44 files changed, 1463 insertions, 1333 deletions

diff --git a/README.md b/README.md
index 2f6ed1e05..fabb8479d 100644
--- a/README.md
+++ b/README.md
@@ -2,13 +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:
 
 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/)
@@ -16,17 +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
-you might encounter critical bugs. That said, it is complete enough to provide a
-useful IDE experience and some people use it as a daily driver.
+rust-analyzer is a work-in-progress, so you might encounter critical bugs. That
+said, it is complete enough to provide a useful IDE experience and some people
+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
-(`code` and `cargo` in `$PATH`, etc), use this:
+To quickly install the rust-analyzer language server and VS Code extension with
+standard setup (`code` and `cargo` in `$PATH`, etc), use this:
 
 ```
 # clone the repo
@@ -44,8 +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
-under the hood, check the [./docs/dev](./docs/dev) folder.
+If you want to **contribute** to rust-analyzer or are just curious about how
+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
diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index 81f999090..5aab5fb8b 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -1,5 +1,4 @@
 //! This module defines `AssistCtx` -- the API surface that is exposed to assists.
-use either::Either;
 use hir::{InFile, SourceAnalyzer, SourceBinder};
 use ra_db::{FileRange, SourceDatabase};
 use ra_fmt::{leading_indent, reindent};
@@ -11,12 +10,36 @@ 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 {
-    Unresolved { label: AssistLabel },
-    Resolved { assist: ResolvedAssist },
+pub(crate) struct Assist(pub(crate) Vec<AssistInfo>);
+
+#[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>;
@@ -84,44 +107,21 @@ impl<'a> AssistCtx<'a> {
     ) -> Option<Assist> {
         let label = AssistLabel::new(label.into(), id);
 
-        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) } }
-        } else {
-            Assist::Unresolved { label }
+            info = info.resolved(action)
         };
 
-        Some(assist)
+        Some(Assist(vec![info]))
     }
 
-    pub(crate) fn add_assist_group(
-        self,
-        id: AssistId,
-        label: impl Into<String>,
-        f: impl FnOnce() -> Vec<ActionBuilder>,
-    ) -> Option<Assist> {
-        let label = AssistLabel::new(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 add_assist_group(self, group_name: impl Into<String>) -> AssistGroup<'a> {
+        AssistGroup { ctx: self, group_name: group_name.into(), assists: Vec::new() }
     }
 
     pub(crate) fn token_at_offset(&self) -> TokenAtOffset<SyntaxToken> {
@@ -155,20 +155,48 @@ impl<'a> AssistCtx<'a> {
     }
 }
 
+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 {
-    /// 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())
@@ -227,7 +255,6 @@ impl ActionBuilder {
             edit: self.edit.finish(),
             cursor_position: self.cursor_position,
             target: self.target,
-            label: self.label,
         }
     }
 }
diff --git a/crates/ra_assists/src/doc_tests.rs b/crates/ra_assists/src/doc_tests.rs
index ae0e5605c..c0f9bc1fb 100644
--- a/crates/ra_assists/src/doc_tests.rs
+++ b/crates/ra_assists/src/doc_tests.rs
@@ -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);
 }
diff --git a/crates/ra_assists/src/doc_tests/generated.rs b/crates/ra_assists/src/doc_tests/generated.rs
index 0d95b957b..4ab09b167 100644
--- a/crates/ra_assists/src/doc_tests/generated.rs
+++ b/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;
 
@@ -161,21 +161,6 @@ 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(
         "add_new",
@@ -592,6 +577,21 @@ 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(
         "split_import",
diff --git a/crates/ra_assists/src/handlers/add_new.rs b/crates/ra_assists/src/handlers/add_new.rs
index a08639311..2701eddb8 100644
--- a/crates/ra_assists/src/handlers/add_new.rs
+++ b/crates/ra_assists/src/handlers/add_new.rs
@@ -1,5 +1,5 @@
 use format_buf::format;
-use hir::InFile;
+use hir::{Adt, InFile};
 use join_to_string::join;
 use ra_syntax::{
     ast::{
@@ -135,16 +135,22 @@ fn find_struct_impl(ctx: &AssistCtx, strukt: &ast::StructDef) -> Option<Option<a
     })?;
     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) {
diff --git a/crates/ra_assists/src/handlers/auto_import.rs b/crates/ra_assists/src/handlers/auto_import.rs
index 84b5474f9..e88c121eb 100644
--- a/crates/ra_assists/src/handlers/auto_import.rs
+++ b/crates/ra_assists/src/handlers/auto_import.rs
@@ -1,13 +1,9 @@
-use hir::ModPath;
 use ra_ide_db::imports_locator::ImportsLocator;
-use ra_syntax::{
-    ast::{self, AstNode},
-    SyntaxNode,
-};
+use ra_syntax::ast::{self, AstNode};
 
 use crate::{
-    assist_ctx::{ActionBuilder, Assist, AssistCtx},
-    auto_import_text_edit, AssistId,
+    assist_ctx::{Assist, AssistCtx},
+    insert_use_statement, AssistId,
 };
 use std::collections::BTreeSet;
 
@@ -67,24 +63,24 @@ pub(crate) fn auto_import(ctx: AssistCtx) -> Option<Assist> {
         return None;
     }
 
-    ctx.add_assist_group(AssistId("auto_import"), format!("Import {}", name_to_import), || {
-        proposed_imports
-            .into_iter()
-            .map(|import| import_to_action(import, &position, &path_to_import_syntax))
-            .collect()
-    })
-}
-
-fn import_to_action(import: ModPath, position: &SyntaxNode, anchor: &SyntaxNode) -> ActionBuilder {
-    let mut action_builder = ActionBuilder::default();
-    action_builder.label(format!("Import `{}`", &import));
-    auto_import_text_edit(position, anchor, &import, action_builder.text_edit_builder());
-    action_builder
+    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_to_import_syntax.text_range());
+            insert_use_statement(
+                &position,
+                path_to_import_syntax,
+                &import,
+                edit.text_edit_builder(),
+            );
+        });
+    }
+    group.finish()
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::helpers::{check_assist, check_assist_not_applicable};
+    use crate::helpers::{check_assist, check_assist_not_applicable, check_assist_target};
 
     use super::*;
 
@@ -255,4 +251,19 @@ mod tests {
             ",
         );
     }
+
+    #[test]
+    fn auto_import_target() {
+        check_assist_target(
+            auto_import,
+            r"
+            struct AssistInfo {
+                group_label: Option<<|>GroupLabel>,
+            }
+
+            mod m { pub struct GroupLabel; }
+            ",
+            "GroupLabel",
+        )
+    }
 }
diff --git a/crates/ra_assists/src/handlers/add_import.rs b/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs
index f03dddac8..b70c88ec2 100644
--- a/crates/ra_assists/src/handlers/add_import.rs
+++ b/crates/ra_assists/src/handlers/replace_qualified_name_with_use.rs
@@ -12,10 +12,10 @@ use crate::{
     AssistId,
 };
 
-/// This function produces sequence of text edits into edit
-/// to import the target path in the most appropriate scope given
-/// the cursor position
-pub fn auto_import_text_edit(
+/// Creates and inserts a use statement for the given path to import.
+/// The use statement is inserted in the scope most appropriate to the
+/// the cursor position given, additionally merged with the existing use imports.
+pub fn insert_use_statement(
     // Ideally the position of the cursor, used to
     position: &SyntaxNode,
     // The statement to use as anchor (last resort)
@@ -37,9 +37,9 @@ pub fn auto_import_text_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) -> 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) -> Option<Assist> {
         }
     };
 
-    ctx.add_assist(AssistId("add_import"), format!("Import {}", fmt_segments(&segments)), |edit| {
-        apply_auto_import(&position, &path, &segments, edit.text_edit_builder());
-    })
+    ctx.add_assist(
+        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],
@@ -567,7 +565,7 @@ fn apply_auto_import(
     let action = best_action_for_target(container.clone(), path.syntax().clone(), target);
     make_assist(&action, target, edit);
     if let Some(last) = path.segment() {
-        // Here we are assuming the assist will provide a  correct use statement
+        // Here we are assuming the assist will provide a correct use statement
         // so we can delete the path qualifier
         edit.delete(TextRange::from_to(
             path.syntax().text_range().start(),
@@ -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 {
diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index eca6dec4b..828a8e9e8 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -12,16 +12,13 @@ mod doc_tests;
 mod utils;
 pub mod ast_transform;
 
-use std::cmp::Ordering;
-
-use either::Either;
 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, AssistHandler};
-pub use crate::handlers::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.
@@ -35,6 +32,9 @@ 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
@@ -45,7 +45,6 @@ impl AssistLabel {
 
 #[derive(Debug, Clone)]
 pub struct AssistAction {
-    pub label: Option<String>,
     pub edit: TextEdit,
     pub cursor_position: Option<TextUnit>,
     // FIXME: This belongs to `AssistLabel`
@@ -55,16 +54,8 @@ pub struct AssistAction {
 #[derive(Debug, Clone)]
 pub struct ResolvedAssist {
     pub label: AssistLabel,
-    pub action_data: Either<AssistAction, Vec<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(),
-        }
-    }
+    pub group_label: Option<GroupLabel>,
+    pub action: AssistAction,
 }
 
 /// Return all the assists applicable at the given position.
@@ -76,10 +67,8 @@ pub fn unresolved_assists(db: &RootDatabase, range: FileRange) -> Vec<AssistLabe
     handlers::all()
         .iter()
         .filter_map(|f| f(ctx.clone()))
-        .map(|a| match a {
-            Assist::Unresolved { label } => label,
-            Assist::Resolved { .. } => unreachable!(),
-        })
+        .flat_map(|it| it.0)
+        .map(|a| a.label)
         .collect()
 }
 
@@ -92,24 +81,13 @@ pub fn resolved_assists(db: &RootDatabase, range: FileRange) -> Vec<ResolvedAssi
     let mut a = handlers::all()
         .iter()
         .filter_map(|f| f(ctx.clone()))
-        .map(|a| match a {
-            Assist::Resolved { assist } => assist,
-            Assist::Unresolved { .. } => unreachable!(),
-        })
+        .flat_map(|it| it.0)
+        .map(|it| it.into_resolved().unwrap())
         .collect::<Vec<_>>();
-    sort_assists(&mut a);
+    a.sort_by_key(|it| it.action.target.map_or(TextUnit::from(!0u32), |it| it.len()));
     a
 }
 
-fn sort_assists(assists: &mut [ResolvedAssist]) {
-    assists.sort_by(|a, b| match (a.get_first_action().target, b.get_first_action().target) {
-        (Some(a), Some(b)) => a.len().cmp(&b.len()),
-        (Some(_), None) => Ordering::Less,
-        (None, Some(_)) => Ordering::Greater,
-        (None, None) => Ordering::Equal,
-    });
-}
-
 mod handlers {
     use crate::AssistHandler;
 
@@ -133,7 +111,7 @@ mod handlers {
     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;
@@ -158,7 +136,7 @@ mod handlers {
             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,
@@ -184,7 +162,7 @@ mod helpers {
     use ra_syntax::TextRange;
     use test_utils::{add_cursor, assert_eq_text, extract_offset, extract_range};
 
-    use crate::{Assist, AssistCtx, AssistHandler};
+    use crate::{AssistCtx, AssistHandler};
 
     pub(crate) fn with_single_file(text: &str) -> (RootDatabase, FileId) {
         let (mut db, file_id) = RootDatabase::with_single_file(text);
@@ -202,10 +180,7 @@ mod helpers {
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
         let assist =
             assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
+        let action = assist.0[0].action.clone().unwrap();
 
         let actual = action.edit.apply(&before);
         let actual_cursor_pos = match action.cursor_position {
@@ -225,10 +200,7 @@ mod helpers {
         let frange = FileRange { file_id, range };
         let assist =
             assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
+        let action = assist.0[0].action.clone().unwrap();
 
         let mut actual = action.edit.apply(&before);
         if let Some(pos) = action.cursor_position {
@@ -244,10 +216,7 @@ mod helpers {
             FileRange { file_id, range: TextRange::offset_len(before_cursor_pos, 0.into()) };
         let assist =
             assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
+        let action = assist.0[0].action.clone().unwrap();
 
         let range = action.target.expect("expected target on action");
         assert_eq_text!(&before[range.start().to_usize()..range.end().to_usize()], target);
@@ -259,10 +228,7 @@ mod helpers {
         let frange = FileRange { file_id, range };
         let assist =
             assist(AssistCtx::new(&db, frange, true)).expect("code action is not applicable");
-        let action = match assist {
-            Assist::Unresolved { .. } => unreachable!(),
-            Assist::Resolved { assist } => assist.get_first_action(),
-        };
+        let action = assist.0[0].action.clone().unwrap();
 
         let range = action.target.expect("expected target on action");
         assert_eq_text!(&before[range.start().to_usize()..range.end().to_usize()], target);
diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index eaacf8c9e..4d9641728 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/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,
-    LocalModuleId, LocalStructFieldId, Lookup, ModuleId, StaticId, StructId, TraitId, TypeAliasId,
-    TypeParamId, UnionId,
+    AdtId, ConstId, DefWithBodyId, EnumId, FunctionId, GenericDefId, HasModule, ImplId,
+    LocalEnumVariantId, LocalModuleId, LocalStructFieldId, Lookup, ModuleId, StaticId, StructId,
+    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;
@@ -270,7 +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)
     }
 
@@ -755,7 +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 {
@@ -789,8 +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 },
@@ -851,9 +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)
     }
 
@@ -950,7 +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));
                     }
                 }
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 86e422779..e1c7b7a20 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -58,7 +58,6 @@ pub use hir_def::{
     type_ref::Mutability,
 };
 pub use hir_expand::{
-    name::{name, Name},
-    HirFileId, InFile, MacroCallId, MacroCallLoc, MacroDefId, MacroFile, Origin,
+    name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc, MacroDefId, MacroFile, Origin,
 };
 pub use hir_ty::{display::HirDisplay, CallableDef};
diff --git a/crates/ra_hir/src/source_analyzer.rs b/crates/ra_hir/src/source_analyzer.rs
index 4f8fc9602..bb9a35c5d 100644
--- a/crates/ra_hir/src/source_analyzer.rs
+++ b/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 } })
     }
 
diff --git a/crates/ra_hir_def/src/generics.rs b/crates/ra_hir_def/src/generics.rs
index e9c28c730..f765e6edc 100644
--- a/crates/ra_hir_def/src/generics.rs
+++ b/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 =
-                    generics.types.alloc(TypeParamData { name: name![Self], default: None });
+                let self_param_id = generics.types.alloc(TypeParamData {
+                    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
+            }
+        })
     }
 }
 
diff --git a/crates/ra_hir_def/src/resolver.rs b/crates/ra_hir_def/src/resolver.rs
index f7bac5801..05cf4646a 100644
--- a/crates/ra_hir_def/src/resolver.rs
+++ b/crates/ra_hir_def/src/resolver.rs
@@ -490,10 +490,12 @@ impl Scope {
             }
             Scope::GenericParams { params, def } => {
                 for (local_id, param) in params.types.iter() {
-                    f(
-                        param.name.clone(),
-                        ScopeDef::GenericParam(TypeParamId { local_id, parent: *def }),
-                    )
+                    if let Some(name) = &param.name {
+                        f(
+                            name.clone(),
+                            ScopeDef::GenericParam(TypeParamId { local_id, parent: *def }),
+                        )
+                    }
                 }
             }
             Scope::ImplBlockScope(i) => {
diff --git a/crates/ra_hir_def/src/type_ref.rs b/crates/ra_hir_def/src/type_ref.rs
index 5f10e9a88..102fdb13d 100644
--- a/crates/ra_hir_def/src/type_ref.rs
+++ b/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> {
diff --git a/crates/ra_hir_expand/src/name.rs b/crates/ra_hir_expand/src/name.rs
index 133805bdb..b2e10f445 100644
--- a/crates/ra_hir_expand/src/name.rs
+++ b/crates/ra_hir_expand/src/name.rs
@@ -187,13 +187,6 @@ pub mod known {
         PartialOrd,
         Eq,
         PartialEq,
-        // FIXME delete those after `ImportResolver` is removed.
-        hash,
-        fmt,
-        io,
-        Display,
-        Iterator,
-        Hasher,
     );
 
     // self/Self cannot be used as an identifier
diff --git a/crates/ra_hir_ty/src/db.rs b/crates/ra_hir_ty/src/db.rs
index eb521c7a0..e9bfcfa17 100644
--- a/crates/ra_hir_ty/src/db.rs
+++ b/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,
-    ValueTyDefId,
+    Binders, CallableDef, GenericPredicate, InferenceResult, PolyFnSig, Substs, TraitRef, Ty,
+    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_idx: u32,
-    ) -> Arc<[GenericPredicate]>;
+        param_id: TypeParamId,
+    ) -> Arc<[Binders<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);
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index e2eda3134..a9d958c8b 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/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 {
-        let ty = Ty::from_hir(
-            self.db,
-            // FIXME use right resolver for block
-            &self.resolver,
-            type_ref,
-        );
+    fn make_ty_with_mode(
+        &mut self,
+        type_ref: &TypeRef,
+        impl_trait_mode: ImplTraitLoweringMode,
+    ) -> Ty {
+        // FIXME use right resolver for block
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
+            .with_impl_trait_mode(impl_trait_mode);
+        let ty = Ty::from_hir(&ctx, type_ref);
         let ty = self.insert_type_vars(ty);
         self.normalize_associated_types_in(ty)
     }
 
-    /// Replaces `impl Trait` in `ty` by type variables and obligations for
-    /// those variables. This is done for function arguments when calling a
-    /// 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,
-        })
+    fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
+        self.make_ty_with_mode(type_ref, ImplTraitLoweringMode::Disallowed)
     }
 
     /// Replaces Ty::Unknown by a new type var, so we can maybe still infer it.
@@ -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 ty = self.make_ty(type_ref);
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver)
+            .with_impl_trait_mode(ImplTraitLoweringMode::Param);
+        let param_tys =
+            data.params.iter().map(|type_ref| Ty::from_hir(&ctx, type_ref)).collect::<Vec<_>>();
+        for (ty, pat) in param_tys.into_iter().zip(body.params.iter()) {
+            let ty = self.insert_type_vars(ty);
+            let ty = self.normalize_associated_types_in(ty);
 
             self.infer_pat(*pat, &ty, BindingMode::default());
         }
-        let return_ty = self.make_ty(&data.ret_type);
-        self.return_ty = self.insert_vars_for_impl_trait(return_ty);
+        let return_ty = self.make_ty_with_mode(&data.ret_type, ImplTraitLoweringMode::Disallowed); // FIXME implement RPIT
+        self.return_ty = return_ty;
     }
 
     fn infer_body(&mut self) {
diff --git a/crates/ra_hir_ty/src/infer/coerce.rs b/crates/ra_hir_ty/src/infer/coerce.rs
index 83c0c2c3f..f68a1439f 100644
--- a/crates/ra_hir_ty/src/infer/coerce.rs
+++ b/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_to_ty = trait_ref.substs.0.get(1)?;
+                let cur_from_ty = trait_ref.value.substs.0.get(0)?;
+                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, .. })
-                                    if p1 != p2 =>
-                                {
+                                (Ty::Bound(idx1), Ty::Bound(idx2)) if idx1 != idx2 => {
                                     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 {
-                        &Ty::Param { idx, .. } => {
+                    field_tys[last_field_id].value.walk(&mut |ty| match ty {
+                        &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 {
-                        &Ty::Param { idx, .. } if idx == unsize_generic_index => {
-                            multiple_used = true
-                        }
+                    field_tys[field_id].value.walk(&mut |ty| match ty {
+                        &Ty::Bound(idx) if idx == unsize_generic_index => multiple_used = true,
                         _ => {}
                     })
                 });
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 31259a01d..3c9c02d03 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/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,
-    TypeCtor, TypeWalk, Uncertain,
+    ApplicationTy, Binders, CallableDef, InferTy, IntTy, Mutability, Obligation, Substs, TraitRef,
+    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())
-                        .subst(&substs);
+                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
                 if let Some(expr) = spread {
@@ -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) =
-            def_generics.as_ref().map_or((0, 0, 0), |g| g.len_split());
+        let (parent_params, self_params, type_params, impl_trait_params) =
+            def_generics.as_ref().map_or((0, 0, 0, 0), |g| g.provenance_split());
+        assert_eq!(self_params, 0); // method shouldn't have another Self param
+        let total_len = parent_params + type_params + impl_trait_params;
         let mut substs = Vec::with_capacity(total_len);
         // Parent arguments are unknown, except for the receiver type
         if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
             for (_id, param) in parent_generics {
-                if param.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);
diff --git a/crates/ra_hir_ty/src/infer/pat.rs b/crates/ra_hir_ty/src/infer/pat.rs
index a14662884..e7283f24c 100644
--- a/crates/ra_hir_ty/src/infer/pat.rs
+++ b/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())
-                .subst(&substs);
+                .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -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);
         }
diff --git a/crates/ra_hir_ty/src/infer/path.rs b/crates/ra_hir_ty/src/infer/path.rs
index 2c1d4831d..686ce7a21 100644
--- a/crates/ra_hir_ty/src/infer/path.rs
+++ b/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);
-        if let Some(self_subst) = self_subst {
-            ty = ty.subst(&self_subst);
-        }
-        let substs = Ty::substs_from_path(self.db, &self.resolver, path, typable);
-        let ty = ty.subst(&substs);
+        let ty = self.db.value_ty(typable);
+        // self_subst is just for the parent
+        let parent_substs = self_subst.unwrap_or_else(Substs::empty);
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+        let substs = Ty::substs_from_path(&ctx, path, typable);
+        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(
-                    self.db,
-                    &self.resolver,
-                    trait_.into(),
-                    resolved_segment,
-                    None,
-                );
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+                let trait_ref =
+                    TraitRef::from_resolved_path(&ctx, 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,
-                    &self.resolver,
+                    &ctx,
                     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,
                 };
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 08d501ccd..c5fe18c85 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/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,
-    HasModule, Lookup, TraitId, TypeAliasId,
+    expr::ExprId, generics::TypeParamProvenance, type_ref::Mutability, AdtId, AssocContainerId,
+    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) {}
-    Param {
-        /// The index of the parameter (starting with parameters from the
-        /// surrounding impl, then the current function).
-        idx: u32,
-        /// 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
-    /// variables, and in `Dyn` and `Opaque` bounds to represent the `Self` type.
+    /// A placeholder for a type parameter; for example, `T` in `fn f<T>(x: T)
+    /// {}` when we're type-checking the body of that function. In this
+    /// situation, we know this stands for *some* type, but don't know the exact
+    /// type.
+    Param(TypeParamId),
+
+    /// A bound type variable. This is used in various places: when representing
+    /// 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
-    /// type parameter.
+    /// A type variable used during type checking.
     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 {
-        Substs(
-            generic_params.iter().map(|(idx, p)| Ty::Param { idx, name: p.name.clone() }).collect(),
-        )
+    pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs {
+        Substs(generic_params.iter().map(|(id, _)| Ty::Param(id)).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.
-    /// 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).
+    /// Substitutes `Ty::Bound` vars with the given substitution.
     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);
                     }
                 }
                 _ => {}
@@ -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(),
@@ -896,9 +912,16 @@ impl HirDisplay for ApplicationTy {
                     }
                 }
                 if self.parameters.len() > 0 {
-                    write!(f, "<")?;
-                    f.write_joined(&*self.parameters.0, ", ")?;
-                    write!(f, ">")?;
+                    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[..total_len], ", ")?;
+                        write!(f, ">")?;
+                    }
                 }
                 write!(f, "(")?;
                 f.write_joined(sig.params(), ", ")?;
@@ -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 {
@@ -1017,66 +1057,7 @@ impl HirDisplay for Ty {
                     Ty::Opaque(_) => write!(f, "impl ")?,
                     _ => unreachable!(),
                 };
-                // Note: This code is written to produce nice results (i.e.
-                // corresponding to surface Rust) for types that can occur in
-                // actual Rust. It will have weird results if the predicates
-                // aren't as expected (i.e. self types = $0, projection
-                // predicates for a certain trait come after the Implemented
-                // predicate for that trait).
-                let mut first = true;
-                let mut angle_open = false;
-                for p in predicates.iter() {
-                    match p {
-                        GenericPredicate::Implemented(trait_ref) => {
-                            if angle_open {
-                                write!(f, ">")?;
-                            }
-                            if !first {
-                                write!(f, " + ")?;
-                            }
-                            // We assume that the self type is $0 (i.e. the
-                            // existential) here, which is the only thing that's
-                            // possible in actual Rust, and hence don't print it
-                            write!(f, "{}", f.db.trait_data(trait_ref.trait_).name.clone())?;
-                            if trait_ref.substs.len() > 1 {
-                                write!(f, "<")?;
-                                f.write_joined(&trait_ref.substs[1..], ", ")?;
-                                // there might be assoc type bindings, so we leave the angle brackets open
-                                angle_open = true;
-                            }
-                        }
-                        GenericPredicate::Projection(projection_pred) => {
-                            // in types in actual Rust, these will always come
-                            // after the corresponding Implemented predicate
-                            if angle_open {
-                                write!(f, ", ")?;
-                            } else {
-                                write!(f, "<")?;
-                                angle_open = true;
-                            }
-                            let name =
-                                f.db.type_alias_data(projection_pred.projection_ty.associated_ty)
-                                    .name
-                                    .clone();
-                            write!(f, "{} = ", name)?;
-                            projection_pred.ty.hir_fmt(f)?;
-                        }
-                        GenericPredicate::Error => {
-                            if angle_open {
-                                // impl Trait<X, {error}>
-                                write!(f, ", ")?;
-                            } else if !first {
-                                // impl Trait + {error}
-                                write!(f, " + ")?;
-                            }
-                            p.hir_fmt(f)?;
-                        }
-                    }
-                    first = false;
-                }
-                if angle_open {
-                    write!(f, ">")?;
-                }
+                write_bounds_like_dyn_trait(&predicates, f)?;
             }
             Ty::Unknown => write!(f, "{{unknown}}")?,
             Ty::Infer(..) => write!(f, "_")?,
@@ -1085,6 +1066,71 @@ impl HirDisplay for Ty {
     }
 }
 
+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
+    // aren't as expected (i.e. self types = $0, projection
+    // predicates for a certain trait come after the Implemented
+    // predicate for that trait).
+    let mut first = true;
+    let mut angle_open = false;
+    for p in predicates.iter() {
+        match p {
+            GenericPredicate::Implemented(trait_ref) => {
+                if angle_open {
+                    write!(f, ">")?;
+                }
+                if !first {
+                    write!(f, " + ")?;
+                }
+                // We assume that the self type is $0 (i.e. the
+                // existential) here, which is the only thing that's
+                // possible in actual Rust, and hence don't print it
+                write!(f, "{}", f.db.trait_data(trait_ref.trait_).name.clone())?;
+                if trait_ref.substs.len() > 1 {
+                    write!(f, "<")?;
+                    f.write_joined(&trait_ref.substs[1..], ", ")?;
+                    // there might be assoc type bindings, so we leave the angle brackets open
+                    angle_open = true;
+                }
+            }
+            GenericPredicate::Projection(projection_pred) => {
+                // in types in actual Rust, these will always come
+                // after the corresponding Implemented predicate
+                if angle_open {
+                    write!(f, ", ")?;
+                } else {
+                    write!(f, "<")?;
+                    angle_open = true;
+                }
+                let name =
+                    f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name.clone();
+                write!(f, "{} = ", name)?;
+                projection_pred.ty.hir_fmt(f)?;
+            }
+            GenericPredicate::Error => {
+                if angle_open {
+                    // impl Trait<X, {error}>
+                    write!(f, ", ")?;
+                } else if !first {
+                    // impl Trait + {error}
+                    write!(f, " + ")?;
+                }
+                p.hir_fmt(f)?;
+            }
+        }
+        first = false;
+    }
+    if angle_open {
+        write!(f, ">")?;
+    }
+    Ok(())
+}
+
 impl TraitRef {
     fn hir_fmt_ext(&self, f: &mut HirFormatter<impl HirDatabase>, use_as: bool) -> fmt::Result {
         if f.should_truncate() {
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 2c2ecee9c..c68c5852b 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/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;
@@ -27,63 +28,158 @@ 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,
-    Ty, TypeCtor, TypeWalk,
+    Binders, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate, ProjectionTy, Substs,
+    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]> =
-                    inner.iter().map(|tr| Ty::from_hir(db, resolver, tr)).collect();
+                let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| Ty::from_hir(ctx, 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| {
-                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
-                    })
+                    .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
                     .collect();
                 Ty::Dyn(predicates)
             }
             TypeRef::ImplTrait(bounds) => {
-                let self_ty = Ty::Bound(0);
-                let predicates = bounds
-                    .iter()
-                    .flat_map(|b| {
-                        GenericPredicate::from_type_bound(db, resolver, b, self_ty.clone())
-                    })
-                    .collect();
-                Ty::Opaque(predicates)
+                match ctx.impl_trait_mode {
+                    ImplTraitLoweringMode::Opaque => {
+                        let self_ty = Ty::Bound(0);
+                        let predicates = bounds
+                            .iter()
+                            .flat_map(|b| {
+                                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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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"));
-            let idx = generics.param_idx(param_id);
-            Some(idx)
+            Some(param_id)
         } else {
             None
         }
     }
 
     pub(crate) fn from_type_relative_path(
-        db: &impl HirDatabase,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         resolution: TypeNs,
         resolved_segment: PathSegment<'_>,
         remaining_segments: PathSegments<'_>,
     ) -> Ty {
         let ty = match resolution {
             TypeNs::TraitId(trait_) => {
-                let trait_ref =
-                    TraitRef::from_resolved_path(db, resolver, trait_, resolved_segment, None);
+                let trait_ref = TraitRef::from_resolved_path(ctx, 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 idx = generics.param_idx(param_id);
-                // FIXME: maybe return name in resolution?
-                let name = generics.param_name(param_id);
-                Ty::Param { idx, name }
+                let generics =
+                    generics(ctx.db, ctx.resolver.generic_def().expect("generics in scope"));
+                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)
+                    }
+                }
             }
-            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::BuiltinType(it) => {
-                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
+            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::TypeAliasId(it) => {
-                Ty::from_hir_path_inner(db, resolver, resolved_segment, it.into())
+            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::AdtId(it) => Ty::from_hir_path_inner(ctx, resolved_segment, it.into()),
+            TypeNs::BuiltinType(it) => Ty::from_hir_path_inner(ctx, resolved_segment, it.into()),
+            TypeNs::TypeAliasId(it) => Ty::from_hir_path_inner(ctx, 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);
-            return Ty::from_type_relative_path(db, resolver, ty, path.segments());
+            let ty = Ty::from_hir(ctx, &type_ref);
+            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(
-            db,
-            resolver,
-            resolution,
-            resolved_segment,
-            remaining_segments,
-        )
+        Ty::from_partly_resolved_hir_path(ctx, resolution, resolved_segment, remaining_segments)
     }
 
     fn select_associated_type(
-        db: &impl HirDatabase,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         self_ty: Ty,
         segment: PathSegment<'_>,
     ) -> Ty {
-        let param_idx = match self_ty {
-            Ty::Param { idx, .. } => idx,
-            _ => return Ty::Unknown, // Error: Ambiguous associated type
-        };
-        let def = match resolver.generic_def() {
+        let def = match ctx.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 traits_from_env = predicates.iter().filter_map(|pred| match pred {
-            GenericPredicate::Implemented(tr) if tr.self_ty() == &self_ty => Some(tr.trait_),
+        let param_id = match self_ty {
+            Ty::Param(id) if ctx.type_param_mode == TypeParamLoweringMode::Placeholder => id,
+            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) {
-                let substs =
-                    Substs::build_for_def(db, t).push(self_ty.clone()).fill_with_unknown().build();
+            if let Some(associated_ty) = ctx.db.trait_data(t).associated_type_by_name(&segment.name)
+            {
+                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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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);
-        db.ty(typable).subst(&substs)
+        let substs = substs_from_path_segment(ctx, segment, generic_def, false);
+        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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-    resolver: &Resolver,
+    ctx: &TyLoweringContext<'_, impl HirDatabase>,
     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 (total_len, parent_len, child_len) = def_generics.map_or((0, 0, 0), |g| g.len_split());
-    substs.extend(iter::repeat(Ty::Unknown).take(parent_len));
-    if add_self_param {
-        // 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);
-    }
+    let def_generics = def_generic.map(|def| generics(ctx.db, def.into()));
+
+    let (parent_params, self_params, type_params, impl_trait_params) =
+        def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
+    substs.extend(iter::repeat(Ty::Unknown).take(parent_params));
     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 };
-        let child_len = child_len - self_param_correction;
-        for arg in generic_args.args.iter().take(child_len) {
+        for arg in generic_args.args.iter().skip(skip).take(expected_num) {
             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 supplied_params..total_len {
+    for _ in substs.len()..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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &Resolver,
+        ctx: &TyLoweringContext<'_, impl HirDatabase>,
         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,
-        resolver: &'a Resolver,
+        ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
         where_predicate: &'a WherePredicate,
     ) -> impl Iterator<Item = GenericPredicate> + 'a {
-        let self_ty = Ty::from_hir(db, resolver, &where_predicate.type_ref);
-        GenericPredicate::from_type_bound(db, resolver, &where_predicate.bound, self_ty)
+        let self_ty = match &where_predicate.target {
+            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,
-        resolver: &'a Resolver,
+        ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
         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| {
-                    assoc_type_bindings_from_type_bound(db, resolver, bound, tr)
-                }),
+                trait_ref
+                    .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,
-    resolver: &'a Resolver,
+    ctx: &'a TyLoweringContext<'a, impl HirDatabase>,
     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 {
-        VariantId::StructId(it) => it.resolver(db),
-        VariantId::UnionId(it) => it.resolver(db),
-        VariantId::EnumVariantId(it) => it.parent.resolver(db),
+    let (resolver, def): (_, GenericDefId) = match variant_id {
+        VariantId::StructId(it) => (it.resolver(db), it.into()),
+        VariantId::UnionId(it) => (it.resolver(db), it.into()),
+        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_idx: u32,
-) -> Arc<[GenericPredicate]> {
-    let resolver = def.resolver(db);
+    param_id: TypeParamId,
+) -> Arc<[Binders<GenericPredicate>]> {
+    let resolver = param_id.parent.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))
-        .flat_map(|pred| GenericPredicate::from_where_predicate(db, &resolver, pred))
+        .filter(|pred| match &pred.target {
+            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_idx: &u32,
-) -> Arc<[GenericPredicate]> {
+    _param_id: &TypeParamId,
+) -> Arc<[Binders<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 ret = Ty::from_hir(db, &resolver, &data.ret_type);
-    FnSig::from_params_and_return(params, ret)
+    let ctx_params = TyLoweringContext::new(db, &resolver)
+        .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
+        .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);
-    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+    let substs = Substs::bound_vars(&generics);
+    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
-        .iter()
-        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
-        .collect::<Vec<_>>();
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
+    let params =
+        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);
-    Ty::apply(TypeCtor::FnDef(def.into()), substs)
+    let substs = Substs::bound_vars(&generics);
+    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
-        .iter()
-        .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
-        .collect::<Vec<_>>();
-    let generics = generics(db, def.parent.into());
-    let substs = Substs::identity(&generics);
-    let ret = type_for_adt(db, def.parent.into()).subst(&substs);
-    FnSig::from_params_and_return(params, ret)
+    let ctx =
+        TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
+    let params =
+        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
+    let ret = type_for_adt(db, def.parent.into());
+    Binders::new(ret.num_binders, FnSig::from_params_and_return(params, ret.value))
 }
 
 /// 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);
-    Ty::apply(TypeCtor::FnDef(EnumVariantId::from(def).into()), substs)
+    let substs = Substs::bound_vars(&generics);
+    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 inner = Ty::from_hir(db, &resolver, type_ref.as_ref().unwrap_or(&TypeRef::Error));
-    inner.subst(&substs)
+    let substs = Substs::bound_vars(&generics);
+    let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
+    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 {
-    Ty::Unknown
+pub(crate) fn ty_recover(db: &impl HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
+    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,
-) -> Ty {
-    Ty::Unknown
+    impl_id: &ImplId,
+) -> Binders<Ty> {
+    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()))?,
+    ))
 }
diff --git a/crates/ra_hir_ty/src/marks.rs b/crates/ra_hir_ty/src/marks.rs
index fe74acf11..0f754eb9c 100644
--- a/crates/ra_hir_ty/src/marks.rs
+++ b/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
 );
diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index 5bacbbd7c..5283bff28 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/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(
diff --git a/crates/ra_hir_ty/src/tests/coercion.rs b/crates/ra_hir_ty/src/tests/coercion.rs
index 76a1b46c0..fc5ef36a5 100644
--- a/crates/ra_hir_ty/src/tests/coercion.rs
+++ b/crates/ra_hir_ty/src/tests/coercion.rs
@@ -75,7 +75,7 @@ fn test2() {
     [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; _]
     [186; 420) '{     ...rr); }': ()
     [196; 199) 'arr': &[u8; _]
@@ -85,14 +85,14 @@ fn test2() {
     [227; 228) 'a': &[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; _]
     [270; 271) 'c': &[u8]
     [280; 287) '{ 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; _]
@@ -164,15 +164,15 @@ fn test(a: A<[u8; 2]>, b: B<[u8; 2]>, c: C<[u8; 2]>) {
     [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; _]>
     [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; _]>
     [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; _]>
     "###
@@ -202,7 +202,7 @@ 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; _]
     [87; 90) '[1]': [i32; _]
@@ -242,7 +242,7 @@ fn test() {
     [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; _]
     [113; 116) '[1]': [i32; _]
@@ -275,7 +275,7 @@ 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; _]
     [98; 101) '[2]': [i32; _]
@@ -320,7 +320,7 @@ fn test(i: 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; _]
     [117; 120) '[2]': [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
diff --git a/crates/ra_hir_ty/src/tests/method_resolution.rs b/crates/ra_hir_ty/src/tests/method_resolution.rs
index ce9a06fde..1722563aa 100644
--- a/crates/ra_hir_ty/src/tests/method_resolution.rs
+++ b/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
     "###
diff --git a/crates/ra_hir_ty/src/tests/patterns.rs b/crates/ra_hir_ty/src/tests/patterns.rs
index cb3890b42..e25d6dbc4 100644
--- a/crates/ra_hir_ty/src/tests/patterns.rs
+++ b/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
     "###
diff --git a/crates/ra_hir_ty/src/tests/regression.rs b/crates/ra_hir_ty/src/tests/regression.rs
index 02bab6dbe..14c8ed3a9 100644
--- a/crates/ra_hir_ty/src/tests/regression.rs
+++ b/crates/ra_hir_ty/src/tests/regression.rs
@@ -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>
     "###
     );
diff --git a/crates/ra_hir_ty/src/tests/simple.rs b/crates/ra_hir_ty/src/tests/simple.rs
index fdab9c187..3803f5938 100644
--- a/crates/ra_hir_ty/src/tests/simple.rs
+++ b/crates/ra_hir_ty/src/tests/simple.rs
@@ -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>
     "###
@@ -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
     "###
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index a6ac18f86..17611ddbf 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/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
     "###
@@ -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<[missing name]>");
+    assert_eq!(t, "ApplyL::Out<T>");
 }
 
 #[test]
@@ -850,6 +848,197 @@ 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!(
@@ -994,29 +1183,17 @@ fn weird_bounds() {
     assert_snapshot!(
         infer(r#"
 trait Trait {}
-fn test() {
-    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;
+fn test(a: impl Trait + 'lifetime, b: impl 'lifetime, c: impl (Trait), d: impl ('lifetime), e: impl ?Sized, f: impl Trait + ?Sized) {
 }
 "#),
         @r###"
-    [26; 237) '{     ...foo; }': ()
-    [36; 37) 'a': impl Trait + {error}
-    [64; 67) 'foo': impl Trait + {error}
-    [77; 78) 'b': impl {error}
-    [97; 100) 'foo': impl {error}
-    [110; 111) 'b': impl Trait
-    [128; 131) 'foo': impl Trait
-    [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}
+    [24; 25) 'a': impl Trait + {error}
+    [51; 52) 'b': impl {error}
+    [70; 71) 'c': impl Trait
+    [87; 88) 'd': impl {error}
+    [108; 109) 'e': impl {error}
+    [124; 125) 'f': impl Trait + {error}
+    [148; 151) '{ }': ()
     "###
     );
 }
@@ -1078,26 +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>
     "###
@@ -1225,6 +1402,32 @@ 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
     assert_snapshot!(
@@ -1270,9 +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>
     "###
@@ -1334,7 +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>
@@ -1444,7 +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
@@ -1452,7 +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
@@ -1605,7 +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> {}
@@ -1637,26 +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; 308) 'S(default())': S<i32>
-    [298; 305) 'default': fn default<i32>() -> T
-    [298; 307) 'default()': i32
+    [296; 297) 'S': S<{unknown}>({unknown}) -> S<{unknown}>
+    [296; 308) 'S(default())': S<{unknown}>
+    [298; 305) 'default': fn default<{unknown}>() -> {unknown}
+    [298; 307) 'default()': {unknown}
     "###
     );
 }
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index fe9cb556c..4974c565b 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -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)]
@@ -142,9 +142,13 @@ impl ToChalk for Ty {
                 let substitution = proj_ty.parameters.to_chalk(db);
                 chalk_ir::AliasTy { associated_ty_id, substitution }.cast().intern()
             }
-            Ty::Param { idx, .. } => {
-                PlaceholderIndex { ui: UniverseIndex::ROOT, idx: idx as usize }
-                    .to_ty::<TypeFamily>()
+            Ty::Param(id) => {
+                let interned_id = db.intern_type_param_id(id);
+                PlaceholderIndex {
+                    ui: UniverseIndex::ROOT,
+                    idx: interned_id.as_intern_id().as_usize(),
+                }
+                .to_ty::<TypeFamily>()
             }
             Ty::Bound(idx) => chalk_ir::TyData::BoundVar(idx as usize).intern(),
             Ty::Infer(_infer_ty) => panic!("uncanonicalized infer ty"),
@@ -177,7 +181,10 @@ impl ToChalk for Ty {
             },
             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::Alias(proj) => {
                 let associated_ty = from_chalk(db, proj.associated_ty_id);
@@ -520,7 +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;
         }
@@ -709,12 +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
@@ -789,20 +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 bound_vars = Substs::bound_vars(&generic_params);
-    let ty = db.ty(type_alias.into()).subst(&bound_vars);
-    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.to_chalk(db) };
+    let ty = db.ty(type_alias.into());
+    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.value.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)
 }
diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index 0b1806a84..508ae9046 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/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 {
-            TypeRef::Path(p) if p == &Path::from(name![Self]) => pred.bound.as_path(),
+        .filter_map(|pred| match &pred.target {
+            WherePredicateTarget::TypeRef(TypeRef::Path(p)) if p == &Path::from(name![Self]) => {
+                pred.bound.as_path()
+            }
+            WherePredicateTarget::TypeParam(local_id) if Some(*local_id) == trait_self => {
+                pred.bound.as_path()
+            }
             _ => None,
         })
         .filter_map(|path| match resolver.resolve_path_in_type_ns_fully(db, path.mod_path()) {
@@ -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())
-            .chain(self.params.types.iter())
-            .enumerate()
-            .map(|(i, (_local_id, p))| (i as u32, p))
+            .flat_map(|it| {
+                it.params
+                    .types
+                    .iter()
+                    .map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p))
+            })
+            .chain(
+                self.params
+                    .types
+                    .iter()
+                    .map(move |(local_id, p)| (TypeParamId { parent: self.def, local_id }, p)),
+            )
     }
 
-    pub(crate) fn iter_parent<'a>(&'a self) -> impl Iterator<Item = (u32, &'a TypeParamData)> + 'a {
-        self.parent_generics
-            .as_ref()
-            .into_iter()
-            .flat_map(|it| it.params.types.iter())
-            .enumerate()
-            .map(|(i, (_local_id, p))| (i as u32, p))
+    pub(crate) fn iter_parent<'a>(
+        &'a self,
+    ) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
+        self.parent_generics.as_ref().into_iter().flat_map(|it| {
+            it.params
+                .types
+                .iter()
+                .map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p))
+        })
     }
 
     pub(crate) fn len(&self) -> usize {
         self.len_split().0
     }
+
     /// (total, parents, child)
     pub(crate) fn len_split(&self) -> (usize, usize, usize) {
         let parent = self.parent_generics.as_ref().map_or(0, |p| p.len());
         let child = self.params.types.len();
         (parent + child, parent, child)
     }
-    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)
     }
 }
 
diff --git a/crates/ra_ide/src/assists.rs b/crates/ra_ide/src/assists.rs
index b60b1a60d..40d56a4f7 100644
--- a/crates/ra_ide/src/assists.rs
+++ b/crates/ra_ide/src/assists.rs
@@ -1,6 +1,5 @@
 //! FIXME: write short doc here
 
-use either::Either;
 use ra_assists::{resolved_assists, AssistAction, AssistLabel};
 use ra_db::{FilePosition, FileRange};
 use ra_ide_db::RootDatabase;
@@ -13,7 +12,8 @@ pub use ra_assists::AssistId;
 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> {
@@ -25,17 +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 {
-                    Either::Left(action) => {
-                        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(),
-                    ),
-                },
+                group_label: assist.group_label.map(|it| it.0),
+                source_change: action_to_edit(assist.action, file_id, assist_label),
             }
         })
         .collect()
@@ -47,9 +38,6 @@ fn action_to_edit(
     assist_label: &AssistLabel,
 ) -> SourceChange {
     let file_edit = SourceFileEdit { file_id, edit: action.edit };
-    SourceChange::source_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 }))
+    SourceChange::source_file_edit(assist_label.label.clone(), file_edit)
+        .with_cursor_opt(action.cursor_position.map(|offset| FilePosition { offset, file_id }))
 }
diff --git a/crates/ra_ide/src/completion/complete_scope.rs b/crates/ra_ide/src/completion/complete_scope.rs
index 64b04ec2b..e2ee86dd1 100644
--- a/crates/ra_ide/src/completion/complete_scope.rs
+++ b/crates/ra_ide/src/completion/complete_scope.rs
@@ -1,12 +1,6 @@
 //! FIXME: write short doc here
 
-use ra_assists::auto_import_text_edit;
-use ra_syntax::{ast, AstNode, SmolStr};
-use ra_text_edit::TextEditBuilder;
-use rustc_hash::FxHashMap;
-
-use crate::completion::{CompletionContext, CompletionItem, CompletionKind, Completions};
-use hir::{ModPath, PathKind};
+use crate::completion::{CompletionContext, Completions};
 
 pub(super) fn complete_scope(acc: &mut Completions, ctx: &CompletionContext) {
     if !ctx.is_trivial_path {
@@ -16,138 +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: &ModPath) -> String {
-    let mut buf = String::with_capacity(64);
-    buf.push_str(name);
-    buf.push_str(" (");
-    buf.push_str(&path.to_string());
-    buf.push_str(")");
-    buf
-}
-
-#[derive(Debug, Clone, Default)]
-pub(crate) struct ImportResolver {
-    // todo: use fst crate or something like that
-    dummy_names: Vec<(SmolStr, ModPath)>,
-}
-
-impl ImportResolver {
-    pub(crate) fn new() -> Self {
-        use hir::name;
-
-        let dummy_names = vec![
-            (
-                SmolStr::new("fmt"),
-                ModPath { kind: PathKind::Plain, segments: vec![name![std], name![fmt]] },
-            ),
-            (
-                SmolStr::new("io"),
-                ModPath { kind: PathKind::Plain, segments: vec![name![std], name![io]] },
-            ),
-            (
-                SmolStr::new("iter"),
-                ModPath { kind: PathKind::Plain, segments: vec![name![std], name![iter]] },
-            ),
-            (
-                SmolStr::new("hash"),
-                ModPath { kind: PathKind::Plain, segments: vec![name![std], name![hash]] },
-            ),
-            (
-                SmolStr::new("Debug"),
-                ModPath {
-                    kind: PathKind::Plain,
-                    segments: vec![name![std], name![fmt], name![Debug]],
-                },
-            ),
-            (
-                SmolStr::new("Display"),
-                ModPath {
-                    kind: PathKind::Plain,
-                    segments: vec![name![std], name![fmt], name![Display]],
-                },
-            ),
-            (
-                SmolStr::new("Hash"),
-                ModPath {
-                    kind: PathKind::Plain,
-                    segments: vec![name![std], name![hash], name![Hash]],
-                },
-            ),
-            (
-                SmolStr::new("Hasher"),
-                ModPath {
-                    kind: PathKind::Plain,
-                    segments: vec![name![std], name![hash], name![Hasher]],
-                },
-            ),
-            (
-                SmolStr::new("Iterator"),
-                ModPath {
-                    kind: PathKind::Plain,
-                    segments: vec![name![std], name![iter], name![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, ModPath> {
-        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)
     }
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index 282f6e8fc..65e8bc856 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -2,20 +2,21 @@
 //! The majority of requests are fulfilled by calling into the `ra_ide` crate.
 
 use std::{
+    collections::hash_map::Entry,
     fmt::Write as _,
     io::Write as _,
     process::{self, Stdio},
 };
 
-use either::Either;
 use lsp_server::ErrorCode;
 use lsp_types::{
     CallHierarchyIncomingCall, CallHierarchyIncomingCallsParams, CallHierarchyItem,
     CallHierarchyOutgoingCall, CallHierarchyOutgoingCallsParams, CallHierarchyPrepareParams,
-    CodeAction, CodeActionResponse, CodeLens, Command, CompletionItem, Diagnostic,
-    DocumentFormattingParams, DocumentHighlight, DocumentSymbol, FoldingRange, FoldingRangeParams,
-    Hover, HoverContents, Location, MarkupContent, MarkupKind, Position, PrepareRenameResponse,
-    Range, RenameParams, SymbolInformation, TextDocumentIdentifier, TextEdit, WorkspaceEdit,
+    CodeAction, CodeActionOrCommand, CodeActionResponse, CodeLens, Command, CompletionItem,
+    Diagnostic, DocumentFormattingParams, DocumentHighlight, DocumentSymbol, FoldingRange,
+    FoldingRangeParams, Hover, HoverContents, Location, MarkupContent, MarkupKind, Position,
+    PrepareRenameResponse, Range, RenameParams, SymbolInformation, TextDocumentIdentifier,
+    TextEdit, WorkspaceEdit,
 };
 use ra_ide::{
     AssistId, FileId, FilePosition, FileRange, Query, RangeInfo, Runnable, RunnableKind,
@@ -685,34 +686,53 @@ pub fn handle_code_action(
         res.push(fix.action.clone());
     }
 
+    let mut groups = FxHashMap::default();
     for assist in world.analysis().assists(FileRange { file_id, range })?.into_iter() {
-        let title = assist.label.clone();
+        let arg = to_value(assist.source_change.try_conv_with(&world)?)?;
+
+        let (command, title, arg) = match assist.group_label {
+            None => ("rust-analyzer.applySourceChange", assist.label.clone(), arg),
+
+            // Group all assists with the same `group_label` into a single CodeAction.
+            Some(group_label) => {
+                match groups.entry(group_label.clone()) {
+                    Entry::Occupied(entry) => {
+                        let idx: usize = *entry.get();
+                        match &mut res[idx] {
+                            CodeActionOrCommand::CodeAction(CodeAction {
+                                command: Some(Command { arguments: Some(arguments), .. }),
+                                ..
+                            }) => match arguments.as_mut_slice() {
+                                [serde_json::Value::Array(arguments)] => arguments.push(arg),
+                                _ => panic!("invalid group"),
+                            },
+                            _ => panic!("invalid group"),
+                        }
+                        continue;
+                    }
+                    Entry::Vacant(entry) => {
+                        entry.insert(res.len());
+                    }
+                }
+                ("rust-analyzer.selectAndApplySourceChange", group_label, to_value(vec![arg])?)
+            }
+        };
 
-        let command = match assist.change_data {
-            Either::Left(change) => Command {
-                title,
-                command: "rust-analyzer.applySourceChange".to_string(),
-                arguments: Some(vec![to_value(change.try_conv_with(&world)?)?]),
-            },
-            Either::Right(changes) => Command {
-                title,
-                command: "rust-analyzer.selectAndApplySourceChange".to_string(),
-                arguments: Some(vec![to_value(
-                    changes
-                        .into_iter()
-                        .map(|change| change.try_conv_with(&world))
-                        .collect::<Result<Vec<_>>>()?,
-                )?]),
-            },
+        let command = Command {
+            title: assist.label.clone(),
+            command: command.to_string(),
+            arguments: Some(vec![arg]),
+        };
+
+        let kind = match assist.id {
+            AssistId("introduce_variable") => Some("refactor.extract.variable".to_string()),
+            AssistId("add_custom_impl") => Some("refactor.rewrite.add_custom_impl".to_string()),
+            _ => None,
         };
 
         let action = CodeAction {
-            title: command.title.clone(),
-            kind: match assist.id {
-                AssistId("introduce_variable") => Some("refactor.extract.variable".to_string()),
-                AssistId("add_custom_impl") => Some("refactor.rewrite.add_custom_impl".to_string()),
-                _ => None,
-            },
+            title,
+            kind,
             diagnostics: None,
             edit: None,
             command: Some(command),
diff --git a/crates/ra_parser/src/syntax_kind/generated.rs b/crates/ra_parser/src/syntax_kind/generated.rs
index 4b301d67a..e27b27ffa 100644
--- a/crates/ra_parser/src/syntax_kind/generated.rs
+++ b/crates/ra_parser/src/syntax_kind/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`
 
 #![allow(bad_style, missing_docs, unreachable_pub)]
 #[doc = r" The kind of syntax node, e.g. `IDENT`, `USE_KW`, or `STRUCT_DEF`."]
diff --git a/crates/ra_syntax/Cargo.toml b/crates/ra_syntax/Cargo.toml
index c5a3d1999..83db943fe 100644
--- a/crates/ra_syntax/Cargo.toml
+++ b/crates/ra_syntax/Cargo.toml
@@ -4,7 +4,7 @@ name = "ra_syntax"
 version = "0.1.0"
 authors = ["rust-analyzer developers"]
 license = "MIT OR Apache-2.0"
-description = "Comment and whitespace preserving parser for the Rust langauge"
+description = "Comment and whitespace preserving parser for the Rust language"
 repository = "https://github.com/rust-analyzer/rust-analyzer"
 
 [lib]
diff --git a/crates/ra_syntax/src/ast/generated.rs b/crates/ra_syntax/src/ast/generated.rs
index 33d5578e7..435135f92 100644
--- a/crates/ra_syntax/src/ast/generated.rs
+++ b/crates/ra_syntax/src/ast/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 crate::{
     ast::{self, AstChildren, AstNode},
diff --git a/docs/dev/README.md b/docs/dev/README.md
index d30727786..732e4bdd3 100644
--- a/docs/dev/README.md
+++ b/docs/dev/README.md
@@ -43,7 +43,7 @@ https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Fwg-rls-2.2E0
 
 We use GitHub Actions for CI. Most of the things, including formatting, are checked by
 `cargo test` so, if `cargo test` passes locally, that's a good sign that CI will
-be green as well. The only exception is that long-running by default a skipped locally.
+be green as well. The only exception is that some long-running tests are skipped locally by default.
 Use `env RUN_SLOW_TESTS=1 cargo test` to run the full suite.
 
 We use bors-ng to enforce the [not rocket science](https://graydon2.dreamwidth.org/1597.html) rule.
@@ -54,9 +54,9 @@ You can run `cargo xtask install-pre-commit-hook` to install git-hook to run rus
 
 All Rust code lives in the `crates` top-level directory, and is organized as a
 single Cargo workspace. The `editors` top-level directory contains code for
-integrating with editors. Currently, it contains plugins for VS Code (in
-typescript) and Emacs (in elisp). The `docs` top-level directory contains both
-developer and user documentation.
+integrating with editors. Currently, it contains the plugin for VS Code (in
+typescript). The `docs` top-level directory contains both developer and user
+documentation.
 
 We have some automation infra in Rust in the `xtask` package. It contains
 stuff like formatting checking, code generation and powers `cargo xtask install`.
@@ -107,8 +107,8 @@ If I need to fix something simultaneously in the server and in the client, I
 feel even more sad. I don't have a specific workflow for this case.
 
 Additionally, I use `cargo run --release -p ra_cli -- analysis-stats
-path/to/some/rust/crate` to run a batch analysis. This is primaraly useful for
-performance optimiations, or for bug minimization.
+path/to/some/rust/crate` to run a batch analysis. This is primarily useful for
+performance optimizations, or for bug minimization.
 
 # Logging
 
diff --git a/docs/user/README.md b/docs/user/README.md
index 082dadd76..3da30a193 100644
--- a/docs/user/README.md
+++ b/docs/user/README.md
@@ -5,8 +5,7 @@ install lsp server, clone the repository and then run `cargo xtask install
 ./crates/ra_lsp_server`). This will produce a binary named `ra_lsp_server` which
 you should be able to use it with any LSP-compatible editor. We use custom
 extensions to LSP, so special client-side support is required to take full
-advantage of rust-analyzer. This repository contains support code for VS Code
-and Emacs.
+advantage of rust-analyzer. This repository contains support code for VS Code.
 
 ```
 $ git clone [email protected]:rust-analyzer/rust-analyzer && cd rust-analyzer
@@ -162,17 +161,12 @@ host.
 
 ## Emacs
 
-Prerequisites:
-
-`emacs-lsp`, `dash` and `ht` packages.
-
-Installation:
+* install recent version of `emacs-lsp` package by following the instructions [here][emacs-lsp]
+* set `lsp-rust-server` to `'rust-analyzer`
+* run `lsp` in a Rust buffer
+* (Optionally) bind commands like `lsp-rust-analyzer-join-lines`, `lsp-extend-selection` and `lsp-rust-analyzer-expand-macro` to keys
 
-* add
-[rust-analyzer.el](../../editors/emacs/rust-analyzer.el)
-to load path and require it in `init.el`
-* run `lsp` in a rust buffer
-* (Optionally) bind commands like `rust-analyzer-join-lines`, `rust-analyzer-extend-selection` and `rust-analyzer-expand-macro` to keys, and enable `rust-analyzer-inlay-hints-mode` to get inline type hints
+[emacs-lsp]: https://github.com/emacs-lsp/lsp-mode
 
 
 ## Vim and NeoVim (coc-rust-analyzer)
diff --git a/docs/user/assists.md b/docs/user/assists.md
index 1e2dd7485..f737a2fa4 100644
--- a/docs/user/assists.md
+++ b/docs/user/assists.md
@@ -154,20 +154,6 @@ impl Trait<u32> for () {
 }
 ```
 
-## `add_import`
-
-Adds a use statement for a given fully-qualified path.
-
-```rust
-// BEFORE
-fn process(map: std::collections::┃HashMap<String, String>) {}
-
-// AFTER
-use std::collections::HashMap;
-
-fn process(map: HashMap<String, String>) {}
-```
-
 ## `add_new`
 
 Adds a new inherent impl for a type.
@@ -568,6 +554,20 @@ fn handle(action: Action) {
 }
 ```
 
+## `replace_qualified_name_with_use`
+
+Adds a use statement for a given fully-qualified name.
+
+```rust
+// BEFORE
+fn process(map: std::collections::┃HashMap<String, String>) {}
+
+// AFTER
+use std::collections::HashMap;
+
+fn process(map: HashMap<String, String>) {}
+```
+
 ## `split_import`
 
 Wraps the tail of import into braces.
diff --git a/editors/emacs/rust-analyzer.el b/editors/emacs/rust-analyzer.el
deleted file mode 100644
index 9b426fcae..000000000
--- a/editors/emacs/rust-analyzer.el
+++ /dev/null
@@ -1,295 +0,0 @@
-;;; rust-analyzer.el --- Rust analyzer emacs bindings for emacs-lsp -*- lexical-binding: t; -*-
-;;; Code:
-
-(require 'lsp)
-(require 'dash)
-(require 'ht)
-
-;; This currently
-;;  - sets up rust-analyzer with emacs-lsp, giving
-;;    - code actions
-;;    - completion (use company-lsp for proper snippet support)
-;;    - imenu support
-;;    - on-type formatting
-;;    - 'hover' type information & documentation (with lsp-ui)
-;;  - implements source changes (for code actions etc.), except for file system changes
-;;  - implements joinLines (you need to bind rust-analyzer-join-lines to a key)
-;;  - implements selectionRanges (either bind lsp-extend-selection to a key, or use expand-region)
-;;  - provides rust-analyzer-inlay-hints-mode for inline type hints
-;;  - provides rust-analyzer-expand-macro to expand macros
-
-;; What's missing:
-;;  - file system changes in apply-source-change
-;;  - semantic highlighting
-;;  - onEnter, parentModule, findMatchingBrace
-;;  - runnables
-;;  - the debugging commands (syntaxTree and analyzerStatus)
-;;  - more
-
-;; Also, there's a problem with company-lsp's caching being too eager, sometimes
-;; resulting in outdated completions.
-
-(defcustom rust-analyzer-command '("ra_lsp_server")
-  ""
-  :type '(repeat (string)))
-
-(defconst rust-analyzer--notification-handlers
-  '(("rust-analyzer/publishDecorations" . (lambda (_w _p)))))
-
-(defconst rust-analyzer--action-handlers
-  '(("rust-analyzer.applySourceChange" .
-     (lambda (p) (rust-analyzer--apply-source-change-command p)))
-    ("rust-analyzer.selectAndApplySourceChange" .
-     (lambda (p) (rust-analyzer--select-and-apply-source-change-command p)))))
-
-(defun rust-analyzer--uri-filename (text-document)
-  (lsp--uri-to-path (gethash "uri" text-document)))
-
-(defun rust-analyzer--goto-lsp-loc (loc)
-  (-let (((&hash "line" "character") loc))
-    (goto-line (1+ line))
-    (move-to-column character)))
-
-(defun rust-analyzer--apply-text-document-edit (edit)
-  "Like lsp--apply-text-document-edit, but it allows nil version."
-  (let* ((ident (gethash "textDocument" edit))
-         (filename (rust-analyzer--uri-filename ident))
-         (version (gethash "version" ident)))
-    (with-current-buffer (find-file-noselect filename)
-      (when (or (not version) (= version (lsp--cur-file-version)))
-        (lsp--apply-text-edits (gethash "edits" edit))))))
-
-(defun rust-analyzer--apply-source-change (data)
-  ;; TODO fileSystemEdits
-  (seq-doseq (it (-> data (ht-get "workspaceEdit") (ht-get "documentChanges")))
-    (rust-analyzer--apply-text-document-edit it))
-  (-when-let (cursor-position (ht-get data "cursorPosition"))
-    (let ((filename (rust-analyzer--uri-filename (ht-get cursor-position "textDocument")))
-          (position (ht-get cursor-position "position")))
-      (find-file filename)
-      (rust-analyzer--goto-lsp-loc position))))
-
-(defun rust-analyzer--apply-source-change-command (p)
-  (let ((data (-> p (ht-get "arguments") (lsp-seq-first))))
-    (rust-analyzer--apply-source-change data)))
-
-(defun rust-analyzer--select-and-apply-source-change-command (p)
-  (let* ((options (-> p (ht-get "arguments") (lsp-seq-first)))
-         (chosen-option (lsp--completing-read "Select option:" options
-                                              (-lambda ((&hash "label")) label))))
-    (rust-analyzer--apply-source-change chosen-option)))
-
-(lsp-register-client
- (make-lsp-client
-  :new-connection (lsp-stdio-connection (lambda () rust-analyzer-command))
-  :notification-handlers (ht<-alist rust-analyzer--notification-handlers)
-  :action-handlers (ht<-alist rust-analyzer--action-handlers)
-  :major-modes '(rust-mode)
-  :ignore-messages nil
-  :server-id 'rust-analyzer))
-
-(defun rust-analyzer--initialized? ()
-  (when-let ((workspace (lsp-find-workspace 'rust-analyzer (buffer-file-name))))
-    (eq 'initialized (lsp--workspace-status workspace))))
-
-(with-eval-after-load 'company-lsp
-  ;; company-lsp provides a snippet handler for rust by default that adds () after function calls, which RA does better
-  (setq company-lsp--snippet-functions (cl-delete "rust" company-lsp--snippet-functions :key #'car :test #'equal)))
-
-;; join lines
-
-(defun rust-analyzer--join-lines-params ()
-  "Join lines params."
-  (list :textDocument (lsp--text-document-identifier)
-        :range (if (use-region-p)
-                   (lsp--region-to-range (region-beginning) (region-end))
-                 (lsp--region-to-range (point) (point)))))
-
-(defun rust-analyzer-join-lines ()
-  (interactive)
-  (->
-   (lsp-send-request (lsp-make-request "rust-analyzer/joinLines"
-                                       (rust-analyzer--join-lines-params)))
-   (rust-analyzer--apply-source-change)))
-
-;; selection ranges
-
-(defun rust-analyzer--add-er-expansion ()
-  (make-variable-buffer-local 'er/try-expand-list)
-  (setq er/try-expand-list (append
-                            er/try-expand-list
-                            '(lsp-extend-selection))))
-
-(with-eval-after-load 'expand-region
-  ;; add the expansion for all existing rust-mode buffers. If expand-region is
-  ;; loaded lazily, it might be loaded when the first rust buffer is opened, and
-  ;; then it's too late for the hook for that buffer
-  (dolist (buf (buffer-list))
-    (with-current-buffer buf
-      (when (eq 'rust-mode major-mode)
-        (rust-analyzer--add-er-expansion))))
-  (add-hook 'rust-mode-hook 'rust-analyzer--add-er-expansion))
-
-;; runnables
-(defvar rust-analyzer--last-runnable nil)
-
-(defun rust-analyzer--runnables-params ()
-  (list :textDocument (lsp--text-document-identifier)
-        :position (lsp--cur-position)))
-
-(defun rust-analyzer--runnables ()
-  (lsp-send-request (lsp-make-request "rust-analyzer/runnables"
-                                      (rust-analyzer--runnables-params))))
-
-(defun rust-analyzer--select-runnable ()
-  (lsp--completing-read
-   "Select runnable:"
-   (if rust-analyzer--last-runnable
-       (cons rust-analyzer--last-runnable (rust-analyzer--runnables))
-       (rust-analyzer--runnables))
-   (-lambda ((&hash "label")) label)))
-
-(defun rust-analyzer-run (runnable)
-  (interactive (list (rust-analyzer--select-runnable)))
-  (-let* (((&hash "env" "bin" "args" "label") runnable)
-          (compilation-environment (-map (-lambda ((k v)) (concat k "=" v)) (ht-items env))))
-    (compilation-start
-     (string-join (append (list bin) args '()) " ")
-     ;; cargo-process-mode is nice, but try to work without it...
-     (if (functionp 'cargo-process-mode) 'cargo-process-mode nil)
-     (lambda (_) (concat "*" label "*")))
-    (setq rust-analyzer--last-runnable runnable)))
-
-(defun rust-analyzer-rerun (&optional runnable)
-  (interactive (list (or rust-analyzer--last-runnable
-                         (rust-analyzer--select-runnable))))
-  (rust-analyzer-run (or runnable rust-analyzer--last-runnable)))
-
-;; analyzer status buffer
-(define-derived-mode rust-analyzer-status-mode special-mode "Rust-Analyzer-Status"
-  "Mode for the rust-analyzer status buffer.")
-
-(defvar-local rust-analyzer--status-buffer-workspace nil)
-
-(defun rust-analyzer-status ()
-  "Displays status information for rust-analyzer."
-  (interactive)
-  (let* ((workspace (lsp-find-workspace 'rust-analyzer (buffer-file-name)))
-         (buf (get-buffer-create (concat "*rust-analyzer status " (with-lsp-workspace workspace (lsp-workspace-root)) "*"))))
-    (with-current-buffer buf
-      (rust-analyzer-status-mode)
-      (setq rust-analyzer--status-buffer-workspace workspace)
-      (rust-analyzer-status-buffer-refresh))
-    (pop-to-buffer buf)))
-
-(defun rust-analyzer-status-buffer-refresh ()
-  (interactive)
-  (when rust-analyzer--status-buffer-workspace
-    (let ((inhibit-read-only t))
-      (erase-buffer)
-      (insert (with-lsp-workspace rust-analyzer--status-buffer-workspace
-                (lsp-send-request (lsp-make-request
-                                   "rust-analyzer/analyzerStatus")))))))
-
-
-(defun rust-analyzer--syntax-tree-params ()
-  "Syntax tree params."
-  (list :textDocument (lsp--text-document-identifier)
-        :range (if (use-region-p)
-                   (lsp--region-to-range (region-beginning) (region-end))
-                 (lsp--region-to-range (point-min) (point-max)))))
-
-(defun rust-analyzer-syntax-tree ()
-  "Displays syntax tree for current buffer."
-  (interactive)
-  (when (eq 'rust-mode major-mode)
-    (let* ((workspace (lsp-find-workspace 'rust-analyzer (buffer-file-name)))
-           (buf (get-buffer-create (concat "*rust-analyzer syntax tree " (with-lsp-workspace workspace (lsp-workspace-root)) "*"))))
-      (when workspace
-        (let ((parse-result (with-lsp-workspace workspace
-                              (lsp-send-request (lsp-make-request
-                                                 "rust-analyzer/syntaxTree"
-                                                 (rust-analyzer--syntax-tree-params))))))
-          (with-current-buffer buf
-            (let ((inhibit-read-only t))
-              (erase-buffer)
-              (insert parse-result)))
-          (pop-to-buffer buf))))))
-
-;; inlay hints
-(defun rust-analyzer--update-inlay-hints (buffer)
-  (if (and (rust-analyzer--initialized?) (eq buffer (current-buffer)))
-    (lsp-request-async
-     "rust-analyzer/inlayHints"
-     (list :textDocument (lsp--text-document-identifier))
-     (lambda (res)
-       (remove-overlays (point-min) (point-max) 'rust-analyzer--inlay-hint t)
-       (dolist (hint res)
-         (-let* (((&hash "range" "label" "kind") hint)
-                 ((beg . end) (lsp--range-to-region range))
-                 (overlay (make-overlay beg end)))
-           (overlay-put overlay 'rust-analyzer--inlay-hint t)
-           (overlay-put overlay 'evaporate t)
-           (cond
-            ((string= kind "TypeHint")
-             (overlay-put overlay 'after-string (propertize (concat ": " label)
-                                                            'font-lock-face 'font-lock-comment-face)))
-            ((string= kind "ParameterHint")
-             (overlay-put overlay 'before-string (propertize (concat label ": ")
-                                                            'font-lock-face 'font-lock-comment-face)))
-            )
-           )))
-     :mode 'tick))
-  nil)
-
-(defvar-local rust-analyzer--inlay-hints-timer nil)
-
-(defun rust-analyzer--inlay-hints-change-handler (&rest rest)
-  (when rust-analyzer--inlay-hints-timer
-    (cancel-timer rust-analyzer--inlay-hints-timer))
-  (setq rust-analyzer--inlay-hints-timer
-        (run-with-idle-timer 0.1 nil #'rust-analyzer--update-inlay-hints (current-buffer))))
-
-(define-minor-mode rust-analyzer-inlay-hints-mode
-  "Mode for showing inlay hints."
-  nil nil nil
-  (cond
-   (rust-analyzer-inlay-hints-mode
-    (rust-analyzer--update-inlay-hints (current-buffer))
-    (add-hook 'lsp-after-initialize-hook #'rust-analyzer--inlay-hints-change-handler nil t)
-    (add-hook 'after-change-functions #'rust-analyzer--inlay-hints-change-handler nil t))
-   (t
-    (remove-overlays (point-min) (point-max) 'rust-analyzer--inlay-hint t)
-    (remove-hook 'lsp-after-initialize-hook #'rust-analyzer--inlay-hints-change-handler t)
-    (remove-hook 'after-change-functions #'rust-analyzer--inlay-hints-change-handler t))))
-
-
-
-;; expand macros
-(defun rust-analyzer-expand-macro ()
-  "Expands the macro call at point recursively."
-  (interactive)
-  (when (eq 'rust-mode major-mode)
-    (let* ((workspace (lsp-find-workspace 'rust-analyzer (buffer-file-name)))
-           (params (list :textDocument (lsp--text-document-identifier)
-                         :position (lsp--cur-position))))
-      (when workspace
-        (let* ((response (with-lsp-workspace workspace
-                           (lsp-send-request (lsp-make-request
-                                              "rust-analyzer/expandMacro"
-                                              params))))
-               (result (when response (ht-get response "expansion"))))
-          (if result
-            (let ((buf (get-buffer-create (concat "*rust-analyzer macro expansion " (with-lsp-workspace workspace (lsp-workspace-root)) "*"))))
-              (with-current-buffer buf
-                (let ((inhibit-read-only t))
-                  (erase-buffer)
-                  (insert result)
-                  (setq buffer-read-only t)
-                  (special-mode)))
-              (pop-to-buffer buf))
-            (message "No macro found at point, or it could not be expanded")))))))
-
-
-(provide 'rust-analyzer)
-;;; rust-analyzer.el ends here
diff --git a/xtask/src/lib.rs b/xtask/src/lib.rs
index 9b0afe8e0..8fdf43e4a 100644
--- a/xtask/src/lib.rs
+++ b/xtask/src/lib.rs
@@ -53,8 +53,7 @@ fn reformat(text: impl std::fmt::Display) -> Result<String> {
     write!(rustfmt.stdin.take().unwrap(), "{}", text)?;
     let output = rustfmt.wait_with_output()?;
     let stdout = String::from_utf8(output.stdout)?;
-    // TODO: update the preable: replace ra_tools with the relevant path
-    let preamble = "Generated file, do not edit by hand, see `crate/ra_tools/src/codegen`";
+    let preamble = "Generated file, do not edit by hand, see `xtask/src/codegen`";
     Ok(format!("//! {}\n\n{}", preamble, stdout))
 }