Merge branch 'master' into kdelorey/complete-trait-impl

.github/workflows/release.yaml

@@ -1,4 +1,4 @@
-name: CI-Release
+name: release
 on:
   push:
     branches:
@@ -132,7 +132,9 @@ jobs:
 
       - name: Create Release
         id: create_release
-        uses: actions/create-release@v1
+        # uses: actions/create-release@v1
+        # https://github.com/actions/create-release/pull/32
+        uses: fleskesvor/create-release@1a72e235c178bf2ae6c51a8ae36febc24568c5fe
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         with:

Cargo.toml

@@ -10,5 +10,24 @@ debug = 0
 incremental = true
 debug = 0 # set this to 1 or 2 to get more useful backtraces in debugger
 
+# ideally, we would use `build-override` here, but some crates are also
+# needed at run-time and we end up compiling them twice
+[profile.release.package.proc-macro2]
+opt-level = 0
+[profile.release.package.quote]
+opt-level = 0
+[profile.release.package.syn]
+opt-level = 0
+[profile.release.package.serde_derive]
+opt-level = 0
+[profile.release.package.chalk-derive]
+opt-level = 0
+[profile.release.package.chalk-macros]
+opt-level = 0
+[profile.release.package.salsa-macros]
+opt-level = 0
+[profile.release.package.xtask]
+opt-level = 0
+
 [patch.'crates-io']
 # rowan = { path = "../rowan" }

README.md

@@ -2,14 +2,13 @@
   <img src="https://user-images.githubusercontent.com/1711539/72443316-5a79f280-37ae-11ea-858f-035209ece2dd.png" alt="rust-analyzer logo">
 </p>
 
-Rust Analyzer is an **experimental** modular compiler frontend for the Rust
+rust-analyzer is an **experimental** modular compiler frontend for the Rust
 language. It is a part of a larger rls-2.0 effort to create excellent IDE
-support for Rust. If you want to get involved, check the rls-2.0 working group
+support for Rust. If you want to get involved, check the rls-2.0 working group:
-in the compiler-team repository:
 
-https://github.com/rust-lang/compiler-team/tree/master/content/working-groups/rls-2.0
+https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0
 
-Work on the Rust Analyzer is sponsored by
+Work on rust-analyzer is sponsored by
 
 [<img src="https://user-images.githubusercontent.com/1711539/58105231-cf306900-7bee-11e9-83d8-9f1102e59d29.png" alt="Ferrous Systems" width="300">](https://ferrous-systems.com/)
 - [Mozilla](https://www.mozilla.org/en-US/)
@@ -17,17 +16,17 @@ Work on the Rust Analyzer is sponsored by
 
 ## Language Server Quick Start
 
-Rust Analyzer is a work-in-progress, so you'll have to build it from source, and
+rust-analyzer is a work-in-progress, so you might encounter critical bugs. That
-you might encounter critical bugs. That said, it is complete enough to provide a
+said, it is complete enough to provide a useful IDE experience and some people
-useful IDE experience and some people use it as a daily driver.
+use it as a daily driver.
 
 To build rust-analyzer, you need:
 
-* latest stable rust for language server itself
+* latest stable Rust for the language server itself
 * latest stable npm and VS Code for VS Code extension
 
-To quickly install rust-analyzer with VS Code extension with standard setup
+To quickly install the rust-analyzer language server and VS Code extension with
-(`code` and `cargo` in `$PATH`, etc), use this:
+standard setup (`code` and `cargo` in `$PATH`, etc), use this:
 
 ```
 # clone the repo
@@ -45,8 +44,8 @@ cannot start, see [./docs/user](./docs/user).
 
 ## Documentation
 
-If you want to **contribute** to rust-analyzer or just curious about how things work
+If you want to **contribute** to rust-analyzer or are just curious about how
-under the hood, check the [./docs/dev](./docs/dev) folder.
+things work under the hood, check the [./docs/dev](./docs/dev) folder.
 
 If you want to **use** rust-analyzer's language server with your editor of
 choice, check [./docs/user](./docs/user) folder. It also contains some tips & tricks to help

bors.toml

@@ -1,6 +1,6 @@
 status = [
     "Rust (ubuntu-latest)",
-    # "Rust (windows-latest)",
+    "Rust (windows-latest)",
     "Rust (macos-latest)",
     "TypeScript"
 ]

crates/ra_assists/Cargo.toml

@@ -16,6 +16,8 @@ either = "1.5"
 ra_syntax = { path = "../ra_syntax" }
 ra_text_edit = { path = "../ra_text_edit" }
 ra_fmt = { path = "../ra_fmt" }
+ra_prof = { path = "../ra_prof" }
 ra_db = { path = "../ra_db" }
+ra_ide_db = { path = "../ra_ide_db" }
 hir = { path = "../ra_hir", package = "ra_hir" }
 test_utils = { path = "../test_utils" }

crates/ra_assists/src/assist_ctx.rs

@@ -1,8 +1,8 @@
 //! This module defines `AssistCtx` -- the API surface that is exposed to assists.
-use either::Either;
+use hir::{InFile, SourceAnalyzer, SourceBinder};
-use hir::{db::HirDatabase, InFile, SourceAnalyzer, SourceBinder};
+use ra_db::{FileRange, SourceDatabase};
-use ra_db::FileRange;
 use ra_fmt::{leading_indent, reindent};
+use ra_ide_db::RootDatabase;
 use ra_syntax::{
     algo::{self, find_covering_element, find_node_at_offset},
     AstNode, SourceFile, SyntaxElement, SyntaxKind, SyntaxNode, SyntaxToken, TextRange, TextUnit,
@@ -10,14 +10,40 @@ use ra_syntax::{
 };
 use ra_text_edit::TextEditBuilder;
 
-use crate::{AssistAction, AssistId, AssistLabel, ResolvedAssist};
+use crate::{AssistAction, AssistId, AssistLabel, GroupLabel, ResolvedAssist};
 
 #[derive(Clone, Debug)]
-pub(crate) enum Assist {
+pub(crate) struct Assist(pub(crate) Vec<AssistInfo>);
-    Unresolved { label: AssistLabel },
+
-    Resolved { assist: ResolvedAssist },
+#[derive(Clone, Debug)]
+pub(crate) struct AssistInfo {
+    pub(crate) label: AssistLabel,
+    pub(crate) group_label: Option<GroupLabel>,
+    pub(crate) action: Option<AssistAction>,
 }
 
+impl AssistInfo {
+    fn new(label: AssistLabel) -> AssistInfo {
+        AssistInfo { label, group_label: None, action: None }
+    }
+
+    fn resolved(self, action: AssistAction) -> AssistInfo {
+        AssistInfo { action: Some(action), ..self }
+    }
+
+    fn with_group(self, group_label: GroupLabel) -> AssistInfo {
+        AssistInfo { group_label: Some(group_label), ..self }
+    }
+
+    pub(crate) fn into_resolved(self) -> Option<ResolvedAssist> {
+        let label = self.label;
+        let group_label = self.group_label;
+        self.action.map(|action| ResolvedAssist { label, group_label, action })
+    }
+}
+
+pub(crate) type AssistHandler = fn(AssistCtx) -> Option<Assist>;
+
 /// `AssistCtx` allows to apply an assist or check if it could be applied.
 ///
 /// Assists use a somewhat over-engineered approach, given the current needs. The
@@ -49,14 +75,14 @@ pub(crate) enum Assist {
 /// moment, because the LSP API is pretty awkward in this place, and it's much
 /// easier to just compute the edit eagerly :-)
 #[derive(Debug)]
-pub(crate) struct AssistCtx<'a, DB> {
+pub(crate) struct AssistCtx<'a> {
-    pub(crate) db: &'a DB,
+    pub(crate) db: &'a RootDatabase,
     pub(crate) frange: FileRange,
     source_file: SourceFile,
     should_compute_edit: bool,
 }
 
-impl<'a, DB> Clone for AssistCtx<'a, DB> {
+impl Clone for AssistCtx<'_> {
     fn clone(&self) -> Self {
         AssistCtx {
             db: self.db,
@@ -67,15 +93,10 @@ impl<'a, DB> Clone for AssistCtx<'a, DB> {
     }
 }
 
-impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
+impl<'a> AssistCtx<'a> {
-    pub(crate) fn with_ctx<F, T>(db: &DB, frange: FileRange, should_compute_edit: bool, f: F) -> T
+    pub fn new(db: &RootDatabase, frange: FileRange, should_compute_edit: bool) -> AssistCtx {
-    where
-        F: FnOnce(AssistCtx<DB>) -> T,
-    {
         let parse = db.parse(frange.file_id);
-
+        AssistCtx { db, frange, source_file: parse.tree(), should_compute_edit }
-        let ctx = AssistCtx { db, frange, source_file: parse.tree(), should_compute_edit };
-        f(ctx)
     }
 
     pub(crate) fn add_assist(
@@ -84,48 +105,23 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
         label: impl Into<String>,
         f: impl FnOnce(&mut ActionBuilder),
     ) -> Option<Assist> {
-        let label = AssistLabel { label: label.into(), id };
+        let label = AssistLabel::new(label.into(), id);
-        assert!(label.label.chars().nth(0).unwrap().is_uppercase());
 
-        let assist = if self.should_compute_edit {
+        let mut info = AssistInfo::new(label);
+        if self.should_compute_edit {
             let action = {
                 let mut edit = ActionBuilder::default();
                 f(&mut edit);
                 edit.build()
             };
-            Assist::Resolved { assist: ResolvedAssist { label, action_data: Either::Left(action) } }
+            info = info.resolved(action)
-        } else {
-            Assist::Unresolved { label }
         };
 
-        Some(assist)
+        Some(Assist(vec![info]))
     }
 
-    #[allow(dead_code)] // will be used for auto import assist with multiple actions
+    pub(crate) fn add_assist_group(self, group_name: impl Into<String>) -> AssistGroup<'a> {
-    pub(crate) fn add_assist_group(
+        AssistGroup { ctx: self, group_name: group_name.into(), assists: Vec::new() }
-        self,
-        id: AssistId,
-        label: impl Into<String>,
-        f: impl FnOnce() -> Vec<ActionBuilder>,
-    ) -> Option<Assist> {
-        let label = AssistLabel { label: label.into(), id };
-        let assist = if self.should_compute_edit {
-            let actions = f();
-            assert!(!actions.is_empty(), "Assist cannot have no");
-
-            Assist::Resolved {
-                assist: ResolvedAssist {
-                    label,
-                    action_data: Either::Right(
-                        actions.into_iter().map(ActionBuilder::build).collect(),
-                    ),
-                },
-            }
-        } else {
-            Assist::Unresolved { label }
-        };
-
-        Some(assist)
     }
 
     pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
@@ -142,7 +138,7 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
     pub(crate) fn covering_element(&self) -> SyntaxElement {
         find_covering_element(self.source_file.syntax(), self.frange.range)
     }
-    pub(crate) fn source_binder(&self) -> SourceBinder<'a, DB> {
+    pub(crate) fn source_binder(&self) -> SourceBinder<'a, RootDatabase> {
         SourceBinder::new(self.db)
     }
     pub(crate) fn source_analyzer(
@@ -159,21 +155,48 @@ impl<'a, DB: HirDatabase> AssistCtx<'a, DB> {
     }
 }
 
+pub(crate) struct AssistGroup<'a> {
+    ctx: AssistCtx<'a>,
+    group_name: String,
+    assists: Vec<AssistInfo>,
+}
+
+impl<'a> AssistGroup<'a> {
+    pub(crate) fn add_assist(
+        &mut self,
+        id: AssistId,
+        label: impl Into<String>,
+        f: impl FnOnce(&mut ActionBuilder),
+    ) {
+        let label = AssistLabel::new(label.into(), id);
+
+        let mut info = AssistInfo::new(label).with_group(GroupLabel(self.group_name.clone()));
+        if self.ctx.should_compute_edit {
+            let action = {
+                let mut edit = ActionBuilder::default();
+                f(&mut edit);
+                edit.build()
+            };
+            info = info.resolved(action)
+        };
+
+        self.assists.push(info)
+    }
+
+    pub(crate) fn finish(self) -> Option<Assist> {
+        assert!(!self.assists.is_empty());
+        Some(Assist(self.assists))
+    }
+}
+
 #[derive(Default)]
 pub(crate) struct ActionBuilder {
     edit: TextEditBuilder,
     cursor_position: Option<TextUnit>,
     target: Option<TextRange>,
-    label: Option<String>,
 }
 
 impl ActionBuilder {
-    #[allow(dead_code)]
-    /// Adds a custom label to the action, if it needs to be different from the assist label
-    pub(crate) fn label(&mut self, label: impl Into<String>) {
-        self.label = Some(label.into())
-    }
-
     /// Replaces specified `range` of text with a given string.
     pub(crate) fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
         self.edit.replace(range, replace_with.into())
@@ -232,7 +255,6 @@ impl ActionBuilder {
             edit: self.edit.finish(),
             cursor_position: self.cursor_position,
             target: self.target,
-            label: self.label,
         }
     }
 }

crates/ra_assists/src/doc_tests.rs

@@ -5,24 +5,24 @@
 
 mod generated;
 
-use ra_db::{fixture::WithFixture, FileRange};
+use ra_db::FileRange;
 use test_utils::{assert_eq_text, extract_range_or_offset};
 
-use crate::test_db::TestDB;
+use crate::resolved_assists;
 
 fn check(assist_id: &str, before: &str, after: &str) {
     let (selection, before) = extract_range_or_offset(before);
-    let (db, file_id) = TestDB::with_single_file(&before);
+    let (db, file_id) = crate::helpers::with_single_file(&before);
     let frange = FileRange { file_id, range: selection.into() };
 
-    let assist = crate::assists(&db, frange)
+    let assist = resolved_assists(&db, frange)
         .into_iter()
         .find(|assist| assist.label.id.0 == assist_id)
         .unwrap_or_else(|| {
             panic!(
                 "\n\nAssist is not applicable: {}\nAvailable assists: {}",
                 assist_id,
-                crate::assists(&db, frange)
+                resolved_assists(&db, frange)
                     .into_iter()
                     .map(|assist| assist.label.id.0)
                     .collect::<Vec<_>>()
@@ -30,6 +30,6 @@ fn check(assist_id: &str, before: &str, after: &str) {
             )
         });
 
-    let actual = assist.get_first_action().edit.apply(&before);
+    let actual = assist.action.edit.apply(&before);
     assert_eq_text!(after, &actual);
 }

crates/ra_assists/src/doc_tests/generated.rs

@@ -1,4 +1,4 @@
-//! Generated file, do not edit by hand, see `crate/ra_tools/src/codegen`
+//! Generated file, do not edit by hand, see `xtask/src/codegen`
 
 use super::check;
 
@@ -160,21 +160,6 @@ impl Trait<u32> for () {
     )
 }
 
-#[test]
-fn doctest_add_import() {
-    check(
-        "add_import",
-        r#####"
-fn process(map: std::collections::<|>HashMap<String, String>) {}
-"#####,
-        r#####"
-use std::collections::HashMap;
-
-fn process(map: HashMap<String, String>) {}
-"#####,
-    )
-}
-
 #[test]
 fn doctest_add_new() {
     check(
@@ -214,6 +199,27 @@ fn main() {
     )
 }
 
+#[test]
+fn doctest_auto_import() {
+    check(
+        "auto_import",
+        r#####"
+fn main() {
+    let map = HashMap<|>::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+        r#####"
+use std::collections::HashMap;
+
+fn main() {
+    let map = HashMap::new();
+}
+pub mod std { pub mod collections { pub struct HashMap { } } }
+"#####,
+    )
+}
+
 #[test]
 fn doctest_change_visibility() {
     check(
@@ -570,6 +576,21 @@ fn handle(action: Action) {
     )
 }
 
+#[test]
+fn doctest_replace_qualified_name_with_use() {
+    check(
+        "replace_qualified_name_with_use",
+        r#####"
+fn process(map: std::collections::<|>HashMap<String, String>) {}
+"#####,
+        r#####"
+use std::collections::HashMap;
+
+fn process(map: HashMap<String, String>) {}
+"#####,
+    )
+}
+
 #[test]
 fn doctest_split_import() {
     check(

crates/ra_assists/src/handlers/add_custom_impl.rs

@@ -1,7 +1,7 @@
 //! FIXME: write short doc here
 
 use crate::{Assist, AssistCtx, AssistId};
-use hir::db::HirDatabase;
+
 use join_to_string::join;
 use ra_syntax::{
     ast::{self, AstNode},
@@ -29,7 +29,7 @@ const DERIVE_TRAIT: &str = "derive";
 //
 // }
 // ```
-pub(crate) fn add_custom_impl(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_custom_impl(ctx: AssistCtx) -> Option<Assist> {
     let input = ctx.find_node_at_offset::<ast::AttrInput>()?;
     let attr = input.syntax().parent().and_then(ast::Attr::cast)?;
 

crates/ra_assists/src/handlers/add_derive.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, AstNode, AttrsOwner},
     SyntaxKind::{COMMENT, WHITESPACE},
@@ -25,7 +24,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     y: u32,
 // }
 // ```
-pub(crate) fn add_derive(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_derive(ctx: AssistCtx) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let node_start = derive_insertion_offset(&nominal)?;
     ctx.add_assist(AssistId("add_derive"), "Add `#[derive]`", |edit| {

crates/ra_assists/src/handlers/add_explicit_type.rs

@@ -1,7 +1,7 @@
-use hir::{db::HirDatabase, HirDisplay};
+use hir::HirDisplay;
 use ra_syntax::{
-    ast::{self, AstNode, LetStmt, NameOwner},
+    ast::{self, AstNode, LetStmt, NameOwner, TypeAscriptionOwner},
-    TextRange, T,
+    TextRange,
 };
 
 use crate::{Assist, AssistCtx, AssistId};
@@ -21,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let x: i32 = 92;
 // }
 // ```
-pub(crate) fn add_explicit_type(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_explicit_type(ctx: AssistCtx) -> Option<Assist> {
     let stmt = ctx.find_node_at_offset::<LetStmt>()?;
     let expr = stmt.initializer()?;
     let pat = stmt.pat()?;
@@ -34,18 +34,22 @@ pub(crate) fn add_explicit_type(ctx: AssistCtx<impl HirDatabase>) -> Option<Assi
     // The binding must have a name
     let name = pat.name()?;
     let name_range = name.syntax().text_range();
-    // Assist should only be applicable if cursor is between 'let' and '='
     let stmt_range = stmt.syntax().text_range();
     let eq_range = stmt.eq_token()?.text_range();
+    // Assist should only be applicable if cursor is between 'let' and '='
     let let_range = TextRange::from_to(stmt_range.start(), eq_range.start());
     let cursor_in_range = ctx.frange.range.is_subrange(&let_range);
     if !cursor_in_range {
         return None;
     }
     // Assist not applicable if the type has already been specified
-    if stmt.syntax().children_with_tokens().any(|child| child.kind() == T![:]) {
+    // and it has no placeholders
+    let ascribed_ty = stmt.ascribed_type();
+    if let Some(ref ty) = ascribed_ty {
+        if ty.syntax().descendants().find_map(ast::PlaceholderType::cast).is_none() {
             return None;
         }
+    }
     // Infer type
     let db = ctx.db;
     let analyzer = ctx.source_analyzer(stmt.syntax(), None);
@@ -60,7 +64,11 @@ pub(crate) fn add_explicit_type(ctx: AssistCtx<impl HirDatabase>) -> Option<Assi
         format!("Insert explicit type '{}'", ty.display(db)),
         |edit| {
             edit.target(pat_range);
+            if let Some(ascribed_ty) = ascribed_ty {
+                edit.replace(ascribed_ty.syntax().text_range(), format!("{}", ty.display(db)));
+            } else {
                 edit.insert(name_range.end(), format!(": {}", ty.display(db)));
+            }
         },
     )
 }
@@ -85,6 +93,40 @@ mod tests {
         );
     }
 
+    #[test]
+    fn add_explicit_type_works_for_underscore() {
+        check_assist(
+            add_explicit_type,
+            "fn f() { let a<|>: _ = 1; }",
+            "fn f() { let a<|>: i32 = 1; }",
+        );
+    }
+
+    #[test]
+    fn add_explicit_type_works_for_nested_underscore() {
+        check_assist(
+            add_explicit_type,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a<|>: Option<_> = Option::Some(1);
+            }"#,
+            r#"
+            enum Option<T> {
+                Some(T),
+                None
+            }
+
+            fn f() {
+                let a<|>: Option<i32> = Option::Some(1);
+            }"#,
+        );
+    }
+
     #[test]
     fn add_explicit_type_works_for_macro_call() {
         check_assist(

crates/ra_assists/src/handlers/add_impl.rs

@@ -1,5 +1,5 @@
 use format_buf::format;
-use hir::db::HirDatabase;
+
 use join_to_string::join;
 use ra_syntax::{
     ast::{self, AstNode, NameOwner, TypeParamsOwner},
@@ -27,7 +27,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //
 // }
 // ```
-pub(crate) fn add_impl(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_impl(ctx: AssistCtx) -> Option<Assist> {
     let nominal = ctx.find_node_at_offset::<ast::NominalDef>()?;
     let name = nominal.name()?;
     ctx.add_assist(AssistId("add_impl"), format!("Implement {}", name.text().as_str()), |edit| {

crates/ra_assists/src/handlers/add_missing_impl_members.rs

@@ -43,7 +43,7 @@ enum AddMissingImplMembersMode {
 //
 // }
 // ```
-pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_missing_impl_members(ctx: AssistCtx) -> Option<Assist> {
     add_missing_impl_members_inner(
         ctx,
         AddMissingImplMembersMode::NoDefaultMethods,
@@ -84,7 +84,7 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Opti
 //
 // }
 // ```
-pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_missing_default_members(ctx: AssistCtx) -> Option<Assist> {
     add_missing_impl_members_inner(
         ctx,
         AddMissingImplMembersMode::DefaultMethodsOnly,
@@ -94,11 +94,12 @@ pub(crate) fn add_missing_default_members(ctx: AssistCtx<impl HirDatabase>) -> O
 }
 
 fn add_missing_impl_members_inner(
-    ctx: AssistCtx<impl HirDatabase>,
+    ctx: AssistCtx,
     mode: AddMissingImplMembersMode,
     assist_id: &'static str,
     label: &'static str,
 ) -> Option<Assist> {
+    let _p = ra_prof::profile("add_missing_impl_members_inner");
     let impl_node = ctx.find_node_at_offset::<ast::ImplBlock>()?;
     let impl_item_list = impl_node.item_list()?;
 

crates/ra_assists/src/handlers/add_new.rs

@@ -1,5 +1,5 @@
 use format_buf::format;
-use hir::{db::HirDatabase, InFile};
+use hir::{Adt, InFile};
 use join_to_string::join;
 use ra_syntax::{
     ast::{
@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // }
 //
 // ```
-pub(crate) fn add_new(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_new(ctx: AssistCtx) -> Option<Assist> {
     let strukt = ctx.find_node_at_offset::<ast::StructDef>()?;
 
     // We want to only apply this to non-union structs with named fields
@@ -128,26 +128,29 @@ fn generate_impl_text(strukt: &ast::StructDef, code: &str) -> String {
 //
 // FIXME: change the new fn checking to a more semantic approach when that's more
 // viable (e.g. we process proc macros, etc)
-fn find_struct_impl(
+fn find_struct_impl(ctx: &AssistCtx, strukt: &ast::StructDef) -> Option<Option<ast::ImplBlock>> {
-    ctx: &AssistCtx<impl HirDatabase>,
-    strukt: &ast::StructDef,
-) -> Option<Option<ast::ImplBlock>> {
     let db = ctx.db;
     let module = strukt.syntax().ancestors().find(|node| {
         ast::Module::can_cast(node.kind()) || ast::SourceFile::can_cast(node.kind())
     })?;
     let mut sb = ctx.source_binder();
 
-    let struct_ty = {
+    let struct_def = {
         let src = InFile { file_id: ctx.frange.file_id.into(), value: strukt.clone() };
-        sb.to_def(src)?.ty(db)
+        sb.to_def(src)?
     };
 
     let block = module.descendants().filter_map(ast::ImplBlock::cast).find_map(|impl_blk| {
         let src = InFile { file_id: ctx.frange.file_id.into(), value: impl_blk.clone() };
         let blk = sb.to_def(src)?;
 
-        let same_ty = blk.target_ty(db) == struct_ty;
+        // FIXME: handle e.g. `struct S<T>; impl<U> S<U> {}`
+        // (we currently use the wrong type parameter)
+        // also we wouldn't want to use e.g. `impl S<u32>`
+        let same_ty = match blk.target_ty(db).as_adt() {
+            Some(def) => def == Adt::Struct(struct_def),
+            None => false,
+        };
         let not_trait_impl = blk.target_trait(db).is_none();
 
         if !(same_ty && not_trait_impl) {

crates/ra_assists/src/handlers/apply_demorgan.rs

@@ -1,8 +1,6 @@
-use super::invert_if::invert_boolean_expression;
-use hir::db::HirDatabase;
 use ra_syntax::ast::{self, AstNode};
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
 
 // Assist: apply_demorgan
 //
@@ -23,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     if !(x == 4 && y) {}
 // }
 // ```
-pub(crate) fn apply_demorgan(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn apply_demorgan(ctx: AssistCtx) -> Option<Assist> {
     let expr = ctx.find_node_at_offset::<ast::BinExpr>()?;
     let op = expr.op_kind()?;
     let op_range = expr.op_token()?.text_range();
@@ -32,12 +30,14 @@ pub(crate) fn apply_demorgan(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist>
     if !cursor_in_range {
         return None;
     }
+
     let lhs = expr.lhs()?;
     let lhs_range = lhs.syntax().text_range();
+    let not_lhs = invert_boolean_expression(lhs);
+
     let rhs = expr.rhs()?;
     let rhs_range = rhs.syntax().text_range();
-    let not_lhs = invert_boolean_expression(&lhs)?;
+    let not_rhs = invert_boolean_expression(rhs);
-    let not_rhs = invert_boolean_expression(&rhs)?;
 
     ctx.add_assist(AssistId("apply_demorgan"), "Apply De Morgan's law", |edit| {
         edit.target(op_range);
@@ -78,12 +78,12 @@ mod tests {
     }
 
     #[test]
-    fn demorgan_doesnt_apply_with_cursor_not_on_op() {
+    fn demorgan_general_case() {
-        check_assist_not_applicable(apply_demorgan, "fn f() { <|> !x || !x }")
+        check_assist(apply_demorgan, "fn f() { x ||<|> x }", "fn f() { !(!x &&<|> !x) }")
     }
 
     #[test]
-    fn demorgan_doesnt_apply_when_operands_arent_negated_already() {
+    fn demorgan_doesnt_apply_with_cursor_not_on_op() {
-        check_assist_not_applicable(apply_demorgan, "fn f() { x ||<|> x }")
+        check_assist_not_applicable(apply_demorgan, "fn f() { <|> !x || !x }")
     }
 }

crates/ra_assists/src/handlers/auto_import.rs

@@ -0,0 +1,293 @@
+use ra_ide_db::imports_locator::ImportsLocator;
+use ra_syntax::ast::{self, AstNode};
+
+use crate::{
+    assist_ctx::{Assist, AssistCtx},
+    insert_use_statement, AssistId,
+};
+use std::collections::BTreeSet;
+
+// Assist: auto_import
+//
+// If the name is unresolved, provides all possible imports for it.
+//
+// ```
+// fn main() {
+//     let map = HashMap<|>::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+// ->
+// ```
+// use std::collections::HashMap;
+//
+// fn main() {
+//     let map = HashMap::new();
+// }
+// # pub mod std { pub mod collections { pub struct HashMap { } } }
+// ```
+pub(crate) fn auto_import(ctx: AssistCtx) -> Option<Assist> {
+    let path_under_caret: ast::Path = ctx.find_node_at_offset()?;
+    if path_under_caret.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
+        return None;
+    }
+
+    let module = path_under_caret.syntax().ancestors().find_map(ast::Module::cast);
+    let position = match module.and_then(|it| it.item_list()) {
+        Some(item_list) => item_list.syntax().clone(),
+        None => {
+            let current_file =
+                path_under_caret.syntax().ancestors().find_map(ast::SourceFile::cast)?;
+            current_file.syntax().clone()
+        }
+    };
+    let source_analyzer = ctx.source_analyzer(&position, None);
+    let module_with_name_to_import = source_analyzer.module()?;
+
+    let name_ref_to_import =
+        path_under_caret.syntax().descendants().find_map(ast::NameRef::cast)?;
+    if source_analyzer
+        .resolve_path(ctx.db, &name_ref_to_import.syntax().ancestors().find_map(ast::Path::cast)?)
+        .is_some()
+    {
+        return None;
+    }
+
+    let name_to_import = name_ref_to_import.syntax().to_string();
+    let proposed_imports = ImportsLocator::new(ctx.db)
+        .find_imports(&name_to_import)
+        .into_iter()
+        .filter_map(|module_def| module_with_name_to_import.find_use_path(ctx.db, module_def))
+        .filter(|use_path| !use_path.segments.is_empty())
+        .take(20)
+        .collect::<BTreeSet<_>>();
+
+    if proposed_imports.is_empty() {
+        return None;
+    }
+
+    let mut group = ctx.add_assist_group(format!("Import {}", name_to_import));
+    for import in proposed_imports {
+        group.add_assist(AssistId("auto_import"), format!("Import `{}`", &import), |edit| {
+            edit.target(path_under_caret.syntax().text_range());
+            insert_use_statement(
+                &position,
+                path_under_caret.syntax(),
+                &import,
+                edit.text_edit_builder(),
+            );
+        });
+    }
+    group.finish()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
+
+    use super::*;
+
+    #[test]
+    fn applicable_when_found_an_import() {
+        check_assist(
+            auto_import,
+            r"
+            <|>PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            <|>use PubMod::PubStruct;
+
+            PubStruct
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn auto_imports_are_merged() {
+        check_assist(
+            auto_import,
+            r"
+            use PubMod::PubStruct1;
+
+            struct Test {
+                test: Pub<|>Struct2<u8>,
+            }
+
+            pub mod PubMod {
+                pub struct PubStruct1;
+                pub struct PubStruct2<T> {
+                    _t: T,
+                }
+            }
+            ",
+            r"
+            use PubMod::{PubStruct2, PubStruct1};
+
+            struct Test {
+                test: Pub<|>Struct2<u8>,
+            }
+
+            pub mod PubMod {
+                pub struct PubStruct1;
+                pub struct PubStruct2<T> {
+                    _t: T,
+                }
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn applicable_when_found_multiple_imports() {
+        check_assist(
+            auto_import,
+            r"
+            PubSt<|>ruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+            r"
+            use PubMod1::PubStruct;
+
+            PubSt<|>ruct
+
+            pub mod PubMod1 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod2 {
+                pub struct PubStruct;
+            }
+            pub mod PubMod3 {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_already_imported_types() {
+        check_assist_not_applicable(
+            auto_import,
+            r"
+            use PubMod::PubStruct;
+
+            PubStruct<|>
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_for_types_with_private_paths() {
+        check_assist_not_applicable(
+            auto_import,
+            r"
+            PrivateStruct<|>
+
+            pub mod PubMod {
+                struct PrivateStruct;
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn not_applicable_when_no_imports_found() {
+        check_assist_not_applicable(
+            auto_import,
+            "
+            PubStruct<|>",
+        );
+    }
+
+    #[test]
+    fn not_applicable_in_import_statements() {
+        check_assist_not_applicable(
+            auto_import,
+            r"
+            use PubStruct<|>;
+
+            pub mod PubMod {
+                pub struct PubStruct;
+            }",
+        );
+    }
+
+    #[test]
+    fn function_import() {
+        check_assist(
+            auto_import,
+            r"
+            test_function<|>
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+            r"
+            use PubMod::test_function;
+
+            test_function<|>
+
+            pub mod PubMod {
+                pub fn test_function() {};
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn auto_import_target() {
+        check_assist_target(
+            auto_import,
+            r"
+            struct AssistInfo {
+                group_label: Option<<|>GroupLabel>,
+            }
+
+            mod m { pub struct GroupLabel; }
+            ",
+            "GroupLabel",
+        )
+    }
+
+    #[test]
+    fn not_applicable_when_path_start_is_imported() {
+        check_assist_not_applicable(
+            auto_import,
+            r"
+            pub mod mod1 {
+                pub mod mod2 {
+                    pub mod mod3 {
+                        pub struct TestStruct;
+                    }
+                }
+            }
+
+            use mod1::mod2;
+            fn main() {
+                mod2::mod3::TestStruct<|>
+            }
+            ",
+        );
+    }
+}

crates/ra_assists/src/handlers/change_visibility.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, NameOwner, VisibilityOwner},
     AstNode,
@@ -22,14 +21,14 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // pub(crate) fn frobnicate() {}
 // ```
-pub(crate) fn change_visibility(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn change_visibility(ctx: AssistCtx) -> Option<Assist> {
     if let Some(vis) = ctx.find_node_at_offset::<ast::Visibility>() {
         return change_vis(ctx, vis);
     }
     add_vis(ctx)
 }
 
-fn add_vis(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+fn add_vis(ctx: AssistCtx) -> Option<Assist> {
     let item_keyword = ctx.token_at_offset().find(|leaf| match leaf.kind() {
         T![fn] | T![mod] | T![struct] | T![enum] | T![trait] => true,
         _ => false,
@@ -75,7 +74,7 @@ fn vis_offset(node: &SyntaxNode) -> TextUnit {
         .unwrap_or_else(|| node.text_range().start())
 }
 
-fn change_vis(ctx: AssistCtx<impl HirDatabase>, vis: ast::Visibility) -> Option<Assist> {
+fn change_vis(ctx: AssistCtx, vis: ast::Visibility) -> Option<Assist> {
     if vis.syntax().text() == "pub" {
         return ctx.add_assist(
             AssistId("change_visibility"),

crates/ra_assists/src/handlers/early_return.rs

@@ -1,6 +1,5 @@
 use std::{iter::once, ops::RangeInclusive};
 
-use hir::db::HirDatabase;
 use ra_syntax::{
     algo::replace_children,
     ast::{self, edit::IndentLevel, make, Block, Pat::TupleStructPat},
@@ -11,6 +10,7 @@ use ra_syntax::{
 
 use crate::{
     assist_ctx::{Assist, AssistCtx},
+    utils::invert_boolean_expression,
     AssistId,
 };
 
@@ -36,7 +36,7 @@ use crate::{
 //     bar();
 // }
 // ```
-pub(crate) fn convert_to_guarded_return(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn convert_to_guarded_return(ctx: AssistCtx) -> Option<Assist> {
     let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
     if if_expr.else_branch().is_some() {
         return None;
@@ -100,9 +100,13 @@ pub(crate) fn convert_to_guarded_return(ctx: AssistCtx<impl HirDatabase>) -> Opt
         let new_block = match if_let_pat {
             None => {
                 // If.
-                let early_expression = &(early_expression.syntax().to_string() + ";");
+                let new_expr = {
-                let new_expr = if_indent_level
+                    let then_branch =
-                    .increase_indent(make::if_expression(&cond_expr, early_expression));
+                        make::block_expr(once(make::expr_stmt(early_expression).into()), None);
+                    let cond = invert_boolean_expression(cond_expr);
+                    let e = make::expr_if(cond, then_branch);
+                    if_indent_level.increase_indent(e)
+                };
                 replace(new_expr.syntax(), &then_block, &parent_block, &if_expr)
             }
             Some((path, bound_ident)) => {

crates/ra_assists/src/handlers/fill_match_arms.rs

@@ -31,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn fill_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn fill_match_arms(ctx: AssistCtx) -> Option<Assist> {
     let match_expr = ctx.find_node_at_offset::<ast::MatchExpr>()?;
     let match_arm_list = match_expr.match_arm_list()?;
 

crates/ra_assists/src/handlers/flip_binexpr.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::ast::{AstNode, BinExpr, BinOp};
 
 use crate::{Assist, AssistCtx, AssistId};
@@ -18,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     let _ = 2 + 90;
 // }
 // ```
-pub(crate) fn flip_binexpr(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_binexpr(ctx: AssistCtx) -> Option<Assist> {
     let expr = ctx.find_node_at_offset::<BinExpr>()?;
     let lhs = expr.lhs()?.syntax().clone();
     let rhs = expr.rhs()?.syntax().clone();

crates/ra_assists/src/handlers/flip_comma.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{algo::non_trivia_sibling, Direction, T};
 
 use crate::{Assist, AssistCtx, AssistId};
@@ -18,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     ((3, 4), (1, 2));
 // }
 // ```
-pub(crate) fn flip_comma(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_comma(ctx: AssistCtx) -> Option<Assist> {
     let comma = ctx.find_token_at_offset(T![,])?;
     let prev = non_trivia_sibling(comma.clone().into(), Direction::Prev)?;
     let next = non_trivia_sibling(comma.clone().into(), Direction::Next)?;

crates/ra_assists/src/handlers/flip_trait_bound.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     algo::non_trivia_sibling,
     ast::{self, AstNode},
@@ -18,7 +17,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // fn foo<T: Copy + Clone>() { }
 // ```
-pub(crate) fn flip_trait_bound(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn flip_trait_bound(ctx: AssistCtx) -> Option<Assist> {
     // We want to replicate the behavior of `flip_binexpr` by only suggesting
     // the assist when the cursor is on a `+`
     let plus = ctx.find_token_at_offset(T![+])?;

crates/ra_assists/src/handlers/inline_local_variable.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, AstNode, AstToken},
     TextRange,
@@ -23,7 +22,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     (1 + 2) * 4;
 // }
 // ```
-pub(crate) fn inline_local_variable(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn inline_local_variable(ctx: AssistCtx) -> Option<Assist> {
     let let_stmt = ctx.find_node_at_offset::<ast::LetStmt>()?;
     let bind_pat = match let_stmt.pat()? {
         ast::Pat::BindPat(pat) => pat,
@@ -47,6 +46,9 @@ pub(crate) fn inline_local_variable(ctx: AssistCtx<impl HirDatabase>) -> Option<
     };
     let analyzer = ctx.source_analyzer(bind_pat.syntax(), None);
     let refs = analyzer.find_all_refs(&bind_pat);
+    if refs.is_empty() {
+        return None;
+    };
 
     let mut wrap_in_parens = vec![true; refs.len()];
 
@@ -645,4 +647,16 @@ fn foo() {
 }",
         );
     }
+
+    #[test]
+    fn test_not_applicable_if_variable_unused() {
+        check_assist_not_applicable(
+            inline_local_variable,
+            "
+fn foo() {
+    let <|>a = 0;
+}
+            ",
+        )
+    }
 }

crates/ra_assists/src/handlers/introduce_variable.rs

@@ -1,5 +1,4 @@
 use format_buf::format;
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, AstNode},
     SyntaxKind::{
@@ -28,7 +27,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     var_name * 4;
 // }
 // ```
-pub(crate) fn introduce_variable(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn introduce_variable(ctx: AssistCtx) -> Option<Assist> {
     if ctx.frange.range.is_empty() {
         return None;
     }

crates/ra_assists/src/handlers/invert_if.rs

@@ -1,8 +1,7 @@
-use hir::db::HirDatabase;
 use ra_syntax::ast::{self, AstNode};
 use ra_syntax::T;
 
-use crate::{Assist, AssistCtx, AssistId};
+use crate::{utils::invert_boolean_expression, Assist, AssistCtx, AssistId};
 
 // Assist: invert_if
 //
@@ -23,7 +22,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // }
 // ```
 
-pub(crate) fn invert_if(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn invert_if(ctx: AssistCtx) -> Option<Assist> {
     let if_keyword = ctx.find_token_at_offset(T![if])?;
     let expr = ast::IfExpr::cast(if_keyword.parent())?;
     let if_range = if_keyword.text_range();
@@ -36,8 +35,8 @@ pub(crate) fn invert_if(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     let then_node = expr.then_branch()?.syntax().clone();
 
     if let ast::ElseBranch::Block(else_block) = expr.else_branch()? {
-        let flip_cond = invert_boolean_expression(&cond)?;
         let cond_range = cond.syntax().text_range();
+        let flip_cond = invert_boolean_expression(cond);
         let else_node = else_block.syntax();
         let else_range = else_node.text_range();
         let then_range = then_node.text_range();
@@ -52,20 +51,6 @@ pub(crate) fn invert_if(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
     None
 }
 
-pub(crate) fn invert_boolean_expression(expr: &ast::Expr) -> Option<ast::Expr> {
-    match expr {
-        ast::Expr::BinExpr(bin) => match bin.op_kind()? {
-            ast::BinOp::NegatedEqualityTest => bin.replace_op(T![==]).map(|it| it.into()),
-            _ => None,
-        },
-        ast::Expr::PrefixExpr(pe) => match pe.op_kind()? {
-            ast::PrefixOp::Not => pe.expr(),
-            _ => None,
-        },
-        _ => None,
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -91,12 +76,16 @@ mod tests {
     }
 
     #[test]
-    fn invert_if_doesnt_apply_with_cursor_not_on_if() {
+    fn invert_if_general_case() {
-        check_assist_not_applicable(invert_if, "fn f() { if !<|>cond { 3 * 2 } else { 1 } }")
+        check_assist(
+            invert_if,
+            "fn f() { i<|>f cond { 3 * 2 } else { 1 } }",
+            "fn f() { i<|>f !cond { 1 } else { 3 * 2 } }",
+        )
     }
 
     #[test]
-    fn invert_if_doesnt_apply_without_negated() {
+    fn invert_if_doesnt_apply_with_cursor_not_on_if() {
-        check_assist_not_applicable(invert_if, "fn f() { i<|>f cond { 3 * 2 } else { 1 } }")
+        check_assist_not_applicable(invert_if, "fn f() { if !<|>cond { 3 * 2 } else { 1 } }")
     }
 }

crates/ra_assists/src/handlers/merge_match_arms.rs

@@ -1,6 +1,11 @@
-use crate::{Assist, AssistCtx, AssistId, TextRange, TextUnit};
+use std::iter::successors;
-use hir::db::HirDatabase;
+
-use ra_syntax::ast::{AstNode, MatchArm};
+use ra_syntax::{
+    ast::{self, AstNode},
+    Direction, TextUnit,
+};
+
+use crate::{Assist, AssistCtx, AssistId, TextRange};
 
 // Assist: merge_match_arms
 //
@@ -26,61 +31,79 @@ use ra_syntax::ast::{AstNode, MatchArm};
 //     }
 // }
 // ```
-pub(crate) fn merge_match_arms(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn merge_match_arms(ctx: AssistCtx) -> Option<Assist> {
-    let current_arm = ctx.find_node_at_offset::<MatchArm>()?;
+    let current_arm = ctx.find_node_at_offset::<ast::MatchArm>()?;
-
-    // We check if the following match arm matches this one. We could, but don't,
-    // compare to the previous match arm as well.
-    let next = current_arm.syntax().next_sibling();
-    let next_arm = MatchArm::cast(next?)?;
-
     // Don't try to handle arms with guards for now - can add support for this later
-    if current_arm.guard().is_some() || next_arm.guard().is_some() {
+    if current_arm.guard().is_some() {
         return None;
     }
-
     let current_expr = current_arm.expr()?;
-    let next_expr = next_arm.expr()?;
+    let current_text_range = current_arm.syntax().text_range();
 
-    // Check for match arm equality by comparing lengths and then string contents
+    enum CursorPos {
-    if current_expr.syntax().text_range().len() != next_expr.syntax().text_range().len() {
+        InExpr(TextUnit),
+        InPat(TextUnit),
+    }
+    let cursor_pos = ctx.frange.range.start();
+    let cursor_pos = if current_expr.syntax().text_range().contains(cursor_pos) {
+        CursorPos::InExpr(current_text_range.end() - cursor_pos)
+    } else {
+        CursorPos::InPat(cursor_pos)
+    };
+
+    // We check if the following match arms match this one. We could, but don't,
+    // compare to the previous match arm as well.
+    let arms_to_merge = successors(Some(current_arm), next_arm)
+        .take_while(|arm| {
+            if arm.guard().is_some() {
+                return false;
+            }
+            match arm.expr() {
+                Some(expr) => expr.syntax().text() == current_expr.syntax().text(),
+                None => false,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    if arms_to_merge.len() <= 1 {
         return None;
     }
-    if current_expr.syntax().text() != next_expr.syntax().text() {
-        return None;
-    }
-
-    let cursor_to_end = current_arm.syntax().text_range().end() - ctx.frange.range.start();
 
     ctx.add_assist(AssistId("merge_match_arms"), "Merge match arms", |edit| {
-        fn contains_placeholder(a: &MatchArm) -> bool {
+        let pats = if arms_to_merge.iter().any(contains_placeholder) {
+            "_".into()
+        } else {
+            arms_to_merge
+                .iter()
+                .flat_map(ast::MatchArm::pats)
+                .map(|x| x.syntax().to_string())
+                .collect::<Vec<String>>()
+                .join(" | ")
+        };
+
+        let arm = format!("{} => {}", pats, current_expr.syntax().text());
+
+        let start = arms_to_merge.first().unwrap().syntax().text_range().start();
+        let end = arms_to_merge.last().unwrap().syntax().text_range().end();
+
+        edit.target(current_text_range);
+        edit.set_cursor(match cursor_pos {
+            CursorPos::InExpr(back_offset) => start + TextUnit::from_usize(arm.len()) - back_offset,
+            CursorPos::InPat(offset) => offset,
+        });
+        edit.replace(TextRange::from_to(start, end), arm);
+    })
+}
+
+fn contains_placeholder(a: &ast::MatchArm) -> bool {
     a.pats().any(|x| match x {
         ra_syntax::ast::Pat::PlaceholderPat(..) => true,
         _ => false,
     })
-        }
+}
 
-        let pats = if contains_placeholder(&current_arm) || contains_placeholder(&next_arm) {
+fn next_arm(arm: &ast::MatchArm) -> Option<ast::MatchArm> {
-            "_".into()
+    arm.syntax().siblings(Direction::Next).skip(1).find_map(ast::MatchArm::cast)
-        } else {
-            let ps: Vec<String> = current_arm
-                .pats()
-                .map(|x| x.syntax().to_string())
-                .chain(next_arm.pats().map(|x| x.syntax().to_string()))
-                .collect();
-            ps.join(" | ")
-        };
-
-        let arm = format!("{} => {}", pats, current_expr.syntax().text());
-        let offset = TextUnit::from_usize(arm.len()) - cursor_to_end;
-
-        let start = current_arm.syntax().text_range().start();
-        let end = next_arm.syntax().text_range().end();
-
-        edit.target(current_arm.syntax().text_range());
-        edit.replace(TextRange::from_to(start, end), arm);
-        edit.set_cursor(start + offset);
-    })
 }
 
 #[cfg(test)]
@@ -184,6 +207,37 @@ mod tests {
         );
     }
 
+    #[test]
+    fn merges_all_subsequent_arms() {
+        check_assist(
+            merge_match_arms,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A<|> => 92,
+                    X::B => 92,
+                    X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+            r#"
+            enum X { A, B, C, D, E }
+
+            fn main() {
+                match X::A {
+                    X::A<|> | X::B | X::C => 92,
+                    X::D => 62,
+                    _ => panic!(),
+                }
+            }
+            "#,
+        )
+    }
+
     #[test]
     fn merge_match_arms_rejects_guards() {
         check_assist_not_applicable(

crates/ra_assists/src/handlers/move_bounds.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, edit, make, AstNode, NameOwner, TypeBoundsOwner},
     SyntaxElement,
@@ -22,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     f(x)
 // }
 // ```
-pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_bounds_to_where_clause(ctx: AssistCtx) -> Option<Assist> {
     let type_param_list = ctx.find_node_at_offset::<ast::TypeParamList>()?;
 
     let mut type_params = type_param_list.type_params();

crates/ra_assists/src/handlers/move_guard.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast,
     ast::{AstNode, AstToken, IfExpr, MatchArm},
@@ -32,7 +31,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx) -> Option<Assist> {
     let match_arm = ctx.find_node_at_offset::<MatchArm>()?;
     let guard = match_arm.guard()?;
     let space_before_guard = guard.syntax().prev_sibling_or_token();
@@ -89,7 +88,7 @@ pub(crate) fn move_guard_to_arm_body(ctx: AssistCtx<impl HirDatabase>) -> Option
 //     }
 // }
 // ```
-pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn move_arm_cond_to_match_guard(ctx: AssistCtx) -> Option<Assist> {
     let match_arm: MatchArm = ctx.find_node_at_offset::<MatchArm>()?;
     let last_match_pat = match_arm.pats().last()?;
 

crates/ra_assists/src/handlers/raw_string.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast, AstToken,
     SyntaxKind::{RAW_STRING, STRING},
@@ -22,7 +21,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     r#"Hello, World!"#;
 // }
 // ```
-pub(crate) fn make_raw_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn make_raw_string(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(STRING).and_then(ast::String::cast)?;
     let value = token.value()?;
     ctx.add_assist(AssistId("make_raw_string"), "Rewrite as raw string", |edit| {
@@ -51,7 +50,7 @@ pub(crate) fn make_raw_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist
 //     "Hello, \"World!\"";
 // }
 // ```
-pub(crate) fn make_usual_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn make_usual_string(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING).and_then(ast::RawString::cast)?;
     let value = token.value()?;
     ctx.add_assist(AssistId("make_usual_string"), "Rewrite as regular string", |edit| {
@@ -77,7 +76,7 @@ pub(crate) fn make_usual_string(ctx: AssistCtx<impl HirDatabase>) -> Option<Assi
 //     r##"Hello, World!"##;
 // }
 // ```
-pub(crate) fn add_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn add_hash(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
     ctx.add_assist(AssistId("add_hash"), "Add # to raw string", |edit| {
         edit.target(token.text_range());
@@ -101,7 +100,7 @@ pub(crate) fn add_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
 //     r"Hello, World!";
 // }
 // ```
-pub(crate) fn remove_hash(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn remove_hash(ctx: AssistCtx) -> Option<Assist> {
     let token = ctx.find_token_at_offset(RAW_STRING)?;
     let text = token.text().as_str();
     if text.starts_with("r\"") {

crates/ra_assists/src/handlers/remove_dbg.rs

@@ -1,4 +1,3 @@
-use hir::db::HirDatabase;
 use ra_syntax::{
     ast::{self, AstNode},
     TextUnit, T,
@@ -21,7 +20,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     92;
 // }
 // ```
-pub(crate) fn remove_dbg(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn remove_dbg(ctx: AssistCtx) -> Option<Assist> {
     let macro_call = ctx.find_node_at_offset::<ast::MacroCall>()?;
 
     if !is_valid_macrocall(&macro_call, "dbg")? {

crates/ra_assists/src/handlers/replace_if_let_with_match.rs

@@ -1,9 +1,11 @@
-use format_buf::format;
+use ra_fmt::unwrap_trivial_block;
-use hir::db::HirDatabase;
+use ra_syntax::{
-use ra_fmt::extract_trivial_expression;
+    ast::{self, make},
-use ra_syntax::{ast, AstNode};
+    AstNode,
+};
 
 use crate::{Assist, AssistCtx, AssistId};
+use ast::edit::IndentLevel;
 
 // Assist: replace_if_let_with_match
 //
@@ -31,7 +33,7 @@ use crate::{Assist, AssistCtx, AssistId};
 //     }
 // }
 // ```
-pub(crate) fn replace_if_let_with_match(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn replace_if_let_with_match(ctx: AssistCtx) -> Option<Assist> {
     let if_expr: ast::IfExpr = ctx.find_node_at_offset()?;
     let cond = if_expr.condition()?;
     let pat = cond.pat()?;
@@ -43,34 +45,26 @@ pub(crate) fn replace_if_let_with_match(ctx: AssistCtx<impl HirDatabase>) -> Opt
     };
 
     ctx.add_assist(AssistId("replace_if_let_with_match"), "Replace with match", |edit| {
-        let match_expr = build_match_expr(expr, pat, then_block, else_block);
+        let match_expr = {
+            let then_arm = {
+                let then_expr = unwrap_trivial_block(then_block);
+                make::match_arm(vec![pat], then_expr)
+            };
+            let else_arm = {
+                let else_expr = unwrap_trivial_block(else_block);
+                make::match_arm(vec![make::placeholder_pat().into()], else_expr)
+            };
+            make::expr_match(expr, make::match_arm_list(vec![then_arm, else_arm]))
+        };
+
+        let match_expr = IndentLevel::from_node(if_expr.syntax()).increase_indent(match_expr);
+
         edit.target(if_expr.syntax().text_range());
-        edit.replace_node_and_indent(if_expr.syntax(), match_expr);
+        edit.set_cursor(if_expr.syntax().text_range().start());
-        edit.set_cursor(if_expr.syntax().text_range().start())
+        edit.replace_ast::<ast::Expr>(if_expr.into(), match_expr.into());
     })
 }
 
-fn build_match_expr(
-    expr: ast::Expr,
-    pat1: ast::Pat,
-    arm1: ast::BlockExpr,
-    arm2: ast::BlockExpr,
-) -> String {
-    let mut buf = String::new();
-    format!(buf, "match {} {{\n", expr.syntax().text());
-    format!(buf, "    {} => {}\n", pat1.syntax().text(), format_arm(&arm1));
-    format!(buf, "    _ => {}\n", format_arm(&arm2));
-    buf.push_str("}");
-    buf
-}
-
-fn format_arm(block: &ast::BlockExpr) -> String {
-    match extract_trivial_expression(block) {
-        Some(e) if !e.syntax().text().contains_char('\n') => format!("{},", e.syntax().text()),
-        _ => block.syntax().text().to_string(),
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs

@@ -1,4 +1,4 @@
-use hir::{self, db::HirDatabase};
+use hir::{self, ModPath};
 use ra_syntax::{
     ast::{self, NameOwner},
     AstNode, Direction, SmolStr,
@@ -12,18 +12,18 @@ use crate::{
     AssistId,
 };
 
-/// This function produces sequence of text edits into edit
+/// Creates and inserts a use statement for the given path to import.
-/// to import the target path in the most appropriate scope given
+/// The use statement is inserted in the scope most appropriate to the
-/// the cursor position
+/// the cursor position given, additionally merged with the existing use imports.
-pub fn auto_import_text_edit(
+pub fn insert_use_statement(
     // Ideally the position of the cursor, used to
     position: &SyntaxNode,
     // The statement to use as anchor (last resort)
     anchor: &SyntaxNode,
-    // The path to import as a sequence of strings
+    path_to_import: &ModPath,
-    target: &[SmolStr],
     edit: &mut TextEditBuilder,
 ) {
+    let target = path_to_import.to_string().split("::").map(SmolStr::new).collect::<Vec<_>>();
     let container = position.ancestors().find_map(|n| {
         if let Some(module) = ast::Module::cast(n.clone()) {
             return module.item_list().map(|it| it.syntax().clone());
@@ -32,14 +32,14 @@ pub fn auto_import_text_edit(
     });
 
     if let Some(container) = container {
-        let action = best_action_for_target(container, anchor.clone(), target);
+        let action = best_action_for_target(container, anchor.clone(), &target);
-        make_assist(&action, target, edit);
+        make_assist(&action, &target, edit);
     }
 }
 
-// Assist: add_import
+// Assist: replace_qualified_name_with_use
 //
-// Adds a use statement for a given fully-qualified path.
+// Adds a use statement for a given fully-qualified name.
 //
 // ```
 // fn process(map: std::collections::<|>HashMap<String, String>) {}
@@ -50,7 +50,7 @@ pub fn auto_import_text_edit(
 //
 // fn process(map: HashMap<String, String>) {}
 // ```
-pub(crate) fn add_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn replace_qualified_name_with_use(ctx: AssistCtx) -> Option<Assist> {
     let path: ast::Path = ctx.find_node_at_offset()?;
     // We don't want to mess with use statements
     if path.syntax().ancestors().find_map(ast::UseItem::cast).is_some() {
@@ -72,9 +72,13 @@ pub(crate) fn add_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("add_import"), format!("Import {}", fmt_segments(&segments)), |edit| {
+    ctx.add_assist(
-        apply_auto_import(&position, &path, &segments, edit.text_edit_builder());
+        AssistId("replace_qualified_name_with_use"),
-    })
+        "Replace qualified path with use",
+        |edit| {
+            replace_with_use(&position, &path, &segments, edit.text_edit_builder());
+        },
+    )
 }
 
 fn collect_path_segments_raw(
@@ -107,12 +111,6 @@ fn collect_path_segments_raw(
     Some(segments.len() - oldlen)
 }
 
-fn fmt_segments(segments: &[SmolStr]) -> String {
-    let mut buf = String::new();
-    fmt_segments_raw(segments, &mut buf);
-    buf
-}
-
 fn fmt_segments_raw(segments: &[SmolStr], buf: &mut String) {
     let mut iter = segments.iter();
     if let Some(s) = iter.next() {
@@ -558,7 +556,7 @@ fn make_assist_add_nested_import(
     }
 }
 
-fn apply_auto_import(
+fn replace_with_use(
     container: &SyntaxNode,
     path: &ast::Path,
     target: &[SmolStr],
@@ -603,9 +601,9 @@ mod tests {
     use super::*;
 
     #[test]
-    fn test_auto_import_add_use_no_anchor() {
+    fn test_replace_add_use_no_anchor() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 std::fmt::Debug<|>
     ",
@@ -617,9 +615,9 @@ Debug<|>
         );
     }
     #[test]
-    fn test_auto_import_add_use_no_anchor_with_item_below() {
+    fn test_replace_add_use_no_anchor_with_item_below() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 std::fmt::Debug<|>
 
@@ -638,9 +636,9 @@ fn main() {
     }
 
     #[test]
-    fn test_auto_import_add_use_no_anchor_with_item_above() {
+    fn test_replace_add_use_no_anchor_with_item_above() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 fn main() {
 }
@@ -659,9 +657,9 @@ Debug<|>
     }
 
     #[test]
-    fn test_auto_import_add_use_no_anchor_2seg() {
+    fn test_replace_add_use_no_anchor_2seg() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 std::fmt<|>::Debug
     ",
@@ -674,9 +672,9 @@ fmt<|>::Debug
     }
 
     #[test]
-    fn test_auto_import_add_use() {
+    fn test_replace_add_use() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use stdx;
 
@@ -694,9 +692,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_file_use_other_anchor() {
+    fn test_replace_file_use_other_anchor() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 impl std::fmt::Debug<|> for Foo {
 }
@@ -711,9 +709,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_add_use_other_anchor_indent() {
+    fn test_replace_add_use_other_anchor_indent() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
     impl std::fmt::Debug<|> for Foo {
     }
@@ -728,9 +726,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_split_different() {
+    fn test_replace_split_different() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt;
 
@@ -747,9 +745,9 @@ impl io<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_split_self_for_use() {
+    fn test_replace_split_self_for_use() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt;
 
@@ -766,9 +764,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_split_self_for_target() {
+    fn test_replace_split_self_for_target() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::Debug;
 
@@ -785,9 +783,9 @@ impl fmt<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_add_to_nested_self_nested() {
+    fn test_replace_add_to_nested_self_nested() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::{Debug, nested::{Display}};
 
@@ -804,9 +802,9 @@ impl nested<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_add_to_nested_self_already_included() {
+    fn test_replace_add_to_nested_self_already_included() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::{Debug, nested::{self, Display}};
 
@@ -823,9 +821,9 @@ impl nested<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_add_to_nested_nested() {
+    fn test_replace_add_to_nested_nested() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::{Debug, nested::{Display}};
 
@@ -842,9 +840,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_split_common_target_longer() {
+    fn test_replace_split_common_target_longer() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::Debug;
 
@@ -861,9 +859,9 @@ impl Display<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_split_common_use_longer() {
+    fn test_replace_split_common_use_longer() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt::nested::Debug;
 
@@ -880,9 +878,9 @@ impl Display<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_use_nested_import() {
+    fn test_replace_use_nested_import() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use crate::{
     ty::{Substs, Ty},
@@ -903,9 +901,9 @@ fn foo() { lower<|>::trait_env() }
     }
 
     #[test]
-    fn test_auto_import_alias() {
+    fn test_replace_alias() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt as foo;
 
@@ -922,9 +920,9 @@ impl Debug<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_not_applicable_one_segment() {
+    fn test_replace_not_applicable_one_segment() {
         check_assist_not_applicable(
-            add_import,
+            replace_qualified_name_with_use,
             "
 impl foo<|> for Foo {
 }
@@ -933,9 +931,9 @@ impl foo<|> for Foo {
     }
 
     #[test]
-    fn test_auto_import_not_applicable_in_use() {
+    fn test_replace_not_applicable_in_use() {
         check_assist_not_applicable(
-            add_import,
+            replace_qualified_name_with_use,
             "
 use std::fmt<|>;
 ",
@@ -943,9 +941,9 @@ use std::fmt<|>;
     }
 
     #[test]
-    fn test_auto_import_add_use_no_anchor_in_mod_mod() {
+    fn test_replace_add_use_no_anchor_in_mod_mod() {
         check_assist(
-            add_import,
+            replace_qualified_name_with_use,
             "
 mod foo {
     mod bar {

crates/ra_assists/src/handlers/split_import.rs

@@ -1,6 +1,5 @@
 use std::iter::successors;
 
-use hir::db::HirDatabase;
 use ra_syntax::{ast, AstNode, TextUnit, T};
 
 use crate::{Assist, AssistCtx, AssistId};
@@ -16,7 +15,7 @@ use crate::{Assist, AssistCtx, AssistId};
 // ```
 // use std::{collections::HashMap};
 // ```
-pub(crate) fn split_import(ctx: AssistCtx<impl HirDatabase>) -> Option<Assist> {
+pub(crate) fn split_import(ctx: AssistCtx) -> Option<Assist> {
     let colon_colon = ctx.find_token_at_offset(T![::])?;
     let path = ast::Path::cast(colon_colon.parent())?;
     let top_path = successors(Some(path), |it| it.parent_path()).last()?;

crates/ra_assists/src/lib.rs

@@ -9,18 +9,16 @@ mod assist_ctx;
 mod marks;
 #[cfg(test)]
 mod doc_tests;
-#[cfg(test)]
+mod utils;
-mod test_db;
 pub mod ast_transform;
 
-use either::Either;
-use hir::db::HirDatabase;
 use ra_db::FileRange;
+use ra_ide_db::RootDatabase;
 use ra_syntax::{TextRange, TextUnit};
 use ra_text_edit::TextEdit;
 
-pub(crate) use crate::assist_ctx::{Assist, AssistCtx};
+pub(crate) use crate::assist_ctx::{Assist, AssistCtx, AssistHandler};
-pub use crate::assists::add_import::auto_import_text_edit;
+pub use crate::handlers::replace_qualified_name_with_use::insert_use_statement;
 
 /// Unique identifier of the assist, should not be shown to the user
 /// directly.
@@ -34,81 +32,64 @@ pub struct AssistLabel {
     pub id: AssistId,
 }
 
+#[derive(Clone, Debug)]
+pub struct GroupLabel(pub String);
+
+impl AssistLabel {
+    pub(crate) fn new(label: String, id: AssistId) -> AssistLabel {
+        // FIXME: make fields private, so that this invariant can't be broken
+        assert!(label.chars().nth(0).unwrap().is_uppercase());
+        AssistLabel { label: label.into(), id }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct AssistAction {
-    pub label: Option<String>,
     pub edit: TextEdit,
     pub cursor_position: Option<TextUnit>,
+    // FIXME: This belongs to `AssistLabel`
     pub target: Option<TextRange>,
 }
 
 #[derive(Debug, Clone)]
 pub struct ResolvedAssist {
     pub label: AssistLabel,
-    pub action_data: Either<AssistAction, Vec<AssistAction>>,
+    pub group_label: Option<GroupLabel>,
-}
+    pub action: AssistAction,
-
-impl ResolvedAssist {
-    pub fn get_first_action(&self) -> AssistAction {
-        match &self.action_data {
-            Either::Left(action) => action.clone(),
-            Either::Right(actions) => actions[0].clone(),
-        }
-    }
 }
 
 /// Return all the assists applicable at the given position.
 ///
 /// Assists are returned in the "unresolved" state, that is only labels are
 /// returned, without actual edits.
-pub fn applicable_assists<H>(db: &H, range: FileRange) -> Vec<AssistLabel>
+pub fn unresolved_assists(db: &RootDatabase, range: FileRange) -> Vec<AssistLabel> {
-where
+    let ctx = AssistCtx::new(db, range, false);
-    H: HirDatabase + 'static,
+    handlers::all()
-{
-    AssistCtx::with_ctx(db, range, false, |ctx| {
-        assists::all()
         .iter()
         .filter_map(|f| f(ctx.clone()))
-            .map(|a| match a {
+        .flat_map(|it| it.0)
-                Assist::Unresolved { label } => label,
+        .map(|a| a.label)
-                Assist::Resolved { .. } => unreachable!(),
-            })
         .collect()
-    })
 }
 
 /// Return all the assists applicable at the given position.
 ///
 /// Assists are returned in the "resolved" state, that is with edit fully
 /// computed.
-pub fn assists<H>(db: &H, range: FileRange) -> Vec<ResolvedAssist>
+pub fn resolved_assists(db: &RootDatabase, range: FileRange) -> Vec<ResolvedAssist> {
-where
+    let ctx = AssistCtx::new(db, range, true);
-    H: HirDatabase + 'static,
+    let mut a = handlers::all()
-{
-    use std::cmp::Ordering;
-
-    AssistCtx::with_ctx(db, range, true, |ctx| {
-        let mut a = assists::all()
         .iter()
         .filter_map(|f| f(ctx.clone()))
-            .map(|a| match a {
+        .flat_map(|it| it.0)
-                Assist::Resolved { assist } => assist,
+        .map(|it| it.into_resolved().unwrap())
-                Assist::Unresolved { .. } => unreachable!(),
-            })
         .collect::<Vec<_>>();
-        a.sort_by(|a, b| match (a.get_first_action().target, b.get_first_action().target) {
+    a.sort_by_key(|it| it.action.target.map_or(TextUnit::from(!0u32), |it| it.len()));
-            (Some(a), Some(b)) => a.len().cmp(&b.len()),
-            (Some(_), None) => Ordering::Less,
-            (None, Some(_)) => Ordering::Greater,
-            (None, None) => Ordering::Equal,
-        });
     a
-    })
 }
 
-mod assists {
+mod handlers {
-    use crate::{Assist, AssistCtx};
+    use crate::AssistHandler;
-    use hir::db::HirDatabase;
 
     mod add_derive;
     mod add_explicit_type;
@@ -116,6 +97,7 @@ mod assists {
     mod add_custom_impl;
     mod add_new;
     mod apply_demorgan;
+    mod auto_import;
     mod invert_if;
     mod flip_comma;
     mod flip_binexpr;
@@ -129,13 +111,13 @@ mod assists {
     mod replace_if_let_with_match;
     mod split_import;
     mod remove_dbg;
-    pub(crate) mod add_import;
+    pub(crate) mod replace_qualified_name_with_use;
     mod add_missing_impl_members;
     mod move_guard;
     mod move_bounds;
     mod early_return;
 
-    pub(crate) fn all<DB: HirDatabase>() -> &'static [fn(AssistCtx<DB>) -> Option<Assist>] {
+    pub(crate) fn all() -> &'static [AssistHandler] {
         &[
             add_derive::add_derive,
             add_explicit_type::add_explicit_type,
@@ -154,7 +136,7 @@ mod assists {
             replace_if_let_with_match::replace_if_let_with_match,
             split_import::split_import,
             remove_dbg::remove_dbg,
-            add_import::add_import,
+            replace_qualified_name_with_use::replace_qualified_name_with_use,
             add_missing_impl_members::add_missing_impl_members,
             add_missing_impl_members::add_missing_default_members,
             inline_local_variable::inline_local_variable,
@@ -166,33 +148,39 @@ mod assists {
             raw_string::make_usual_string,
             raw_string::remove_hash,
             early_return::convert_to_guarded_return,
+            auto_import::auto_import,
         ]
     }
 }
 
 #[cfg(test)]
 mod helpers {
-    use ra_db::{fixture::WithFixture, FileRange};
+    use std::sync::Arc;
+
+    use ra_db::{fixture::WithFixture, FileId, FileRange, SourceDatabaseExt};
+    use ra_ide_db::{symbol_index::SymbolsDatabase, RootDatabase};
     use ra_syntax::TextRange;
     use test_utils::{add_cursor, assert_eq_text, extract_offset, extract_range};
 
-    use crate::{test_db::TestDB, Assist, AssistCtx};
+    use crate::{AssistCtx, AssistHandler};
 
-    pub(crate) fn check_assist(
+    pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
+        let (mut db, file_id) = RootDatabase::with_single_file(text);
-        before: &str,
+        // FIXME: ideally, this should be done by the above `RootDatabase::with_single_file`,
-        after: &str,
+        // but it looks like this might need specialization? :(
-    ) {
+        let local_roots = vec![db.file_source_root(file_id)];
+        db.set_local_roots(Arc::new(local_roots));
+        (db, file_id)
+    }
+
+    pub(crate) fn check_assist(assist: AssistHandler, before: &str, after: &str) {
         let (before_cursor_pos, before) = extract_offset(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange =
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
         let assist =
-            AssistCtx::with_ctx(&db, frange, true, assist).expect("code action is not applicable");
+            assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
+        let action = assist.0[0].action.clone().unwrap();
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
 
         let actual = action.edit.apply(&before);
         let actual_cursor_pos = match action.cursor_position {
@@ -206,20 +194,13 @@ mod helpers {
         assert_eq_text!(after, &actual);
     }
 
-    pub(crate) fn check_assist_range(
+    pub(crate) fn check_assist_range(assist: AssistHandler, before: &str, after: &str) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
-        before: &str,
-        after: &str,
-    ) {
         let (range, before) = extract_range(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange = FileRange { file_id, range };
         let assist =
-            AssistCtx::with_ctx(&db, frange, true, assist).expect("code action is not applicable");
+            assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
+        let action = assist.0[0].action.clone().unwrap();
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
 
         let mut actual = action.edit.apply(&before);
         if let Some(pos) = action.cursor_position {
@@ -228,85 +209,65 @@ mod helpers {
         assert_eq_text!(after, &actual);
     }
 
-    pub(crate) fn check_assist_target(
+    pub(crate) fn check_assist_target(assist: AssistHandler, before: &str, target: &str) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
-        before: &str,
-        target: &str,
-    ) {
         let (before_cursor_pos, before) = extract_offset(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange =
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
         let assist =
-            AssistCtx::with_ctx(&db, frange, true, assist).expect("code action is not applicable");
+            assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
+        let action = assist.0[0].action.clone().unwrap();
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
 
         let range = action.target.expect("expected target on action");
         assert_eq_text!(&before[range.start().to_usize()..range.end().to_usize()], target);
     }
 
-    pub(crate) fn check_assist_range_target(
+    pub(crate) fn check_assist_range_target(assist: AssistHandler, before: &str, target: &str) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
-        before: &str,
-        target: &str,
-    ) {
         let (range, before) = extract_range(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange = FileRange { file_id, range };
         let assist =
-            AssistCtx::with_ctx(&db, frange, true, assist).expect("code action is not applicable");
+            assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
+        let action = assist.0[0].action.clone().unwrap();
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
 
         let range = action.target.expect("expected target on action");
         assert_eq_text!(&before[range.start().to_usize()..range.end().to_usize()], target);
     }
 
-    pub(crate) fn check_assist_not_applicable(
+    pub(crate) fn check_assist_not_applicable(assist: AssistHandler, before: &str) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
-        before: &str,
-    ) {
         let (before_cursor_pos, before) = extract_offset(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange =
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
-        let assist = AssistCtx::with_ctx(&db, frange, true, assist);
+        let assist = assist(AssistCtx::new(&db, frange, true));
         assert!(assist.is_none());
     }
 
-    pub(crate) fn check_assist_range_not_applicable(
+    pub(crate) fn check_assist_range_not_applicable(assist: AssistHandler, before: &str) {
-        assist: fn(AssistCtx<TestDB>) -> Option<Assist>,
-        before: &str,
-    ) {
         let (range, before) = extract_range(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = with_single_file(&before);
         let frange = FileRange { file_id, range };
-        let assist = AssistCtx::with_ctx(&db, frange, true, assist);
+        let assist = assist(AssistCtx::new(&db, frange, true));
         assert!(assist.is_none());
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use ra_db::{fixture::WithFixture, FileRange};
+    use ra_db::FileRange;
     use ra_syntax::TextRange;
     use test_utils::{extract_offset, extract_range};
 
-    use crate::test_db::TestDB;
+    use crate::{helpers, resolved_assists};
 
     #[test]
     fn assist_order_field_struct() {
         let before = "struct Foo { <|>bar: u32 }";
         let (before_cursor_pos, before) = extract_offset(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = helpers::with_single_file(&before);
         let frange =
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
-        let assists = super::assists(&db, frange);
+        let assists = resolved_assists(&db, frange);
         let mut assists = assists.iter();
 
         assert_eq!(
@@ -327,9 +288,9 @@ mod tests {
             }
         }";
         let (range, before) = extract_range(before);
-        let (db, file_id) = TestDB::with_single_file(&before);
+        let (db, file_id) = helpers::with_single_file(&before);
         let frange = FileRange { file_id, range };
-        let assists = super::assists(&db, frange);
+        let assists = resolved_assists(&db, frange);
         let mut assists = assists.iter();
 
         assert_eq!(assists.next().expect("expected assist").label.label, "Extract into variable");

crates/ra_assists/src/test_db.rs

@@ -1,45 +0,0 @@
-//! Database used for testing `ra_assists`.
-
-use std::sync::Arc;
-
-use ra_db::{salsa, CrateId, FileId, FileLoader, FileLoaderDelegate, RelativePath};
-
-#[salsa::database(
-    ra_db::SourceDatabaseExtStorage,
-    ra_db::SourceDatabaseStorage,
-    hir::db::InternDatabaseStorage,
-    hir::db::AstDatabaseStorage,
-    hir::db::DefDatabaseStorage,
-    hir::db::HirDatabaseStorage
-)]
-#[derive(Debug, Default)]
-pub struct TestDB {
-    runtime: salsa::Runtime<TestDB>,
-}
-
-impl salsa::Database for TestDB {
-    fn salsa_runtime(&self) -> &salsa::Runtime<Self> {
-        &self.runtime
-    }
-    fn salsa_runtime_mut(&mut self) -> &mut salsa::Runtime<Self> {
-        &mut self.runtime
-    }
-}
-
-impl std::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_relative_path(
-        &self,
-        anchor: FileId,
-        relative_path: &RelativePath,
-    ) -> Option<FileId> {
-        FileLoaderDelegate(self).resolve_relative_path(anchor, relative_path)
-    }
-    fn relevant_crates(&self, file_id: FileId) -> Arc<Vec<CrateId>> {
-        FileLoaderDelegate(self).relevant_crates(file_id)
-    }
-}

crates/ra_assists/src/utils.rs

@@ -0,0 +1,27 @@
+//! Assorted functions shared by several assists.
+
+use ra_syntax::{
+    ast::{self, make},
+    T,
+};
+
+pub(crate) fn invert_boolean_expression(expr: ast::Expr) -> ast::Expr {
+    if let Some(expr) = invert_special_case(&expr) {
+        return expr;
+    }
+    make::expr_prefix(T![!], expr)
+}
+
+fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
+    match expr {
+        ast::Expr::BinExpr(bin) => match bin.op_kind()? {
+            ast::BinOp::NegatedEqualityTest => bin.replace_op(T![==]).map(|it| it.into()),
+            ast::BinOp::EqualityTest => bin.replace_op(T![!=]).map(|it| it.into()),
+            _ => None,
+        },
+        ast::Expr::PrefixExpr(pe) if pe.op_kind()? == ast::PrefixOp::Not => pe.expr(),
+        // FIXME:
+        // ast::Expr::Literal(true | false )
+        _ => None,
+    }
+}

crates/ra_cargo_watch/Cargo.toml

@@ -11,7 +11,8 @@ log = "0.4.3"
 cargo_metadata = "0.9.1"
 jod-thread = "0.1.0"
 parking_lot = "0.10.0"
+serde_json = "1.0.45"
 
 [dev-dependencies]
-insta = "0.12.0"
+insta = "0.13.0"
 serde_json = "1.0"

crates/ra_cargo_watch/src/conv.rs

@@ -1,12 +1,11 @@
 //! This module provides the functionality needed to convert diagnostics from
 //! `cargo check` json format to the LSP diagnostic format.
 use cargo_metadata::diagnostic::{
-    Applicability, Diagnostic as RustDiagnostic, DiagnosticLevel, DiagnosticSpan,
+    Diagnostic as RustDiagnostic, DiagnosticLevel, DiagnosticSpan, DiagnosticSpanMacroExpansion,
-    DiagnosticSpanMacroExpansion,
 };
 use lsp_types::{
-    Diagnostic, DiagnosticRelatedInformation, DiagnosticSeverity, DiagnosticTag, Location,
+    CodeAction, Diagnostic, DiagnosticRelatedInformation, DiagnosticSeverity, DiagnosticTag,
-    NumberOrString, Position, Range, Url,
+    Location, NumberOrString, Position, Range, TextEdit, Url, WorkspaceEdit,
 };
 use std::{
     fmt::Write,
@@ -117,38 +116,9 @@ fn is_deprecated(rd: &RustDiagnostic) -> bool {
     }
 }
 
-#[derive(Debug)]
-pub struct SuggestedFix {
-    pub title: String,
-    pub location: Location,
-    pub replacement: String,
-    pub applicability: Applicability,
-    pub diagnostics: Vec<Diagnostic>,
-}
-
-impl std::cmp::PartialEq<SuggestedFix> for SuggestedFix {
-    fn eq(&self, other: &SuggestedFix) -> bool {
-        if self.title == other.title
-            && self.location == other.location
-            && self.replacement == other.replacement
-        {
-            // Applicability doesn't impl PartialEq...
-            match (&self.applicability, &other.applicability) {
-                (Applicability::MachineApplicable, Applicability::MachineApplicable) => true,
-                (Applicability::HasPlaceholders, Applicability::HasPlaceholders) => true,
-                (Applicability::MaybeIncorrect, Applicability::MaybeIncorrect) => true,
-                (Applicability::Unspecified, Applicability::Unspecified) => true,
-                _ => false,
-            }
-        } else {
-            false
-        }
-    }
-}
-
 enum MappedRustChildDiagnostic {
     Related(DiagnosticRelatedInformation),
-    SuggestedFix(SuggestedFix),
+    SuggestedFix(CodeAction),
     MessageLine(String),
 }
 
@@ -176,12 +146,20 @@ fn map_rust_child_diagnostic(
             rd.message.clone()
         };
 
-        MappedRustChildDiagnostic::SuggestedFix(SuggestedFix {
+        let edit = {
+            let edits = vec![TextEdit::new(location.range, suggested_replacement.clone())];
+            let mut edit_map = std::collections::HashMap::new();
+            edit_map.insert(location.uri, edits);
+            WorkspaceEdit::new(edit_map)
+        };
+
+        MappedRustChildDiagnostic::SuggestedFix(CodeAction {
             title,
-            location,
+            kind: Some("quickfix".to_string()),
-            replacement: suggested_replacement.clone(),
+            diagnostics: None,
-            applicability: span.suggestion_applicability.clone().unwrap_or(Applicability::Unknown),
+            edit: Some(edit),
-            diagnostics: vec![],
+            command: None,
+            is_preferred: None,
         })
     } else {
         MappedRustChildDiagnostic::Related(DiagnosticRelatedInformation {
@@ -195,7 +173,7 @@ fn map_rust_child_diagnostic(
 pub(crate) struct MappedRustDiagnostic {
     pub location: Location,
     pub diagnostic: Diagnostic,
-    pub suggested_fixes: Vec<SuggestedFix>,
+    pub fixes: Vec<CodeAction>,
 }
 
 /// Converts a Rust root diagnostic to LSP form
@@ -250,15 +228,13 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         }
     }
 
-    let mut suggested_fixes = vec![];
+    let mut fixes = vec![];
     let mut message = rd.message.clone();
     for child in &rd.children {
         let child = map_rust_child_diagnostic(&child, workspace_root);
         match child {
             MappedRustChildDiagnostic::Related(related) => related_information.push(related),
-            MappedRustChildDiagnostic::SuggestedFix(suggested_fix) => {
+            MappedRustChildDiagnostic::SuggestedFix(code_action) => fixes.push(code_action.into()),
-                suggested_fixes.push(suggested_fix)
-            }
             MappedRustChildDiagnostic::MessageLine(message_line) => {
                 write!(&mut message, "\n{}", message_line).unwrap();
 
@@ -295,7 +271,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
         tags: if !tags.is_empty() { Some(tags) } else { None },
     };
 
-    Some(MappedRustDiagnostic { location, diagnostic, suggested_fixes })
+    Some(MappedRustDiagnostic { location, diagnostic, fixes })
 }
 
 /// Returns a `Url` object from a given path, will lowercase drive letters if present.

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_clippy_pass_by_ref.snap

@@ -61,11 +61,19 @@ MappedRustDiagnostic {
         ),
         tags: None,
     },
-    suggested_fixes: [
+    fixes: [
-        SuggestedFix {
+        CodeAction {
             title: "consider passing by value instead: \'self\'",
-            location: Location {
+            kind: Some(
-                uri: "file:///test/compiler/mir/tagset.rs",
+                "quickfix",
+            ),
+            diagnostics: None,
+            edit: Some(
+                WorkspaceEdit {
+                    changes: Some(
+                        {
+                            "file:///test/compiler/mir/tagset.rs": [
+                                TextEdit {
                                     range: Range {
                                         start: Position {
                                             line: 41,
@@ -76,10 +84,16 @@ MappedRustDiagnostic {
                                             character: 28,
                                         },
                                     },
+                                    new_text: "self",
                                 },
-            replacement: "self",
+                            ],
-            applicability: Unspecified,
+                        },
-            diagnostics: [],
+                    ),
+                    document_changes: None,
+                },
+            ),
+            command: None,
+            is_preferred: None,
         },
     ],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_handles_macro_location.snap

@@ -42,5 +42,5 @@ MappedRustDiagnostic {
         related_information: None,
         tags: None,
     },
-    suggested_fixes: [],
+    fixes: [],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_macro_compiler_error.snap

@@ -57,5 +57,5 @@ MappedRustDiagnostic {
         ),
         tags: None,
     },
-    suggested_fixes: [],
+    fixes: [],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_incompatible_type_for_trait.snap

@@ -42,5 +42,5 @@ MappedRustDiagnostic {
         related_information: None,
         tags: None,
     },
-    suggested_fixes: [],
+    fixes: [],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_mismatched_type.snap

@@ -42,5 +42,5 @@ MappedRustDiagnostic {
         related_information: None,
         tags: None,
     },
-    suggested_fixes: [],
+    fixes: [],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_unused_variable.snap

@@ -46,11 +46,19 @@ MappedRustDiagnostic {
             ],
         ),
     },
-    suggested_fixes: [
+    fixes: [
-        SuggestedFix {
+        CodeAction {
             title: "consider prefixing with an underscore: \'_foo\'",
-            location: Location {
+            kind: Some(
-                uri: "file:///test/driver/subcommand/repl.rs",
+                "quickfix",
+            ),
+            diagnostics: None,
+            edit: Some(
+                WorkspaceEdit {
+                    changes: Some(
+                        {
+                            "file:///test/driver/subcommand/repl.rs": [
+                                TextEdit {
                                     range: Range {
                                         start: Position {
                                             line: 290,
@@ -61,10 +69,16 @@ MappedRustDiagnostic {
                                             character: 11,
                                         },
                                     },
+                                    new_text: "_foo",
                                 },
-            replacement: "_foo",
+                            ],
-            applicability: MachineApplicable,
+                        },
-            diagnostics: [],
+                    ),
+                    document_changes: None,
+                },
+            ),
+            command: None,
+            is_preferred: None,
         },
     ],
 }

crates/ra_cargo_watch/src/conv/snapshots/ra_cargo_watch__conv__test__snap_rustc_wrong_number_of_parameters.snap

@@ -61,5 +61,5 @@ MappedRustDiagnostic {
         ),
         tags: None,
     },
-    suggested_fixes: [],
+    fixes: [],
 }

crates/ra_cargo_watch/src/lib.rs

@@ -4,22 +4,20 @@
 use cargo_metadata::Message;
 use crossbeam_channel::{never, select, unbounded, Receiver, RecvError, Sender};
 use lsp_types::{
-    Diagnostic, Url, WorkDoneProgress, WorkDoneProgressBegin, WorkDoneProgressEnd,
+    CodeAction, CodeActionOrCommand, Diagnostic, Url, WorkDoneProgress, WorkDoneProgressBegin,
-    WorkDoneProgressReport,
+    WorkDoneProgressEnd, WorkDoneProgressReport,
 };
-use parking_lot::RwLock;
 use std::{
-    collections::HashMap,
+    io::{BufRead, BufReader},
     path::PathBuf,
     process::{Command, Stdio},
-    sync::Arc,
     thread::JoinHandle,
     time::Instant,
 };
 
 mod conv;
 
-use crate::conv::{map_rust_diagnostic_to_lsp, MappedRustDiagnostic, SuggestedFix};
+use crate::conv::{map_rust_diagnostic_to_lsp, MappedRustDiagnostic};
 
 pub use crate::conv::url_from_path_with_drive_lowercasing;
 
@@ -38,7 +36,6 @@ pub struct CheckOptions {
 #[derive(Debug)]
 pub struct CheckWatcher {
     pub task_recv: Receiver<CheckTask>,
-    pub state: Arc<RwLock<CheckState>>,
     cmd_send: Option<Sender<CheckCommand>>,
     handle: Option<JoinHandle<()>>,
 }
@@ -46,7 +43,6 @@ pub struct CheckWatcher {
 impl CheckWatcher {
     pub fn new(options: &CheckOptions, workspace_root: PathBuf) -> CheckWatcher {
         let options = options.clone();
-        let state = Arc::new(RwLock::new(CheckState::new()));
 
         let (task_send, task_recv) = unbounded::<CheckTask>();
         let (cmd_send, cmd_recv) = unbounded::<CheckCommand>();
@@ -54,13 +50,12 @@ impl CheckWatcher {
             let mut check = CheckWatcherThread::new(options, workspace_root);
             check.run(&task_send, &cmd_recv);
         });
-        CheckWatcher { task_recv, cmd_send: Some(cmd_send), handle: Some(handle), state }
+        CheckWatcher { task_recv, cmd_send: Some(cmd_send), handle: Some(handle) }
     }
 
     /// Returns a CheckWatcher that doesn't actually do anything
     pub fn dummy() -> CheckWatcher {
-        let state = Arc::new(RwLock::new(CheckState::new()));
+        CheckWatcher { task_recv: never(), cmd_send: None, handle: None }
-        CheckWatcher { task_recv: never(), cmd_send: None, handle: None, state }
     }
 
     /// Schedule a re-start of the cargo check worker.
@@ -87,84 +82,13 @@ impl std::ops::Drop for CheckWatcher {
     }
 }
 
-#[derive(Debug)]
-pub struct CheckState {
-    diagnostic_collection: HashMap<Url, Vec<Diagnostic>>,
-    suggested_fix_collection: HashMap<Url, Vec<SuggestedFix>>,
-}
-
-impl CheckState {
-    fn new() -> CheckState {
-        CheckState {
-            diagnostic_collection: HashMap::new(),
-            suggested_fix_collection: HashMap::new(),
-        }
-    }
-
-    /// Clear the cached diagnostics, and schedule updating diagnostics by the
-    /// server, to clear stale results.
-    pub fn clear(&mut self) -> Vec<Url> {
-        let cleared_files: Vec<Url> = self.diagnostic_collection.keys().cloned().collect();
-        self.diagnostic_collection.clear();
-        self.suggested_fix_collection.clear();
-        cleared_files
-    }
-
-    pub fn diagnostics_for(&self, uri: &Url) -> Option<&[Diagnostic]> {
-        self.diagnostic_collection.get(uri).map(|d| d.as_slice())
-    }
-
-    pub fn fixes_for(&self, uri: &Url) -> Option<&[SuggestedFix]> {
-        self.suggested_fix_collection.get(uri).map(|d| d.as_slice())
-    }
-
-    pub fn add_diagnostic_with_fixes(&mut self, file_uri: Url, diagnostic: DiagnosticWithFixes) {
-        for fix in diagnostic.suggested_fixes {
-            self.add_suggested_fix_for_diagnostic(fix, &diagnostic.diagnostic);
-        }
-        self.add_diagnostic(file_uri, diagnostic.diagnostic);
-    }
-
-    fn add_diagnostic(&mut self, file_uri: Url, diagnostic: Diagnostic) {
-        let diagnostics = self.diagnostic_collection.entry(file_uri).or_default();
-
-        // If we're building multiple targets it's possible we've already seen this diagnostic
-        let is_duplicate = diagnostics.iter().any(|d| are_diagnostics_equal(d, &diagnostic));
-        if is_duplicate {
-            return;
-        }
-
-        diagnostics.push(diagnostic);
-    }
-
-    fn add_suggested_fix_for_diagnostic(
-        &mut self,
-        mut suggested_fix: SuggestedFix,
-        diagnostic: &Diagnostic,
-    ) {
-        let file_uri = suggested_fix.location.uri.clone();
-        let file_suggestions = self.suggested_fix_collection.entry(file_uri).or_default();
-
-        let existing_suggestion: Option<&mut SuggestedFix> =
-            file_suggestions.iter_mut().find(|s| s == &&suggested_fix);
-        if let Some(existing_suggestion) = existing_suggestion {
-            // The existing suggestion also applies to this new diagnostic
-            existing_suggestion.diagnostics.push(diagnostic.clone());
-        } else {
-            // We haven't seen this suggestion before
-            suggested_fix.diagnostics.push(diagnostic.clone());
-            file_suggestions.push(suggested_fix);
-        }
-    }
-}
-
 #[derive(Debug)]
 pub enum CheckTask {
     /// Request a clearing of all cached diagnostics from the check watcher
     ClearDiagnostics,
 
     /// Request adding a diagnostic with fixes included to a file
-    AddDiagnostic(Url, DiagnosticWithFixes),
+    AddDiagnostic { url: Url, diagnostic: Diagnostic, fixes: Vec<CodeActionOrCommand> },
 
     /// Request check progress notification to client
     Status(WorkDoneProgress),
@@ -216,8 +140,10 @@ impl CheckWatcherThread {
                 self.last_update_req.take();
                 task_send.send(CheckTask::ClearDiagnostics).unwrap();
 
-                // By replacing the watcher, we drop the previous one which
+                // Replace with a dummy watcher first so we drop the original and wait for completion
-                // causes it to shut down automatically.
+                std::mem::replace(&mut self.watcher, WatchThread::dummy());
+
+                // Then create the actual new watcher
                 self.watcher = WatchThread::new(&self.options, &self.workspace_root);
             }
         }
@@ -277,10 +203,17 @@ impl CheckWatcherThread {
                         None => return,
                     };
 
-                let MappedRustDiagnostic { location, diagnostic, suggested_fixes } = map_result;
+                let MappedRustDiagnostic { location, diagnostic, fixes } = map_result;
+                let fixes = fixes
+                    .into_iter()
+                    .map(|fix| {
+                        CodeAction { diagnostics: Some(vec![diagnostic.clone()]), ..fix }.into()
+                    })
+                    .collect();
 
-                let diagnostic = DiagnosticWithFixes { diagnostic, suggested_fixes };
+                task_send
-                task_send.send(CheckTask::AddDiagnostic(location.uri, diagnostic)).unwrap();
+                    .send(CheckTask::AddDiagnostic { url: location.uri, diagnostic, fixes })
+                    .unwrap();
             }
 
             CheckEvent::Msg(Message::BuildScriptExecuted(_msg)) => {}
@@ -292,7 +225,7 @@ impl CheckWatcherThread {
 #[derive(Debug)]
 pub struct DiagnosticWithFixes {
     diagnostic: Diagnostic,
-    suggested_fixes: Vec<SuggestedFix>,
+    fixes: Vec<CodeAction>,
 }
 
 /// WatchThread exists to wrap around the communication needed to be able to
@@ -341,6 +274,7 @@ impl WatchThread {
                 .args(&args)
                 .stdout(Stdio::piped())
                 .stderr(Stdio::null())
+                .stdin(Stdio::null())
                 .spawn()
                 .expect("couldn't launch cargo");
 
@@ -348,15 +282,45 @@ impl WatchThread {
             // which will break out of the loop, and continue the shutdown
             let _ = message_send.send(CheckEvent::Begin);
 
-            for message in cargo_metadata::parse_messages(command.stdout.take().unwrap()) {
+            // We manually read a line at a time, instead of using serde's
-                let message = match message {
+            // stream deserializers, because the deserializer cannot recover
-                    Ok(message) => message,
+            // from an error, resulting in it getting stuck, because we try to
+            // be resillient against failures.
+            //
+            // Because cargo only outputs one JSON object per line, we can
+            // simply skip a line if it doesn't parse, which just ignores any
+            // erroneus output.
+            let stdout = BufReader::new(command.stdout.take().unwrap());
+            for line in stdout.lines() {
+                let line = match line {
+                    Ok(line) => line,
                     Err(err) => {
-                        log::error!("Invalid json from cargo check, ignoring: {}", err);
+                        log::error!("Couldn't read line from cargo: {}", err);
                         continue;
                     }
                 };
 
+                let message = serde_json::from_str::<cargo_metadata::Message>(&line);
+                let message = match message {
+                    Ok(message) => message,
+                    Err(err) => {
+                        log::error!(
+                            "Invalid json from cargo check, ignoring ({}): {:?} ",
+                            err,
+                            line
+                        );
+                        continue;
+                    }
+                };
+
+                // Skip certain kinds of messages to only spend time on what's useful
+                match &message {
+                    Message::CompilerArtifact(artifact) if artifact.fresh => continue,
+                    Message::BuildScriptExecuted(_) => continue,
+                    Message::Unknown => continue,
+                    _ => {}
+                }
+
                 match message_send.send(CheckEvent::Msg(message)) {
                     Ok(()) => {}
                     Err(_err) => {
@@ -396,10 +360,3 @@ impl std::ops::Drop for WatchThread {
         }
     }
 }
-
-fn are_diagnostics_equal(left: &Diagnostic, right: &Diagnostic) -> bool {
-    left.source == right.source
-        && left.severity == right.severity
-        && left.range == right.range
-        && left.message == right.message
-}

crates/ra_cli/Cargo.toml

@@ -7,7 +7,7 @@ publish = false
 
 [dependencies]
 pico-args = "0.3.0"
-env_logger = { version = "0.7.1", default-features = false, features = ["humantime"] }
+env_logger = { version = "0.7.1", default-features = false }
 
 ra_syntax = { path = "../ra_syntax" }
 ra_ide = { path = "../ra_ide" }

crates/ra_cli/src/analysis_stats.rs

@@ -171,12 +171,12 @@ pub fn run(
     println!(
         "Expressions of unknown type: {} ({}%)",
         num_exprs_unknown,
-        if num_exprs > 0 { (num_exprs_unknown * 100 / num_exprs) } else { 100 }
+        if num_exprs > 0 { num_exprs_unknown * 100 / num_exprs } else { 100 }
     );
     println!(
         "Expressions of partially unknown type: {} ({}%)",
         num_exprs_partially_unknown,
-        if num_exprs > 0 { (num_exprs_partially_unknown * 100 / num_exprs) } else { 100 }
+        if num_exprs > 0 { num_exprs_partially_unknown * 100 / num_exprs } else { 100 }
     );
     println!("Type mismatches: {}", num_type_mismatches);
     println!("Inference: {:?}, {}", inference_time.elapsed(), ra_prof::memory_usage());

crates/ra_db/src/fixture.rs

@@ -8,8 +8,8 @@ use rustc_hash::FxHashMap;
 use test_utils::{extract_offset, parse_fixture, CURSOR_MARKER};
 
 use crate::{
-    CrateGraph, CrateId, Edition, Env, FileId, FilePosition, RelativePathBuf, SourceDatabaseExt,
+    input::CrateName, CrateGraph, CrateId, Edition, Env, FileId, FilePosition, RelativePathBuf,
-    SourceRoot, SourceRootId,
+    SourceDatabaseExt, SourceRoot, SourceRootId,
 };
 
 pub const WORKSPACE: SourceRootId = SourceRootId(0);
@@ -139,7 +139,7 @@ fn with_files(db: &mut dyn SourceDatabaseExt, fixture: &str) -> Option<FilePosit
         for (from, to) in crate_deps {
             let from_id = crates[&from];
             let to_id = crates[&to];
-            crate_graph.add_dep(from_id, to.into(), to_id).unwrap();
+            crate_graph.add_dep(from_id, CrateName::new(&to).unwrap(), to_id).unwrap();
         }
     }
 

crates/ra_db/src/input.rs

@@ -83,6 +83,26 @@ pub struct CrateGraph {
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct CrateId(pub u32);
 
+pub struct CrateName(SmolStr);
+
+impl CrateName {
+    /// Crates a crate name, checking for dashes in the string provided.
+    /// Dashes are not allowed in the crate names,
+    /// hence the input string is returned as `Err` for those cases.
+    pub fn new(name: &str) -> Result<CrateName, &str> {
+        if name.contains('-') {
+            Err(name)
+        } else {
+            Ok(Self(SmolStr::new(name)))
+        }
+    }
+
+    /// Crates a crate name, unconditionally replacing the dashes with underscores.
+    pub fn normalize_dashes(name: &str) -> CrateName {
+        Self(SmolStr::new(name.replace('-', "_")))
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct CrateData {
     file_id: FileId,
@@ -131,13 +151,13 @@ impl CrateGraph {
     pub fn add_dep(
         &mut self,
         from: CrateId,
-        name: SmolStr,
+        name: CrateName,
         to: CrateId,
     ) -> Result<(), CyclicDependenciesError> {
         if self.dfs_find(from, to, &mut FxHashSet::default()) {
             return Err(CyclicDependenciesError);
         }
-        self.arena.get_mut(&from).unwrap().add_dep(name, to);
+        self.arena.get_mut(&from).unwrap().add_dep(name.0, to);
         Ok(())
     }
 
@@ -268,7 +288,7 @@ pub struct CyclicDependenciesError;
 
 #[cfg(test)]
 mod tests {
-    use super::{CfgOptions, CrateGraph, Edition::Edition2018, Env, FileId, SmolStr};
+    use super::{CfgOptions, CrateGraph, CrateName, Dependency, Edition::Edition2018, Env, FileId};
 
     #[test]
     fn it_should_panic_because_of_cycle_dependencies() {
@@ -279,9 +299,9 @@ mod tests {
             graph.add_crate_root(FileId(2u32), Edition2018, CfgOptions::default(), Env::default());
         let crate3 =
             graph.add_crate_root(FileId(3u32), Edition2018, CfgOptions::default(), Env::default());
-        assert!(graph.add_dep(crate1, SmolStr::new("crate2"), crate2).is_ok());
+        assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
-        assert!(graph.add_dep(crate2, SmolStr::new("crate3"), crate3).is_ok());
+        assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
-        assert!(graph.add_dep(crate3, SmolStr::new("crate1"), crate1).is_err());
+        assert!(graph.add_dep(crate3, CrateName::new("crate1").unwrap(), crate1).is_err());
     }
 
     #[test]
@@ -293,7 +313,23 @@ mod tests {
             graph.add_crate_root(FileId(2u32), Edition2018, CfgOptions::default(), Env::default());
         let crate3 =
             graph.add_crate_root(FileId(3u32), Edition2018, CfgOptions::default(), Env::default());
-        assert!(graph.add_dep(crate1, SmolStr::new("crate2"), crate2).is_ok());
+        assert!(graph.add_dep(crate1, CrateName::new("crate2").unwrap(), crate2).is_ok());
-        assert!(graph.add_dep(crate2, SmolStr::new("crate3"), crate3).is_ok());
+        assert!(graph.add_dep(crate2, CrateName::new("crate3").unwrap(), crate3).is_ok());
+    }
+
+    #[test]
+    fn dashes_are_normalized() {
+        let mut graph = CrateGraph::default();
+        let crate1 =
+            graph.add_crate_root(FileId(1u32), Edition2018, CfgOptions::default(), Env::default());
+        let crate2 =
+            graph.add_crate_root(FileId(2u32), Edition2018, CfgOptions::default(), Env::default());
+        assert!(graph
+            .add_dep(crate1, CrateName::normalize_dashes("crate-name-with-dashes"), crate2)
+            .is_ok());
+        assert_eq!(
+            graph.dependencies(crate1).collect::<Vec<_>>(),
+            vec![&Dependency { crate_id: crate2, name: "crate_name_with_dashes".into() }]
+        );
     }
 }

crates/ra_db/src/lib.rs

@@ -10,7 +10,9 @@ use ra_syntax::{ast, Parse, SourceFile, TextRange, TextUnit};
 
 pub use crate::{
     cancellation::Canceled,
-    input::{CrateGraph, CrateId, Dependency, Edition, Env, FileId, SourceRoot, SourceRootId},
+    input::{
+        CrateGraph, CrateId, CrateName, Dependency, Edition, Env, FileId, SourceRoot, SourceRootId,
+    },
 };
 pub use relative_path::{RelativePath, RelativePathBuf};
 pub use salsa;

crates/ra_fmt/src/lib.rs

@@ -35,8 +35,14 @@ fn prev_tokens(token: SyntaxToken) -> impl Iterator<Item = SyntaxToken> {
     successors(token.prev_token(), |token| token.prev_token())
 }
 
-pub fn extract_trivial_expression(expr: &ast::BlockExpr) -> Option<ast::Expr> {
+pub fn unwrap_trivial_block(block: ast::BlockExpr) -> ast::Expr {
-    let block = expr.block()?;
+    extract_trivial_expression(&block)
+        .filter(|expr| !expr.syntax().text().contains_char('\n'))
+        .unwrap_or_else(|| block.into())
+}
+
+pub fn extract_trivial_expression(block: &ast::BlockExpr) -> Option<ast::Expr> {
+    let block = block.block()?;
     let expr = block.expr()?;
     let non_trivial_children = block.syntax().children().filter(|it| match it.kind() {
         WHITESPACE | T!['{'] | T!['}'] => false,

crates/ra_hir/src/code_model.rs

@@ -10,9 +10,9 @@ use hir_def::{
     per_ns::PerNs,
     resolver::HasResolver,
     type_ref::{Mutability, TypeRef},
-    AdtId, ConstId, DefWithBodyId, EnumId, FunctionId, HasModule, ImplId, LocalEnumVariantId,
+    AdtId, ConstId, DefWithBodyId, EnumId, FunctionId, GenericDefId, HasModule, ImplId,
-    LocalModuleId, LocalStructFieldId, Lookup, ModuleId, StaticId, StructId, TraitId, TypeAliasId,
+    LocalEnumVariantId, LocalModuleId, LocalStructFieldId, Lookup, ModuleId, StaticId, StructId,
-    TypeParamId, UnionId,
+    TraitId, TypeAliasId, TypeParamId, UnionId,
 };
 use hir_expand::{
     diagnostics::DiagnosticSink,
@@ -21,7 +21,7 @@ use hir_expand::{
 };
 use hir_ty::{
     autoderef, display::HirFormatter, expr::ExprValidator, method_resolution, ApplicationTy,
-    Canonical, InEnvironment, TraitEnvironment, Ty, TyDefId, TypeCtor, TypeWalk,
+    Canonical, InEnvironment, Substs, TraitEnvironment, Ty, TyDefId, TypeCtor,
 };
 use ra_db::{CrateId, Edition, FileId};
 use ra_prof::profile;
@@ -119,7 +119,7 @@ impl_froms!(
     BuiltinType
 );
 
-pub use hir_def::{attr::Attrs, visibility::Visibility, AssocItemId};
+pub use hir_def::{attr::Attrs, item_scope::ItemInNs, visibility::Visibility, AssocItemId};
 use rustc_hash::FxHashSet;
 
 impl Module {
@@ -238,11 +238,16 @@ impl Module {
         item: ModuleDef,
     ) -> Option<hir_def::path::ModPath> {
         // FIXME expose namespace choice
-        hir_def::find_path::find_path(
+        hir_def::find_path::find_path(db, determine_item_namespace(item), self.into())
-            db,
+    }
-            hir_def::item_scope::ItemInNs::Types(item.into()),
+}
-            self.into(),
+
-        )
+fn determine_item_namespace(module_def: ModuleDef) -> ItemInNs {
+    match module_def {
+        ModuleDef::Static(_) | ModuleDef::Const(_) | ModuleDef::Function(_) => {
+            ItemInNs::Values(module_def.into())
+        }
+        _ => ItemInNs::Types(module_def.into()),
     }
 }
 
@@ -265,7 +270,13 @@ impl StructField {
 
     pub fn ty(&self, db: &impl HirDatabase) -> Type {
         let var_id = self.parent.into();
-        let ty = db.field_types(var_id)[self.id].clone();
+        let generic_def_id: GenericDefId = match self.parent {
+            VariantDef::Struct(it) => it.id.into(),
+            VariantDef::Union(it) => it.id.into(),
+            VariantDef::EnumVariant(it) => it.parent.id.into(),
+        };
+        let substs = Substs::type_params(db, generic_def_id);
+        let ty = db.field_types(var_id)[self.id].clone().subst(&substs);
         Type::new(db, self.parent.module(db).id.krate.into(), var_id, ty)
     }
 
@@ -750,7 +761,7 @@ pub struct TypeParam {
 impl TypeParam {
     pub fn name(self, db: &impl HirDatabase) -> Name {
         let params = db.generic_params(self.id.parent);
-        params.types[self.id.local_id].name.clone()
+        params.types[self.id.local_id].name.clone().unwrap_or_else(Name::missing)
     }
 
     pub fn module(self, db: &impl HirDatabase) -> Module {
@@ -784,8 +795,9 @@ impl ImplBlock {
     pub fn target_ty(&self, db: &impl HirDatabase) -> Type {
         let impl_data = db.impl_data(self.id);
         let resolver = self.id.resolver(db);
+        let ctx = hir_ty::TyLoweringContext::new(db, &resolver);
         let environment = TraitEnvironment::lower(db, &resolver);
-        let ty = Ty::from_hir(db, &resolver, &impl_data.target_type);
+        let ty = Ty::from_hir(&ctx, &impl_data.target_type);
         Type {
             krate: self.id.lookup(db).container.module(db).krate,
             ty: InEnvironment { value: ty, environment },
@@ -846,9 +858,10 @@ impl Type {
     fn from_def(
         db: &impl HirDatabase,
         krate: CrateId,
-        def: impl HasResolver + Into<TyDefId>,
+        def: impl HasResolver + Into<TyDefId> + Into<GenericDefId>,
     ) -> Type {
-        let ty = db.ty(def.into());
+        let substs = Substs::type_params(db, def);
+        let ty = db.ty(def.into()).subst(&substs);
         Type::new(db, krate, def, ty)
     }
 
@@ -945,7 +958,7 @@ impl Type {
             match a_ty.ctor {
                 TypeCtor::Tuple { .. } => {
                     for ty in a_ty.parameters.iter() {
-                        let ty = ty.clone().subst(&a_ty.parameters);
+                        let ty = ty.clone();
                         res.push(self.derived(ty));
                     }
                 }

crates/ra_hir/src/db.rs

@@ -1,20 +1,24 @@
 //! FIXME: write short doc here
 
 pub use hir_def::db::{
-    BodyQuery, BodyWithSourceMapQuery, ComputeCrateDefMapQuery, ConstDataQuery,
+    AttrsQuery, BodyQuery, BodyWithSourceMapQuery, ComputeCrateDefMapQuery, ConstDataQuery,
     CrateLangItemsQuery, DefDatabase, DefDatabaseStorage, DocumentationQuery, EnumDataQuery,
-    ExprScopesQuery, FunctionDataQuery, GenericParamsQuery, ImplDataQuery, InternDatabase,
+    ExprScopesQuery, FunctionDataQuery, GenericParamsQuery, ImplDataQuery, InternConstQuery,
-    InternDatabaseStorage, LangItemQuery, ModuleLangItemsQuery, RawItemsQuery, StaticDataQuery,
+    InternDatabase, InternDatabaseStorage, InternEnumQuery, InternFunctionQuery, InternImplQuery,
-    StructDataQuery, TraitDataQuery, TypeAliasDataQuery,
+    InternStaticQuery, InternStructQuery, InternTraitQuery, InternTypeAliasQuery, InternUnionQuery,
+    LangItemQuery, ModuleLangItemsQuery, RawItemsQuery, StaticDataQuery, StructDataQuery,
+    TraitDataQuery, TypeAliasDataQuery, UnionDataQuery,
 };
 pub use hir_expand::db::{
-    AstDatabase, AstDatabaseStorage, AstIdMapQuery, MacroArgQuery, MacroDefQuery, MacroExpandQuery,
+    AstDatabase, AstDatabaseStorage, AstIdMapQuery, InternMacroQuery, MacroArgQuery, MacroDefQuery,
-    ParseMacroQuery,
+    MacroExpandQuery, ParseMacroQuery,
 };
 pub use hir_ty::db::{
-    AssociatedTyDataQuery, CallableItemSignatureQuery, DoInferQuery, FieldTypesQuery,
+    AssociatedTyDataQuery, AssociatedTyValueQuery, CallableItemSignatureQuery, DoInferQuery,
-    GenericDefaultsQuery, GenericPredicatesQuery, HirDatabase, HirDatabaseStorage, ImplDatumQuery,
+    FieldTypesQuery, GenericDefaultsQuery, GenericPredicatesForParamQuery, GenericPredicatesQuery,
-    ImplsForTraitQuery, ImplsInCrateQuery, StructDatumQuery, TraitDatumQuery, TraitSolveQuery,
+    HirDatabase, HirDatabaseStorage, ImplDatumQuery, ImplSelfTyQuery, ImplTraitQuery,
+    ImplsForTraitQuery, ImplsInCrateQuery, InternAssocTyValueQuery, InternChalkImplQuery,
+    InternTypeCtorQuery, StructDatumQuery, TraitDatumQuery, TraitSolveQuery, TraitSolverQuery,
     TyQuery, ValueTyQuery,
 };
 

crates/ra_hir/src/source_analyzer.rs

@@ -178,6 +178,10 @@ impl SourceAnalyzer {
         }
     }
 
+    fn trait_env(&self, db: &impl HirDatabase) -> Arc<TraitEnvironment> {
+        TraitEnvironment::lower(db, &self.resolver)
+    }
+
     pub fn type_of(&self, db: &impl HirDatabase, expr: &ast::Expr) -> Option<Type> {
         let expr_id = if let Some(expr) = self.expand_expr(db, InFile::new(self.file_id, expr)) {
             self.body_source_map.as_ref()?.node_expr(expr.as_ref())?
@@ -186,14 +190,14 @@ impl SourceAnalyzer {
         };
 
         let ty = self.infer.as_ref()?[expr_id].clone();
-        let environment = TraitEnvironment::lower(db, &self.resolver);
+        let environment = self.trait_env(db);
         Some(Type { krate: self.resolver.krate()?, ty: InEnvironment { value: ty, environment } })
     }
 
     pub fn type_of_pat(&self, db: &impl HirDatabase, pat: &ast::Pat) -> Option<Type> {
         let pat_id = self.pat_id(pat)?;
         let ty = self.infer.as_ref()?[pat_id].clone();
-        let environment = TraitEnvironment::lower(db, &self.resolver);
+        let environment = self.trait_env(db);
         Some(Type { krate: self.resolver.krate()?, ty: InEnvironment { value: ty, environment } })
     }
 

crates/ra_hir_def/Cargo.toml

@@ -26,4 +26,4 @@ ra_cfg = { path = "../ra_cfg" }
 tt = { path = "../ra_tt", package = "ra_tt" }
 
 [dev-dependencies]
-insta = "0.12.0"
+insta = "0.13.0"

crates/ra_hir_def/src/find_path.rs

@@ -7,10 +7,39 @@ use crate::{
     visibility::Visibility,
     CrateId, ModuleDefId, ModuleId,
 };
-use hir_expand::name::Name;
+use hir_expand::name::{known, Name};
+use test_utils::tested_by;
 
 const MAX_PATH_LEN: usize = 15;
 
+impl ModPath {
+    fn starts_with_std(&self) -> bool {
+        self.segments.first().filter(|&first_segment| first_segment == &known::std).is_some()
+    }
+
+    // When std library is present, paths starting with `std::`
+    // should be preferred over paths starting with `core::` and `alloc::`
+    fn should_start_with_std(&self) -> bool {
+        self.segments
+            .first()
+            .filter(|&first_segment| {
+                first_segment == &known::alloc || first_segment == &known::core
+            })
+            .is_some()
+    }
+
+    fn len(&self) -> usize {
+        self.segments.len()
+            + match self.kind {
+                PathKind::Plain => 0,
+                PathKind::Super(i) => i as usize,
+                PathKind::Crate => 1,
+                PathKind::Abs => 0,
+                PathKind::DollarCrate(_) => 1,
+            }
+    }
+}
+
 // FIXME: handle local items
 
 /// Find a path that can be used to refer to a certain item. This can depend on
@@ -112,22 +141,26 @@ fn find_path_inner(
             Some(path) => path,
         };
         path.segments.push(name);
-        if path_len(&path) < best_path_len {
+
-            best_path_len = path_len(&path);
+        let new_path =
-            best_path = Some(path);
+            if let Some(best_path) = best_path { select_best_path(best_path, path) } else { path };
-        }
+        best_path_len = new_path.len();
+        best_path = Some(new_path);
     }
     best_path
 }
 
-fn path_len(path: &ModPath) -> usize {
+fn select_best_path(old_path: ModPath, new_path: ModPath) -> ModPath {
-    path.segments.len()
+    if old_path.starts_with_std() && new_path.should_start_with_std() {
-        + match path.kind {
+        tested_by!(prefer_std_paths);
-            PathKind::Plain => 0,
+        old_path
-            PathKind::Super(i) => i as usize,
+    } else if new_path.starts_with_std() && old_path.should_start_with_std() {
-            PathKind::Crate => 1,
+        tested_by!(prefer_std_paths);
-            PathKind::Abs => 0,
+        new_path
-            PathKind::DollarCrate(_) => 1,
+    } else if new_path.len() < old_path.len() {
+        new_path
+    } else {
+        old_path
     }
 }
 
@@ -201,6 +234,7 @@ mod tests {
     use hir_expand::hygiene::Hygiene;
     use ra_db::fixture::WithFixture;
     use ra_syntax::ast::AstNode;
+    use test_utils::covers;
 
     /// `code` needs to contain a cursor marker; checks that `find_path` for the
     /// item the `path` refers to returns that same path when called from the
@@ -452,4 +486,41 @@ mod tests {
         "#;
         check_found_path(code, "crate::foo::S");
     }
+
+    #[test]
+    fn prefer_std_paths_over_alloc() {
+        covers!(prefer_std_paths);
+        let code = r#"
+        //- /main.rs crate:main deps:alloc,std
+        <|>
+
+        //- /std.rs crate:std deps:alloc
+        pub mod sync {
+            pub use alloc::sync::Arc;
+        }
+
+        //- /zzz.rs crate:alloc
+        pub mod sync {
+            pub struct Arc;
+        }
+        "#;
+        check_found_path(code, "std::sync::Arc");
+    }
+
+    #[test]
+    fn prefer_shorter_paths_if_not_alloc() {
+        let code = r#"
+        //- /main.rs crate:main deps:megaalloc,std
+        <|>
+
+        //- /std.rs crate:std deps:megaalloc
+        pub mod sync {
+            pub use megaalloc::sync::Arc;
+        }
+
+        //- /zzz.rs crate:megaalloc
+        pub struct Arc;
+        "#;
+        check_found_path(code, "megaalloc::Arc");
+    }
 }

crates/ra_hir_def/src/generics.rs

@@ -27,8 +27,16 @@ use crate::{
 /// Data about a generic parameter (to a function, struct, impl, ...).
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct TypeParamData {
-    pub name: Name,
+    pub name: Option<Name>,
     pub default: Option<TypeRef>,
+    pub provenance: TypeParamProvenance,
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum TypeParamProvenance {
+    TypeParamList,
+    TraitSelf,
+    ArgumentImplTrait,
 }
 
 /// Data about the generic parameters of a function, struct, impl, etc.
@@ -45,10 +53,17 @@ pub struct GenericParams {
 /// associated type bindings like `Iterator<Item = u32>`.
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct WherePredicate {
-    pub type_ref: TypeRef,
+    pub target: WherePredicateTarget,
     pub bound: TypeBound,
 }
 
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub enum WherePredicateTarget {
+    TypeRef(TypeRef),
+    /// For desugared where predicates that can directly refer to a type param.
+    TypeParam(LocalTypeParamId),
+}
+
 type SourceMap = ArenaMap<LocalTypeParamId, Either<ast::TraitDef, ast::TypeParam>>;
 
 impl GenericParams {
@@ -68,6 +83,11 @@ impl GenericParams {
             GenericDefId::FunctionId(it) => {
                 let src = it.lookup(db).source(db);
                 generics.fill(&mut sm, &src.value);
+                // lower `impl Trait` in arguments
+                let data = db.function_data(it);
+                for param in &data.params {
+                    generics.fill_implicit_impl_trait_args(param);
+                }
                 src.file_id
             }
             GenericDefId::AdtId(AdtId::StructId(it)) => {
@@ -89,8 +109,11 @@ impl GenericParams {
                 let src = it.lookup(db).source(db);
 
                 // traits get the Self type as an implicit first type parameter
-                let self_param_id =
+                let self_param_id = generics.types.alloc(TypeParamData {
-                    generics.types.alloc(TypeParamData { name: name![Self], default: None });
+                    name: Some(name![Self]),
+                    default: None,
+                    provenance: TypeParamProvenance::TraitSelf,
+                });
                 sm.insert(self_param_id, Either::Left(src.value.clone()));
                 // add super traits as bounds on Self
                 // i.e., trait Foo: Bar is equivalent to trait Foo where Self: Bar
@@ -142,7 +165,11 @@ impl GenericParams {
             let name = type_param.name().map_or_else(Name::missing, |it| it.as_name());
             // FIXME: Use `Path::from_src`
             let default = type_param.default_type().map(TypeRef::from_ast);
-            let param = TypeParamData { name: name.clone(), default };
+            let param = TypeParamData {
+                name: Some(name.clone()),
+                default,
+                provenance: TypeParamProvenance::TypeParamList,
+            };
             let param_id = self.types.alloc(param);
             sm.insert(param_id, Either::Right(type_param.clone()));
 
@@ -170,11 +197,43 @@ impl GenericParams {
             return;
         }
         let bound = TypeBound::from_ast(bound);
-        self.where_predicates.push(WherePredicate { type_ref, bound });
+        self.where_predicates
+            .push(WherePredicate { target: WherePredicateTarget::TypeRef(type_ref), bound });
+    }
+
+    fn fill_implicit_impl_trait_args(&mut self, type_ref: &TypeRef) {
+        type_ref.walk(&mut |type_ref| {
+            if let TypeRef::ImplTrait(bounds) = type_ref {
+                let param = TypeParamData {
+                    name: None,
+                    default: None,
+                    provenance: TypeParamProvenance::ArgumentImplTrait,
+                };
+                let param_id = self.types.alloc(param);
+                for bound in bounds {
+                    self.where_predicates.push(WherePredicate {
+                        target: WherePredicateTarget::TypeParam(param_id),
+                        bound: bound.clone(),
+                    });
+                }
+            }
+        });
     }
 
     pub fn find_by_name(&self, name: &Name) -> Option<LocalTypeParamId> {
-        self.types.iter().find_map(|(id, p)| if &p.name == name { Some(id) } else { None })
+        self.types
+            .iter()
+            .find_map(|(id, p)| if p.name.as_ref() == Some(name) { Some(id) } else { None })
+    }
+
+    pub fn find_trait_self_param(&self) -> Option<LocalTypeParamId> {
+        self.types.iter().find_map(|(id, p)| {
+            if p.provenance == TypeParamProvenance::TraitSelf {
+                Some(id)
+            } else {
+                None
+            }
+        })
     }
 }
 

crates/ra_hir_def/src/marks.rs

@@ -13,4 +13,5 @@ test_utils::marks!(
     macro_dollar_crate_self
     macro_dollar_crate_other
     infer_resolve_while_let
+    prefer_std_paths
 );

crates/ra_hir_def/src/nameres.rs

@@ -229,6 +229,46 @@ impl CrateDefMap {
             self.resolve_path_fp_with_macro(db, ResolveMode::Other, original_module, path, shadow);
         (res.resolved_def, res.segment_index)
     }
+
+    // FIXME: this can use some more human-readable format (ideally, an IR
+    // even), as this should be a great debugging aid.
+    pub fn dump(&self) -> String {
+        let mut buf = String::new();
+        go(&mut buf, self, "\ncrate", self.root);
+        return buf.trim().to_string();
+
+        fn go(buf: &mut String, map: &CrateDefMap, path: &str, module: LocalModuleId) {
+            *buf += path;
+            *buf += "\n";
+
+            let mut entries: Vec<_> = map.modules[module].scope.resolutions().collect();
+            entries.sort_by_key(|(name, _)| name.clone());
+
+            for (name, def) in entries {
+                *buf += &format!("{}:", name);
+
+                if def.types.is_some() {
+                    *buf += " t";
+                }
+                if def.values.is_some() {
+                    *buf += " v";
+                }
+                if def.macros.is_some() {
+                    *buf += " m";
+                }
+                if def.is_none() {
+                    *buf += " _";
+                }
+
+                *buf += "\n";
+            }
+
+            for (name, child) in map.modules[module].children.iter() {
+                let path = path.to_string() + &format!("::{}", name);
+                go(buf, map, &path, *child);
+            }
+        }
+    }
 }
 
 impl ModuleData {

crates/ra_hir_def/src/nameres/collector.rs

@@ -22,7 +22,7 @@ use crate::{
         diagnostics::DefDiagnostic, mod_resolution::ModDir, path_resolution::ReachedFixedPoint,
         raw, BuiltinShadowMode, CrateDefMap, ModuleData, ModuleOrigin, ResolveMode,
     },
-    path::{ModPath, PathKind},
+    path::{ImportAlias, ModPath, PathKind},
     per_ns::PerNs,
     visibility::Visibility,
     AdtId, AstId, ConstLoc, ContainerId, EnumLoc, EnumVariantId, FunctionLoc, ImplLoc, Intern,
@@ -438,7 +438,11 @@ where
         } else {
             match import.path.segments.last() {
                 Some(last_segment) => {
-                    let name = import.alias.clone().unwrap_or_else(|| last_segment.clone());
+                    let name = match &import.alias {
+                        Some(ImportAlias::Alias(name)) => name.clone(),
+                        Some(ImportAlias::Underscore) => last_segment.clone(), // FIXME rust-analyzer#2736
+                        None => last_segment.clone(),
+                    };
                     log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def);
 
                     // extern crates in the crate root are special-cased to insert entries into the extern prelude: rust-lang/rust#54658

crates/ra_hir_def/src/nameres/raw.rs

@@ -22,8 +22,11 @@ use ra_syntax::{
 use test_utils::tested_by;
 
 use crate::{
-    attr::Attrs, db::DefDatabase, path::ModPath, visibility::RawVisibility, FileAstId, HirFileId,
+    attr::Attrs,
-    InFile,
+    db::DefDatabase,
+    path::{ImportAlias, ModPath},
+    visibility::RawVisibility,
+    FileAstId, HirFileId, InFile,
 };
 
 /// `RawItems` is a set of top-level items in a file (except for impls).
@@ -145,7 +148,7 @@ impl_arena_id!(Import);
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ImportData {
     pub(super) path: ModPath,
-    pub(super) alias: Option<Name>,
+    pub(super) alias: Option<ImportAlias>,
     pub(super) is_glob: bool,
     pub(super) is_prelude: bool,
     pub(super) is_extern_crate: bool,
@@ -353,7 +356,11 @@ impl RawItemsCollector {
             let path = ModPath::from_name_ref(&name_ref);
             let visibility =
                 RawVisibility::from_ast_with_hygiene(extern_crate.visibility(), &self.hygiene);
-            let alias = extern_crate.alias().and_then(|a| a.name()).map(|it| it.as_name());
+            let alias = extern_crate.alias().map(|a| {
+                a.name()
+                    .map(|it| it.as_name())
+                    .map_or(ImportAlias::Underscore, |a| ImportAlias::Alias(a))
+            });
             let attrs = self.parse_attrs(&extern_crate);
             // FIXME: cfg_attr
             let is_macro_use = extern_crate.has_atom_attr("macro_use");

crates/ra_hir_def/src/nameres/tests.rs

@@ -10,11 +10,10 @@ use insta::assert_snapshot;
 use ra_db::{fixture::WithFixture, SourceDatabase};
 use test_utils::covers;
 
-use crate::{db::DefDatabase, nameres::*, test_db::TestDB, LocalModuleId};
+use crate::{db::DefDatabase, nameres::*, test_db::TestDB};
 
 fn def_map(fixture: &str) -> String {
-    let dm = compute_crate_def_map(fixture);
+    compute_crate_def_map(fixture).dump()
-    render_crate_def_map(&dm)
 }
 
 fn compute_crate_def_map(fixture: &str) -> Arc<CrateDefMap> {
@@ -23,44 +22,6 @@ fn compute_crate_def_map(fixture: &str) -> Arc<CrateDefMap> {
     db.crate_def_map(krate)
 }
 
-fn render_crate_def_map(map: &CrateDefMap) -> String {
-    let mut buf = String::new();
-    go(&mut buf, map, "\ncrate", map.root);
-    return buf.trim().to_string();
-
-    fn go(buf: &mut String, map: &CrateDefMap, path: &str, module: LocalModuleId) {
-        *buf += path;
-        *buf += "\n";
-
-        let mut entries: Vec<_> = map.modules[module].scope.resolutions().collect();
-        entries.sort_by_key(|(name, _)| name.clone());
-
-        for (name, def) in entries {
-            *buf += &format!("{}:", name);
-
-            if def.types.is_some() {
-                *buf += " t";
-            }
-            if def.values.is_some() {
-                *buf += " v";
-            }
-            if def.macros.is_some() {
-                *buf += " m";
-            }
-            if def.is_none() {
-                *buf += " _";
-            }
-
-            *buf += "\n";
-        }
-
-        for (name, child) in map.modules[module].children.iter() {
-            let path = path.to_string() + &format!("::{}", name);
-            go(buf, map, &path, *child);
-        }
-    }
-}
-
 #[test]
 fn crate_def_map_smoke_test() {
     let map = def_map(

crates/ra_hir_def/src/path.rs

@@ -16,13 +16,13 @@ use ra_syntax::ast;
 
 use crate::{type_ref::TypeRef, InFile};
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct ModPath {
     pub kind: PathKind,
     pub segments: Vec<Name>,
 }
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub enum PathKind {
     Plain,
     /// `self::` is `Super(0)`
@@ -34,6 +34,14 @@ pub enum PathKind {
     DollarCrate(CrateId),
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ImportAlias {
+    /// Unnamed alias, as in `use Foo as _;`
+    Underscore,
+    /// Named alias
+    Alias(Name),
+}
+
 impl ModPath {
     pub fn from_src(path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
         lower::lower_path(path, hygiene).map(|it| it.mod_path)
@@ -57,7 +65,7 @@ impl ModPath {
     pub(crate) fn expand_use_item(
         item_src: InFile<ast::UseItem>,
         hygiene: &Hygiene,
-        mut cb: impl FnMut(ModPath, &ast::UseTree, /* is_glob */ bool, Option<Name>),
+        mut cb: impl FnMut(ModPath, &ast::UseTree, /* is_glob */ bool, Option<ImportAlias>),
     ) {
         if let Some(tree) = item_src.value.use_tree() {
             lower::lower_use_tree(None, tree, hygiene, &mut cb);

crates/ra_hir_def/src/path/lower/lower_use.rs

@@ -4,20 +4,17 @@
 use std::iter;
 
 use either::Either;
-use hir_expand::{
+use hir_expand::{hygiene::Hygiene, name::AsName};
-    hygiene::Hygiene,
-    name::{AsName, Name},
-};
 use ra_syntax::ast::{self, NameOwner};
 use test_utils::tested_by;
 
-use crate::path::{ModPath, PathKind};
+use crate::path::{ImportAlias, ModPath, PathKind};
 
 pub(crate) fn lower_use_tree(
     prefix: Option<ModPath>,
     tree: ast::UseTree,
     hygiene: &Hygiene,
-    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<Name>),
+    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<ImportAlias>),
 ) {
     if let Some(use_tree_list) = tree.use_tree_list() {
         let prefix = match tree.path() {
@@ -34,7 +31,11 @@ pub(crate) fn lower_use_tree(
             lower_use_tree(prefix.clone(), child_tree, hygiene, cb);
         }
     } else {
-        let alias = tree.alias().and_then(|a| a.name()).map(|a| a.as_name());
+        let alias = tree.alias().map(|a| {
+            a.name()
+                .map(|it| it.as_name())
+                .map_or(ImportAlias::Underscore, |a| ImportAlias::Alias(a))
+        });
         let is_glob = tree.has_star();
         if let Some(ast_path) = tree.path() {
             // Handle self in a path.

crates/ra_hir_def/src/resolver.rs

@@ -490,12 +490,14 @@ impl Scope {
             }
             Scope::GenericParams { params, def } => {
                 for (local_id, param) in params.types.iter() {
+                    if let Some(name) = &param.name {
                         f(
-                        param.name.clone(),
+                            name.clone(),
                             ScopeDef::GenericParam(TypeParamId { local_id, parent: *def }),
                         )
                     }
                 }
+            }
             Scope::ImplBlockScope(i) => {
                 f(name![Self], ScopeDef::ImplSelfType((*i).into()));
             }

crates/ra_hir_def/src/type_ref.rs

@@ -124,6 +124,48 @@ impl TypeRef {
     pub(crate) fn unit() -> TypeRef {
         TypeRef::Tuple(Vec::new())
     }
+
+    pub fn walk(&self, f: &mut impl FnMut(&TypeRef)) {
+        go(self, f);
+
+        fn go(type_ref: &TypeRef, f: &mut impl FnMut(&TypeRef)) {
+            f(type_ref);
+            match type_ref {
+                TypeRef::Fn(types) | TypeRef::Tuple(types) => types.iter().for_each(|t| go(t, f)),
+                TypeRef::RawPtr(type_ref, _)
+                | TypeRef::Reference(type_ref, _)
+                | TypeRef::Array(type_ref)
+                | TypeRef::Slice(type_ref) => go(&type_ref, f),
+                TypeRef::ImplTrait(bounds) | TypeRef::DynTrait(bounds) => {
+                    for bound in bounds {
+                        match bound {
+                            TypeBound::Path(path) => go_path(path, f),
+                            TypeBound::Error => (),
+                        }
+                    }
+                }
+                TypeRef::Path(path) => go_path(path, f),
+                TypeRef::Never | TypeRef::Placeholder | TypeRef::Error => {}
+            };
+        }
+
+        fn go_path(path: &Path, f: &mut impl FnMut(&TypeRef)) {
+            if let Some(type_ref) = path.type_anchor() {
+                go(type_ref, f);
+            }
+            for segment in path.segments().iter() {
+                if let Some(args_and_bindings) = segment.args_and_bindings {
+                    for arg in &args_and_bindings.args {
+                        let crate::path::GenericArg::Type(type_ref) = arg;
+                        go(type_ref, f);
+                    }
+                    for (_, type_ref) in &args_and_bindings.bindings {
+                        go(type_ref, f);
+                    }
+                }
+            }
+        }
+    }
 }
 
 pub(crate) fn type_bounds_from_ast(type_bounds_opt: Option<ast::TypeBoundList>) -> Vec<TypeBound> {

crates/ra_hir_expand/src/name.rs

@@ -141,6 +141,8 @@ pub mod known {
         macro_rules,
         // Components of known path (value or mod name)
         std,
+        core,
+        alloc,
         iter,
         ops,
         future,

crates/ra_hir_ty/Cargo.toml

@@ -21,11 +21,11 @@ ra_prof = { path = "../ra_prof" }
 ra_syntax = { path = "../ra_syntax" }
 test_utils = { path = "../test_utils" }
 
-chalk-solve =   { git = "https://github.com/rust-lang/chalk.git", rev = "ff65b5ac9860f3c36bd892c865ab23d5ff0bbae5" }
+chalk-solve =   { git = "https://github.com/rust-lang/chalk.git", rev = "af48f302a1f571b3ca418f7c5aa639a144a34f75" }
-chalk-rust-ir = { git = "https://github.com/rust-lang/chalk.git", rev = "ff65b5ac9860f3c36bd892c865ab23d5ff0bbae5" }
+chalk-rust-ir = { git = "https://github.com/rust-lang/chalk.git", rev = "af48f302a1f571b3ca418f7c5aa639a144a34f75" }
-chalk-ir =      { git = "https://github.com/rust-lang/chalk.git", rev = "ff65b5ac9860f3c36bd892c865ab23d5ff0bbae5" }
+chalk-ir =      { git = "https://github.com/rust-lang/chalk.git", rev = "af48f302a1f571b3ca418f7c5aa639a144a34f75" }
 
 lalrpop-intern = "0.15.1"
 
 [dev-dependencies]
-insta = "0.12.0"
+insta = "0.13.0"

crates/ra_hir_ty/src/db.rs

@@ -3,17 +3,18 @@
 use std::sync::Arc;
 
 use hir_def::{
-    db::DefDatabase, DefWithBodyId, GenericDefId, ImplId, LocalStructFieldId, TraitId, VariantId,
+    db::DefDatabase, DefWithBodyId, GenericDefId, ImplId, LocalStructFieldId, TraitId, TypeParamId,
+    VariantId,
 };
 use ra_arena::map::ArenaMap;
-use ra_db::{salsa, CrateId};
+use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 
 use crate::{
     method_resolution::CrateImplBlocks,
     traits::{chalk, AssocTyValue, Impl},
-    CallableDef, FnSig, GenericPredicate, InferenceResult, Substs, TraitRef, Ty, TyDefId, TypeCtor,
+    Binders, CallableDef, GenericPredicate, InferenceResult, PolyFnSig, Substs, TraitRef, Ty,
-    ValueTyDefId,
+    TyDefId, TypeCtor, ValueTyDefId,
 };
 
 #[salsa::query_group(HirDatabaseStorage)]
@@ -27,34 +28,33 @@ pub trait HirDatabase: DefDatabase {
 
     #[salsa::invoke(crate::lower::ty_query)]
     #[salsa::cycle(crate::lower::ty_recover)]
-    fn ty(&self, def: TyDefId) -> Ty;
+    fn ty(&self, def: TyDefId) -> Binders<Ty>;
 
     #[salsa::invoke(crate::lower::value_ty_query)]
-    fn value_ty(&self, def: ValueTyDefId) -> Ty;
+    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) -> Ty;
+    fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
 
     #[salsa::invoke(crate::lower::impl_trait_query)]
-    fn impl_trait(&self, def: ImplId) -> Option<TraitRef>;
+    fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
     #[salsa::invoke(crate::lower::field_types_query)]
-    fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalStructFieldId, Ty>>;
+    fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalStructFieldId, Binders<Ty>>>;
 
     #[salsa::invoke(crate::callable_item_sig)]
-    fn callable_item_signature(&self, def: CallableDef) -> FnSig;
+    fn callable_item_signature(&self, def: CallableDef) -> PolyFnSig;
 
     #[salsa::invoke(crate::lower::generic_predicates_for_param_query)]
     #[salsa::cycle(crate::lower::generic_predicates_for_param_recover)]
     fn generic_predicates_for_param(
         &self,
-        def: GenericDefId,
+        param_id: TypeParamId,
-        param_idx: u32,
+    ) -> Arc<[Binders<GenericPredicate>]>;
-    ) -> Arc<[GenericPredicate]>;
 
     #[salsa::invoke(crate::lower::generic_predicates_query)]
-    fn generic_predicates(&self, def: GenericDefId) -> Arc<[GenericPredicate]>;
+    fn generic_predicates(&self, def: GenericDefId) -> Arc<[Binders<GenericPredicate>]>;
 
     #[salsa::invoke(crate::lower::generic_defaults_query)]
     fn generic_defaults(&self, def: GenericDefId) -> Substs;
@@ -77,6 +77,8 @@ pub trait HirDatabase: DefDatabase {
     #[salsa::interned]
     fn intern_type_ctor(&self, type_ctor: TypeCtor) -> crate::TypeCtorId;
     #[salsa::interned]
+    fn intern_type_param_id(&self, param_id: TypeParamId) -> GlobalTypeParamId;
+    #[salsa::interned]
     fn intern_chalk_impl(&self, impl_: Impl) -> crate::traits::GlobalImplId;
     #[salsa::interned]
     fn intern_assoc_ty_value(&self, assoc_ty_value: AssocTyValue) -> crate::traits::AssocTyValueId;
@@ -117,3 +119,7 @@ fn infer(db: &impl HirDatabase, def: DefWithBodyId) -> Arc<InferenceResult> {
 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);

crates/ra_hir_ty/src/infer.rs

@@ -34,7 +34,6 @@ use hir_expand::{diagnostics::DiagnosticSink, name::name};
 use ra_arena::map::ArenaMap;
 use ra_prof::profile;
 use ra_syntax::SmolStr;
-use test_utils::tested_by;
 
 use super::{
     primitive::{FloatTy, IntTy},
@@ -42,7 +41,9 @@ use super::{
     ApplicationTy, GenericPredicate, InEnvironment, ProjectionTy, Substs, TraitEnvironment,
     TraitRef, Ty, TypeCtor, TypeWalk, Uncertain,
 };
-use crate::{db::HirDatabase, infer::diagnostics::InferenceDiagnostic};
+use crate::{
+    db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
+};
 
 pub(crate) use unify::unify;
 
@@ -271,38 +272,21 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         self.result.diagnostics.push(diagnostic);
     }
 
-    fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
+    fn make_ty_with_mode(
-        let ty = Ty::from_hir(
+        &mut self,
-            self.db,
+        type_ref: &TypeRef,
+        impl_trait_mode: ImplTraitLoweringMode,
+    ) -> Ty {
         // FIXME use right resolver for block
-            &self.resolver,
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
-            type_ref,
+            .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)
     }
 
-    /// Replaces `impl Trait` in `ty` by type variables and obligations for
+    fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
-    /// those variables. This is done for function arguments when calling a
+        self.make_ty_with_mode(type_ref, ImplTraitLoweringMode::Disallowed)
-    /// function, and for return types when inside the function body, i.e. in
-    /// the cases where the `impl Trait` is 'transparent'. In other cases, `impl
-    /// Trait` is represented by `Ty::Opaque`.
-    fn insert_vars_for_impl_trait(&mut self, ty: Ty) -> Ty {
-        ty.fold(&mut |ty| match ty {
-            Ty::Opaque(preds) => {
-                tested_by!(insert_vars_for_impl_trait);
-                let var = self.table.new_type_var();
-                let var_subst = Substs::builder(1).push(var.clone()).build();
-                self.obligations.extend(
-                    preds
-                        .iter()
-                        .map(|pred| pred.clone().subst_bound_vars(&var_subst))
-                        .filter_map(Obligation::from_predicate),
-                );
-                var
-            }
-            _ => ty,
-        })
     }
 
     /// Replaces Ty::Unknown by a new type var, so we can maybe still infer it.
@@ -446,19 +430,20 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             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
         match resolver.resolve_path_in_type_ns_fully(self.db, path.mod_path()) {
             Some(TypeNs::AdtId(AdtId::StructId(strukt))) => {
-                let substs = Ty::substs_from_path(self.db, resolver, path, strukt.into());
+                let substs = Ty::substs_from_path(&ctx, path, strukt.into());
                 let ty = self.db.ty(strukt.into());
-                let ty = self.insert_type_vars(ty.apply_substs(substs));
+                let ty = self.insert_type_vars(ty.subst(&substs));
                 (ty, Some(strukt.into()))
             }
             Some(TypeNs::EnumVariantId(var)) => {
-                let substs = Ty::substs_from_path(self.db, resolver, path, var.into());
+                let substs = Ty::substs_from_path(&ctx, path, var.into());
                 let ty = self.db.ty(var.parent.into());
-                let ty = self.insert_type_vars(ty.apply_substs(substs));
+                let ty = self.insert_type_vars(ty.subst(&substs));
                 (ty, Some(var.into()))
             }
             Some(_) | None => (Ty::Unknown, None),
@@ -471,13 +456,18 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
 
     fn collect_fn(&mut self, data: &FunctionData) {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
-        for (type_ref, pat) in data.params.iter().zip(body.params.iter()) {
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
-            let ty = self.make_ty(type_ref);
+            .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(&data.ret_type);
+        let return_ty = self.make_ty_with_mode(&data.ret_type, ImplTraitLoweringMode::Disallowed); // FIXME implement RPIT
-        self.return_ty = self.insert_vars_for_impl_trait(return_ty);
+        self.return_ty = return_ty;
     }
 
     fn infer_body(&mut self) {

crates/ra_hir_ty/src/infer/coerce.rs

@@ -57,8 +57,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let trait_ref = db.impl_trait(impl_id)?;
 
                 // `CoerseUnsized` has one generic parameter for the target type.
-                let cur_from_ty = trait_ref.substs.0.get(0)?;
+                let cur_from_ty = trait_ref.value.substs.0.get(0)?;
-                let cur_to_ty = trait_ref.substs.0.get(1)?;
+                let cur_to_ty = trait_ref.value.substs.0.get(1)?;
 
                 match (&cur_from_ty, cur_to_ty) {
                     (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => {
@@ -66,9 +66,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                         // This works for smart-pointer-like coercion, which covers all impls from std.
                         st1.iter().zip(st2.iter()).enumerate().find_map(|(i, (ty1, ty2))| {
                             match (ty1, ty2) {
-                                (Ty::Param { idx: p1, .. }, Ty::Param { idx: p2, .. })
+                                (Ty::Bound(idx1), Ty::Bound(idx2)) if idx1 != idx2 => {
-                                    if p1 != p2 =>
-                                {
                                     Some(((*ctor1, *ctor2), i))
                                 }
                                 _ => None,
@@ -256,8 +254,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let unsize_generic_index = {
                     let mut index = None;
                     let mut multiple_param = false;
-                    field_tys[last_field_id].walk(&mut |ty| match ty {
+                    field_tys[last_field_id].value.walk(&mut |ty| match ty {
-                        &Ty::Param { idx, .. } => {
+                        &Ty::Bound(idx) => {
                             if index.is_none() {
                                 index = Some(idx);
                             } else if Some(idx) != index {
@@ -276,10 +274,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 // Check other fields do not involve it.
                 let mut multiple_used = false;
                 fields.for_each(|(field_id, _data)| {
-                    field_tys[field_id].walk(&mut |ty| match ty {
+                    field_tys[field_id].value.walk(&mut |ty| match ty {
-                        &Ty::Param { idx, .. } if idx == unsize_generic_index => {
+                        &Ty::Bound(idx) if idx == unsize_generic_index => multiple_used = true,
-                            multiple_used = true
-                        }
                         _ => {}
                     })
                 });

crates/ra_hir_ty/src/infer/expr.rs

@@ -10,7 +10,7 @@ use hir_def::{
     resolver::resolver_for_expr,
     AdtId, AssocContainerId, Lookup, StructFieldId,
 };
-use hir_expand::name::{name, Name};
+use hir_expand::name::Name;
 use ra_syntax::ast::RangeOp;
 
 use crate::{
@@ -19,8 +19,8 @@ use crate::{
     method_resolution, op,
     traits::InEnvironment,
     utils::{generics, variant_data, Generics},
-    ApplicationTy, CallableDef, InferTy, IntTy, Mutability, Obligation, Substs, TraitRef, Ty,
+    ApplicationTy, Binders, CallableDef, InferTy, IntTy, Mutability, Obligation, Substs, TraitRef,
-    TypeCtor, TypeWalk, Uncertain,
+    Ty, TypeCtor, Uncertain,
 };
 
 use super::{BindingMode, Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch};
@@ -236,8 +236,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                         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())
+                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
-                        .subst(&substs);
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
                 if let Some(expr) = spread {
@@ -588,10 +587,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 self.write_method_resolution(tgt_expr, func);
                 (ty, self.db.value_ty(func.into()), Some(generics(self.db, func.into())))
             }
-            None => (receiver_ty, Ty::Unknown, None),
+            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.apply_substs(substs);
+        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) {
@@ -635,7 +634,6 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     continue;
                 }
 
-                let param_ty = self.insert_vars_for_impl_trait(param_ty);
                 let param_ty = self.normalize_associated_types_in(param_ty);
                 self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
             }
@@ -648,13 +646,15 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         generic_args: Option<&GenericArgs>,
         receiver_ty: &Ty,
     ) -> Substs {
-        let (total_len, _parent_len, child_len) =
+        let (parent_params, self_params, type_params, impl_trait_params) =
-            def_generics.as_ref().map_or((0, 0, 0), |g| g.len_split());
+            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.name == name![Self] {
+                if param.provenance == hir_def::generics::TypeParamProvenance::TraitSelf {
                     substs.push(receiver_ty.clone());
                 } else {
                     substs.push(Ty::Unknown);
@@ -664,7 +664,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         // 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(child_len) {
+            for arg in generic_args.args.iter().take(type_params) {
                 match arg {
                     GenericArg::Type(type_ref) => {
                         let ty = self.make_ty(type_ref);

crates/ra_hir_ty/src/infer/pat.rs

@@ -12,7 +12,7 @@ use hir_expand::name::Name;
 use test_utils::tested_by;
 
 use super::{BindingMode, InferenceContext};
-use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor, TypeWalk};
+use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor};
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn infer_tuple_struct_pat(
@@ -34,8 +34,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             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())
+                .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
-                .subst(&substs);
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -65,7 +64,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         for subpat in subpats {
             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
             let expected_ty =
-                matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone()).subst(&substs);
+                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);
         }

crates/ra_hir_ty/src/infer/path.rs

@@ -9,9 +9,9 @@ use hir_def::{
 };
 use hir_expand::name::Name;
 
-use crate::{db::HirDatabase, method_resolution, Substs, Ty, TypeWalk, ValueTyDefId};
+use crate::{db::HirDatabase, method_resolution, Substs, Ty, ValueTyDefId};
 
-use super::{ExprOrPatId, InferenceContext, TraitEnvironment, TraitRef};
+use super::{ExprOrPatId, InferenceContext, TraitRef};
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     pub(super) fn infer_path(
@@ -39,7 +39,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
             let ty = self.make_ty(type_ref);
             let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
-            let ty = Ty::from_type_relative_path(self.db, resolver, ty, remaining_segments_for_ty);
+            let ctx = crate::lower::TyLoweringContext::new(self.db, &resolver);
+            let ty = Ty::from_type_relative_path(&ctx, ty, remaining_segments_for_ty);
             self.resolve_ty_assoc_item(
                 ty,
                 &path.segments().last().expect("path had at least one segment").name,
@@ -69,12 +70,16 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             ValueNs::EnumVariantId(it) => it.into(),
         };
 
-        let mut ty = self.db.value_ty(typable);
+        let ty = self.db.value_ty(typable);
-        if let Some(self_subst) = self_subst {
+        // self_subst is just for the parent
-            ty = ty.subst(&self_subst);
+        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(self.db, &self.resolver, path, typable);
+        let substs = Ty::substs_from_path(&ctx, path, typable);
-        let ty = ty.subst(&substs);
+        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)
     }
 
@@ -98,13 +103,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             (TypeNs::TraitId(trait_), true) => {
                 let segment =
                     remaining_segments.last().expect("there should be at least one segment here");
-                let trait_ref = TraitRef::from_resolved_path(
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
-                    self.db,
+                let trait_ref =
-                    &self.resolver,
+                    TraitRef::from_resolved_path(&ctx, trait_.into(), resolved_segment, None);
-                    trait_.into(),
-                    resolved_segment,
-                    None,
-                );
                 self.resolve_trait_assoc_item(trait_ref, segment, id)
             }
             (def, _) => {
@@ -114,9 +115,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 // 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(
-                    self.db,
+                    &ctx,
-                    &self.resolver,
                     def,
                     resolved_segment,
                     remaining_segments_for_ty,
@@ -173,13 +174,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             AssocItemId::ConstId(c) => ValueNs::ConstId(c),
             AssocItemId::TypeAliasId(_) => unreachable!(),
         };
-        let substs = Substs::build_for_def(self.db, item)
-            .use_parent_substs(&trait_ref.substs)
-            .fill_with_params()
-            .build();
 
         self.write_assoc_resolution(id, item);
-        Some((def, Some(substs)))
+        Some((def, Some(trait_ref.substs)))
     }
 
     fn resolve_ty_assoc_item(
@@ -193,14 +190,13 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         }
 
         let canonical_ty = self.canonicalizer().canonicalize_ty(ty.clone());
-        let env = TraitEnvironment::lower(self.db, &self.resolver);
         let krate = self.resolver.krate()?;
         let traits_in_scope = self.resolver.traits_in_scope(self.db);
 
         method_resolution::iterate_method_candidates(
             &canonical_ty.value,
             self.db,
-            env,
+            self.trait_env.clone(),
             krate,
             &traits_in_scope,
             Some(name),
@@ -219,12 +215,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             .fill(iter::repeat_with(|| self.table.new_type_var()))
                             .build();
                         let impl_self_ty = self.db.impl_self_ty(impl_id).subst(&impl_substs);
-                        let substs = Substs::build_for_def(self.db, item)
-                            .use_parent_substs(&impl_substs)
-                            .fill_with_params()
-                            .build();
                         self.unify(&impl_self_ty, &ty);
-                        Some(substs)
+                        Some(impl_substs)
                     }
                     AssocContainerId::TraitId(trait_) => {
                         // we're picking this method
@@ -232,15 +224,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             .push(ty.clone())
                             .fill(std::iter::repeat_with(|| self.table.new_type_var()))
                             .build();
-                        let substs = Substs::build_for_def(self.db, item)
-                            .use_parent_substs(&trait_substs)
-                            .fill_with_params()
-                            .build();
                         self.obligations.push(super::Obligation::Trait(TraitRef {
                             trait_,
-                            substs: trait_substs,
+                            substs: trait_substs.clone(),
                         }));
-                        Some(substs)
+                        Some(trait_substs)
                     }
                     AssocContainerId::ContainerId(_) => None,
                 };

crates/ra_hir_ty/src/lib.rs

@@ -44,8 +44,8 @@ use std::sync::Arc;
 use std::{fmt, iter, mem};
 
 use hir_def::{
-    expr::ExprId, type_ref::Mutability, AdtId, AssocContainerId, DefWithBodyId, GenericDefId,
+    expr::ExprId, generics::TypeParamProvenance, type_ref::Mutability, AdtId, AssocContainerId,
-    HasModule, Lookup, TraitId, TypeAliasId,
+    DefWithBodyId, GenericDefId, HasModule, Lookup, TraitId, TypeAliasId, TypeParamId,
 };
 use hir_expand::name::Name;
 use ra_db::{impl_intern_key, salsa, CrateId};
@@ -60,7 +60,9 @@ use display::{HirDisplay, HirFormatter};
 pub use autoderef::autoderef;
 pub use infer::{do_infer_query, InferTy, InferenceResult};
 pub use lower::CallableDef;
-pub use lower::{callable_item_sig, TyDefId, ValueTyDefId};
+pub use lower::{
+    callable_item_sig, ImplTraitLoweringMode, TyDefId, TyLoweringContext, ValueTyDefId,
+};
 pub use traits::{InEnvironment, Obligation, ProjectionPredicate, TraitEnvironment};
 
 /// A type constructor or type name: this might be something like the primitive
@@ -285,22 +287,20 @@ pub enum Ty {
     /// trait and all its parameters are fully known.
     Projection(ProjectionTy),
 
-    /// A type parameter; for example, `T` in `fn f<T>(x: T) {}
+    /// A placeholder for a type parameter; for example, `T` in `fn f<T>(x: T)
-    Param {
+    /// {}` when we're type-checking the body of that function. In this
-        /// The index of the parameter (starting with parameters from the
+    /// situation, we know this stands for *some* type, but don't know the exact
-        /// surrounding impl, then the current function).
+    /// type.
-        idx: u32,
+    Param(TypeParamId),
-        /// The name of the parameter, for displaying.
-        // FIXME get rid of this
-        name: Name,
-    },
 
-    /// A bound type variable. Used during trait resolution to represent Chalk
+    /// A bound type variable. This is used in various places: when representing
-    /// variables, and in `Dyn` and `Opaque` bounds to represent the `Self` type.
+    /// some polymorphic type like the type of function `fn f<T>`, the type
+    /// parameters get turned into variables; during trait resolution, inference
+    /// variables get turned into bound variables and back; and in `Dyn` the
+    /// `Self` type is represented with a bound variable as well.
     Bound(u32),
 
-    /// A type variable used during type checking. Not to be confused with a
+    /// A type variable used during type checking.
-    /// type parameter.
     Infer(InferTy),
 
     /// A trait object (`dyn Trait` or bare `Trait` in pre-2018 Rust).
@@ -364,15 +364,19 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn identity(generic_params: &Generics) -> Substs {
+    pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs {
-        Substs(
+        Substs(generic_params.iter().map(|(id, _)| Ty::Param(id)).collect())
-            generic_params.iter().map(|(idx, p)| Ty::Param { idx, name: p.name.clone() }).collect(),
+    }
-        )
+
+    /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
+    pub fn type_params(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> Substs {
+        let params = generics(db, def.into());
+        Substs::type_params_for_generics(&params)
     }
 
     /// Return Substs that replace each parameter by a bound variable.
     pub(crate) fn bound_vars(generic_params: &Generics) -> Substs {
-        Substs(generic_params.iter().map(|(idx, _p)| Ty::Bound(idx)).collect())
+        Substs(generic_params.iter().enumerate().map(|(idx, _)| Ty::Bound(idx as u32)).collect())
     }
 
     pub fn build_for_def(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> SubstsBuilder {
@@ -420,11 +424,6 @@ impl SubstsBuilder {
         self.fill((starting_from..).map(Ty::Bound))
     }
 
-    pub fn fill_with_params(self) -> Self {
-        let start = self.vec.len() as u32;
-        self.fill((start..).map(|idx| Ty::Param { idx, name: Name::missing() }))
-    }
-
     pub fn fill_with_unknown(self) -> Self {
         self.fill(iter::repeat(Ty::Unknown))
     }
@@ -451,6 +450,32 @@ impl Deref for Substs {
     }
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct Binders<T> {
+    pub num_binders: usize,
+    pub value: T,
+}
+
+impl<T> Binders<T> {
+    pub fn new(num_binders: usize, value: T) -> Self {
+        Self { num_binders, value }
+    }
+}
+
+impl<T: TypeWalk> Binders<T> {
+    /// Substitutes all variables.
+    pub fn subst(self, subst: &Substs) -> T {
+        assert_eq!(subst.len(), self.num_binders);
+        self.value.subst_bound_vars(subst)
+    }
+
+    /// Substitutes just a prefix of the variables (shifting the rest).
+    pub fn subst_prefix(self, subst: &Substs) -> Binders<T> {
+        assert!(subst.len() < self.num_binders);
+        Binders::new(self.num_binders - subst.len(), self.value.subst_bound_vars(subst))
+    }
+}
+
 /// A trait with type parameters. This includes the `Self`, so this represents a concrete type implementing the trait.
 /// Name to be bikeshedded: TraitBound? TraitImplements?
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
@@ -551,6 +576,9 @@ pub struct FnSig {
     params_and_return: Arc<[Ty]>,
 }
 
+/// A polymorphic function signature.
+pub type PolyFnSig = Binders<FnSig>;
+
 impl FnSig {
     pub fn from_params_and_return(mut params: Vec<Ty>, ret: Ty) -> FnSig {
         params.push(ret);
@@ -730,22 +758,7 @@ pub trait TypeWalk {
         self
     }
 
-    /// Replaces type parameters in this type using the given `Substs`. (So e.g.
+    /// Substitutes `Ty::Bound` vars with the given substitution.
-    /// if `self` is `&[T]`, where type parameter T has index 0, and the
-    /// `Substs` contain `u32` at index 0, we'll have `&[u32]` afterwards.)
-    fn subst(self, substs: &Substs) -> Self
-    where
-        Self: Sized,
-    {
-        self.fold(&mut |ty| match ty {
-            Ty::Param { idx, name } => {
-                substs.get(idx as usize).cloned().unwrap_or(Ty::Param { idx, name })
-            }
-            ty => ty,
-        })
-    }
-
-    /// Substitutes `Ty::Bound` vars (as opposed to type parameters).
     fn subst_bound_vars(mut self, substs: &Substs) -> Self
     where
         Self: Sized,
@@ -755,6 +768,9 @@ pub trait TypeWalk {
                 &mut Ty::Bound(idx) => {
                     if idx as usize >= binders && (idx as usize - binders) < substs.len() {
                         *ty = substs.0[idx as usize - binders].clone();
+                    } else if idx as usize >= binders + substs.len() {
+                        // shift free binders
+                        *ty = Ty::Bound(idx - substs.len() as u32);
                     }
                 }
                 _ => {}
@@ -847,7 +863,7 @@ impl HirDisplay for ApplicationTy {
             }
             TypeCtor::Array => {
                 let t = self.parameters.as_single();
-                write!(f, "[{};_]", t.display(f.db))?;
+                write!(f, "[{}; _]", t.display(f.db))?;
             }
             TypeCtor::RawPtr(m) => {
                 let t = self.parameters.as_single();
@@ -880,7 +896,7 @@ impl HirDisplay for ApplicationTy {
                 write!(f, ") -> {}", sig.ret().display(f.db))?;
             }
             TypeCtor::FnDef(def) => {
-                let sig = f.db.callable_item_signature(def);
+                let sig = f.db.callable_item_signature(def).subst(&self.parameters);
                 let name = match def {
                     CallableDef::FunctionId(ff) => f.db.function_data(ff).name.clone(),
                     CallableDef::StructId(s) => f.db.struct_data(s).name.clone(),
@@ -896,10 +912,17 @@ impl HirDisplay for ApplicationTy {
                     }
                 }
                 if self.parameters.len() > 0 {
+                    let generics = generics(f.db, 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, ", ")?;
+                        f.write_joined(&self.parameters.0[..total_len], ", ")?;
                         write!(f, ">")?;
                     }
+                }
                 write!(f, "(")?;
                 f.write_joined(sig.params(), ", ")?;
                 write!(f, ") -> {}", sig.ret().display(f.db))?;
@@ -1009,7 +1032,24 @@ impl HirDisplay for Ty {
         match self {
             Ty::Apply(a_ty) => a_ty.hir_fmt(f)?,
             Ty::Projection(p_ty) => p_ty.hir_fmt(f)?,
-            Ty::Param { name, .. } => write!(f, "{}", name)?,
+            Ty::Param(id) => {
+                let generics = generics(f.db, 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)?,
             Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
                 match self {
@@ -1017,6 +1057,19 @@ impl HirDisplay for Ty {
                     Ty::Opaque(_) => write!(f, "impl ")?,
                     _ => unreachable!(),
                 };
+                write_bounds_like_dyn_trait(&predicates, f)?;
+            }
+            Ty::Unknown => write!(f, "{{unknown}}")?,
+            Ty::Infer(..) => write!(f, "_")?,
+        }
+        Ok(())
+    }
+}
+
+fn write_bounds_like_dyn_trait(
+    predicates: &[GenericPredicate],
+    f: &mut HirFormatter<impl HirDatabase>,
+) -> fmt::Result {
     // 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
@@ -1055,9 +1108,7 @@ impl HirDisplay for Ty {
                     angle_open = true;
                 }
                 let name =
-                                f.db.type_alias_data(projection_pred.projection_ty.associated_ty)
+                    f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name.clone();
-                                    .name
-                                    .clone();
                 write!(f, "{} = ", name)?;
                 projection_pred.ty.hir_fmt(f)?;
             }
@@ -1077,12 +1128,7 @@ impl HirDisplay for Ty {
     if angle_open {
         write!(f, ">")?;
     }
-            }
-            Ty::Unknown => write!(f, "{{unknown}}")?,
-            Ty::Infer(..) => write!(f, "_")?,
-        }
     Ok(())
-    }
 }
 
 impl TraitRef {

crates/ra_hir_ty/src/lower.rs

@@ -10,12 +10,13 @@ use std::sync::Arc;
 
 use hir_def::{
     builtin_type::BuiltinType,
-    generics::WherePredicate,
+    generics::{TypeParamProvenance, WherePredicate, WherePredicateTarget},
     path::{GenericArg, Path, PathSegment, PathSegments},
     resolver::{HasResolver, Resolver, TypeNs},
     type_ref::{TypeBound, TypeRef},
     AdtId, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId, HasModule, ImplId,
-    LocalStructFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, UnionId, VariantId,
+    LocalStructFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, TypeParamId, UnionId,
+    VariantId,
 };
 use ra_arena::map::ArenaMap;
 use ra_db::CrateId;
@@ -27,64 +28,159 @@ use crate::{
         all_super_traits, associated_type_by_name_including_super_traits, generics, make_mut_slice,
         variant_data,
     },
-    FnSig, GenericPredicate, ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef,
+    Binders, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate, ProjectionTy, Substs,
-    Ty, TypeCtor, TypeWalk,
+    TraitEnvironment, TraitRef, Ty, TypeCtor,
 };
 
+#[derive(Debug)]
+pub struct TyLoweringContext<'a, DB: HirDatabase> {
+    pub db: &'a DB,
+    pub resolver: &'a Resolver,
+    /// Note: Conceptually, it's thinkable that we could be in a location where
+    /// some type params should be represented as placeholders, and others
+    /// should be converted to variables. I think in practice, this isn't
+    /// possible currently, so this should be fine for now.
+    pub type_param_mode: TypeParamLoweringMode,
+    pub impl_trait_mode: ImplTraitLoweringMode,
+    pub impl_trait_counter: std::cell::Cell<u16>,
+}
+
+impl<'a, DB: HirDatabase> TyLoweringContext<'a, DB> {
+    pub fn new(db: &'a DB, resolver: &'a Resolver) -> Self {
+        let impl_trait_counter = std::cell::Cell::new(0);
+        let impl_trait_mode = ImplTraitLoweringMode::Disallowed;
+        let type_param_mode = TypeParamLoweringMode::Placeholder;
+        Self { db, resolver, impl_trait_mode, impl_trait_counter, type_param_mode }
+    }
+
+    pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
+        Self { impl_trait_mode, ..self }
+    }
+
+    pub fn with_type_param_mode(self, type_param_mode: TypeParamLoweringMode) -> Self {
+        Self { type_param_mode, ..self }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ImplTraitLoweringMode {
+    /// `impl Trait` gets lowered into an opaque type that doesn't unify with
+    /// anything except itself. This is used in places where values flow 'out',
+    /// i.e. for arguments of the function we're currently checking, and return
+    /// types of functions we're calling.
+    Opaque,
+    /// `impl Trait` gets lowered into a type variable. Used for argument
+    /// position impl Trait when inside the respective function, since it allows
+    /// us to support that without Chalk.
+    Param,
+    /// `impl Trait` gets lowered into a variable that can unify with some
+    /// type. This is used in places where values flow 'in', i.e. for arguments
+    /// of functions we're calling, and the return type of the function we're
+    /// currently checking.
+    Variable,
+    /// `impl Trait` is disallowed and will be an error.
+    Disallowed,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum TypeParamLoweringMode {
+    Placeholder,
+    Variable,
+}
+
 impl Ty {
-    pub fn from_hir(db: &impl HirDatabase, resolver: &Resolver, type_ref: &TypeRef) -> Self {
+    pub fn from_hir(ctx: &TyLoweringContext<'_, impl HirDatabase>, type_ref: &TypeRef) -> Self {
         match type_ref {
             TypeRef::Never => Ty::simple(TypeCtor::Never),
             TypeRef::Tuple(inner) => {
-                let inner_tys: Arc<[Ty]> =
+                let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| Ty::from_hir(ctx, tr)).collect();
-                    inner.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect();
                 Ty::apply(
                     TypeCtor::Tuple { cardinality: inner_tys.len() as u16 },
                     Substs(inner_tys),
                 )
             }
-            TypeRef::Path(path) => Ty::from_hir_path(db, resolver, path),
+            TypeRef::Path(path) => Ty::from_hir_path(ctx, path),
             TypeRef::RawPtr(inner, mutability) => {
-                let inner_ty = Ty::from_hir(db, resolver, inner);
+                let inner_ty = Ty::from_hir(ctx, inner);
                 Ty::apply_one(TypeCtor::RawPtr(*mutability), inner_ty)
             }
             TypeRef::Array(inner) => {
-                let inner_ty = Ty::from_hir(db, resolver, inner);
+                let inner_ty = Ty::from_hir(ctx, inner);
                 Ty::apply_one(TypeCtor::Array, inner_ty)
             }
             TypeRef::Slice(inner) => {
-                let inner_ty = Ty::from_hir(db, resolver, inner);
+                let inner_ty = Ty::from_hir(ctx, inner);
                 Ty::apply_one(TypeCtor::Slice, inner_ty)
             }
             TypeRef::Reference(inner, mutability) => {
-                let inner_ty = Ty::from_hir(db, resolver, inner);
+                let inner_ty = Ty::from_hir(ctx, inner);
                 Ty::apply_one(TypeCtor::Ref(*mutability), inner_ty)
             }
             TypeRef::Placeholder => Ty::Unknown,
             TypeRef::Fn(params) => {
-                let sig = Substs(params.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect());
+                let sig = Substs(params.iter().map(|tr| Ty::from_hir(ctx, tr)).collect());
                 Ty::apply(TypeCtor::FnPtr { num_args: sig.len() as u16 - 1 }, sig)
             }
             TypeRef::DynTrait(bounds) => {
                 let self_ty = Ty::Bound(0);
                 let predicates = bounds
                     .iter()
-                    .flat_map(|b| {
+                    .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
-                    })
                     .collect();
                 Ty::Dyn(predicates)
             }
             TypeRef::ImplTrait(bounds) => {
+                match ctx.impl_trait_mode {
+                    ImplTraitLoweringMode::Opaque => {
                         let self_ty = Ty::Bound(0);
                         let predicates = bounds
                             .iter()
                             .flat_map(|b| {
-                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
+                                GenericPredicate::from_type_bound(ctx, b, self_ty.clone())
                             })
                             .collect();
                         Ty::Opaque(predicates)
                     }
+                    ImplTraitLoweringMode::Param => {
+                        let idx = ctx.impl_trait_counter.get();
+                        ctx.impl_trait_counter.set(idx + 1);
+                        if let Some(def) = ctx.resolver.generic_def() {
+                            let generics = generics(ctx.db, def);
+                            let param = generics
+                                .iter()
+                                .filter(|(_, data)| {
+                                    data.provenance == TypeParamProvenance::ArgumentImplTrait
+                                })
+                                .nth(idx as usize)
+                                .map_or(Ty::Unknown, |(id, _)| Ty::Param(id));
+                            param
+                        } else {
+                            Ty::Unknown
+                        }
+                    }
+                    ImplTraitLoweringMode::Variable => {
+                        let idx = ctx.impl_trait_counter.get();
+                        ctx.impl_trait_counter.set(idx + 1);
+                        let (parent_params, self_params, list_params, _impl_trait_params) =
+                            if let Some(def) = ctx.resolver.generic_def() {
+                                let generics = generics(ctx.db, def);
+                                generics.provenance_split()
+                            } else {
+                                (0, 0, 0, 0)
+                            };
+                        Ty::Bound(
+                            idx as u32
+                                + parent_params as u32
+                                + self_params as u32
+                                + list_params as u32,
+                        )
+                    }
+                    ImplTraitLoweringMode::Disallowed => {
+                        // FIXME: report error
+                        Ty::Unknown
+                    }
+                }
+            }
             TypeRef::Error => Ty::Unknown,
         }
     }
@@ -93,10 +189,9 @@ impl Ty {
     /// lower the self types of the predicates since that could lead to cycles.
     /// So we just check here if the `type_ref` resolves to a generic param, and which.
     fn from_hir_only_param(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         type_ref: &TypeRef,
-    ) -> Option<u32> {
+    ) -> Option<TypeParamId> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
             _ => return None,
@@ -107,29 +202,26 @@ impl Ty {
         if path.segments().len() > 1 {
             return None;
         }
-        let resolution = match resolver.resolve_path_in_type_ns(db, path.mod_path()) {
+        let resolution = match ctx.resolver.resolve_path_in_type_ns(ctx.db, path.mod_path()) {
             Some((it, None)) => it,
             _ => return None,
         };
         if let TypeNs::GenericParam(param_id) = resolution {
-            let generics = generics(db, resolver.generic_def().expect("generics in scope"));
+            Some(param_id)
-            let idx = generics.param_idx(param_id);
-            Some(idx)
         } else {
             None
         }
     }
 
     pub(crate) fn from_type_relative_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         ty: Ty,
         remaining_segments: PathSegments<'_>,
     ) -> Ty {
         if remaining_segments.len() == 1 {
             // resolve unselected assoc types
             let segment = remaining_segments.first().unwrap();
-            Ty::select_associated_type(db, resolver, ty, segment)
+            Ty::select_associated_type(ctx, ty, segment)
         } else if remaining_segments.len() > 1 {
             // FIXME report error (ambiguous associated type)
             Ty::Unknown
@@ -139,20 +231,18 @@ impl Ty {
     }
 
     pub(crate) fn from_partly_resolved_hir_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         resolution: TypeNs,
         resolved_segment: PathSegment<'_>,
         remaining_segments: PathSegments<'_>,
     ) -> Ty {
         let ty = match resolution {
             TypeNs::TraitId(trait_) => {
-                let trait_ref =
+                let trait_ref = TraitRef::from_resolved_path(ctx, trait_, resolved_segment, None);
-                    TraitRef::from_resolved_path(db, resolver, trait_, resolved_segment, None);
                 return if remaining_segments.len() == 1 {
                     let segment = remaining_segments.first().unwrap();
                     let associated_ty = associated_type_by_name_including_super_traits(
-                        db,
+                        ctx.db,
                         trait_ref.trait_,
                         &segment.name,
                     );
@@ -177,37 +267,55 @@ impl Ty {
                 };
             }
             TypeNs::GenericParam(param_id) => {
-                let generics = generics(db, resolver.generic_def().expect("generics in scope"));
+                let generics =
-                let idx = generics.param_idx(param_id);
+                    generics(ctx.db, ctx.resolver.generic_def().expect("generics in scope"));
-                // FIXME: maybe return name in resolution?
+                match ctx.type_param_mode {
-                let name = generics.param_name(param_id);
+                    TypeParamLoweringMode::Placeholder => Ty::Param(param_id),
-                Ty::Param { idx, name }
+                    TypeParamLoweringMode::Variable => {
+                        let idx = generics.param_idx(param_id).expect("matching generics");
+                        Ty::Bound(idx)
+                    }
+                }
+            }
+            TypeNs::SelfType(impl_id) => {
+                let generics = generics(ctx.db, impl_id.into());
+                let substs = match ctx.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => {
+                        Substs::type_params_for_generics(&generics)
+                    }
+                    TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
+                };
+                ctx.db.impl_self_ty(impl_id).subst(&substs)
+            }
+            TypeNs::AdtSelfType(adt) => {
+                let generics = generics(ctx.db, adt.into());
+                let substs = match ctx.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => {
+                        Substs::type_params_for_generics(&generics)
+                    }
+                    TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
+                };
+                ctx.db.ty(adt.into()).subst(&substs)
             }
-            TypeNs::SelfType(impl_id) => db.impl_self_ty(impl_id).clone(),
-            TypeNs::AdtSelfType(adt) => db.ty(adt.into()),
 
-            TypeNs::AdtId(it) => Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into()),
+            TypeNs::AdtId(it) => Ty::from_hir_path_inner(ctx, resolved_segment, it.into()),
-            TypeNs::BuiltinType(it) => {
+            TypeNs::BuiltinType(it) => Ty::from_hir_path_inner(ctx, resolved_segment, it.into()),
-                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
+            TypeNs::TypeAliasId(it) => Ty::from_hir_path_inner(ctx, resolved_segment, it.into()),
-            }
-            TypeNs::TypeAliasId(it) => {
-                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
-            }
             // FIXME: report error
             TypeNs::EnumVariantId(_) => return Ty::Unknown,
         };
 
-        Ty::from_type_relative_path(db, resolver, ty, remaining_segments)
+        Ty::from_type_relative_path(ctx, ty, remaining_segments)
     }
 
-    pub(crate) fn from_hir_path(db: &impl HirDatabase, resolver: &Resolver, path: &Path) -> Ty {
+    pub(crate) fn from_hir_path(ctx: &TyLoweringContext<'_, impl HirDatabase>, path: &Path) -> Ty {
         // Resolve the path (in type namespace)
         if let Some(type_ref) = path.type_anchor() {
-            let ty = Ty::from_hir(db, resolver, &type_ref);
+            let ty = Ty::from_hir(ctx, &type_ref);
-            return Ty::from_type_relative_path(db, resolver, ty, path.segments());
+            return Ty::from_type_relative_path(ctx, ty, path.segments());
         }
         let (resolution, remaining_index) =
-            match resolver.resolve_path_in_type_ns(db, path.mod_path()) {
+            match ctx.resolver.resolve_path_in_type_ns(ctx.db, path.mod_path()) {
                 Some(it) => it,
                 None => return Ty::Unknown,
             };
@@ -218,39 +326,44 @@ impl Ty {
             ),
             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
         };
-        Ty::from_partly_resolved_hir_path(
+        Ty::from_partly_resolved_hir_path(ctx, resolution, resolved_segment, remaining_segments)
-            db,
-            resolver,
-            resolution,
-            resolved_segment,
-            remaining_segments,
-        )
     }
 
     fn select_associated_type(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         self_ty: Ty,
         segment: PathSegment<'_>,
     ) -> Ty {
-        let param_idx = match self_ty {
+        let def = match ctx.resolver.generic_def() {
-            Ty::Param { idx, .. } => idx,
-            _ => return Ty::Unknown, // Error: Ambiguous associated type
-        };
-        let def = match resolver.generic_def() {
             Some(def) => def,
             None => return Ty::Unknown, // this can't actually happen
         };
-        let predicates = db.generic_predicates_for_param(def.into(), param_idx);
+        let param_id = match self_ty {
-        let traits_from_env = predicates.iter().filter_map(|pred| match pred {
+            Ty::Param(id) if ctx.type_param_mode == TypeParamLoweringMode::Placeholder => id,
-            GenericPredicate::Implemented(tr) if tr.self_ty() == &self_ty => Some(tr.trait_),
+            Ty::Bound(idx) if ctx.type_param_mode == TypeParamLoweringMode::Variable => {
+                let generics = generics(ctx.db, def);
+                let param_id = if let Some((id, _)) = generics.iter().nth(idx as usize) {
+                    id
+                } else {
+                    return Ty::Unknown;
+                };
+                param_id
+            }
+            _ => return Ty::Unknown, // Error: Ambiguous associated type
+        };
+        let predicates = ctx.db.generic_predicates_for_param(param_id);
+        let traits_from_env = predicates.iter().filter_map(|pred| match &pred.value {
+            GenericPredicate::Implemented(tr) => Some(tr.trait_),
             _ => None,
         });
-        let traits = traits_from_env.flat_map(|t| all_super_traits(db, t));
+        let traits = traits_from_env.flat_map(|t| all_super_traits(ctx.db, t));
         for t in traits {
-            if let Some(associated_ty) = db.trait_data(t).associated_type_by_name(&segment.name) {
+            if let Some(associated_ty) = ctx.db.trait_data(t).associated_type_by_name(&segment.name)
-                let substs =
+            {
-                    Substs::build_for_def(db, t).push(self_ty.clone()).fill_with_unknown().build();
+                let substs = Substs::build_for_def(ctx.db, t)
+                    .push(self_ty.clone())
+                    .fill_with_unknown()
+                    .build();
                 // FIXME handle type parameters on the segment
                 return Ty::Projection(ProjectionTy { associated_ty, parameters: substs });
             }
@@ -259,8 +372,7 @@ impl Ty {
     }
 
     fn from_hir_path_inner(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         segment: PathSegment<'_>,
         typable: TyDefId,
     ) -> Ty {
@@ -269,15 +381,14 @@ impl Ty {
             TyDefId::AdtId(it) => Some(it.into()),
             TyDefId::TypeAliasId(it) => Some(it.into()),
         };
-        let substs = substs_from_path_segment(db, resolver, segment, generic_def, false);
+        let substs = substs_from_path_segment(ctx, segment, generic_def, false);
-        db.ty(typable).subst(&substs)
+        ctx.db.ty(typable).subst(&substs)
     }
 
     /// Collect generic arguments from a path into a `Substs`. See also
     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
     pub(super) fn substs_from_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         path: &Path,
         // Note that we don't call `db.value_type(resolved)` here,
         // `ValueTyDefId` is just a convenient way to pass generics and
@@ -305,52 +416,49 @@ impl Ty {
                 (segment, Some(var.parent.into()))
             }
         };
-        substs_from_path_segment(db, resolver, segment, generic_def, false)
+        substs_from_path_segment(ctx, segment, generic_def, false)
     }
 }
 
 pub(super) fn substs_from_path_segment(
-    db: &impl HirDatabase,
+    ctx: &TyLoweringContext<'_, impl HirDatabase>,
-    resolver: &Resolver,
     segment: PathSegment<'_>,
     def_generic: Option<GenericDefId>,
-    add_self_param: bool,
+    _add_self_param: bool,
 ) -> Substs {
     let mut substs = Vec::new();
-    let def_generics = def_generic.map(|def| generics(db, def.into()));
+    let def_generics = def_generic.map(|def| generics(ctx.db, def.into()));
 
-    let (total_len, parent_len, child_len) = def_generics.map_or((0, 0, 0), |g| g.len_split());
+    let (parent_params, self_params, type_params, impl_trait_params) =
-    substs.extend(iter::repeat(Ty::Unknown).take(parent_len));
+        def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
-    if add_self_param {
+    substs.extend(iter::repeat(Ty::Unknown).take(parent_params));
-        // FIXME this add_self_param argument is kind of a hack: Traits have the
-        // Self type as an implicit first type parameter, but it can't be
-        // actually provided in the type arguments
-        // (well, actually sometimes it can, in the form of type-relative paths: `<Foo as Default>::default()`)
-        substs.push(Ty::Unknown);
-    }
     if let Some(generic_args) = &segment.args_and_bindings {
+        if !generic_args.has_self_type {
+            substs.extend(iter::repeat(Ty::Unknown).take(self_params));
+        }
+        let expected_num =
+            if generic_args.has_self_type { self_params + type_params } else { type_params };
+        let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
         // if args are provided, it should be all of them, but we can't rely on that
-        let self_param_correction = if add_self_param { 1 } else { 0 };
+        for arg in generic_args.args.iter().skip(skip).take(expected_num) {
-        let child_len = child_len - self_param_correction;
-        for arg in generic_args.args.iter().take(child_len) {
             match arg {
                 GenericArg::Type(type_ref) => {
-                    let ty = Ty::from_hir(db, resolver, type_ref);
+                    let ty = Ty::from_hir(ctx, type_ref);
                     substs.push(ty);
                 }
             }
         }
     }
+    let total_len = parent_params + self_params + type_params + impl_trait_params;
     // add placeholders for args that were not provided
-    let supplied_params = substs.len();
+    for _ in substs.len()..total_len {
-    for _ in supplied_params..total_len {
         substs.push(Ty::Unknown);
     }
     assert_eq!(substs.len(), total_len);
 
     // handle defaults
     if let Some(def_generic) = def_generic {
-        let default_substs = db.generic_defaults(def_generic.into());
+        let default_substs = ctx.db.generic_defaults(def_generic.into());
         assert_eq!(substs.len(), default_substs.len());
 
         for (i, default_ty) in default_substs.iter().enumerate() {
@@ -365,27 +473,25 @@ pub(super) fn substs_from_path_segment(
 
 impl TraitRef {
     fn from_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         path: &Path,
         explicit_self_ty: Option<Ty>,
     ) -> Option<Self> {
-        let resolved = match resolver.resolve_path_in_type_ns_fully(db, path.mod_path())? {
+        let resolved = match ctx.resolver.resolve_path_in_type_ns_fully(ctx.db, path.mod_path())? {
             TypeNs::TraitId(tr) => tr,
             _ => return None,
         };
         let segment = path.segments().last().expect("path should have at least one segment");
-        Some(TraitRef::from_resolved_path(db, resolver, resolved.into(), segment, explicit_self_ty))
+        Some(TraitRef::from_resolved_path(ctx, resolved.into(), segment, explicit_self_ty))
     }
 
     pub(crate) fn from_resolved_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         resolved: TraitId,
         segment: PathSegment<'_>,
         explicit_self_ty: Option<Ty>,
     ) -> Self {
-        let mut substs = TraitRef::substs_from_path(db, resolver, segment, resolved);
+        let mut substs = TraitRef::substs_from_path(ctx, segment, resolved);
         if let Some(self_ty) = explicit_self_ty {
             make_mut_slice(&mut substs.0)[0] = self_ty;
         }
@@ -393,8 +499,7 @@ impl TraitRef {
     }
 
     fn from_hir(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         type_ref: &TypeRef,
         explicit_self_ty: Option<Ty>,
     ) -> Option<Self> {
@@ -402,28 +507,26 @@ impl TraitRef {
             TypeRef::Path(path) => path,
             _ => return None,
         };
-        TraitRef::from_path(db, resolver, path, explicit_self_ty)
+        TraitRef::from_path(ctx, path, explicit_self_ty)
     }
 
     fn substs_from_path(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         segment: PathSegment<'_>,
         resolved: TraitId,
     ) -> Substs {
         let has_self_param =
             segment.args_and_bindings.as_ref().map(|a| a.has_self_type).unwrap_or(false);
-        substs_from_path_segment(db, resolver, segment, Some(resolved.into()), !has_self_param)
+        substs_from_path_segment(ctx, segment, Some(resolved.into()), !has_self_param)
     }
 
     pub(crate) fn from_type_bound(
-        db: &impl HirDatabase,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
-        resolver: &Resolver,
         bound: &TypeBound,
         self_ty: Ty,
     ) -> Option<TraitRef> {
         match bound {
-            TypeBound::Path(path) => TraitRef::from_path(db, resolver, path, Some(self_ty)),
+            TypeBound::Path(path) => TraitRef::from_path(ctx, path, Some(self_ty)),
             TypeBound::Error => None,
         }
     }
@@ -431,33 +534,44 @@ impl TraitRef {
 
 impl GenericPredicate {
     pub(crate) fn from_where_predicate<'a>(
-        db: &'a impl HirDatabase,
+        ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
-        resolver: &'a Resolver,
         where_predicate: &'a WherePredicate,
     ) -> impl Iterator<Item = GenericPredicate> + 'a {
-        let self_ty = Ty::from_hir(db, resolver, &where_predicate.type_ref);
+        let self_ty = match &where_predicate.target {
-        GenericPredicate::from_type_bound(db, resolver, &where_predicate.bound, self_ty)
+            WherePredicateTarget::TypeRef(type_ref) => Ty::from_hir(ctx, type_ref),
+            WherePredicateTarget::TypeParam(param_id) => {
+                let generic_def = ctx.resolver.generic_def().expect("generics in scope");
+                let generics = generics(ctx.db, generic_def);
+                let param_id = hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
+                match ctx.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => Ty::Param(param_id),
+                    TypeParamLoweringMode::Variable => {
+                        let idx = generics.param_idx(param_id).expect("matching generics");
+                        Ty::Bound(idx)
+                    }
+                }
+            }
+        };
+        GenericPredicate::from_type_bound(ctx, &where_predicate.bound, self_ty)
     }
 
     pub(crate) fn from_type_bound<'a>(
-        db: &'a impl HirDatabase,
+        ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
-        resolver: &'a Resolver,
         bound: &'a TypeBound,
         self_ty: Ty,
     ) -> impl Iterator<Item = GenericPredicate> + 'a {
-        let trait_ref = TraitRef::from_type_bound(db, &resolver, bound, self_ty);
+        let trait_ref = TraitRef::from_type_bound(ctx, bound, self_ty);
         iter::once(trait_ref.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented))
             .chain(
-                trait_ref.into_iter().flat_map(move |tr| {
+                trait_ref
-                    assoc_type_bindings_from_type_bound(db, resolver, bound, tr)
+                    .into_iter()
-                }),
+                    .flat_map(move |tr| assoc_type_bindings_from_type_bound(ctx, bound, tr)),
             )
     }
 }
 
 fn assoc_type_bindings_from_type_bound<'a>(
-    db: &'a impl HirDatabase,
+    ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
-    resolver: &'a Resolver,
     bound: &'a TypeBound,
     trait_ref: TraitRef,
 ) -> impl Iterator<Item = GenericPredicate> + 'a {
@@ -471,21 +585,21 @@ fn assoc_type_bindings_from_type_bound<'a>(
         .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
         .map(move |(name, type_ref)| {
             let associated_ty =
-                associated_type_by_name_including_super_traits(db, trait_ref.trait_, &name);
+                associated_type_by_name_including_super_traits(ctx.db, trait_ref.trait_, &name);
             let associated_ty = match associated_ty {
                 None => return GenericPredicate::Error,
                 Some(t) => t,
             };
             let projection_ty =
                 ProjectionTy { associated_ty, parameters: trait_ref.substs.clone() };
-            let ty = Ty::from_hir(db, resolver, type_ref);
+            let ty = Ty::from_hir(ctx, type_ref);
             let projection_predicate = ProjectionPredicate { projection_ty, ty };
             GenericPredicate::Projection(projection_predicate)
         })
 }
 
 /// Build the signature of a callable item (function, struct or enum variant).
-pub fn callable_item_sig(db: &impl HirDatabase, def: CallableDef) -> FnSig {
+pub fn callable_item_sig(db: &impl HirDatabase, def: CallableDef) -> PolyFnSig {
     match def {
         CallableDef::FunctionId(f) => fn_sig_for_fn(db, f),
         CallableDef::StructId(s) => fn_sig_for_struct_constructor(db, s),
@@ -497,16 +611,19 @@ pub fn callable_item_sig(db: &impl HirDatabase, def: CallableDef) -> FnSig {
 pub(crate) fn field_types_query(
     db: &impl HirDatabase,
     variant_id: VariantId,
-) -> Arc<ArenaMap<LocalStructFieldId, Ty>> {
+) -> Arc<ArenaMap<LocalStructFieldId, Binders<Ty>>> {
     let var_data = variant_data(db, variant_id);
-    let resolver = match variant_id {
+    let (resolver, def): (_, GenericDefId) = match variant_id {
-        VariantId::StructId(it) => it.resolver(db),
+        VariantId::StructId(it) => (it.resolver(db), it.into()),
-        VariantId::UnionId(it) => it.resolver(db),
+        VariantId::UnionId(it) => (it.resolver(db), it.into()),
-        VariantId::EnumVariantId(it) => it.parent.resolver(db),
+        VariantId::EnumVariantId(it) => (it.parent.resolver(db), it.parent.into()),
     };
+    let generics = generics(db, def);
     let mut res = ArenaMap::default();
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     for (field_id, field_data) in var_data.fields().iter() {
-        res.insert(field_id, Ty::from_hir(db, &resolver, &field_data.type_ref))
+        res.insert(field_id, Binders::new(generics.len(), Ty::from_hir(&ctx, &field_data.type_ref)))
     }
     Arc::new(res)
 }
@@ -521,32 +638,43 @@ pub(crate) fn field_types_query(
 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 pub(crate) fn generic_predicates_for_param_query(
     db: &impl HirDatabase,
-    def: GenericDefId,
+    param_id: TypeParamId,
-    param_idx: u32,
+) -> Arc<[Binders<GenericPredicate>]> {
-) -> Arc<[GenericPredicate]> {
+    let resolver = param_id.parent.resolver(db);
-    let resolver = def.resolver(db);
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
+    let generics = generics(db, param_id.parent);
     resolver
         .where_predicates_in_scope()
         // we have to filter out all other predicates *first*, before attempting to lower them
-        .filter(|pred| Ty::from_hir_only_param(db, &resolver, &pred.type_ref) == Some(param_idx))
+        .filter(|pred| match &pred.target {
-        .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+            WherePredicateTarget::TypeRef(type_ref) => {
+                Ty::from_hir_only_param(&ctx, type_ref) == Some(param_id)
+            }
+            WherePredicateTarget::TypeParam(local_id) => *local_id == param_id.local_id,
+        })
+        .flat_map(|pred| {
+            GenericPredicate::from_where_predicate(&ctx, pred)
+                .map(|p| Binders::new(generics.len(), p))
+        })
         .collect()
 }
 
 pub(crate) fn generic_predicates_for_param_recover(
     _db: &impl HirDatabase,
     _cycle: &[String],
-    _def: &GenericDefId,
+    _param_id: &TypeParamId,
-    _param_idx: &u32,
+) -> Arc<[Binders<GenericPredicate>]> {
-) -> Arc<[GenericPredicate]> {
     Arc::new([])
 }
 
 impl TraitEnvironment {
     pub fn lower(db: &impl HirDatabase, resolver: &Resolver) -> Arc<TraitEnvironment> {
+        let ctx = TyLoweringContext::new(db, &resolver)
+            .with_type_param_mode(TypeParamLoweringMode::Placeholder);
         let predicates = resolver
             .where_predicates_in_scope()
-            .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+            .flat_map(|pred| GenericPredicate::from_where_predicate(&ctx, pred))
             .collect::<Vec<_>>();
 
         Arc::new(TraitEnvironment { predicates })
@@ -557,57 +685,74 @@ impl TraitEnvironment {
 pub(crate) fn generic_predicates_query(
     db: &impl HirDatabase,
     def: GenericDefId,
-) -> Arc<[GenericPredicate]> {
+) -> Arc<[Binders<GenericPredicate>]> {
     let resolver = def.resolver(db);
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
+    let generics = generics(db, def);
     resolver
         .where_predicates_in_scope()
-        .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+        .flat_map(|pred| {
+            GenericPredicate::from_where_predicate(&ctx, pred)
+                .map(|p| Binders::new(generics.len(), p))
+        })
         .collect()
 }
 
 /// Resolve the default type params from generics
 pub(crate) fn generic_defaults_query(db: &impl HirDatabase, def: GenericDefId) -> Substs {
     let resolver = def.resolver(db);
+    let ctx = TyLoweringContext::new(db, &resolver);
     let generic_params = generics(db, def.into());
 
     let defaults = generic_params
         .iter()
-        .map(|(_idx, p)| p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(db, &resolver, t)))
+        .map(|(_idx, p)| p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(&ctx, t)))
         .collect();
 
     Substs(defaults)
 }
 
-fn fn_sig_for_fn(db: &impl HirDatabase, def: FunctionId) -> FnSig {
+fn fn_sig_for_fn(db: &impl HirDatabase, def: FunctionId) -> PolyFnSig {
     let data = db.function_data(def);
     let resolver = def.resolver(db);
-    let params = data.params.iter().map(|tr| Ty::from_hir(db, &resolver, tr)).collect::<Vec<_>>();
+    let ctx_params = TyLoweringContext::new(db, &resolver)
-    let ret = Ty::from_hir(db, &resolver, &data.ret_type);
+        .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
-    FnSig::from_params_and_return(params, ret)
+        .with_type_param_mode(TypeParamLoweringMode::Variable);
+    let params = data.params.iter().map(|tr| Ty::from_hir(&ctx_params, tr)).collect::<Vec<_>>();
+    let ctx_ret = ctx_params.with_impl_trait_mode(ImplTraitLoweringMode::Opaque);
+    let ret = Ty::from_hir(&ctx_ret, &data.ret_type);
+    let generics = generics(db, def.into());
+    let num_binders = generics.len();
+    Binders::new(num_binders, FnSig::from_params_and_return(params, ret))
 }
 
 /// Build the declared type of a function. This should not need to look at the
 /// function body.
-fn type_for_fn(db: &impl HirDatabase, def: FunctionId) -> Ty {
+fn type_for_fn(db: &impl HirDatabase, def: FunctionId) -> Binders<Ty> {
     let generics = generics(db, def.into());
-    let substs = Substs::identity(&generics);
+    let substs = Substs::bound_vars(&generics);
-    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+    Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(def.into()), substs))
 }
 
 /// Build the declared type of a const.
-fn type_for_const(db: &impl HirDatabase, def: ConstId) -> Ty {
+fn type_for_const(db: &impl HirDatabase, def: ConstId) -> Binders<Ty> {
     let data = db.const_data(def);
+    let generics = generics(db, def.into());
     let resolver = def.resolver(db);
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 
-    Ty::from_hir(db, &resolver, &data.type_ref)
+    Binders::new(generics.len(), Ty::from_hir(&ctx, &data.type_ref))
 }
 
 /// Build the declared type of a static.
-fn type_for_static(db: &impl HirDatabase, def: StaticId) -> Ty {
+fn type_for_static(db: &impl HirDatabase, def: StaticId) -> Binders<Ty> {
     let data = db.static_data(def);
     let resolver = def.resolver(db);
+    let ctx = TyLoweringContext::new(db, &resolver);
 
-    Ty::from_hir(db, &resolver, &data.type_ref)
+    Binders::new(0, Ty::from_hir(&ctx, &data.type_ref))
 }
 
 /// Build the declared type of a static.
@@ -621,68 +766,69 @@ fn type_for_builtin(def: BuiltinType) -> Ty {
     })
 }
 
-fn fn_sig_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> FnSig {
+fn fn_sig_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> PolyFnSig {
     let struct_data = db.struct_data(def.into());
     let fields = struct_data.variant_data.fields();
     let resolver = def.resolver(db);
-    let params = fields
+    let ctx =
-        .iter()
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
+    let params =
-        .collect::<Vec<_>>();
+        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
     let ret = type_for_adt(db, def.into());
-    FnSig::from_params_and_return(params, ret)
+    Binders::new(ret.num_binders, FnSig::from_params_and_return(params, ret.value))
 }
 
 /// Build the type of a tuple struct constructor.
-fn type_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> Ty {
+fn type_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> Binders<Ty> {
     let struct_data = db.struct_data(def.into());
     if struct_data.variant_data.is_unit() {
         return type_for_adt(db, def.into()); // Unit struct
     }
     let generics = generics(db, def.into());
-    let substs = Substs::identity(&generics);
+    let substs = Substs::bound_vars(&generics);
-    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+    Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(def.into()), substs))
 }
 
-fn fn_sig_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> FnSig {
+fn fn_sig_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> PolyFnSig {
     let enum_data = db.enum_data(def.parent);
     let var_data = &enum_data.variants[def.local_id];
     let fields = var_data.variant_data.fields();
     let resolver = def.parent.resolver(db);
-    let params = fields
+    let ctx =
-        .iter()
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
+    let params =
-        .collect::<Vec<_>>();
+        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
-    let generics = generics(db, def.parent.into());
+    let ret = type_for_adt(db, def.parent.into());
-    let substs = Substs::identity(&generics);
+    Binders::new(ret.num_binders, FnSig::from_params_and_return(params, ret.value))
-    let ret = type_for_adt(db, def.parent.into()).subst(&substs);
-    FnSig::from_params_and_return(params, ret)
 }
 
 /// Build the type of a tuple enum variant constructor.
-fn type_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> Ty {
+fn type_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId) -> Binders<Ty> {
     let enum_data = db.enum_data(def.parent);
     let var_data = &enum_data.variants[def.local_id].variant_data;
     if var_data.is_unit() {
         return type_for_adt(db, def.parent.into()); // Unit variant
     }
     let generics = generics(db, def.parent.into());
-    let substs = Substs::identity(&generics);
+    let substs = Substs::bound_vars(&generics);
-    Ty::apply(TypeCtor::FnDef(EnumVariantId::from(def).into()), substs)
+    Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(EnumVariantId::from(def).into()), substs))
 }
 
-fn type_for_adt(db: &impl HirDatabase, adt: AdtId) -> Ty {
+fn type_for_adt(db: &impl HirDatabase, adt: AdtId) -> Binders<Ty> {
     let generics = generics(db, adt.into());
-    Ty::apply(TypeCtor::Adt(adt), Substs::identity(&generics))
+    let substs = Substs::bound_vars(&generics);
+    Binders::new(substs.len(), Ty::apply(TypeCtor::Adt(adt), substs))
 }
 
-fn type_for_type_alias(db: &impl HirDatabase, t: TypeAliasId) -> Ty {
+fn type_for_type_alias(db: &impl HirDatabase, t: TypeAliasId) -> Binders<Ty> {
     let generics = generics(db, t.into());
     let resolver = t.resolver(db);
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     let type_ref = &db.type_alias_data(t).type_ref;
-    let substs = Substs::identity(&generics);
+    let substs = Substs::bound_vars(&generics);
-    let inner = Ty::from_hir(db, &resolver, type_ref.as_ref().unwrap_or(&TypeRef::Error));
+    let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
-    inner.subst(&substs)
+    Binders::new(substs.len(), inner)
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
@@ -736,19 +882,24 @@ impl_froms!(ValueTyDefId: FunctionId, StructId, EnumVariantId, ConstId, StaticId
 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
 /// the constructor function `(usize) -> Foo` which lives in the values
 /// namespace.
-pub(crate) fn ty_query(db: &impl HirDatabase, def: TyDefId) -> Ty {
+pub(crate) fn ty_query(db: &impl HirDatabase, def: TyDefId) -> Binders<Ty> {
     match def {
-        TyDefId::BuiltinType(it) => type_for_builtin(it),
+        TyDefId::BuiltinType(it) => Binders::new(0, type_for_builtin(it)),
         TyDefId::AdtId(it) => type_for_adt(db, it),
         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
     }
 }
 
-pub(crate) fn ty_recover(_db: &impl HirDatabase, _cycle: &[String], _def: &TyDefId) -> Ty {
+pub(crate) fn ty_recover(db: &impl HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
-    Ty::Unknown
+    let num_binders = match *def {
+        TyDefId::BuiltinType(_) => 0,
+        TyDefId::AdtId(it) => generics(db, it.into()).len(),
+        TyDefId::TypeAliasId(it) => generics(db, it.into()).len(),
+    };
+    Binders::new(num_binders, Ty::Unknown)
 }
 
-pub(crate) fn value_ty_query(db: &impl HirDatabase, def: ValueTyDefId) -> Ty {
+pub(crate) fn value_ty_query(db: &impl HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
     match def {
         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
         ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
@@ -758,24 +909,36 @@ pub(crate) fn value_ty_query(db: &impl HirDatabase, def: ValueTyDefId) -> Ty {
     }
 }
 
-pub(crate) fn impl_self_ty_query(db: &impl HirDatabase, impl_id: ImplId) -> Ty {
+pub(crate) fn impl_self_ty_query(db: &impl HirDatabase, impl_id: ImplId) -> Binders<Ty> {
     let impl_data = db.impl_data(impl_id);
     let resolver = impl_id.resolver(db);
-    Ty::from_hir(db, &resolver, &impl_data.target_type)
+    let generics = generics(db, impl_id.into());
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
+    Binders::new(generics.len(), Ty::from_hir(&ctx, &impl_data.target_type))
 }
 
 pub(crate) fn impl_self_ty_recover(
-    _db: &impl HirDatabase,
+    db: &impl HirDatabase,
     _cycle: &[String],
-    _impl_id: &ImplId,
+    impl_id: &ImplId,
-) -> Ty {
+) -> Binders<Ty> {
-    Ty::Unknown
+    let generics = generics(db, (*impl_id).into());
+    Binders::new(generics.len(), Ty::Unknown)
 }
 
-pub(crate) fn impl_trait_query(db: &impl HirDatabase, impl_id: ImplId) -> Option<TraitRef> {
+pub(crate) fn impl_trait_query(
+    db: &impl HirDatabase,
+    impl_id: ImplId,
+) -> Option<Binders<TraitRef>> {
     let impl_data = db.impl_data(impl_id);
     let resolver = impl_id.resolver(db);
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     let self_ty = db.impl_self_ty(impl_id);
     let target_trait = impl_data.target_trait.as_ref()?;
-    TraitRef::from_hir(db, &resolver, target_trait, Some(self_ty.clone()))
+    Some(Binders::new(
+        self_ty.num_binders,
+        TraitRef::from_hir(&ctx, target_trait, Some(self_ty.value.clone()))?,
+    ))
 }

crates/ra_hir_ty/src/marks.rs

@@ -6,5 +6,4 @@ test_utils::marks!(
     type_var_resolves_to_int_var
     match_ergonomics_ref
     coerce_merge_fail_fallback
-    insert_vars_for_impl_trait
 );

crates/ra_hir_ty/src/method_resolution.rs

@@ -61,11 +61,11 @@ impl CrateImplBlocks {
             for impl_id in module_data.scope.impls() {
                 match db.impl_trait(impl_id) {
                     Some(tr) => {
-                        res.impls_by_trait.entry(tr.trait_).or_default().push(impl_id);
+                        res.impls_by_trait.entry(tr.value.trait_).or_default().push(impl_id);
                     }
                     None => {
                         let self_ty = db.impl_self_ty(impl_id);
-                        if let Some(self_ty_fp) = TyFingerprint::for_impl(&self_ty) {
+                        if let Some(self_ty_fp) = TyFingerprint::for_impl(&self_ty.value) {
                             res.impls.entry(self_ty_fp).or_default().push(impl_id);
                         }
                     }
@@ -496,7 +496,7 @@ fn transform_receiver_ty(
         AssocContainerId::ContainerId(_) => unreachable!(),
     };
     let sig = db.callable_item_signature(function_id.into());
-    Some(sig.params()[0].clone().subst(&substs))
+    Some(sig.value.params()[0].clone().subst_bound_vars(&substs))
 }
 
 pub fn implements_trait(

crates/ra_hir_ty/src/tests/coercion.rs

@@ -71,42 +71,42 @@ fn test2() {
     [82; 93) '{ loop {} }': T
     [84; 91) 'loop {}': !
     [89; 91) '{}': ()
-    [122; 133) '{ loop {} }': *mut [T;_]
+    [122; 133) '{ loop {} }': *mut [T; _]
     [124; 131) 'loop {}': !
     [129; 131) '{}': ()
     [160; 173) '{     gen() }': *mut [U]
-    [166; 169) 'gen': fn gen<U>() -> *mut [T;_]
+    [166; 169) 'gen': fn gen<U>() -> *mut [U; _]
-    [166; 171) 'gen()': *mut [U;_]
+    [166; 171) 'gen()': *mut [U; _]
     [186; 420) '{     ...rr); }': ()
-    [196; 199) 'arr': &[u8;_]
+    [196; 199) 'arr': &[u8; _]
-    [212; 216) '&[1]': &[u8;_]
+    [212; 216) '&[1]': &[u8; _]
-    [213; 216) '[1]': [u8;_]
+    [213; 216) '[1]': [u8; _]
     [214; 215) '1': u8
     [227; 228) 'a': &[u8]
-    [237; 240) 'arr': &[u8;_]
+    [237; 240) 'arr': &[u8; _]
     [250; 251) 'b': u8
-    [254; 255) 'f': fn f<u8>(&[T]) -> T
+    [254; 255) 'f': fn f<u8>(&[u8]) -> u8
     [254; 260) 'f(arr)': u8
-    [256; 259) 'arr': &[u8;_]
+    [256; 259) 'arr': &[u8; _]
     [270; 271) 'c': &[u8]
     [280; 287) '{ arr }': &[u8]
-    [282; 285) 'arr': &[u8;_]
+    [282; 285) 'arr': &[u8; _]
     [297; 298) 'd': u8
-    [301; 302) 'g': fn g<u8>(S<&[T]>) -> T
+    [301; 302) 'g': fn g<u8>(S<&[u8]>) -> u8
     [301; 316) 'g(S { a: arr })': u8
     [303; 315) 'S { a: arr }': S<&[u8]>
-    [310; 313) 'arr': &[u8;_]
+    [310; 313) 'arr': &[u8; _]
-    [326; 327) 'e': [&[u8];_]
+    [326; 327) 'e': [&[u8]; _]
-    [341; 346) '[arr]': [&[u8];_]
+    [341; 346) '[arr]': [&[u8]; _]
-    [342; 345) 'arr': &[u8;_]
+    [342; 345) 'arr': &[u8; _]
-    [356; 357) 'f': [&[u8];_]
+    [356; 357) 'f': [&[u8]; _]
-    [371; 379) '[arr; 2]': [&[u8];_]
+    [371; 379) '[arr; 2]': [&[u8]; _]
-    [372; 375) 'arr': &[u8;_]
+    [372; 375) 'arr': &[u8; _]
     [377; 378) '2': usize
     [389; 390) 'g': (&[u8], &[u8])
     [407; 417) '(arr, arr)': (&[u8], &[u8])
-    [408; 411) 'arr': &[u8;_]
+    [408; 411) 'arr': &[u8; _]
-    [413; 416) 'arr': &[u8;_]
+    [413; 416) 'arr': &[u8; _]
     "###
     );
 }
@@ -122,8 +122,8 @@ fn test() {
         @r###"
     [11; 40) '{     ...[1]; }': ()
     [21; 22) 'x': &[i32]
-    [33; 37) '&[1]': &[i32;_]
+    [33; 37) '&[1]': &[i32; _]
-    [34; 37) '[1]': [i32;_]
+    [34; 37) '[1]': [i32; _]
     [35; 36) '1': i32
     "###);
 }
@@ -159,22 +159,22 @@ fn test(a: A<[u8; 2]>, b: B<[u8; 2]>, c: C<[u8; 2]>) {
     [334; 335) 'x': C<[T]>
     [355; 360) '{ x }': C<[T]>
     [357; 358) 'x': C<[T]>
-    [370; 371) 'a': A<[u8;_]>
+    [370; 371) 'a': A<[u8; _]>
-    [385; 386) 'b': B<[u8;_]>
+    [385; 386) 'b': B<[u8; _]>
-    [400; 401) 'c': C<[u8;_]>
+    [400; 401) 'c': C<[u8; _]>
     [415; 481) '{     ...(c); }': ()
     [425; 426) 'd': A<[{unknown}]>
-    [429; 433) 'foo1': fn foo1<{unknown}>(A<[T]>) -> A<[T]>
+    [429; 433) 'foo1': fn foo1<{unknown}>(A<[{unknown}]>) -> A<[{unknown}]>
     [429; 436) 'foo1(a)': A<[{unknown}]>
-    [434; 435) 'a': A<[u8;_]>
+    [434; 435) 'a': A<[u8; _]>
     [446; 447) 'e': B<[u8]>
-    [450; 454) 'foo2': fn foo2<u8>(B<[T]>) -> B<[T]>
+    [450; 454) 'foo2': fn foo2<u8>(B<[u8]>) -> B<[u8]>
     [450; 457) 'foo2(b)': B<[u8]>
-    [455; 456) 'b': B<[u8;_]>
+    [455; 456) 'b': B<[u8; _]>
     [467; 468) 'f': C<[u8]>
-    [471; 475) 'foo3': fn foo3<u8>(C<[T]>) -> C<[T]>
+    [471; 475) 'foo3': fn foo3<u8>(C<[u8]>) -> C<[u8]>
     [471; 478) 'foo3(c)': C<[u8]>
-    [476; 477) 'c': C<[u8;_]>
+    [476; 477) 'c': C<[u8; _]>
     "###
     );
 }
@@ -202,14 +202,14 @@ fn test() {
     [64; 123) 'if tru...     }': &[i32]
     [67; 71) 'true': bool
     [72; 97) '{     ...     }': &[i32]
-    [82; 85) 'foo': fn foo<i32>(&[T]) -> &[T]
+    [82; 85) 'foo': fn foo<i32>(&[i32]) -> &[i32]
     [82; 91) 'foo(&[1])': &[i32]
-    [86; 90) '&[1]': &[i32;_]
+    [86; 90) '&[1]': &[i32; _]
-    [87; 90) '[1]': [i32;_]
+    [87; 90) '[1]': [i32; _]
     [88; 89) '1': i32
-    [103; 123) '{     ...     }': &[i32;_]
+    [103; 123) '{     ...     }': &[i32; _]
-    [113; 117) '&[1]': &[i32;_]
+    [113; 117) '&[1]': &[i32; _]
-    [114; 117) '[1]': [i32;_]
+    [114; 117) '[1]': [i32; _]
     [115; 116) '1': i32
     "###
     );
@@ -237,15 +237,15 @@ fn test() {
     [60; 61) 'x': &[i32]
     [64; 123) 'if tru...     }': &[i32]
     [67; 71) 'true': bool
-    [72; 92) '{     ...     }': &[i32;_]
+    [72; 92) '{     ...     }': &[i32; _]
-    [82; 86) '&[1]': &[i32;_]
+    [82; 86) '&[1]': &[i32; _]
-    [83; 86) '[1]': [i32;_]
+    [83; 86) '[1]': [i32; _]
     [84; 85) '1': i32
     [98; 123) '{     ...     }': &[i32]
-    [108; 111) 'foo': fn foo<i32>(&[T]) -> &[T]
+    [108; 111) 'foo': fn foo<i32>(&[i32]) -> &[i32]
     [108; 117) 'foo(&[1])': &[i32]
-    [112; 116) '&[1]': &[i32;_]
+    [112; 116) '&[1]': &[i32; _]
-    [113; 116) '[1]': [i32;_]
+    [113; 116) '[1]': [i32; _]
     [114; 115) '1': i32
     "###
     );
@@ -275,18 +275,18 @@ fn test(i: i32) {
     [70; 147) 'match ...     }': &[i32]
     [76; 77) 'i': i32
     [88; 89) '2': i32
-    [93; 96) 'foo': fn foo<i32>(&[T]) -> &[T]
+    [93; 96) 'foo': fn foo<i32>(&[i32]) -> &[i32]
     [93; 102) 'foo(&[2])': &[i32]
-    [97; 101) '&[2]': &[i32;_]
+    [97; 101) '&[2]': &[i32; _]
-    [98; 101) '[2]': [i32;_]
+    [98; 101) '[2]': [i32; _]
     [99; 100) '2': i32
     [112; 113) '1': i32
-    [117; 121) '&[1]': &[i32;_]
+    [117; 121) '&[1]': &[i32; _]
-    [118; 121) '[1]': [i32;_]
+    [118; 121) '[1]': [i32; _]
     [119; 120) '1': i32
     [131; 132) '_': i32
-    [136; 140) '&[3]': &[i32;_]
+    [136; 140) '&[3]': &[i32; _]
-    [137; 140) '[3]': [i32;_]
+    [137; 140) '[3]': [i32; _]
     [138; 139) '3': i32
     "###
     );
@@ -316,18 +316,18 @@ fn test(i: i32) {
     [70; 147) 'match ...     }': &[i32]
     [76; 77) 'i': i32
     [88; 89) '1': i32
-    [93; 97) '&[1]': &[i32;_]
+    [93; 97) '&[1]': &[i32; _]
-    [94; 97) '[1]': [i32;_]
+    [94; 97) '[1]': [i32; _]
     [95; 96) '1': i32
     [107; 108) '2': i32
-    [112; 115) 'foo': fn foo<i32>(&[T]) -> &[T]
+    [112; 115) 'foo': fn foo<i32>(&[i32]) -> &[i32]
     [112; 121) 'foo(&[2])': &[i32]
-    [116; 120) '&[2]': &[i32;_]
+    [116; 120) '&[2]': &[i32; _]
-    [117; 120) '[2]': [i32;_]
+    [117; 120) '[2]': [i32; _]
     [118; 119) '2': i32
     [131; 132) '_': i32
-    [136; 140) '&[3]': &[i32;_]
+    [136; 140) '&[3]': &[i32; _]
-    [137; 140) '[3]': [i32;_]
+    [137; 140) '[3]': [i32; _]
     [138; 139) '3': i32
     "###
     );
@@ -438,16 +438,16 @@ fn test() {
     [43; 45) '*x': T
     [44; 45) 'x': &T
     [58; 127) '{     ...oo); }': ()
-    [64; 73) 'takes_ref': fn takes_ref<Foo>(&T) -> T
+    [64; 73) 'takes_ref': fn takes_ref<Foo>(&Foo) -> Foo
     [64; 79) 'takes_ref(&Foo)': Foo
     [74; 78) '&Foo': &Foo
     [75; 78) 'Foo': Foo
-    [85; 94) 'takes_ref': fn takes_ref<&Foo>(&T) -> T
+    [85; 94) 'takes_ref': fn takes_ref<&Foo>(&&Foo) -> &Foo
     [85; 101) 'takes_...&&Foo)': &Foo
     [95; 100) '&&Foo': &&Foo
     [96; 100) '&Foo': &Foo
     [97; 100) 'Foo': Foo
-    [107; 116) 'takes_ref': fn takes_ref<&&Foo>(&T) -> T
+    [107; 116) 'takes_ref': fn takes_ref<&&Foo>(&&&Foo) -> &&Foo
     [107; 124) 'takes_...&&Foo)': &&Foo
     [117; 123) '&&&Foo': &&&Foo
     [118; 123) '&&Foo': &&Foo

crates/ra_hir_ty/src/tests/method_resolution.rs

@@ -27,7 +27,7 @@ fn test() {
     [66; 73) 'loop {}': !
     [71; 73) '{}': ()
     [133; 160) '{     ...o"); }': ()
-    [139; 149) '<[_]>::foo': fn foo<u8>(&[T]) -> T
+    [139; 149) '<[_]>::foo': fn foo<u8>(&[u8]) -> u8
     [139; 157) '<[_]>:..."foo")': u8
     [150; 156) 'b"foo"': &[u8]
     "###
@@ -175,7 +175,7 @@ fn test() {
     [98; 101) 'val': T
     [123; 155) '{     ...32); }': ()
     [133; 134) 'a': Gen<u32>
-    [137; 146) 'Gen::make': fn make<u32>(T) -> Gen<T>
+    [137; 146) 'Gen::make': fn make<u32>(u32) -> Gen<u32>
     [137; 152) 'Gen::make(0u32)': Gen<u32>
     [147; 151) '0u32': u32
     "###
@@ -206,7 +206,7 @@ fn test() {
     [95; 98) '{ }': ()
     [118; 146) '{     ...e(); }': ()
     [128; 129) 'a': Gen<u32>
-    [132; 141) 'Gen::make': fn make<u32>() -> Gen<T>
+    [132; 141) 'Gen::make': fn make<u32>() -> Gen<u32>
     [132; 143) 'Gen::make()': Gen<u32>
     "###
     );
@@ -260,7 +260,7 @@ fn test() {
     [91; 94) '{ }': ()
     [114; 149) '{     ...e(); }': ()
     [124; 125) 'a': Gen<u32>
-    [128; 144) 'Gen::<...::make': fn make<u32>() -> Gen<T>
+    [128; 144) 'Gen::<...::make': fn make<u32>() -> Gen<u32>
     [128; 146) 'Gen::<...make()': Gen<u32>
     "###
     );
@@ -291,7 +291,7 @@ fn test() {
     [117; 120) '{ }': ()
     [140; 180) '{     ...e(); }': ()
     [150; 151) 'a': Gen<u32, u64>
-    [154; 175) 'Gen::<...::make': fn make<u64>() -> Gen<u32, T>
+    [154; 175) 'Gen::<...::make': fn make<u64>() -> Gen<u32, u64>
     [154; 177) 'Gen::<...make()': Gen<u32, u64>
     "###
     );
@@ -475,7 +475,7 @@ fn test() {
         @r###"
     [33; 37) 'self': &Self
     [102; 127) '{     ...d(); }': ()
-    [108; 109) 'S': S<u32>(T) -> S<T>
+    [108; 109) 'S': S<u32>(u32) -> S<u32>
     [108; 115) 'S(1u32)': S<u32>
     [108; 124) 'S(1u32...thod()': u32
     [110; 114) '1u32': u32
@@ -501,13 +501,13 @@ fn test() {
         @r###"
     [87; 193) '{     ...t(); }': ()
     [97; 99) 's1': S
-    [105; 121) 'Defaul...efault': fn default<S>() -> Self
+    [105; 121) 'Defaul...efault': fn default<S>() -> S
     [105; 123) 'Defaul...ault()': S
     [133; 135) 's2': S
-    [138; 148) 'S::default': fn default<S>() -> Self
+    [138; 148) 'S::default': fn default<S>() -> S
     [138; 150) 'S::default()': S
     [160; 162) 's3': S
-    [165; 188) '<S as ...efault': fn default<S>() -> Self
+    [165; 188) '<S as ...efault': fn default<S>() -> S
     [165; 190) '<S as ...ault()': S
     "###
     );
@@ -533,13 +533,13 @@ fn test() {
         @r###"
     [127; 211) '{     ...e(); }': ()
     [137; 138) 'a': u32
-    [141; 148) 'S::make': fn make<S, u32>() -> T
+    [141; 148) 'S::make': fn make<S, u32>() -> u32
     [141; 150) 'S::make()': u32
     [160; 161) 'b': u64
-    [164; 178) 'G::<u64>::make': fn make<G<u64>, u64>() -> T
+    [164; 178) 'G::<u64>::make': fn make<G<u64>, u64>() -> u64
     [164; 180) 'G::<u6...make()': u64
     [190; 191) 'c': f64
-    [199; 206) 'G::make': fn make<G<f64>, f64>() -> T
+    [199; 206) 'G::make': fn make<G<f64>, f64>() -> f64
     [199; 208) 'G::make()': f64
     "###
     );
@@ -567,19 +567,19 @@ fn test() {
         @r###"
     [135; 313) '{     ...e(); }': ()
     [145; 146) 'a': (u32, i64)
-    [149; 163) 'S::make::<i64>': fn make<S, u32, i64>() -> (T, U)
+    [149; 163) 'S::make::<i64>': fn make<S, u32, i64>() -> (u32, i64)
     [149; 165) 'S::mak...i64>()': (u32, i64)
     [175; 176) 'b': (u32, i64)
-    [189; 196) 'S::make': fn make<S, u32, i64>() -> (T, U)
+    [189; 196) 'S::make': fn make<S, u32, i64>() -> (u32, i64)
     [189; 198) 'S::make()': (u32, i64)
     [208; 209) 'c': (u32, i64)
-    [212; 233) 'G::<u3...:<i64>': fn make<G<u32>, u32, i64>() -> (T, U)
+    [212; 233) 'G::<u3...:<i64>': fn make<G<u32>, u32, i64>() -> (u32, i64)
     [212; 235) 'G::<u3...i64>()': (u32, i64)
     [245; 246) 'd': (u32, i64)
-    [259; 273) 'G::make::<i64>': fn make<G<u32>, u32, i64>() -> (T, U)
+    [259; 273) 'G::make::<i64>': fn make<G<u32>, u32, i64>() -> (u32, i64)
     [259; 275) 'G::mak...i64>()': (u32, i64)
     [285; 286) 'e': (u32, i64)
-    [301; 308) 'G::make': fn make<G<u32>, u32, i64>() -> (T, U)
+    [301; 308) 'G::make': fn make<G<u32>, u32, i64>() -> (u32, i64)
     [301; 310) 'G::make()': (u32, i64)
     "###
     );
@@ -601,7 +601,7 @@ fn test() {
         @r###"
     [101; 127) '{     ...e(); }': ()
     [111; 112) 'a': (S<i32>, i64)
-    [115; 122) 'S::make': fn make<S<i32>, i64>() -> (Self, T)
+    [115; 122) 'S::make': fn make<S<i32>, i64>() -> (S<i32>, i64)
     [115; 124) 'S::make()': (S<i32>, i64)
     "###
     );
@@ -625,10 +625,10 @@ fn test() {
         @r###"
     [131; 203) '{     ...e(); }': ()
     [141; 142) 'a': (S<u64>, i64)
-    [158; 165) 'S::make': fn make<S<u64>, i64>() -> (Self, T)
+    [158; 165) 'S::make': fn make<S<u64>, i64>() -> (S<u64>, i64)
     [158; 167) 'S::make()': (S<u64>, i64)
     [177; 178) 'b': (S<u32>, i32)
-    [191; 198) 'S::make': fn make<S<u32>, i32>() -> (Self, T)
+    [191; 198) 'S::make': fn make<S<u32>, i32>() -> (S<u32>, i32)
     [191; 200) 'S::make()': (S<u32>, i32)
     "###
     );
@@ -651,10 +651,10 @@ fn test() {
         @r###"
     [107; 211) '{     ...>(); }': ()
     [117; 118) 'a': (S<u64>, i64, u8)
-    [121; 150) '<S as ...::<u8>': fn make<S<u64>, i64, u8>() -> (Self, T, U)
+    [121; 150) '<S as ...::<u8>': fn make<S<u64>, i64, u8>() -> (S<u64>, i64, u8)
     [121; 152) '<S as ...<u8>()': (S<u64>, i64, u8)
     [162; 163) 'b': (S<u64>, i64, u8)
-    [182; 206) 'Trait:...::<u8>': fn make<S<u64>, i64, u8>() -> (Self, T, U)
+    [182; 206) 'Trait:...::<u8>': fn make<S<u64>, i64, u8>() -> (S<u64>, i64, u8)
     [182; 208) 'Trait:...<u8>()': (S<u64>, i64, u8)
     "###
     );
@@ -697,7 +697,7 @@ fn test<U, T: Trait<U>>(t: T) {
     [71; 72) 't': T
     [77; 96) '{     ...d(); }': ()
     [83; 84) 't': T
-    [83; 93) 't.method()': [missing name]
+    [83; 93) 't.method()': U
     "###
     );
 }
@@ -728,7 +728,7 @@ fn test() {
     [157; 158) 'S': S
     [157; 165) 'S.into()': u64
     [175; 176) 'z': u64
-    [179; 196) 'Into::...::into': fn into<S, u64>(Self) -> T
+    [179; 196) 'Into::...::into': fn into<S, u64>(S) -> u64
     [179; 199) 'Into::...nto(S)': u64
     [197; 198) 'S': S
     "###

crates/ra_hir_ty/src/tests/patterns.rs

@@ -96,13 +96,13 @@ fn test() {
     [38; 42) 'A(n)': A<i32>
     [40; 41) 'n': &i32
     [45; 50) '&A(1)': &A<i32>
-    [46; 47) 'A': A<i32>(T) -> A<T>
+    [46; 47) 'A': A<i32>(i32) -> A<i32>
     [46; 50) 'A(1)': A<i32>
     [48; 49) '1': i32
     [60; 64) 'A(n)': A<i32>
     [62; 63) 'n': &mut i32
     [67; 76) '&mut A(1)': &mut A<i32>
-    [72; 73) 'A': A<i32>(T) -> A<T>
+    [72; 73) 'A': A<i32>(i32) -> A<i32>
     [72; 76) 'A(1)': A<i32>
     [74; 75) '1': i32
     "###

crates/ra_hir_ty/src/tests/regression.rs

@@ -102,7 +102,7 @@ fn test() {
     [11; 48) '{     ...&y]; }': ()
     [21; 22) 'y': &{unknown}
     [25; 32) 'unknown': &{unknown}
-    [38; 45) '[y, &y]': [&&{unknown};_]
+    [38; 45) '[y, &y]': [&&{unknown}; _]
     [39; 40) 'y': &{unknown}
     [42; 44) '&y': &&{unknown}
     [43; 44) 'y': &{unknown}
@@ -128,7 +128,7 @@ fn test() {
     [25; 32) 'unknown': &&{unknown}
     [42; 43) 'y': &&{unknown}
     [46; 53) 'unknown': &&{unknown}
-    [59; 77) '[(x, y..., &x)]': [(&&&{unknown}, &&&{unknown});_]
+    [59; 77) '[(x, y..., &x)]': [(&&&{unknown}, &&&{unknown}); _]
     [60; 66) '(x, y)': (&&&{unknown}, &&&{unknown})
     [61; 62) 'x': &&{unknown}
     [64; 65) 'y': &&{unknown}
@@ -180,8 +180,8 @@ fn test_line_buffer() {
 "#),
         @r###"
     [23; 53) '{     ...n']; }': ()
-    [29; 50) '&[0, b...b'\n']': &[u8;_]
+    [29; 50) '&[0, b...b'\n']': &[u8; _]
-    [30; 50) '[0, b'...b'\n']': [u8;_]
+    [30; 50) '[0, b'...b'\n']': [u8; _]
     [31; 32) '0': u8
     [34; 39) 'b'\n'': u8
     [41; 42) '1': u8
@@ -346,7 +346,7 @@ pub fn main_loop() {
     @r###"
     [144; 146) '{}': ()
     [169; 198) '{     ...t(); }': ()
-    [175; 193) 'FxHash...efault': fn default<{unknown}, FxHasher>() -> HashSet<T, H>
+    [175; 193) 'FxHash...efault': fn default<{unknown}, FxHasher>() -> HashSet<{unknown}, FxHasher>
     [175; 195) 'FxHash...ault()': HashSet<{unknown}, FxHasher>
     "###
     );

crates/ra_hir_ty/src/tests/simple.rs

@@ -28,7 +28,7 @@ mod boxed {
 
 "#,
     );
-    assert_eq!("(Box<i32>, Box<Box<i32>>, Box<&i32>, Box<[i32;_]>)", type_at_pos(&db, pos));
+    assert_eq!("(Box<i32>, Box<Box<i32>>, Box<&i32>, Box<[i32; _]>)", type_at_pos(&db, pos));
 }
 
 #[test]
@@ -754,15 +754,15 @@ fn test() {
     [289; 295) 'self.0': T
     [315; 353) '{     ...))); }': ()
     [325; 326) 't': &i32
-    [329; 335) 'A::foo': fn foo<i32>(&A<T>) -> &T
+    [329; 335) 'A::foo': fn foo<i32>(&A<i32>) -> &i32
     [329; 350) 'A::foo...42))))': &i32
     [336; 349) '&&B(B(A(42)))': &&B<B<A<i32>>>
     [337; 349) '&B(B(A(42)))': &B<B<A<i32>>>
-    [338; 339) 'B': B<B<A<i32>>>(T) -> B<T>
+    [338; 339) 'B': B<B<A<i32>>>(B<A<i32>>) -> B<B<A<i32>>>
     [338; 349) 'B(B(A(42)))': B<B<A<i32>>>
-    [340; 341) 'B': B<A<i32>>(T) -> B<T>
+    [340; 341) 'B': B<A<i32>>(A<i32>) -> B<A<i32>>
     [340; 348) 'B(A(42))': B<A<i32>>
-    [342; 343) 'A': A<i32>(T) -> A<T>
+    [342; 343) 'A': A<i32>(i32) -> A<i32>
     [342; 347) 'A(42)': A<i32>
     [344; 346) '42': i32
     "###
@@ -817,16 +817,16 @@ fn test(a: A<i32>) {
     [326; 327) 'a': A<i32>
     [337; 383) '{     ...))); }': ()
     [347; 348) 't': &i32
-    [351; 352) 'A': A<i32>(*mut T) -> A<T>
+    [351; 352) 'A': A<i32>(*mut i32) -> A<i32>
     [351; 365) 'A(0 as *mut _)': A<i32>
     [351; 380) 'A(0 as...B(a)))': &i32
     [353; 354) '0': i32
     [353; 364) '0 as *mut _': *mut i32
     [370; 379) '&&B(B(a))': &&B<B<A<i32>>>
     [371; 379) '&B(B(a))': &B<B<A<i32>>>
-    [372; 373) 'B': B<B<A<i32>>>(T) -> B<T>
+    [372; 373) 'B': B<B<A<i32>>>(B<A<i32>>) -> B<B<A<i32>>>
     [372; 379) 'B(B(a))': B<B<A<i32>>>
-    [374; 375) 'B': B<A<i32>>(T) -> B<T>
+    [374; 375) 'B': B<A<i32>>(A<i32>) -> B<A<i32>>
     [374; 378) 'B(a)': B<A<i32>>
     [376; 377) 'a': A<i32>
     "###
@@ -1061,55 +1061,55 @@ fn test(x: &str, y: isize) {
     [9; 10) 'x': &str
     [18; 19) 'y': isize
     [28; 293) '{     ... []; }': ()
-    [38; 39) 'a': [&str;_]
+    [38; 39) 'a': [&str; _]
-    [42; 45) '[x]': [&str;_]
+    [42; 45) '[x]': [&str; _]
     [43; 44) 'x': &str
-    [55; 56) 'b': [[&str;_];_]
+    [55; 56) 'b': [[&str; _]; _]
-    [59; 65) '[a, a]': [[&str;_];_]
+    [59; 65) '[a, a]': [[&str; _]; _]
-    [60; 61) 'a': [&str;_]
+    [60; 61) 'a': [&str; _]
-    [63; 64) 'a': [&str;_]
+    [63; 64) 'a': [&str; _]
-    [75; 76) 'c': [[[&str;_];_];_]
+    [75; 76) 'c': [[[&str; _]; _]; _]
-    [79; 85) '[b, b]': [[[&str;_];_];_]
+    [79; 85) '[b, b]': [[[&str; _]; _]; _]
-    [80; 81) 'b': [[&str;_];_]
+    [80; 81) 'b': [[&str; _]; _]
-    [83; 84) 'b': [[&str;_];_]
+    [83; 84) 'b': [[&str; _]; _]
-    [96; 97) 'd': [isize;_]
+    [96; 97) 'd': [isize; _]
-    [100; 112) '[y, 1, 2, 3]': [isize;_]
+    [100; 112) '[y, 1, 2, 3]': [isize; _]
     [101; 102) 'y': isize
     [104; 105) '1': isize
     [107; 108) '2': isize
     [110; 111) '3': isize
-    [122; 123) 'd': [isize;_]
+    [122; 123) 'd': [isize; _]
-    [126; 138) '[1, y, 2, 3]': [isize;_]
+    [126; 138) '[1, y, 2, 3]': [isize; _]
     [127; 128) '1': isize
     [130; 131) 'y': isize
     [133; 134) '2': isize
     [136; 137) '3': isize
-    [148; 149) 'e': [isize;_]
+    [148; 149) 'e': [isize; _]
-    [152; 155) '[y]': [isize;_]
+    [152; 155) '[y]': [isize; _]
     [153; 154) 'y': isize
-    [165; 166) 'f': [[isize;_];_]
+    [165; 166) 'f': [[isize; _]; _]
-    [169; 175) '[d, d]': [[isize;_];_]
+    [169; 175) '[d, d]': [[isize; _]; _]
-    [170; 171) 'd': [isize;_]
+    [170; 171) 'd': [isize; _]
-    [173; 174) 'd': [isize;_]
+    [173; 174) 'd': [isize; _]
-    [185; 186) 'g': [[isize;_];_]
+    [185; 186) 'g': [[isize; _]; _]
-    [189; 195) '[e, e]': [[isize;_];_]
+    [189; 195) '[e, e]': [[isize; _]; _]
-    [190; 191) 'e': [isize;_]
+    [190; 191) 'e': [isize; _]
-    [193; 194) 'e': [isize;_]
+    [193; 194) 'e': [isize; _]
-    [206; 207) 'h': [i32;_]
+    [206; 207) 'h': [i32; _]
-    [210; 216) '[1, 2]': [i32;_]
+    [210; 216) '[1, 2]': [i32; _]
     [211; 212) '1': i32
     [214; 215) '2': i32
-    [226; 227) 'i': [&str;_]
+    [226; 227) 'i': [&str; _]
-    [230; 240) '["a", "b"]': [&str;_]
+    [230; 240) '["a", "b"]': [&str; _]
     [231; 234) '"a"': &str
     [236; 239) '"b"': &str
-    [251; 252) 'b': [[&str;_];_]
+    [251; 252) 'b': [[&str; _]; _]
-    [255; 265) '[a, ["b"]]': [[&str;_];_]
+    [255; 265) '[a, ["b"]]': [[&str; _]; _]
-    [256; 257) 'a': [&str;_]
+    [256; 257) 'a': [&str; _]
-    [259; 264) '["b"]': [&str;_]
+    [259; 264) '["b"]': [&str; _]
     [260; 263) '"b"': &str
-    [275; 276) 'x': [u8;_]
+    [275; 276) 'x': [u8; _]
-    [288; 290) '[]': [u8;_]
+    [288; 290) '[]': [u8; _]
     "###
     );
 }
@@ -1169,16 +1169,16 @@ fn test() {
 "#),
         @r###"
     [76; 184) '{     ...one; }': ()
-    [82; 83) 'A': A<i32>(T) -> A<T>
+    [82; 83) 'A': A<i32>(i32) -> A<i32>
     [82; 87) 'A(42)': A<i32>
     [84; 86) '42': i32
-    [93; 94) 'A': A<u128>(T) -> A<T>
+    [93; 94) 'A': A<u128>(u128) -> A<u128>
     [93; 102) 'A(42u128)': A<u128>
     [95; 101) '42u128': u128
-    [108; 112) 'Some': Some<&str>(T) -> Option<T>
+    [108; 112) 'Some': Some<&str>(&str) -> Option<&str>
     [108; 117) 'Some("x")': Option<&str>
     [113; 116) '"x"': &str
-    [123; 135) 'Option::Some': Some<&str>(T) -> Option<T>
+    [123; 135) 'Option::Some': Some<&str>(&str) -> Option<&str>
     [123; 140) 'Option...e("x")': Option<&str>
     [136; 139) '"x"': &str
     [146; 150) 'None': Option<{unknown}>
@@ -1205,14 +1205,14 @@ fn test() {
     [21; 26) '{ t }': T
     [23; 24) 't': T
     [38; 98) '{     ...(1); }': ()
-    [44; 46) 'id': fn id<u32>(T) -> T
+    [44; 46) 'id': fn id<u32>(u32) -> u32
     [44; 52) 'id(1u32)': u32
     [47; 51) '1u32': u32
-    [58; 68) 'id::<i128>': fn id<i128>(T) -> T
+    [58; 68) 'id::<i128>': fn id<i128>(i128) -> i128
     [58; 71) 'id::<i128>(1)': i128
     [69; 70) '1': i128
     [81; 82) 'x': u64
-    [90; 92) 'id': fn id<u64>(T) -> T
+    [90; 92) 'id': fn id<u64>(u64) -> u64
     [90; 95) 'id(1)': u64
     [93; 94) '1': u64
     "###
@@ -1220,7 +1220,7 @@ fn test() {
 }
 
 #[test]
-fn infer_impl_generics() {
+fn infer_impl_generics_basic() {
     assert_snapshot!(
         infer(r#"
 struct A<T1, T2> {
@@ -1349,16 +1349,16 @@ fn test() -> i128 {
     [146; 147) 'x': i128
     [150; 151) '1': i128
     [162; 163) 'y': i128
-    [166; 168) 'id': fn id<i128>(T) -> T
+    [166; 168) 'id': fn id<i128>(i128) -> i128
     [166; 171) 'id(x)': i128
     [169; 170) 'x': i128
     [182; 183) 'a': A<i128>
     [186; 200) 'A { x: id(y) }': A<i128>
-    [193; 195) 'id': fn id<i128>(T) -> T
+    [193; 195) 'id': fn id<i128>(i128) -> i128
     [193; 198) 'id(y)': i128
     [196; 197) 'y': i128
     [211; 212) 'z': i128
-    [215; 217) 'id': fn id<i128>(T) -> T
+    [215; 217) 'id': fn id<i128>(i128) -> i128
     [215; 222) 'id(a.x)': i128
     [218; 219) 'a': A<i128>
     [218; 221) 'a.x': i128
@@ -1502,14 +1502,14 @@ fn test() {
     [78; 158) '{     ...(1); }': ()
     [88; 89) 'y': u32
     [92; 97) '10u32': u32
-    [103; 105) 'id': fn id<u32>(T) -> T
+    [103; 105) 'id': fn id<u32>(u32) -> u32
     [103; 108) 'id(y)': u32
     [106; 107) 'y': u32
     [118; 119) 'x': bool
-    [128; 133) 'clone': fn clone<bool>(&T) -> T
+    [128; 133) 'clone': fn clone<bool>(&bool) -> bool
     [128; 136) 'clone(z)': bool
     [134; 135) 'z': &bool
-    [142; 152) 'id::<i128>': fn id<i128>(T) -> T
+    [142; 152) 'id::<i128>': fn id<i128>(i128) -> i128
     [142; 155) 'id::<i128>(1)': i128
     [153; 154) '1': i128
     "###

crates/ra_hir_ty/src/tests/traits.rs

@@ -1,7 +1,6 @@
 use insta::assert_snapshot;
 
 use ra_db::fixture::WithFixture;
-use test_utils::covers;
 
 use super::{infer, infer_with_mismatches, type_at, type_at_pos};
 use crate::test_db::TestDB;
@@ -261,10 +260,10 @@ fn test() {
     [92; 94) '{}': ()
     [105; 144) '{     ...(s); }': ()
     [115; 116) 's': S<u32>
-    [119; 120) 'S': S<u32>(T) -> S<T>
+    [119; 120) 'S': S<u32>(u32) -> S<u32>
     [119; 129) 'S(unknown)': S<u32>
     [121; 128) 'unknown': u32
-    [135; 138) 'foo': fn foo<S<u32>>(T) -> ()
+    [135; 138) 'foo': fn foo<S<u32>>(S<u32>) -> ()
     [135; 141) 'foo(s)': ()
     [139; 140) 's': S<u32>
     "###
@@ -289,11 +288,11 @@ fn test() {
     [98; 100) '{}': ()
     [111; 163) '{     ...(s); }': ()
     [121; 122) 's': S<u32>
-    [125; 126) 'S': S<u32>(T) -> S<T>
+    [125; 126) 'S': S<u32>(u32) -> S<u32>
     [125; 135) 'S(unknown)': S<u32>
     [127; 134) 'unknown': u32
     [145; 146) 'x': u32
-    [154; 157) 'foo': fn foo<u32, S<u32>>(T) -> U
+    [154; 157) 'foo': fn foo<u32, S<u32>>(S<u32>) -> u32
     [154; 160) 'foo(s)': u32
     [158; 159) 's': S<u32>
     "###
@@ -358,15 +357,15 @@ fn test() {
     [221; 223) '{}': ()
     [234; 300) '{     ...(S); }': ()
     [244; 245) 'x': u32
-    [248; 252) 'foo1': fn foo1<S>(T) -> <T as Iterable>::Item
+    [248; 252) 'foo1': fn foo1<S>(S) -> <S as Iterable>::Item
     [248; 255) 'foo1(S)': u32
     [253; 254) 'S': S
     [265; 266) 'y': u32
-    [269; 273) 'foo2': fn foo2<S>(T) -> <T as Iterable>::Item
+    [269; 273) 'foo2': fn foo2<S>(S) -> <S as Iterable>::Item
     [269; 276) 'foo2(S)': u32
     [274; 275) 'S': S
     [286; 287) 'z': u32
-    [290; 294) 'foo3': fn foo3<S>(T) -> <T as Iterable>::Item
+    [290; 294) 'foo3': fn foo3<S>(S) -> <S as Iterable>::Item
     [290; 297) 'foo3(S)': u32
     [295; 296) 'S': S
     "###
@@ -479,7 +478,7 @@ fn indexing_arrays() {
         @r###"
     [10; 26) '{ &mut...[2]; }': ()
     [12; 23) '&mut [9][2]': &mut {unknown}
-    [17; 20) '[9]': [i32;_]
+    [17; 20) '[9]': [i32; _]
     [17; 23) '[9][2]': {unknown}
     [18; 19) '9': i32
     [21; 22) '2': i32
@@ -822,8 +821,7 @@ fn test<T: ApplyL>() {
 "#,
     );
     // inside the generic function, the associated type gets normalized to a placeholder `ApplL::Out<T>` [https://rust-lang.github.io/rustc-guide/traits/associated-types.html#placeholder-associated-types].
-    // FIXME: fix type parameter names going missing when going through Chalk
+    assert_eq!(t, "ApplyL::Out<T>");
-    assert_eq!(t, "ApplyL::Out<[missing name]>");
 }
 
 #[test]
@@ -850,6 +848,198 @@ fn test<T: ApplyL>(t: T) {
 }
 
 #[test]
+fn argument_impl_trait() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait<T> {
+    fn foo(&self) -> T;
+    fn foo2(&self) -> i64;
+}
+fn bar(x: impl Trait<u16>) {}
+struct S<T>(T);
+impl<T> Trait<T> for S<T> {}
+
+fn test(x: impl Trait<u64>, y: &impl Trait<u32>) {
+    x;
+    y;
+    let z = S(1);
+    bar(z);
+    x.foo();
+    y.foo();
+    z.foo();
+    x.foo2();
+    y.foo2();
+    z.foo2();
+}
+"#, true),
+        @r###"
+    [30; 34) 'self': &Self
+    [55; 59) 'self': &Self
+    [78; 79) 'x': impl Trait<u16>
+    [98; 100) '{}': ()
+    [155; 156) 'x': impl Trait<u64>
+    [175; 176) 'y': &impl Trait<u32>
+    [196; 324) '{     ...2(); }': ()
+    [202; 203) 'x': impl Trait<u64>
+    [209; 210) 'y': &impl Trait<u32>
+    [220; 221) 'z': S<u16>
+    [224; 225) 'S': S<u16>(u16) -> S<u16>
+    [224; 228) 'S(1)': S<u16>
+    [226; 227) '1': u16
+    [234; 237) 'bar': fn bar(S<u16>) -> ()
+    [234; 240) 'bar(z)': ()
+    [238; 239) 'z': S<u16>
+    [246; 247) 'x': impl Trait<u64>
+    [246; 253) 'x.foo()': u64
+    [259; 260) 'y': &impl Trait<u32>
+    [259; 266) 'y.foo()': u32
+    [272; 273) 'z': S<u16>
+    [272; 279) 'z.foo()': u16
+    [285; 286) 'x': impl Trait<u64>
+    [285; 293) 'x.foo2()': i64
+    [299; 300) 'y': &impl Trait<u32>
+    [299; 307) 'y.foo2()': i64
+    [313; 314) 'z': S<u16>
+    [313; 321) 'z.foo2()': i64
+    "###
+    );
+}
+
+#[test]
+fn argument_impl_trait_type_args_1() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait {}
+trait Foo {
+    // this function has an implicit Self param, an explicit type param,
+    // and an implicit impl Trait param!
+    fn bar<T>(x: impl Trait) -> T { loop {} }
+}
+fn foo<T>(x: impl Trait) -> T { loop {} }
+struct S;
+impl Trait for S {}
+struct F;
+impl Foo for F {}
+
+fn test() {
+    Foo::bar(S);
+    <F as Foo>::bar(S);
+    F::bar(S);
+    Foo::bar::<u32>(S);
+    <F as Foo>::bar::<u32>(S);
+
+    foo(S);
+    foo::<u32>(S);
+    foo::<u32, i32>(S); // we should ignore the extraneous i32
+}
+"#, true),
+        @r###"
+    [156; 157) 'x': impl Trait
+    [176; 187) '{ loop {} }': T
+    [178; 185) 'loop {}': !
+    [183; 185) '{}': ()
+    [200; 201) 'x': impl Trait
+    [220; 231) '{ loop {} }': T
+    [222; 229) 'loop {}': !
+    [227; 229) '{}': ()
+    [301; 510) '{     ... i32 }': ()
+    [307; 315) 'Foo::bar': fn bar<{unknown}, {unknown}>(S) -> {unknown}
+    [307; 318) 'Foo::bar(S)': {unknown}
+    [316; 317) 'S': S
+    [324; 339) '<F as Foo>::bar': fn bar<F, {unknown}>(S) -> {unknown}
+    [324; 342) '<F as ...bar(S)': {unknown}
+    [340; 341) 'S': S
+    [348; 354) 'F::bar': fn bar<F, {unknown}>(S) -> {unknown}
+    [348; 357) 'F::bar(S)': {unknown}
+    [355; 356) 'S': S
+    [363; 378) 'Foo::bar::<u32>': fn bar<{unknown}, u32>(S) -> u32
+    [363; 381) 'Foo::b...32>(S)': u32
+    [379; 380) 'S': S
+    [387; 409) '<F as ...:<u32>': fn bar<F, u32>(S) -> u32
+    [387; 412) '<F as ...32>(S)': u32
+    [410; 411) 'S': S
+    [419; 422) 'foo': fn foo<{unknown}>(S) -> {unknown}
+    [419; 425) 'foo(S)': {unknown}
+    [423; 424) 'S': S
+    [431; 441) 'foo::<u32>': fn foo<u32>(S) -> u32
+    [431; 444) 'foo::<u32>(S)': u32
+    [442; 443) 'S': S
+    [450; 465) 'foo::<u32, i32>': fn foo<u32>(S) -> u32
+    [450; 468) 'foo::<...32>(S)': u32
+    [466; 467) 'S': S
+    "###
+    );
+}
+
+#[test]
+fn argument_impl_trait_type_args_2() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait {}
+struct S;
+impl Trait for S {}
+struct F<T>;
+impl<T> F<T> {
+    fn foo<U>(self, x: impl Trait) -> (T, U) { loop {} }
+}
+
+fn test() {
+    F.foo(S);
+    F::<u32>.foo(S);
+    F::<u32>.foo::<i32>(S);
+    F::<u32>.foo::<i32, u32>(S); // extraneous argument should be ignored
+}
+"#, true),
+        @r###"
+    [88; 92) 'self': F<T>
+    [94; 95) 'x': impl Trait
+    [119; 130) '{ loop {} }': (T, U)
+    [121; 128) 'loop {}': !
+    [126; 128) '{}': ()
+    [144; 284) '{     ...ored }': ()
+    [150; 151) 'F': F<{unknown}>
+    [150; 158) 'F.foo(S)': ({unknown}, {unknown})
+    [156; 157) 'S': S
+    [164; 172) 'F::<u32>': F<u32>
+    [164; 179) 'F::<u32>.foo(S)': (u32, {unknown})
+    [177; 178) 'S': S
+    [185; 193) 'F::<u32>': F<u32>
+    [185; 207) 'F::<u3...32>(S)': (u32, i32)
+    [205; 206) 'S': S
+    [213; 221) 'F::<u32>': F<u32>
+    [213; 240) 'F::<u3...32>(S)': (u32, i32)
+    [238; 239) 'S': S
+    "###
+    );
+}
+
+#[test]
+fn argument_impl_trait_to_fn_pointer() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait {}
+fn foo(x: impl Trait) { loop {} }
+struct S;
+impl Trait for S {}
+
+fn test() {
+    let f: fn(S) -> () = foo;
+}
+"#, true),
+        @r###"
+    [23; 24) 'x': impl Trait
+    [38; 49) '{ loop {} }': ()
+    [40; 47) 'loop {}': !
+    [45; 47) '{}': ()
+    [91; 124) '{     ...foo; }': ()
+    [101; 102) 'f': fn(S) -> ()
+    [118; 121) 'foo': fn foo(S) -> ()
+    "###
+    );
+}
+
+#[test]
+#[ignore]
 fn impl_trait() {
     assert_snapshot!(
         infer(r#"
@@ -993,34 +1183,23 @@ fn weird_bounds() {
     assert_snapshot!(
         infer(r#"
 trait Trait {}
-fn test() {
+fn test(a: impl Trait + 'lifetime, b: impl 'lifetime, c: impl (Trait), d: impl ('lifetime), e: impl ?Sized, f: impl Trait + ?Sized) {
-    let a: impl Trait + 'lifetime = foo;
-    let b: impl 'lifetime = foo;
-    let b: impl (Trait) = foo;
-    let b: impl ('lifetime) = foo;
-    let d: impl ?Sized = foo;
-    let e: impl Trait + ?Sized = foo;
 }
 "#),
         @r###"
-    [26; 237) '{     ...foo; }': ()
+    [24; 25) 'a': impl Trait + {error}
-    [36; 37) 'a': impl Trait + {error}
+    [51; 52) 'b': impl {error}
-    [64; 67) 'foo': impl Trait + {error}
+    [70; 71) 'c': impl Trait
-    [77; 78) 'b': impl {error}
+    [87; 88) 'd': impl {error}
-    [97; 100) 'foo': impl {error}
+    [108; 109) 'e': impl {error}
-    [110; 111) 'b': impl Trait
+    [124; 125) 'f': impl Trait + {error}
-    [128; 131) 'foo': impl Trait
+    [148; 151) '{ }': ()
-    [141; 142) 'b': impl {error}
-    [163; 166) 'foo': impl {error}
-    [176; 177) 'd': impl {error}
-    [193; 196) 'foo': impl {error}
-    [206; 207) 'e': impl Trait + {error}
-    [231; 234) 'foo': impl Trait + {error}
     "###
     );
 }
 
 #[test]
+#[ignore]
 fn error_bound_chalk() {
     let t = type_at(
         r#"
@@ -1076,26 +1255,26 @@ fn test<T: Trait<Type = u32>>(x: T, y: impl Trait<Type = i64>) {
     [296; 299) 'get': fn get<T>(T) -> <T as Trait>::Type
     [296; 302) 'get(x)': {unknown}
     [300; 301) 'x': T
-    [308; 312) 'get2': fn get2<{unknown}, T>(T) -> U
+    [308; 312) 'get2': fn get2<{unknown}, T>(T) -> {unknown}
     [308; 315) 'get2(x)': {unknown}
     [313; 314) 'x': T
-    [321; 324) 'get': fn get<impl Trait<Type = i64>>(T) -> <T as Trait>::Type
+    [321; 324) 'get': fn get<impl Trait<Type = i64>>(impl Trait<Type = i64>) -> <impl Trait<Type = i64> as Trait>::Type
     [321; 327) 'get(y)': {unknown}
     [325; 326) 'y': impl Trait<Type = i64>
-    [333; 337) 'get2': fn get2<{unknown}, impl Trait<Type = i64>>(T) -> U
+    [333; 337) 'get2': fn get2<{unknown}, impl Trait<Type = i64>>(impl Trait<Type = i64>) -> {unknown}
     [333; 340) 'get2(y)': {unknown}
     [338; 339) 'y': impl Trait<Type = i64>
-    [346; 349) 'get': fn get<S<u64>>(T) -> <T as Trait>::Type
+    [346; 349) 'get': fn get<S<u64>>(S<u64>) -> <S<u64> as Trait>::Type
     [346; 357) 'get(set(S))': u64
-    [350; 353) 'set': fn set<S<u64>>(T) -> T
+    [350; 353) 'set': fn set<S<u64>>(S<u64>) -> S<u64>
     [350; 356) 'set(S)': S<u64>
     [354; 355) 'S': S<u64>
-    [363; 367) 'get2': fn get2<u64, S<u64>>(T) -> U
+    [363; 367) 'get2': fn get2<u64, S<u64>>(S<u64>) -> u64
     [363; 375) 'get2(set(S))': u64
-    [368; 371) 'set': fn set<S<u64>>(T) -> T
+    [368; 371) 'set': fn set<S<u64>>(S<u64>) -> S<u64>
     [368; 374) 'set(S)': S<u64>
     [372; 373) 'S': S<u64>
-    [381; 385) 'get2': fn get2<str, S<str>>(T) -> U
+    [381; 385) 'get2': fn get2<str, S<str>>(S<str>) -> str
     [381; 395) 'get2(S::<str>)': str
     [386; 394) 'S::<str>': S<str>
     "###
@@ -1222,6 +1401,32 @@ fn test<T: Trait1, U: Trait2>(x: T, y: U) {
     );
 }
 
+#[test]
+fn super_trait_impl_trait_method_resolution() {
+    assert_snapshot!(
+        infer(r#"
+mod foo {
+    trait SuperTrait {
+        fn foo(&self) -> u32 {}
+    }
+}
+trait Trait1: foo::SuperTrait {}
+
+fn test(x: &impl Trait1) {
+    x.foo();
+}
+"#),
+        @r###"
+    [50; 54) 'self': &Self
+    [63; 65) '{}': ()
+    [116; 117) 'x': &impl Trait1
+    [133; 149) '{     ...o(); }': ()
+    [139; 140) 'x': &impl Trait1
+    [139; 146) 'x.foo()': u32
+    "###
+    );
+}
+
 #[test]
 fn super_trait_cycle() {
     // This just needs to not crash
@@ -1268,9 +1473,9 @@ fn test() {
     [157; 160) '{t}': T
     [158; 159) 't': T
     [259; 280) '{     ...S)); }': ()
-    [265; 269) 'get2': fn get2<u64, S<u64>>(T) -> U
+    [265; 269) 'get2': fn get2<u64, S<u64>>(S<u64>) -> u64
     [265; 277) 'get2(set(S))': u64
-    [270; 273) 'set': fn set<S<u64>>(T) -> T
+    [270; 273) 'set': fn set<S<u64>>(S<u64>) -> S<u64>
     [270; 276) 'set(S)': S<u64>
     [274; 275) 'S': S<u64>
     "###
@@ -1332,7 +1537,7 @@ fn test() {
     [173; 175) '{}': ()
     [189; 308) '{     ... 1); }': ()
     [199; 200) 'x': Option<u32>
-    [203; 215) 'Option::Some': Some<u32>(T) -> Option<T>
+    [203; 215) 'Option::Some': Some<u32>(u32) -> Option<u32>
     [203; 221) 'Option...(1u32)': Option<u32>
     [216; 220) '1u32': u32
     [227; 228) 'x': Option<u32>
@@ -1442,7 +1647,7 @@ fn test() {
     [340; 342) '{}': ()
     [356; 515) '{     ... S); }': ()
     [366; 368) 'x1': u64
-    [371; 375) 'foo1': fn foo1<S, u64, |S| -> u64>(T, F) -> U
+    [371; 375) 'foo1': fn foo1<S, u64, |S| -> u64>(S, |S| -> u64) -> u64
     [371; 394) 'foo1(S...hod())': u64
     [376; 377) 'S': S
     [379; 393) '|s| s.method()': |S| -> u64
@@ -1450,7 +1655,7 @@ fn test() {
     [383; 384) 's': S
     [383; 393) 's.method()': u64
     [404; 406) 'x2': u64
-    [409; 413) 'foo2': fn foo2<S, u64, |S| -> u64>(F, T) -> U
+    [409; 413) 'foo2': fn foo2<S, u64, |S| -> u64>(|S| -> u64, S) -> u64
     [409; 432) 'foo2(|...(), S)': u64
     [414; 428) '|s| s.method()': |S| -> u64
     [415; 416) 's': S
@@ -1603,7 +1808,6 @@ fn test<T, U>() where T: Trait<U::Item>, U: Trait<T::Item> {
 
 #[test]
 fn unify_impl_trait() {
-    covers!(insert_vars_for_impl_trait);
     assert_snapshot!(
         infer_with_mismatches(r#"
 trait Trait<T> {}
@@ -1635,26 +1839,26 @@ fn test() -> impl Trait<i32> {
     [172; 183) '{ loop {} }': T
     [174; 181) 'loop {}': !
     [179; 181) '{}': ()
-    [214; 310) '{     ...t()) }': S<i32>
+    [214; 310) '{     ...t()) }': S<{unknown}>
     [224; 226) 's1': S<u32>
-    [229; 230) 'S': S<u32>(T) -> S<T>
+    [229; 230) 'S': S<u32>(u32) -> S<u32>
     [229; 241) 'S(default())': S<u32>
-    [231; 238) 'default': fn default<u32>() -> T
+    [231; 238) 'default': fn default<u32>() -> u32
     [231; 240) 'default()': u32
-    [247; 250) 'foo': fn foo(impl Trait<u32>) -> ()
+    [247; 250) 'foo': fn foo(S<u32>) -> ()
     [247; 254) 'foo(s1)': ()
     [251; 253) 's1': S<u32>
     [264; 265) 'x': i32
-    [273; 276) 'bar': fn bar<i32>(impl Trait<T>) -> T
+    [273; 276) 'bar': fn bar<i32>(S<i32>) -> i32
     [273; 290) 'bar(S(...lt()))': i32
-    [277; 278) 'S': S<i32>(T) -> S<T>
+    [277; 278) 'S': S<i32>(i32) -> S<i32>
     [277; 289) 'S(default())': S<i32>
-    [279; 286) 'default': fn default<i32>() -> T
+    [279; 286) 'default': fn default<i32>() -> i32
     [279; 288) 'default()': i32
-    [296; 297) 'S': S<i32>(T) -> S<T>
+    [296; 297) 'S': S<{unknown}>({unknown}) -> S<{unknown}>
-    [296; 308) 'S(default())': S<i32>
+    [296; 308) 'S(default())': S<{unknown}>
-    [298; 305) 'default': fn default<i32>() -> T
+    [298; 305) 'default': fn default<{unknown}>() -> {unknown}
-    [298; 307) 'default()': i32
+    [298; 307) 'default()': {unknown}
     "###
     );
 }

crates/ra_hir_ty/src/traits.rs

@@ -50,10 +50,19 @@ impl TraitSolver {
             Err(_) => ra_db::Canceled::throw(),
         };
 
+        let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
+
         let solution = panic::catch_unwind({
             let solver = panic::AssertUnwindSafe(&mut solver);
             let context = panic::AssertUnwindSafe(&context);
-            move || solver.0.solve(context.0, goal)
+            move || {
+                solver.0.solve_limited(context.0, goal, || {
+                    context.0.db.check_canceled();
+                    let remaining = fuel.get();
+                    fuel.set(remaining - 1);
+                    remaining > 0
+                })
+            }
         });
 
         let solution = match solution {
@@ -78,7 +87,9 @@ impl TraitSolver {
 /// 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.
-const CHALK_SOLVER_MAX_SIZE: usize = 4;
+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> {
@@ -97,7 +108,8 @@ pub(crate) fn trait_solver_query(
 }
 
 fn create_chalk_solver() -> chalk_solve::Solver<TypeFamily> {
-    let solver_choice = chalk_solve::SolverChoice::SLG { max_size: CHALK_SOLVER_MAX_SIZE };
+    let solver_choice =
+        chalk_solve::SolverChoice::SLG { max_size: CHALK_SOLVER_MAX_SIZE, expected_answers: None };
     solver_choice.into_solver()
 }
 
@@ -232,7 +244,6 @@ fn solution_from_chalk(
     let convert_subst = |subst: chalk_ir::Canonical<chalk_ir::Substitution<TypeFamily>>| {
         let value = subst
             .value
-            .parameters
             .into_iter()
             .map(|p| {
                 let ty = match p.ty() {

crates/ra_hir_ty/src/traits/chalk.rs

@@ -3,7 +3,7 @@ use std::{fmt, sync::Arc};
 
 use log::debug;
 
-use chalk_ir::{cast::Cast, Parameter, PlaceholderIndex, TypeName, UniverseIndex};
+use chalk_ir::{cast::Cast, GoalData, Parameter, PlaceholderIndex, TypeName, UniverseIndex};
 
 use hir_def::{AssocContainerId, AssocItemId, GenericDefId, HasModule, Lookup, TypeAliasId};
 use ra_db::{
@@ -14,7 +14,7 @@ use ra_db::{
 use super::{builtin, AssocTyValue, Canonical, ChalkContext, Impl, Obligation};
 use crate::{
     db::HirDatabase, display::HirDisplay, utils::generics, ApplicationTy, GenericPredicate,
-    ProjectionTy, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
+    ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
 };
 
 #[derive(Debug, Copy, Clone, Hash, PartialOrd, Ord, PartialEq, Eq)]
@@ -24,6 +24,8 @@ impl chalk_ir::family::TypeFamily for TypeFamily {
     type InternedType = Box<chalk_ir::TyData<Self>>;
     type InternedLifetime = chalk_ir::LifetimeData<Self>;
     type InternedParameter = chalk_ir::ParameterData<Self>;
+    type InternedGoal = Arc<GoalData<Self>>;
+    type InternedSubstitution = Vec<Parameter<Self>>;
     type DefId = InternId;
 
     // FIXME: implement these
@@ -48,8 +50,8 @@ impl chalk_ir::family::TypeFamily for TypeFamily {
         None
     }
 
-    fn debug_projection(
+    fn debug_alias(
-        _projection: &chalk_ir::ProjectionTy<Self>,
+        _projection: &chalk_ir::AliasTy<Self>,
         _fmt: &mut fmt::Formatter<'_>,
     ) -> Option<fmt::Result> {
         None
@@ -78,6 +80,24 @@ impl chalk_ir::family::TypeFamily for TypeFamily {
     fn parameter_data(parameter: &chalk_ir::ParameterData<Self>) -> &chalk_ir::ParameterData<Self> {
         parameter
     }
+
+    fn intern_goal(goal: GoalData<Self>) -> Arc<GoalData<Self>> {
+        Arc::new(goal)
+    }
+
+    fn goal_data(goal: &Arc<GoalData<Self>>) -> &GoalData<Self> {
+        goal
+    }
+
+    fn intern_substitution<E>(
+        data: impl IntoIterator<Item = Result<Parameter<Self>, E>>,
+    ) -> Result<Vec<Parameter<Self>>, E> {
+        data.into_iter().collect()
+    }
+
+    fn substitution_data(substitution: &Vec<Parameter<Self>>) -> &[Parameter<Self>] {
+        substitution
+    }
 }
 
 impl chalk_ir::family::HasTypeFamily for TypeFamily {
@@ -114,16 +134,20 @@ impl ToChalk for Ty {
         match self {
             Ty::Apply(apply_ty) => {
                 let name = apply_ty.ctor.to_chalk(db);
-                let parameters = apply_ty.parameters.to_chalk(db);
+                let substitution = apply_ty.parameters.to_chalk(db);
-                chalk_ir::ApplicationTy { name, parameters }.cast().intern()
+                chalk_ir::ApplicationTy { name, substitution }.cast().intern()
             }
             Ty::Projection(proj_ty) => {
                 let associated_ty_id = proj_ty.associated_ty.to_chalk(db);
-                let parameters = proj_ty.parameters.to_chalk(db);
+                let substitution = proj_ty.parameters.to_chalk(db);
-                chalk_ir::ProjectionTy { associated_ty_id, parameters }.cast().intern()
+                chalk_ir::AliasTy { associated_ty_id, substitution }.cast().intern()
+            }
+            Ty::Param(id) => {
+                let interned_id = db.intern_type_param_id(id);
+                PlaceholderIndex {
+                    ui: UniverseIndex::ROOT,
+                    idx: interned_id.as_intern_id().as_usize(),
                 }
-            Ty::Param { idx, .. } => {
-                PlaceholderIndex { ui: UniverseIndex::ROOT, idx: idx as usize }
                 .to_ty::<TypeFamily>()
             }
             Ty::Bound(idx) => chalk_ir::TyData::BoundVar(idx as usize).intern(),
@@ -135,23 +159,13 @@ impl ToChalk for Ty {
                     .cloned()
                     .map(|p| p.to_chalk(db))
                     .collect();
-                let bounded_ty = chalk_ir::BoundedTy { bounds: make_binders(where_clauses, 1) };
+                let bounded_ty = chalk_ir::DynTy { bounds: make_binders(where_clauses, 1) };
                 chalk_ir::TyData::Dyn(bounded_ty).intern()
             }
-            Ty::Opaque(predicates) => {
+            Ty::Opaque(_) | Ty::Unknown => {
-                let where_clauses = predicates
+                let substitution = chalk_ir::Substitution::empty();
-                    .iter()
-                    .filter(|p| !p.is_error())
-                    .cloned()
-                    .map(|p| p.to_chalk(db))
-                    .collect();
-                let bounded_ty = chalk_ir::BoundedTy { bounds: make_binders(where_clauses, 1) };
-                chalk_ir::TyData::Opaque(bounded_ty).intern()
-            }
-            Ty::Unknown => {
-                let parameters = Vec::new();
                 let name = TypeName::Error;
-                chalk_ir::ApplicationTy { name, parameters }.cast().intern()
+                chalk_ir::ApplicationTy { name, substitution }.cast().intern()
             }
         }
     }
@@ -161,20 +175,23 @@ impl ToChalk for Ty {
                 TypeName::Error => Ty::Unknown,
                 _ => {
                     let ctor = from_chalk(db, apply_ty.name);
-                    let parameters = from_chalk(db, apply_ty.parameters);
+                    let parameters = from_chalk(db, apply_ty.substitution);
                     Ty::Apply(ApplicationTy { ctor, parameters })
                 }
             },
             chalk_ir::TyData::Placeholder(idx) => {
                 assert_eq!(idx.ui, UniverseIndex::ROOT);
-                Ty::Param { idx: idx.idx as u32, name: crate::Name::missing() }
+                let interned_id = crate::db::GlobalTypeParamId::from_intern_id(
+                    crate::salsa::InternId::from(idx.idx),
+                );
+                Ty::Param(db.lookup_intern_type_param_id(interned_id))
             }
-            chalk_ir::TyData::Projection(proj) => {
+            chalk_ir::TyData::Alias(proj) => {
                 let associated_ty = from_chalk(db, proj.associated_ty_id);
-                let parameters = from_chalk(db, proj.parameters);
+                let parameters = from_chalk(db, proj.substitution);
                 Ty::Projection(ProjectionTy { associated_ty, parameters })
             }
-            chalk_ir::TyData::ForAll(_) => unimplemented!(),
+            chalk_ir::TyData::Function(_) => unimplemented!(),
             chalk_ir::TyData::BoundVar(idx) => Ty::Bound(idx as u32),
             chalk_ir::TyData::InferenceVar(_iv) => Ty::Unknown,
             chalk_ir::TyData::Dyn(where_clauses) => {
@@ -183,27 +200,18 @@ impl ToChalk for Ty {
                     where_clauses.bounds.value.into_iter().map(|c| from_chalk(db, c)).collect();
                 Ty::Dyn(predicates)
             }
-            chalk_ir::TyData::Opaque(where_clauses) => {
-                assert_eq!(where_clauses.bounds.binders.len(), 1);
-                let predicates =
-                    where_clauses.bounds.value.into_iter().map(|c| from_chalk(db, c)).collect();
-                Ty::Opaque(predicates)
-            }
         }
     }
 }
 
 impl ToChalk for Substs {
-    type Chalk = Vec<chalk_ir::Parameter<TypeFamily>>;
+    type Chalk = chalk_ir::Substitution<TypeFamily>;
 
-    fn to_chalk(self, db: &impl HirDatabase) -> Vec<Parameter<TypeFamily>> {
+    fn to_chalk(self, db: &impl HirDatabase) -> chalk_ir::Substitution<TypeFamily> {
-        self.iter().map(|ty| ty.clone().to_chalk(db).cast()).collect()
+        chalk_ir::Substitution::from(self.iter().map(|ty| ty.clone().to_chalk(db)))
     }
 
-    fn from_chalk(
+    fn from_chalk(db: &impl HirDatabase, parameters: chalk_ir::Substitution<TypeFamily>) -> Substs {
-        db: &impl HirDatabase,
-        parameters: Vec<chalk_ir::Parameter<TypeFamily>>,
-    ) -> Substs {
         let tys = parameters
             .into_iter()
             .map(|p| match p.ty() {
@@ -220,13 +228,13 @@ impl ToChalk for TraitRef {
 
     fn to_chalk(self: TraitRef, db: &impl HirDatabase) -> chalk_ir::TraitRef<TypeFamily> {
         let trait_id = self.trait_.to_chalk(db);
-        let parameters = self.substs.to_chalk(db);
+        let substitution = self.substs.to_chalk(db);
-        chalk_ir::TraitRef { trait_id, parameters }
+        chalk_ir::TraitRef { trait_id, substitution }
     }
 
     fn from_chalk(db: &impl HirDatabase, trait_ref: chalk_ir::TraitRef<TypeFamily>) -> Self {
         let trait_ = from_chalk(db, trait_ref.trait_id);
-        let substs = from_chalk(db, trait_ref.parameters);
+        let substs = from_chalk(db, trait_ref.substitution);
         TraitRef { trait_, substs }
     }
 }
@@ -317,8 +325,8 @@ impl ToChalk for GenericPredicate {
                 make_binders(chalk_ir::WhereClause::Implemented(trait_ref.to_chalk(db)), 0)
             }
             GenericPredicate::Projection(projection_pred) => make_binders(
-                chalk_ir::WhereClause::ProjectionEq(chalk_ir::ProjectionEq {
+                chalk_ir::WhereClause::AliasEq(chalk_ir::AliasEq {
-                    projection: projection_pred.projection_ty.to_chalk(db),
+                    alias: projection_pred.projection_ty.to_chalk(db),
                     ty: projection_pred.ty.to_chalk(db),
                 }),
                 0,
@@ -335,8 +343,8 @@ impl ToChalk for GenericPredicate {
             chalk_ir::WhereClause::Implemented(tr) => {
                 GenericPredicate::Implemented(from_chalk(db, tr))
             }
-            chalk_ir::WhereClause::ProjectionEq(projection_eq) => {
+            chalk_ir::WhereClause::AliasEq(projection_eq) => {
-                let projection_ty = from_chalk(db, projection_eq.projection);
+                let projection_ty = from_chalk(db, projection_eq.alias);
                 let ty = from_chalk(db, projection_eq.ty);
                 GenericPredicate::Projection(super::ProjectionPredicate { projection_ty, ty })
             }
@@ -345,22 +353,22 @@ impl ToChalk for GenericPredicate {
 }
 
 impl ToChalk for ProjectionTy {
-    type Chalk = chalk_ir::ProjectionTy<TypeFamily>;
+    type Chalk = chalk_ir::AliasTy<TypeFamily>;
 
-    fn to_chalk(self, db: &impl HirDatabase) -> chalk_ir::ProjectionTy<TypeFamily> {
+    fn to_chalk(self, db: &impl HirDatabase) -> chalk_ir::AliasTy<TypeFamily> {
-        chalk_ir::ProjectionTy {
+        chalk_ir::AliasTy {
             associated_ty_id: self.associated_ty.to_chalk(db),
-            parameters: self.parameters.to_chalk(db),
+            substitution: self.parameters.to_chalk(db),
         }
     }
 
     fn from_chalk(
         db: &impl HirDatabase,
-        projection_ty: chalk_ir::ProjectionTy<TypeFamily>,
+        projection_ty: chalk_ir::AliasTy<TypeFamily>,
     ) -> ProjectionTy {
         ProjectionTy {
             associated_ty: from_chalk(db, projection_ty.associated_ty_id),
-            parameters: from_chalk(db, projection_ty.parameters),
+            parameters: from_chalk(db, projection_ty.substitution),
         }
     }
 }
@@ -369,10 +377,7 @@ impl ToChalk for super::ProjectionPredicate {
     type Chalk = chalk_ir::Normalize<TypeFamily>;
 
     fn to_chalk(self, db: &impl HirDatabase) -> chalk_ir::Normalize<TypeFamily> {
-        chalk_ir::Normalize {
+        chalk_ir::Normalize { alias: self.projection_ty.to_chalk(db), ty: self.ty.to_chalk(db) }
-            projection: self.projection_ty.to_chalk(db),
-            ty: self.ty.to_chalk(db),
-        }
     }
 
     fn from_chalk(_db: &impl HirDatabase, _normalize: chalk_ir::Normalize<TypeFamily>) -> Self {
@@ -522,7 +527,7 @@ fn convert_where_clauses(
     let generic_predicates = db.generic_predicates(def);
     let mut result = Vec::with_capacity(generic_predicates.len());
     for pred in generic_predicates.iter() {
-        if pred.is_error() {
+        if pred.value.is_error() {
             // skip errored predicates completely
             continue;
         }
@@ -711,12 +716,12 @@ fn impl_block_datum(
     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");
+        .expect("invalid impl passed to Chalk")
+        .value;
     let impl_data = db.impl_data(impl_id);
 
     let generic_params = generics(db, impl_id.into());
     let bound_vars = Substs::bound_vars(&generic_params);
-    let trait_ref = trait_ref.subst(&bound_vars);
     let trait_ = trait_ref.trait_;
     let impl_type = if impl_id.lookup(db).container.module(db).krate == krate {
         chalk_rust_ir::ImplType::Local
@@ -791,20 +796,18 @@ fn type_alias_associated_ty_value(
         _ => panic!("assoc ty value should be in impl"),
     };
 
-    let trait_ref = db.impl_trait(impl_id).expect("assoc ty value should not exist"); // we don't return any assoc ty values if the impl'd trait can't be resolved
+    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 generic_params = generics(db, impl_id.into());
+    let ty = db.ty(type_alias.into());
-    let bound_vars = Substs::bound_vars(&generic_params);
+    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.value.to_chalk(db) };
-    let ty = db.ty(type_alias.into()).subst(&bound_vars);
-    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.to_chalk(db) };
     let value = chalk_rust_ir::AssociatedTyValue {
         impl_id: Impl::ImplBlock(impl_id.into()).to_chalk(db),
         associated_ty_id: assoc_ty.to_chalk(db),
-        value: make_binders(value_bound, bound_vars.len()),
+        value: make_binders(value_bound, ty.num_binders),
     };
     Arc::new(value)
 }

crates/ra_hir_ty/src/utils.rs

@@ -2,10 +2,11 @@
 //! 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},
+    generics::{GenericParams, TypeParamData, TypeParamProvenance},
     path::Path,
     resolver::{HasResolver, TypeNs},
     type_ref::TypeRef,
@@ -19,11 +20,18 @@ fn direct_super_traits(db: &impl DefDatabase, trait_: TraitId) -> Vec<TraitId> {
     // 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)
-    db.generic_params(trait_.into())
+    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.type_ref {
+        .filter_map(|pred| match &pred.target {
-            TypeRef::Path(p) if p == &Path::from(name![Self]) => pred.bound.as_path(),
+            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()) {
@@ -95,41 +103,77 @@ pub(crate) struct Generics {
 }
 
 impl Generics {
-    pub(crate) fn iter<'a>(&'a self) -> impl Iterator<Item = (u32, &'a TypeParamData)> + 'a {
+    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())
+            .flat_map(|it| {
-            .chain(self.params.types.iter())
+                it.params
-            .enumerate()
+                    .types
-            .map(|(i, (_local_id, p))| (i as u32, p))
+                    .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 = (u32, &'a TypeParamData)> + 'a {
+    pub(crate) fn iter_parent<'a>(
-        self.parent_generics
+        &'a self,
-            .as_ref()
+    ) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
-            .into_iter()
+        self.parent_generics.as_ref().into_iter().flat_map(|it| {
-            .flat_map(|it| it.params.types.iter())
+            it.params
-            .enumerate()
+                .types
-            .map(|(i, (_local_id, p))| (i as u32, p))
+                .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)
     }
-    pub(crate) fn param_idx(&self, param: TypeParamId) -> u32 {
+
-        self.find_param(param).0
+    /// (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_name(&self, param: TypeParamId) -> Name {
+
-        self.find_param(param).1.name.clone()
+    pub(crate) fn param_idx(&self, param: TypeParamId) -> Option<u32> {
+        Some(self.find_param(param)?.0)
     }
-    fn find_param(&self, param: TypeParamId) -> (u32, &TypeParamData) {
+
+    fn find_param(&self, param: TypeParamId) -> Option<(u32, &TypeParamData)> {
         if param.parent == self.def {
             let (idx, (_local_id, data)) = self
                 .params
@@ -139,9 +183,10 @@ impl Generics {
                 .find(|(_, (idx, _))| *idx == param.local_id)
                 .unwrap();
             let (_total, parent_len, _child) = self.len_split();
-            return ((parent_len + idx) as u32, data);
+            Some(((parent_len + idx) as u32, data))
+        } else {
+            self.parent_generics.as_ref().and_then(|g| g.find_param(param))
         }
-        self.parent_generics.as_ref().unwrap().find_param(param)
     }
 }
 

crates/ra_ide/Cargo.toml

@@ -28,6 +28,7 @@ once_cell = "1.2.0"
 ra_syntax = { path = "../ra_syntax" }
 ra_text_edit = { path = "../ra_text_edit" }
 ra_db = { path = "../ra_db" }
+ra_ide_db = { path = "../ra_ide_db" }
 ra_cfg = { path = "../ra_cfg" }
 ra_fmt = { path = "../ra_fmt" }
 ra_prof = { path = "../ra_prof" }
@@ -39,7 +40,7 @@ ra_assists = { path = "../ra_assists" }
 hir = { path = "../ra_hir", package = "ra_hir" }
 
 [dev-dependencies]
-insta = "0.12.0"
+insta = "0.13.0"
 
 [dev-dependencies.proptest]
 version = "0.9.0"

crates/ra_ide/src/assists.rs

@@ -1,22 +1,23 @@
 //! FIXME: write short doc here
 
+use ra_assists::{resolved_assists, AssistAction, AssistLabel};
 use ra_db::{FilePosition, FileRange};
+use ra_ide_db::RootDatabase;
 
-use crate::{db::RootDatabase, FileId, SourceChange, SourceFileEdit};
+use crate::{FileId, SourceChange, SourceFileEdit};
 
-use either::Either;
 pub use ra_assists::AssistId;
-use ra_assists::{AssistAction, AssistLabel};
 
 #[derive(Debug)]
 pub struct Assist {
     pub id: AssistId,
     pub label: String,
-    pub change_data: Either<SourceChange, Vec<SourceChange>>,
+    pub group_label: Option<String>,
+    pub source_change: SourceChange,
 }
 
 pub(crate) fn assists(db: &RootDatabase, frange: FileRange) -> Vec<Assist> {
-    ra_assists::assists(db, frange)
+    resolved_assists(db, frange)
         .into_iter()
         .map(|assist| {
             let file_id = frange.file_id;
@@ -24,17 +25,8 @@ pub(crate) fn assists(db: &RootDatabase, frange: FileRange) -> Vec<Assist> {
             Assist {
                 id: assist_label.id,
                 label: assist_label.label.clone(),
-                change_data: match assist.action_data {
+                group_label: assist.group_label.map(|it| it.0),
-                    Either::Left(action) => {
+                source_change: action_to_edit(assist.action, file_id, assist_label),
-                        Either::Left(action_to_edit(action, file_id, assist_label))
-                    }
-                    Either::Right(actions) => Either::Right(
-                        actions
-                            .into_iter()
-                            .map(|action| action_to_edit(action, file_id, assist_label))
-                            .collect(),
-                    ),
-                },
             }
         })
         .collect()
@@ -46,9 +38,6 @@ fn action_to_edit(
     assist_label: &AssistLabel,
 ) -> SourceChange {
     let file_edit = SourceFileEdit { file_id, edit: action.edit };
-    SourceChange::source_file_edit(
+    SourceChange::source_file_edit(assist_label.label.clone(), file_edit)
-        action.label.unwrap_or_else(|| assist_label.label.clone()),
-        file_edit,
-    )
         .with_cursor_opt(action.cursor_position.map(|offset| FilePosition { offset, file_id }))
 }

crates/ra_ide/src/call_hierarchy.rs

@@ -3,6 +3,7 @@
 use indexmap::IndexMap;
 
 use hir::db::AstDatabase;
+use ra_ide_db::RootDatabase;
 use ra_syntax::{
     ast::{self, DocCommentsOwner},
     match_ast, AstNode, TextRange,
@@ -10,7 +11,6 @@ use ra_syntax::{
 
 use crate::{
     call_info::FnCallNode,
-    db::RootDatabase,
     display::{ShortLabel, ToNav},
     expand::descend_into_macros,
     goto_definition, references, FilePosition, NavigationTarget, RangeInfo,

crates/ra_ide/src/call_info.rs

@@ -1,15 +1,13 @@
 //! FIXME: write short doc here
 use hir::db::AstDatabase;
+use ra_ide_db::RootDatabase;
 use ra_syntax::{
     ast::{self, ArgListOwner},
     match_ast, AstNode, SyntaxNode,
 };
-
 use test_utils::tested_by;
 
-use crate::{
+use crate::{expand::descend_into_macros, CallInfo, FilePosition, FunctionSignature};
-    db::RootDatabase, expand::descend_into_macros, CallInfo, FilePosition, FunctionSignature,
-};
 
 /// Computes parameter information for the given call expression.
 pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<CallInfo> {

crates/ra_ide/src/completion.rs

@@ -18,6 +18,7 @@ mod complete_macro_in_item_position;
 mod complete_trait_impl;
 
 use ra_db::SourceDatabase;
+use ra_ide_db::RootDatabase;
 
 #[cfg(test)]
 use crate::completion::completion_item::do_completion;
@@ -26,7 +27,7 @@ use crate::{
         completion_context::CompletionContext,
         completion_item::{CompletionKind, Completions},
     },
-    db, FilePosition,
+    FilePosition,
 };
 
 pub use crate::completion::completion_item::{
@@ -55,7 +56,7 @@ pub use crate::completion::completion_item::{
 /// `foo` *should* be present among the completion variants. Filtering by
 /// identifier prefix/fuzzy match should be done higher in the stack, together
 /// with ordering of completions (currently this is done by the client).
-pub(crate) fn completions(db: &db::RootDatabase, position: FilePosition) -> Option<Completions> {
+pub(crate) fn completions(db: &RootDatabase, position: FilePosition) -> Option<Completions> {
     let original_parse = db.parse(position.file_id);
     let ctx = CompletionContext::new(db, &original_parse, position)?;
 

crates/ra_ide/src/completion/complete_scope.rs

@@ -1,11 +1,6 @@
 //! FIXME: write short doc here
 
-use ra_assists::auto_import_text_edit;
+use crate::completion::{CompletionContext, Completions};
-use ra_syntax::{ast, AstNode, SmolStr};
-use ra_text_edit::TextEditBuilder;
-use rustc_hash::FxHashMap;
-
-use crate::completion::{CompletionContext, CompletionItem, CompletionKind, Completions};
 
 pub(super) fn complete_scope(acc: &mut Completions, ctx: &CompletionContext) {
     if !ctx.is_trivial_path {
@@ -15,120 +10,14 @@ pub(super) fn complete_scope(acc: &mut Completions, ctx: &CompletionContext) {
     ctx.analyzer.process_all_names(ctx.db, &mut |name, res| {
         acc.add_resolution(ctx, name.to_string(), &res)
     });
-
-    // auto-import
-    // We fetch ident from the original file, because we need to pre-filter auto-imports
-    if ast::NameRef::cast(ctx.token.parent()).is_some() {
-        let import_resolver = ImportResolver::new();
-        let import_names = import_resolver.all_names(ctx.token.text());
-        import_names.into_iter().for_each(|(name, path)| {
-            let edit = {
-                let mut builder = TextEditBuilder::default();
-                builder.replace(ctx.source_range(), name.to_string());
-                auto_import_text_edit(
-                    &ctx.token.parent(),
-                    &ctx.token.parent(),
-                    &path,
-                    &mut builder,
-                );
-                builder.finish()
-            };
-
-            // Hack: copied this check form conv.rs beacause auto import can produce edits
-            // that invalidate assert in conv_with.
-            if edit
-                .as_atoms()
-                .iter()
-                .filter(|atom| !ctx.source_range().is_subrange(&atom.delete))
-                .all(|atom| ctx.source_range().intersection(&atom.delete).is_none())
-            {
-                CompletionItem::new(
-                    CompletionKind::Reference,
-                    ctx.source_range(),
-                    build_import_label(&name, &path),
-                )
-                .text_edit(edit)
-                .add_to(acc);
-            }
-        });
-    }
-}
-
-fn build_import_label(name: &str, path: &[SmolStr]) -> String {
-    let mut buf = String::with_capacity(64);
-    buf.push_str(name);
-    buf.push_str(" (");
-    fmt_import_path(path, &mut buf);
-    buf.push_str(")");
-    buf
-}
-
-fn fmt_import_path(path: &[SmolStr], buf: &mut String) {
-    let mut segments = path.iter();
-    if let Some(s) = segments.next() {
-        buf.push_str(&s);
-    }
-    for s in segments {
-        buf.push_str("::");
-        buf.push_str(&s);
-    }
-}
-
-#[derive(Debug, Clone, Default)]
-pub(crate) struct ImportResolver {
-    // todo: use fst crate or something like that
-    dummy_names: Vec<(SmolStr, Vec<SmolStr>)>,
-}
-
-impl ImportResolver {
-    pub(crate) fn new() -> Self {
-        let dummy_names = vec![
-            (SmolStr::new("fmt"), vec![SmolStr::new("std"), SmolStr::new("fmt")]),
-            (SmolStr::new("io"), vec![SmolStr::new("std"), SmolStr::new("io")]),
-            (SmolStr::new("iter"), vec![SmolStr::new("std"), SmolStr::new("iter")]),
-            (SmolStr::new("hash"), vec![SmolStr::new("std"), SmolStr::new("hash")]),
-            (
-                SmolStr::new("Debug"),
-                vec![SmolStr::new("std"), SmolStr::new("fmt"), SmolStr::new("Debug")],
-            ),
-            (
-                SmolStr::new("Display"),
-                vec![SmolStr::new("std"), SmolStr::new("fmt"), SmolStr::new("Display")],
-            ),
-            (
-                SmolStr::new("Hash"),
-                vec![SmolStr::new("std"), SmolStr::new("hash"), SmolStr::new("Hash")],
-            ),
-            (
-                SmolStr::new("Hasher"),
-                vec![SmolStr::new("std"), SmolStr::new("hash"), SmolStr::new("Hasher")],
-            ),
-            (
-                SmolStr::new("Iterator"),
-                vec![SmolStr::new("std"), SmolStr::new("iter"), SmolStr::new("Iterator")],
-            ),
-        ];
-
-        ImportResolver { dummy_names }
-    }
-
-    // Returns a map of importable items filtered by name.
-    // The map associates item name with its full path.
-    // todo: should return Resolutions
-    pub(crate) fn all_names(&self, name: &str) -> FxHashMap<SmolStr, Vec<SmolStr>> {
-        if name.len() > 1 {
-            self.dummy_names.iter().filter(|(n, _)| n.contains(name)).cloned().collect()
-        } else {
-            FxHashMap::default()
-        }
-    }
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::completion::{do_completion, CompletionItem, CompletionKind};
     use insta::assert_debug_snapshot;
 
+    use crate::completion::{do_completion, CompletionItem, CompletionKind};
+
     fn do_reference_completion(code: &str) -> Vec<CompletionItem> {
         do_completion(code, CompletionKind::Reference)
     }

crates/ra_ide/src/completion/complete_trait_impl.rs

@@ -2,7 +2,7 @@ use crate::completion::{CompletionContext, Completions, CompletionItem, Completi
 
 use ra_syntax::ast::{self, NameOwner, AstNode};
 
-use hir::{self, db::HirDatabase};
+use hir::{self, db::HirDatabase, Docs};
 
 
 pub(crate) fn complete_trait_impl(acc: &mut Completions, ctx: &CompletionContext) {

crates/ra_ide/src/completion/completion_context.rs

@@ -1,5 +1,6 @@
 //! FIXME: write short doc here
 
+use ra_ide_db::RootDatabase;
 use ra_syntax::{
     algo::{find_covering_element, find_node_at_offset},
     ast, AstNode, Parse, SourceFile,
@@ -8,13 +9,13 @@ use ra_syntax::{
 };
 use ra_text_edit::AtomTextEdit;
 
-use crate::{db, FilePosition};
+use crate::FilePosition;
 
 /// `CompletionContext` is created early during completion to figure out, where
 /// exactly is the cursor, syntax-wise.
 #[derive(Debug)]
 pub(crate) struct CompletionContext<'a> {
-    pub(super) db: &'a db::RootDatabase,
+    pub(super) db: &'a RootDatabase,
     pub(super) analyzer: hir::SourceAnalyzer,
     pub(super) offset: TextUnit,
     pub(super) token: SyntaxToken,
@@ -49,7 +50,7 @@ pub(crate) struct CompletionContext<'a> {
 
 impl<'a> CompletionContext<'a> {
     pub(super) fn new(
-        db: &'a db::RootDatabase,
+        db: &'a RootDatabase,
         original_parse: &'a Parse<ast::SourceFile>,
         position: FilePosition,
     ) -> Option<CompletionContext<'a>> {

crates/ra_ide/src/diagnostics.rs

@@ -5,6 +5,7 @@ use std::cell::RefCell;
 use hir::diagnostics::{AstDiagnostic, Diagnostic as _, DiagnosticSink};
 use itertools::Itertools;
 use ra_db::{RelativePath, SourceDatabase, SourceDatabaseExt};
+use ra_ide_db::RootDatabase;
 use ra_prof::profile;
 use ra_syntax::{
     algo,
@@ -13,7 +14,7 @@ use ra_syntax::{
 };
 use ra_text_edit::{TextEdit, TextEditBuilder};
 
-use crate::{db::RootDatabase, Diagnostic, FileId, FileSystemEdit, SourceChange, SourceFileEdit};
+use crate::{Diagnostic, FileId, FileSystemEdit, SourceChange, SourceFileEdit};
 
 #[derive(Debug, Copy, Clone)]
 pub enum Severity {

crates/ra_ide/src/display/function_signature.rs

@@ -4,13 +4,11 @@ use std::fmt::{self, Display};
 
 use hir::{Docs, Documentation, HasSource, HirDisplay};
 use join_to_string::join;
+use ra_ide_db::RootDatabase;
 use ra_syntax::ast::{self, AstNode, NameOwner, VisibilityOwner};
 use std::convert::From;
 
-use crate::{
+use crate::display::{generic_parameters, where_predicates};
-    db,
-    display::{generic_parameters, where_predicates},
-};
 
 #[derive(Debug)]
 pub enum CallableKind {
@@ -48,13 +46,13 @@ impl FunctionSignature {
         self
     }
 
-    pub(crate) fn from_hir(db: &db::RootDatabase, function: hir::Function) -> Self {
+    pub(crate) fn from_hir(db: &RootDatabase, function: hir::Function) -> Self {
         let doc = function.docs(db);
         let ast_node = function.source(db).value;
         FunctionSignature::from(&ast_node).with_doc_opt(doc)
     }
 
-    pub(crate) fn from_struct(db: &db::RootDatabase, st: hir::Struct) -> Option<Self> {
+    pub(crate) fn from_struct(db: &RootDatabase, st: hir::Struct) -> Option<Self> {
         let node: ast::StructDef = st.source(db).value;
         match node.kind() {
             ast::StructKind::Record(_) => return None,
@@ -86,10 +84,7 @@ impl FunctionSignature {
         )
     }
 
-    pub(crate) fn from_enum_variant(
+    pub(crate) fn from_enum_variant(db: &RootDatabase, variant: hir::EnumVariant) -> Option<Self> {
-        db: &db::RootDatabase,
-        variant: hir::EnumVariant,
-    ) -> Option<Self> {
         let node: ast::EnumVariant = variant.source(db).value;
         match node.kind() {
             ast::StructKind::Record(_) | ast::StructKind::Unit => return None,
@@ -126,7 +121,7 @@ impl FunctionSignature {
         )
     }
 
-    pub(crate) fn from_macro(db: &db::RootDatabase, macro_def: hir::MacroDef) -> Option<Self> {
+    pub(crate) fn from_macro(db: &RootDatabase, macro_def: hir::MacroDef) -> Option<Self> {
         let node: ast::MacroCall = macro_def.source(db).value;
 
         let params = vec![];

crates/ra_ide/src/display/navigation_target.rs

@@ -3,6 +3,7 @@
 use either::Either;
 use hir::{AssocItem, FieldSource, HasSource, InFile, ModuleSource};
 use ra_db::{FileId, SourceDatabase};
+use ra_ide_db::RootDatabase;
 use ra_syntax::{
     ast::{self, DocCommentsOwner, NameOwner},
     match_ast, AstNode, SmolStr,
@@ -10,7 +11,7 @@ use ra_syntax::{
     TextRange,
 };
 
-use crate::{db::RootDatabase, expand::original_range, FileSymbol};
+use crate::{expand::original_range, FileSymbol};
 
 use super::short_label::ShortLabel;