    ) -> Ty {
+        let (ty, def) = self.resolve_variant(path);
+        let var_data = def.map(|it| variant_data(self.db.upcast(), it));
+        if let Some(variant) = def {
+            self.write_variant_resolution(id.into(), variant);
+        }
+
+        self.unify(&ty, expected);
+
+        let substs = ty.substs().unwrap_or_else(Substs::empty);
+
+        let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
+        for subpat in subpats {
+            let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
+            if let Some(local_id) = matching_field {
+                let field_def = FieldId { parent: def.unwrap(), local_id };
+                self.result.record_field_pat_resolutions.insert(subpat.pat, field_def);
+            }
+
+            let expected_ty =
+                matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+            self.infer_pat(subpat.pat, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    pub(super) fn infer_pat(
+        &mut self,
+        pat: PatId,
+        mut expected: &Ty,
+        mut default_bm: BindingMode,
+    ) -> Ty {
+        let body = Arc::clone(&self.body); // avoid borrow checker problem
+
+        if is_non_ref_pat(&body, pat) {
+            while let Some((inner, mutability)) = expected.as_reference() {
+                expected = inner;
+                default_bm = match default_bm {
+                    BindingMode::Move => BindingMode::Ref(mutability),
+                    BindingMode::Ref(Mutability::Shared) => BindingMode::Ref(Mutability::Shared),
+                    BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
+                }
+            }
+        } else if let Pat::Ref { .. } = &body[pat] {
+            mark::hit!(match_ergonomics_ref);
+            // When you encounter a `&pat` pattern, reset to Move.
+            // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
+            default_bm = BindingMode::Move;
+        }
+
+        // Lose mutability.
+        let default_bm = default_bm;
+        let expected = expected;
+
+        let ty = match &body[pat] {
+            Pat::Tuple { ref args, .. } => {
+                let expectations = match expected.as_tuple() {
+                    Some(parameters) => &*parameters.0,
+                    _ => &[],
+                };
+                let expectations_iter = expectations.iter().chain(repeat(&Ty::Unknown));
+
+                let inner_tys = args
+                    .iter()
+                    .zip(expectations_iter)
+                    .map(|(&pat, ty)| self.infer_pat(pat, ty, default_bm))
+                    .collect();
+
+                Ty::apply(TypeCtor::Tuple { cardinality: args.len() as u16 }, Substs(inner_tys))
+            }
+            Pat::Or(ref pats) => {
+                if let Some((first_pat, rest)) = pats.split_first() {
+                    let ty = self.infer_pat(*first_pat, expected, default_bm);
+                    for pat in rest {
+                        self.infer_pat(*pat, expected, default_bm);
+                    }
+                    ty
+                } else {
+                    Ty::Unknown
+                }
+            }
+            Pat::Ref { pat, mutability } => {
+                let expectation = match expected.as_reference() {
+                    Some((inner_ty, exp_mut)) => {
+                        if *mutability != exp_mut {
+                            // FIXME: emit type error?
+                        }
+                        inner_ty
+                    }
+                    _ => &Ty::Unknown,
+                };
+                let subty = self.infer_pat(*pat, expectation, default_bm);
+                Ty::apply_one(TypeCtor::Ref(*mutability), subty)
+            }
+            Pat::TupleStruct { path: p, args: subpats, .. } => {
+                self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm, pat)
+            }
+            Pat::Record { path: p, args: fields, ellipsis: _ } => {
+                self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
+            }
+            Pat::Path(path) => {
+                // FIXME use correct resolver for the surrounding expression
+                let resolver = self.resolver.clone();
+                self.infer_path(&resolver, &path, pat.into()).unwrap_or(Ty::Unknown)
+            }
+            Pat::Bind { mode, name: _, subpat } => {
+                let mode = if mode == &BindingAnnotation::Unannotated {
+                    default_bm
+                } else {
+                    BindingMode::convert(*mode)
+                };
+                let inner_ty = if let Some(subpat) = subpat {
+                    self.infer_pat(*subpat, expected, default_bm)
+                } else {
+                    expected.clone()
+                };
+                let inner_ty = self.insert_type_vars_shallow(inner_ty);
+
+                let bound_ty = match mode {
+                    BindingMode::Ref(mutability) => {
+                        Ty::apply_one(TypeCtor::Ref(mutability), inner_ty.clone())
+                    }
+                    BindingMode::Move => inner_ty.clone(),
+                };
+                let bound_ty = self.resolve_ty_as_possible(bound_ty);
+                self.write_pat_ty(pat, bound_ty);
+                return inner_ty;
+            }
+            Pat::Slice { prefix, slice, suffix } => {
+                let (container_ty, elem_ty) = match &expected {
+                    ty_app!(TypeCtor::Array, st) => (TypeCtor::Array, st.as_single().clone()),
+                    ty_app!(TypeCtor::Slice, st) => (TypeCtor::Slice, st.as_single().clone()),
+                    _ => (TypeCtor::Slice, Ty::Unknown),
+                };
+
+                for pat_id in prefix.iter().chain(suffix) {
+                    self.infer_pat(*pat_id, &elem_ty, default_bm);
+                }
+
+                let pat_ty = Ty::apply_one(container_ty, elem_ty);
+                if let Some(slice_pat_id) = slice {
+                    self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
+                }
+
+                pat_ty
+            }
+            Pat::Wild => expected.clone(),
+            Pat::Range { start, end } => {
+                let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
+                let end_ty = self.infer_expr(*end, &Expectation::has_type(start_ty));
+                end_ty
+            }
+            Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
+            Pat::Missing => Ty::Unknown,
+        };
+        // use a new type variable if we got Ty::Unknown here
+        let ty = self.insert_type_vars_shallow(ty);
+        if !self.unify(&ty, expected) {
+            // FIXME record mismatch, we need to change the type of self.type_mismatches for that
+        }
+        let ty = self.resolve_ty_as_possible(ty);
+        self.write_pat_ty(pat, ty.clone());
+        ty
+    }
+}
+
+fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
+    match &body[pat] {
+        Pat::Tuple { .. }
+        | Pat::TupleStruct { .. }
+        | Pat::Record { .. }
+        | Pat::Range { .. }
+        | Pat::Slice { .. } => true,
+        Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
+        // FIXME: Path/Lit might actually evaluate to ref, but inference is unimplemented.
+        Pat::Path(..) => true,
+        Pat::Lit(expr) => match body[*expr] {
+            Expr::Literal(Literal::String(..)) => false,
+            _ => true,
+        },
+        Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Missing => false,
+    }
+}

crates/hir_ty/src/infer/path.rs

@@ -0,0 +1,287 @@
+//! Path expression resolution.
+
+use std::iter;
+
+use hir_def::{
+    path::{Path, PathSegment},
+    resolver::{ResolveValueResult, Resolver, TypeNs, ValueNs},
+    AdtId, AssocContainerId, AssocItemId, EnumVariantId, Lookup,
+};
+use hir_expand::name::Name;
+
+use crate::{method_resolution, Substs, Ty, ValueTyDefId};
+
+use super::{ExprOrPatId, InferenceContext, TraitRef};
+
+impl<'a> InferenceContext<'a> {
+    pub(super) fn infer_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let ty = self.resolve_value_path(resolver, path, id)?;
+        let ty = self.insert_type_vars(ty);
+        let ty = self.normalize_associated_types_in(ty);
+        Some(ty)
+    }
+
+    fn resolve_value_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let (value, self_subst) = if let Some(type_ref) = path.type_anchor() {
+            if path.segments().is_empty() {
+                // This can't actually happen syntax-wise
+                return None;
+            }
+            let ty = self.make_ty(type_ref);
+            let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
+            let ctx = crate::lower::TyLoweringContext::new(self.db, &resolver);
+            let (ty, _) = Ty::from_type_relative_path(&ctx, ty, None, remaining_segments_for_ty);
+            self.resolve_ty_assoc_item(
+                ty,
+                &path.segments().last().expect("path had at least one segment").name,
+                id,
+            )?
+        } else {
+            let value_or_partial =
+                resolver.resolve_path_in_value_ns(self.db.upcast(), path.mod_path())?;
+
+            match value_or_partial {
+                ResolveValueResult::ValueNs(it) => (it, None),
+                ResolveValueResult::Partial(def, remaining_index) => {
+                    self.resolve_assoc_item(def, path, remaining_index, id)?
+                }
+            }
+        };
+
+        let typable: ValueTyDefId = match value {
+            ValueNs::LocalBinding(pat) => {
+                let ty = self.result.type_of_pat.get(pat)?.clone();
+                let ty = self.resolve_ty_as_possible(ty);
+                return Some(ty);
+            }
+            ValueNs::FunctionId(it) => it.into(),
+            ValueNs::ConstId(it) => it.into(),
+            ValueNs::StaticId(it) => it.into(),
+            ValueNs::StructId(it) => {
+                self.write_variant_resolution(id, it.into());
+
+                it.into()
+            }
+            ValueNs::EnumVariantId(it) => {
+                self.write_variant_resolution(id, it.into());
+
+                it.into()
+            }
+            ValueNs::ImplSelf(impl_id) => {
+                let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
+                let substs = Substs::type_params_for_generics(&generics);
+                let ty = self.db.impl_self_ty(impl_id).subst(&substs);
+                if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
+                    let ty = self.db.value_ty(struct_id.into()).subst(&substs);
+                    return Some(ty);
+                } else {
+                    // FIXME: diagnostic, invalid Self reference
+                    return None;
+                }
+            }
+        };
+
+        let ty = self.db.value_ty(typable);
+        // self_subst is just for the parent
+        let parent_substs = self_subst.unwrap_or_else(Substs::empty);
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+        let substs = Ty::substs_from_path(&ctx, path, typable, true);
+        let full_substs = Substs::builder(substs.len())
+            .use_parent_substs(&parent_substs)
+            .fill(substs.0[parent_substs.len()..].iter().cloned())
+            .build();
+        let ty = ty.subst(&full_substs);
+        Some(ty)
+    }
+
+    fn resolve_assoc_item(
+        &mut self,
+        def: TypeNs,
+        path: &Path,
+        remaining_index: usize,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        assert!(remaining_index < path.segments().len());
+        // there may be more intermediate segments between the resolved one and
+        // the end. Only the last segment needs to be resolved to a value; from
+        // the segments before that, we need to get either a type or a trait ref.
+
+        let resolved_segment = path.segments().get(remaining_index - 1).unwrap();
+        let remaining_segments = path.segments().skip(remaining_index);
+        let is_before_last = remaining_segments.len() == 1;
+
+        match (def, is_before_last) {
+            (TypeNs::TraitId(trait_), true) => {
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+                let trait_ref = TraitRef::from_resolved_path(&ctx, trait_, resolved_segment, None);
+                self.resolve_trait_assoc_item(trait_ref, segment, id)
+            }
+            (def, _) => {
+                // Either we already have a type (e.g. `Vec::new`), or we have a
+                // trait but it's not the last segment, so the next segment
+                // should resolve to an associated type of that trait (e.g. `<T
+                // as Iterator>::Item::default`)
+                let remaining_segments_for_ty =
+                    remaining_segments.take(remaining_segments.len() - 1);
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+                let (ty, _) = Ty::from_partly_resolved_hir_path(
+                    &ctx,
+                    def,
+                    resolved_segment,
+                    remaining_segments_for_ty,
+                    true,
+                );
+                if let Ty::Unknown = ty {
+                    return None;
+                }
+
+                let ty = self.insert_type_vars(ty);
+                let ty = self.normalize_associated_types_in(ty);
+
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+
+                self.resolve_ty_assoc_item(ty, &segment.name, id)
+            }
+        }
+    }
+
+    fn resolve_trait_assoc_item(
+        &mut self,
+        trait_ref: TraitRef,
+        segment: PathSegment<'_>,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        let trait_ = trait_ref.trait_;
+        let item =
+            self.db.trait_data(trait_).items.iter().map(|(_name, id)| (*id)).find_map(|item| {
+                match item {
+                    AssocItemId::FunctionId(func) => {
+                        if segment.name == &self.db.function_data(func).name {
+                            Some(AssocItemId::FunctionId(func))
+                        } else {
+                            None
+                        }
+                    }
+
+                    AssocItemId::ConstId(konst) => {
+                        if self
+                            .db
+                            .const_data(konst)
+                            .name
+                            .as_ref()
+                            .map_or(false, |n| n == segment.name)
+                        {
+                            Some(AssocItemId::ConstId(konst))
+                        } else {
+                            None
+                        }
+                    }
+                    AssocItemId::TypeAliasId(_) => None,
+                }
+            })?;
+        let def = match item {
+            AssocItemId::FunctionId(f) => ValueNs::FunctionId(f),
+            AssocItemId::ConstId(c) => ValueNs::ConstId(c),
+            AssocItemId::TypeAliasId(_) => unreachable!(),
+        };
+
+        self.write_assoc_resolution(id, item);
+        Some((def, Some(trait_ref.substs)))
+    }
+
+    fn resolve_ty_assoc_item(
+        &mut self,
+        ty: Ty,
+        name: &Name,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        if let Ty::Unknown = ty {
+            return None;
+        }
+
+        if let Some(result) = self.resolve_enum_variant_on_ty(&ty, name, id) {
+            return Some(result);
+        }
+
+        let canonical_ty = self.canonicalizer().canonicalize_ty(ty.clone());
+        let krate = self.resolver.krate()?;
+        let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
+
+        method_resolution::iterate_method_candidates(
+            &canonical_ty.value,
+            self.db,
+            self.trait_env.clone(),
+            krate,
+            &traits_in_scope,
+            Some(name),
+            method_resolution::LookupMode::Path,
+            move |_ty, item| {
+                let (def, container) = match item {
+                    AssocItemId::FunctionId(f) => {
+                        (ValueNs::FunctionId(f), f.lookup(self.db.upcast()).container)
+                    }
+                    AssocItemId::ConstId(c) => {
+                        (ValueNs::ConstId(c), c.lookup(self.db.upcast()).container)
+                    }
+                    AssocItemId::TypeAliasId(_) => unreachable!(),
+                };
+                let substs = match container {
+                    AssocContainerId::ImplId(impl_id) => {
+                        let impl_substs = Substs::build_for_def(self.db, impl_id)
+                            .fill(iter::repeat_with(|| self.table.new_type_var()))
+                            .build();
+                        let impl_self_ty = self.db.impl_self_ty(impl_id).subst(&impl_substs);
+                        self.unify(&impl_self_ty, &ty);
+                        Some(impl_substs)
+                    }
+                    AssocContainerId::TraitId(trait_) => {
+                        // we're picking this method
+                        let trait_substs = Substs::build_for_def(self.db, trait_)
+                            .push(ty.clone())
+                            .fill(std::iter::repeat_with(|| self.table.new_type_var()))
+                            .build();
+                        self.obligations.push(super::Obligation::Trait(TraitRef {
+                            trait_,
+                            substs: trait_substs.clone(),
+                        }));
+                        Some(trait_substs)
+                    }
+                    AssocContainerId::ContainerId(_) => None,
+                };
+
+                self.write_assoc_resolution(id, item);
+                Some((def, substs))
+            },
+        )
+    }
+
+    fn resolve_enum_variant_on_ty(
+        &mut self,
+        ty: &Ty,
+        name: &Name,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        let (enum_id, subst) = match ty.as_adt() {
+            Some((AdtId::EnumId(e), subst)) => (e, subst),
+            _ => return None,
+        };
+        let enum_data = self.db.enum_data(enum_id);
+        let local_id = enum_data.variant(name)?;
+        let variant = EnumVariantId { parent: enum_id, local_id };
+        self.write_variant_resolution(id, variant.into());
+        Some((ValueNs::EnumVariantId(variant), Some(subst.clone())))
+    }
+}

crates/hir_ty/src/infer/unify.rs

@@ -0,0 +1,474 @@
+//! Unification and canonicalization logic.
+
+use std::borrow::Cow;
+
+use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
+
+use test_utils::mark;
+
+use super::{InferenceContext, Obligation};
+use crate::{
+    BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferTy, Substs, Ty,
+    TyKind, TypeCtor, TypeWalk,
+};
+
+impl<'a> InferenceContext<'a> {
+    pub(super) fn canonicalizer<'b>(&'b mut self) -> Canonicalizer<'a, 'b>
+    where
+        'a: 'b,
+    {
+        Canonicalizer { ctx: self, free_vars: Vec::new(), var_stack: Vec::new() }
+    }
+}
+
+pub(super) struct Canonicalizer<'a, 'b>
+where
+    'a: 'b,
+{
+    ctx: &'b mut InferenceContext<'a>,
+    free_vars: Vec<InferTy>,
+    /// A stack of type variables that is used to detect recursive types (which
+    /// are an error, but we need to protect against them to avoid stack
+    /// overflows).
+    var_stack: Vec<TypeVarId>,
+}
+
+#[derive(Debug)]
+pub(super) struct Canonicalized<T> {
+    pub value: Canonical<T>,
+    free_vars: Vec<InferTy>,
+}
+
+impl<'a, 'b> Canonicalizer<'a, 'b>
+where
+    'a: 'b,
+{
+    fn add(&mut self, free_var: InferTy) -> usize {
+        self.free_vars.iter().position(|&v| v == free_var).unwrap_or_else(|| {
+            let next_index = self.free_vars.len();
+            self.free_vars.push(free_var);
+            next_index
+        })
+    }
+
+    fn do_canonicalize<T: TypeWalk>(&mut self, t: T, binders: DebruijnIndex) -> T {
+        t.fold_binders(
+            &mut |ty, binders| match ty {
+                Ty::Infer(tv) => {
+                    let inner = tv.to_inner();
+                    if self.var_stack.contains(&inner) {
+                        // recursive type
+                        return tv.fallback_value();
+                    }
+                    if let Some(known_ty) =
+                        self.ctx.table.var_unification_table.inlined_probe_value(inner).known()
+                    {
+                        self.var_stack.push(inner);
+                        let result = self.do_canonicalize(known_ty.clone(), binders);
+                        self.var_stack.pop();
+                        result
+                    } else {
+                        let root = self.ctx.table.var_unification_table.find(inner);
+                        let free_var = match tv {
+                            InferTy::TypeVar(_) => InferTy::TypeVar(root),
+                            InferTy::IntVar(_) => InferTy::IntVar(root),
+                            InferTy::FloatVar(_) => InferTy::FloatVar(root),
+                            InferTy::MaybeNeverTypeVar(_) => InferTy::MaybeNeverTypeVar(root),
+                        };
+                        let position = self.add(free_var);
+                        Ty::Bound(BoundVar::new(binders, position))
+                    }
+                }
+                _ => ty,
+            },
+            binders,
+        )
+    }
+
+    fn into_canonicalized<T>(self, result: T) -> Canonicalized<T> {
+        let kinds = self
+            .free_vars
+            .iter()
+            .map(|v| match v {
+                // mapping MaybeNeverTypeVar to the same kind as general ones
+                // should be fine, because as opposed to int or float type vars,
+                // they don't restrict what kind of type can go into them, they
+                // just affect fallback.
+                InferTy::TypeVar(_) | InferTy::MaybeNeverTypeVar(_) => TyKind::General,
+                InferTy::IntVar(_) => TyKind::Integer,
+                InferTy::FloatVar(_) => TyKind::Float,
+            })
+            .collect();
+        Canonicalized { value: Canonical { value: result, kinds }, free_vars: self.free_vars }
+    }
+
+    pub(crate) fn canonicalize_ty(mut self, ty: Ty) -> Canonicalized<Ty> {
+        let result = self.do_canonicalize(ty, DebruijnIndex::INNERMOST);
+        self.into_canonicalized(result)
+    }
+
+    pub(crate) fn canonicalize_obligation(
+        mut self,
+        obligation: InEnvironment<Obligation>,
+    ) -> Canonicalized<InEnvironment<Obligation>> {
+        let result = match obligation.value {
+            Obligation::Trait(tr) => {
+                Obligation::Trait(self.do_canonicalize(tr, DebruijnIndex::INNERMOST))
+            }
+            Obligation::Projection(pr) => {
+                Obligation::Projection(self.do_canonicalize(pr, DebruijnIndex::INNERMOST))
+            }
+        };
+        self.into_canonicalized(InEnvironment {
+            value: result,
+            environment: obligation.environment,
+        })
+    }
+}
+
+impl<T> Canonicalized<T> {
+    pub fn decanonicalize_ty(&self, mut ty: Ty) -> Ty {
+        ty.walk_mut_binders(
+            &mut |ty, binders| {
+                if let &mut Ty::Bound(bound) = ty {
+                    if bound.debruijn >= binders {
+                        *ty = Ty::Infer(self.free_vars[bound.index]);
+                    }
+                }
+            },
+            DebruijnIndex::INNERMOST,
+        );
+        ty
+    }
+
+    pub fn apply_solution(&self, ctx: &mut InferenceContext<'_>, solution: Canonical<Substs>) {
+        // the solution may contain new variables, which we need to convert to new inference vars
+        let new_vars = Substs(
+            solution
+                .kinds
+                .iter()
+                .map(|k| match k {
+                    TyKind::General => ctx.table.new_type_var(),
+                    TyKind::Integer => ctx.table.new_integer_var(),
+                    TyKind::Float => ctx.table.new_float_var(),
+                })
+                .collect(),
+        );
+        for (i, ty) in solution.value.into_iter().enumerate() {
+            let var = self.free_vars[i];
+            // eagerly replace projections in the type; we may be getting types
+            // e.g. from where clauses where this hasn't happened yet
+            let ty = ctx.normalize_associated_types_in(ty.clone().subst_bound_vars(&new_vars));
+            ctx.table.unify(&Ty::Infer(var), &ty);
+        }
+    }
+}
+
+pub fn unify(tys: &Canonical<(Ty, Ty)>) -> Option<Substs> {
+    let mut table = InferenceTable::new();
+    let vars = Substs(
+        tys.kinds
+            .iter()
+            // we always use type vars here because we want everything to
+            // fallback to Unknown in the end (kind of hacky, as below)
+            .map(|_| table.new_type_var())
+            .collect(),
+    );
+    let ty1_with_vars = tys.value.0.clone().subst_bound_vars(&vars);
+    let ty2_with_vars = tys.value.1.clone().subst_bound_vars(&vars);
+    if !table.unify(&ty1_with_vars, &ty2_with_vars) {
+        return None;
+    }
+    // default any type vars that weren't unified back to their original bound vars
+    // (kind of hacky)
+    for (i, var) in vars.iter().enumerate() {
+        if &*table.resolve_ty_shallow(var) == var {
+            table.unify(var, &Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, i)));
+        }
+    }
+    Some(
+        Substs::builder(tys.kinds.len())
+            .fill(vars.iter().map(|v| table.resolve_ty_completely(v.clone())))
+            .build(),
+    )
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct InferenceTable {
+    pub(super) var_unification_table: InPlaceUnificationTable<TypeVarId>,
+}
+
+impl InferenceTable {
+    pub fn new() -> Self {
+        InferenceTable { var_unification_table: InPlaceUnificationTable::new() }
+    }
+
+    pub fn new_type_var(&mut self) -> Ty {
+        Ty::Infer(InferTy::TypeVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
+    }
+
+    pub fn new_integer_var(&mut self) -> Ty {
+        Ty::Infer(InferTy::IntVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
+    }
+
+    pub fn new_float_var(&mut self) -> Ty {
+        Ty::Infer(InferTy::FloatVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
+    }
+
+    pub fn new_maybe_never_type_var(&mut self) -> Ty {
+        Ty::Infer(InferTy::MaybeNeverTypeVar(
+            self.var_unification_table.new_key(TypeVarValue::Unknown),
+        ))
+    }
+
+    pub fn resolve_ty_completely(&mut self, ty: Ty) -> Ty {
+        self.resolve_ty_completely_inner(&mut Vec::new(), ty)
+    }
+
+    pub fn resolve_ty_as_possible(&mut self, ty: Ty) -> Ty {
+        self.resolve_ty_as_possible_inner(&mut Vec::new(), ty)
+    }
+
+    pub fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
+        self.unify_inner(ty1, ty2, 0)
+    }
+
+    pub fn unify_substs(&mut self, substs1: &Substs, substs2: &Substs, depth: usize) -> bool {
+        substs1.0.iter().zip(substs2.0.iter()).all(|(t1, t2)| self.unify_inner(t1, t2, depth))
+    }
+
+    fn unify_inner(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
+        if depth > 1000 {
+            // prevent stackoverflows
+            panic!("infinite recursion in unification");
+        }
+        if ty1 == ty2 {
+            return true;
+        }
+        // try to resolve type vars first
+        let ty1 = self.resolve_ty_shallow(ty1);
+        let ty2 = self.resolve_ty_shallow(ty2);
+        match (&*ty1, &*ty2) {
+            (Ty::Apply(a_ty1), Ty::Apply(a_ty2)) if a_ty1.ctor == a_ty2.ctor => {
+                self.unify_substs(&a_ty1.parameters, &a_ty2.parameters, depth + 1)
+            }
+
+            _ => self.unify_inner_trivial(&ty1, &ty2, depth),
+        }
+    }
+
+    pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
+        match (ty1, ty2) {
+            (Ty::Unknown, _) | (_, Ty::Unknown) => true,
+
+            (Ty::Placeholder(p1), Ty::Placeholder(p2)) if *p1 == *p2 => true,
+
+            (Ty::Dyn(dyn1), Ty::Dyn(dyn2)) if dyn1.len() == dyn2.len() => {
+                for (pred1, pred2) in dyn1.iter().zip(dyn2.iter()) {
+                    if !self.unify_preds(pred1, pred2, depth + 1) {
+                        return false;
+                    }
+                }
+                true
+            }
+
+            (Ty::Infer(InferTy::TypeVar(tv1)), Ty::Infer(InferTy::TypeVar(tv2)))
+            | (Ty::Infer(InferTy::IntVar(tv1)), Ty::Infer(InferTy::IntVar(tv2)))
+            | (Ty::Infer(InferTy::FloatVar(tv1)), Ty::Infer(InferTy::FloatVar(tv2)))
+            | (
+                Ty::Infer(InferTy::MaybeNeverTypeVar(tv1)),
+                Ty::Infer(InferTy::MaybeNeverTypeVar(tv2)),
+            ) => {
+                // both type vars are unknown since we tried to resolve them
+                self.var_unification_table.union(*tv1, *tv2);
+                true
+            }
+
+            // The order of MaybeNeverTypeVar matters here.
+            // Unifying MaybeNeverTypeVar and TypeVar will let the latter become MaybeNeverTypeVar.
+            // Unifying MaybeNeverTypeVar and other concrete type will let the former become it.
+            (Ty::Infer(InferTy::TypeVar(tv)), other)
+            | (other, Ty::Infer(InferTy::TypeVar(tv)))
+            | (Ty::Infer(InferTy::MaybeNeverTypeVar(tv)), other)
+            | (other, Ty::Infer(InferTy::MaybeNeverTypeVar(tv)))
+            | (Ty::Infer(InferTy::IntVar(tv)), other @ ty_app!(TypeCtor::Int(_)))
+            | (other @ ty_app!(TypeCtor::Int(_)), Ty::Infer(InferTy::IntVar(tv)))
+            | (Ty::Infer(InferTy::FloatVar(tv)), other @ ty_app!(TypeCtor::Float(_)))
+            | (other @ ty_app!(TypeCtor::Float(_)), Ty::Infer(InferTy::FloatVar(tv))) => {
+                // the type var is unknown since we tried to resolve it
+                self.var_unification_table.union_value(*tv, TypeVarValue::Known(other.clone()));
+                true
+            }
+
+            _ => false,
+        }
+    }
+
+    fn unify_preds(
+        &mut self,
+        pred1: &GenericPredicate,
+        pred2: &GenericPredicate,
+        depth: usize,
+    ) -> bool {
+        match (pred1, pred2) {
+            (GenericPredicate::Implemented(tr1), GenericPredicate::Implemented(tr2))
+                if tr1.trait_ == tr2.trait_ =>
+            {
+                self.unify_substs(&tr1.substs, &tr2.substs, depth + 1)
+            }
+            (GenericPredicate::Projection(proj1), GenericPredicate::Projection(proj2))
+                if proj1.projection_ty.associated_ty == proj2.projection_ty.associated_ty =>
+            {
+                self.unify_substs(
+                    &proj1.projection_ty.parameters,
+                    &proj2.projection_ty.parameters,
+                    depth + 1,
+                ) && self.unify_inner(&proj1.ty, &proj2.ty, depth + 1)
+            }
+            _ => false,
+        }
+    }
+
+    /// If `ty` is a type variable with known type, returns that type;
+    /// otherwise, return ty.
+    pub fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
+        let mut ty = Cow::Borrowed(ty);
+        // The type variable could resolve to a int/float variable. Hence try
+        // resolving up to three times; each type of variable shouldn't occur
+        // more than once
+        for i in 0..3 {
+            if i > 0 {
+                mark::hit!(type_var_resolves_to_int_var);
+            }
+            match &*ty {
+                Ty::Infer(tv) => {
+                    let inner = tv.to_inner();
+                    match self.var_unification_table.inlined_probe_value(inner).known() {
+                        Some(known_ty) => {
+                            // The known_ty can't be a type var itself
+                            ty = Cow::Owned(known_ty.clone());
+                        }
+                        _ => return ty,
+                    }
+                }
+                _ => return ty,
+            }
+        }
+        log::error!("Inference variable still not resolved: {:?}", ty);
+        ty
+    }
+
+    /// Resolves the type as far as currently possible, replacing type variables
+    /// by their known types. All types returned by the infer_* functions should
+    /// be resolved as far as possible, i.e. contain no type variables with
+    /// known type.
+    fn resolve_ty_as_possible_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
+        ty.fold(&mut |ty| match ty {
+            Ty::Infer(tv) => {
+                let inner = tv.to_inner();
+                if tv_stack.contains(&inner) {
+                    mark::hit!(type_var_cycles_resolve_as_possible);
+                    // recursive type
+                    return tv.fallback_value();
+                }
+                if let Some(known_ty) =
+                    self.var_unification_table.inlined_probe_value(inner).known()
+                {
+                    // known_ty may contain other variables that are known by now
+                    tv_stack.push(inner);
+                    let result = self.resolve_ty_as_possible_inner(tv_stack, known_ty.clone());
+                    tv_stack.pop();
+                    result
+                } else {
+                    ty
+                }
+            }
+            _ => ty,
+        })
+    }
+
+    /// Resolves the type completely; type variables without known type are
+    /// replaced by Ty::Unknown.
+    fn resolve_ty_completely_inner(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
+        ty.fold(&mut |ty| match ty {
+            Ty::Infer(tv) => {
+                let inner = tv.to_inner();
+                if tv_stack.contains(&inner) {
+                    mark::hit!(type_var_cycles_resolve_completely);
+                    // recursive type
+                    return tv.fallback_value();
+                }
+                if let Some(known_ty) =
+                    self.var_unification_table.inlined_probe_value(inner).known()
+                {
+                    // known_ty may contain other variables that are known by now
+                    tv_stack.push(inner);
+                    let result = self.resolve_ty_completely_inner(tv_stack, known_ty.clone());
+                    tv_stack.pop();
+                    result
+                } else {
+                    tv.fallback_value()
+                }
+            }
+            _ => ty,
+        })
+    }
+}
+
+/// The ID of a type variable.
+#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+pub struct TypeVarId(pub(super) u32);
+
+impl UnifyKey for TypeVarId {
+    type Value = TypeVarValue;
+
+    fn index(&self) -> u32 {
+        self.0
+    }
+
+    fn from_index(i: u32) -> Self {
+        TypeVarId(i)
+    }
+
+    fn tag() -> &'static str {
+        "TypeVarId"
+    }
+}
+
+/// The value of a type variable: either we already know the type, or we don't
+/// know it yet.
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum TypeVarValue {
+    Known(Ty),
+    Unknown,
+}
+
+impl TypeVarValue {
+    fn known(&self) -> Option<&Ty> {
+        match self {
+            TypeVarValue::Known(ty) => Some(ty),
+            TypeVarValue::Unknown => None,
+        }
+    }
+}
+
+impl UnifyValue for TypeVarValue {
+    type Error = NoError;
+
+    fn unify_values(value1: &Self, value2: &Self) -> Result<Self, NoError> {
+        match (value1, value2) {
+            // We should never equate two type variables, both of which have
+            // known types. Instead, we recursively equate those types.
+            (TypeVarValue::Known(t1), TypeVarValue::Known(t2)) => panic!(
+                "equating two type variables, both of which have known types: {:?} and {:?}",
+                t1, t2
+            ),
+
+            // If one side is known, prefer that one.
+            (TypeVarValue::Known(..), TypeVarValue::Unknown) => Ok(value1.clone()),
+            (TypeVarValue::Unknown, TypeVarValue::Known(..)) => Ok(value2.clone()),
+
+            (TypeVarValue::Unknown, TypeVarValue::Unknown) => Ok(TypeVarValue::Unknown),
+        }
+    }
+}

crates/hir_ty/src/method_resolution.rs

@@ -0,0 +1,769 @@
+//! This module is concerned with finding methods that a given type provides.
+//! For details about how this works in rustc, see the method lookup page in the
+//! [rustc guide](https://rust-lang.github.io/rustc-guide/method-lookup.html)
+//! and the corresponding code mostly in librustc_typeck/check/method/probe.rs.
+use std::{iter, sync::Arc};
+
+use arrayvec::ArrayVec;
+use base_db::CrateId;
+use hir_def::{
+    builtin_type::{IntBitness, Signedness},
+    lang_item::LangItemTarget,
+    type_ref::Mutability,
+    AssocContainerId, AssocItemId, FunctionId, HasModule, ImplId, Lookup, TraitId,
+};
+use hir_expand::name::Name;
+use rustc_hash::{FxHashMap, FxHashSet};
+
+use super::Substs;
+use crate::{
+    autoderef,
+    db::HirDatabase,
+    primitive::{FloatBitness, FloatTy, IntTy},
+    utils::all_super_traits,
+    ApplicationTy, Canonical, DebruijnIndex, InEnvironment, TraitEnvironment, TraitRef, Ty, TyKind,
+    TypeCtor, TypeWalk,
+};
+
+/// This is used as a key for indexing impls.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum TyFingerprint {
+    Apply(TypeCtor),
+}
+
+impl TyFingerprint {
+    /// Creates a TyFingerprint for looking up an impl. Only certain types can
+    /// have impls: if we have some `struct S`, we can have an `impl S`, but not
+    /// `impl &S`. Hence, this will return `None` for reference types and such.
+    pub(crate) fn for_impl(ty: &Ty) -> Option<TyFingerprint> {
+        match ty {
+            Ty::Apply(a_ty) => Some(TyFingerprint::Apply(a_ty.ctor)),
+            _ => None,
+        }
+    }
+}
+
+pub(crate) const ALL_INT_FPS: [TyFingerprint; 12] = [
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::X8,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::X16,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::X32,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::X64,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::X128,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Unsigned,
+        bitness: IntBitness::Xsize,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::X8,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::X16,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::X32,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::X64,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::X128,
+    })),
+    TyFingerprint::Apply(TypeCtor::Int(IntTy {
+        signedness: Signedness::Signed,
+        bitness: IntBitness::Xsize,
+    })),
+];
+
+pub(crate) const ALL_FLOAT_FPS: [TyFingerprint; 2] = [
+    TyFingerprint::Apply(TypeCtor::Float(FloatTy { bitness: FloatBitness::X32 })),
+    TyFingerprint::Apply(TypeCtor::Float(FloatTy { bitness: FloatBitness::X64 })),
+];
+
+/// Trait impls defined or available in some crate.
+#[derive(Debug, Eq, PartialEq)]
+pub struct TraitImpls {
+    // If the `Option<TyFingerprint>` is `None`, the impl may apply to any self type.
+    map: FxHashMap<TraitId, FxHashMap<Option<TyFingerprint>, Vec<ImplId>>>,
+}
+
+impl TraitImpls {
+    pub(crate) fn trait_impls_in_crate_query(db: &dyn HirDatabase, krate: CrateId) -> Arc<Self> {
+        let _p = profile::span("trait_impls_in_crate_query");
+        let mut impls = Self { map: FxHashMap::default() };
+
+        let crate_def_map = db.crate_def_map(krate);
+        for (_module_id, module_data) in crate_def_map.modules.iter() {
+            for impl_id in module_data.scope.impls() {
+                let target_trait = match db.impl_trait(impl_id) {
+                    Some(tr) => tr.value.trait_,
+                    None => continue,
+                };
+                let self_ty = db.impl_self_ty(impl_id);
+                let self_ty_fp = TyFingerprint::for_impl(&self_ty.value);
+                impls
+                    .map
+                    .entry(target_trait)
+                    .or_default()
+                    .entry(self_ty_fp)
+                    .or_default()
+                    .push(impl_id);
+            }
+        }
+
+        Arc::new(impls)
+    }
+
+    pub(crate) fn trait_impls_in_deps_query(db: &dyn HirDatabase, krate: CrateId) -> Arc<Self> {
+        let _p = profile::span("trait_impls_in_deps_query");
+        let crate_graph = db.crate_graph();
+        let mut res = Self { map: FxHashMap::default() };
+
+        for krate in crate_graph.transitive_deps(krate) {
+            res.merge(&db.trait_impls_in_crate(krate));
+        }
+
+        Arc::new(res)
+    }
+
+    fn merge(&mut self, other: &Self) {
+        for (trait_, other_map) in &other.map {
+            let map = self.map.entry(*trait_).or_default();
+            for (fp, impls) in other_map {
+                let vec = map.entry(*fp).or_default();
+                vec.extend(impls);
+            }
+        }
+    }
+
+    /// Queries all impls of the given trait.
+    pub fn for_trait(&self, trait_: TraitId) -> impl Iterator<Item = ImplId> + '_ {
+        self.map
+            .get(&trait_)
+            .into_iter()
+            .flat_map(|map| map.values().flat_map(|v| v.iter().copied()))
+    }
+
+    /// Queries all impls of `trait_` that may apply to `self_ty`.
+    pub fn for_trait_and_self_ty(
+        &self,
+        trait_: TraitId,
+        self_ty: TyFingerprint,
+    ) -> impl Iterator<Item = ImplId> + '_ {
+        self.map
+            .get(&trait_)
+            .into_iter()
+            .flat_map(move |map| map.get(&None).into_iter().chain(map.get(&Some(self_ty))))
+            .flat_map(|v| v.iter().copied())
+    }
+
+    pub fn all_impls(&self) -> impl Iterator<Item = ImplId> + '_ {
+        self.map.values().flat_map(|map| map.values().flat_map(|v| v.iter().copied()))
+    }
+}
+
+/// Inherent impls defined in some crate.
+///
+/// Inherent impls can only be defined in the crate that also defines the self type of the impl
+/// (note that some primitives are considered to be defined by both libcore and liballoc).
+///
+/// This makes inherent impl lookup easier than trait impl lookup since we only have to consider a
+/// single crate.
+#[derive(Debug, Eq, PartialEq)]
+pub struct InherentImpls {
+    map: FxHashMap<TyFingerprint, Vec<ImplId>>,
+}
+
+impl InherentImpls {
+    pub(crate) fn inherent_impls_in_crate_query(db: &dyn HirDatabase, krate: CrateId) -> Arc<Self> {
+        let mut map: FxHashMap<_, Vec<_>> = FxHashMap::default();
+
+        let crate_def_map = db.crate_def_map(krate);
+        for (_module_id, module_data) in crate_def_map.modules.iter() {
+            for impl_id in module_data.scope.impls() {
+                let data = db.impl_data(impl_id);
+                if data.target_trait.is_some() {
+                    continue;
+                }
+
+                let self_ty = db.impl_self_ty(impl_id);
+                if let Some(fp) = TyFingerprint::for_impl(&self_ty.value) {
+                    map.entry(fp).or_default().push(impl_id);
+                }
+            }
+        }
+
+        Arc::new(Self { map })
+    }
+
+    pub fn for_self_ty(&self, self_ty: &Ty) -> &[ImplId] {
+        match TyFingerprint::for_impl(self_ty) {
+            Some(fp) => self.map.get(&fp).map(|vec| vec.as_ref()).unwrap_or(&[]),
+            None => &[],
+        }
+    }
+
+    pub fn all_impls(&self) -> impl Iterator<Item = ImplId> + '_ {
+        self.map.values().flat_map(|v| v.iter().copied())
+    }
+}
+
+impl Ty {
+    pub fn def_crates(
+        &self,
+        db: &dyn HirDatabase,
+        cur_crate: CrateId,
+    ) -> Option<ArrayVec<[CrateId; 2]>> {
+        // Types like slice can have inherent impls in several crates, (core and alloc).
+        // The corresponding impls are marked with lang items, so we can use them to find the required crates.
+        macro_rules! lang_item_crate {
+            ($($name:expr),+ $(,)?) => {{
+                let mut v = ArrayVec::<[LangItemTarget; 2]>::new();
+                $(
+                    v.extend(db.lang_item(cur_crate, $name.into()));
+                )+
+                v
+            }};
+        }
+
+        let lang_item_targets = match self {
+            Ty::Apply(a_ty) => match a_ty.ctor {
+                TypeCtor::Adt(def_id) => {
+                    return Some(std::iter::once(def_id.module(db.upcast()).krate).collect())
+                }
+                TypeCtor::Bool => lang_item_crate!("bool"),
+                TypeCtor::Char => lang_item_crate!("char"),
+                TypeCtor::Float(f) => match f.bitness {
+                    // There are two lang items: one in libcore (fXX) and one in libstd (fXX_runtime)
+                    FloatBitness::X32 => lang_item_crate!("f32", "f32_runtime"),
+                    FloatBitness::X64 => lang_item_crate!("f64", "f64_runtime"),
+                },
+                TypeCtor::Int(i) => lang_item_crate!(i.ty_to_string()),
+                TypeCtor::Str => lang_item_crate!("str_alloc", "str"),
+                TypeCtor::Slice => lang_item_crate!("slice_alloc", "slice"),
+                TypeCtor::RawPtr(Mutability::Shared) => lang_item_crate!("const_ptr"),
+                TypeCtor::RawPtr(Mutability::Mut) => lang_item_crate!("mut_ptr"),
+                _ => return None,
+            },
+            _ => return None,
+        };
+        let res = lang_item_targets
+            .into_iter()
+            .filter_map(|it| match it {
+                LangItemTarget::ImplDefId(it) => Some(it),
+                _ => None,
+            })
+            .map(|it| it.lookup(db.upcast()).container.module(db.upcast()).krate)
+            .collect();
+        Some(res)
+    }
+}
+/// Look up the method with the given name, returning the actual autoderefed
+/// receiver type (but without autoref applied yet).
+pub(crate) fn lookup_method(
+    ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: &Name,
+) -> Option<(Ty, FunctionId)> {
+    iterate_method_candidates(
+        ty,
+        db,
+        env,
+        krate,
+        &traits_in_scope,
+        Some(name),
+        LookupMode::MethodCall,
+        |ty, f| match f {
+            AssocItemId::FunctionId(f) => Some((ty.clone(), f)),
+            _ => None,
+        },
+    )
+}
+
+/// Whether we're looking up a dotted method call (like `v.len()`) or a path
+/// (like `Vec::new`).
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LookupMode {
+    /// Looking up a method call like `v.len()`: We only consider candidates
+    /// that have a `self` parameter, and do autoderef.
+    MethodCall,
+    /// Looking up a path like `Vec::new` or `Vec::default`: We consider all
+    /// candidates including associated constants, but don't do autoderef.
+    Path,
+}
+
+// This would be nicer if it just returned an iterator, but that runs into
+// lifetime problems, because we need to borrow temp `CrateImplDefs`.
+// FIXME add a context type here?
+pub fn iterate_method_candidates<T>(
+    ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    mode: LookupMode,
+    mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
+) -> Option<T> {
+    let mut slot = None;
+    iterate_method_candidates_impl(
+        ty,
+        db,
+        env,
+        krate,
+        traits_in_scope,
+        name,
+        mode,
+        &mut |ty, item| {
+            assert!(slot.is_none());
+            slot = callback(ty, item);
+            slot.is_some()
+        },
+    );
+    slot
+}
+
+fn iterate_method_candidates_impl(
+    ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    mode: LookupMode,
+    callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    match mode {
+        LookupMode::MethodCall => {
+            // For method calls, rust first does any number of autoderef, and then one
+            // autoref (i.e. when the method takes &self or &mut self). We just ignore
+            // the autoref currently -- when we find a method matching the given name,
+            // we assume it fits.
+
+            // Also note that when we've got a receiver like &S, even if the method we
+            // find in the end takes &self, we still do the autoderef step (just as
+            // rustc does an autoderef and then autoref again).
+            let ty = InEnvironment { value: ty.clone(), environment: env.clone() };
+
+            // We have to be careful about the order we're looking at candidates
+            // in here. Consider the case where we're resolving `x.clone()`
+            // where `x: &Vec<_>`. This resolves to the clone method with self
+            // type `Vec<_>`, *not* `&_`. I.e. we need to consider methods where
+            // the receiver type exactly matches before cases where we have to
+            // do autoref. But in the autoderef steps, the `&_` self type comes
+            // up *before* the `Vec<_>` self type.
+            //
+            // On the other hand, we don't want to just pick any by-value method
+            // before any by-autoref method; it's just that we need to consider
+            // the methods by autoderef order of *receiver types*, not *self
+            // types*.
+
+            let deref_chain = autoderef_method_receiver(db, krate, ty);
+            for i in 0..deref_chain.len() {
+                if iterate_method_candidates_with_autoref(
+                    &deref_chain[i..],
+                    db,
+                    env.clone(),
+                    krate,
+                    traits_in_scope,
+                    name,
+                    callback,
+                ) {
+                    return true;
+                }
+            }
+            false
+        }
+        LookupMode::Path => {
+            // No autoderef for path lookups
+            iterate_method_candidates_for_self_ty(
+                &ty,
+                db,
+                env,
+                krate,
+                traits_in_scope,
+                name,
+                callback,
+            )
+        }
+    }
+}
+
+fn iterate_method_candidates_with_autoref(
+    deref_chain: &[Canonical<Ty>],
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    if iterate_method_candidates_by_receiver(
+        &deref_chain[0],
+        &deref_chain[1..],
+        db,
+        env.clone(),
+        krate,
+        &traits_in_scope,
+        name,
+        &mut callback,
+    ) {
+        return true;
+    }
+    let refed = Canonical {
+        kinds: deref_chain[0].kinds.clone(),
+        value: Ty::apply_one(TypeCtor::Ref(Mutability::Shared), deref_chain[0].value.clone()),
+    };
+    if iterate_method_candidates_by_receiver(
+        &refed,
+        deref_chain,
+        db,
+        env.clone(),
+        krate,
+        &traits_in_scope,
+        name,
+        &mut callback,
+    ) {
+        return true;
+    }
+    let ref_muted = Canonical {
+        kinds: deref_chain[0].kinds.clone(),
+        value: Ty::apply_one(TypeCtor::Ref(Mutability::Mut), deref_chain[0].value.clone()),
+    };
+    if iterate_method_candidates_by_receiver(
+        &ref_muted,
+        deref_chain,
+        db,
+        env,
+        krate,
+        &traits_in_scope,
+        name,
+        &mut callback,
+    ) {
+        return true;
+    }
+    false
+}
+
+fn iterate_method_candidates_by_receiver(
+    receiver_ty: &Canonical<Ty>,
+    rest_of_deref_chain: &[Canonical<Ty>],
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    // We're looking for methods with *receiver* type receiver_ty. These could
+    // be found in any of the derefs of receiver_ty, so we have to go through
+    // that.
+    for self_ty in std::iter::once(receiver_ty).chain(rest_of_deref_chain) {
+        if iterate_inherent_methods(self_ty, db, name, Some(receiver_ty), krate, &mut callback) {
+            return true;
+        }
+    }
+    for self_ty in std::iter::once(receiver_ty).chain(rest_of_deref_chain) {
+        if iterate_trait_method_candidates(
+            self_ty,
+            db,
+            env.clone(),
+            krate,
+            &traits_in_scope,
+            name,
+            Some(receiver_ty),
+            &mut callback,
+        ) {
+            return true;
+        }
+    }
+    false
+}
+
+fn iterate_method_candidates_for_self_ty(
+    self_ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    if iterate_inherent_methods(self_ty, db, name, None, krate, &mut callback) {
+        return true;
+    }
+    iterate_trait_method_candidates(self_ty, db, env, krate, traits_in_scope, name, None, callback)
+}
+
+fn iterate_trait_method_candidates(
+    self_ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    traits_in_scope: &FxHashSet<TraitId>,
+    name: Option<&Name>,
+    receiver_ty: Option<&Canonical<Ty>>,
+    callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    // if ty is `dyn Trait`, the trait doesn't need to be in scope
+    let inherent_trait =
+        self_ty.value.dyn_trait().into_iter().flat_map(|t| all_super_traits(db.upcast(), t));
+    let env_traits = if let Ty::Placeholder(_) = self_ty.value {
+        // if we have `T: Trait` in the param env, the trait doesn't need to be in scope
+        env.trait_predicates_for_self_ty(&self_ty.value)
+            .map(|tr| tr.trait_)
+            .flat_map(|t| all_super_traits(db.upcast(), t))
+            .collect()
+    } else {
+        Vec::new()
+    };
+    let traits =
+        inherent_trait.chain(env_traits.into_iter()).chain(traits_in_scope.iter().copied());
+    'traits: for t in traits {
+        let data = db.trait_data(t);
+
+        // we'll be lazy about checking whether the type implements the
+        // trait, but if we find out it doesn't, we'll skip the rest of the
+        // iteration
+        let mut known_implemented = false;
+        for (_name, item) in data.items.iter() {
+            if !is_valid_candidate(db, name, receiver_ty, *item, self_ty) {
+                continue;
+            }
+            if !known_implemented {
+                let goal = generic_implements_goal(db, env.clone(), t, self_ty.clone());
+                if db.trait_solve(krate, goal).is_none() {
+                    continue 'traits;
+                }
+            }
+            known_implemented = true;
+            if callback(&self_ty.value, *item) {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+fn iterate_inherent_methods(
+    self_ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    name: Option<&Name>,
+    receiver_ty: Option<&Canonical<Ty>>,
+    krate: CrateId,
+    callback: &mut dyn FnMut(&Ty, AssocItemId) -> bool,
+) -> bool {
+    let def_crates = match self_ty.value.def_crates(db, krate) {
+        Some(k) => k,
+        None => return false,
+    };
+    for krate in def_crates {
+        let impls = db.inherent_impls_in_crate(krate);
+
+        for &impl_def in impls.for_self_ty(&self_ty.value) {
+            for &item in db.impl_data(impl_def).items.iter() {
+                if !is_valid_candidate(db, name, receiver_ty, item, self_ty) {
+                    continue;
+                }
+                // we have to check whether the self type unifies with the type
+                // that the impl is for. If we have a receiver type, this
+                // already happens in `is_valid_candidate` above; if not, we
+                // check it here
+                if receiver_ty.is_none() && inherent_impl_substs(db, impl_def, self_ty).is_none() {
+                    test_utils::mark::hit!(impl_self_type_match_without_receiver);
+                    continue;
+                }
+                if callback(&self_ty.value, item) {
+                    return true;
+                }
+            }
+        }
+    }
+    false
+}
+
+/// Returns the self type for the index trait call.
+pub fn resolve_indexing_op(
+    db: &dyn HirDatabase,
+    ty: &Canonical<Ty>,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    index_trait: TraitId,
+) -> Option<Canonical<Ty>> {
+    let ty = InEnvironment { value: ty.clone(), environment: env.clone() };
+    let deref_chain = autoderef_method_receiver(db, krate, ty);
+    for ty in deref_chain {
+        let goal = generic_implements_goal(db, env.clone(), index_trait, ty.clone());
+        if db.trait_solve(krate, goal).is_some() {
+            return Some(ty);
+        }
+    }
+    None
+}
+
+fn is_valid_candidate(
+    db: &dyn HirDatabase,
+    name: Option<&Name>,
+    receiver_ty: Option<&Canonical<Ty>>,
+    item: AssocItemId,
+    self_ty: &Canonical<Ty>,
+) -> bool {
+    match item {
+        AssocItemId::FunctionId(m) => {
+            let data = db.function_data(m);
+            if let Some(name) = name {
+                if &data.name != name {
+                    return false;
+                }
+            }
+            if let Some(receiver_ty) = receiver_ty {
+                if !data.has_self_param {
+                    return false;
+                }
+                let transformed_receiver_ty = match transform_receiver_ty(db, m, self_ty) {
+                    Some(ty) => ty,
+                    None => return false,
+                };
+                if transformed_receiver_ty != receiver_ty.value {
+                    return false;
+                }
+            }
+            true
+        }
+        AssocItemId::ConstId(c) => {
+            let data = db.const_data(c);
+            name.map_or(true, |name| data.name.as_ref() == Some(name)) && receiver_ty.is_none()
+        }
+        _ => false,
+    }
+}
+
+pub(crate) fn inherent_impl_substs(
+    db: &dyn HirDatabase,
+    impl_id: ImplId,
+    self_ty: &Canonical<Ty>,
+) -> Option<Substs> {
+    // we create a var for each type parameter of the impl; we need to keep in
+    // mind here that `self_ty` might have vars of its own
+    let vars = Substs::build_for_def(db, impl_id)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, self_ty.kinds.len())
+        .build();
+    let self_ty_with_vars = db.impl_self_ty(impl_id).subst(&vars);
+    let mut kinds = self_ty.kinds.to_vec();
+    kinds.extend(iter::repeat(TyKind::General).take(vars.len()));
+    let tys = Canonical { kinds: kinds.into(), value: (self_ty_with_vars, self_ty.value.clone()) };
+    let substs = super::infer::unify(&tys);
+    // We only want the substs for the vars we added, not the ones from self_ty.
+    // Also, if any of the vars we added are still in there, we replace them by
+    // Unknown. I think this can only really happen if self_ty contained
+    // Unknown, and in that case we want the result to contain Unknown in those
+    // places again.
+    substs.map(|s| fallback_bound_vars(s.suffix(vars.len()), self_ty.kinds.len()))
+}
+
+/// This replaces any 'free' Bound vars in `s` (i.e. those with indices past
+/// num_vars_to_keep) by `Ty::Unknown`.
+fn fallback_bound_vars(s: Substs, num_vars_to_keep: usize) -> Substs {
+    s.fold_binders(
+        &mut |ty, binders| {
+            if let Ty::Bound(bound) = &ty {
+                if bound.index >= num_vars_to_keep && bound.debruijn >= binders {
+                    Ty::Unknown
+                } else {
+                    ty
+                }
+            } else {
+                ty
+            }
+        },
+        DebruijnIndex::INNERMOST,
+    )
+}
+
+fn transform_receiver_ty(
+    db: &dyn HirDatabase,
+    function_id: FunctionId,
+    self_ty: &Canonical<Ty>,
+) -> Option<Ty> {
+    let substs = match function_id.lookup(db.upcast()).container {
+        AssocContainerId::TraitId(_) => Substs::build_for_def(db, function_id)
+            .push(self_ty.value.clone())
+            .fill_with_unknown()
+            .build(),
+        AssocContainerId::ImplId(impl_id) => inherent_impl_substs(db, impl_id, &self_ty)?,
+        AssocContainerId::ContainerId(_) => unreachable!(),
+    };
+    let sig = db.callable_item_signature(function_id.into());
+    Some(sig.value.params()[0].clone().subst_bound_vars(&substs))
+}
+
+pub fn implements_trait(
+    ty: &Canonical<Ty>,
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    krate: CrateId,
+    trait_: TraitId,
+) -> bool {
+    let goal = generic_implements_goal(db, env, trait_, ty.clone());
+    let solution = db.trait_solve(krate, goal);
+
+    solution.is_some()
+}
+
+/// This creates Substs for a trait with the given Self type and type variables
+/// for all other parameters, to query Chalk with it.
+fn generic_implements_goal(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    trait_: TraitId,
+    self_ty: Canonical<Ty>,
+) -> Canonical<InEnvironment<super::Obligation>> {
+    let mut kinds = self_ty.kinds.to_vec();
+    let substs = super::Substs::build_for_def(db, trait_)
+        .push(self_ty.value)
+        .fill_with_bound_vars(DebruijnIndex::INNERMOST, kinds.len())
+        .build();
+    kinds.extend(iter::repeat(TyKind::General).take(substs.len() - 1));
+    let trait_ref = TraitRef { trait_, substs };
+    let obligation = super::Obligation::Trait(trait_ref);
+    Canonical { kinds: kinds.into(), value: InEnvironment::new(env, obligation) }
+}
+
+fn autoderef_method_receiver(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    ty: InEnvironment<Canonical<Ty>>,
+) -> Vec<Canonical<Ty>> {
+    let mut deref_chain: Vec<_> = autoderef::autoderef(db, Some(krate), ty).collect();
+    // As a last step, we can do array unsizing (that's the only unsizing that rustc does for method receivers!)
+    if let Some(Ty::Apply(ApplicationTy { ctor: TypeCtor::Array, parameters })) =
+        deref_chain.last().map(|ty| &ty.value)
+    {
+        let kinds = deref_chain.last().unwrap().kinds.clone();
+        let unsized_ty = Ty::apply(TypeCtor::Slice, parameters.clone());
+        deref_chain.push(Canonical { value: unsized_ty, kinds })
+    }
+    deref_chain
+}

crates/hir_ty/src/op.rs

@@ -0,0 +1,58 @@
+//! Helper functions for binary operator type inference.
+use hir_def::expr::{ArithOp, BinaryOp, CmpOp};
+
+use super::{InferTy, Ty, TypeCtor};
+use crate::ApplicationTy;
+
+pub(super) fn binary_op_return_ty(op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Ty {
+    match op {
+        BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => Ty::simple(TypeCtor::Bool),
+        BinaryOp::Assignment { .. } => Ty::unit(),
+        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => match lhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int(..) | TypeCtor::Float(..) => lhs_ty,
+                _ => Ty::Unknown,
+            },
+            Ty::Infer(InferTy::IntVar(..)) | Ty::Infer(InferTy::FloatVar(..)) => lhs_ty,
+            _ => Ty::Unknown,
+        },
+        BinaryOp::ArithOp(_) => match rhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int(..) | TypeCtor::Float(..) => rhs_ty,
+                _ => Ty::Unknown,
+            },
+            Ty::Infer(InferTy::IntVar(..)) | Ty::Infer(InferTy::FloatVar(..)) => rhs_ty,
+            _ => Ty::Unknown,
+        },
+    }
+}
+
+pub(super) fn binary_op_rhs_expectation(op: BinaryOp, lhs_ty: Ty) -> Ty {
+    match op {
+        BinaryOp::LogicOp(..) => Ty::simple(TypeCtor::Bool),
+        BinaryOp::Assignment { op: None } => lhs_ty,
+        BinaryOp::CmpOp(CmpOp::Eq { .. }) => match lhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int(..)
+                | TypeCtor::Float(..)
+                | TypeCtor::Str
+                | TypeCtor::Char
+                | TypeCtor::Bool => lhs_ty,
+                _ => Ty::Unknown,
+            },
+            Ty::Infer(InferTy::IntVar(..)) | Ty::Infer(InferTy::FloatVar(..)) => lhs_ty,
+            _ => Ty::Unknown,
+        },
+        BinaryOp::ArithOp(ArithOp::Shl) | BinaryOp::ArithOp(ArithOp::Shr) => Ty::Unknown,
+        BinaryOp::CmpOp(CmpOp::Ord { .. })
+        | BinaryOp::Assignment { op: Some(_) }
+        | BinaryOp::ArithOp(_) => match lhs_ty {
+            Ty::Apply(ApplicationTy { ctor, .. }) => match ctor {
+                TypeCtor::Int(..) | TypeCtor::Float(..) => lhs_ty,
+                _ => Ty::Unknown,
+            },
+            Ty::Infer(InferTy::IntVar(..)) | Ty::Infer(InferTy::FloatVar(..)) => lhs_ty,
+            _ => Ty::Unknown,
+        },
+    }
+}

crates/hir_ty/src/primitive.rs

@@ -0,0 +1,139 @@
+//! Defines primitive types, which have a couple of peculiarities:
+//!
+//! * during type inference, they can be uncertain (ie, `let x = 92;`)
+//! * they don't belong to any particular crate.
+
+use std::fmt;
+
+pub use hir_def::builtin_type::{BuiltinFloat, BuiltinInt, FloatBitness, IntBitness, Signedness};
+
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
+pub struct IntTy {
+    pub signedness: Signedness,
+    pub bitness: IntBitness,
+}
+
+impl fmt::Debug for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.ty_to_string())
+    }
+}
+
+impl IntTy {
+    pub fn isize() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::Xsize }
+    }
+
+    pub fn i8() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::X8 }
+    }
+
+    pub fn i16() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::X16 }
+    }
+
+    pub fn i32() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::X32 }
+    }
+
+    pub fn i64() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::X64 }
+    }
+
+    pub fn i128() -> IntTy {
+        IntTy { signedness: Signedness::Signed, bitness: IntBitness::X128 }
+    }
+
+    pub fn usize() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::Xsize }
+    }
+
+    pub fn u8() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::X8 }
+    }
+
+    pub fn u16() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::X16 }
+    }
+
+    pub fn u32() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::X32 }
+    }
+
+    pub fn u64() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::X64 }
+    }
+
+    pub fn u128() -> IntTy {
+        IntTy { signedness: Signedness::Unsigned, bitness: IntBitness::X128 }
+    }
+
+    pub fn ty_to_string(self) -> &'static str {
+        match (self.signedness, self.bitness) {
+            (Signedness::Signed, IntBitness::Xsize) => "isize",
+            (Signedness::Signed, IntBitness::X8) => "i8",
+            (Signedness::Signed, IntBitness::X16) => "i16",
+            (Signedness::Signed, IntBitness::X32) => "i32",
+            (Signedness::Signed, IntBitness::X64) => "i64",
+            (Signedness::Signed, IntBitness::X128) => "i128",
+            (Signedness::Unsigned, IntBitness::Xsize) => "usize",
+            (Signedness::Unsigned, IntBitness::X8) => "u8",
+            (Signedness::Unsigned, IntBitness::X16) => "u16",
+            (Signedness::Unsigned, IntBitness::X32) => "u32",
+            (Signedness::Unsigned, IntBitness::X64) => "u64",
+            (Signedness::Unsigned, IntBitness::X128) => "u128",
+        }
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+pub struct FloatTy {
+    pub bitness: FloatBitness,
+}
+
+impl fmt::Debug for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.ty_to_string())
+    }
+}
+
+impl FloatTy {
+    pub fn f32() -> FloatTy {
+        FloatTy { bitness: FloatBitness::X32 }
+    }
+
+    pub fn f64() -> FloatTy {
+        FloatTy { bitness: FloatBitness::X64 }
+    }
+
+    pub fn ty_to_string(self) -> &'static str {
+        match self.bitness {
+            FloatBitness::X32 => "f32",
+            FloatBitness::X64 => "f64",
+        }
+    }
+}
+
+impl From<BuiltinInt> for IntTy {
+    fn from(t: BuiltinInt) -> Self {
+        IntTy { signedness: t.signedness, bitness: t.bitness }
+    }
+}
+
+impl From<BuiltinFloat> for FloatTy {
+    fn from(t: BuiltinFloat) -> Self {
+        FloatTy { bitness: t.bitness }
+    }
+}

crates/hir_ty/src/test_db.rs

@@ -0,0 +1,136 @@
+//! Database used for testing `hir`.
+
+use std::{
+    fmt, panic,
+    sync::{Arc, Mutex},
+};
+
+use base_db::{salsa, CrateId, FileId, FileLoader, FileLoaderDelegate, SourceDatabase, Upcast};
+use hir_def::{db::DefDatabase, ModuleId};
+use hir_expand::db::AstDatabase;
+use rustc_hash::{FxHashMap, FxHashSet};
+use syntax::TextRange;
+use test_utils::extract_annotations;
+
+#[salsa::database(
+    base_db::SourceDatabaseExtStorage,
+    base_db::SourceDatabaseStorage,
+    hir_expand::db::AstDatabaseStorage,
+    hir_def::db::InternDatabaseStorage,
+    hir_def::db::DefDatabaseStorage,
+    crate::db::HirDatabaseStorage
+)]
+#[derive(Default)]
+pub struct TestDB {
+    storage: salsa::Storage<TestDB>,
+    events: Mutex<Option<Vec<salsa::Event>>>,
+}
+impl fmt::Debug for TestDB {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TestDB").finish()
+    }
+}
+
+impl Upcast<dyn AstDatabase> for TestDB {
+    fn upcast(&self) -> &(dyn AstDatabase + 'static) {
+        &*self
+    }
+}
+
+impl Upcast<dyn DefDatabase> for TestDB {
+    fn upcast(&self) -> &(dyn DefDatabase + 'static) {
+        &*self
+    }
+}
+
+impl salsa::Database for TestDB {
+    fn salsa_event(&self, event: salsa::Event) {
+        let mut events = self.events.lock().unwrap();
+        if let Some(events) = &mut *events {
+            events.push(event);
+        }
+    }
+}
+
+impl salsa::ParallelDatabase for TestDB {
+    fn snapshot(&self) -> salsa::Snapshot<TestDB> {
+        salsa::Snapshot::new(TestDB {
+            storage: self.storage.snapshot(),
+            events: Default::default(),
+        })
+    }
+}
+
+impl panic::RefUnwindSafe for TestDB {}
+
+impl FileLoader for TestDB {
+    fn file_text(&self, file_id: FileId) -> Arc<String> {
+        FileLoaderDelegate(self).file_text(file_id)
+    }
+    fn resolve_path(&self, anchor: FileId, path: &str) -> Option<FileId> {
+        FileLoaderDelegate(self).resolve_path(anchor, path)
+    }
+    fn relevant_crates(&self, file_id: FileId) -> Arc<FxHashSet<CrateId>> {
+        FileLoaderDelegate(self).relevant_crates(file_id)
+    }
+}
+
+impl TestDB {
+    pub(crate) fn module_for_file(&self, file_id: FileId) -> ModuleId {
+        for &krate in self.relevant_crates(file_id).iter() {
+            let crate_def_map = self.crate_def_map(krate);
+            for (local_id, data) in crate_def_map.modules.iter() {
+                if data.origin.file_id() == Some(file_id) {
+                    return ModuleId { krate, local_id };
+                }
+            }
+        }
+        panic!("Can't find module for file")
+    }
+
+    pub(crate) fn extract_annotations(&self) -> FxHashMap<FileId, Vec<(TextRange, String)>> {
+        let mut files = Vec::new();
+        let crate_graph = self.crate_graph();
+        for krate in crate_graph.iter() {
+            let crate_def_map = self.crate_def_map(krate);
+            for (module_id, _) in crate_def_map.modules.iter() {
+                let file_id = crate_def_map[module_id].origin.file_id();
+                files.extend(file_id)
+            }
+        }
+        files
+            .into_iter()
+            .filter_map(|file_id| {
+                let text = self.file_text(file_id);
+                let annotations = extract_annotations(&text);
+                if annotations.is_empty() {
+                    return None;
+                }
+                Some((file_id, annotations))
+            })
+            .collect()
+    }
+}
+
+impl TestDB {
+    pub fn log(&self, f: impl FnOnce()) -> Vec<salsa::Event> {
+        *self.events.lock().unwrap() = Some(Vec::new());
+        f();
+        self.events.lock().unwrap().take().unwrap()
+    }
+
+    pub fn log_executed(&self, f: impl FnOnce()) -> Vec<String> {
+        let events = self.log(f);
+        events
+            .into_iter()
+            .filter_map(|e| match e.kind {
+                // This pretty horrible, but `Debug` is the only way to inspect
+                // QueryDescriptor at the moment.
+                salsa::EventKind::WillExecute { database_key } => {
+                    Some(format!("{:?}", database_key.debug(self)))
+                }
+                _ => None,
+            })
+            .collect()
+    }
+}

crates/hir_ty/src/tests.rs

@@ -0,0 +1,359 @@
+mod never_type;
+mod coercion;
+mod regression;
+mod simple;
+mod patterns;
+mod traits;
+mod method_resolution;
+mod macros;
+mod display_source_code;
+
+use std::sync::Arc;
+
+use base_db::{fixture::WithFixture, FileRange, SourceDatabase, SourceDatabaseExt};
+use expect::Expect;
+use hir_def::{
+    body::{BodySourceMap, SyntheticSyntax},
+    child_by_source::ChildBySource,
+    db::DefDatabase,
+    item_scope::ItemScope,
+    keys,
+    nameres::CrateDefMap,
+    AssocItemId, DefWithBodyId, LocalModuleId, Lookup, ModuleDefId,
+};
+use hir_expand::{db::AstDatabase, InFile};
+use stdx::format_to;
+use syntax::{
+    algo,
+    ast::{self, AstNode},
+    SyntaxNode,
+};
+
+use crate::{
+    db::HirDatabase, display::HirDisplay, infer::TypeMismatch, test_db::TestDB, InferenceResult, Ty,
+};
+
+// These tests compare the inference results for all expressions in a file
+// against snapshots of the expected results using expect. Use
+// `env UPDATE_EXPECT=1 cargo test -p hir_ty` to update the snapshots.
+
+fn setup_tracing() -> tracing::subscriber::DefaultGuard {
+    use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};
+    use tracing_tree::HierarchicalLayer;
+    let filter = EnvFilter::from_env("CHALK_DEBUG");
+    let layer = HierarchicalLayer::default()
+        .with_indent_lines(true)
+        .with_ansi(false)
+        .with_indent_amount(2)
+        .with_writer(std::io::stderr);
+    let subscriber = Registry::default().with(filter).with(layer);
+    tracing::subscriber::set_default(subscriber)
+}
+
+fn check_types(ra_fixture: &str) {
+    check_types_impl(ra_fixture, false)
+}
+
+fn check_types_source_code(ra_fixture: &str) {
+    check_types_impl(ra_fixture, true)
+}
+
+fn check_types_impl(ra_fixture: &str, display_source: bool) {
+    let _tracing = setup_tracing();
+    let db = TestDB::with_files(ra_fixture);
+    let mut checked_one = false;
+    for (file_id, annotations) in db.extract_annotations() {
+        for (range, expected) in annotations {
+            let ty = type_at_range(&db, FileRange { file_id, range });
+            let actual = if display_source {
+                let module = db.module_for_file(file_id);
+                ty.display_source_code(&db, module).unwrap()
+            } else {
+                ty.display(&db).to_string()
+            };
+            assert_eq!(expected, actual);
+            checked_one = true;
+        }
+    }
+    assert!(checked_one, "no `//^` annotations found");
+}
+
+fn type_at_range(db: &TestDB, pos: FileRange) -> Ty {
+    let file = db.parse(pos.file_id).ok().unwrap();
+    let expr = algo::find_node_at_range::<ast::Expr>(file.syntax(), pos.range).unwrap();
+    let fn_def = expr.syntax().ancestors().find_map(ast::Fn::cast).unwrap();
+    let module = db.module_for_file(pos.file_id);
+    let func = *module.child_by_source(db)[keys::FUNCTION]
+        .get(&InFile::new(pos.file_id.into(), fn_def))
+        .unwrap();
+
+    let (_body, source_map) = db.body_with_source_map(func.into());
+    if let Some(expr_id) = source_map.node_expr(InFile::new(pos.file_id.into(), &expr)) {
+        let infer = db.infer(func.into());
+        return infer[expr_id].clone();
+    }
+    panic!("Can't find expression")
+}
+
+fn infer(ra_fixture: &str) -> String {
+    infer_with_mismatches(ra_fixture, false)
+}
+
+fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
+    let _tracing = setup_tracing();
+    let (db, file_id) = TestDB::with_single_file(content);
+
+    let mut buf = String::new();
+
+    let mut infer_def = |inference_result: Arc<InferenceResult>,
+                         body_source_map: Arc<BodySourceMap>| {
+        let mut types: Vec<(InFile<SyntaxNode>, &Ty)> = Vec::new();
+        let mut mismatches: Vec<(InFile<SyntaxNode>, &TypeMismatch)> = Vec::new();
+
+        for (pat, ty) in inference_result.type_of_pat.iter() {
+            let syntax_ptr = match body_source_map.pat_syntax(pat) {
+                Ok(sp) => {
+                    let root = db.parse_or_expand(sp.file_id).unwrap();
+                    sp.map(|ptr| {
+                        ptr.either(
+                            |it| it.to_node(&root).syntax().clone(),
+                            |it| it.to_node(&root).syntax().clone(),
+                        )
+                    })
+                }
+                Err(SyntheticSyntax) => continue,
+            };
+            types.push((syntax_ptr, ty));
+        }
+
+        for (expr, ty) in inference_result.type_of_expr.iter() {
+            let node = match body_source_map.expr_syntax(expr) {
+                Ok(sp) => {
+                    let root = db.parse_or_expand(sp.file_id).unwrap();
+                    sp.map(|ptr| ptr.to_node(&root).syntax().clone())
+                }
+                Err(SyntheticSyntax) => continue,
+            };
+            types.push((node.clone(), ty));
+            if let Some(mismatch) = inference_result.type_mismatch_for_expr(expr) {
+                mismatches.push((node, mismatch));
+            }
+        }
+
+        // sort ranges for consistency
+        types.sort_by_key(|(node, _)| {
+            let range = node.value.text_range();
+            (range.start(), range.end())
+        });
+        for (node, ty) in &types {
+            let (range, text) = if let Some(self_param) = ast::SelfParam::cast(node.value.clone()) {
+                (self_param.self_token().unwrap().text_range(), "self".to_string())
+            } else {
+                (node.value.text_range(), node.value.text().to_string().replace("\n", " "))
+            };
+            let macro_prefix = if node.file_id != file_id.into() { "!" } else { "" };
+            format_to!(
+                buf,
+                "{}{:?} '{}': {}\n",
+                macro_prefix,
+                range,
+                ellipsize(text, 15),
+                ty.display(&db)
+            );
+        }
+        if include_mismatches {
+            mismatches.sort_by_key(|(node, _)| {
+                let range = node.value.text_range();
+                (range.start(), range.end())
+            });
+            for (src_ptr, mismatch) in &mismatches {
+                let range = src_ptr.value.text_range();
+                let macro_prefix = if src_ptr.file_id != file_id.into() { "!" } else { "" };
+                format_to!(
+                    buf,
+                    "{}{:?}: expected {}, got {}\n",
+                    macro_prefix,
+                    range,
+                    mismatch.expected.display(&db),
+                    mismatch.actual.display(&db),
+                );
+            }
+        }
+    };
+
+    let module = db.module_for_file(file_id);
+    let crate_def_map = db.crate_def_map(module.krate);
+
+    let mut defs: Vec<DefWithBodyId> = Vec::new();
+    visit_module(&db, &crate_def_map, module.local_id, &mut |it| defs.push(it));
+    defs.sort_by_key(|def| match def {
+        DefWithBodyId::FunctionId(it) => {
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id).syntax().text_range().start()
+        }
+        DefWithBodyId::ConstId(it) => {
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id).syntax().text_range().start()
+        }
+        DefWithBodyId::StaticId(it) => {
+            let loc = it.lookup(&db);
+            let tree = db.item_tree(loc.id.file_id);
+            tree.source(&db, loc.id).syntax().text_range().start()
+        }
+    });
+    for def in defs {
+        let (_body, source_map) = db.body_with_source_map(def);
+        let infer = db.infer(def);
+        infer_def(infer, source_map);
+    }
+
+    buf.truncate(buf.trim_end().len());
+    buf
+}
+
+fn visit_module(
+    db: &TestDB,
+    crate_def_map: &CrateDefMap,
+    module_id: LocalModuleId,
+    cb: &mut dyn FnMut(DefWithBodyId),
+) {
+    visit_scope(db, crate_def_map, &crate_def_map[module_id].scope, cb);
+    for impl_id in crate_def_map[module_id].scope.impls() {
+        let impl_data = db.impl_data(impl_id);
+        for &item in impl_data.items.iter() {
+            match item {
+                AssocItemId::FunctionId(it) => {
+                    let def = it.into();
+                    cb(def);
+                    let body = db.body(def);
+                    visit_scope(db, crate_def_map, &body.item_scope, cb);
+                }
+                AssocItemId::ConstId(it) => {
+                    let def = it.into();
+                    cb(def);
+                    let body = db.body(def);
+                    visit_scope(db, crate_def_map, &body.item_scope, cb);
+                }
+                AssocItemId::TypeAliasId(_) => (),
+            }
+        }
+    }
+
+    fn visit_scope(
+        db: &TestDB,
+        crate_def_map: &CrateDefMap,
+        scope: &ItemScope,
+        cb: &mut dyn FnMut(DefWithBodyId),
+    ) {
+        for decl in scope.declarations() {
+            match decl {
+                ModuleDefId::FunctionId(it) => {
+                    let def = it.into();
+                    cb(def);
+                    let body = db.body(def);
+                    visit_scope(db, crate_def_map, &body.item_scope, cb);
+                }
+                ModuleDefId::ConstId(it) => {
+                    let def = it.into();
+                    cb(def);
+                    let body = db.body(def);
+                    visit_scope(db, crate_def_map, &body.item_scope, cb);
+                }
+                ModuleDefId::StaticId(it) => {
+                    let def = it.into();
+                    cb(def);
+                    let body = db.body(def);
+                    visit_scope(db, crate_def_map, &body.item_scope, cb);
+                }
+                ModuleDefId::TraitId(it) => {
+                    let trait_data = db.trait_data(it);
+                    for &(_, item) in trait_data.items.iter() {
+                        match item {
+                            AssocItemId::FunctionId(it) => cb(it.into()),
+                            AssocItemId::ConstId(it) => cb(it.into()),
+                            AssocItemId::TypeAliasId(_) => (),
+                        }
+                    }
+                }
+                ModuleDefId::ModuleId(it) => visit_module(db, crate_def_map, it.local_id, cb),
+                _ => (),
+            }
+        }
+    }
+}
+
+fn ellipsize(mut text: String, max_len: usize) -> String {
+    if text.len() <= max_len {
+        return text;
+    }
+    let ellipsis = "...";
+    let e_len = ellipsis.len();
+    let mut prefix_len = (max_len - e_len) / 2;
+    while !text.is_char_boundary(prefix_len) {
+        prefix_len += 1;
+    }
+    let mut suffix_len = max_len - e_len - prefix_len;
+    while !text.is_char_boundary(text.len() - suffix_len) {
+        suffix_len += 1;
+    }
+    text.replace_range(prefix_len..text.len() - suffix_len, ellipsis);
+    text
+}
+
+#[test]
+fn typing_whitespace_inside_a_function_should_not_invalidate_types() {
+    let (mut db, pos) = TestDB::with_position(
+        "
+        //- /lib.rs
+        fn foo() -> i32 {
+            <|>1 + 1
+        }
+    ",
+    );
+    {
+        let events = db.log_executed(|| {
+            let module = db.module_for_file(pos.file_id);
+            let crate_def_map = db.crate_def_map(module.krate);
+            visit_module(&db, &crate_def_map, module.local_id, &mut |def| {
+                db.infer(def);
+            });
+        });
+        assert!(format!("{:?}", events).contains("infer"))
+    }
+
+    let new_text = "
+        fn foo() -> i32 {
+            1
+            +
+            1
+        }
+    "
+    .to_string();
+
+    db.set_file_text(pos.file_id, Arc::new(new_text));
+
+    {
+        let events = db.log_executed(|| {
+            let module = db.module_for_file(pos.file_id);
+            let crate_def_map = db.crate_def_map(module.krate);
+            visit_module(&db, &crate_def_map, module.local_id, &mut |def| {
+                db.infer(def);
+            });
+        });
+        assert!(!format!("{:?}", events).contains("infer"), "{:#?}", events)
+    }
+}
+
+fn check_infer(ra_fixture: &str, expect: Expect) {
+    let mut actual = infer(ra_fixture);
+    actual.push('\n');
+    expect.assert_eq(&actual);
+}
+
+fn check_infer_with_mismatches(ra_fixture: &str, expect: Expect) {
+    let mut actual = infer_with_mismatches(ra_fixture, true);
+    actual.push('\n');
+    expect.assert_eq(&actual);
+}

crates/hir_ty/src/tests/coercion.rs

@@ -0,0 +1,861 @@
+use expect::expect;
+use test_utils::mark;
+
+use super::{check_infer, check_infer_with_mismatches};
+
+#[test]
+fn infer_block_expr_type_mismatch() {
+    check_infer(
+        r"
+        fn test() {
+            let a: i32 = { 1i64 };
+        }
+        ",
+        expect![[r"
+            10..40 '{     ...4 }; }': ()
+            20..21 'a': i32
+            29..37 '{ 1i64 }': i64
+            31..35 '1i64': i64
+        "]],
+    );
+}
+
+#[test]
+fn coerce_places() {
+    check_infer(
+        r#"
+        struct S<T> { a: T }
+
+        fn f<T>(_: &[T]) -> T { loop {} }
+        fn g<T>(_: S<&[T]>) -> T { loop {} }
+
+        fn gen<T>() -> *mut [T; 2] { loop {} }
+        fn test1<U>() -> *mut [U] {
+            gen()
+        }
+
+        fn test2() {
+            let arr: &[u8; 1] = &[1];
+
+            let a: &[_] = arr;
+            let b = f(arr);
+            let c: &[_] = { arr };
+            let d = g(S { a: arr });
+            let e: [&[_]; 1] = [arr];
+            let f: [&[_]; 2] = [arr; 2];
+            let g: (&[_], &[_]) = (arr, arr);
+        }
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+        "#,
+        expect![[r"
+            30..31 '_': &[T]
+            44..55 '{ loop {} }': T
+            46..53 'loop {}': !
+            51..53 '{}': ()
+            64..65 '_': S<&[T]>
+            81..92 '{ loop {} }': T
+            83..90 'loop {}': !
+            88..90 '{}': ()
+            121..132 '{ loop {} }': *mut [T; _]
+            123..130 'loop {}': !
+            128..130 '{}': ()
+            159..172 '{     gen() }': *mut [U]
+            165..168 'gen': fn gen<U>() -> *mut [U; _]
+            165..170 'gen()': *mut [U; _]
+            185..419 '{     ...rr); }': ()
+            195..198 'arr': &[u8; _]
+            211..215 '&[1]': &[u8; _]
+            212..215 '[1]': [u8; _]
+            213..214 '1': u8
+            226..227 'a': &[u8]
+            236..239 'arr': &[u8; _]
+            249..250 'b': u8
+            253..254 'f': fn f<u8>(&[u8]) -> u8
+            253..259 'f(arr)': u8
+            255..258 'arr': &[u8; _]
+            269..270 'c': &[u8]
+            279..286 '{ arr }': &[u8]
+            281..284 'arr': &[u8; _]
+            296..297 'd': u8
+            300..301 'g': fn g<u8>(S<&[u8]>) -> u8
+            300..315 'g(S { a: arr })': u8
+            302..314 'S { a: arr }': S<&[u8]>
+            309..312 'arr': &[u8; _]
+            325..326 'e': [&[u8]; _]
+            340..345 '[arr]': [&[u8]; _]
+            341..344 'arr': &[u8; _]
+            355..356 'f': [&[u8]; _]
+            370..378 '[arr; 2]': [&[u8]; _]
+            371..374 'arr': &[u8; _]
+            376..377 '2': usize
+            388..389 'g': (&[u8], &[u8])
+            406..416 '(arr, arr)': (&[u8], &[u8])
+            407..410 'arr': &[u8; _]
+            412..415 'arr': &[u8; _]
+        "]],
+    );
+}
+
+#[test]
+fn infer_let_stmt_coerce() {
+    check_infer(
+        r"
+        fn test() {
+            let x: &[isize] = &[1];
+            let x: *const [isize] = &[1];
+        }
+        ",
+        expect![[r"
+            10..75 '{     ...[1]; }': ()
+            20..21 'x': &[isize]
+            34..38 '&[1]': &[isize; _]
+            35..38 '[1]': [isize; _]
+            36..37 '1': isize
+            48..49 'x': *const [isize]
+            68..72 '&[1]': &[isize; _]
+            69..72 '[1]': [isize; _]
+            70..71 '1': isize
+        "]],
+    );
+}
+
+#[test]
+fn infer_custom_coerce_unsized() {
+    check_infer(
+        r#"
+        struct A<T: ?Sized>(*const T);
+        struct B<T: ?Sized>(*const T);
+        struct C<T: ?Sized> { inner: *const T }
+
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<B<U>> for B<T> {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<C<U>> for C<T> {}
+
+        fn foo1<T>(x: A<[T]>) -> A<[T]> { x }
+        fn foo2<T>(x: B<[T]>) -> B<[T]> { x }
+        fn foo3<T>(x: C<[T]>) -> C<[T]> { x }
+
+        fn test(a: A<[u8; 2]>, b: B<[u8; 2]>, c: C<[u8; 2]>) {
+            let d = foo1(a);
+            let e = foo2(b);
+            let f = foo3(c);
+        }
+
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+        "#,
+        expect![[r"
+            257..258 'x': A<[T]>
+            278..283 '{ x }': A<[T]>
+            280..281 'x': A<[T]>
+            295..296 'x': B<[T]>
+            316..321 '{ x }': B<[T]>
+            318..319 'x': B<[T]>
+            333..334 'x': C<[T]>
+            354..359 '{ x }': C<[T]>
+            356..357 'x': C<[T]>
+            369..370 'a': A<[u8; _]>
+            384..385 'b': B<[u8; _]>
+            399..400 'c': C<[u8; _]>
+            414..480 '{     ...(c); }': ()
+            424..425 'd': A<[{unknown}]>
+            428..432 'foo1': fn foo1<{unknown}>(A<[{unknown}]>) -> A<[{unknown}]>
+            428..435 'foo1(a)': A<[{unknown}]>
+            433..434 'a': A<[u8; _]>
+            445..446 'e': B<[u8]>
+            449..453 'foo2': fn foo2<u8>(B<[u8]>) -> B<[u8]>
+            449..456 'foo2(b)': B<[u8]>
+            454..455 'b': B<[u8; _]>
+            466..467 'f': C<[u8]>
+            470..474 'foo3': fn foo3<u8>(C<[u8]>) -> C<[u8]>
+            470..477 'foo3(c)': C<[u8]>
+            475..476 'c': C<[u8; _]>
+        "]],
+    );
+}
+
+#[test]
+fn infer_if_coerce() {
+    check_infer(
+        r#"
+        fn foo<T>(x: &[T]) -> &[T] { loop {} }
+        fn test() {
+            let x = if true {
+                foo(&[1])
+            } else {
+                &[1]
+            };
+        }
+
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        "#,
+        expect![[r"
+            10..11 'x': &[T]
+            27..38 '{ loop {} }': &[T]
+            29..36 'loop {}': !
+            34..36 '{}': ()
+            49..125 '{     ...  }; }': ()
+            59..60 'x': &[i32]
+            63..122 'if tru...     }': &[i32]
+            66..70 'true': bool
+            71..96 '{     ...     }': &[i32]
+            81..84 'foo': fn foo<i32>(&[i32]) -> &[i32]
+            81..90 'foo(&[1])': &[i32]
+            85..89 '&[1]': &[i32; _]
+            86..89 '[1]': [i32; _]
+            87..88 '1': i32
+            102..122 '{     ...     }': &[i32; _]
+            112..116 '&[1]': &[i32; _]
+            113..116 '[1]': [i32; _]
+            114..115 '1': i32
+        "]],
+    );
+}
+
+#[test]
+fn infer_if_else_coerce() {
+    check_infer(
+        r#"
+        fn foo<T>(x: &[T]) -> &[T] { loop {} }
+        fn test() {
+            let x = if true {
+                &[1]
+            } else {
+                foo(&[1])
+            };
+        }
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+        "#,
+        expect![[r"
+            10..11 'x': &[T]
+            27..38 '{ loop {} }': &[T]
+            29..36 'loop {}': !
+            34..36 '{}': ()
+            49..125 '{     ...  }; }': ()
+            59..60 'x': &[i32]
+            63..122 'if tru...     }': &[i32]
+            66..70 'true': bool
+            71..91 '{     ...     }': &[i32; _]
+            81..85 '&[1]': &[i32; _]
+            82..85 '[1]': [i32; _]
+            83..84 '1': i32
+            97..122 '{     ...     }': &[i32]
+            107..110 'foo': fn foo<i32>(&[i32]) -> &[i32]
+            107..116 'foo(&[1])': &[i32]
+            111..115 '&[1]': &[i32; _]
+            112..115 '[1]': [i32; _]
+            113..114 '1': i32
+        "]],
+    )
+}
+
+#[test]
+fn infer_match_first_coerce() {
+    check_infer(
+        r#"
+        fn foo<T>(x: &[T]) -> &[T] { loop {} }
+        fn test(i: i32) {
+            let x = match i {
+                2 => foo(&[2]),
+                1 => &[1],
+                _ => &[3],
+            };
+        }
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        "#,
+        expect![[r"
+            10..11 'x': &[T]
+            27..38 '{ loop {} }': &[T]
+            29..36 'loop {}': !
+            34..36 '{}': ()
+            47..48 'i': i32
+            55..149 '{     ...  }; }': ()
+            65..66 'x': &[i32]
+            69..146 'match ...     }': &[i32]
+            75..76 'i': i32
+            87..88 '2': i32
+            87..88 '2': i32
+            92..95 'foo': fn foo<i32>(&[i32]) -> &[i32]
+            92..101 'foo(&[2])': &[i32]
+            96..100 '&[2]': &[i32; _]
+            97..100 '[2]': [i32; _]
+            98..99 '2': i32
+            111..112 '1': i32
+            111..112 '1': i32
+            116..120 '&[1]': &[i32; _]
+            117..120 '[1]': [i32; _]
+            118..119 '1': i32
+            130..131 '_': i32
+            135..139 '&[3]': &[i32; _]
+            136..139 '[3]': [i32; _]
+            137..138 '3': i32
+    "]],
+    );
+}
+
+#[test]
+fn infer_match_second_coerce() {
+    check_infer(
+        r#"
+        fn foo<T>(x: &[T]) -> &[T] { loop {} }
+        fn test(i: i32) {
+            let x = match i {
+                1 => &[1],
+                2 => foo(&[2]),
+                _ => &[3],
+            };
+        }
+
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T: ?Sized> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<'a, 'b: 'a, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+        impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+        "#,
+        expect![[r"
+            10..11 'x': &[T]
+            27..38 '{ loop {} }': &[T]
+            29..36 'loop {}': !
+            34..36 '{}': ()
+            47..48 'i': i32
+            55..149 '{     ...  }; }': ()
+            65..66 'x': &[i32]
+            69..146 'match ...     }': &[i32]
+            75..76 'i': i32
+            87..88 '1': i32
+            87..88 '1': i32
+            92..96 '&[1]': &[i32; _]
+            93..96 '[1]': [i32; _]
+            94..95 '1': i32
+            106..107 '2': i32
+            106..107 '2': i32
+            111..114 'foo': fn foo<i32>(&[i32]) -> &[i32]
+            111..120 'foo(&[2])': &[i32]
+            115..119 '&[2]': &[i32; _]
+            116..119 '[2]': [i32; _]
+            117..118 '2': i32
+            130..131 '_': i32
+            135..139 '&[3]': &[i32; _]
+            136..139 '[3]': [i32; _]
+            137..138 '3': i32
+    "]],
+    );
+}
+
+#[test]
+fn coerce_merge_one_by_one1() {
+    mark::check!(coerce_merge_fail_fallback);
+
+    check_infer(
+        r"
+        fn test() {
+            let t = &mut 1;
+            let x = match 1 {
+                1 => t as *mut i32,
+                2 => t as &i32,
+                _ => t as *const i32,
+            };
+        }
+        ",
+        expect![[r"
+            10..144 '{     ...  }; }': ()
+            20..21 't': &mut i32
+            24..30 '&mut 1': &mut i32
+            29..30 '1': i32
+            40..41 'x': *const i32
+            44..141 'match ...     }': *const i32
+            50..51 '1': i32
+            62..63 '1': i32
+            62..63 '1': i32
+            67..68 't': &mut i32
+            67..80 't as *mut i32': *mut i32
+            90..91 '2': i32
+            90..91 '2': i32
+            95..96 't': &mut i32
+            95..104 't as &i32': &i32
+            114..115 '_': i32
+            119..120 't': &mut i32
+            119..134 't as *const i32': *const i32
+    "]],
+    );
+}
+
+#[test]
+fn return_coerce_unknown() {
+    check_infer_with_mismatches(
+        r"
+        fn foo() -> u32 {
+            return unknown;
+        }
+        ",
+        expect![[r"
+            16..39 '{     ...own; }': u32
+            22..36 'return unknown': !
+            29..36 'unknown': u32
+        "]],
+    );
+}
+
+#[test]
+fn coerce_autoderef() {
+    check_infer_with_mismatches(
+        r"
+        struct Foo;
+        fn takes_ref_foo(x: &Foo) {}
+        fn test() {
+            takes_ref_foo(&Foo);
+            takes_ref_foo(&&Foo);
+            takes_ref_foo(&&&Foo);
+        }
+        ",
+        expect![[r"
+            29..30 'x': &Foo
+            38..40 '{}': ()
+            51..132 '{     ...oo); }': ()
+            57..70 'takes_ref_foo': fn takes_ref_foo(&Foo)
+            57..76 'takes_...(&Foo)': ()
+            71..75 '&Foo': &Foo
+            72..75 'Foo': Foo
+            82..95 'takes_ref_foo': fn takes_ref_foo(&Foo)
+            82..102 'takes_...&&Foo)': ()
+            96..101 '&&Foo': &&Foo
+            97..101 '&Foo': &Foo
+            98..101 'Foo': Foo
+            108..121 'takes_ref_foo': fn takes_ref_foo(&Foo)
+            108..129 'takes_...&&Foo)': ()
+            122..128 '&&&Foo': &&&Foo
+            123..128 '&&Foo': &&Foo
+            124..128 '&Foo': &Foo
+            125..128 'Foo': Foo
+        "]],
+    );
+}
+
+#[test]
+fn coerce_autoderef_generic() {
+    check_infer_with_mismatches(
+        r"
+        struct Foo;
+        fn takes_ref<T>(x: &T) -> T { *x }
+        fn test() {
+            takes_ref(&Foo);
+            takes_ref(&&Foo);
+            takes_ref(&&&Foo);
+        }
+        ",
+        expect![[r"
+            28..29 'x': &T
+            40..46 '{ *x }': T
+            42..44 '*x': T
+            43..44 'x': &T
+            57..126 '{     ...oo); }': ()
+            63..72 'takes_ref': fn takes_ref<Foo>(&Foo) -> Foo
+            63..78 'takes_ref(&Foo)': Foo
+            73..77 '&Foo': &Foo
+            74..77 'Foo': Foo
+            84..93 'takes_ref': fn takes_ref<&Foo>(&&Foo) -> &Foo
+            84..100 'takes_...&&Foo)': &Foo
+            94..99 '&&Foo': &&Foo
+            95..99 '&Foo': &Foo
+            96..99 'Foo': Foo
+            106..115 'takes_ref': fn takes_ref<&&Foo>(&&&Foo) -> &&Foo
+            106..123 'takes_...&&Foo)': &&Foo
+            116..122 '&&&Foo': &&&Foo
+            117..122 '&&Foo': &&Foo
+            118..122 '&Foo': &Foo
+            119..122 'Foo': Foo
+        "]],
+    );
+}
+
+#[test]
+fn coerce_autoderef_block() {
+    check_infer_with_mismatches(
+        r#"
+        struct String {}
+        #[lang = "deref"]
+        trait Deref { type Target; }
+        impl Deref for String { type Target = str; }
+        fn takes_ref_str(x: &str) {}
+        fn returns_string() -> String { loop {} }
+        fn test() {
+            takes_ref_str(&{ returns_string() });
+        }
+        "#,
+        expect![[r"
+            126..127 'x': &str
+            135..137 '{}': ()
+            168..179 '{ loop {} }': String
+            170..177 'loop {}': !
+            175..177 '{}': ()
+            190..235 '{     ... }); }': ()
+            196..209 'takes_ref_str': fn takes_ref_str(&str)
+            196..232 'takes_...g() })': ()
+            210..231 '&{ ret...ng() }': &String
+            211..231 '{ retu...ng() }': String
+            213..227 'returns_string': fn returns_string() -> String
+            213..229 'return...ring()': String
+        "]],
+    );
+}
+
+#[test]
+fn closure_return_coerce() {
+    check_infer_with_mismatches(
+        r"
+        fn foo() {
+            let x = || {
+                if true {
+                    return &1u32;
+                }
+                &&1u32
+            };
+        }
+        ",
+        expect![[r"
+            9..105 '{     ...  }; }': ()
+            19..20 'x': || -> &u32
+            23..102 '|| {  ...     }': || -> &u32
+            26..102 '{     ...     }': &u32
+            36..81 'if tru...     }': ()
+            39..43 'true': bool
+            44..81 '{     ...     }': ()
+            58..70 'return &1u32': !
+            65..70 '&1u32': &u32
+            66..70 '1u32': u32
+            90..96 '&&1u32': &&u32
+            91..96 '&1u32': &u32
+            92..96 '1u32': u32
+        "]],
+    );
+}
+
+#[test]
+fn coerce_fn_item_to_fn_ptr() {
+    check_infer_with_mismatches(
+        r"
+        fn foo(x: u32) -> isize { 1 }
+        fn test() {
+            let f: fn(u32) -> isize = foo;
+        }
+        ",
+        expect![[r"
+            7..8 'x': u32
+            24..29 '{ 1 }': isize
+            26..27 '1': isize
+            40..78 '{     ...foo; }': ()
+            50..51 'f': fn(u32) -> isize
+            72..75 'foo': fn foo(u32) -> isize
+        "]],
+    );
+}
+
+#[test]
+fn coerce_fn_items_in_match_arms() {
+    mark::check!(coerce_fn_reification);
+
+    check_infer_with_mismatches(
+        r"
+        fn foo1(x: u32) -> isize { 1 }
+        fn foo2(x: u32) -> isize { 2 }
+        fn foo3(x: u32) -> isize { 3 }
+        fn test() {
+            let x = match 1 {
+                1 => foo1,
+                2 => foo2,
+                _ => foo3,
+            };
+        }
+        ",
+        expect![[r"
+            8..9 'x': u32
+            25..30 '{ 1 }': isize
+            27..28 '1': isize
+            39..40 'x': u32
+            56..61 '{ 2 }': isize
+            58..59 '2': isize
+            70..71 'x': u32
+            87..92 '{ 3 }': isize
+            89..90 '3': isize
+            103..192 '{     ...  }; }': ()
+            113..114 'x': fn(u32) -> isize
+            117..189 'match ...     }': fn(u32) -> isize
+            123..124 '1': i32
+            135..136 '1': i32
+            135..136 '1': i32
+            140..144 'foo1': fn foo1(u32) -> isize
+            154..155 '2': i32
+            154..155 '2': i32
+            159..163 'foo2': fn foo2(u32) -> isize
+            173..174 '_': i32
+            178..182 'foo3': fn foo3(u32) -> isize
+        "]],
+    );
+}
+
+#[test]
+fn coerce_closure_to_fn_ptr() {
+    check_infer_with_mismatches(
+        r"
+        fn test() {
+            let f: fn(u32) -> isize = |x| { 1 };
+        }
+        ",
+        expect![[r"
+            10..54 '{     ...1 }; }': ()
+            20..21 'f': fn(u32) -> isize
+            42..51 '|x| { 1 }': |u32| -> isize
+            43..44 'x': u32
+            46..51 '{ 1 }': isize
+            48..49 '1': isize
+        "]],
+    );
+}
+
+#[test]
+fn coerce_placeholder_ref() {
+    // placeholders should unify, even behind references
+    check_infer_with_mismatches(
+        r"
+        struct S<T> { t: T }
+        impl<TT> S<TT> {
+            fn get(&self) -> &TT {
+                &self.t
+            }
+        }
+        ",
+        expect![[r"
+            50..54 'self': &S<TT>
+            63..86 '{     ...     }': &TT
+            73..80 '&self.t': &TT
+            74..78 'self': &S<TT>
+            74..80 'self.t': TT
+        "]],
+    );
+}
+
+#[test]
+fn coerce_unsize_array() {
+    check_infer_with_mismatches(
+        r#"
+        #[lang = "unsize"]
+        pub trait Unsize<T> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+        fn test() {
+            let f: &[usize] = &[1, 2, 3];
+        }
+        "#,
+        expect![[r"
+            161..198 '{     ... 3]; }': ()
+            171..172 'f': &[usize]
+            185..195 '&[1, 2, 3]': &[usize; _]
+            186..195 '[1, 2, 3]': [usize; _]
+            187..188 '1': usize
+            190..191 '2': usize
+            193..194 '3': usize
+        "]],
+    );
+}
+
+#[test]
+fn coerce_unsize_trait_object_simple() {
+    check_infer_with_mismatches(
+        r#"
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+        trait Foo<T, U> {}
+        trait Bar<U, T, X>: Foo<T, U> {}
+        trait Baz<T, X>: Bar<usize, T, X> {}
+
+        struct S<T, X>;
+        impl<T, X> Foo<T, usize> for S<T, X> {}
+        impl<T, X> Bar<usize, T, X> for S<T, X> {}
+        impl<T, X> Baz<T, X> for S<T, X> {}
+
+        fn test() {
+            let obj: &dyn Baz<i8, i16> = &S;
+            let obj: &dyn Bar<_, i8, i16> = &S;
+            let obj: &dyn Foo<i8, _> = &S;
+        }
+        "#,
+        expect![[r"
+            424..539 '{     ... &S; }': ()
+            434..437 'obj': &dyn Baz<i8, i16>
+            459..461 '&S': &S<i8, i16>
+            460..461 'S': S<i8, i16>
+            471..474 'obj': &dyn Bar<usize, i8, i16>
+            499..501 '&S': &S<i8, i16>
+            500..501 'S': S<i8, i16>
+            511..514 'obj': &dyn Foo<i8, usize>
+            534..536 '&S': &S<i8, {unknown}>
+            535..536 'S': S<i8, {unknown}>
+        "]],
+    );
+}
+
+#[test]
+// The rust reference says this should be possible, but rustc doesn't implement
+// it. We used to support it, but Chalk doesn't.
+#[ignore]
+fn coerce_unsize_trait_object_to_trait_object() {
+    check_infer_with_mismatches(
+        r#"
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+        trait Foo<T, U> {}
+        trait Bar<U, T, X>: Foo<T, U> {}
+        trait Baz<T, X>: Bar<usize, T, X> {}
+
+        struct S<T, X>;
+        impl<T, X> Foo<T, usize> for S<T, X> {}
+        impl<T, X> Bar<usize, T, X> for S<T, X> {}
+        impl<T, X> Baz<T, X> for S<T, X> {}
+
+        fn test() {
+            let obj: &dyn Baz<i8, i16> = &S;
+            let obj: &dyn Bar<_, _, _> = obj;
+            let obj: &dyn Foo<_, _> = obj;
+            let obj2: &dyn Baz<i8, i16> = &S;
+            let _: &dyn Foo<_, _> = obj2;
+        }
+        "#,
+        expect![[r"
+            424..609 '{     ...bj2; }': ()
+            434..437 'obj': &dyn Baz<i8, i16>
+            459..461 '&S': &S<i8, i16>
+            460..461 'S': S<i8, i16>
+            471..474 'obj': &dyn Bar<usize, i8, i16>
+            496..499 'obj': &dyn Baz<i8, i16>
+            509..512 'obj': &dyn Foo<i8, usize>
+            531..534 'obj': &dyn Bar<usize, i8, i16>
+            544..548 'obj2': &dyn Baz<i8, i16>
+            570..572 '&S': &S<i8, i16>
+            571..572 'S': S<i8, i16>
+            582..583 '_': &dyn Foo<i8, usize>
+            602..606 'obj2': &dyn Baz<i8, i16>
+        "]],
+    );
+}
+
+#[test]
+fn coerce_unsize_super_trait_cycle() {
+    check_infer_with_mismatches(
+        r#"
+        #[lang = "sized"]
+        pub trait Sized {}
+        #[lang = "unsize"]
+        pub trait Unsize<T> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+        trait A {}
+        trait B: C + A {}
+        trait C: B {}
+        trait D: C
+
+        struct S;
+        impl A for S {}
+        impl B for S {}
+        impl C for S {}
+        impl D for S {}
+
+        fn test() {
+            let obj: &dyn D = &S;
+            let obj: &dyn A = &S;
+        }
+        "#,
+        expect![[r"
+            328..383 '{     ... &S; }': ()
+            338..341 'obj': &dyn D
+            352..354 '&S': &S
+            353..354 'S': S
+            364..367 'obj': &dyn A
+            378..380 '&S': &S
+            379..380 'S': S
+        "]],
+    );
+}
+
+#[ignore]
+#[test]
+fn coerce_unsize_generic() {
+    // FIXME: Implement this
+    // https://doc.rust-lang.org/reference/type-coercions.html#unsized-coercions
+    check_infer_with_mismatches(
+        r#"
+        #[lang = "unsize"]
+        pub trait Unsize<T> {}
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        impl<T: Unsize<U>, U> CoerceUnsized<&U> for &T {}
+
+        struct Foo<T> { t: T };
+        struct Bar<T>(Foo<T>);
+
+        fn test() {
+            let _: &Foo<[usize]> = &Foo { t: [1, 2, 3] };
+            let _: &Bar<[usize]> = &Bar(Foo { t: [1, 2, 3] });
+        }
+        "#,
+        expect![[r"
+        "]],
+    );
+}

crates/hir_ty/src/tests/display_source_code.rs

@@ -0,0 +1,41 @@
+use super::check_types_source_code;
+
+#[test]
+fn qualify_path_to_submodule() {
+    check_types_source_code(
+        r#"
+mod foo {
+    pub struct Foo;
+}
+
+fn bar() {
+    let foo: foo::Foo = foo::Foo;
+    foo
+}  //^ foo::Foo
+
+"#,
+    );
+}
+
+#[test]
+fn omit_default_type_parameters() {
+    check_types_source_code(
+        r#"
+struct Foo<T = u8> { t: T }
+fn main() {
+    let foo = Foo { t: 5u8 };
+    foo;
+}  //^ Foo
+"#,
+    );
+
+    check_types_source_code(
+        r#"
+struct Foo<K, T = u8> { k: K, t: T }
+fn main() {
+    let foo = Foo { k: 400, t: 5u8 };
+    foo;
+}   //^ Foo<i32>
+"#,
+    );
+}

crates/hir_ty/src/tests/macros.rs

@@ -0,0 +1,787 @@
+use std::fs;
+
+use expect::expect;
+use test_utils::project_dir;
+
+use super::{check_infer, check_types};
+
+#[test]
+fn cfg_impl_def() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:foo cfg:test
+use foo::S as T;
+struct S;
+
+#[cfg(test)]
+impl S {
+    fn foo1(&self) -> i32 { 0 }
+}
+
+#[cfg(not(test))]
+impl S {
+    fn foo2(&self) -> i32 { 0 }
+}
+
+fn test() {
+    let t = (S.foo1(), S.foo2(), T.foo3(), T.foo4());
+    t;
+} //^ (i32, {unknown}, i32, {unknown})
+
+//- /foo.rs crate:foo
+struct S;
+
+#[cfg(not(test))]
+impl S {
+    fn foo3(&self) -> i32 { 0 }
+}
+
+#[cfg(test)]
+impl S {
+    fn foo4(&self) -> i32 { 0 }
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_macros_expanded() {
+    check_infer(
+        r#"
+        struct Foo(Vec<i32>);
+
+        macro_rules! foo {
+            ($($item:expr),*) => {
+                    {
+                        Foo(vec![$($item,)*])
+                    }
+            };
+        }
+
+        fn main() {
+            let x = foo!(1,2);
+        }
+        "#,
+        expect![[r#"
+            !0..17 '{Foo(v...,2,])}': Foo
+            !1..4 'Foo': Foo({unknown}) -> Foo
+            !1..16 'Foo(vec![1,2,])': Foo
+            !5..15 'vec![1,2,]': {unknown}
+            155..181 '{     ...,2); }': ()
+            165..166 'x': Foo
+        "#]],
+    );
+}
+
+#[test]
+fn infer_legacy_textual_scoped_macros_expanded() {
+    check_infer(
+        r#"
+        struct Foo(Vec<i32>);
+
+        #[macro_use]
+        mod m {
+            macro_rules! foo {
+                ($($item:expr),*) => {
+                    {
+                        Foo(vec![$($item,)*])
+                    }
+                };
+            }
+        }
+
+        fn main() {
+            let x = foo!(1,2);
+            let y = crate::foo!(1,2);
+        }
+        "#,
+        expect![[r#"
+            !0..17 '{Foo(v...,2,])}': Foo
+            !1..4 'Foo': Foo({unknown}) -> Foo
+            !1..16 'Foo(vec![1,2,])': Foo
+            !5..15 'vec![1,2,]': {unknown}
+            194..250 '{     ...,2); }': ()
+            204..205 'x': Foo
+            227..228 'y': {unknown}
+            231..247 'crate:...!(1,2)': {unknown}
+        "#]],
+    );
+}
+
+#[test]
+fn infer_path_qualified_macros_expanded() {
+    check_infer(
+        r#"
+        #[macro_export]
+        macro_rules! foo {
+            () => { 42i32 }
+        }
+
+        mod m {
+            pub use super::foo as bar;
+        }
+
+        fn main() {
+            let x = crate::foo!();
+            let y = m::bar!();
+        }
+        "#,
+        expect![[r#"
+            !0..5 '42i32': i32
+            !0..5 '42i32': i32
+            110..163 '{     ...!(); }': ()
+            120..121 'x': i32
+            147..148 'y': i32
+        "#]],
+    );
+}
+
+#[test]
+fn expr_macro_expanded_in_various_places() {
+    check_infer(
+        r#"
+        macro_rules! spam {
+            () => (1isize);
+        }
+
+        fn spam() {
+            spam!();
+            (spam!());
+            spam!().spam(spam!());
+            for _ in spam!() {}
+            || spam!();
+            while spam!() {}
+            break spam!();
+            return spam!();
+            match spam!() {
+                _ if spam!() => spam!(),
+            }
+            spam!()(spam!());
+            Spam { spam: spam!() };
+            spam!()[spam!()];
+            await spam!();
+            spam!() as usize;
+            &spam!();
+            -spam!();
+            spam!()..spam!();
+            spam!() + spam!();
+        }
+        "#,
+        expect![[r#"
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            !0..6 '1isize': isize
+            53..456 '{     ...!(); }': ()
+            87..108 'spam!(...am!())': {unknown}
+            114..133 'for _ ...!() {}': ()
+            118..119 '_': {unknown}
+            131..133 '{}': ()
+            138..148 '|| spam!()': || -> isize
+            154..170 'while ...!() {}': ()
+            168..170 '{}': ()
+            175..188 'break spam!()': !
+            194..208 'return spam!()': !
+            214..268 'match ...     }': isize
+            238..239 '_': isize
+            273..289 'spam!(...am!())': {unknown}
+            295..317 'Spam {...m!() }': {unknown}
+            323..339 'spam!(...am!()]': {unknown}
+            364..380 'spam!(... usize': usize
+            386..394 '&spam!()': &isize
+            400..408 '-spam!()': isize
+            414..430 'spam!(...pam!()': {unknown}
+            436..453 'spam!(...pam!()': isize
+        "#]],
+    );
+}
+
+#[test]
+fn infer_type_value_macro_having_same_name() {
+    check_infer(
+        r#"
+        #[macro_export]
+        macro_rules! foo {
+            () => {
+                mod foo {
+                    pub use super::foo;
+                }
+            };
+            ($x:tt) => {
+                $x
+            };
+        }
+
+        foo!();
+
+        fn foo() {
+            let foo = foo::foo!(42i32);
+        }
+        "#,
+        expect![[r#"
+            !0..5 '42i32': i32
+            170..205 '{     ...32); }': ()
+            180..183 'foo': i32
+        "#]],
+    );
+}
+
+#[test]
+fn processes_impls_generated_by_macros() {
+    check_types(
+        r#"
+macro_rules! m {
+    ($ident:ident) => (impl Trait for $ident {})
+}
+trait Trait { fn foo(self) -> u128 {} }
+struct S;
+m!(S);
+fn test() { S.foo(); }
+                //^ u128
+"#,
+    );
+}
+
+#[test]
+fn infer_assoc_items_generated_by_macros() {
+    check_types(
+        r#"
+macro_rules! m {
+    () => (fn foo(&self) -> u128 {0})
+}
+struct S;
+impl S {
+    m!();
+}
+
+fn test() { S.foo(); }
+                //^ u128
+"#,
+    );
+}
+
+#[test]
+fn infer_assoc_items_generated_by_macros_chain() {
+    check_types(
+        r#"
+macro_rules! m_inner {
+    () => {fn foo(&self) -> u128 {0}}
+}
+macro_rules! m {
+    () => {m_inner!();}
+}
+
+struct S;
+impl S {
+    m!();
+}
+
+fn test() { S.foo(); }
+                //^ u128
+"#,
+    );
+}
+
+#[test]
+fn infer_macro_with_dollar_crate_is_correct_in_expr() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:foo
+fn test() {
+    let x = (foo::foo!(1), foo::foo!(2));
+    x;
+} //^ (i32, usize)
+
+//- /lib.rs crate:foo
+#[macro_export]
+macro_rules! foo {
+    (1) => { $crate::bar!() };
+    (2) => { 1 + $crate::baz() };
+}
+
+#[macro_export]
+macro_rules! bar {
+    () => { 42 }
+}
+
+pub fn baz() -> usize { 31usize }
+"#,
+    );
+}
+
+#[test]
+fn infer_macro_with_dollar_crate_is_correct_in_trait_associate_type() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:foo
+use foo::Trait;
+
+fn test() {
+    let msg = foo::Message(foo::MessageRef);
+    let r = msg.deref();
+    r;
+  //^ &MessageRef
+}
+
+//- /lib.rs crate:foo
+pub struct MessageRef;
+pub struct Message(MessageRef);
+
+pub trait Trait {
+    type Target;
+    fn deref(&self) -> &Self::Target;
+}
+
+#[macro_export]
+macro_rules! expand {
+    () => {
+        impl Trait for Message {
+            type Target = $crate::MessageRef;
+            fn deref(&self) ->  &Self::Target {
+                &self.0
+            }
+        }
+    }
+}
+
+expand!();
+"#,
+    );
+}
+
+#[test]
+fn infer_type_value_non_legacy_macro_use_as() {
+    check_infer(
+        r#"
+        mod m {
+            macro_rules! _foo {
+                ($x:ident) => { type $x = u64; }
+            }
+            pub(crate) use _foo as foo;
+        }
+
+        m::foo!(foo);
+        use foo as bar;
+        fn f() -> bar { 0 }
+        fn main() {
+            let _a  = f();
+        }
+        "#,
+        expect![[r#"
+            158..163 '{ 0 }': u64
+            160..161 '0': u64
+            174..196 '{     ...f(); }': ()
+            184..186 '_a': u64
+            190..191 'f': fn f() -> u64
+            190..193 'f()': u64
+        "#]],
+    );
+}
+
+#[test]
+fn infer_local_macro() {
+    check_infer(
+        r#"
+        fn main() {
+            macro_rules! foo {
+                () => { 1usize }
+            }
+            let _a  = foo!();
+        }
+        "#,
+        expect![[r#"
+            !0..6 '1usize': usize
+            10..89 '{     ...!(); }': ()
+            16..65 'macro_...     }': {unknown}
+            74..76 '_a': usize
+        "#]],
+    );
+}
+
+#[test]
+fn infer_local_inner_macros() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:foo
+fn test() {
+    let x = foo::foo!(1);
+    x;
+} //^ i32
+
+//- /lib.rs crate:foo
+#[macro_export(local_inner_macros)]
+macro_rules! foo {
+    (1) => { bar!() };
+}
+
+#[macro_export]
+macro_rules! bar {
+    () => { 42 }
+}
+
+"#,
+    );
+}
+
+#[test]
+fn infer_builtin_macros_line() {
+    check_infer(
+        r#"
+        #[rustc_builtin_macro]
+        macro_rules! line {() => {}}
+
+        fn main() {
+            let x = line!();
+        }
+        "#,
+        expect![[r#"
+            !0..1 '0': i32
+            63..87 '{     ...!(); }': ()
+            73..74 'x': i32
+        "#]],
+    );
+}
+
+#[test]
+fn infer_builtin_macros_file() {
+    check_infer(
+        r#"
+        #[rustc_builtin_macro]
+        macro_rules! file {() => {}}
+
+        fn main() {
+            let x = file!();
+        }
+        "#,
+        expect![[r#"
+            !0..2 '""': &str
+            63..87 '{     ...!(); }': ()
+            73..74 'x': &str
+        "#]],
+    );
+}
+
+#[test]
+fn infer_builtin_macros_column() {
+    check_infer(
+        r#"
+        #[rustc_builtin_macro]
+        macro_rules! column {() => {}}
+
+        fn main() {
+            let x = column!();
+        }
+        "#,
+        expect![[r#"
+            !0..1 '0': i32
+            65..91 '{     ...!(); }': ()
+            75..76 'x': i32
+        "#]],
+    );
+}
+
+#[test]
+fn infer_builtin_macros_concat() {
+    check_infer(
+        r#"
+        #[rustc_builtin_macro]
+        macro_rules! concat {() => {}}
+
+        fn main() {
+            let x = concat!("hello", concat!("world", "!"));
+        }
+        "#,
+        expect![[r#"
+            !0..13 '"helloworld!"': &str
+            65..121 '{     ...")); }': ()
+            75..76 'x': &str
+        "#]],
+    );
+}
+
+#[test]
+fn infer_builtin_macros_include() {
+    check_types(
+        r#"
+//- /main.rs
+#[rustc_builtin_macro]
+macro_rules! include {() => {}}
+
+include!("foo.rs");
+
+fn main() {
+    bar();
+}     //^ u32
+
+//- /foo.rs
+fn bar() -> u32 {0}
+"#,
+    );
+}
+
+#[test]
+#[ignore]
+fn include_accidentally_quadratic() {
+    let file = project_dir().join("crates/syntax/test_data/accidentally_quadratic");
+    let big_file = fs::read_to_string(file).unwrap();
+    let big_file = vec![big_file; 10].join("\n");
+
+    let fixture = r#"
+//- /main.rs
+#[rustc_builtin_macro]
+macro_rules! include {() => {}}
+
+include!("foo.rs");
+
+fn main() {
+    RegisterBlock { };
+                  //^ RegisterBlock
+}
+    "#;
+    let fixture = format!("{}\n//- /foo.rs\n{}", fixture, big_file);
+    check_types(&fixture);
+}
+
+#[test]
+fn infer_builtin_macros_include_concat() {
+    check_types(
+        r#"
+//- /main.rs
+#[rustc_builtin_macro]
+macro_rules! include {() => {}}
+
+#[rustc_builtin_macro]
+macro_rules! concat {() => {}}
+
+include!(concat!("f", "oo.rs"));
+
+fn main() {
+    bar();
+}     //^ u32
+
+//- /foo.rs
+fn bar() -> u32 {0}
+"#,
+    );
+}
+
+#[test]
+fn infer_builtin_macros_include_concat_with_bad_env_should_failed() {
+    check_types(
+        r#"
+//- /main.rs
+#[rustc_builtin_macro]
+macro_rules! include {() => {}}
+
+#[rustc_builtin_macro]
+macro_rules! concat {() => {}}
+
+#[rustc_builtin_macro]
+macro_rules! env {() => {}}
+
+include!(concat!(env!("OUT_DIR"), "/foo.rs"));
+
+fn main() {
+    bar();
+}     //^ {unknown}
+
+//- /foo.rs
+fn bar() -> u32 {0}
+"#,
+    );
+}
+
+#[test]
+fn infer_builtin_macros_include_itself_should_failed() {
+    check_types(
+        r#"
+#[rustc_builtin_macro]
+macro_rules! include {() => {}}
+
+include!("main.rs");
+
+fn main() {
+            0
+} //^ i32
+"#,
+    );
+}
+
+#[test]
+fn infer_builtin_macros_concat_with_lazy() {
+    check_infer(
+        r#"
+        macro_rules! hello {() => {"hello"}}
+
+        #[rustc_builtin_macro]
+        macro_rules! concat {() => {}}
+
+        fn main() {
+            let x = concat!(hello!(), concat!("world", "!"));
+        }
+        "#,
+        expect![[r#"
+            !0..13 '"helloworld!"': &str
+            103..160 '{     ...")); }': ()
+            113..114 'x': &str
+        "#]],
+    );
+}
+
+#[test]
+fn infer_builtin_macros_env() {
+    check_infer(
+        r#"
+        //- /main.rs env:foo=bar
+        #[rustc_builtin_macro]
+        macro_rules! env {() => {}}
+
+        fn main() {
+            let x = env!("foo");
+        }
+        "#,
+        expect![[r#"
+            !0..22 '"__RA_...TED__"': &str
+            62..90 '{     ...o"); }': ()
+            72..73 'x': &str
+        "#]],
+    );
+}
+
+#[test]
+fn infer_derive_clone_simple() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:core
+#[derive(Clone)]
+struct S;
+fn test() {
+    S.clone();
+}         //^ S
+
+//- /lib.rs crate:core
+#[prelude_import]
+use clone::*;
+mod clone {
+    trait Clone {
+        fn clone(&self) -> Self;
+    }
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_derive_clone_in_core() {
+    check_types(
+        r#"
+//- /lib.rs crate:core
+#[prelude_import]
+use clone::*;
+mod clone {
+    trait Clone {
+        fn clone(&self) -> Self;
+    }
+}
+#[derive(Clone)]
+pub struct S;
+
+//- /main.rs crate:main deps:core
+use core::S;
+fn test() {
+    S.clone();
+}         //^ S
+"#,
+    );
+}
+
+#[test]
+fn infer_derive_clone_with_params() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:core
+#[derive(Clone)]
+struct S;
+#[derive(Clone)]
+struct Wrapper<T>(T);
+struct NonClone;
+fn test() {
+    (Wrapper(S).clone(), Wrapper(NonClone).clone());
+  //^ (Wrapper<S>, {unknown})
+}
+
+//- /lib.rs crate:core
+#[prelude_import]
+use clone::*;
+mod clone {
+    trait Clone {
+        fn clone(&self) -> Self;
+    }
+}
+"#,
+    );
+}
+
+#[test]
+fn infer_custom_derive_simple() {
+    // FIXME: this test current now do nothing
+    check_types(
+        r#"
+//- /main.rs crate:main
+use foo::Foo;
+
+#[derive(Foo)]
+struct S{}
+
+fn test() {
+    S{};
+}   //^ S
+"#,
+    );
+}
+
+#[test]
+fn macro_in_arm() {
+    check_infer(
+        r#"
+        macro_rules! unit {
+            () => { () };
+        }
+
+        fn main() {
+            let x = match () {
+                unit!() => 92u32,
+            };
+        }
+        "#,
+        expect![[r#"
+            51..110 '{     ...  }; }': ()
+            61..62 'x': u32
+            65..107 'match ...     }': u32
+            71..73 '()': ()
+            84..91 'unit!()': ()
+            95..100 '92u32': u32
+        "#]],
+    );
+}

crates/hir_ty/src/tests/never_type.rs

@@ -0,0 +1,409 @@
+use expect::expect;
+
+use super::{check_infer_with_mismatches, check_types};
+
+#[test]
+fn infer_never1() {
+    check_types(
+        r#"
+fn test() {
+    let t = return;
+    t;
+} //^ !
+"#,
+    );
+}
+
+#[test]
+fn infer_never2() {
+    check_types(
+        r#"
+fn gen<T>() -> T { loop {} }
+
+fn test() {
+    let a = gen();
+    if false { a } else { loop {} };
+    a;
+} //^ !
+"#,
+    );
+}
+
+#[test]
+fn infer_never3() {
+    check_types(
+        r#"
+fn gen<T>() -> T { loop {} }
+
+fn test() {
+    let a = gen();
+    if false { loop {} } else { a };
+    a;
+  //^ !
+}
+"#,
+    );
+}
+
+#[test]
+fn never_type_in_generic_args() {
+    check_types(
+        r#"
+enum Option<T> { None, Some(T) }
+
+fn test() {
+    let a = if true { Option::None } else { Option::Some(return) };
+    a;
+} //^ Option<!>
+"#,
+    );
+}
+
+#[test]
+fn never_type_can_be_reinferred1() {
+    check_types(
+        r#"
+fn gen<T>() -> T { loop {} }
+
+fn test() {
+    let a = gen();
+    if false { loop {} } else { a };
+    a;
+  //^ ()
+    if false { a };
+}
+"#,
+    );
+}
+
+#[test]
+fn never_type_can_be_reinferred2() {
+    check_types(
+        r#"
+enum Option<T> { None, Some(T) }
+
+fn test() {
+    let a = if true { Option::None } else { Option::Some(return) };
+    a;
+  //^ Option<i32>
+    match 42 {
+        42 => a,
+        _ => Option::Some(42),
+    };
+}
+"#,
+    );
+}
+
+#[test]
+fn never_type_can_be_reinferred3() {
+    check_types(
+        r#"
+enum Option<T> { None, Some(T) }
+
+fn test() {
+    let a = if true { Option::None } else { Option::Some(return) };
+    a;
+  //^ Option<&str>
+    match 42 {
+        42 => a,
+        _ => Option::Some("str"),
+    };
+}
+"#,
+    );
+}
+
+#[test]
+fn match_no_arm() {
+    check_types(
+        r#"
+enum Void {}
+
+fn test(a: Void) {
+    let t = match a {};
+    t;
+} //^ !
+"#,
+    );
+}
+
+#[test]
+fn match_unknown_arm() {
+    check_types(
+        r#"
+fn test(a: Option) {
+    let t = match 0 {
+        _ => unknown,
+    };
+    t;
+} //^ {unknown}
+"#,
+    );
+}
+
+#[test]
+fn if_never() {
+    check_types(
+        r#"
+fn test() {
+    let i = if true {
+        loop {}
+    } else {
+        3.0
+    };
+    i;
+} //^ f64
+"#,
+    );
+}
+
+#[test]
+fn if_else_never() {
+    check_types(
+        r#"
+fn test(input: bool) {
+    let i = if input {
+        2.0
+    } else {
+        return
+    };
+    i;
+} //^ f64
+"#,
+    );
+}
+
+#[test]
+fn match_first_arm_never() {
+    check_types(
+        r#"
+fn test(a: i32) {
+    let i = match a {
+        1 => return,
+        2 => 2.0,
+        3 => loop {},
+        _ => 3.0,
+    };
+    i;
+} //^ f64
+"#,
+    );
+}
+
+#[test]
+fn match_second_arm_never() {
+    check_types(
+        r#"
+fn test(a: i32) {
+    let i = match a {
+        1 => 3.0,
+        2 => loop {},
+        3 => 3.0,
+        _ => return,
+    };
+    i;
+} //^ f64
+"#,
+    );
+}
+
+#[test]
+fn match_all_arms_never() {
+    check_types(
+        r#"
+fn test(a: i32) {
+    let i = match a {
+        2 => return,
+        _ => loop {},
+    };
+    i;
+} //^ !
+"#,
+    );
+}
+
+#[test]
+fn match_no_never_arms() {
+    check_types(
+        r#"
+fn test(a: i32) {
+    let i = match a {
+        2 => 2.0,
+        _ => 3.0,
+    };
+    i;
+} //^ f64
+"#,
+    );
+}
+
+#[test]
+fn diverging_expression_1() {
+    check_infer_with_mismatches(
+        r"
+        //- /main.rs
+        fn test1() {
+            let x: u32 = return;
+        }
+        fn test2() {
+            let x: u32 = { return; };
+        }
+        fn test3() {
+            let x: u32 = loop {};
+        }
+        fn test4() {
+            let x: u32 = { loop {} };
+        }
+        fn test5() {
+            let x: u32 = { if true { loop {}; } else { loop {}; } };
+        }
+        fn test6() {
+            let x: u32 = { let y: u32 = { loop {}; }; };
+        }
+        ",
+        expect![[r"
+            11..39 '{     ...urn; }': ()
+            21..22 'x': u32
+            30..36 'return': !
+            51..84 '{     ...; }; }': ()
+            61..62 'x': u32
+            70..81 '{ return; }': u32
+            72..78 'return': !
+            96..125 '{     ... {}; }': ()
+            106..107 'x': u32
+            115..122 'loop {}': !
+            120..122 '{}': ()
+            137..170 '{     ...} }; }': ()
+            147..148 'x': u32
+            156..167 '{ loop {} }': u32
+            158..165 'loop {}': !
+            163..165 '{}': ()
+            182..246 '{     ...} }; }': ()
+            192..193 'x': u32
+            201..243 '{ if t...}; } }': u32
+            203..241 'if tru... {}; }': u32
+            206..210 'true': bool
+            211..223 '{ loop {}; }': u32
+            213..220 'loop {}': !
+            218..220 '{}': ()
+            229..241 '{ loop {}; }': u32
+            231..238 'loop {}': !
+            236..238 '{}': ()
+            258..310 '{     ...; }; }': ()
+            268..269 'x': u32
+            277..307 '{ let ...; }; }': u32
+            283..284 'y': u32
+            292..304 '{ loop {}; }': u32
+            294..301 'loop {}': !
+            299..301 '{}': ()
+        "]],
+    );
+}
+
+#[test]
+fn diverging_expression_2() {
+    check_infer_with_mismatches(
+        r#"
+        //- /main.rs
+        fn test1() {
+            // should give type mismatch
+            let x: u32 = { loop {}; "foo" };
+        }
+        "#,
+        expect![[r#"
+            11..84 '{     ..." }; }': ()
+            54..55 'x': u32
+            63..81 '{ loop...foo" }': &str
+            65..72 'loop {}': !
+            70..72 '{}': ()
+            74..79 '"foo"': &str
+            63..81: expected u32, got &str
+            74..79: expected u32, got &str
+        "#]],
+    );
+}
+
+#[test]
+fn diverging_expression_3_break() {
+    check_infer_with_mismatches(
+        r"
+        //- /main.rs
+        fn test1() {
+            // should give type mismatch
+            let x: u32 = { loop { break; } };
+        }
+        fn test2() {
+            // should give type mismatch
+            let x: u32 = { for a in b { break; }; };
+            // should give type mismatch as well
+            let x: u32 = { for a in b {}; };
+            // should give type mismatch as well
+            let x: u32 = { for a in b { return; }; };
+        }
+        fn test3() {
+            // should give type mismatch
+            let x: u32 = { while true { break; }; };
+            // should give type mismatch as well -- there's an implicit break, even if it's never hit
+            let x: u32 = { while true {}; };
+            // should give type mismatch as well
+            let x: u32 = { while true { return; }; };
+        }
+        ",
+        expect![[r"
+            11..85 '{     ...} }; }': ()
+            54..55 'x': u32
+            63..82 '{ loop...k; } }': ()
+            65..80 'loop { break; }': ()
+            70..80 '{ break; }': ()
+            72..77 'break': !
+            63..82: expected u32, got ()
+            65..80: expected u32, got ()
+            97..343 '{     ...; }; }': ()
+            140..141 'x': u32
+            149..175 '{ for ...; }; }': ()
+            151..172 'for a ...eak; }': ()
+            155..156 'a': {unknown}
+            160..161 'b': {unknown}
+            162..172 '{ break; }': ()
+            164..169 'break': !
+            226..227 'x': u32
+            235..253 '{ for ... {}; }': ()
+            237..250 'for a in b {}': ()
+            241..242 'a': {unknown}
+            246..247 'b': {unknown}
+            248..250 '{}': ()
+            304..305 'x': u32
+            313..340 '{ for ...; }; }': ()
+            315..337 'for a ...urn; }': ()
+            319..320 'a': {unknown}
+            324..325 'b': {unknown}
+            326..337 '{ return; }': ()
+            328..334 'return': !
+            149..175: expected u32, got ()
+            235..253: expected u32, got ()
+            313..340: expected u32, got ()
+            355..654 '{     ...; }; }': ()
+            398..399 'x': u32
+            407..433 '{ whil...; }; }': ()
+            409..430 'while ...eak; }': ()
+            415..419 'true': bool
+            420..430 '{ break; }': ()
+            422..427 'break': !
+            537..538 'x': u32
+            546..564 '{ whil... {}; }': ()
+            548..561 'while true {}': ()
+            554..558 'true': bool
+            559..561 '{}': ()
+            615..616 'x': u32
+            624..651 '{ whil...; }; }': ()
+            626..648 'while ...urn; }': ()
+            632..636 'true': bool
+            637..648 '{ return; }': ()
+            639..645 'return': !
+            407..433: expected u32, got ()
+            546..564: expected u32, got ()
+            624..651: expected u32, got ()
+        "]],
+    );
+}

crates/hir_ty/src/tests/patterns.rs

@@ -0,0 +1,656 @@
+use expect::expect;
+use test_utils::mark;
+
+use super::{check_infer, check_infer_with_mismatches};
+
+#[test]
+fn infer_pattern() {
+    check_infer(
+        r#"
+        fn test(x: &i32) {
+            let y = x;
+            let &z = x;
+            let a = z;
+            let (c, d) = (1, "hello");
+
+            for (e, f) in some_iter {
+                let g = e;
+            }
+
+            if let [val] = opt {
+                let h = val;
+            }
+
+            let lambda = |a: u64, b, c: i32| { a + b; c };
+
+            let ref ref_to_x = x;
+            let mut mut_x = x;
+            let ref mut mut_ref_to_x = x;
+            let k = mut_ref_to_x;
+        }
+        "#,
+        expect![[r#"
+            8..9 'x': &i32
+            17..368 '{     ...o_x; }': ()
+            27..28 'y': &i32
+            31..32 'x': &i32
+            42..44 '&z': &i32
+            43..44 'z': i32
+            47..48 'x': &i32
+            58..59 'a': i32
+            62..63 'z': i32
+            73..79 '(c, d)': (i32, &str)
+            74..75 'c': i32
+            77..78 'd': &str
+            82..94 '(1, "hello")': (i32, &str)
+            83..84 '1': i32
+            86..93 '"hello"': &str
+            101..151 'for (e...     }': ()
+            105..111 '(e, f)': ({unknown}, {unknown})
+            106..107 'e': {unknown}
+            109..110 'f': {unknown}
+            115..124 'some_iter': {unknown}
+            125..151 '{     ...     }': ()
+            139..140 'g': {unknown}
+            143..144 'e': {unknown}
+            157..204 'if let...     }': ()
+            164..169 '[val]': [{unknown}]
+            165..168 'val': {unknown}
+            172..175 'opt': [{unknown}]
+            176..204 '{     ...     }': ()
+            190..191 'h': {unknown}
+            194..197 'val': {unknown}
+            214..220 'lambda': |u64, u64, i32| -> i32
+            223..255 '|a: u6...b; c }': |u64, u64, i32| -> i32
+            224..225 'a': u64
+            232..233 'b': u64
+            235..236 'c': i32
+            243..255 '{ a + b; c }': i32
+            245..246 'a': u64
+            245..250 'a + b': u64
+            249..250 'b': u64
+            252..253 'c': i32
+            266..278 'ref ref_to_x': &&i32
+            281..282 'x': &i32
+            292..301 'mut mut_x': &i32
+            304..305 'x': &i32
+            315..335 'ref mu...f_to_x': &mut &i32
+            338..339 'x': &i32
+            349..350 'k': &mut &i32
+            353..365 'mut_ref_to_x': &mut &i32
+        "#]],
+    );
+}
+
+#[test]
+fn infer_literal_pattern() {
+    check_infer_with_mismatches(
+        r#"
+        fn any<T>() -> T { loop {} }
+        fn test(x: &i32) {
+            if let "foo" = any() {}
+            if let 1 = any() {}
+            if let 1u32 = any() {}
+            if let 1f32 = any() {}
+            if let 1.0 = any() {}
+            if let true = any() {}
+        }
+        "#,
+        expect![[r#"
+            17..28 '{ loop {} }': T
+            19..26 'loop {}': !
+            24..26 '{}': ()
+            37..38 'x': &i32
+            46..208 '{     ...) {} }': ()
+            52..75 'if let...y() {}': ()
+            59..64 '"foo"': &str
+            59..64 '"foo"': &str
+            67..70 'any': fn any<&str>() -> &str
+            67..72 'any()': &str
+            73..75 '{}': ()
+            80..99 'if let...y() {}': ()
+            87..88 '1': i32
+            87..88 '1': i32
+            91..94 'any': fn any<i32>() -> i32
+            91..96 'any()': i32
+            97..99 '{}': ()
+            104..126 'if let...y() {}': ()
+            111..115 '1u32': u32
+            111..115 '1u32': u32
+            118..121 'any': fn any<u32>() -> u32
+            118..123 'any()': u32
+            124..126 '{}': ()
+            131..153 'if let...y() {}': ()
+            138..142 '1f32': f32
+            138..142 '1f32': f32
+            145..148 'any': fn any<f32>() -> f32
+            145..150 'any()': f32
+            151..153 '{}': ()
+            158..179 'if let...y() {}': ()
+            165..168 '1.0': f64
+            165..168 '1.0': f64
+            171..174 'any': fn any<f64>() -> f64
+            171..176 'any()': f64
+            177..179 '{}': ()
+            184..206 'if let...y() {}': ()
+            191..195 'true': bool
+            191..195 'true': bool
+            198..201 'any': fn any<bool>() -> bool
+            198..203 'any()': bool
+            204..206 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_range_pattern() {
+    check_infer_with_mismatches(
+        r#"
+        fn test(x: &i32) {
+            if let 1..76 = 2u32 {}
+            if let 1..=76 = 2u32 {}
+        }
+        "#,
+        expect![[r#"
+            8..9 'x': &i32
+            17..75 '{     ...2 {} }': ()
+            23..45 'if let...u32 {}': ()
+            30..35 '1..76': u32
+            38..42 '2u32': u32
+            43..45 '{}': ()
+            50..73 'if let...u32 {}': ()
+            57..63 '1..=76': u32
+            66..70 '2u32': u32
+            71..73 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_ergonomics() {
+    check_infer(
+        r#"
+        struct A<T>(T);
+
+        fn test() {
+            let A(n) = &A(1);
+            let A(n) = &mut A(1);
+        }
+        "#,
+        expect![[r#"
+            27..78 '{     ...(1); }': ()
+            37..41 'A(n)': A<i32>
+            39..40 'n': &i32
+            44..49 '&A(1)': &A<i32>
+            45..46 'A': A<i32>(i32) -> A<i32>
+            45..49 'A(1)': A<i32>
+            47..48 '1': i32
+            59..63 'A(n)': A<i32>
+            61..62 'n': &mut i32
+            66..75 '&mut A(1)': &mut A<i32>
+            71..72 'A': A<i32>(i32) -> A<i32>
+            71..75 'A(1)': A<i32>
+            73..74 '1': i32
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_ergonomics_ref() {
+    mark::check!(match_ergonomics_ref);
+    check_infer(
+        r#"
+        fn test() {
+            let v = &(1, &2);
+            let (_, &w) = v;
+        }
+        "#,
+        expect![[r#"
+            10..56 '{     ...= v; }': ()
+            20..21 'v': &(i32, &i32)
+            24..32 '&(1, &2)': &(i32, &i32)
+            25..32 '(1, &2)': (i32, &i32)
+            26..27 '1': i32
+            29..31 '&2': &i32
+            30..31 '2': i32
+            42..49 '(_, &w)': (i32, &i32)
+            43..44 '_': i32
+            46..48 '&w': &i32
+            47..48 'w': i32
+            52..53 'v': &(i32, &i32)
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_slice() {
+    check_infer(
+        r#"
+        fn test() {
+            let slice: &[f64] = &[0.0];
+            match slice {
+                &[] => {},
+                &[a] => {
+                    a;
+                },
+                &[b, c] => {
+                    b;
+                    c;
+                }
+                _ => {}
+            }
+        }
+        "#,
+        expect![[r#"
+            10..209 '{     ...   } }': ()
+            20..25 'slice': &[f64]
+            36..42 '&[0.0]': &[f64; _]
+            37..42 '[0.0]': [f64; _]
+            38..41 '0.0': f64
+            48..207 'match ...     }': ()
+            54..59 'slice': &[f64]
+            70..73 '&[]': &[f64]
+            71..73 '[]': [f64]
+            77..79 '{}': ()
+            89..93 '&[a]': &[f64]
+            90..93 '[a]': [f64]
+            91..92 'a': f64
+            97..123 '{     ...     }': ()
+            111..112 'a': f64
+            133..140 '&[b, c]': &[f64]
+            134..140 '[b, c]': [f64]
+            135..136 'b': f64
+            138..139 'c': f64
+            144..185 '{     ...     }': ()
+            158..159 'b': f64
+            173..174 'c': f64
+            194..195 '_': &[f64]
+            199..201 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_string_literal() {
+    check_infer_with_mismatches(
+        r#"
+        fn test() {
+            let s: &str = "hello";
+            match s {
+                "hello" => {}
+                _ => {}
+            }
+        }
+        "#,
+        expect![[r#"
+            10..98 '{     ...   } }': ()
+            20..21 's': &str
+            30..37 '"hello"': &str
+            43..96 'match ...     }': ()
+            49..50 's': &str
+            61..68 '"hello"': &str
+            61..68 '"hello"': &str
+            72..74 '{}': ()
+            83..84 '_': &str
+            88..90 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_or() {
+    check_infer_with_mismatches(
+        r#"
+        fn test() {
+            let s: &str = "hello";
+            match s {
+                "hello" | "world" => {}
+                _ => {}
+            }
+        }
+        "#,
+        expect![[r#"
+            10..108 '{     ...   } }': ()
+            20..21 's': &str
+            30..37 '"hello"': &str
+            43..106 'match ...     }': ()
+            49..50 's': &str
+            61..68 '"hello"': &str
+            61..68 '"hello"': &str
+            61..78 '"hello...world"': &str
+            71..78 '"world"': &str
+            71..78 '"world"': &str
+            82..84 '{}': ()
+            93..94 '_': &str
+            98..100 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_pattern_match_arr() {
+    check_infer(
+        r#"
+        fn test() {
+            let arr: [f64; 2] = [0.0, 1.0];
+            match arr {
+                [1.0, a] => {
+                    a;
+                },
+                [b, c] => {
+                    b;
+                    c;
+                }
+            }
+        }
+        "#,
+        expect![[r#"
+            10..179 '{     ...   } }': ()
+            20..23 'arr': [f64; _]
+            36..46 '[0.0, 1.0]': [f64; _]
+            37..40 '0.0': f64
+            42..45 '1.0': f64
+            52..177 'match ...     }': ()
+            58..61 'arr': [f64; _]
+            72..80 '[1.0, a]': [f64; _]
+            73..76 '1.0': f64
+            73..76 '1.0': f64
+            78..79 'a': f64
+            84..110 '{     ...     }': ()
+            98..99 'a': f64
+            120..126 '[b, c]': [f64; _]
+            121..122 'b': f64
+            124..125 'c': f64
+            130..171 '{     ...     }': ()
+            144..145 'b': f64
+            159..160 'c': f64
+        "#]],
+    );
+}
+
+#[test]
+fn infer_adt_pattern() {
+    check_infer(
+        r#"
+        enum E {
+            A { x: usize },
+            B
+        }
+
+        struct S(u32, E);
+
+        fn test() {
+            let e = E::A { x: 3 };
+
+            let S(y, z) = foo;
+            let E::A { x: new_var } = e;
+
+            match e {
+                E::A { x } => x,
+                E::B if foo => 1,
+                E::B => 10,
+            };
+
+            let ref d @ E::A { .. } = e;
+            d;
+        }
+        "#,
+        expect![[r#"
+            67..288 '{     ...  d; }': ()
+            77..78 'e': E
+            81..94 'E::A { x: 3 }': E
+            91..92 '3': usize
+            105..112 'S(y, z)': S
+            107..108 'y': u32
+            110..111 'z': E
+            115..118 'foo': S
+            128..147 'E::A {..._var }': E
+            138..145 'new_var': usize
+            150..151 'e': E
+            158..244 'match ...     }': usize
+            164..165 'e': E
+            176..186 'E::A { x }': E
+            183..184 'x': usize
+            190..191 'x': usize
+            201..205 'E::B': E
+            209..212 'foo': bool
+            216..217 '1': usize
+            227..231 'E::B': E
+            235..237 '10': usize
+            255..274 'ref d ...{ .. }': &E
+            263..274 'E::A { .. }': E
+            277..278 'e': E
+            284..285 'd': &E
+        "#]],
+    );
+}
+
+#[test]
+fn enum_variant_through_self_in_pattern() {
+    check_infer(
+        r#"
+        enum E {
+            A { x: usize },
+            B(usize),
+            C
+        }
+
+        impl E {
+            fn test() {
+                match (loop {}) {
+                    Self::A { x } => { x; },
+                    Self::B(x) => { x; },
+                    Self::C => {},
+                };
+            }
+        }
+        "#,
+        expect![[r#"
+            75..217 '{     ...     }': ()
+            85..210 'match ...     }': ()
+            92..99 'loop {}': !
+            97..99 '{}': ()
+            115..128 'Self::A { x }': E
+            125..126 'x': usize
+            132..138 '{ x; }': ()
+            134..135 'x': usize
+            152..162 'Self::B(x)': E
+            160..161 'x': usize
+            166..172 '{ x; }': ()
+            168..169 'x': usize
+            186..193 'Self::C': E
+            197..199 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_generics_in_patterns() {
+    check_infer(
+        r#"
+        struct A<T> {
+            x: T,
+        }
+
+        enum Option<T> {
+            Some(T),
+            None,
+        }
+
+        fn test(a1: A<u32>, o: Option<u64>) {
+            let A { x: x2 } = a1;
+            let A::<i64> { x: x3 } = A { x: 1 };
+            match o {
+                Option::Some(t) => t,
+                _ => 1,
+            };
+        }
+        "#,
+        expect![[r#"
+            78..80 'a1': A<u32>
+            90..91 'o': Option<u64>
+            106..243 '{     ...  }; }': ()
+            116..127 'A { x: x2 }': A<u32>
+            123..125 'x2': u32
+            130..132 'a1': A<u32>
+            142..160 'A::<i6...: x3 }': A<i64>
+            156..158 'x3': i64
+            163..173 'A { x: 1 }': A<i64>
+            170..171 '1': i64
+            179..240 'match ...     }': u64
+            185..186 'o': Option<u64>
+            197..212 'Option::Some(t)': Option<u64>
+            210..211 't': u64
+            216..217 't': u64
+            227..228 '_': Option<u64>
+            232..233 '1': u64
+        "#]],
+    );
+}
+
+#[test]
+fn infer_const_pattern() {
+    check_infer_with_mismatches(
+        r#"
+        enum Option<T> { None }
+        use Option::None;
+        struct Foo;
+        const Bar: usize = 1;
+
+        fn test() {
+            let a: Option<u32> = None;
+            let b: Option<i64> = match a {
+                None => None,
+            };
+            let _: () = match () { Foo => Foo }; // Expected mismatch
+            let _: () = match () { Bar => Bar }; // Expected mismatch
+        }
+        "#,
+        expect![[r#"
+            73..74 '1': usize
+            87..309 '{     ...atch }': ()
+            97..98 'a': Option<u32>
+            114..118 'None': Option<u32>
+            128..129 'b': Option<i64>
+            145..182 'match ...     }': Option<i64>
+            151..152 'a': Option<u32>
+            163..167 'None': Option<u32>
+            171..175 'None': Option<i64>
+            192..193 '_': ()
+            200..223 'match ... Foo }': Foo
+            206..208 '()': ()
+            211..214 'Foo': Foo
+            218..221 'Foo': Foo
+            254..255 '_': ()
+            262..285 'match ... Bar }': usize
+            268..270 '()': ()
+            273..276 'Bar': usize
+            280..283 'Bar': usize
+            200..223: expected (), got Foo
+            262..285: expected (), got usize
+        "#]],
+    );
+}
+
+#[test]
+fn infer_guard() {
+    check_infer(
+        r#"
+struct S;
+impl S { fn foo(&self) -> bool { false } }
+
+fn main() {
+    match S {
+        s if s.foo() => (),
+    }
+}
+        "#,
+        expect![[r#"
+            27..31 'self': &S
+            41..50 '{ false }': bool
+            43..48 'false': bool
+            64..115 '{     ...   } }': ()
+            70..113 'match ...     }': ()
+            76..77 'S': S
+            88..89 's': S
+            93..94 's': S
+            93..100 's.foo()': bool
+            104..106 '()': ()
+    "#]],
+    )
+}
+
+#[test]
+fn match_ergonomics_in_closure_params() {
+    check_infer(
+        r#"
+        #[lang = "fn_once"]
+        trait FnOnce<Args> {
+            type Output;
+        }
+
+        fn foo<T, U, F: FnOnce(T) -> U>(t: T, f: F) -> U { loop {} }
+
+        fn test() {
+            foo(&(1, "a"), |&(x, y)| x); // normal, no match ergonomics
+            foo(&(1, "a"), |(x, y)| x);
+        }
+        "#,
+        expect![[r#"
+            93..94 't': T
+            99..100 'f': F
+            110..121 '{ loop {} }': U
+            112..119 'loop {}': !
+            117..119 '{}': ()
+            133..232 '{     ... x); }': ()
+            139..142 'foo': fn foo<&(i32, &str), i32, |&(i32, &str)| -> i32>(&(i32, &str), |&(i32, &str)| -> i32) -> i32
+            139..166 'foo(&(...y)| x)': i32
+            143..152 '&(1, "a")': &(i32, &str)
+            144..152 '(1, "a")': (i32, &str)
+            145..146 '1': i32
+            148..151 '"a"': &str
+            154..165 '|&(x, y)| x': |&(i32, &str)| -> i32
+            155..162 '&(x, y)': &(i32, &str)
+            156..162 '(x, y)': (i32, &str)
+            157..158 'x': i32
+            160..161 'y': &str
+            164..165 'x': i32
+            203..206 'foo': fn foo<&(i32, &str), &i32, |&(i32, &str)| -> &i32>(&(i32, &str), |&(i32, &str)| -> &i32) -> &i32
+            203..229 'foo(&(...y)| x)': &i32
+            207..216 '&(1, "a")': &(i32, &str)
+            208..216 '(1, "a")': (i32, &str)
+            209..210 '1': i32
+            212..215 '"a"': &str
+            218..228 '|(x, y)| x': |&(i32, &str)| -> &i32
+            219..225 '(x, y)': (i32, &str)
+            220..221 'x': &i32
+            223..224 'y': &&str
+            227..228 'x': &i32
+        "#]],
+    );
+}
+
+#[test]
+fn slice_tail_pattern() {
+    check_infer(
+        r#"
+        fn foo(params: &[i32]) {
+            match params {
+                [head, tail @ ..] => {
+                }
+            }
+        }
+        "#,
+        expect![[r#"
+            7..13 'params': &[i32]
+            23..92 '{     ...   } }': ()
+            29..90 'match ...     }': ()
+            35..41 'params': &[i32]
+            52..69 '[head,... @ ..]': [i32]
+            53..57 'head': &i32
+            59..68 'tail @ ..': &[i32]
+            66..68 '..': [i32]
+            73..84 '{         }': ()
+        "#]],
+    );
+}

crates/hir_ty/src/tests/regression.rs

@@ -0,0 +1,842 @@
+use expect::expect;
+use test_utils::mark;
+
+use super::{check_infer, check_types};
+
+#[test]
+fn bug_484() {
+    check_infer(
+        r#"
+        fn test() {
+            let x = if true {};
+        }
+        "#,
+        expect![[r#"
+            10..37 '{     ... {}; }': ()
+            20..21 'x': ()
+            24..34 'if true {}': ()
+            27..31 'true': bool
+            32..34 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn no_panic_on_field_of_enum() {
+    check_infer(
+        r#"
+        enum X {}
+
+        fn test(x: X) {
+            x.some_field;
+        }
+        "#,
+        expect![[r#"
+            19..20 'x': X
+            25..46 '{     ...eld; }': ()
+            31..32 'x': X
+            31..43 'x.some_field': {unknown}
+        "#]],
+    );
+}
+
+#[test]
+fn bug_585() {
+    check_infer(
+        r#"
+        fn test() {
+            X {};
+            match x {
+                A::B {} => (),
+                A::Y() => (),
+            }
+        }
+        "#,
+        expect![[r#"
+            10..88 '{     ...   } }': ()
+            16..20 'X {}': {unknown}
+            26..86 'match ...     }': ()
+            32..33 'x': {unknown}
+            44..51 'A::B {}': {unknown}
+            55..57 '()': ()
+            67..73 'A::Y()': {unknown}
+            77..79 '()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn bug_651() {
+    check_infer(
+        r#"
+        fn quux() {
+            let y = 92;
+            1 + y;
+        }
+        "#,
+        expect![[r#"
+            10..40 '{     ...+ y; }': ()
+            20..21 'y': i32
+            24..26 '92': i32
+            32..33 '1': i32
+            32..37 '1 + y': i32
+            36..37 'y': i32
+        "#]],
+    );
+}
+
+#[test]
+fn recursive_vars() {
+    mark::check!(type_var_cycles_resolve_completely);
+    mark::check!(type_var_cycles_resolve_as_possible);
+    check_infer(
+        r#"
+        fn test() {
+            let y = unknown;
+            [y, &y];
+        }
+        "#,
+        expect![[r#"
+            10..47 '{     ...&y]; }': ()
+            20..21 'y': &{unknown}
+            24..31 'unknown': &{unknown}
+            37..44 '[y, &y]': [&&{unknown}; _]
+            38..39 'y': &{unknown}
+            41..43 '&y': &&{unknown}
+            42..43 'y': &{unknown}
+        "#]],
+    );
+}
+
+#[test]
+fn recursive_vars_2() {
+    check_infer(
+        r#"
+        fn test() {
+            let x = unknown;
+            let y = unknown;
+            [(x, y), (&y, &x)];
+        }
+        "#,
+        expect![[r#"
+            10..79 '{     ...x)]; }': ()
+            20..21 'x': &&{unknown}
+            24..31 'unknown': &&{unknown}
+            41..42 'y': &&{unknown}
+            45..52 'unknown': &&{unknown}
+            58..76 '[(x, y..., &x)]': [(&&&{unknown}, &&&{unknown}); _]
+            59..65 '(x, y)': (&&&{unknown}, &&&{unknown})
+            60..61 'x': &&{unknown}
+            63..64 'y': &&{unknown}
+            67..75 '(&y, &x)': (&&&{unknown}, &&&{unknown})
+            68..70 '&y': &&&{unknown}
+            69..70 'y': &&{unknown}
+            72..74 '&x': &&&{unknown}
+            73..74 'x': &&{unknown}
+        "#]],
+    );
+}
+
+#[test]
+fn infer_std_crash_1() {
+    // caused stack overflow, taken from std
+    check_infer(
+        r#"
+        enum Maybe<T> {
+            Real(T),
+            Fake,
+        }
+
+        fn write() {
+            match something_unknown {
+                Maybe::Real(ref mut something) => (),
+            }
+        }
+        "#,
+        expect![[r#"
+            53..138 '{     ...   } }': ()
+            59..136 'match ...     }': ()
+            65..82 'someth...nknown': Maybe<{unknown}>
+            93..123 'Maybe:...thing)': Maybe<{unknown}>
+            105..122 'ref mu...ething': &mut {unknown}
+            127..129 '()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_std_crash_2() {
+    mark::check!(type_var_resolves_to_int_var);
+    // caused "equating two type variables, ...", taken from std
+    check_infer(
+        r#"
+        fn test_line_buffer() {
+            &[0, b'\n', 1, b'\n'];
+        }
+        "#,
+        expect![[r#"
+            22..52 '{     ...n']; }': ()
+            28..49 '&[0, b...b'\n']': &[u8; _]
+            29..49 '[0, b'...b'\n']': [u8; _]
+            30..31 '0': u8
+            33..38 'b'\n'': u8
+            40..41 '1': u8
+            43..48 'b'\n'': u8
+        "#]],
+    );
+}
+
+#[test]
+fn infer_std_crash_3() {
+    // taken from rustc
+    check_infer(
+        r#"
+        pub fn compute() {
+            match nope!() {
+                SizeSkeleton::Pointer { non_zero: true, tail } => {}
+            }
+        }
+        "#,
+        expect![[r#"
+            17..107 '{     ...   } }': ()
+            23..105 'match ...     }': ()
+            29..36 'nope!()': {unknown}
+            47..93 'SizeSk...tail }': {unknown}
+            81..85 'true': bool
+            81..85 'true': bool
+            87..91 'tail': {unknown}
+            97..99 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_std_crash_4() {
+    // taken from rustc
+    check_infer(
+        r#"
+        pub fn primitive_type() {
+            match *self {
+                BorrowedRef { type_: Primitive(p), ..} => {},
+            }
+        }
+        "#,
+        expect![[r#"
+            24..105 '{     ...   } }': ()
+            30..103 'match ...     }': ()
+            36..41 '*self': {unknown}
+            37..41 'self': {unknown}
+            52..90 'Borrow...), ..}': {unknown}
+            73..85 'Primitive(p)': {unknown}
+            83..84 'p': {unknown}
+            94..96 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn infer_std_crash_5() {
+    // taken from rustc
+    check_infer(
+        r#"
+        fn extra_compiler_flags() {
+            for content in doesnt_matter {
+                let name = if doesnt_matter {
+                    first
+                } else {
+                    &content
+                };
+
+                let content = if ICE_REPORT_COMPILER_FLAGS_STRIP_VALUE.contains(&name) {
+                    name
+                } else {
+                    content
+                };
+            }
+        }
+        "#,
+        expect![[r#"
+            26..322 '{     ...   } }': ()
+            32..320 'for co...     }': ()
+            36..43 'content': &{unknown}
+            47..60 'doesnt_matter': {unknown}
+            61..320 '{     ...     }': ()
+            75..79 'name': &&{unknown}
+            82..166 'if doe...     }': &&{unknown}
+            85..98 'doesnt_matter': bool
+            99..128 '{     ...     }': &&{unknown}
+            113..118 'first': &&{unknown}
+            134..166 '{     ...     }': &&{unknown}
+            148..156 '&content': &&{unknown}
+            149..156 'content': &{unknown}
+            181..188 'content': &{unknown}
+            191..313 'if ICE...     }': &{unknown}
+            194..231 'ICE_RE..._VALUE': {unknown}
+            194..247 'ICE_RE...&name)': bool
+            241..246 '&name': &&&{unknown}
+            242..246 'name': &&{unknown}
+            248..276 '{     ...     }': &&{unknown}
+            262..266 'name': &&{unknown}
+            282..313 '{     ...     }': &{unknown}
+            296..303 'content': &{unknown}
+        "#]],
+    );
+}
+
+#[test]
+fn infer_nested_generics_crash() {
+    // another crash found typechecking rustc
+    check_infer(
+        r#"
+        struct Canonical<V> {
+            value: V,
+        }
+        struct QueryResponse<V> {
+            value: V,
+        }
+        fn test<R>(query_response: Canonical<QueryResponse<R>>) {
+            &query_response.value;
+        }
+        "#,
+        expect![[r#"
+            91..105 'query_response': Canonical<QueryResponse<R>>
+            136..166 '{     ...lue; }': ()
+            142..163 '&query....value': &QueryResponse<R>
+            143..157 'query_response': Canonical<QueryResponse<R>>
+            143..163 'query_....value': QueryResponse<R>
+        "#]],
+    );
+}
+
+#[test]
+fn infer_paren_macro_call() {
+    check_infer(
+        r#"
+        macro_rules! bar { () => {0u32} }
+        fn test() {
+            let a = (bar!());
+        }
+        "#,
+        expect![[r#"
+            !0..4 '0u32': u32
+            44..69 '{     ...()); }': ()
+            54..55 'a': u32
+        "#]],
+    );
+}
+
+#[test]
+fn bug_1030() {
+    check_infer(
+        r#"
+        struct HashSet<T, H>;
+        struct FxHasher;
+        type FxHashSet<T> = HashSet<T, FxHasher>;
+
+        impl<T, H> HashSet<T, H> {
+            fn default() -> HashSet<T, H> {}
+        }
+
+        pub fn main_loop() {
+            FxHashSet::default();
+        }
+        "#,
+        expect![[r#"
+            143..145 '{}': ()
+            168..197 '{     ...t(); }': ()
+            174..192 'FxHash...efault': fn default<{unknown}, FxHasher>() -> HashSet<{unknown}, FxHasher>
+            174..194 'FxHash...ault()': HashSet<{unknown}, FxHasher>
+        "#]],
+    );
+}
+
+#[test]
+fn issue_2669() {
+    check_infer(
+        r#"
+        trait A {}
+        trait Write {}
+        struct Response<T> {}
+
+        trait D {
+            fn foo();
+        }
+
+        impl<T:A> D for Response<T> {
+            fn foo() {
+                end();
+                fn end<W: Write>() {
+                    let _x: T =  loop {};
+                }
+            }
+        }
+        "#,
+        expect![[r#"
+            119..214 '{     ...     }': ()
+            129..132 'end': fn end<{unknown}>()
+            129..134 'end()': ()
+            163..208 '{     ...     }': ()
+            181..183 '_x': !
+            190..197 'loop {}': !
+            195..197 '{}': ()
+        "#]],
+    )
+}
+
+#[test]
+fn issue_2705() {
+    check_infer(
+        r#"
+        trait Trait {}
+        fn test() {
+            <Trait<u32>>::foo()
+        }
+        "#,
+        expect![[r#"
+            25..52 '{     ...oo() }': ()
+            31..48 '<Trait...>::foo': {unknown}
+            31..50 '<Trait...:foo()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_2683_chars_impl() {
+    check_types(
+        r#"
+//- /main.rs crate:main deps:std
+fn test() {
+    let chars: std::str::Chars<'_>;
+    (chars.next(), chars.nth(1));
+} //^ (Option<char>, Option<char>)
+
+//- /std.rs crate:std
+#[prelude_import]
+use prelude::*;
+
+pub mod prelude {
+    pub use crate::iter::Iterator;
+    pub use crate::option::Option;
+}
+
+pub mod iter {
+    pub use self::traits::Iterator;
+    pub mod traits {
+        pub use self::iterator::Iterator;
+
+        pub mod iterator {
+            pub trait Iterator {
+                type Item;
+                fn next(&mut self) -> Option<Self::Item>;
+                fn nth(&mut self, n: usize) -> Option<Self::Item> {}
+            }
+        }
+    }
+}
+
+pub mod option {
+    pub enum Option<T> {}
+}
+
+pub mod str {
+    pub struct Chars<'a> {}
+    impl<'a> Iterator for Chars<'a> {
+        type Item = char;
+        fn next(&mut self) -> Option<char> {}
+    }
+}
+"#,
+    );
+}
+
+#[test]
+fn issue_3642_bad_macro_stackover() {
+    check_types(
+        r#"
+#[macro_export]
+macro_rules! match_ast {
+    (match $node:ident { $($tt:tt)* }) => { match_ast!(match ($node) { $($tt)* }) };
+
+    (match ($node:expr) {
+        $( ast::$ast:ident($it:ident) => $res:expr, )*
+        _ => $catch_all:expr $(,)?
+    }) => {{
+        $( if let Some($it) = ast::$ast::cast($node.clone()) { $res } else )*
+        { $catch_all }
+    }};
+}
+
+fn main() {
+    let anchor = match_ast! {
+       //^ ()
+        match parent {
+            as => {},
+            _ => return None
+        }
+    };
+}"#,
+    );
+}
+
+#[test]
+fn issue_3999_slice() {
+    check_infer(
+        r#"
+        fn foo(params: &[usize]) {
+            match params {
+                [ps @ .., _] => {}
+            }
+        }
+        "#,
+        expect![[r#"
+            7..13 'params': &[usize]
+            25..80 '{     ...   } }': ()
+            31..78 'match ...     }': ()
+            37..43 'params': &[usize]
+            54..66 '[ps @ .., _]': [usize]
+            55..62 'ps @ ..': &[usize]
+            60..62 '..': [usize]
+            64..65 '_': usize
+            70..72 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_3999_struct() {
+    // rust-analyzer should not panic on seeing this malformed
+    // record pattern.
+    check_infer(
+        r#"
+        struct Bar {
+            a: bool,
+        }
+        fn foo(b: Bar) {
+            match b {
+                Bar { a: .. } => {},
+            }
+        }
+        "#,
+        expect![[r#"
+            35..36 'b': Bar
+            43..95 '{     ...   } }': ()
+            49..93 'match ...     }': ()
+            55..56 'b': Bar
+            67..80 'Bar { a: .. }': Bar
+            76..78 '..': bool
+            84..86 '{}': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4235_name_conflicts() {
+    check_infer(
+        r#"
+        struct FOO {}
+        static FOO:FOO = FOO {};
+
+        impl FOO {
+            fn foo(&self) {}
+        }
+
+        fn main() {
+            let a = &FOO;
+            a.foo();
+        }
+        "#,
+        expect![[r#"
+            31..37 'FOO {}': FOO
+            63..67 'self': &FOO
+            69..71 '{}': ()
+            85..119 '{     ...o(); }': ()
+            95..96 'a': &FOO
+            99..103 '&FOO': &FOO
+            100..103 'FOO': FOO
+            109..110 'a': &FOO
+            109..116 'a.foo()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4465_dollar_crate_at_type() {
+    check_infer(
+        r#"
+        pub struct Foo {}
+        pub fn anything<T>() -> T {
+            loop {}
+        }
+        macro_rules! foo {
+            () => {{
+                let r: $crate::Foo = anything();
+                r
+            }};
+        }
+        fn main() {
+            let _a = foo!();
+        }
+        "#,
+        expect![[r#"
+            44..59 '{     loop {} }': T
+            50..57 'loop {}': !
+            55..57 '{}': ()
+            !0..31 '{letr:...g();r}': Foo
+            !4..5 'r': Foo
+            !18..26 'anything': fn anything<Foo>() -> Foo
+            !18..28 'anything()': Foo
+            !29..30 'r': Foo
+            163..187 '{     ...!(); }': ()
+            173..175 '_a': Foo
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4053_diesel_where_clauses() {
+    check_infer(
+        r#"
+        trait BoxedDsl<DB> {
+            type Output;
+            fn internal_into_boxed(self) -> Self::Output;
+        }
+
+        struct SelectStatement<From, Select, Distinct, Where, Order, LimitOffset, GroupBy, Locking> {
+            order: Order,
+        }
+
+        trait QueryFragment<DB: Backend> {}
+
+        trait Into<T> { fn into(self) -> T; }
+
+        impl<F, S, D, W, O, LOf, DB> BoxedDsl<DB>
+            for SelectStatement<F, S, D, W, O, LOf, G>
+        where
+            O: Into<dyn QueryFragment<DB>>,
+        {
+            type Output = XXX;
+
+            fn internal_into_boxed(self) -> Self::Output {
+                self.order.into();
+            }
+        }
+        "#,
+        expect![[r#"
+            65..69 'self': Self
+            267..271 'self': Self
+            466..470 'self': SelectStatement<F, S, D, W, O, LOf, {unknown}, {unknown}>
+            488..522 '{     ...     }': ()
+            498..502 'self': SelectStatement<F, S, D, W, O, LOf, {unknown}, {unknown}>
+            498..508 'self.order': O
+            498..515 'self.o...into()': dyn QueryFragment<DB>
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4953() {
+    check_infer(
+        r#"
+        pub struct Foo(pub i64);
+        impl Foo {
+            fn test() -> Self { Self(0i64) }
+        }
+        "#,
+        expect![[r#"
+            58..72 '{ Self(0i64) }': Foo
+            60..64 'Self': Foo(i64) -> Foo
+            60..70 'Self(0i64)': Foo
+            65..69 '0i64': i64
+        "#]],
+    );
+    check_infer(
+        r#"
+        pub struct Foo<T>(pub T);
+        impl Foo<i64> {
+            fn test() -> Self { Self(0i64) }
+        }
+        "#,
+        expect![[r#"
+            64..78 '{ Self(0i64) }': Foo<i64>
+            66..70 'Self': Foo<i64>(i64) -> Foo<i64>
+            66..76 'Self(0i64)': Foo<i64>
+            71..75 '0i64': i64
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4931() {
+    check_infer(
+        r#"
+        trait Div<T> {
+            type Output;
+        }
+
+        trait CheckedDiv: Div<()> {}
+
+        trait PrimInt: CheckedDiv<Output = ()> {
+            fn pow(self);
+        }
+
+        fn check<T: PrimInt>(i: T) {
+            i.pow();
+        }
+        "#,
+        expect![[r#"
+            117..121 'self': Self
+            148..149 'i': T
+            154..170 '{     ...w(); }': ()
+            160..161 'i': T
+            160..167 'i.pow()': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4885() {
+    check_infer(
+        r#"
+        #[lang = "coerce_unsized"]
+        pub trait CoerceUnsized<T> {}
+
+        trait Future {
+            type Output;
+        }
+        trait Foo<R> {
+            type Bar;
+        }
+        fn foo<R, K>(key: &K) -> impl Future<Output = K::Bar>
+        where
+            K: Foo<R>,
+        {
+            bar(key)
+        }
+        fn bar<R, K>(key: &K) -> impl Future<Output = K::Bar>
+        where
+            K: Foo<R>,
+        {
+        }
+        "#,
+        expect![[r#"
+            136..139 'key': &K
+            198..214 '{     ...key) }': impl Future<Output = <K as Foo<R>>::Bar>
+            204..207 'bar': fn bar<R, K>(&K) -> impl Future<Output = <K as Foo<R>>::Bar>
+            204..212 'bar(key)': impl Future<Output = <K as Foo<R>>::Bar>
+            208..211 'key': &K
+            228..231 'key': &K
+            290..293 '{ }': ()
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4800() {
+    check_infer(
+        r#"
+        trait Debug {}
+
+        struct Foo<T>;
+
+        type E1<T> = (T, T, T);
+        type E2<T> = E1<E1<E1<(T, T, T)>>>;
+
+        impl Debug for Foo<E2<()>> {}
+
+        struct Request;
+
+        pub trait Future {
+            type Output;
+        }
+
+        pub struct PeerSet<D>;
+
+        impl<D> Service<Request> for PeerSet<D>
+        where
+            D: Discover,
+            D::Key: Debug,
+        {
+            type Error = ();
+            type Future = dyn Future<Output = Self::Error>;
+
+            fn call(&mut self) -> Self::Future {
+                loop {}
+            }
+        }
+
+        pub trait Discover {
+            type Key;
+        }
+
+        pub trait Service<Request> {
+            type Error;
+            type Future: Future<Output = Self::Error>;
+            fn call(&mut self) -> Self::Future;
+        }
+        "#,
+        expect![[r#"
+            379..383 'self': &mut PeerSet<D>
+            401..424 '{     ...     }': dyn Future<Output = ()>
+            411..418 'loop {}': !
+            416..418 '{}': ()
+            575..579 'self': &mut Self
+        "#]],
+    );
+}
+
+#[test]
+fn issue_4966() {
+    check_infer(
+        r#"
+        pub trait IntoIterator {
+            type Item;
+        }
+
+        struct Repeat<A> { element: A }
+
+        struct Map<F> { f: F }
+
+        struct Vec<T> {}
+
+        #[lang = "deref"]
+        pub trait Deref {
+            type Target;
+        }
+
+        impl<T> Deref for Vec<T> {
+            type Target = [T];
+        }
+
+        fn from_iter<A, T: IntoIterator<Item = A>>(iter: T) -> Vec<A> {}
+
+        fn main() {
+            let inner = Map { f: |_: &f64| 0.0 };
+
+            let repeat = Repeat { element: inner };
+
+            let vec = from_iter(repeat);
+
+            vec.foo_bar();
+        }
+        "#,
+        expect![[r#"
+            270..274 'iter': T
+            289..291 '{}': ()
+            303..447 '{     ...r(); }': ()
+            313..318 'inner': Map<|&f64| -> f64>
+            321..345 'Map { ... 0.0 }': Map<|&f64| -> f64>
+            330..343 '|_: &f64| 0.0': |&f64| -> f64
+            331..332 '_': &f64
+            340..343 '0.0': f64
+            356..362 'repeat': Repeat<Map<|&f64| -> f64>>
+            365..390 'Repeat...nner }': Repeat<Map<|&f64| -> f64>>
+            383..388 'inner': Map<|&f64| -> f64>
+            401..404 'vec': Vec<IntoIterator::Item<Repeat<Map<|&f64| -> f64>>>>
+            407..416 'from_iter': fn from_iter<IntoIterator::Item<Repeat<Map<|&f64| -> f64>>>, Repeat<Map<|&f64| -> f64>>>(Repeat<Map<|&f64| -> f64>>) -> Vec<IntoIterator::Item<Repeat<Map<|&f64| -> f64>>>>
+            407..424 'from_i...epeat)': Vec<IntoIterator::Item<Repeat<Map<|&f64| -> f64>>>>
+            417..423 'repeat': Repeat<Map<|&f64| -> f64>>
+            431..434 'vec': Vec<IntoIterator::Item<Repeat<Map<|&f64| -> f64>>>>
+            431..444 'vec.foo_bar()': {unknown}
+        "#]],
+    );
+}

crates/hir_ty/src/traits.rs

@@ -0,0 +1,272 @@
+//! Trait solving using Chalk.
+use std::sync::Arc;
+
+use base_db::CrateId;
+use chalk_ir::cast::Cast;
+use chalk_solve::Solver;
+use hir_def::{lang_item::LangItemTarget, TraitId};
+
+use crate::{db::HirDatabase, DebruijnIndex, Substs};
+
+use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
+
+use self::chalk::{from_chalk, Interner, ToChalk};
+
+pub(crate) mod chalk;
+
+// This controls the maximum size of types Chalk considers. If we set this too
+// high, we can run into slow edge cases; if we set it too low, Chalk won't
+// find some solutions.
+// FIXME this is currently hardcoded in the recursive solver
+// const CHALK_SOLVER_MAX_SIZE: usize = 10;
+
+/// This controls how much 'time' we give the Chalk solver before giving up.
+const CHALK_SOLVER_FUEL: i32 = 100;
+
+#[derive(Debug, Copy, Clone)]
+struct ChalkContext<'a> {
+    db: &'a dyn HirDatabase,
+    krate: CrateId,
+}
+
+fn create_chalk_solver() -> chalk_recursive::RecursiveSolver<Interner> {
+    let overflow_depth = 100;
+    let caching_enabled = true;
+    chalk_recursive::RecursiveSolver::new(overflow_depth, caching_enabled)
+}
+
+/// A set of clauses that we assume to be true. E.g. if we are inside this function:
+/// ```rust
+/// fn foo<T: Default>(t: T) {}
+/// ```
+/// we assume that `T: Default`.
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct TraitEnvironment {
+    pub predicates: Vec<GenericPredicate>,
+}
+
+impl TraitEnvironment {
+    /// Returns trait refs with the given self type which are supposed to hold
+    /// in this trait env. E.g. if we are in `foo<T: SomeTrait>()`, this will
+    /// find that `T: SomeTrait` if we call it for `T`.
+    pub(crate) fn trait_predicates_for_self_ty<'a>(
+        &'a self,
+        ty: &'a Ty,
+    ) -> impl Iterator<Item = &'a TraitRef> + 'a {
+        self.predicates.iter().filter_map(move |pred| match pred {
+            GenericPredicate::Implemented(tr) if tr.self_ty() == ty => Some(tr),
+            _ => None,
+        })
+    }
+}
+
+/// Something (usually a goal), along with an environment.
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct InEnvironment<T> {
+    pub environment: Arc<TraitEnvironment>,
+    pub value: T,
+}
+
+impl<T> InEnvironment<T> {
+    pub fn new(environment: Arc<TraitEnvironment>, value: T) -> InEnvironment<T> {
+        InEnvironment { environment, value }
+    }
+}
+
+/// Something that needs to be proven (by Chalk) during type checking, e.g. that
+/// a certain type implements a certain trait. Proving the Obligation might
+/// result in additional information about inference variables.
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub enum Obligation {
+    /// Prove that a certain type implements a trait (the type is the `Self` type
+    /// parameter to the `TraitRef`).
+    Trait(TraitRef),
+    Projection(ProjectionPredicate),
+}
+
+impl Obligation {
+    pub fn from_predicate(predicate: GenericPredicate) -> Option<Obligation> {
+        match predicate {
+            GenericPredicate::Implemented(trait_ref) => Some(Obligation::Trait(trait_ref)),
+            GenericPredicate::Projection(projection_pred) => {
+                Some(Obligation::Projection(projection_pred))
+            }
+            GenericPredicate::Error => None,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct ProjectionPredicate {
+    pub projection_ty: ProjectionTy,
+    pub ty: Ty,
+}
+
+impl TypeWalk for ProjectionPredicate {
+    fn walk(&self, f: &mut impl FnMut(&Ty)) {
+        self.projection_ty.walk(f);
+        self.ty.walk(f);
+    }
+
+    fn walk_mut_binders(
+        &mut self,
+        f: &mut impl FnMut(&mut Ty, DebruijnIndex),
+        binders: DebruijnIndex,
+    ) {
+        self.projection_ty.walk_mut_binders(f, binders);
+        self.ty.walk_mut_binders(f, binders);
+    }
+}
+
+/// Solve a trait goal using Chalk.
+pub(crate) fn trait_solve_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    goal: Canonical<InEnvironment<Obligation>>,
+) -> Option<Solution> {
+    let _p = profile::span("trait_solve_query").detail(|| match &goal.value.value {
+        Obligation::Trait(it) => db.trait_data(it.trait_).name.to_string(),
+        Obligation::Projection(_) => "projection".to_string(),
+    });
+    log::info!("trait_solve_query({})", goal.value.value.display(db));
+
+    if let Obligation::Projection(pred) = &goal.value.value {
+        if let Ty::Bound(_) = &pred.projection_ty.parameters[0] {
+            // Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
+            return Some(Solution::Ambig(Guidance::Unknown));
+        }
+    }
+
+    let canonical = goal.to_chalk(db).cast(&Interner);
+
+    // We currently don't deal with universes (I think / hope they're not yet
+    // relevant for our use cases?)
+    let u_canonical = chalk_ir::UCanonical { canonical, universes: 1 };
+    let solution = solve(db, krate, &u_canonical);
+    solution.map(|solution| solution_from_chalk(db, solution))
+}
+
+fn solve(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
+) -> Option<chalk_solve::Solution<Interner>> {
+    let context = ChalkContext { db, krate };
+    log::debug!("solve goal: {:?}", goal);
+    let mut solver = create_chalk_solver();
+
+    let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
+
+    let should_continue = || {
+        context.db.check_canceled();
+        let remaining = fuel.get();
+        fuel.set(remaining - 1);
+        if remaining == 0 {
+            log::debug!("fuel exhausted");
+        }
+        remaining > 0
+    };
+    let mut solve = || {
+        let solution = solver.solve_limited(&context, goal, should_continue);
+        log::debug!("solve({:?}) => {:?}", goal, solution);
+        solution
+    };
+    // don't set the TLS for Chalk unless Chalk debugging is active, to make
+    // extra sure we only use it for debugging
+    let solution =
+        if is_chalk_debug() { chalk::tls::set_current_program(db, solve) } else { solve() };
+
+    solution
+}
+
+fn is_chalk_debug() -> bool {
+    std::env::var("CHALK_DEBUG").is_ok()
+}
+
+fn solution_from_chalk(
+    db: &dyn HirDatabase,
+    solution: chalk_solve::Solution<Interner>,
+) -> Solution {
+    let convert_subst = |subst: chalk_ir::Canonical<chalk_ir::Substitution<Interner>>| {
+        let result = from_chalk(db, subst);
+        SolutionVariables(result)
+    };
+    match solution {
+        chalk_solve::Solution::Unique(constr_subst) => {
+            let subst = chalk_ir::Canonical {
+                value: constr_subst.value.subst,
+                binders: constr_subst.binders,
+            };
+            Solution::Unique(convert_subst(subst))
+        }
+        chalk_solve::Solution::Ambig(chalk_solve::Guidance::Definite(subst)) => {
+            Solution::Ambig(Guidance::Definite(convert_subst(subst)))
+        }
+        chalk_solve::Solution::Ambig(chalk_solve::Guidance::Suggested(subst)) => {
+            Solution::Ambig(Guidance::Suggested(convert_subst(subst)))
+        }
+        chalk_solve::Solution::Ambig(chalk_solve::Guidance::Unknown) => {
+            Solution::Ambig(Guidance::Unknown)
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct SolutionVariables(pub Canonical<Substs>);
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+/// A (possible) solution for a proposed goal.
+pub enum Solution {
+    /// The goal indeed holds, and there is a unique value for all existential
+    /// variables.
+    Unique(SolutionVariables),
+
+    /// The goal may be provable in multiple ways, but regardless we may have some guidance
+    /// for type inference. In this case, we don't return any lifetime
+    /// constraints, since we have not "committed" to any particular solution
+    /// yet.
+    Ambig(Guidance),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+/// When a goal holds ambiguously (e.g., because there are multiple possible
+/// solutions), we issue a set of *guidance* back to type inference.
+pub enum Guidance {
+    /// The existential variables *must* have the given values if the goal is
+    /// ever to hold, but that alone isn't enough to guarantee the goal will
+    /// actually hold.
+    Definite(SolutionVariables),
+
+    /// There are multiple plausible values for the existentials, but the ones
+    /// here are suggested as the preferred choice heuristically. These should
+    /// be used for inference fallback only.
+    Suggested(SolutionVariables),
+
+    /// There's no useful information to feed back to type inference
+    Unknown,
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum FnTrait {
+    FnOnce,
+    FnMut,
+    Fn,
+}
+
+impl FnTrait {
+    fn lang_item_name(self) -> &'static str {
+        match self {
+            FnTrait::FnOnce => "fn_once",
+            FnTrait::FnMut => "fn_mut",
+            FnTrait::Fn => "fn",
+        }
+    }
+
+    pub fn get_id(&self, db: &dyn HirDatabase, krate: CrateId) -> Option<TraitId> {
+        let target = db.lang_item(krate, self.lang_item_name().into())?;
+        match target {
+            LangItemTarget::TraitId(t) => Some(t),
+            _ => None,
+        }
+    }
+}

crates/hir_ty/src/traits/chalk.rs

@@ -0,0 +1,586 @@
+//! Conversion code from/to Chalk.
+use std::sync::Arc;
+
+use log::debug;
+
+use chalk_ir::{fold::shift::Shift, CanonicalVarKinds, GenericArg, TypeName};
+use chalk_solve::rust_ir::{self, OpaqueTyDatumBound, WellKnownTrait};
+
+use base_db::{salsa::InternKey, CrateId};
+use hir_def::{
+    lang_item::{lang_attr, LangItemTarget},
+    AssocContainerId, AssocItemId, HasModule, Lookup, TypeAliasId,
+};
+
+use super::ChalkContext;
+use crate::{
+    db::HirDatabase,
+    display::HirDisplay,
+    method_resolution::{TyFingerprint, ALL_FLOAT_FPS, ALL_INT_FPS},
+    utils::generics,
+    CallableDefId, DebruijnIndex, FnSig, GenericPredicate, Substs, Ty, TypeCtor,
+};
+use mapping::{
+    convert_where_clauses, generic_predicate_to_inline_bound, make_binders, TypeAliasAsValue,
+};
+
+pub use self::interner::*;
+
+pub(super) mod tls;
+mod interner;
+mod mapping;
+
+pub(super) trait ToChalk {
+    type Chalk;
+    fn to_chalk(self, db: &dyn HirDatabase) -> Self::Chalk;
+    fn from_chalk(db: &dyn HirDatabase, chalk: Self::Chalk) -> Self;
+}
+
+pub(super) fn from_chalk<T, ChalkT>(db: &dyn HirDatabase, chalk: ChalkT) -> T
+where
+    T: ToChalk<Chalk = ChalkT>,
+{
+    T::from_chalk(db, chalk)
+}
+
+impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
+    fn associated_ty_data(&self, id: AssocTypeId) -> Arc<AssociatedTyDatum> {
+        self.db.associated_ty_data(id)
+    }
+    fn trait_datum(&self, trait_id: TraitId) -> Arc<TraitDatum> {
+        self.db.trait_datum(self.krate, trait_id)
+    }
+    fn adt_datum(&self, struct_id: AdtId) -> Arc<StructDatum> {
+        self.db.struct_datum(self.krate, struct_id)
+    }
+    fn adt_repr(&self, _struct_id: AdtId) -> rust_ir::AdtRepr {
+        rust_ir::AdtRepr { repr_c: false, repr_packed: false }
+    }
+    fn impl_datum(&self, impl_id: ImplId) -> Arc<ImplDatum> {
+        self.db.impl_datum(self.krate, impl_id)
+    }
+
+    fn fn_def_datum(
+        &self,
+        fn_def_id: chalk_ir::FnDefId<Interner>,
+    ) -> Arc<rust_ir::FnDefDatum<Interner>> {
+        self.db.fn_def_datum(self.krate, fn_def_id)
+    }
+
+    fn impls_for_trait(
+        &self,
+        trait_id: TraitId,
+        parameters: &[GenericArg<Interner>],
+        binders: &CanonicalVarKinds<Interner>,
+    ) -> Vec<ImplId> {
+        debug!("impls_for_trait {:?}", trait_id);
+        let trait_: hir_def::TraitId = from_chalk(self.db, trait_id);
+
+        let ty: Ty = from_chalk(self.db, parameters[0].assert_ty_ref(&Interner).clone());
+
+        fn binder_kind(ty: &Ty, binders: &CanonicalVarKinds<Interner>) -> Option<chalk_ir::TyKind> {
+            if let Ty::Bound(bv) = ty {
+                let binders = binders.as_slice(&Interner);
+                if bv.debruijn == DebruijnIndex::INNERMOST {
+                    if let chalk_ir::VariableKind::Ty(tk) = binders[bv.index].kind {
+                        return Some(tk);
+                    }
+                }
+            }
+            None
+        }
+
+        let self_ty_fp = TyFingerprint::for_impl(&ty);
+        let fps: &[TyFingerprint] = match binder_kind(&ty, binders) {
+            Some(chalk_ir::TyKind::Integer) => &ALL_INT_FPS,
+            Some(chalk_ir::TyKind::Float) => &ALL_FLOAT_FPS,
+            _ => self_ty_fp.as_ref().map(std::slice::from_ref).unwrap_or(&[]),
+        };
+
+        // Note: Since we're using impls_for_trait, only impls where the trait
+        // can be resolved should ever reach Chalk. `impl_datum` relies on that
+        // and will panic if the trait can't be resolved.
+        let in_deps = self.db.trait_impls_in_deps(self.krate);
+        let in_self = self.db.trait_impls_in_crate(self.krate);
+        let impl_maps = [in_deps, in_self];
+
+        let id_to_chalk = |id: hir_def::ImplId| id.to_chalk(self.db);
+
+        let result: Vec<_> = if fps.is_empty() {
+            debug!("Unrestricted search for {:?} impls...", trait_);
+            impl_maps
+                .iter()
+                .flat_map(|crate_impl_defs| crate_impl_defs.for_trait(trait_).map(id_to_chalk))
+                .collect()
+        } else {
+            impl_maps
+                .iter()
+                .flat_map(|crate_impl_defs| {
+                    fps.iter().flat_map(move |fp| {
+                        crate_impl_defs.for_trait_and_self_ty(trait_, *fp).map(id_to_chalk)
+                    })
+                })
+                .collect()
+        };
+
+        debug!("impls_for_trait returned {} impls", result.len());
+        result
+    }
+    fn impl_provided_for(&self, auto_trait_id: TraitId, struct_id: AdtId) -> bool {
+        debug!("impl_provided_for {:?}, {:?}", auto_trait_id, struct_id);
+        false // FIXME
+    }
+    fn associated_ty_value(&self, id: AssociatedTyValueId) -> Arc<AssociatedTyValue> {
+        self.db.associated_ty_value(self.krate, id)
+    }
+
+    fn custom_clauses(&self) -> Vec<chalk_ir::ProgramClause<Interner>> {
+        vec![]
+    }
+    fn local_impls_to_coherence_check(&self, _trait_id: TraitId) -> Vec<ImplId> {
+        // We don't do coherence checking (yet)
+        unimplemented!()
+    }
+    fn interner(&self) -> &Interner {
+        &Interner
+    }
+    fn well_known_trait_id(
+        &self,
+        well_known_trait: rust_ir::WellKnownTrait,
+    ) -> Option<chalk_ir::TraitId<Interner>> {
+        let lang_attr = lang_attr_from_well_known_trait(well_known_trait);
+        let trait_ = match self.db.lang_item(self.krate, lang_attr.into()) {
+            Some(LangItemTarget::TraitId(trait_)) => trait_,
+            _ => return None,
+        };
+        Some(trait_.to_chalk(self.db))
+    }
+
+    fn program_clauses_for_env(
+        &self,
+        environment: &chalk_ir::Environment<Interner>,
+    ) -> chalk_ir::ProgramClauses<Interner> {
+        self.db.program_clauses_for_chalk_env(self.krate, environment.clone())
+    }
+
+    fn opaque_ty_data(&self, id: chalk_ir::OpaqueTyId<Interner>) -> Arc<OpaqueTyDatum> {
+        let interned_id = crate::db::InternedOpaqueTyId::from(id);
+        let full_id = self.db.lookup_intern_impl_trait_id(interned_id);
+        let (func, idx) = match full_id {
+            crate::OpaqueTyId::ReturnTypeImplTrait(func, idx) => (func, idx),
+        };
+        let datas =
+            self.db.return_type_impl_traits(func).expect("impl trait id without impl traits");
+        let data = &datas.value.impl_traits[idx as usize];
+        let bound = OpaqueTyDatumBound {
+            bounds: make_binders(
+                data.bounds
+                    .value
+                    .iter()
+                    .cloned()
+                    .filter(|b| !b.is_error())
+                    .map(|b| b.to_chalk(self.db))
+                    .collect(),
+                1,
+            ),
+            where_clauses: make_binders(vec![], 0),
+        };
+        let num_vars = datas.num_binders;
+        Arc::new(OpaqueTyDatum { opaque_ty_id: id, bound: make_binders(bound, num_vars) })
+    }
+
+    fn hidden_opaque_type(&self, _id: chalk_ir::OpaqueTyId<Interner>) -> chalk_ir::Ty<Interner> {
+        // FIXME: actually provide the hidden type; it is relevant for auto traits
+        Ty::Unknown.to_chalk(self.db)
+    }
+
+    fn is_object_safe(&self, _trait_id: chalk_ir::TraitId<Interner>) -> bool {
+        // FIXME: implement actual object safety
+        true
+    }
+
+    fn closure_kind(
+        &self,
+        _closure_id: chalk_ir::ClosureId<Interner>,
+        _substs: &chalk_ir::Substitution<Interner>,
+    ) -> rust_ir::ClosureKind {
+        // Fn is the closure kind that implements all three traits
+        rust_ir::ClosureKind::Fn
+    }
+    fn closure_inputs_and_output(
+        &self,
+        _closure_id: chalk_ir::ClosureId<Interner>,
+        substs: &chalk_ir::Substitution<Interner>,
+    ) -> chalk_ir::Binders<rust_ir::FnDefInputsAndOutputDatum<Interner>> {
+        let sig_ty: Ty =
+            from_chalk(self.db, substs.at(&Interner, 0).assert_ty_ref(&Interner).clone());
+        let sig = FnSig::from_fn_ptr_substs(
+            &sig_ty.substs().expect("first closure param should be fn ptr"),
+            false,
+        );
+        let io = rust_ir::FnDefInputsAndOutputDatum {
+            argument_types: sig.params().iter().map(|ty| ty.clone().to_chalk(self.db)).collect(),
+            return_type: sig.ret().clone().to_chalk(self.db),
+        };
+        make_binders(io.shifted_in(&Interner), 0)
+    }
+    fn closure_upvars(
+        &self,
+        _closure_id: chalk_ir::ClosureId<Interner>,
+        _substs: &chalk_ir::Substitution<Interner>,
+    ) -> chalk_ir::Binders<chalk_ir::Ty<Interner>> {
+        let ty = Ty::unit().to_chalk(self.db);
+        make_binders(ty, 0)
+    }
+    fn closure_fn_substitution(
+        &self,
+        _closure_id: chalk_ir::ClosureId<Interner>,
+        _substs: &chalk_ir::Substitution<Interner>,
+    ) -> chalk_ir::Substitution<Interner> {
+        Substs::empty().to_chalk(self.db)
+    }
+
+    fn trait_name(&self, _trait_id: chalk_ir::TraitId<Interner>) -> String {
+        unimplemented!()
+    }
+    fn adt_name(&self, _struct_id: chalk_ir::AdtId<Interner>) -> String {
+        unimplemented!()
+    }
+    fn assoc_type_name(&self, _assoc_ty_id: chalk_ir::AssocTypeId<Interner>) -> String {
+        unimplemented!()
+    }
+    fn opaque_type_name(&self, _opaque_ty_id: chalk_ir::OpaqueTyId<Interner>) -> String {
+        unimplemented!()
+    }
+    fn fn_def_name(&self, _fn_def_id: chalk_ir::FnDefId<Interner>) -> String {
+        unimplemented!()
+    }
+}
+
+pub(crate) fn program_clauses_for_chalk_env_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    environment: chalk_ir::Environment<Interner>,
+) -> chalk_ir::ProgramClauses<Interner> {
+    chalk_solve::program_clauses_for_env(&ChalkContext { db, krate }, &environment)
+}
+
+pub(crate) fn associated_ty_data_query(
+    db: &dyn HirDatabase,
+    id: AssocTypeId,
+) -> Arc<AssociatedTyDatum> {
+    debug!("associated_ty_data {:?}", id);
+    let type_alias: TypeAliasId = from_chalk(db, id);
+    let trait_ = match type_alias.lookup(db.upcast()).container {
+        AssocContainerId::TraitId(t) => t,
+        _ => panic!("associated type not in trait"),
+    };
+
+    // Lower bounds -- we could/should maybe move this to a separate query in `lower`
+    let type_alias_data = db.type_alias_data(type_alias);
+    let generic_params = generics(db.upcast(), type_alias.into());
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let resolver = hir_def::resolver::HasResolver::resolver(type_alias, db.upcast());
+    let ctx = crate::TyLoweringContext::new(db, &resolver)
+        .with_type_param_mode(crate::lower::TypeParamLoweringMode::Variable);
+    let self_ty = Ty::Bound(crate::BoundVar::new(crate::DebruijnIndex::INNERMOST, 0));
+    let bounds = type_alias_data
+        .bounds
+        .iter()
+        .flat_map(|bound| GenericPredicate::from_type_bound(&ctx, bound, self_ty.clone()))
+        .filter_map(|pred| generic_predicate_to_inline_bound(db, &pred, &self_ty))
+        .map(|bound| make_binders(bound.shifted_in(&Interner), 0))
+        .collect();
+
+    let where_clauses = convert_where_clauses(db, type_alias.into(), &bound_vars);
+    let bound_data = rust_ir::AssociatedTyDatumBound { bounds, where_clauses };
+    let datum = AssociatedTyDatum {
+        trait_id: trait_.to_chalk(db),
+        id,
+        name: type_alias,
+        binders: make_binders(bound_data, generic_params.len()),
+    };
+    Arc::new(datum)
+}
+
+pub(crate) fn trait_datum_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    trait_id: TraitId,
+) -> Arc<TraitDatum> {
+    debug!("trait_datum {:?}", trait_id);
+    let trait_: hir_def::TraitId = from_chalk(db, trait_id);
+    let trait_data = db.trait_data(trait_);
+    debug!("trait {:?} = {:?}", trait_id, trait_data.name);
+    let generic_params = generics(db.upcast(), trait_.into());
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let flags = rust_ir::TraitFlags {
+        auto: trait_data.auto,
+        upstream: trait_.lookup(db.upcast()).container.module(db.upcast()).krate != krate,
+        non_enumerable: true,
+        coinductive: false, // only relevant for Chalk testing
+        // FIXME: set these flags correctly
+        marker: false,
+        fundamental: false,
+    };
+    let where_clauses = convert_where_clauses(db, trait_.into(), &bound_vars);
+    let associated_ty_ids =
+        trait_data.associated_types().map(|type_alias| type_alias.to_chalk(db)).collect();
+    let trait_datum_bound = rust_ir::TraitDatumBound { where_clauses };
+    let well_known =
+        lang_attr(db.upcast(), trait_).and_then(|name| well_known_trait_from_lang_attr(&name));
+    let trait_datum = TraitDatum {
+        id: trait_id,
+        binders: make_binders(trait_datum_bound, bound_vars.len()),
+        flags,
+        associated_ty_ids,
+        well_known,
+    };
+    Arc::new(trait_datum)
+}
+
+fn well_known_trait_from_lang_attr(name: &str) -> Option<WellKnownTrait> {
+    Some(match name {
+        "sized" => WellKnownTrait::Sized,
+        "copy" => WellKnownTrait::Copy,
+        "clone" => WellKnownTrait::Clone,
+        "drop" => WellKnownTrait::Drop,
+        "fn_once" => WellKnownTrait::FnOnce,
+        "fn_mut" => WellKnownTrait::FnMut,
+        "fn" => WellKnownTrait::Fn,
+        "unsize" => WellKnownTrait::Unsize,
+        _ => return None,
+    })
+}
+
+fn lang_attr_from_well_known_trait(attr: WellKnownTrait) -> &'static str {
+    match attr {
+        WellKnownTrait::Sized => "sized",
+        WellKnownTrait::Copy => "copy",
+        WellKnownTrait::Clone => "clone",
+        WellKnownTrait::Drop => "drop",
+        WellKnownTrait::FnOnce => "fn_once",
+        WellKnownTrait::FnMut => "fn_mut",
+        WellKnownTrait::Fn => "fn",
+        WellKnownTrait::Unsize => "unsize",
+    }
+}
+
+pub(crate) fn struct_datum_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    struct_id: AdtId,
+) -> Arc<StructDatum> {
+    debug!("struct_datum {:?}", struct_id);
+    let type_ctor: TypeCtor = from_chalk(db, TypeName::Adt(struct_id));
+    debug!("struct {:?} = {:?}", struct_id, type_ctor);
+    let num_params = type_ctor.num_ty_params(db);
+    let upstream = type_ctor.krate(db) != Some(krate);
+    let where_clauses = type_ctor
+        .as_generic_def()
+        .map(|generic_def| {
+            let generic_params = generics(db.upcast(), generic_def);
+            let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+            convert_where_clauses(db, generic_def, &bound_vars)
+        })
+        .unwrap_or_else(Vec::new);
+    let flags = rust_ir::AdtFlags {
+        upstream,
+        // FIXME set fundamental and phantom_data flags correctly
+        fundamental: false,
+        phantom_data: false,
+    };
+    // FIXME provide enum variants properly (for auto traits)
+    let variant = rust_ir::AdtVariantDatum {
+        fields: Vec::new(), // FIXME add fields (only relevant for auto traits),
+    };
+    let struct_datum_bound = rust_ir::AdtDatumBound { variants: vec![variant], where_clauses };
+    let struct_datum = StructDatum {
+        // FIXME set ADT kind
+        kind: rust_ir::AdtKind::Struct,
+        id: struct_id,
+        binders: make_binders(struct_datum_bound, num_params),
+        flags,
+    };
+    Arc::new(struct_datum)
+}
+
+pub(crate) fn impl_datum_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    impl_id: ImplId,
+) -> Arc<ImplDatum> {
+    let _p = profile::span("impl_datum");
+    debug!("impl_datum {:?}", impl_id);
+    let impl_: hir_def::ImplId = from_chalk(db, impl_id);
+    impl_def_datum(db, krate, impl_id, impl_)
+}
+
+fn impl_def_datum(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    chalk_id: ImplId,
+    impl_id: hir_def::ImplId,
+) -> Arc<ImplDatum> {
+    let trait_ref = db
+        .impl_trait(impl_id)
+        // ImplIds for impls where the trait ref can't be resolved should never reach Chalk
+        .expect("invalid impl passed to Chalk")
+        .value;
+    let impl_data = db.impl_data(impl_id);
+
+    let generic_params = generics(db.upcast(), impl_id.into());
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let trait_ = trait_ref.trait_;
+    let impl_type = if impl_id.lookup(db.upcast()).container.module(db.upcast()).krate == krate {
+        rust_ir::ImplType::Local
+    } else {
+        rust_ir::ImplType::External
+    };
+    let where_clauses = convert_where_clauses(db, impl_id.into(), &bound_vars);
+    let negative = impl_data.is_negative;
+    debug!(
+        "impl {:?}: {}{} where {:?}",
+        chalk_id,
+        if negative { "!" } else { "" },
+        trait_ref.display(db),
+        where_clauses
+    );
+    let trait_ref = trait_ref.to_chalk(db);
+
+    let polarity = if negative { rust_ir::Polarity::Negative } else { rust_ir::Polarity::Positive };
+
+    let impl_datum_bound = rust_ir::ImplDatumBound { trait_ref, where_clauses };
+    let trait_data = db.trait_data(trait_);
+    let associated_ty_value_ids = impl_data
+        .items
+        .iter()
+        .filter_map(|item| match item {
+            AssocItemId::TypeAliasId(type_alias) => Some(*type_alias),
+            _ => None,
+        })
+        .filter(|&type_alias| {
+            // don't include associated types that don't exist in the trait
+            let name = &db.type_alias_data(type_alias).name;
+            trait_data.associated_type_by_name(name).is_some()
+        })
+        .map(|type_alias| TypeAliasAsValue(type_alias).to_chalk(db))
+        .collect();
+    debug!("impl_datum: {:?}", impl_datum_bound);
+    let impl_datum = ImplDatum {
+        binders: make_binders(impl_datum_bound, bound_vars.len()),
+        impl_type,
+        polarity,
+        associated_ty_value_ids,
+    };
+    Arc::new(impl_datum)
+}
+
+pub(crate) fn associated_ty_value_query(
+    db: &dyn HirDatabase,
+    krate: CrateId,
+    id: AssociatedTyValueId,
+) -> Arc<AssociatedTyValue> {
+    let type_alias: TypeAliasAsValue = from_chalk(db, id);
+    type_alias_associated_ty_value(db, krate, type_alias.0)
+}
+
+fn type_alias_associated_ty_value(
+    db: &dyn HirDatabase,
+    _krate: CrateId,
+    type_alias: TypeAliasId,
+) -> Arc<AssociatedTyValue> {
+    let type_alias_data = db.type_alias_data(type_alias);
+    let impl_id = match type_alias.lookup(db.upcast()).container {
+        AssocContainerId::ImplId(it) => it,
+        _ => panic!("assoc ty value should be in impl"),
+    };
+
+    let trait_ref = db.impl_trait(impl_id).expect("assoc ty value should not exist").value; // we don't return any assoc ty values if the impl'd trait can't be resolved
+
+    let assoc_ty = db
+        .trait_data(trait_ref.trait_)
+        .associated_type_by_name(&type_alias_data.name)
+        .expect("assoc ty value should not exist"); // validated when building the impl data as well
+    let ty = db.ty(type_alias.into());
+    let value_bound = rust_ir::AssociatedTyValueBound { ty: ty.value.to_chalk(db) };
+    let value = rust_ir::AssociatedTyValue {
+        impl_id: impl_id.to_chalk(db),
+        associated_ty_id: assoc_ty.to_chalk(db),
+        value: make_binders(value_bound, ty.num_binders),
+    };
+    Arc::new(value)
+}
+
+pub(crate) fn fn_def_datum_query(
+    db: &dyn HirDatabase,
+    _krate: CrateId,
+    fn_def_id: FnDefId,
+) -> Arc<FnDefDatum> {
+    let callable_def: CallableDefId = from_chalk(db, fn_def_id);
+    let generic_params = generics(db.upcast(), callable_def.into());
+    let sig = db.callable_item_signature(callable_def);
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let where_clauses = convert_where_clauses(db, callable_def.into(), &bound_vars);
+    let bound = rust_ir::FnDefDatumBound {
+        // Note: Chalk doesn't actually use this information yet as far as I am aware, but we provide it anyway
+        inputs_and_output: make_binders(
+            rust_ir::FnDefInputsAndOutputDatum {
+                argument_types: sig
+                    .value
+                    .params()
+                    .iter()
+                    .map(|ty| ty.clone().to_chalk(db))
+                    .collect(),
+                return_type: sig.value.ret().clone().to_chalk(db),
+            }
+            .shifted_in(&Interner),
+            0,
+        ),
+        where_clauses,
+    };
+    let datum = FnDefDatum {
+        id: fn_def_id,
+        abi: (),
+        safety: chalk_ir::Safety::Safe,
+        variadic: sig.value.is_varargs,
+        binders: make_binders(bound, sig.num_binders),
+    };
+    Arc::new(datum)
+}
+
+impl From<FnDefId> for crate::db::InternedCallableDefId {
+    fn from(fn_def_id: FnDefId) -> Self {
+        InternKey::from_intern_id(fn_def_id.0)
+    }
+}
+
+impl From<crate::db::InternedCallableDefId> for FnDefId {
+    fn from(callable_def_id: crate::db::InternedCallableDefId) -> Self {
+        chalk_ir::FnDefId(callable_def_id.as_intern_id())
+    }
+}
+
+impl From<OpaqueTyId> for crate::db::InternedOpaqueTyId {
+    fn from(id: OpaqueTyId) -> Self {
+        InternKey::from_intern_id(id.0)
+    }
+}
+
+impl From<crate::db::InternedOpaqueTyId> for OpaqueTyId {
+    fn from(id: crate::db::InternedOpaqueTyId) -> Self {
+        chalk_ir::OpaqueTyId(id.as_intern_id())
+    }
+}
+
+impl From<chalk_ir::ClosureId<Interner>> for crate::db::ClosureId {
+    fn from(id: chalk_ir::ClosureId<Interner>) -> Self {
+        Self::from_intern_id(id.0)
+    }
+}
+
+impl From<crate::db::ClosureId> for chalk_ir::ClosureId<Interner> {
+    fn from(id: crate::db::ClosureId) -> Self {
+        chalk_ir::ClosureId(id.as_intern_id())
+    }
+}

crates/hir_ty/src/traits/chalk/interner.rs

@@ -0,0 +1,383 @@
+//! Implementation of the Chalk `Interner` trait, which allows customizing the
+//! representation of the various objects Chalk deals with (types, goals etc.).
+
+use super::tls;
+use base_db::salsa::InternId;
+use chalk_ir::{GenericArg, Goal, GoalData};
+use hir_def::TypeAliasId;
+use std::{fmt, sync::Arc};
+
+#[derive(Debug, Copy, Clone, Hash, PartialOrd, Ord, PartialEq, Eq)]
+pub struct Interner;
+
+pub type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
+pub type AssociatedTyDatum = chalk_solve::rust_ir::AssociatedTyDatum<Interner>;
+pub type TraitId = chalk_ir::TraitId<Interner>;
+pub type TraitDatum = chalk_solve::rust_ir::TraitDatum<Interner>;
+pub type AdtId = chalk_ir::AdtId<Interner>;
+pub type StructDatum = chalk_solve::rust_ir::AdtDatum<Interner>;
+pub type ImplId = chalk_ir::ImplId<Interner>;
+pub type ImplDatum = chalk_solve::rust_ir::ImplDatum<Interner>;
+pub type AssociatedTyValueId = chalk_solve::rust_ir::AssociatedTyValueId<Interner>;
+pub type AssociatedTyValue = chalk_solve::rust_ir::AssociatedTyValue<Interner>;
+pub type FnDefId = chalk_ir::FnDefId<Interner>;
+pub type FnDefDatum = chalk_solve::rust_ir::FnDefDatum<Interner>;
+pub type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
+pub type OpaqueTyDatum = chalk_solve::rust_ir::OpaqueTyDatum<Interner>;
+
+impl chalk_ir::interner::Interner for Interner {
+    type InternedType = Box<chalk_ir::TyData<Self>>; // FIXME use Arc?
+    type InternedLifetime = chalk_ir::LifetimeData<Self>;
+    type InternedConst = Arc<chalk_ir::ConstData<Self>>;
+    type InternedConcreteConst = ();
+    type InternedGenericArg = chalk_ir::GenericArgData<Self>;
+    type InternedGoal = Arc<GoalData<Self>>;
+    type InternedGoals = Vec<Goal<Self>>;
+    type InternedSubstitution = Vec<GenericArg<Self>>;
+    type InternedProgramClause = chalk_ir::ProgramClauseData<Self>;
+    type InternedProgramClauses = Arc<[chalk_ir::ProgramClause<Self>]>;
+    type InternedQuantifiedWhereClauses = Vec<chalk_ir::QuantifiedWhereClause<Self>>;
+    type InternedVariableKinds = Vec<chalk_ir::VariableKind<Self>>;
+    type InternedCanonicalVarKinds = Vec<chalk_ir::CanonicalVarKind<Self>>;
+    type InternedConstraints = Vec<chalk_ir::InEnvironment<chalk_ir::Constraint<Self>>>;
+    type DefId = InternId;
+    type InternedAdtId = hir_def::AdtId;
+    type Identifier = TypeAliasId;
+    type FnAbi = ();
+
+    fn debug_adt_id(type_kind_id: AdtId, fmt: &mut fmt::Formatter<'_>) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_struct_id(type_kind_id, fmt)))
+    }
+
+    fn debug_trait_id(type_kind_id: TraitId, fmt: &mut fmt::Formatter<'_>) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_trait_id(type_kind_id, fmt)))
+    }
+
+    fn debug_assoc_type_id(id: AssocTypeId, fmt: &mut fmt::Formatter<'_>) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_assoc_type_id(id, fmt)))
+    }
+
+    fn debug_alias(
+        alias: &chalk_ir::AliasTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_alias(alias, fmt)))
+    }
+
+    fn debug_projection_ty(
+        proj: &chalk_ir::ProjectionTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_projection_ty(proj, fmt)))
+    }
+
+    fn debug_opaque_ty(
+        opaque_ty: &chalk_ir::OpaqueTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_opaque_ty(opaque_ty, fmt)))
+    }
+
+    fn debug_opaque_ty_id(
+        opaque_ty_id: chalk_ir::OpaqueTyId<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_opaque_ty_id(opaque_ty_id, fmt)))
+    }
+
+    fn debug_ty(ty: &chalk_ir::Ty<Interner>, fmt: &mut fmt::Formatter<'_>) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_ty(ty, fmt)))
+    }
+
+    fn debug_lifetime(
+        lifetime: &chalk_ir::Lifetime<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_lifetime(lifetime, fmt)))
+    }
+
+    fn debug_generic_arg(
+        parameter: &GenericArg<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_generic_arg(parameter, fmt)))
+    }
+
+    fn debug_goal(goal: &Goal<Interner>, fmt: &mut fmt::Formatter<'_>) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_goal(goal, fmt)))
+    }
+
+    fn debug_goals(
+        goals: &chalk_ir::Goals<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_goals(goals, fmt)))
+    }
+
+    fn debug_program_clause_implication(
+        pci: &chalk_ir::ProgramClauseImplication<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_program_clause_implication(pci, fmt)))
+    }
+
+    fn debug_application_ty(
+        application_ty: &chalk_ir::ApplicationTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_application_ty(application_ty, fmt)))
+    }
+
+    fn debug_substitution(
+        substitution: &chalk_ir::Substitution<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_substitution(substitution, fmt)))
+    }
+
+    fn debug_separator_trait_ref(
+        separator_trait_ref: &chalk_ir::SeparatorTraitRef<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| {
+            Some(prog?.debug_separator_trait_ref(separator_trait_ref, fmt))
+        })
+    }
+
+    fn debug_fn_def_id(
+        fn_def_id: chalk_ir::FnDefId<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_fn_def_id(fn_def_id, fmt)))
+    }
+    fn debug_const(
+        constant: &chalk_ir::Const<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_const(constant, fmt)))
+    }
+    fn debug_variable_kinds(
+        variable_kinds: &chalk_ir::VariableKinds<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_variable_kinds(variable_kinds, fmt)))
+    }
+    fn debug_variable_kinds_with_angles(
+        variable_kinds: &chalk_ir::VariableKinds<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| {
+            Some(prog?.debug_variable_kinds_with_angles(variable_kinds, fmt))
+        })
+    }
+    fn debug_canonical_var_kinds(
+        canonical_var_kinds: &chalk_ir::CanonicalVarKinds<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| {
+            Some(prog?.debug_canonical_var_kinds(canonical_var_kinds, fmt))
+        })
+    }
+    fn debug_program_clause(
+        clause: &chalk_ir::ProgramClause<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_program_clause(clause, fmt)))
+    }
+    fn debug_program_clauses(
+        clauses: &chalk_ir::ProgramClauses<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_program_clauses(clauses, fmt)))
+    }
+    fn debug_quantified_where_clauses(
+        clauses: &chalk_ir::QuantifiedWhereClauses<Self>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        tls::with_current_program(|prog| Some(prog?.debug_quantified_where_clauses(clauses, fmt)))
+    }
+
+    fn intern_ty(&self, ty: chalk_ir::TyData<Self>) -> Box<chalk_ir::TyData<Self>> {
+        Box::new(ty)
+    }
+
+    fn ty_data<'a>(&self, ty: &'a Box<chalk_ir::TyData<Self>>) -> &'a chalk_ir::TyData<Self> {
+        ty
+    }
+
+    fn intern_lifetime(
+        &self,
+        lifetime: chalk_ir::LifetimeData<Self>,
+    ) -> chalk_ir::LifetimeData<Self> {
+        lifetime
+    }
+
+    fn lifetime_data<'a>(
+        &self,
+        lifetime: &'a chalk_ir::LifetimeData<Self>,
+    ) -> &'a chalk_ir::LifetimeData<Self> {
+        lifetime
+    }
+
+    fn intern_const(&self, constant: chalk_ir::ConstData<Self>) -> Arc<chalk_ir::ConstData<Self>> {
+        Arc::new(constant)
+    }
+
+    fn const_data<'a>(
+        &self,
+        constant: &'a Arc<chalk_ir::ConstData<Self>>,
+    ) -> &'a chalk_ir::ConstData<Self> {
+        constant
+    }
+
+    fn const_eq(&self, _ty: &Box<chalk_ir::TyData<Self>>, _c1: &(), _c2: &()) -> bool {
+        true
+    }
+
+    fn intern_generic_arg(
+        &self,
+        parameter: chalk_ir::GenericArgData<Self>,
+    ) -> chalk_ir::GenericArgData<Self> {
+        parameter
+    }
+
+    fn generic_arg_data<'a>(
+        &self,
+        parameter: &'a chalk_ir::GenericArgData<Self>,
+    ) -> &'a chalk_ir::GenericArgData<Self> {
+        parameter
+    }
+
+    fn intern_goal(&self, goal: GoalData<Self>) -> Arc<GoalData<Self>> {
+        Arc::new(goal)
+    }
+
+    fn intern_goals<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<Goal<Self>, E>>,
+    ) -> Result<Self::InternedGoals, E> {
+        data.into_iter().collect()
+    }
+
+    fn goal_data<'a>(&self, goal: &'a Arc<GoalData<Self>>) -> &'a GoalData<Self> {
+        goal
+    }
+
+    fn goals_data<'a>(&self, goals: &'a Vec<Goal<Interner>>) -> &'a [Goal<Interner>] {
+        goals
+    }
+
+    fn intern_substitution<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<GenericArg<Self>, E>>,
+    ) -> Result<Vec<GenericArg<Self>>, E> {
+        data.into_iter().collect()
+    }
+
+    fn substitution_data<'a>(
+        &self,
+        substitution: &'a Vec<GenericArg<Self>>,
+    ) -> &'a [GenericArg<Self>] {
+        substitution
+    }
+
+    fn intern_program_clause(
+        &self,
+        data: chalk_ir::ProgramClauseData<Self>,
+    ) -> chalk_ir::ProgramClauseData<Self> {
+        data
+    }
+
+    fn program_clause_data<'a>(
+        &self,
+        clause: &'a chalk_ir::ProgramClauseData<Self>,
+    ) -> &'a chalk_ir::ProgramClauseData<Self> {
+        clause
+    }
+
+    fn intern_program_clauses<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<chalk_ir::ProgramClause<Self>, E>>,
+    ) -> Result<Arc<[chalk_ir::ProgramClause<Self>]>, E> {
+        data.into_iter().collect()
+    }
+
+    fn program_clauses_data<'a>(
+        &self,
+        clauses: &'a Arc<[chalk_ir::ProgramClause<Self>]>,
+    ) -> &'a [chalk_ir::ProgramClause<Self>] {
+        &clauses
+    }
+
+    fn intern_quantified_where_clauses<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<chalk_ir::QuantifiedWhereClause<Self>, E>>,
+    ) -> Result<Self::InternedQuantifiedWhereClauses, E> {
+        data.into_iter().collect()
+    }
+
+    fn quantified_where_clauses_data<'a>(
+        &self,
+        clauses: &'a Self::InternedQuantifiedWhereClauses,
+    ) -> &'a [chalk_ir::QuantifiedWhereClause<Self>] {
+        clauses
+    }
+
+    fn intern_generic_arg_kinds<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<chalk_ir::VariableKind<Self>, E>>,
+    ) -> Result<Self::InternedVariableKinds, E> {
+        data.into_iter().collect()
+    }
+
+    fn variable_kinds_data<'a>(
+        &self,
+        parameter_kinds: &'a Self::InternedVariableKinds,
+    ) -> &'a [chalk_ir::VariableKind<Self>] {
+        &parameter_kinds
+    }
+
+    fn intern_canonical_var_kinds<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<chalk_ir::CanonicalVarKind<Self>, E>>,
+    ) -> Result<Self::InternedCanonicalVarKinds, E> {
+        data.into_iter().collect()
+    }
+
+    fn canonical_var_kinds_data<'a>(
+        &self,
+        canonical_var_kinds: &'a Self::InternedCanonicalVarKinds,
+    ) -> &'a [chalk_ir::CanonicalVarKind<Self>] {
+        &canonical_var_kinds
+    }
+
+    fn intern_constraints<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<chalk_ir::InEnvironment<chalk_ir::Constraint<Self>>, E>>,
+    ) -> Result<Self::InternedConstraints, E> {
+        data.into_iter().collect()
+    }
+
+    fn constraints_data<'a>(
+        &self,
+        constraints: &'a Self::InternedConstraints,
+    ) -> &'a [chalk_ir::InEnvironment<chalk_ir::Constraint<Self>>] {
+        constraints
+    }
+    fn debug_closure_id(
+        _fn_def_id: chalk_ir::ClosureId<Self>,
+        _fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        None
+    }
+    fn debug_constraints(
+        _clauses: &chalk_ir::Constraints<Self>,
+        _fmt: &mut fmt::Formatter<'_>,
+    ) -> Option<fmt::Result> {
+        None
+    }
+}
+
+impl chalk_ir::interner::HasInterner for Interner {
+    type Interner = Self;
+}

crates/hir_ty/src/traits/chalk/mapping.rs

@@ -0,0 +1,787 @@
+//! This module contains the implementations of the `ToChalk` trait, which
+//! handles conversion between our data types and their corresponding types in
+//! Chalk (in both directions); plus some helper functions for more specialized
+//! conversions.
+
+use chalk_ir::{
+    cast::Cast, fold::shift::Shift, interner::HasInterner, PlaceholderIndex, Scalar, TypeName,
+    UniverseIndex,
+};
+use chalk_solve::rust_ir;
+
+use base_db::salsa::InternKey;
+use hir_def::{type_ref::Mutability, AssocContainerId, GenericDefId, Lookup, TypeAliasId};
+
+use crate::{
+    db::HirDatabase,
+    primitive::{FloatBitness, FloatTy, IntBitness, IntTy, Signedness},
+    traits::{Canonical, Obligation},
+    ApplicationTy, CallableDefId, GenericPredicate, InEnvironment, OpaqueTy, OpaqueTyId,
+    ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeCtor,
+};
+
+use super::interner::*;
+use super::*;
+
+impl ToChalk for Ty {
+    type Chalk = chalk_ir::Ty<Interner>;
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Ty<Interner> {
+        match self {
+            Ty::Apply(apply_ty) => match apply_ty.ctor {
+                TypeCtor::Ref(m) => ref_to_chalk(db, m, apply_ty.parameters),
+                TypeCtor::Array => array_to_chalk(db, apply_ty.parameters),
+                TypeCtor::FnPtr { num_args: _, is_varargs } => {
+                    let substitution = apply_ty.parameters.to_chalk(db).shifted_in(&Interner);
+                    chalk_ir::TyData::Function(chalk_ir::FnPointer {
+                        num_binders: 0,
+                        abi: (),
+                        safety: chalk_ir::Safety::Safe,
+                        variadic: is_varargs,
+                        substitution,
+                    })
+                    .intern(&Interner)
+                }
+                _ => {
+                    let name = apply_ty.ctor.to_chalk(db);
+                    let substitution = apply_ty.parameters.to_chalk(db);
+                    chalk_ir::ApplicationTy { name, substitution }.cast(&Interner).intern(&Interner)
+                }
+            },
+            Ty::Projection(proj_ty) => {
+                let associated_ty_id = proj_ty.associated_ty.to_chalk(db);
+                let substitution = proj_ty.parameters.to_chalk(db);
+                chalk_ir::AliasTy::Projection(chalk_ir::ProjectionTy {
+                    associated_ty_id,
+                    substitution,
+                })
+                .cast(&Interner)
+                .intern(&Interner)
+            }
+            Ty::Placeholder(id) => {
+                let interned_id = db.intern_type_param_id(id);
+                PlaceholderIndex {
+                    ui: UniverseIndex::ROOT,
+                    idx: interned_id.as_intern_id().as_usize(),
+                }
+                .to_ty::<Interner>(&Interner)
+            }
+            Ty::Bound(idx) => chalk_ir::TyData::BoundVar(idx).intern(&Interner),
+            Ty::Infer(_infer_ty) => panic!("uncanonicalized infer ty"),
+            Ty::Dyn(predicates) => {
+                let where_clauses = chalk_ir::QuantifiedWhereClauses::from_iter(
+                    &Interner,
+                    predicates.iter().filter(|p| !p.is_error()).cloned().map(|p| p.to_chalk(db)),
+                );
+                let bounded_ty = chalk_ir::DynTy {
+                    bounds: make_binders(where_clauses, 1),
+                    lifetime: FAKE_PLACEHOLDER.to_lifetime(&Interner),
+                };
+                chalk_ir::TyData::Dyn(bounded_ty).intern(&Interner)
+            }
+            Ty::Opaque(opaque_ty) => {
+                let opaque_ty_id = opaque_ty.opaque_ty_id.to_chalk(db);
+                let substitution = opaque_ty.parameters.to_chalk(db);
+                chalk_ir::TyData::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
+                    opaque_ty_id,
+                    substitution,
+                }))
+                .intern(&Interner)
+            }
+            Ty::Unknown => {
+                let substitution = chalk_ir::Substitution::empty(&Interner);
+                let name = TypeName::Error;
+                chalk_ir::ApplicationTy { name, substitution }.cast(&Interner).intern(&Interner)
+            }
+        }
+    }
+    fn from_chalk(db: &dyn HirDatabase, chalk: chalk_ir::Ty<Interner>) -> Self {
+        match chalk.data(&Interner).clone() {
+            chalk_ir::TyData::Apply(apply_ty) => match apply_ty.name {
+                TypeName::Error => Ty::Unknown,
+                TypeName::Ref(m) => ref_from_chalk(db, m, apply_ty.substitution),
+                TypeName::Array => array_from_chalk(db, apply_ty.substitution),
+                _ => {
+                    let ctor = from_chalk(db, apply_ty.name);
+                    let parameters = from_chalk(db, apply_ty.substitution);
+                    Ty::Apply(ApplicationTy { ctor, parameters })
+                }
+            },
+            chalk_ir::TyData::Placeholder(idx) => {
+                assert_eq!(idx.ui, UniverseIndex::ROOT);
+                let interned_id = crate::db::GlobalTypeParamId::from_intern_id(
+                    crate::salsa::InternId::from(idx.idx),
+                );
+                Ty::Placeholder(db.lookup_intern_type_param_id(interned_id))
+            }
+            chalk_ir::TyData::Alias(chalk_ir::AliasTy::Projection(proj)) => {
+                let associated_ty = from_chalk(db, proj.associated_ty_id);
+                let parameters = from_chalk(db, proj.substitution);
+                Ty::Projection(ProjectionTy { associated_ty, parameters })
+            }
+            chalk_ir::TyData::Alias(chalk_ir::AliasTy::Opaque(opaque_ty)) => {
+                let impl_trait_id = from_chalk(db, opaque_ty.opaque_ty_id);
+                let parameters = from_chalk(db, opaque_ty.substitution);
+                Ty::Opaque(OpaqueTy { opaque_ty_id: impl_trait_id, parameters })
+            }
+            chalk_ir::TyData::Function(chalk_ir::FnPointer {
+                num_binders,
+                variadic,
+                substitution,
+                ..
+            }) => {
+                assert_eq!(num_binders, 0);
+                let parameters: Substs = from_chalk(
+                    db,
+                    substitution.shifted_out(&Interner).expect("fn ptr should have no binders"),
+                );
+                Ty::Apply(ApplicationTy {
+                    ctor: TypeCtor::FnPtr {
+                        num_args: (parameters.len() - 1) as u16,
+                        is_varargs: variadic,
+                    },
+                    parameters,
+                })
+            }
+            chalk_ir::TyData::BoundVar(idx) => Ty::Bound(idx),
+            chalk_ir::TyData::InferenceVar(_iv, _kind) => Ty::Unknown,
+            chalk_ir::TyData::Dyn(where_clauses) => {
+                assert_eq!(where_clauses.bounds.binders.len(&Interner), 1);
+                let predicates = where_clauses
+                    .bounds
+                    .skip_binders()
+                    .iter(&Interner)
+                    .map(|c| from_chalk(db, c.clone()))
+                    .collect();
+                Ty::Dyn(predicates)
+            }
+        }
+    }
+}
+
+const FAKE_PLACEHOLDER: PlaceholderIndex =
+    PlaceholderIndex { ui: UniverseIndex::ROOT, idx: usize::MAX };
+
+/// We currently don't model lifetimes, but Chalk does. So, we have to insert a
+/// fake lifetime here, because Chalks built-in logic may expect it to be there.
+fn ref_to_chalk(
+    db: &dyn HirDatabase,
+    mutability: Mutability,
+    subst: Substs,
+) -> chalk_ir::Ty<Interner> {
+    let arg = subst[0].clone().to_chalk(db);
+    let lifetime = FAKE_PLACEHOLDER.to_lifetime(&Interner);
+    chalk_ir::ApplicationTy {
+        name: TypeName::Ref(mutability.to_chalk(db)),
+        substitution: chalk_ir::Substitution::from_iter(
+            &Interner,
+            vec![lifetime.cast(&Interner), arg.cast(&Interner)],
+        ),
+    }
+    .intern(&Interner)
+}
+
+/// Here we remove the lifetime from the type we got from Chalk.
+fn ref_from_chalk(
+    db: &dyn HirDatabase,
+    mutability: chalk_ir::Mutability,
+    subst: chalk_ir::Substitution<Interner>,
+) -> Ty {
+    let tys = subst
+        .iter(&Interner)
+        .filter_map(|p| Some(from_chalk(db, p.ty(&Interner)?.clone())))
+        .collect();
+    Ty::apply(TypeCtor::Ref(from_chalk(db, mutability)), Substs(tys))
+}
+
+/// We currently don't model constants, but Chalk does. So, we have to insert a
+/// fake constant here, because Chalks built-in logic may expect it to be there.
+fn array_to_chalk(db: &dyn HirDatabase, subst: Substs) -> chalk_ir::Ty<Interner> {
+    let arg = subst[0].clone().to_chalk(db);
+    let usize_ty = chalk_ir::ApplicationTy {
+        name: TypeName::Scalar(Scalar::Uint(chalk_ir::UintTy::Usize)),
+        substitution: chalk_ir::Substitution::empty(&Interner),
+    }
+    .intern(&Interner);
+    let const_ = FAKE_PLACEHOLDER.to_const(&Interner, usize_ty);
+    chalk_ir::ApplicationTy {
+        name: TypeName::Array,
+        substitution: chalk_ir::Substitution::from_iter(
+            &Interner,
+            vec![arg.cast(&Interner), const_.cast(&Interner)],
+        ),
+    }
+    .intern(&Interner)
+}
+
+/// Here we remove the const from the type we got from Chalk.
+fn array_from_chalk(db: &dyn HirDatabase, subst: chalk_ir::Substitution<Interner>) -> Ty {
+    let tys = subst
+        .iter(&Interner)
+        .filter_map(|p| Some(from_chalk(db, p.ty(&Interner)?.clone())))
+        .collect();
+    Ty::apply(TypeCtor::Array, Substs(tys))
+}
+
+impl ToChalk for Substs {
+    type Chalk = chalk_ir::Substitution<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Substitution<Interner> {
+        chalk_ir::Substitution::from_iter(&Interner, self.iter().map(|ty| ty.clone().to_chalk(db)))
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, parameters: chalk_ir::Substitution<Interner>) -> Substs {
+        let tys = parameters
+            .iter(&Interner)
+            .map(|p| match p.ty(&Interner) {
+                Some(ty) => from_chalk(db, ty.clone()),
+                None => unimplemented!(),
+            })
+            .collect();
+        Substs(tys)
+    }
+}
+
+impl ToChalk for TraitRef {
+    type Chalk = chalk_ir::TraitRef<Interner>;
+
+    fn to_chalk(self: TraitRef, db: &dyn HirDatabase) -> chalk_ir::TraitRef<Interner> {
+        let trait_id = self.trait_.to_chalk(db);
+        let substitution = self.substs.to_chalk(db);
+        chalk_ir::TraitRef { trait_id, substitution }
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, trait_ref: chalk_ir::TraitRef<Interner>) -> Self {
+        let trait_ = from_chalk(db, trait_ref.trait_id);
+        let substs = from_chalk(db, trait_ref.substitution);
+        TraitRef { trait_, substs }
+    }
+}
+
+impl ToChalk for hir_def::TraitId {
+    type Chalk = TraitId;
+
+    fn to_chalk(self, _db: &dyn HirDatabase) -> TraitId {
+        chalk_ir::TraitId(self.as_intern_id())
+    }
+
+    fn from_chalk(_db: &dyn HirDatabase, trait_id: TraitId) -> hir_def::TraitId {
+        InternKey::from_intern_id(trait_id.0)
+    }
+}
+
+impl ToChalk for OpaqueTyId {
+    type Chalk = chalk_ir::OpaqueTyId<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::OpaqueTyId<Interner> {
+        db.intern_impl_trait_id(self).into()
+    }
+
+    fn from_chalk(
+        db: &dyn HirDatabase,
+        opaque_ty_id: chalk_ir::OpaqueTyId<Interner>,
+    ) -> OpaqueTyId {
+        db.lookup_intern_impl_trait_id(opaque_ty_id.into())
+    }
+}
+
+impl ToChalk for TypeCtor {
+    type Chalk = TypeName<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> TypeName<Interner> {
+        match self {
+            TypeCtor::AssociatedType(type_alias) => {
+                let type_id = type_alias.to_chalk(db);
+                TypeName::AssociatedType(type_id)
+            }
+
+            TypeCtor::OpaqueType(impl_trait_id) => {
+                let id = impl_trait_id.to_chalk(db);
+                TypeName::OpaqueType(id)
+            }
+
+            TypeCtor::Bool => TypeName::Scalar(Scalar::Bool),
+            TypeCtor::Char => TypeName::Scalar(Scalar::Char),
+            TypeCtor::Int(int_ty) => TypeName::Scalar(int_ty_to_chalk(int_ty)),
+            TypeCtor::Float(FloatTy { bitness: FloatBitness::X32 }) => {
+                TypeName::Scalar(Scalar::Float(chalk_ir::FloatTy::F32))
+            }
+            TypeCtor::Float(FloatTy { bitness: FloatBitness::X64 }) => {
+                TypeName::Scalar(Scalar::Float(chalk_ir::FloatTy::F64))
+            }
+
+            TypeCtor::Tuple { cardinality } => TypeName::Tuple(cardinality.into()),
+            TypeCtor::RawPtr(mutability) => TypeName::Raw(mutability.to_chalk(db)),
+            TypeCtor::Slice => TypeName::Slice,
+            TypeCtor::Array => TypeName::Array,
+            TypeCtor::Ref(mutability) => TypeName::Ref(mutability.to_chalk(db)),
+            TypeCtor::Str => TypeName::Str,
+            TypeCtor::FnDef(callable_def) => {
+                let id = callable_def.to_chalk(db);
+                TypeName::FnDef(id)
+            }
+            TypeCtor::Never => TypeName::Never,
+
+            TypeCtor::Closure { def, expr } => {
+                let closure_id = db.intern_closure((def, expr));
+                TypeName::Closure(closure_id.into())
+            }
+
+            TypeCtor::Adt(adt_id) => TypeName::Adt(chalk_ir::AdtId(adt_id)),
+
+            TypeCtor::FnPtr { .. } => {
+                // This should not be reached, since Chalk doesn't represent
+                // function pointers with TypeName
+                unreachable!()
+            }
+        }
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, type_name: TypeName<Interner>) -> TypeCtor {
+        match type_name {
+            TypeName::Adt(struct_id) => TypeCtor::Adt(struct_id.0),
+            TypeName::AssociatedType(type_id) => TypeCtor::AssociatedType(from_chalk(db, type_id)),
+            TypeName::OpaqueType(opaque_type_id) => {
+                TypeCtor::OpaqueType(from_chalk(db, opaque_type_id))
+            }
+
+            TypeName::Scalar(Scalar::Bool) => TypeCtor::Bool,
+            TypeName::Scalar(Scalar::Char) => TypeCtor::Char,
+            TypeName::Scalar(Scalar::Int(int_ty)) => TypeCtor::Int(IntTy {
+                signedness: Signedness::Signed,
+                bitness: bitness_from_chalk_int(int_ty),
+            }),
+            TypeName::Scalar(Scalar::Uint(uint_ty)) => TypeCtor::Int(IntTy {
+                signedness: Signedness::Unsigned,
+                bitness: bitness_from_chalk_uint(uint_ty),
+            }),
+            TypeName::Scalar(Scalar::Float(chalk_ir::FloatTy::F32)) => {
+                TypeCtor::Float(FloatTy { bitness: FloatBitness::X32 })
+            }
+            TypeName::Scalar(Scalar::Float(chalk_ir::FloatTy::F64)) => {
+                TypeCtor::Float(FloatTy { bitness: FloatBitness::X64 })
+            }
+            TypeName::Tuple(cardinality) => TypeCtor::Tuple { cardinality: cardinality as u16 },
+            TypeName::Raw(mutability) => TypeCtor::RawPtr(from_chalk(db, mutability)),
+            TypeName::Slice => TypeCtor::Slice,
+            TypeName::Ref(mutability) => TypeCtor::Ref(from_chalk(db, mutability)),
+            TypeName::Str => TypeCtor::Str,
+            TypeName::Never => TypeCtor::Never,
+
+            TypeName::FnDef(fn_def_id) => {
+                let callable_def = from_chalk(db, fn_def_id);
+                TypeCtor::FnDef(callable_def)
+            }
+            TypeName::Array => TypeCtor::Array,
+
+            TypeName::Closure(id) => {
+                let id: crate::db::ClosureId = id.into();
+                let (def, expr) = db.lookup_intern_closure(id);
+                TypeCtor::Closure { def, expr }
+            }
+
+            TypeName::Error => {
+                // this should not be reached, since we don't represent TypeName::Error with TypeCtor
+                unreachable!()
+            }
+        }
+    }
+}
+
+fn bitness_from_chalk_uint(uint_ty: chalk_ir::UintTy) -> IntBitness {
+    use chalk_ir::UintTy;
+
+    match uint_ty {
+        UintTy::Usize => IntBitness::Xsize,
+        UintTy::U8 => IntBitness::X8,
+        UintTy::U16 => IntBitness::X16,
+        UintTy::U32 => IntBitness::X32,
+        UintTy::U64 => IntBitness::X64,
+        UintTy::U128 => IntBitness::X128,
+    }
+}
+
+fn bitness_from_chalk_int(int_ty: chalk_ir::IntTy) -> IntBitness {
+    use chalk_ir::IntTy;
+
+    match int_ty {
+        IntTy::Isize => IntBitness::Xsize,
+        IntTy::I8 => IntBitness::X8,
+        IntTy::I16 => IntBitness::X16,
+        IntTy::I32 => IntBitness::X32,
+        IntTy::I64 => IntBitness::X64,
+        IntTy::I128 => IntBitness::X128,
+    }
+}
+
+fn int_ty_to_chalk(int_ty: IntTy) -> Scalar {
+    use chalk_ir::{IntTy, UintTy};
+
+    match int_ty.signedness {
+        Signedness::Signed => Scalar::Int(match int_ty.bitness {
+            IntBitness::Xsize => IntTy::Isize,
+            IntBitness::X8 => IntTy::I8,
+            IntBitness::X16 => IntTy::I16,
+            IntBitness::X32 => IntTy::I32,
+            IntBitness::X64 => IntTy::I64,
+            IntBitness::X128 => IntTy::I128,
+        }),
+        Signedness::Unsigned => Scalar::Uint(match int_ty.bitness {
+            IntBitness::Xsize => UintTy::Usize,
+            IntBitness::X8 => UintTy::U8,
+            IntBitness::X16 => UintTy::U16,
+            IntBitness::X32 => UintTy::U32,
+            IntBitness::X64 => UintTy::U64,
+            IntBitness::X128 => UintTy::U128,
+        }),
+    }
+}
+
+impl ToChalk for Mutability {
+    type Chalk = chalk_ir::Mutability;
+    fn to_chalk(self, _db: &dyn HirDatabase) -> Self::Chalk {
+        match self {
+            Mutability::Shared => chalk_ir::Mutability::Not,
+            Mutability::Mut => chalk_ir::Mutability::Mut,
+        }
+    }
+    fn from_chalk(_db: &dyn HirDatabase, chalk: Self::Chalk) -> Self {
+        match chalk {
+            chalk_ir::Mutability::Mut => Mutability::Mut,
+            chalk_ir::Mutability::Not => Mutability::Shared,
+        }
+    }
+}
+
+impl ToChalk for hir_def::ImplId {
+    type Chalk = ImplId;
+
+    fn to_chalk(self, _db: &dyn HirDatabase) -> ImplId {
+        chalk_ir::ImplId(self.as_intern_id())
+    }
+
+    fn from_chalk(_db: &dyn HirDatabase, impl_id: ImplId) -> hir_def::ImplId {
+        InternKey::from_intern_id(impl_id.0)
+    }
+}
+
+impl ToChalk for CallableDefId {
+    type Chalk = FnDefId;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> FnDefId {
+        db.intern_callable_def(self).into()
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, fn_def_id: FnDefId) -> CallableDefId {
+        db.lookup_intern_callable_def(fn_def_id.into())
+    }
+}
+
+impl ToChalk for TypeAliasId {
+    type Chalk = AssocTypeId;
+
+    fn to_chalk(self, _db: &dyn HirDatabase) -> AssocTypeId {
+        chalk_ir::AssocTypeId(self.as_intern_id())
+    }
+
+    fn from_chalk(_db: &dyn HirDatabase, type_alias_id: AssocTypeId) -> TypeAliasId {
+        InternKey::from_intern_id(type_alias_id.0)
+    }
+}
+
+pub struct TypeAliasAsValue(pub TypeAliasId);
+
+impl ToChalk for TypeAliasAsValue {
+    type Chalk = AssociatedTyValueId;
+
+    fn to_chalk(self, _db: &dyn HirDatabase) -> AssociatedTyValueId {
+        rust_ir::AssociatedTyValueId(self.0.as_intern_id())
+    }
+
+    fn from_chalk(
+        _db: &dyn HirDatabase,
+        assoc_ty_value_id: AssociatedTyValueId,
+    ) -> TypeAliasAsValue {
+        TypeAliasAsValue(TypeAliasId::from_intern_id(assoc_ty_value_id.0))
+    }
+}
+
+impl ToChalk for GenericPredicate {
+    type Chalk = chalk_ir::QuantifiedWhereClause<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::QuantifiedWhereClause<Interner> {
+        match self {
+            GenericPredicate::Implemented(trait_ref) => {
+                let chalk_trait_ref = trait_ref.to_chalk(db);
+                let chalk_trait_ref = chalk_trait_ref.shifted_in(&Interner);
+                make_binders(chalk_ir::WhereClause::Implemented(chalk_trait_ref), 0)
+            }
+            GenericPredicate::Projection(projection_pred) => {
+                let ty = projection_pred.ty.to_chalk(db).shifted_in(&Interner);
+                let projection = projection_pred.projection_ty.to_chalk(db).shifted_in(&Interner);
+                let alias = chalk_ir::AliasTy::Projection(projection);
+                make_binders(chalk_ir::WhereClause::AliasEq(chalk_ir::AliasEq { alias, ty }), 0)
+            }
+            GenericPredicate::Error => panic!("tried passing GenericPredicate::Error to Chalk"),
+        }
+    }
+
+    fn from_chalk(
+        db: &dyn HirDatabase,
+        where_clause: chalk_ir::QuantifiedWhereClause<Interner>,
+    ) -> GenericPredicate {
+        // we don't produce any where clauses with binders and can't currently deal with them
+        match where_clause
+            .skip_binders()
+            .shifted_out(&Interner)
+            .expect("unexpected bound vars in where clause")
+        {
+            chalk_ir::WhereClause::Implemented(tr) => {
+                GenericPredicate::Implemented(from_chalk(db, tr))
+            }
+            chalk_ir::WhereClause::AliasEq(projection_eq) => {
+                let projection_ty = from_chalk(
+                    db,
+                    match projection_eq.alias {
+                        chalk_ir::AliasTy::Projection(p) => p,
+                        _ => unimplemented!(),
+                    },
+                );
+                let ty = from_chalk(db, projection_eq.ty);
+                GenericPredicate::Projection(ProjectionPredicate { projection_ty, ty })
+            }
+
+            chalk_ir::WhereClause::LifetimeOutlives(_) => {
+                // we shouldn't get these from Chalk
+                panic!("encountered LifetimeOutlives from Chalk")
+            }
+
+            chalk_ir::WhereClause::TypeOutlives(_) => {
+                // we shouldn't get these from Chalk
+                panic!("encountered TypeOutlives from Chalk")
+            }
+        }
+    }
+}
+
+impl ToChalk for ProjectionTy {
+    type Chalk = chalk_ir::ProjectionTy<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::ProjectionTy<Interner> {
+        chalk_ir::ProjectionTy {
+            associated_ty_id: self.associated_ty.to_chalk(db),
+            substitution: self.parameters.to_chalk(db),
+        }
+    }
+
+    fn from_chalk(
+        db: &dyn HirDatabase,
+        projection_ty: chalk_ir::ProjectionTy<Interner>,
+    ) -> ProjectionTy {
+        ProjectionTy {
+            associated_ty: from_chalk(db, projection_ty.associated_ty_id),
+            parameters: from_chalk(db, projection_ty.substitution),
+        }
+    }
+}
+
+impl ToChalk for ProjectionPredicate {
+    type Chalk = chalk_ir::AliasEq<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::AliasEq<Interner> {
+        chalk_ir::AliasEq {
+            alias: chalk_ir::AliasTy::Projection(self.projection_ty.to_chalk(db)),
+            ty: self.ty.to_chalk(db),
+        }
+    }
+
+    fn from_chalk(_db: &dyn HirDatabase, _normalize: chalk_ir::AliasEq<Interner>) -> Self {
+        unimplemented!()
+    }
+}
+
+impl ToChalk for Obligation {
+    type Chalk = chalk_ir::DomainGoal<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::DomainGoal<Interner> {
+        match self {
+            Obligation::Trait(tr) => tr.to_chalk(db).cast(&Interner),
+            Obligation::Projection(pr) => pr.to_chalk(db).cast(&Interner),
+        }
+    }
+
+    fn from_chalk(_db: &dyn HirDatabase, _goal: chalk_ir::DomainGoal<Interner>) -> Self {
+        unimplemented!()
+    }
+}
+
+impl<T> ToChalk for Canonical<T>
+where
+    T: ToChalk,
+    T::Chalk: HasInterner<Interner = Interner>,
+{
+    type Chalk = chalk_ir::Canonical<T::Chalk>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Canonical<T::Chalk> {
+        let kinds = self
+            .kinds
+            .iter()
+            .map(|k| match k {
+                TyKind::General => chalk_ir::TyKind::General,
+                TyKind::Integer => chalk_ir::TyKind::Integer,
+                TyKind::Float => chalk_ir::TyKind::Float,
+            })
+            .map(|tk| {
+                chalk_ir::CanonicalVarKind::new(
+                    chalk_ir::VariableKind::Ty(tk),
+                    chalk_ir::UniverseIndex::ROOT,
+                )
+            });
+        let value = self.value.to_chalk(db);
+        chalk_ir::Canonical {
+            value,
+            binders: chalk_ir::CanonicalVarKinds::from_iter(&Interner, kinds),
+        }
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, canonical: chalk_ir::Canonical<T::Chalk>) -> Canonical<T> {
+        let kinds = canonical
+            .binders
+            .iter(&Interner)
+            .map(|k| match k.kind {
+                chalk_ir::VariableKind::Ty(tk) => match tk {
+                    chalk_ir::TyKind::General => TyKind::General,
+                    chalk_ir::TyKind::Integer => TyKind::Integer,
+                    chalk_ir::TyKind::Float => TyKind::Float,
+                },
+                chalk_ir::VariableKind::Lifetime => panic!("unexpected lifetime from Chalk"),
+                chalk_ir::VariableKind::Const(_) => panic!("unexpected const from Chalk"),
+            })
+            .collect();
+        Canonical { kinds, value: from_chalk(db, canonical.value) }
+    }
+}
+
+impl ToChalk for Arc<TraitEnvironment> {
+    type Chalk = chalk_ir::Environment<Interner>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::Environment<Interner> {
+        let mut clauses = Vec::new();
+        for pred in &self.predicates {
+            if pred.is_error() {
+                // for env, we just ignore errors
+                continue;
+            }
+            let program_clause: chalk_ir::ProgramClause<Interner> =
+                pred.clone().to_chalk(db).cast(&Interner);
+            clauses.push(program_clause.into_from_env_clause(&Interner));
+        }
+        chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses)
+    }
+
+    fn from_chalk(
+        _db: &dyn HirDatabase,
+        _env: chalk_ir::Environment<Interner>,
+    ) -> Arc<TraitEnvironment> {
+        unimplemented!()
+    }
+}
+
+impl<T: ToChalk> ToChalk for InEnvironment<T>
+where
+    T::Chalk: chalk_ir::interner::HasInterner<Interner = Interner>,
+{
+    type Chalk = chalk_ir::InEnvironment<T::Chalk>;
+
+    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::InEnvironment<T::Chalk> {
+        chalk_ir::InEnvironment {
+            environment: self.environment.to_chalk(db),
+            goal: self.value.to_chalk(db),
+        }
+    }
+
+    fn from_chalk(
+        db: &dyn HirDatabase,
+        in_env: chalk_ir::InEnvironment<T::Chalk>,
+    ) -> InEnvironment<T> {
+        InEnvironment {
+            environment: from_chalk(db, in_env.environment),
+            value: from_chalk(db, in_env.goal),
+        }
+    }
+}
+
+pub(super) fn make_binders<T>(value: T, num_vars: usize) -> chalk_ir::Binders<T>
+where
+    T: HasInterner<Interner = Interner>,
+{
+    chalk_ir::Binders::new(
+        chalk_ir::VariableKinds::from_iter(
+            &Interner,
+            std::iter::repeat(chalk_ir::VariableKind::Ty(chalk_ir::TyKind::General)).take(num_vars),
+        ),
+        value,
+    )
+}
+
+pub(super) fn convert_where_clauses(
+    db: &dyn HirDatabase,
+    def: GenericDefId,
+    substs: &Substs,
+) -> Vec<chalk_ir::QuantifiedWhereClause<Interner>> {
+    let generic_predicates = db.generic_predicates(def);
+    let mut result = Vec::with_capacity(generic_predicates.len());
+    for pred in generic_predicates.iter() {
+        if pred.value.is_error() {
+            // skip errored predicates completely
+            continue;
+        }
+        result.push(pred.clone().subst(substs).to_chalk(db));
+    }
+    result
+}
+
+pub(super) fn generic_predicate_to_inline_bound(
+    db: &dyn HirDatabase,
+    pred: &GenericPredicate,
+    self_ty: &Ty,
+) -> Option<rust_ir::InlineBound<Interner>> {
+    // An InlineBound is like a GenericPredicate, except the self type is left out.
+    // We don't have a special type for this, but Chalk does.
+    match pred {
+        GenericPredicate::Implemented(trait_ref) => {
+            if &trait_ref.substs[0] != self_ty {
+                // we can only convert predicates back to type bounds if they
+                // have the expected self type
+                return None;
+            }
+            let args_no_self = trait_ref.substs[1..]
+                .iter()
+                .map(|ty| ty.clone().to_chalk(db).cast(&Interner))
+                .collect();
+            let trait_bound =
+                rust_ir::TraitBound { trait_id: trait_ref.trait_.to_chalk(db), args_no_self };
+            Some(rust_ir::InlineBound::TraitBound(trait_bound))
+        }
+        GenericPredicate::Projection(proj) => {
+            if &proj.projection_ty.parameters[0] != self_ty {
+                return None;
+            }
+            let trait_ = match proj.projection_ty.associated_ty.lookup(db.upcast()).container {
+                AssocContainerId::TraitId(t) => t,
+                _ => panic!("associated type not in trait"),
+            };
+            let args_no_self = proj.projection_ty.parameters[1..]
+                .iter()
+                .map(|ty| ty.clone().to_chalk(db).cast(&Interner))
+                .collect();
+            let alias_eq_bound = rust_ir::AliasEqBound {
+                value: proj.ty.clone().to_chalk(db),
+                trait_bound: rust_ir::TraitBound { trait_id: trait_.to_chalk(db), args_no_self },
+                associated_ty_id: proj.projection_ty.associated_ty.to_chalk(db),
+                parameters: Vec::new(), // FIXME we don't support generic associated types yet
+            };
+            Some(rust_ir::InlineBound::AliasEqBound(alias_eq_bound))
+        }
+        GenericPredicate::Error => None,
+    }
+}

crates/hir_ty/src/traits/chalk/tls.rs

@@ -0,0 +1,358 @@
+//! Implementation of Chalk debug helper functions using TLS.
+use std::fmt;
+
+use chalk_ir::{AliasTy, GenericArg, Goal, Goals, Lifetime, ProgramClauseImplication, TypeName};
+use itertools::Itertools;
+
+use super::{from_chalk, Interner};
+use crate::{db::HirDatabase, CallableDefId, TypeCtor};
+use hir_def::{AdtId, AssocContainerId, DefWithBodyId, Lookup, TypeAliasId};
+
+pub use unsafe_tls::{set_current_program, with_current_program};
+
+pub struct DebugContext<'a>(&'a dyn HirDatabase);
+
+impl DebugContext<'_> {
+    pub fn debug_struct_id(
+        &self,
+        id: super::AdtId,
+        f: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let type_ctor: TypeCtor = from_chalk(self.0, TypeName::Adt(id));
+        match type_ctor {
+            TypeCtor::Bool => write!(f, "bool")?,
+            TypeCtor::Char => write!(f, "char")?,
+            TypeCtor::Int(t) => write!(f, "{}", t)?,
+            TypeCtor::Float(t) => write!(f, "{}", t)?,
+            TypeCtor::Str => write!(f, "str")?,
+            TypeCtor::Slice => write!(f, "slice")?,
+            TypeCtor::Array => write!(f, "array")?,
+            TypeCtor::RawPtr(m) => write!(f, "*{}", m.as_keyword_for_ptr())?,
+            TypeCtor::Ref(m) => write!(f, "&{}", m.as_keyword_for_ref())?,
+            TypeCtor::Never => write!(f, "!")?,
+            TypeCtor::Tuple { .. } => {
+                write!(f, "()")?;
+            }
+            TypeCtor::FnPtr { .. } => {
+                write!(f, "fn")?;
+            }
+            TypeCtor::FnDef(def) => {
+                let name = match def {
+                    CallableDefId::FunctionId(ff) => self.0.function_data(ff).name.clone(),
+                    CallableDefId::StructId(s) => self.0.struct_data(s).name.clone(),
+                    CallableDefId::EnumVariantId(e) => {
+                        let enum_data = self.0.enum_data(e.parent);
+                        enum_data.variants[e.local_id].name.clone()
+                    }
+                };
+                match def {
+                    CallableDefId::FunctionId(_) => write!(f, "{{fn {}}}", name)?,
+                    CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {
+                        write!(f, "{{ctor {}}}", name)?
+                    }
+                }
+            }
+            TypeCtor::Adt(def_id) => {
+                let name = match def_id {
+                    AdtId::StructId(it) => self.0.struct_data(it).name.clone(),
+                    AdtId::UnionId(it) => self.0.union_data(it).name.clone(),
+                    AdtId::EnumId(it) => self.0.enum_data(it).name.clone(),
+                };
+                write!(f, "{}", name)?;
+            }
+            TypeCtor::AssociatedType(type_alias) => {
+                let trait_ = match type_alias.lookup(self.0.upcast()).container {
+                    AssocContainerId::TraitId(it) => it,
+                    _ => panic!("not an associated type"),
+                };
+                let trait_name = self.0.trait_data(trait_).name.clone();
+                let name = self.0.type_alias_data(type_alias).name.clone();
+                write!(f, "{}::{}", trait_name, name)?;
+            }
+            TypeCtor::OpaqueType(opaque_ty_id) => match opaque_ty_id {
+                crate::OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                    write!(f, "{{impl trait {} of {:?}}}", idx, func)?;
+                }
+            },
+            TypeCtor::Closure { def, expr } => {
+                write!(f, "{{closure {:?} in ", expr.into_raw())?;
+                match def {
+                    DefWithBodyId::FunctionId(func) => {
+                        write!(f, "fn {}", self.0.function_data(func).name)?
+                    }
+                    DefWithBodyId::StaticId(s) => {
+                        if let Some(name) = self.0.static_data(s).name.as_ref() {
+                            write!(f, "body of static {}", name)?;
+                        } else {
+                            write!(f, "body of unnamed static {:?}", s)?;
+                        }
+                    }
+                    DefWithBodyId::ConstId(c) => {
+                        if let Some(name) = self.0.const_data(c).name.as_ref() {
+                            write!(f, "body of const {}", name)?;
+                        } else {
+                            write!(f, "body of unnamed const {:?}", c)?;
+                        }
+                    }
+                };
+                write!(f, "}}")?;
+            }
+        }
+        Ok(())
+    }
+
+    pub fn debug_trait_id(
+        &self,
+        id: super::TraitId,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let trait_: hir_def::TraitId = from_chalk(self.0, id);
+        let trait_data = self.0.trait_data(trait_);
+        write!(fmt, "{}", trait_data.name)
+    }
+
+    pub fn debug_assoc_type_id(
+        &self,
+        id: super::AssocTypeId,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let type_alias: TypeAliasId = from_chalk(self.0, id);
+        let type_alias_data = self.0.type_alias_data(type_alias);
+        let trait_ = match type_alias.lookup(self.0.upcast()).container {
+            AssocContainerId::TraitId(t) => t,
+            _ => panic!("associated type not in trait"),
+        };
+        let trait_data = self.0.trait_data(trait_);
+        write!(fmt, "{}::{}", trait_data.name, type_alias_data.name)
+    }
+
+    pub fn debug_opaque_ty_id(
+        &self,
+        opaque_ty_id: chalk_ir::OpaqueTyId<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        fmt.debug_struct("OpaqueTyId").field("index", &opaque_ty_id.0).finish()
+    }
+
+    pub fn debug_alias(
+        &self,
+        alias_ty: &AliasTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        match alias_ty {
+            AliasTy::Projection(projection_ty) => self.debug_projection_ty(projection_ty, fmt),
+            AliasTy::Opaque(opaque_ty) => self.debug_opaque_ty(opaque_ty, fmt),
+        }
+    }
+
+    pub fn debug_projection_ty(
+        &self,
+        projection_ty: &chalk_ir::ProjectionTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let type_alias: TypeAliasId = from_chalk(self.0, projection_ty.associated_ty_id);
+        let type_alias_data = self.0.type_alias_data(type_alias);
+        let trait_ = match type_alias.lookup(self.0.upcast()).container {
+            AssocContainerId::TraitId(t) => t,
+            _ => panic!("associated type not in trait"),
+        };
+        let trait_data = self.0.trait_data(trait_);
+        let params = projection_ty.substitution.as_slice(&Interner);
+        write!(fmt, "<{:?} as {}", &params[0], trait_data.name,)?;
+        if params.len() > 1 {
+            write!(
+                fmt,
+                "<{}>",
+                &params[1..].iter().format_with(", ", |x, f| f(&format_args!("{:?}", x))),
+            )?;
+        }
+        write!(fmt, ">::{}", type_alias_data.name)
+    }
+
+    pub fn debug_opaque_ty(
+        &self,
+        opaque_ty: &chalk_ir::OpaqueTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", opaque_ty.opaque_ty_id)
+    }
+
+    pub fn debug_ty(
+        &self,
+        ty: &chalk_ir::Ty<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", ty.data(&Interner))
+    }
+
+    pub fn debug_lifetime(
+        &self,
+        lifetime: &Lifetime<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", lifetime.data(&Interner))
+    }
+
+    pub fn debug_generic_arg(
+        &self,
+        parameter: &GenericArg<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", parameter.data(&Interner).inner_debug())
+    }
+
+    pub fn debug_goal(
+        &self,
+        goal: &Goal<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let goal_data = goal.data(&Interner);
+        write!(fmt, "{:?}", goal_data)
+    }
+
+    pub fn debug_goals(
+        &self,
+        goals: &Goals<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", goals.debug(&Interner))
+    }
+
+    pub fn debug_program_clause_implication(
+        &self,
+        pci: &ProgramClauseImplication<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", pci.debug(&Interner))
+    }
+
+    pub fn debug_application_ty(
+        &self,
+        application_ty: &chalk_ir::ApplicationTy<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", application_ty.debug(&Interner))
+    }
+
+    pub fn debug_substitution(
+        &self,
+        substitution: &chalk_ir::Substitution<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", substitution.debug(&Interner))
+    }
+
+    pub fn debug_separator_trait_ref(
+        &self,
+        separator_trait_ref: &chalk_ir::SeparatorTraitRef<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        write!(fmt, "{:?}", separator_trait_ref.debug(&Interner))
+    }
+
+    pub fn debug_fn_def_id(
+        &self,
+        fn_def_id: chalk_ir::FnDefId<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> Result<(), fmt::Error> {
+        let def: CallableDefId = from_chalk(self.0, fn_def_id);
+        let name = match def {
+            CallableDefId::FunctionId(ff) => self.0.function_data(ff).name.clone(),
+            CallableDefId::StructId(s) => self.0.struct_data(s).name.clone(),
+            CallableDefId::EnumVariantId(e) => {
+                let enum_data = self.0.enum_data(e.parent);
+                enum_data.variants[e.local_id].name.clone()
+            }
+        };
+        match def {
+            CallableDefId::FunctionId(_) => write!(fmt, "{{fn {}}}", name),
+            CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {
+                write!(fmt, "{{ctor {}}}", name)
+            }
+        }
+    }
+
+    pub fn debug_const(
+        &self,
+        _constant: &chalk_ir::Const<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "const")
+    }
+
+    pub fn debug_variable_kinds(
+        &self,
+        variable_kinds: &chalk_ir::VariableKinds<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", variable_kinds.as_slice(&Interner))
+    }
+    pub fn debug_variable_kinds_with_angles(
+        &self,
+        variable_kinds: &chalk_ir::VariableKinds<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", variable_kinds.inner_debug(&Interner))
+    }
+    pub fn debug_canonical_var_kinds(
+        &self,
+        canonical_var_kinds: &chalk_ir::CanonicalVarKinds<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", canonical_var_kinds.as_slice(&Interner))
+    }
+    pub fn debug_program_clause(
+        &self,
+        clause: &chalk_ir::ProgramClause<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", clause.data(&Interner))
+    }
+    pub fn debug_program_clauses(
+        &self,
+        clauses: &chalk_ir::ProgramClauses<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", clauses.as_slice(&Interner))
+    }
+    pub fn debug_quantified_where_clauses(
+        &self,
+        clauses: &chalk_ir::QuantifiedWhereClauses<Interner>,
+        fmt: &mut fmt::Formatter<'_>,
+    ) -> fmt::Result {
+        write!(fmt, "{:?}", clauses.as_slice(&Interner))
+    }
+}
+
+mod unsafe_tls {
+    use super::DebugContext;
+    use crate::db::HirDatabase;
+    use scoped_tls::scoped_thread_local;
+
+    scoped_thread_local!(static PROGRAM: DebugContext);
+
+    pub fn with_current_program<R>(
+        op: impl for<'a> FnOnce(Option<&'a DebugContext<'a>>) -> R,
+    ) -> R {
+        if PROGRAM.is_set() {
+            PROGRAM.with(|prog| op(Some(prog)))
+        } else {
+            op(None)
+        }
+    }
+
+    pub fn set_current_program<OP, R>(p: &dyn HirDatabase, op: OP) -> R
+    where
+        OP: FnOnce() -> R,
+    {
+        let ctx = DebugContext(p);
+        // we're transmuting the lifetime in the DebugContext to static. This is
+        // fine because we only keep the reference for the lifetime of this
+        // function, *and* the only way to access the context is through
+        // `with_current_program`, which hides the lifetime through the `for`
+        // type.
+        let static_p: &DebugContext<'static> =
+            unsafe { std::mem::transmute::<&DebugContext, &DebugContext<'static>>(&ctx) };
+        PROGRAM.set(static_p, || op())
+    }
+}

crates/hir_ty/src/utils.rs

@@ -0,0 +1,257 @@
+//! Helper functions for working with def, which don't need to be a separate
+//! query, but can't be computed directly from `*Data` (ie, which need a `db`).
+use std::sync::Arc;
+
+use hir_def::generics::WherePredicateTarget;
+use hir_def::{
+    adt::VariantData,
+    db::DefDatabase,
+    generics::{GenericParams, TypeParamData, TypeParamProvenance},
+    path::Path,
+    resolver::{HasResolver, TypeNs},
+    type_ref::TypeRef,
+    AssocContainerId, GenericDefId, Lookup, TraitId, TypeAliasId, TypeParamId, VariantId,
+};
+use hir_expand::name::{name, Name};
+
+use crate::{db::HirDatabase, GenericPredicate, TraitRef};
+
+fn direct_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
+    let resolver = trait_.resolver(db);
+    // returning the iterator directly doesn't easily work because of
+    // lifetime problems, but since there usually shouldn't be more than a
+    // few direct traits this should be fine (we could even use some kind of
+    // SmallVec if performance is a concern)
+    let generic_params = db.generic_params(trait_.into());
+    let trait_self = generic_params.find_trait_self_param();
+    generic_params
+        .where_predicates
+        .iter()
+        .filter_map(|pred| match &pred.target {
+            WherePredicateTarget::TypeRef(TypeRef::Path(p)) if p == &Path::from(name![Self]) => {
+                pred.bound.as_path()
+            }
+            WherePredicateTarget::TypeParam(local_id) if Some(*local_id) == trait_self => {
+                pred.bound.as_path()
+            }
+            _ => None,
+        })
+        .filter_map(|path| match resolver.resolve_path_in_type_ns_fully(db, path.mod_path()) {
+            Some(TypeNs::TraitId(t)) => Some(t),
+            _ => None,
+        })
+        .collect()
+}
+
+fn direct_super_trait_refs(db: &dyn HirDatabase, trait_ref: &TraitRef) -> Vec<TraitRef> {
+    // returning the iterator directly doesn't easily work because of
+    // lifetime problems, but since there usually shouldn't be more than a
+    // few direct traits this should be fine (we could even use some kind of
+    // SmallVec if performance is a concern)
+    let generic_params = db.generic_params(trait_ref.trait_.into());
+    let trait_self = match generic_params.find_trait_self_param() {
+        Some(p) => TypeParamId { parent: trait_ref.trait_.into(), local_id: p },
+        None => return Vec::new(),
+    };
+    db.generic_predicates_for_param(trait_self)
+        .iter()
+        .filter_map(|pred| {
+            pred.as_ref().filter_map(|pred| match pred {
+                GenericPredicate::Implemented(tr) => Some(tr.clone()),
+                _ => None,
+            })
+        })
+        .map(|pred| pred.subst(&trait_ref.substs))
+        .collect()
+}
+
+/// Returns an iterator over the whole super trait hierarchy (including the
+/// trait itself).
+pub(super) fn all_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
+    // we need to take care a bit here to avoid infinite loops in case of cycles
+    // (i.e. if we have `trait A: B; trait B: A;`)
+    let mut result = vec![trait_];
+    let mut i = 0;
+    while i < result.len() {
+        let t = result[i];
+        // yeah this is quadratic, but trait hierarchies should be flat
+        // enough that this doesn't matter
+        for tt in direct_super_traits(db, t) {
+            if !result.contains(&tt) {
+                result.push(tt);
+            }
+        }
+        i += 1;
+    }
+    result
+}
+
+/// Given a trait ref (`Self: Trait`), builds all the implied trait refs for
+/// super traits. The original trait ref will be included. So the difference to
+/// `all_super_traits` is that we keep track of type parameters; for example if
+/// we have `Self: Trait<u32, i32>` and `Trait<T, U>: OtherTrait<U>` we'll get
+/// `Self: OtherTrait<i32>`.
+pub(super) fn all_super_trait_refs(db: &dyn HirDatabase, trait_ref: TraitRef) -> Vec<TraitRef> {
+    // we need to take care a bit here to avoid infinite loops in case of cycles
+    // (i.e. if we have `trait A: B; trait B: A;`)
+    let mut result = vec![trait_ref];
+    let mut i = 0;
+    while i < result.len() {
+        let t = &result[i];
+        // yeah this is quadratic, but trait hierarchies should be flat
+        // enough that this doesn't matter
+        for tt in direct_super_trait_refs(db, t) {
+            if !result.iter().any(|tr| tr.trait_ == tt.trait_) {
+                result.push(tt);
+            }
+        }
+        i += 1;
+    }
+    result
+}
+
+pub(super) fn associated_type_by_name_including_super_traits(
+    db: &dyn HirDatabase,
+    trait_ref: TraitRef,
+    name: &Name,
+) -> Option<(TraitRef, TypeAliasId)> {
+    all_super_trait_refs(db, trait_ref).into_iter().find_map(|t| {
+        let assoc_type = db.trait_data(t.trait_).associated_type_by_name(name)?;
+        Some((t, assoc_type))
+    })
+}
+
+pub(super) fn variant_data(db: &dyn DefDatabase, var: VariantId) -> Arc<VariantData> {
+    match var {
+        VariantId::StructId(it) => db.struct_data(it).variant_data.clone(),
+        VariantId::UnionId(it) => db.union_data(it).variant_data.clone(),
+        VariantId::EnumVariantId(it) => {
+            db.enum_data(it.parent).variants[it.local_id].variant_data.clone()
+        }
+    }
+}
+
+/// Helper for mutating `Arc<[T]>` (i.e. `Arc::make_mut` for Arc slices).
+/// The underlying values are cloned if there are other strong references.
+pub(crate) fn make_mut_slice<T: Clone>(a: &mut Arc<[T]>) -> &mut [T] {
+    if Arc::get_mut(a).is_none() {
+        *a = a.iter().cloned().collect();
+    }
+    Arc::get_mut(a).unwrap()
+}
+
+pub(crate) fn generics(db: &dyn DefDatabase, def: GenericDefId) -> Generics {
+    let parent_generics = parent_generic_def(db, def).map(|def| Box::new(generics(db, def)));
+    Generics { def, params: db.generic_params(def), parent_generics }
+}
+
+#[derive(Debug)]
+pub(crate) struct Generics {
+    def: GenericDefId,
+    pub(crate) params: Arc<GenericParams>,
+    parent_generics: Option<Box<Generics>>,
+}
+
+impl Generics {
+    pub(crate) fn iter<'a>(
+        &'a self,
+    ) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
+        self.parent_generics
+            .as_ref()
+            .into_iter()
+            .flat_map(|it| {
+                it.params
+                    .types
+                    .iter()
+                    .map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p))
+            })
+            .chain(
+                self.params
+                    .types
+                    .iter()
+                    .map(move |(local_id, p)| (TypeParamId { parent: self.def, local_id }, p)),
+            )
+    }
+
+    pub(crate) fn iter_parent<'a>(
+        &'a self,
+    ) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
+        self.parent_generics.as_ref().into_iter().flat_map(|it| {
+            it.params
+                .types
+                .iter()
+                .map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p))
+        })
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.len_split().0
+    }
+
+    /// (total, parents, child)
+    pub(crate) fn len_split(&self) -> (usize, usize, usize) {
+        let parent = self.parent_generics.as_ref().map_or(0, |p| p.len());
+        let child = self.params.types.len();
+        (parent + child, parent, child)
+    }
+
+    /// (parent total, self param, type param list, impl trait)
+    pub(crate) fn provenance_split(&self) -> (usize, usize, usize, usize) {
+        let parent = self.parent_generics.as_ref().map_or(0, |p| p.len());
+        let self_params = self
+            .params
+            .types
+            .iter()
+            .filter(|(_, p)| p.provenance == TypeParamProvenance::TraitSelf)
+            .count();
+        let list_params = self
+            .params
+            .types
+            .iter()
+            .filter(|(_, p)| p.provenance == TypeParamProvenance::TypeParamList)
+            .count();
+        let impl_trait_params = self
+            .params
+            .types
+            .iter()
+            .filter(|(_, p)| p.provenance == TypeParamProvenance::ArgumentImplTrait)
+            .count();
+        (parent, self_params, list_params, impl_trait_params)
+    }
+
+    pub(crate) fn param_idx(&self, param: TypeParamId) -> Option<usize> {
+        Some(self.find_param(param)?.0)
+    }
+
+    fn find_param(&self, param: TypeParamId) -> Option<(usize, &TypeParamData)> {
+        if param.parent == self.def {
+            let (idx, (_local_id, data)) = self
+                .params
+                .types
+                .iter()
+                .enumerate()
+                .find(|(_, (idx, _))| *idx == param.local_id)
+                .unwrap();
+            let (_total, parent_len, _child) = self.len_split();
+            Some((parent_len + idx, data))
+        } else {
+            self.parent_generics.as_ref().and_then(|g| g.find_param(param))
+        }
+    }
+}
+
+fn parent_generic_def(db: &dyn DefDatabase, def: GenericDefId) -> Option<GenericDefId> {
+    let container = match def {
+        GenericDefId::FunctionId(it) => it.lookup(db).container,
+        GenericDefId::TypeAliasId(it) => it.lookup(db).container,
+        GenericDefId::ConstId(it) => it.lookup(db).container,
+        GenericDefId::EnumVariantId(it) => return Some(it.parent.into()),
+        GenericDefId::AdtId(_) | GenericDefId::TraitId(_) | GenericDefId::ImplId(_) => return None,
+    };
+
+    match container {
+        AssocContainerId::ImplId(it) => Some(it.into()),
+        AssocContainerId::TraitId(it) => Some(it.into()),
+        AssocContainerId::ContainerId(_) => None,
+    }
+}