16 files changed, 441 insertions, 72 deletions

diff --git a/Cargo.lock b/Cargo.lock
index f94cea814..4412b0708 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -113,8 +113,8 @@ checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
 
 [[package]]
 name = "chalk-derive"
-version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -124,8 +124,8 @@ dependencies = [
 
 [[package]]
 name = "chalk-engine"
-version = "0.9.0"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "chalk-macros",
  "rustc-hash",
@@ -133,8 +133,8 @@ dependencies = [
 
 [[package]]
 name = "chalk-ir"
-version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "chalk-derive",
  "chalk-engine",
@@ -143,16 +143,16 @@ dependencies = [
 
 [[package]]
 name = "chalk-macros"
-version = "0.1.1"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "lazy_static",
 ]
 
 [[package]]
 name = "chalk-rust-ir"
-version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "chalk-derive",
  "chalk-engine",
@@ -162,8 +162,8 @@ dependencies = [
 
 [[package]]
 name = "chalk-solve"
-version = "0.1.0"
-source = "git+https://github.com/rust-lang/chalk.git?rev=2c072cc830d04af5f10b390e6643327f85108282#2c072cc830d04af5f10b390e6643327f85108282"
+version = "0.10.1-dev"
+source = "git+https://github.com/rust-lang/chalk.git?rev=3e9c2503ae9c5277c2acb74624dc267876dd89b3#3e9c2503ae9c5277c2acb74624dc267876dd89b3"
 dependencies = [
  "chalk-derive",
  "chalk-engine",
diff --git a/crates/ra_hir/src/semantics.rs b/crates/ra_hir/src/semantics.rs
index 515e5eb17..7c1f79f27 100644
--- a/crates/ra_hir/src/semantics.rs
+++ b/crates/ra_hir/src/semantics.rs
@@ -23,7 +23,7 @@ use crate::{
     db::HirDatabase,
     diagnostics::Diagnostic,
     semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
-    source_analyzer::{resolve_hir_path, SourceAnalyzer},
+    source_analyzer::{resolve_hir_path, resolve_hir_path_qualifier, SourceAnalyzer},
     AssocItem, Field, Function, HirFileId, ImplDef, InFile, Local, MacroDef, Module, ModuleDef,
     Name, Origin, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam,
 };
@@ -451,6 +451,23 @@ impl<'a, DB: HirDatabase> SemanticsScope<'a, DB> {
     pub fn resolve_hir_path(&self, path: &Path) -> Option<PathResolution> {
         resolve_hir_path(self.db, &self.resolver, path)
     }
+
+    /// Resolves a path where we know it is a qualifier of another path.
+    ///
+    /// For example, if we have:
+    /// ```
+    /// mod my {
+    ///     pub mod foo {
+    ///         struct Bar;
+    ///     }
+    ///
+    ///     pub fn foo() {}
+    /// }
+    /// ```
+    /// then we know that `foo` in `my::foo::Bar` refers to the module, not the function.
+    pub fn resolve_hir_path_qualifier(&self, path: &Path) -> Option<PathResolution> {
+        resolve_hir_path_qualifier(self.db, &self.resolver, path)
+    }
 }
 
 // FIXME: Change `HasSource` trait to work with `Semantics` and remove this?
diff --git a/crates/ra_hir/src/source_analyzer.rs b/crates/ra_hir/src/source_analyzer.rs
index c862a4f48..4b509f07c 100644
--- a/crates/ra_hir/src/source_analyzer.rs
+++ b/crates/ra_hir/src/source_analyzer.rs
@@ -226,6 +226,17 @@ impl SourceAnalyzer {
         // This must be a normal source file rather than macro file.
         let hir_path =
             crate::Path::from_src(path.clone(), &Hygiene::new(db.upcast(), self.file_id))?;
+
+        // Case where path is a qualifier of another path, e.g. foo::bar::Baz where we
+        // trying to resolve foo::bar.
+        if let Some(outer_path) = path.syntax().parent().and_then(ast::Path::cast) {
+            if let Some(qualifier) = outer_path.qualifier() {
+                if path == &qualifier {
+                    return resolve_hir_path_qualifier(db, &self.resolver, &hir_path);
+                }
+            }
+        }
+
         resolve_hir_path(db, &self.resolver, &hir_path)
     }
 
@@ -404,6 +415,7 @@ pub(crate) fn resolve_hir_path(
             TypeNs::BuiltinType(it) => PathResolution::Def(it.into()),
             TypeNs::TraitId(it) => PathResolution::Def(Trait::from(it).into()),
         });
+
     let body_owner = resolver.body_owner();
     let values =
         resolver.resolve_path_in_value_ns_fully(db.upcast(), path.mod_path()).and_then(|val| {
@@ -426,9 +438,48 @@ pub(crate) fn resolve_hir_path(
         .resolve_module_path_in_items(db.upcast(), path.mod_path())
         .take_types()
         .map(|it| PathResolution::Def(it.into()));
+
     types.or(values).or(items).or_else(|| {
         resolver
             .resolve_path_as_macro(db.upcast(), path.mod_path())
             .map(|def| PathResolution::Macro(def.into()))
     })
 }
+
+/// Resolves a path where we know it is a qualifier of another path.
+///
+/// For example, if we have:
+/// ```
+/// mod my {
+///     pub mod foo {
+///         struct Bar;
+///     }
+///
+///     pub fn foo() {}
+/// }
+/// ```
+/// then we know that `foo` in `my::foo::Bar` refers to the module, not the function.
+pub(crate) fn resolve_hir_path_qualifier(
+    db: &dyn HirDatabase,
+    resolver: &Resolver,
+    path: &crate::Path,
+) -> Option<PathResolution> {
+    let items = resolver
+        .resolve_module_path_in_items(db.upcast(), path.mod_path())
+        .take_types()
+        .map(|it| PathResolution::Def(it.into()));
+
+    if items.is_some() {
+        return items;
+    }
+
+    resolver.resolve_path_in_type_ns_fully(db.upcast(), path.mod_path()).map(|ty| match ty {
+        TypeNs::SelfType(it) => PathResolution::SelfType(it.into()),
+        TypeNs::GenericParam(id) => PathResolution::TypeParam(TypeParam { id }),
+        TypeNs::AdtSelfType(it) | TypeNs::AdtId(it) => PathResolution::Def(Adt::from(it).into()),
+        TypeNs::EnumVariantId(it) => PathResolution::Def(EnumVariant::from(it).into()),
+        TypeNs::TypeAliasId(it) => PathResolution::Def(TypeAlias::from(it).into()),
+        TypeNs::BuiltinType(it) => PathResolution::Def(it.into()),
+        TypeNs::TraitId(it) => PathResolution::Def(Trait::from(it).into()),
+    })
+}
diff --git a/crates/ra_hir_ty/Cargo.toml b/crates/ra_hir_ty/Cargo.toml
index 65db6d1b0..5fc0ec5e3 100644
--- a/crates/ra_hir_ty/Cargo.toml
+++ b/crates/ra_hir_ty/Cargo.toml
@@ -27,9 +27,9 @@ test_utils = { path = "../test_utils" }
 
 scoped-tls = "1"
 
-chalk-solve =   { git = "https://github.com/rust-lang/chalk.git", rev = "2c072cc830d04af5f10b390e6643327f85108282" }
-chalk-rust-ir = { git = "https://github.com/rust-lang/chalk.git", rev = "2c072cc830d04af5f10b390e6643327f85108282" }
-chalk-ir =      { git = "https://github.com/rust-lang/chalk.git", rev = "2c072cc830d04af5f10b390e6643327f85108282" }
+chalk-solve =   { git = "https://github.com/rust-lang/chalk.git", rev = "3e9c2503ae9c5277c2acb74624dc267876dd89b3" }
+chalk-rust-ir = { git = "https://github.com/rust-lang/chalk.git", rev = "3e9c2503ae9c5277c2acb74624dc267876dd89b3" }
+chalk-ir =      { git = "https://github.com/rust-lang/chalk.git", rev = "3e9c2503ae9c5277c2acb74624dc267876dd89b3" }
 
 [dev-dependencies]
 insta = "0.16.0"
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index ccc4348f4..daea02f88 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -808,15 +808,13 @@ impl Ty {
         }
     }
 
-    /// If this is an `impl Trait` or `dyn Trait`, returns that trait.
-    pub fn inherent_trait(&self) -> Option<TraitId> {
+    /// If this is a `dyn Trait`, returns that trait.
+    pub fn dyn_trait(&self) -> Option<TraitId> {
         match self {
-            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
-                predicates.iter().find_map(|pred| match pred {
-                    GenericPredicate::Implemented(tr) => Some(tr.trait_),
-                    _ => None,
-                })
-            }
+            Ty::Dyn(predicates) => predicates.iter().find_map(|pred| match pred {
+                GenericPredicate::Implemented(tr) => Some(tr.trait_),
+                _ => None,
+            }),
             _ => None,
         }
     }
diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index 657284fd0..0851e16a8 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -408,8 +408,9 @@ fn iterate_trait_method_candidates<T>(
     receiver_ty: Option<&Canonical<Ty>>,
     mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
 ) -> Option<T> {
-    // if ty is `impl Trait` or `dyn Trait`, the trait doesn't need to be in scope
-    let inherent_trait = self_ty.value.inherent_trait().into_iter();
+    // if ty is `dyn Trait`, the trait doesn't need to be in scope
+    let inherent_trait =
+        self_ty.value.dyn_trait().into_iter().flat_map(|t| all_super_traits(db.upcast(), t));
     let env_traits = if let Ty::Placeholder(_) = self_ty.value {
         // if we have `T: Trait` in the param env, the trait doesn't need to be in scope
         env.trait_predicates_for_self_ty(&self_ty.value)
@@ -601,11 +602,6 @@ pub fn implements_trait(
     krate: CrateId,
     trait_: TraitId,
 ) -> bool {
-    if ty.value.inherent_trait() == Some(trait_) {
-        // FIXME this is a bit of a hack, since Chalk should say the same thing
-        // anyway, but currently Chalk doesn't implement `dyn/impl Trait` yet
-        return true;
-    }
     let goal = generic_implements_goal(db, env, trait_, ty.clone());
     let solution = db.trait_solve(krate, goal);
 
diff --git a/crates/ra_hir_ty/src/tests/method_resolution.rs b/crates/ra_hir_ty/src/tests/method_resolution.rs
index 67f964ab5..9c2c9e1d2 100644
--- a/crates/ra_hir_ty/src/tests/method_resolution.rs
+++ b/crates/ra_hir_ty/src/tests/method_resolution.rs
@@ -1096,3 +1096,34 @@ fn test() { (S {}).method()<|>; }
     );
     assert_eq!(t, "()");
 }
+
+#[test]
+fn dyn_trait_super_trait_not_in_scope() {
+    assert_snapshot!(
+        infer(r#"
+mod m {
+    pub trait SuperTrait {
+        fn foo(&self) -> u32 { 0 }
+    }
+}
+trait Trait: m::SuperTrait {}
+
+struct S;
+impl m::SuperTrait for S {}
+impl Trait for S {}
+
+fn test(d: &dyn Trait) {
+    d.foo();
+}
+"#),
+        @r###"
+    52..56 'self': &Self
+    65..70 '{ 0 }': u32
+    67..68 '0': u32
+    177..178 'd': &dyn Trait
+    192..208 '{     ...o(); }': ()
+    198..199 'd': &dyn Trait
+    198..205 'd.foo()': u32
+    "###
+    );
+}
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index 1ccb7c3b4..5870618a0 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -182,7 +182,10 @@ impl chalk_ir::interner::Interner for Interner {
         Arc::new(goal)
     }
 
-    fn intern_goals(&self, data: impl IntoIterator<Item = Goal<Self>>) -> Self::InternedGoals {
+    fn intern_goals<E>(
+        &self,
+        data: impl IntoIterator<Item = Result<Goal<Self>, E>>,
+    ) -> Result<Self::InternedGoals, E> {
         data.into_iter().collect()
     }
 
@@ -222,10 +225,10 @@ impl chalk_ir::interner::Interner for Interner {
         clause
     }
 
-    fn intern_program_clauses(
+    fn intern_program_clauses<E>(
         &self,
-        data: impl IntoIterator<Item = chalk_ir::ProgramClause<Self>>,
-    ) -> Arc<[chalk_ir::ProgramClause<Self>]> {
+        data: impl IntoIterator<Item = Result<chalk_ir::ProgramClause<Self>, E>>,
+    ) -> Result<Arc<[chalk_ir::ProgramClause<Self>]>, E> {
         data.into_iter().collect()
     }
 
@@ -236,10 +239,10 @@ impl chalk_ir::interner::Interner for Interner {
         &clauses
     }
 
-    fn intern_quantified_where_clauses(
+    fn intern_quantified_where_clauses<E>(
         &self,
-        data: impl IntoIterator<Item = chalk_ir::QuantifiedWhereClause<Self>>,
-    ) -> Self::InternedQuantifiedWhereClauses {
+        data: impl IntoIterator<Item = Result<chalk_ir::QuantifiedWhereClause<Self>, E>>,
+    ) -> Result<Self::InternedQuantifiedWhereClauses, E> {
         data.into_iter().collect()
     }
 
@@ -250,10 +253,10 @@ impl chalk_ir::interner::Interner for Interner {
         clauses
     }
 
-    fn intern_parameter_kinds(
+    fn intern_parameter_kinds<E>(
         &self,
-        data: impl IntoIterator<Item = chalk_ir::ParameterKind<()>>,
-    ) -> Self::InternedParameterKinds {
+        data: impl IntoIterator<Item = Result<chalk_ir::ParameterKind<()>, E>>,
+    ) -> Result<Self::InternedParameterKinds, E> {
         data.into_iter().collect()
     }
 
@@ -264,10 +267,10 @@ impl chalk_ir::interner::Interner for Interner {
         &parameter_kinds
     }
 
-    fn intern_canonical_var_kinds(
+    fn intern_canonical_var_kinds<E>(
         &self,
-        data: impl IntoIterator<Item = chalk_ir::ParameterKind<UniverseIndex>>,
-    ) -> Self::InternedCanonicalVarKinds {
+        data: impl IntoIterator<Item = Result<chalk_ir::ParameterKind<UniverseIndex>, E>>,
+    ) -> Result<Self::InternedCanonicalVarKinds, E> {
         data.into_iter().collect()
     }
 
@@ -460,6 +463,14 @@ impl ToChalk for TypeCtor {
             TypeName::Struct(struct_id) => db.lookup_intern_type_ctor(struct_id.into()),
             TypeName::AssociatedType(type_id) => TypeCtor::AssociatedType(from_chalk(db, type_id)),
             TypeName::OpaqueType(_) => unreachable!(),
+
+            TypeName::Scalar(_) => unreachable!(),
+            TypeName::Tuple(_) => unreachable!(),
+            TypeName::Raw(_) => unreachable!(),
+            TypeName::Slice => unreachable!(),
+            TypeName::Ref(_) => unreachable!(),
+            TypeName::Str => unreachable!(),
+
             TypeName::Error => {
                 // this should not be reached, since we don't represent TypeName::Error with TypeCtor
                 unreachable!()
@@ -862,12 +873,6 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
         // We don't do coherence checking (yet)
         unimplemented!()
     }
-    fn as_struct_id(&self, id: &TypeName<Interner>) -> Option<StructId> {
-        match id {
-            TypeName::Struct(struct_id) => Some(*struct_id),
-            _ => None,
-        }
-    }
     fn interner(&self) -> &Interner {
         &Interner
     }
@@ -892,6 +897,20 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
     ) -> Arc<chalk_rust_ir::OpaqueTyDatum<Interner>> {
         unimplemented!()
     }
+
+    fn force_impl_for(
+        &self,
+        _well_known: chalk_rust_ir::WellKnownTrait,
+        _ty: &chalk_ir::TyData<Interner>,
+    ) -> Option<bool> {
+        // this method is mostly for rustc
+        None
+    }
+
+    fn is_object_safe(&self, _trait_id: chalk_ir::TraitId<Interner>) -> bool {
+        // FIXME: implement actual object safety
+        true
+    }
 }
 
 pub(crate) fn program_clauses_for_chalk_env_query(
diff --git a/crates/ra_ide/src/completion/complete_qualified_path.rs b/crates/ra_ide/src/completion/complete_qualified_path.rs
index 7fcd22525..db7430454 100644
--- a/crates/ra_ide/src/completion/complete_qualified_path.rs
+++ b/crates/ra_ide/src/completion/complete_qualified_path.rs
@@ -20,7 +20,7 @@ pub(super) fn complete_qualified_path(acc: &mut Completions, ctx: &CompletionCon
     let scope = ctx.scope();
     let context_module = scope.module();
 
-    let res = match scope.resolve_hir_path(&path) {
+    let res = match scope.resolve_hir_path_qualifier(&path) {
         Some(res) => res,
         None => return,
     };
@@ -226,6 +226,34 @@ mod tests {
     }
 
     #[test]
+    fn completes_mod_with_same_name_as_function() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                use self::my::<|>;
+
+                mod my {
+                    pub struct Bar;
+                }
+
+                fn my() {}
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "Bar",
+                source_range: 31..31,
+                delete: 31..31,
+                insert: "Bar",
+                kind: Struct,
+            },
+        ]
+        "###
+        );
+    }
+
+    #[test]
     fn path_visibility() {
         assert_debug_snapshot!(
             do_reference_completion(
diff --git a/crates/ra_ide/src/hover.rs b/crates/ra_ide/src/hover.rs
index 06d4f1c63..befa977c7 100644
--- a/crates/ra_ide/src/hover.rs
+++ b/crates/ra_ide/src/hover.rs
@@ -921,4 +921,21 @@ fn func(foo: i32) { if true { <|>foo; }; }
             &["unsafe trait foo"],
         );
     }
+
+    #[test]
+    fn test_hover_mod_with_same_name_as_function() {
+        check_hover_result(
+            "
+            //- /lib.rs
+            use self::m<|>y::Bar;
+
+            mod my {
+                pub struct Bar;
+            }
+
+            fn my() {}
+            ",
+            &["mod my"],
+        );
+    }
 }
diff --git a/crates/ra_ide/src/references/rename.rs b/crates/ra_ide/src/references/rename.rs
index 2cbb82c1a..410dae75c 100644
--- a/crates/ra_ide/src/references/rename.rs
+++ b/crates/ra_ide/src/references/rename.rs
@@ -4,14 +4,16 @@ use hir::{ModuleSource, Semantics};
 use ra_db::{RelativePath, RelativePathBuf, SourceDatabaseExt};
 use ra_ide_db::RootDatabase;
 use ra_syntax::{
-    algo::find_node_at_offset, ast, lex_single_valid_syntax_kind, AstNode, SyntaxKind, SyntaxNode,
+    algo::find_node_at_offset, ast, ast::TypeAscriptionOwner, lex_single_valid_syntax_kind,
+    AstNode, SyntaxKind, SyntaxNode, SyntaxToken,
 };
 use ra_text_edit::TextEdit;
+use std::convert::TryInto;
 use test_utils::tested_by;
 
 use crate::{
     references::find_all_refs, FilePosition, FileSystemEdit, RangeInfo, Reference, ReferenceKind,
-    SourceChange, SourceFileEdit, TextRange,
+    SourceChange, SourceFileEdit, TextRange, TextSize,
 };
 
 pub(crate) fn rename(
@@ -21,17 +23,21 @@ pub(crate) fn rename(
 ) -> Option<RangeInfo<SourceChange>> {
     match lex_single_valid_syntax_kind(new_name)? {
         SyntaxKind::IDENT | SyntaxKind::UNDERSCORE => (),
+        SyntaxKind::SELF_KW => return rename_to_self(db, position),
         _ => return None,
     }
 
     let sema = Semantics::new(db);
     let source_file = sema.parse(position.file_id);
-    if let Some((ast_name, ast_module)) =
-        find_name_and_module_at_offset(source_file.syntax(), position)
-    {
+    let syntax = source_file.syntax();
+    if let Some((ast_name, ast_module)) = find_name_and_module_at_offset(syntax, position) {
         let range = ast_name.syntax().text_range();
         rename_mod(&sema, &ast_name, &ast_module, position, new_name)
             .map(|info| RangeInfo::new(range, info))
+    } else if let Some(self_token) =
+        syntax.token_at_offset(position.offset).find(|t| t.kind() == SyntaxKind::SELF_KW)
+    {
+        rename_self_to_param(db, position, self_token, new_name)
     } else {
         rename_reference(sema.db, position, new_name)
     }
@@ -125,6 +131,112 @@ fn rename_mod(
     Some(SourceChange::from_edits("Rename", source_file_edits, file_system_edits))
 }
 
+fn rename_to_self(db: &RootDatabase, position: FilePosition) -> Option<RangeInfo<SourceChange>> {
+    let sema = Semantics::new(db);
+    let source_file = sema.parse(position.file_id);
+    let syn = source_file.syntax();
+
+    let fn_def = find_node_at_offset::<ast::FnDef>(syn, position.offset)?;
+    let params = fn_def.param_list()?;
+    if params.self_param().is_some() {
+        return None; // method already has self param
+    }
+    let first_param = params.params().next()?;
+    let mutable = match first_param.ascribed_type() {
+        Some(ast::TypeRef::ReferenceType(rt)) => rt.mut_token().is_some(),
+        _ => return None, // not renaming other types
+    };
+
+    let RangeInfo { range, info: refs } = find_all_refs(db, position, None)?;
+
+    let param_range = first_param.syntax().text_range();
+    let (param_ref, usages): (Vec<Reference>, Vec<Reference>) = refs
+        .into_iter()
+        .partition(|reference| param_range.intersect(reference.file_range.range).is_some());
+
+    if param_ref.is_empty() {
+        return None;
+    }
+
+    let mut edits = usages
+        .into_iter()
+        .map(|reference| source_edit_from_reference(reference, "self"))
+        .collect::<Vec<_>>();
+
+    edits.push(SourceFileEdit {
+        file_id: position.file_id,
+        edit: TextEdit::replace(
+            param_range,
+            String::from(if mutable { "&mut self" } else { "&self" }),
+        ),
+    });
+
+    Some(RangeInfo::new(range, SourceChange::source_file_edits("Rename", edits)))
+}
+
+fn text_edit_from_self_param(
+    syn: &SyntaxNode,
+    self_param: &ast::SelfParam,
+    new_name: &str,
+) -> Option<TextEdit> {
+    fn target_type_name(impl_def: &ast::ImplDef) -> Option<String> {
+        if let Some(ast::TypeRef::PathType(p)) = impl_def.target_type() {
+            return Some(p.path()?.segment()?.name_ref()?.text().to_string());
+        }
+        None
+    }
+
+    let impl_def =
+        find_node_at_offset::<ast::ImplDef>(syn, self_param.syntax().text_range().start())?;
+    let type_name = target_type_name(&impl_def)?;
+
+    let mut replacement_text = String::from(new_name);
+    replacement_text.push_str(": ");
+    replacement_text.push_str(self_param.mut_token().map_or("&", |_| "&mut "));
+    replacement_text.push_str(type_name.as_str());
+
+    Some(TextEdit::replace(self_param.syntax().text_range(), replacement_text))
+}
+
+fn rename_self_to_param(
+    db: &RootDatabase,
+    position: FilePosition,
+    self_token: SyntaxToken,
+    new_name: &str,
+) -> Option<RangeInfo<SourceChange>> {
+    let sema = Semantics::new(db);
+    let source_file = sema.parse(position.file_id);
+    let syn = source_file.syntax();
+
+    let text = db.file_text(position.file_id);
+    let fn_def = find_node_at_offset::<ast::FnDef>(syn, position.offset)?;
+    let search_range = fn_def.syntax().text_range();
+
+    let mut edits: Vec<SourceFileEdit> = vec![];
+
+    for (idx, _) in text.match_indices("self") {
+        let offset: TextSize = idx.try_into().unwrap();
+        if !search_range.contains_inclusive(offset) {
+            continue;
+        }
+        if let Some(ref usage) =
+            syn.token_at_offset(offset).find(|t| t.kind() == SyntaxKind::SELF_KW)
+        {
+            let edit = if let Some(ref self_param) = ast::SelfParam::cast(usage.parent()) {
+                text_edit_from_self_param(syn, self_param, new_name)?
+            } else {
+                TextEdit::replace(usage.text_range(), String::from(new_name))
+            };
+            edits.push(SourceFileEdit { file_id: position.file_id, edit });
+        }
+    }
+
+    let range = ast::SelfParam::cast(self_token.parent())
+        .map_or(self_token.text_range(), |p| p.syntax().text_range());
+
+    Some(RangeInfo::new(range, SourceChange::source_file_edits("Rename", edits)))
+}
+
 fn rename_reference(
     db: &RootDatabase,
     position: FilePosition,
@@ -774,6 +886,95 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_parameter_to_self() {
+        test_rename(
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(foo<|>: &mut Foo) -> i32 {
+            foo.i
+        }
+    }
+    "#,
+            "self",
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(&mut self) -> i32 {
+            self.i
+        }
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn test_self_to_parameter() {
+        test_rename(
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(&mut <|>self) -> i32 {
+            self.i
+        }
+    }
+    "#,
+            "foo",
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(foo: &mut Foo) -> i32 {
+            foo.i
+        }
+    }
+    "#,
+        );
+    }
+
+    #[test]
+    fn test_self_in_path_to_parameter() {
+        test_rename(
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(&self) -> i32 {
+            let self_var = 1;
+            self<|>.i
+        }
+    }
+    "#,
+            "foo",
+            r#"
+    struct Foo {
+        i: i32,
+    }
+
+    impl Foo {
+        fn f(foo: &Foo) -> i32 {
+            let self_var = 1;
+            foo.i
+        }
+    }
+    "#,
+        );
+    }
+
     fn test_rename(text: &str, new_name: &str, expected: &str) {
         let (analysis, position) = single_file_with_position(text);
         let source_change = analysis.rename(position, new_name).unwrap();
diff --git a/crates/ra_mbe/src/mbe_expander/transcriber.rs b/crates/ra_mbe/src/mbe_expander/transcriber.rs
index 4b173edd3..7c9bb4d00 100644
--- a/crates/ra_mbe/src/mbe_expander/transcriber.rs
+++ b/crates/ra_mbe/src/mbe_expander/transcriber.rs
@@ -1,4 +1,4 @@
-//! Transcraber takes a template, like `fn $ident() {}`, a set of bindings like
+//! Transcriber takes a template, like `fn $ident() {}`, a set of bindings like
 //! `$ident => foo`, interpolates variables in the template, to get `fn foo() {}`
 
 use ra_syntax::SmolStr;
@@ -53,7 +53,8 @@ impl Bindings {
 pub(super) fn transcribe(template: &tt::Subtree, bindings: &Bindings) -> ExpandResult<tt::Subtree> {
     assert!(template.delimiter == None);
     let mut ctx = ExpandCtx { bindings: &bindings, nesting: Vec::new() };
-    expand_subtree(&mut ctx, template)
+    let mut arena: Vec<tt::TokenTree> = Vec::new();
+    expand_subtree(&mut ctx, template, &mut arena)
 }
 
 #[derive(Debug)]
@@ -73,8 +74,13 @@ struct ExpandCtx<'a> {
     nesting: Vec<NestingState>,
 }
 
-fn expand_subtree(ctx: &mut ExpandCtx, template: &tt::Subtree) -> ExpandResult<tt::Subtree> {
-    let mut buf: Vec<tt::TokenTree> = Vec::new();
+fn expand_subtree(
+    ctx: &mut ExpandCtx,
+    template: &tt::Subtree,
+    arena: &mut Vec<tt::TokenTree>,
+) -> ExpandResult<tt::Subtree> {
+    // remember how many elements are in the arena now - when returning, we want to drain exactly how many elements we added. This way, the recursive uses of the arena get their own "view" of the arena, but will reuse the allocation
+    let start_elements = arena.len();
     let mut err = None;
     for op in parse_template(template) {
         let op = match op {
@@ -85,25 +91,27 @@ fn expand_subtree(ctx: &mut ExpandCtx, template: &tt::Subtree) -> ExpandResult<t
             }
         };
         match op {
-            Op::TokenTree(tt @ tt::TokenTree::Leaf(..)) => buf.push(tt.clone()),
+            Op::TokenTree(tt @ tt::TokenTree::Leaf(..)) => arena.push(tt.clone()),
             Op::TokenTree(tt::TokenTree::Subtree(tt)) => {
-                let ExpandResult(tt, e) = expand_subtree(ctx, tt);
+                let ExpandResult(tt, e) = expand_subtree(ctx, tt, arena);
                 err = err.or(e);
-                buf.push(tt.into());
+                arena.push(tt.into());
             }
             Op::Var { name, kind: _ } => {
                 let ExpandResult(fragment, e) = expand_var(ctx, name);
                 err = err.or(e);
-                push_fragment(&mut buf, fragment);
+                push_fragment(arena, fragment);
             }
             Op::Repeat { subtree, kind, separator } => {
-                let ExpandResult(fragment, e) = expand_repeat(ctx, subtree, kind, separator);
+                let ExpandResult(fragment, e) = expand_repeat(ctx, subtree, kind, separator, arena);
                 err = err.or(e);
-                push_fragment(&mut buf, fragment)
+                push_fragment(arena, fragment)
             }
         }
     }
-    ExpandResult(tt::Subtree { delimiter: template.delimiter, token_trees: buf }, err)
+    // drain the elements added in this instance of expand_subtree
+    let tts = arena.drain(start_elements..arena.len()).collect();
+    ExpandResult(tt::Subtree { delimiter: template.delimiter, token_trees: tts }, err)
 }
 
 fn expand_var(ctx: &mut ExpandCtx, v: &SmolStr) -> ExpandResult<Fragment> {
@@ -155,6 +163,7 @@ fn expand_repeat(
     template: &tt::Subtree,
     kind: RepeatKind,
     separator: Option<Separator>,
+    arena: &mut Vec<tt::TokenTree>,
 ) -> ExpandResult<Fragment> {
     let mut buf: Vec<tt::TokenTree> = Vec::new();
     ctx.nesting.push(NestingState { idx: 0, at_end: false, hit: false });
@@ -165,7 +174,7 @@ fn expand_repeat(
     let mut counter = 0;
 
     loop {
-        let ExpandResult(mut t, e) = expand_subtree(ctx, template);
+        let ExpandResult(mut t, e) = expand_subtree(ctx, template, arena);
         let nesting_state = ctx.nesting.last_mut().unwrap();
         if nesting_state.at_end || !nesting_state.hit {
             break;
diff --git a/crates/ra_parser/src/lib.rs b/crates/ra_parser/src/lib.rs
index e08ad4dae..eeb8ad66b 100644
--- a/crates/ra_parser/src/lib.rs
+++ b/crates/ra_parser/src/lib.rs
@@ -25,7 +25,7 @@ pub(crate) use token_set::TokenSet;
 pub use syntax_kind::SyntaxKind;
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct ParseError(pub String);
+pub struct ParseError(pub Box<String>);
 
 /// `TokenSource` abstracts the source of the tokens parser operates on.
 ///
diff --git a/crates/ra_parser/src/parser.rs b/crates/ra_parser/src/parser.rs
index faa63d53f..4f59b0a23 100644
--- a/crates/ra_parser/src/parser.rs
+++ b/crates/ra_parser/src/parser.rs
@@ -192,7 +192,7 @@ impl<'t> Parser<'t> {
     /// structured errors with spans and notes, like rustc
     /// does.
     pub(crate) fn error<T: Into<String>>(&mut self, message: T) {
-        let msg = ParseError(message.into());
+        let msg = ParseError(Box::new(message.into()));
         self.push_event(Event::Error { msg })
     }
 
diff --git a/crates/ra_syntax/src/syntax_node.rs b/crates/ra_syntax/src/syntax_node.rs
index f9d379abf..e566af7e8 100644
--- a/crates/ra_syntax/src/syntax_node.rs
+++ b/crates/ra_syntax/src/syntax_node.rs
@@ -70,6 +70,6 @@ impl SyntaxTreeBuilder {
     }
 
     pub fn error(&mut self, error: ra_parser::ParseError, text_pos: TextSize) {
-        self.errors.push(SyntaxError::new_at_offset(error.0, text_pos))
+        self.errors.push(SyntaxError::new_at_offset(*error.0, text_pos))
     }
 }
diff --git a/crates/ra_tt/src/buffer.rs b/crates/ra_tt/src/buffer.rs
index 14b3f707d..5967f44cd 100644
--- a/crates/ra_tt/src/buffer.rs
+++ b/crates/ra_tt/src/buffer.rs
@@ -42,7 +42,9 @@ impl<'t> TokenBuffer<'t> {
         buffers: &mut Vec<Box<[Entry<'t>]>>,
         next: Option<EntryPtr>,
     ) -> usize {
-        let mut entries = vec![];
+        // Must contain everything in tokens and then the Entry::End
+        let start_capacity = tokens.len() + 1;
+        let mut entries = Vec::with_capacity(start_capacity);
         let mut children = vec![];
 
         for (idx, tt) in tokens.iter().enumerate() {