Complete diagnostics in ty lowering groundwork

Implement diagnostics in all places left: generics (predicates, defaults, const params' types), fields, and type aliases.

Unfortunately this results in a 20mb addition in `analysis-stats .` due to many type methods returning an addition diagnostics result now (even if it's `None` in most cases). I'm not sure if this can be improved.

An alternative strategy that can prevent the memory usage growth is to never produce diagnostics in hir-ty methods. Instead, lower all types in the hir crate when computing diagnostics from scratch (with diagnostics this time). But this has two serious disadvantages:
 1. This can cause code duplication (although it can probably be not that bad, it will still mean a lot more code).
 2. I believe we eventually want to compute diagnostics for the *entire* workspace (either on-type or on-save or something alike), so users can know when they have diagnostics even in inactive files. Choosing this approach will mean we lose all precomputed salsa queries. For one file this is fine, for the whole workspace this will be very slow.

crates/hir-ty/src/db.rs

@@ -22,7 +22,7 @@ use crate::{
     consteval::ConstEvalError,
     dyn_compatibility::DynCompatibilityViolation,
     layout::{Layout, LayoutError},
-    lower::{GenericDefaults, GenericPredicates},
+    lower::{Diagnostics, GenericDefaults, GenericPredicates},
     method_resolution::{InherentImpls, TraitImpls, TyFingerprint},
     mir::{BorrowckResult, MirBody, MirLowerError},
     Binders, ClosureId, Const, FnDefId, ImplTraitId, ImplTraits, InferenceResult, Interner,
@@ -115,21 +115,35 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[ra_salsa::cycle(crate::lower::ty_recover)]
     fn ty(&self, def: TyDefId) -> Binders<Ty>;
 
+    #[ra_salsa::invoke(crate::lower::type_for_type_alias_with_diagnostics_query)]
+    fn type_for_type_alias_with_diagnostics(&self, def: TypeAliasId) -> (Binders<Ty>, Diagnostics);
+
     /// Returns the type of the value of the given constant, or `None` if the `ValueTyDefId` is
     /// a `StructId` or `EnumVariantId` with a record constructor.
     #[ra_salsa::invoke(crate::lower::value_ty_query)]
     fn value_ty(&self, def: ValueTyDefId) -> Option<Binders<Ty>>;
 
+    #[ra_salsa::invoke(crate::lower::impl_self_ty_with_diagnostics_query)]
+    #[ra_salsa::cycle(crate::lower::impl_self_ty_with_diagnostics_recover)]
+    fn impl_self_ty_with_diagnostics(&self, def: ImplId) -> (Binders<Ty>, Diagnostics);
     #[ra_salsa::invoke(crate::lower::impl_self_ty_query)]
-    #[ra_salsa::cycle(crate::lower::impl_self_ty_recover)]
     fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
 
+    #[ra_salsa::invoke(crate::lower::const_param_ty_with_diagnostics_query)]
+    fn const_param_ty_with_diagnostics(&self, def: ConstParamId) -> (Ty, Diagnostics);
     #[ra_salsa::invoke(crate::lower::const_param_ty_query)]
     fn const_param_ty(&self, def: ConstParamId) -> Ty;
 
+    #[ra_salsa::invoke(crate::lower::impl_trait_with_diagnostics_query)]
+    fn impl_trait_with_diagnostics(&self, def: ImplId) -> Option<(Binders<TraitRef>, Diagnostics)>;
     #[ra_salsa::invoke(crate::lower::impl_trait_query)]
     fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
+    #[ra_salsa::invoke(crate::lower::field_types_with_diagnostics_query)]
+    fn field_types_with_diagnostics(
+        &self,
+        var: VariantId,
+    ) -> (Arc<ArenaMap<LocalFieldId, Binders<Ty>>>, Diagnostics);
     #[ra_salsa::invoke(crate::lower::field_types_query)]
     fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>>;
 
@@ -154,6 +168,11 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[ra_salsa::invoke(crate::lower::generic_predicates_query)]
     fn generic_predicates(&self, def: GenericDefId) -> GenericPredicates;
 
+    #[ra_salsa::invoke(crate::lower::generic_predicates_without_parent_with_diagnostics_query)]
+    fn generic_predicates_without_parent_with_diagnostics(
+        &self,
+        def: GenericDefId,
+    ) -> (GenericPredicates, Diagnostics);
     #[ra_salsa::invoke(crate::lower::generic_predicates_without_parent_query)]
     fn generic_predicates_without_parent(&self, def: GenericDefId) -> GenericPredicates;
 
@@ -164,8 +183,13 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[ra_salsa::invoke(crate::lower::trait_environment_query)]
     fn trait_environment(&self, def: GenericDefId) -> Arc<TraitEnvironment>;
 
+    #[ra_salsa::invoke(crate::lower::generic_defaults_with_diagnostics_query)]
+    #[ra_salsa::cycle(crate::lower::generic_defaults_with_diagnostics_recover)]
+    fn generic_defaults_with_diagnostics(
+        &self,
+        def: GenericDefId,
+    ) -> (GenericDefaults, Diagnostics);
     #[ra_salsa::invoke(crate::lower::generic_defaults_query)]
-    #[ra_salsa::cycle(crate::lower::generic_defaults_recover)]
     fn generic_defaults(&self, def: GenericDefId) -> GenericDefaults;
 
     #[ra_salsa::invoke(InherentImpls::inherent_impls_in_crate_query)]

crates/hir-ty/src/generics.rs

@@ -55,6 +55,10 @@ impl Generics {
         self.def
     }
 
+    pub(crate) fn self_types_map(&self) -> &TypesMap {
+        &self.params.types_map
+    }
+
     pub(crate) fn iter_id(&self) -> impl Iterator<Item = GenericParamId> + '_ {
         self.iter_self_id().chain(self.iter_parent_id())
     }
@@ -86,15 +90,13 @@ impl Generics {
         self.iter_self().chain(self.iter_parent())
     }
 
-    pub(crate) fn iter_with_types_map(
+    pub(crate) fn iter_parents_with_types_map(
         &self,
     ) -> impl Iterator<Item = ((GenericParamId, GenericParamDataRef<'_>), &TypesMap)> + '_ {
-        self.iter_self().zip(std::iter::repeat(&self.params.types_map)).chain(
-            self.iter_parent().zip(
-                self.parent_generics()
-                    .into_iter()
-                    .flat_map(|it| std::iter::repeat(&it.params.types_map)),
-            ),
+        self.iter_parent().zip(
+            self.parent_generics()
+                .into_iter()
+                .flat_map(|it| std::iter::repeat(&it.params.types_map)),
         )
     }
 

crates/hir-ty/src/lib.rs

@@ -90,7 +90,8 @@ pub use infer::{
 pub use interner::Interner;
 pub use lower::{
     associated_type_shorthand_candidates, GenericArgsProhibitedReason, ImplTraitLoweringMode,
-    ParamLoweringMode, TyDefId, TyLoweringContext, TyLoweringDiagnosticKind, ValueTyDefId,
+    ParamLoweringMode, TyDefId, TyLoweringContext, TyLoweringDiagnostic, TyLoweringDiagnosticKind,
+    ValueTyDefId,
 };
 pub use mapping::{
     from_assoc_type_id, from_chalk_trait_id, from_foreign_def_id, from_placeholder_idx,

crates/hir-ty/src/lower.rs

@@ -48,7 +48,7 @@ use rustc_pattern_analysis::Captures;
 use smallvec::SmallVec;
 use stdx::{impl_from, never};
 use syntax::ast;
-use triomphe::Arc;
+use triomphe::{Arc, ThinArc};
 
 use crate::{
     all_super_traits,
@@ -1652,11 +1652,24 @@ fn named_associated_type_shorthand_candidates<R>(
     }
 }
 
-/// Build the type of all specific fields of a struct or enum variant.
+pub(crate) type Diagnostics = Option<ThinArc<(), TyLoweringDiagnostic>>;
+
+fn create_diagnostics(diagnostics: Vec<TyLoweringDiagnostic>) -> Diagnostics {
+    (!diagnostics.is_empty()).then(|| ThinArc::from_header_and_iter((), diagnostics.into_iter()))
+}
+
 pub(crate) fn field_types_query(
     db: &dyn HirDatabase,
     variant_id: VariantId,
 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
+    db.field_types_with_diagnostics(variant_id).0
+}
+
+/// Build the type of all specific fields of a struct or enum variant.
+pub(crate) fn field_types_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    variant_id: VariantId,
+) -> (Arc<ArenaMap<LocalFieldId, Binders<Ty>>>, Diagnostics) {
     let var_data = variant_id.variant_data(db.upcast());
     let (resolver, def): (_, GenericDefId) = match variant_id {
         VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
@@ -1672,7 +1685,7 @@ pub(crate) fn field_types_query(
     for (field_id, field_data) in var_data.fields().iter() {
         res.insert(field_id, make_binders(db, &generics, ctx.lower_ty(field_data.type_ref)));
     }
-    Arc::new(res)
+    (Arc::new(res), create_diagnostics(ctx.diagnostics))
 }
 
 /// This query exists only to be used when resolving short-hand associated types
@@ -1873,15 +1886,22 @@ pub(crate) fn generic_predicates_query(
     db: &dyn HirDatabase,
     def: GenericDefId,
 ) -> GenericPredicates {
-    generic_predicates_filtered_by(db, def, |_, _| true)
+    generic_predicates_filtered_by(db, def, |_, _| true).0
 }
 
-/// Resolve the where clause(s) of an item with generics,
-/// except the ones inherited from the parent
 pub(crate) fn generic_predicates_without_parent_query(
     db: &dyn HirDatabase,
     def: GenericDefId,
 ) -> GenericPredicates {
+    db.generic_predicates_without_parent_with_diagnostics(def).0
+}
+
+/// Resolve the where clause(s) of an item with generics,
+/// except the ones inherited from the parent
+pub(crate) fn generic_predicates_without_parent_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    def: GenericDefId,
+) -> (GenericPredicates, Diagnostics) {
     generic_predicates_filtered_by(db, def, |_, d| *d == def)
 }
 
@@ -1891,7 +1911,7 @@ fn generic_predicates_filtered_by<F>(
     db: &dyn HirDatabase,
     def: GenericDefId,
     filter: F,
-) -> GenericPredicates
+) -> (GenericPredicates, Diagnostics)
 where
     F: Fn(&WherePredicate, &GenericDefId) -> bool,
 {
@@ -1932,7 +1952,10 @@ where
             );
         };
     }
-    GenericPredicates(predicates.is_empty().not().then(|| predicates.into()))
+    (
+        GenericPredicates(predicates.is_empty().not().then(|| predicates.into())),
+        create_diagnostics(ctx.diagnostics),
+    )
 }
 
 /// Generate implicit `: Sized` predicates for all generics that has no `?Sized` bound.
@@ -1985,75 +2008,110 @@ impl ops::Deref for GenericDefaults {
     }
 }
 
-/// Resolve the default type params from generics
 pub(crate) fn generic_defaults_query(db: &dyn HirDatabase, def: GenericDefId) -> GenericDefaults {
+    db.generic_defaults_with_diagnostics(def).0
+}
+
+/// Resolve the default type params from generics.
+///
+/// Diagnostics are only returned for this `GenericDefId` (returned defaults include parents).
+pub(crate) fn generic_defaults_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    def: GenericDefId,
+) -> (GenericDefaults, Diagnostics) {
     let generic_params = generics(db.upcast(), def);
     if generic_params.len() == 0 {
-        return GenericDefaults(None);
+        return (GenericDefaults(None), None);
     }
     let resolver = def.resolver(db.upcast());
     let parent_start_idx = generic_params.len_self();
 
-    let mut ctx = TyLoweringContext::new(db, &resolver, TypesMap::EMPTY, def.into())
-        .with_impl_trait_mode(ImplTraitLoweringMode::Disallowed)
-        .with_type_param_mode(ParamLoweringMode::Variable);
-    GenericDefaults(Some(Arc::from_iter(generic_params.iter_with_types_map().enumerate().map(
-        |(idx, ((id, p), types_map))| {
-            ctx.types_map = types_map;
-            match p {
-                GenericParamDataRef::TypeParamData(p) => {
-                    let ty = p.default.as_ref().map_or(TyKind::Error.intern(Interner), |ty| {
-                        // Each default can only refer to previous parameters.
-                        // Type variable default referring to parameter coming
-                        // after it is forbidden (FIXME: report diagnostic)
-                        fallback_bound_vars(ctx.lower_ty(*ty), idx, parent_start_idx)
-                    });
-                    crate::make_binders(db, &generic_params, ty.cast(Interner))
-                }
-                GenericParamDataRef::ConstParamData(p) => {
-                    let GenericParamId::ConstParamId(id) = id else {
-                        unreachable!("Unexpected lifetime or type argument")
-                    };
+    let mut ctx =
+        TyLoweringContext::new(db, &resolver, generic_params.self_types_map(), def.into())
+            .with_impl_trait_mode(ImplTraitLoweringMode::Disallowed)
+            .with_type_param_mode(ParamLoweringMode::Variable);
+    let mut idx = 0;
+    let mut defaults = generic_params
+        .iter_self()
+        .map(|(id, p)| {
+            let result =
+                handle_generic_param(&mut ctx, idx, id, p, parent_start_idx, &generic_params);
+            idx += 1;
+            result
+        })
+        .collect::<Vec<_>>();
+    let diagnostics = create_diagnostics(mem::take(&mut ctx.diagnostics));
+    defaults.extend(generic_params.iter_parents_with_types_map().map(|((id, p), types_map)| {
+        ctx.types_map = types_map;
+        let result = handle_generic_param(&mut ctx, idx, id, p, parent_start_idx, &generic_params);
+        idx += 1;
+        result
+    }));
+    let defaults = GenericDefaults(Some(Arc::from_iter(defaults)));
+    return (defaults, diagnostics);
 
-                    let mut val = p.default.as_ref().map_or_else(
-                        || unknown_const_as_generic(db.const_param_ty(id)),
-                        |c| {
-                            let param_ty = ctx.lower_ty(p.ty);
-                            let c = ctx.lower_const(c, param_ty);
-                            c.cast(Interner)
-                        },
-                    );
-                    // Each default can only refer to previous parameters, see above.
-                    val = fallback_bound_vars(val, idx, parent_start_idx);
-                    make_binders(db, &generic_params, val)
-                }
-                GenericParamDataRef::LifetimeParamData(_) => {
-                    make_binders(db, &generic_params, error_lifetime().cast(Interner))
-                }
+    fn handle_generic_param(
+        ctx: &mut TyLoweringContext<'_>,
+        idx: usize,
+        id: GenericParamId,
+        p: GenericParamDataRef<'_>,
+        parent_start_idx: usize,
+        generic_params: &Generics,
+    ) -> Binders<crate::GenericArg> {
+        match p {
+            GenericParamDataRef::TypeParamData(p) => {
+                let ty = p.default.as_ref().map_or(TyKind::Error.intern(Interner), |ty| {
+                    // Each default can only refer to previous parameters.
+                    // Type variable default referring to parameter coming
+                    // after it is forbidden (FIXME: report diagnostic)
+                    fallback_bound_vars(ctx.lower_ty(*ty), idx, parent_start_idx)
+                });
+                crate::make_binders(ctx.db, generic_params, ty.cast(Interner))
             }
-        },
-    ))))
+            GenericParamDataRef::ConstParamData(p) => {
+                let GenericParamId::ConstParamId(id) = id else {
+                    unreachable!("Unexpected lifetime or type argument")
+                };
+
+                let mut val = p.default.as_ref().map_or_else(
+                    || unknown_const_as_generic(ctx.db.const_param_ty(id)),
+                    |c| {
+                        let param_ty = ctx.lower_ty(p.ty);
+                        let c = ctx.lower_const(c, param_ty);
+                        c.cast(Interner)
+                    },
+                );
+                // Each default can only refer to previous parameters, see above.
+                val = fallback_bound_vars(val, idx, parent_start_idx);
+                make_binders(ctx.db, generic_params, val)
+            }
+            GenericParamDataRef::LifetimeParamData(_) => {
+                make_binders(ctx.db, generic_params, error_lifetime().cast(Interner))
+            }
+        }
+    }
 }
 
-pub(crate) fn generic_defaults_recover(
+pub(crate) fn generic_defaults_with_diagnostics_recover(
     db: &dyn HirDatabase,
     _cycle: &Cycle,
     def: &GenericDefId,
-) -> GenericDefaults {
+) -> (GenericDefaults, Diagnostics) {
     let generic_params = generics(db.upcast(), *def);
     if generic_params.len() == 0 {
-        return GenericDefaults(None);
+        return (GenericDefaults(None), None);
     }
     // FIXME: this code is not covered in tests.
     // we still need one default per parameter
-    GenericDefaults(Some(Arc::from_iter(generic_params.iter_id().map(|id| {
+    let defaults = GenericDefaults(Some(Arc::from_iter(generic_params.iter_id().map(|id| {
         let val = match id {
             GenericParamId::TypeParamId(_) => TyKind::Error.intern(Interner).cast(Interner),
             GenericParamId::ConstParamId(id) => unknown_const_as_generic(db.const_param_ty(id)),
             GenericParamId::LifetimeParamId(_) => error_lifetime().cast(Interner),
         };
         crate::make_binders(db, &generic_params, val)
-    }))))
+    }))));
+    (defaults, None)
 }
 
 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
@@ -2196,7 +2254,10 @@ fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
     make_binders(db, &generics, ty)
 }
 
-fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
+pub(crate) fn type_for_type_alias_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    t: TypeAliasId,
+) -> (Binders<Ty>, Diagnostics) {
     let generics = generics(db.upcast(), t.into());
     let resolver = t.resolver(db.upcast());
     let type_alias_data = db.type_alias_data(t);
@@ -2211,7 +2272,7 @@ fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
             .map(|type_ref| ctx.lower_ty(type_ref))
             .unwrap_or_else(|| TyKind::Error.intern(Interner))
     };
-    make_binders(db, &generics, inner)
+    (make_binders(db, &generics, inner), create_diagnostics(ctx.diagnostics))
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -2254,7 +2315,7 @@ pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
     match def {
         TyDefId::BuiltinType(it) => Binders::empty(Interner, TyBuilder::builtin(it)),
         TyDefId::AdtId(it) => type_for_adt(db, it),
-        TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
+        TyDefId::TypeAliasId(it) => db.type_for_type_alias_with_diagnostics(it).0,
     }
 }
 
@@ -2279,47 +2340,73 @@ pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Option<
 }
 
 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
+    db.impl_self_ty_with_diagnostics(impl_id).0
+}
+
+pub(crate) fn impl_self_ty_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    impl_id: ImplId,
+) -> (Binders<Ty>, Diagnostics) {
     let impl_data = db.impl_data(impl_id);
     let resolver = impl_id.resolver(db.upcast());
     let generics = generics(db.upcast(), impl_id.into());
     let mut ctx = TyLoweringContext::new(db, &resolver, &impl_data.types_map, impl_id.into())
         .with_type_param_mode(ParamLoweringMode::Variable);
-    make_binders(db, &generics, ctx.lower_ty(impl_data.self_ty))
+    (
+        make_binders(db, &generics, ctx.lower_ty(impl_data.self_ty)),
+        create_diagnostics(ctx.diagnostics),
+    )
+}
+
+pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
+    db.const_param_ty_with_diagnostics(def).0
 }
 
 // returns None if def is a type arg
-pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
+pub(crate) fn const_param_ty_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    def: ConstParamId,
+) -> (Ty, Diagnostics) {
     let parent_data = db.generic_params(def.parent());
     let data = &parent_data[def.local_id()];
     let resolver = def.parent().resolver(db.upcast());
     let mut ctx =
         TyLoweringContext::new(db, &resolver, &parent_data.types_map, def.parent().into());
-    match data {
+    let ty = match data {
         TypeOrConstParamData::TypeParamData(_) => {
             never!();
             Ty::new(Interner, TyKind::Error)
         }
         TypeOrConstParamData::ConstParamData(d) => ctx.lower_ty(d.ty),
-    }
+    };
+    (ty, create_diagnostics(ctx.diagnostics))
 }
 
-pub(crate) fn impl_self_ty_recover(
+pub(crate) fn impl_self_ty_with_diagnostics_recover(
     db: &dyn HirDatabase,
     _cycle: &Cycle,
     impl_id: &ImplId,
-) -> Binders<Ty> {
+) -> (Binders<Ty>, Diagnostics) {
     let generics = generics(db.upcast(), (*impl_id).into());
-    make_binders(db, &generics, TyKind::Error.intern(Interner))
+    (make_binders(db, &generics, TyKind::Error.intern(Interner)), None)
 }
 
 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
+    db.impl_trait_with_diagnostics(impl_id).map(|it| it.0)
+}
+
+pub(crate) fn impl_trait_with_diagnostics_query(
+    db: &dyn HirDatabase,
+    impl_id: ImplId,
+) -> Option<(Binders<TraitRef>, Diagnostics)> {
     let impl_data = db.impl_data(impl_id);
     let resolver = impl_id.resolver(db.upcast());
     let mut ctx = TyLoweringContext::new(db, &resolver, &impl_data.types_map, impl_id.into())
         .with_type_param_mode(ParamLoweringMode::Variable);
     let (self_ty, binders) = db.impl_self_ty(impl_id).into_value_and_skipped_binders();
     let target_trait = impl_data.target_trait.as_ref()?;
-    Some(Binders::new(binders, ctx.lower_trait_ref(target_trait, self_ty)?))
+    let trait_ref = Binders::new(binders, ctx.lower_trait_ref(target_trait, self_ty)?);
+    Some((trait_ref, create_diagnostics(ctx.diagnostics)))
 }
 
 pub(crate) fn return_type_impl_traits(