28 files changed, 691 insertions, 180 deletions

diff --git a/crates/ra_hir/src/semantics.rs b/crates/ra_hir/src/semantics.rs
index 2707e422d..0b477f0e9 100644
--- a/crates/ra_hir/src/semantics.rs
+++ b/crates/ra_hir/src/semantics.rs
@@ -20,6 +20,7 @@ use rustc_hash::{FxHashMap, FxHashSet};
 
 use crate::{
     db::HirDatabase,
+    diagnostics::Diagnostic,
     semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
     source_analyzer::{resolve_hir_path, SourceAnalyzer},
     AssocItem, Function, HirFileId, ImplDef, InFile, Local, MacroDef, Module, ModuleDef, Name,
@@ -126,6 +127,13 @@ impl<'db, DB: HirDatabase> Semantics<'db, DB> {
         original_range(self.db, node.as_ref())
     }
 
+    pub fn diagnostics_range(&self, diagnostics: &dyn Diagnostic) -> FileRange {
+        let src = diagnostics.source();
+        let root = self.db.parse_or_expand(src.file_id).unwrap();
+        let node = src.value.to_node(&root);
+        original_range(self.db, src.with_value(&node))
+    }
+
     pub fn ancestors_with_macros(&self, node: SyntaxNode) -> impl Iterator<Item = SyntaxNode> + '_ {
         let node = self.find_file(node);
         node.ancestors_with_macros(self.db).map(|it| it.value)
diff --git a/crates/ra_hir/src/source_analyzer.rs b/crates/ra_hir/src/source_analyzer.rs
index 58ae6ce41..23af400b8 100644
--- a/crates/ra_hir/src/source_analyzer.rs
+++ b/crates/ra_hir/src/source_analyzer.rs
@@ -23,7 +23,7 @@ use hir_ty::{
 };
 use ra_syntax::{
     ast::{self, AstNode},
-    SyntaxNode, SyntaxNodePtr, TextUnit,
+    SyntaxNode, TextRange, TextUnit,
 };
 
 use crate::{
@@ -56,7 +56,7 @@ impl SourceAnalyzer {
         let scopes = db.expr_scopes(def);
         let scope = match offset {
             None => scope_for(&scopes, &source_map, node),
-            Some(offset) => scope_for_offset(&scopes, &source_map, node.with_value(offset)),
+            Some(offset) => scope_for_offset(db, &scopes, &source_map, node.with_value(offset)),
         };
         let resolver = resolver_for_scope(db.upcast(), def, scope);
         SourceAnalyzer {
@@ -304,6 +304,7 @@ fn scope_for(
 }
 
 fn scope_for_offset(
+    db: &dyn HirDatabase,
     scopes: &ExprScopes,
     source_map: &BodySourceMap,
     offset: InFile<TextUnit>,
@@ -317,21 +318,63 @@ fn scope_for_offset(
             if source.file_id != offset.file_id {
                 return None;
             }
-            let syntax_node_ptr = source.value.syntax_node_ptr();
-            Some((syntax_node_ptr, scope))
+            let root = source.file_syntax(db.upcast());
+            let node = source.value.to_node(&root);
+            Some((node.syntax().text_range(), scope))
         })
         // find containing scope
-        .min_by_key(|(ptr, _scope)| {
+        .min_by_key(|(expr_range, _scope)| {
             (
-                !(ptr.range().start() <= offset.value && offset.value <= ptr.range().end()),
-                ptr.range().len(),
+                !(expr_range.start() <= offset.value && offset.value <= expr_range.end()),
+                expr_range.len(),
             )
         })
-        .map(|(ptr, scope)| {
-            adjust(scopes, source_map, ptr, offset.file_id, offset.value).unwrap_or(*scope)
+        .map(|(expr_range, scope)| {
+            adjust(db, scopes, source_map, expr_range, offset.file_id, offset.value)
+                .unwrap_or(*scope)
         })
 }
 
+// XXX: during completion, cursor might be outside of any particular
+// expression. Try to figure out the correct scope...
+fn adjust(
+    db: &dyn HirDatabase,
+    scopes: &ExprScopes,
+    source_map: &BodySourceMap,
+    expr_range: TextRange,
+    file_id: HirFileId,
+    offset: TextUnit,
+) -> Option<ScopeId> {
+    let child_scopes = scopes
+        .scope_by_expr()
+        .iter()
+        .filter_map(|(id, scope)| {
+            let source = source_map.expr_syntax(*id).ok()?;
+            // FIXME: correctly handle macro expansion
+            if source.file_id != file_id {
+                return None;
+            }
+            let root = source.file_syntax(db.upcast());
+            let node = source.value.to_node(&root);
+            Some((node.syntax().text_range(), scope))
+        })
+        .filter(|(range, _)| {
+            range.start() <= offset && range.is_subrange(&expr_range) && *range != expr_range
+        });
+
+    child_scopes
+        .max_by(|(r1, _), (r2, _)| {
+            if r2.is_subrange(&r1) {
+                std::cmp::Ordering::Greater
+            } else if r1.is_subrange(&r2) {
+                std::cmp::Ordering::Less
+            } else {
+                r1.start().cmp(&r2.start())
+            }
+        })
+        .map(|(_ptr, scope)| *scope)
+}
+
 pub(crate) fn resolve_hir_path(
     db: &dyn HirDatabase,
     resolver: &Resolver,
@@ -376,41 +419,3 @@ pub(crate) fn resolve_hir_path(
             .map(|def| PathResolution::Macro(def.into()))
     })
 }
-
-// XXX: during completion, cursor might be outside of any particular
-// expression. Try to figure out the correct scope...
-fn adjust(
-    scopes: &ExprScopes,
-    source_map: &BodySourceMap,
-    ptr: SyntaxNodePtr,
-    file_id: HirFileId,
-    offset: TextUnit,
-) -> Option<ScopeId> {
-    let r = ptr.range();
-    let child_scopes = scopes
-        .scope_by_expr()
-        .iter()
-        .filter_map(|(id, scope)| {
-            let source = source_map.expr_syntax(*id).ok()?;
-            // FIXME: correctly handle macro expansion
-            if source.file_id != file_id {
-                return None;
-            }
-            let syntax_node_ptr = source.value.syntax_node_ptr();
-            Some((syntax_node_ptr, scope))
-        })
-        .map(|(ptr, scope)| (ptr.range(), scope))
-        .filter(|(range, _)| range.start() <= offset && range.is_subrange(&r) && *range != r);
-
-    child_scopes
-        .max_by(|(r1, _), (r2, _)| {
-            if r2.is_subrange(&r1) {
-                std::cmp::Ordering::Greater
-            } else if r1.is_subrange(&r2) {
-                std::cmp::Ordering::Less
-            } else {
-                r1.start().cmp(&r2.start())
-            }
-        })
-        .map(|(_ptr, scope)| *scope)
-}
diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index eafaf48c1..3b169440a 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -210,7 +210,7 @@ pub struct BodySourceMap {
     expr_map_back: ArenaMap<ExprId, Result<ExprSource, SyntheticSyntax>>,
     pat_map: FxHashMap<PatSource, PatId>,
     pat_map_back: ArenaMap<PatId, Result<PatSource, SyntheticSyntax>>,
-    field_map: FxHashMap<(ExprId, usize), AstPtr<ast::RecordField>>,
+    field_map: FxHashMap<(ExprId, usize), InFile<AstPtr<ast::RecordField>>>,
     expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
 }
 
@@ -303,7 +303,7 @@ impl BodySourceMap {
         self.pat_map.get(&src).cloned()
     }
 
-    pub fn field_syntax(&self, expr: ExprId, field: usize) -> AstPtr<ast::RecordField> {
+    pub fn field_syntax(&self, expr: ExprId, field: usize) -> InFile<AstPtr<ast::RecordField>> {
         self.field_map[&(expr, field)].clone()
     }
 }
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index 79abe55ce..82a52804d 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -320,7 +320,8 @@ impl ExprCollector<'_> {
 
                 let res = self.alloc_expr(record_lit, syntax_ptr);
                 for (i, ptr) in field_ptrs.into_iter().enumerate() {
-                    self.source_map.field_map.insert((res, i), ptr);
+                    let src = self.expander.to_source(ptr);
+                    self.source_map.field_map.insert((res, i), src);
                 }
                 res
             }
@@ -650,6 +651,7 @@ impl ExprCollector<'_> {
             ast::Pat::SlicePat(p) => {
                 let SlicePatComponents { prefix, slice, suffix } = p.components();
 
+                // FIXME properly handle `DotDotPat`
                 Pat::Slice {
                     prefix: prefix.into_iter().map(|p| self.collect_pat(p)).collect(),
                     slice: slice.map(|p| self.collect_pat(p)),
@@ -666,9 +668,15 @@ impl ExprCollector<'_> {
                     Pat::Missing
                 }
             }
-            ast::Pat::DotDotPat(_) => unreachable!(
-                "`DotDotPat` requires special handling and should not be mapped to a Pat."
-            ),
+            ast::Pat::DotDotPat(_) => {
+                // `DotDotPat` requires special handling and should not be mapped
+                // to a Pat. Here we are using `Pat::Missing` as a fallback for
+                // when `DotDotPat` is mapped to `Pat`, which can easily happen
+                // when the source code being analyzed has a malformed pattern
+                // which includes `..` in a place where it isn't valid.
+
+                Pat::Missing
+            }
             // FIXME: implement
             ast::Pat::BoxPat(_) | ast::Pat::RangePat(_) | ast::Pat::MacroPat(_) => Pat::Missing,
         };
diff --git a/crates/ra_hir_def/src/builtin_type.rs b/crates/ra_hir_def/src/builtin_type.rs
index d14901a9b..0f872b5c0 100644
--- a/crates/ra_hir_def/src/builtin_type.rs
+++ b/crates/ra_hir_def/src/builtin_type.rs
@@ -5,7 +5,7 @@
 
 use std::fmt;
 
-use hir_expand::name::{name, Name};
+use hir_expand::name::{name, AsName, Name};
 
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
 pub enum Signedness {
@@ -75,33 +75,39 @@ impl BuiltinType {
     ];
 }
 
-impl fmt::Display for BuiltinType {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let type_name = match self {
-            BuiltinType::Char => "char",
-            BuiltinType::Bool => "bool",
-            BuiltinType::Str => "str",
+impl AsName for BuiltinType {
+    fn as_name(&self) -> Name {
+        match self {
+            BuiltinType::Char => name![char],
+            BuiltinType::Bool => name![bool],
+            BuiltinType::Str => name![str],
             BuiltinType::Int(BuiltinInt { signedness, bitness }) => match (signedness, bitness) {
-                (Signedness::Signed, IntBitness::Xsize) => "isize",
-                (Signedness::Signed, IntBitness::X8) => "i8",
-                (Signedness::Signed, IntBitness::X16) => "i16",
-                (Signedness::Signed, IntBitness::X32) => "i32",
-                (Signedness::Signed, IntBitness::X64) => "i64",
-                (Signedness::Signed, IntBitness::X128) => "i128",
-
-                (Signedness::Unsigned, IntBitness::Xsize) => "usize",
-                (Signedness::Unsigned, IntBitness::X8) => "u8",
-                (Signedness::Unsigned, IntBitness::X16) => "u16",
-                (Signedness::Unsigned, IntBitness::X32) => "u32",
-                (Signedness::Unsigned, IntBitness::X64) => "u64",
-                (Signedness::Unsigned, IntBitness::X128) => "u128",
+                (Signedness::Signed, IntBitness::Xsize) => name![isize],
+                (Signedness::Signed, IntBitness::X8) => name![i8],
+                (Signedness::Signed, IntBitness::X16) => name![i16],
+                (Signedness::Signed, IntBitness::X32) => name![i32],
+                (Signedness::Signed, IntBitness::X64) => name![i64],
+                (Signedness::Signed, IntBitness::X128) => name![i128],
+
+                (Signedness::Unsigned, IntBitness::Xsize) => name![usize],
+                (Signedness::Unsigned, IntBitness::X8) => name![u8],
+                (Signedness::Unsigned, IntBitness::X16) => name![u16],
+                (Signedness::Unsigned, IntBitness::X32) => name![u32],
+                (Signedness::Unsigned, IntBitness::X64) => name![u64],
+                (Signedness::Unsigned, IntBitness::X128) => name![u128],
             },
             BuiltinType::Float(BuiltinFloat { bitness }) => match bitness {
-                FloatBitness::X32 => "f32",
-                FloatBitness::X64 => "f64",
+                FloatBitness::X32 => name![f32],
+                FloatBitness::X64 => name![f64],
             },
-        };
-        f.write_str(type_name)
+        }
+    }
+}
+
+impl fmt::Display for BuiltinType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let type_name = self.as_name();
+        type_name.fmt(f)
     }
 }
 
diff --git a/crates/ra_hir_def/src/diagnostics.rs b/crates/ra_hir_def/src/diagnostics.rs
index cfa0f2f76..510c5e064 100644
--- a/crates/ra_hir_def/src/diagnostics.rs
+++ b/crates/ra_hir_def/src/diagnostics.rs
@@ -20,7 +20,7 @@ impl Diagnostic for UnresolvedModule {
         "unresolved module".to_string()
     }
     fn source(&self) -> InFile<SyntaxNodePtr> {
-        InFile { file_id: self.file, value: self.decl.clone().into() }
+        InFile::new(self.file, self.decl.clone().into())
     }
     fn as_any(&self) -> &(dyn Any + Send + 'static) {
         self
diff --git a/crates/ra_hir_def/src/find_path.rs b/crates/ra_hir_def/src/find_path.rs
index d58ac6ba5..81eff5bfe 100644
--- a/crates/ra_hir_def/src/find_path.rs
+++ b/crates/ra_hir_def/src/find_path.rs
@@ -7,7 +7,7 @@ use crate::{
     visibility::Visibility,
     CrateId, ModuleDefId, ModuleId,
 };
-use hir_expand::name::{known, Name};
+use hir_expand::name::{known, AsName, Name};
 use test_utils::tested_by;
 
 const MAX_PATH_LEN: usize = 15;
@@ -113,6 +113,11 @@ fn find_path_inner(
         }
     }
 
+    // - if the item is a builtin, it's in scope
+    if let ItemInNs::Types(ModuleDefId::BuiltinType(builtin)) = item {
+        return Some(ModPath::from_segments(PathKind::Plain, vec![builtin.as_name()]));
+    }
+
     // Recursive case:
     // - if the item is an enum variant, refer to it via the enum
     if let Some(ModuleDefId::EnumVariantId(variant)) = item.as_module_def_id() {
@@ -523,4 +528,18 @@ mod tests {
         "#;
         check_found_path(code, "megaalloc::Arc");
     }
+
+    #[test]
+    fn builtins_are_in_scope() {
+        let code = r#"
+        //- /main.rs
+        <|>
+
+        pub mod primitive {
+            pub use u8;
+        }
+        "#;
+        check_found_path(code, "u8");
+        check_found_path(code, "u16");
+    }
 }
diff --git a/crates/ra_hir_expand/src/diagnostics.rs b/crates/ra_hir_expand/src/diagnostics.rs
index 108c1e38c..99209c6e8 100644
--- a/crates/ra_hir_expand/src/diagnostics.rs
+++ b/crates/ra_hir_expand/src/diagnostics.rs
@@ -16,16 +16,13 @@
 
 use std::{any::Any, fmt};
 
-use ra_syntax::{SyntaxNode, SyntaxNodePtr, TextRange};
+use ra_syntax::{SyntaxNode, SyntaxNodePtr};
 
 use crate::{db::AstDatabase, InFile};
 
 pub trait Diagnostic: Any + Send + Sync + fmt::Debug + 'static {
     fn message(&self) -> String;
     fn source(&self) -> InFile<SyntaxNodePtr>;
-    fn highlight_range(&self) -> TextRange {
-        self.source().value.range()
-    }
     fn as_any(&self) -> &(dyn Any + Send + 'static);
 }
 
diff --git a/crates/ra_hir_ty/src/diagnostics.rs b/crates/ra_hir_ty/src/diagnostics.rs
index 927896d6f..c8fd54861 100644
--- a/crates/ra_hir_ty/src/diagnostics.rs
+++ b/crates/ra_hir_ty/src/diagnostics.rs
@@ -21,7 +21,7 @@ impl Diagnostic for NoSuchField {
     }
 
     fn source(&self) -> InFile<SyntaxNodePtr> {
-        InFile { file_id: self.file, value: self.field.clone().into() }
+        InFile::new(self.file, self.field.clone().into())
     }
 
     fn as_any(&self) -> &(dyn Any + Send + 'static) {
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 246b0e9be..b6d9b3438 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -682,10 +682,10 @@ mod diagnostics {
         ) {
             match self {
                 InferenceDiagnostic::NoSuchField { expr, field } => {
-                    let file = owner.lookup(db.upcast()).source(db.upcast()).file_id;
+                    let source = owner.lookup(db.upcast()).source(db.upcast());
                     let (_, source_map) = db.body_with_source_map(owner.into());
                     let field = source_map.field_syntax(*expr, *field);
-                    sink.push(NoSuchField { file, field })
+                    sink.push(NoSuchField { file: source.file_id, field: field.value })
                 }
             }
         }
diff --git a/crates/ra_hir_ty/src/infer/coerce.rs b/crates/ra_hir_ty/src/infer/coerce.rs
index 959b1e212..89200255a 100644
--- a/crates/ra_hir_ty/src/infer/coerce.rs
+++ b/crates/ra_hir_ty/src/infer/coerce.rs
@@ -51,7 +51,7 @@ impl<'a> InferenceContext<'a> {
             // Trivial cases, this should go after `never` check to
             // avoid infer result type to be never
             _ => {
-                if self.table.unify_inner_trivial(&from_ty, &to_ty) {
+                if self.table.unify_inner_trivial(&from_ty, &to_ty, 0) {
                     return true;
                 }
             }
@@ -175,7 +175,7 @@ impl<'a> InferenceContext<'a> {
                     return self.table.unify_substs(st1, st2, 0);
                 }
                 _ => {
-                    if self.table.unify_inner_trivial(&derefed_ty, &to_ty) {
+                    if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) {
                         return true;
                     }
                 }
diff --git a/crates/ra_hir_ty/src/infer/unify.rs b/crates/ra_hir_ty/src/infer/unify.rs
index 5f6cea8d3..ab0bc8b70 100644
--- a/crates/ra_hir_ty/src/infer/unify.rs
+++ b/crates/ra_hir_ty/src/infer/unify.rs
@@ -8,7 +8,8 @@ use test_utils::tested_by;
 
 use super::{InferenceContext, Obligation};
 use crate::{
-    BoundVar, Canonical, DebruijnIndex, InEnvironment, InferTy, Substs, Ty, TypeCtor, TypeWalk,
+    BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferTy, Substs, Ty,
+    TypeCtor, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -226,16 +227,26 @@ impl InferenceTable {
             (Ty::Apply(a_ty1), Ty::Apply(a_ty2)) if a_ty1.ctor == a_ty2.ctor => {
                 self.unify_substs(&a_ty1.parameters, &a_ty2.parameters, depth + 1)
             }
-            _ => self.unify_inner_trivial(&ty1, &ty2),
+
+            _ => self.unify_inner_trivial(&ty1, &ty2, depth),
         }
     }
 
-    pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
+    pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
         match (ty1, ty2) {
             (Ty::Unknown, _) | (_, Ty::Unknown) => true,
 
             (Ty::Placeholder(p1), Ty::Placeholder(p2)) if *p1 == *p2 => true,
 
+            (Ty::Dyn(dyn1), Ty::Dyn(dyn2)) if dyn1.len() == dyn2.len() => {
+                for (pred1, pred2) in dyn1.iter().zip(dyn2.iter()) {
+                    if !self.unify_preds(pred1, pred2, depth + 1) {
+                        return false;
+                    }
+                }
+                true
+            }
+
             (Ty::Infer(InferTy::TypeVar(tv1)), Ty::Infer(InferTy::TypeVar(tv2)))
             | (Ty::Infer(InferTy::IntVar(tv1)), Ty::Infer(InferTy::IntVar(tv2)))
             | (Ty::Infer(InferTy::FloatVar(tv1)), Ty::Infer(InferTy::FloatVar(tv2)))
@@ -268,6 +279,31 @@ impl InferenceTable {
         }
     }
 
+    fn unify_preds(
+        &mut self,
+        pred1: &GenericPredicate,
+        pred2: &GenericPredicate,
+        depth: usize,
+    ) -> bool {
+        match (pred1, pred2) {
+            (GenericPredicate::Implemented(tr1), GenericPredicate::Implemented(tr2))
+                if tr1.trait_ == tr2.trait_ =>
+            {
+                self.unify_substs(&tr1.substs, &tr2.substs, depth + 1)
+            }
+            (GenericPredicate::Projection(proj1), GenericPredicate::Projection(proj2))
+                if proj1.projection_ty.associated_ty == proj2.projection_ty.associated_ty =>
+            {
+                self.unify_substs(
+                    &proj1.projection_ty.parameters,
+                    &proj2.projection_ty.parameters,
+                    depth + 1,
+                ) && self.unify_inner(&proj1.ty, &proj2.ty, depth + 1)
+            }
+            _ => false,
+        }
+    }
+
     /// If `ty` is a type variable with known type, returns that type;
     /// otherwise, return ty.
     pub fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 2677f3af2..a4b8d6683 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -396,12 +396,12 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by a bound variable.
-    pub(crate) fn bound_vars(generic_params: &Generics) -> Substs {
+    pub(crate) fn bound_vars(generic_params: &Generics, debruijn: DebruijnIndex) -> Substs {
         Substs(
             generic_params
                 .iter()
                 .enumerate()
-                .map(|(idx, _)| Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, idx)))
+                .map(|(idx, _)| Ty::Bound(BoundVar::new(debruijn, idx)))
                 .collect(),
         )
     }
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index cc1ac8e3e..c2812e178 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -39,6 +39,7 @@ use crate::{
 pub struct TyLoweringContext<'a> {
     pub db: &'a dyn HirDatabase,
     pub resolver: &'a Resolver,
+    in_binders: DebruijnIndex,
     /// 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
@@ -53,7 +54,27 @@ impl<'a> TyLoweringContext<'a> {
         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 }
+        let in_binders = DebruijnIndex::INNERMOST;
+        Self { db, resolver, in_binders, impl_trait_mode, impl_trait_counter, type_param_mode }
+    }
+
+    pub fn with_shifted_in<T>(
+        &self,
+        debruijn: DebruijnIndex,
+        f: impl FnOnce(&TyLoweringContext) -> T,
+    ) -> T {
+        let new_ctx = Self {
+            in_binders: self.in_binders.shifted_in_from(debruijn),
+            impl_trait_counter: std::cell::Cell::new(self.impl_trait_counter.get()),
+            ..*self
+        };
+        let result = f(&new_ctx);
+        self.impl_trait_counter.set(new_ctx.impl_trait_counter.get());
+        result
+    }
+
+    pub fn shifted_in(self, debruijn: DebruijnIndex) -> Self {
+        Self { in_binders: self.in_binders.shifted_in_from(debruijn), ..self }
     }
 
     pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
@@ -134,22 +155,26 @@ impl Ty {
             }
             TypeRef::DynTrait(bounds) => {
                 let self_ty = Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, 0));
-                let predicates = bounds
-                    .iter()
-                    .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                    .collect();
+                let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+                    bounds
+                        .iter()
+                        .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
+                        .collect()
+                });
                 Ty::Dyn(predicates)
             }
             TypeRef::ImplTrait(bounds) => {
                 match ctx.impl_trait_mode {
                     ImplTraitLoweringMode::Opaque => {
                         let self_ty = Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, 0));
-                        let predicates = bounds
-                            .iter()
-                            .flat_map(|b| {
-                                GenericPredicate::from_type_bound(ctx, b, self_ty.clone())
-                            })
-                            .collect();
+                        let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+                            bounds
+                                .iter()
+                                .flat_map(|b| {
+                                    GenericPredicate::from_type_bound(ctx, b, self_ty.clone())
+                                })
+                                .collect()
+                        });
                         Ty::Opaque(predicates)
                     }
                     ImplTraitLoweringMode::Param => {
@@ -180,7 +205,7 @@ impl Ty {
                                 (0, 0, 0, 0)
                             };
                         Ty::Bound(BoundVar::new(
-                            DebruijnIndex::INNERMOST,
+                            ctx.in_binders,
                             idx as usize + parent_params + self_params + list_params,
                         ))
                     }
@@ -293,7 +318,7 @@ impl Ty {
                     TypeParamLoweringMode::Placeholder => Ty::Placeholder(param_id),
                     TypeParamLoweringMode::Variable => {
                         let idx = generics.param_idx(param_id).expect("matching generics");
-                        Ty::Bound(BoundVar::new(DebruijnIndex::INNERMOST, idx))
+                        Ty::Bound(BoundVar::new(ctx.in_binders, idx))
                     }
                 }
             }
@@ -303,7 +328,9 @@ impl Ty {
                     TypeParamLoweringMode::Placeholder => {
                         Substs::type_params_for_generics(&generics)
                     }
-                    TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
+                    TypeParamLoweringMode::Variable => {
+                        Substs::bound_vars(&generics, ctx.in_binders)
+                    }
                 };
                 ctx.db.impl_self_ty(impl_id).subst(&substs)
             }
@@ -313,7 +340,9 @@ impl Ty {
                     TypeParamLoweringMode::Placeholder => {
                         Substs::type_params_for_generics(&generics)
                     }
-                    TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
+                    TypeParamLoweringMode::Variable => {
+                        Substs::bound_vars(&generics, ctx.in_binders)
+                    }
                 };
                 ctx.db.ty(adt.into()).subst(&substs)
             }
@@ -797,7 +826,7 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
 /// function body.
 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
     let generics = generics(db.upcast(), def.into());
-    let substs = Substs::bound_vars(&generics);
+    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
     Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(def.into()), substs))
 }
 
@@ -851,7 +880,7 @@ fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<T
         return type_for_adt(db, def.into());
     }
     let generics = generics(db.upcast(), def.into());
-    let substs = Substs::bound_vars(&generics);
+    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
     Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(def.into()), substs))
 }
 
@@ -876,13 +905,13 @@ fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -
         return type_for_adt(db, def.parent.into());
     }
     let generics = generics(db.upcast(), def.parent.into());
-    let substs = Substs::bound_vars(&generics);
+    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
     Binders::new(substs.len(), Ty::apply(TypeCtor::FnDef(def.into()), substs))
 }
 
 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
     let generics = generics(db.upcast(), adt.into());
-    let substs = Substs::bound_vars(&generics);
+    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
     Binders::new(substs.len(), Ty::apply(TypeCtor::Adt(adt), substs))
 }
 
@@ -892,7 +921,7 @@ fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
     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::bound_vars(&generics);
+    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
     let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
     Binders::new(substs.len(), inner)
 }
diff --git a/crates/ra_hir_ty/src/tests/regression.rs b/crates/ra_hir_ty/src/tests/regression.rs
index d69115a2f..61284d672 100644
--- a/crates/ra_hir_ty/src/tests/regression.rs
+++ b/crates/ra_hir_ty/src/tests/regression.rs
@@ -484,3 +484,52 @@ fn main() {
 
     assert_eq!("()", super::type_at_pos(&db, pos));
 }
+
+#[test]
+fn issue_3999_slice() {
+    assert_snapshot!(
+        infer(r#"
+fn foo(params: &[usize]) {
+    match params {
+        [ps @ .., _] => {}
+    }
+}
+"#),
+        @r###"
+    [8; 14) 'params': &[usize]
+    [26; 81) '{     ...   } }': ()
+    [32; 79) 'match ...     }': ()
+    [38; 44) 'params': &[usize]
+    [55; 67) '[ps @ .., _]': [usize]
+    [65; 66) '_': usize
+    [71; 73) '{}': ()
+    "###
+    );
+}
+
+#[test]
+fn issue_3999_struct() {
+    // rust-analyzer should not panic on seeing this malformed
+    // record pattern.
+    assert_snapshot!(
+        infer(r#"
+struct Bar {
+    a: bool,
+}
+fn foo(b: Bar) {
+    match b {
+        Bar { a: .. } => {},
+    }
+}
+"#),
+        @r###"
+    [36; 37) 'b': Bar
+    [44; 96) '{     ...   } }': ()
+    [50; 94) 'match ...     }': ()
+    [56; 57) 'b': Bar
+    [68; 81) 'Bar { a: .. }': Bar
+    [77; 79) '..': bool
+    [85; 87) '{}': ()
+    "###
+    );
+}
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index 0a889f805..a46f03b7f 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -1211,6 +1211,42 @@ fn test(x: dyn Trait<u64>, y: &dyn Trait<u64>) {
 }
 
 #[test]
+fn dyn_trait_in_impl() {
+    assert_snapshot!(
+        infer(r#"
+trait Trait<T, U> {
+    fn foo(&self) -> (T, U);
+}
+struct S<T, U> {}
+impl<T, U> S<T, U> {
+    fn bar(&self) -> &dyn Trait<T, U> { loop {} }
+}
+trait Trait2<T, U> {
+    fn baz(&self) -> (T, U);
+}
+impl<T, U> Trait2<T, U> for dyn Trait<T, U> { }
+
+fn test(s: S<u32, i32>) {
+    s.bar().baz();
+}
+"#),
+        @r###"
+    [33; 37) 'self': &Self
+    [103; 107) 'self': &S<T, U>
+    [129; 140) '{ loop {} }': &dyn Trait<T, U>
+    [131; 138) 'loop {}': !
+    [136; 138) '{}': ()
+    [176; 180) 'self': &Self
+    [252; 253) 's': S<u32, i32>
+    [268; 290) '{     ...z(); }': ()
+    [274; 275) 's': S<u32, i32>
+    [274; 281) 's.bar()': &dyn Trait<u32, i32>
+    [274; 287) 's.bar().baz()': (u32, i32)
+    "###
+    );
+}
+
+#[test]
 fn dyn_trait_bare() {
     assert_snapshot!(
         infer(r#"
@@ -2204,3 +2240,201 @@ fn test(x: Box<dyn Trait>) {
     );
     assert_eq!(t, "()");
 }
+
+#[test]
+fn string_to_owned() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct String {}
+pub trait ToOwned {
+    type Owned;
+    fn to_owned(&self) -> Self::Owned;
+}
+impl ToOwned for str {
+    type Owned = String;
+}
+fn test() {
+    "foo".to_owned()<|>;
+}
+"#,
+    );
+    assert_eq!(t, "String");
+}
+
+#[test]
+fn iterator_chain() {
+    assert_snapshot!(
+        infer(r#"
+//- /main.rs
+#[lang = "fn_once"]
+trait FnOnce<Args> {
+    type Output;
+}
+#[lang = "fn_mut"]
+trait FnMut<Args>: FnOnce<Args> { }
+
+enum Option<T> { Some(T), None }
+use Option::*;
+
+pub trait Iterator {
+    type Item;
+
+    fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
+    where
+        F: FnMut(Self::Item) -> Option<B>,
+    { loop {} }
+
+    fn for_each<F>(self, f: F)
+    where
+        F: FnMut(Self::Item),
+    { loop {} }
+}
+
+pub trait IntoIterator {
+    type Item;
+    type IntoIter: Iterator<Item = Self::Item>;
+    fn into_iter(self) -> Self::IntoIter;
+}
+
+pub struct FilterMap<I, F> { }
+impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
+where
+    F: FnMut(I::Item) -> Option<B>,
+{
+    type Item = B;
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: Iterator> IntoIterator for I {
+    type Item = I::Item;
+    type IntoIter = I;
+
+    fn into_iter(self) -> I {
+        self
+    }
+}
+
+struct Vec<T> {}
+impl<T> Vec<T> {
+    fn new() -> Self { loop {} }
+}
+
+impl<T> IntoIterator for Vec<T> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+}
+
+pub struct IntoIter<T> { }
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+}
+
+fn main() {
+    Vec::<i32>::new().into_iter()
+      .filter_map(|x| if x > 0 { Some(x as u32) } else { None })
+      .for_each(|y| { y; });
+}
+"#),
+        @r###"
+    [240; 244) 'self': Self
+    [246; 247) 'f': F
+    [331; 342) '{ loop {} }': FilterMap<Self, F>
+    [333; 340) 'loop {}': !
+    [338; 340) '{}': ()
+    [363; 367) 'self': Self
+    [369; 370) 'f': F
+    [419; 430) '{ loop {} }': ()
+    [421; 428) 'loop {}': !
+    [426; 428) '{}': ()
+    [539; 543) 'self': Self
+    [868; 872) 'self': I
+    [879; 899) '{     ...     }': I
+    [889; 893) 'self': I
+    [958; 969) '{ loop {} }': Vec<T>
+    [960; 967) 'loop {}': !
+    [965; 967) '{}': ()
+    [1156; 1287) '{     ... }); }': ()
+    [1162; 1177) 'Vec::<i32>::new': fn new<i32>() -> Vec<i32>
+    [1162; 1179) 'Vec::<...:new()': Vec<i32>
+    [1162; 1191) 'Vec::<...iter()': IntoIter<i32>
+    [1162; 1256) 'Vec::<...one })': FilterMap<IntoIter<i32>, |i32| -> Option<u32>>
+    [1162; 1284) 'Vec::<... y; })': ()
+    [1210; 1255) '|x| if...None }': |i32| -> Option<u32>
+    [1211; 1212) 'x': i32
+    [1214; 1255) 'if x >...None }': Option<u32>
+    [1217; 1218) 'x': i32
+    [1217; 1222) 'x > 0': bool
+    [1221; 1222) '0': i32
+    [1223; 1241) '{ Some...u32) }': Option<u32>
+    [1225; 1229) 'Some': Some<u32>(u32) -> Option<u32>
+    [1225; 1239) 'Some(x as u32)': Option<u32>
+    [1230; 1231) 'x': i32
+    [1230; 1238) 'x as u32': u32
+    [1247; 1255) '{ None }': Option<u32>
+    [1249; 1253) 'None': Option<u32>
+    [1273; 1283) '|y| { y; }': |u32| -> ()
+    [1274; 1275) 'y': u32
+    [1277; 1283) '{ y; }': ()
+    [1279; 1280) 'y': u32
+    "###
+    );
+}
+
+#[test]
+fn nested_assoc() {
+    let t = type_at(
+        r#"
+//- /main.rs
+struct Bar;
+struct Foo;
+
+trait A {
+    type OutputA;
+}
+
+impl A for Bar {
+    type OutputA = Foo;
+}
+
+trait B {
+    type Output;
+    fn foo() -> Self::Output;
+}
+
+impl<T:A> B for T {
+    type Output = T::OutputA;
+    fn foo() -> Self::Output { loop {} }
+}
+
+fn main() {
+    Bar::foo()<|>;
+}
+"#,
+    );
+    assert_eq!(t, "Foo");
+}
+
+#[test]
+fn trait_object_no_coercion() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Foo {}
+
+fn foo(x: &dyn Foo) {}
+
+fn test(x: &dyn Foo) {
+    foo(x);
+}
+"#, true),
+        @r###"
+    [22; 23) 'x': &dyn Foo
+    [35; 37) '{}': ()
+    [47; 48) 'x': &dyn Foo
+    [60; 75) '{     foo(x); }': ()
+    [66; 69) 'foo': fn foo(&dyn Foo)
+    [66; 72) 'foo(x)': ()
+    [70; 71) 'x': &dyn Foo
+    "###
+    );
+}
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index 60d70d18e..e00a82db2 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -17,7 +17,7 @@ use ra_db::{
 use super::{builtin, AssocTyValue, Canonical, ChalkContext, Impl, Obligation};
 use crate::{
     db::HirDatabase, display::HirDisplay, method_resolution::TyFingerprint, utils::generics,
-    ApplicationTy, GenericPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
+    ApplicationTy, DebruijnIndex, GenericPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor,
 };
 
 pub(super) mod tls;
@@ -815,7 +815,7 @@ pub(crate) fn associated_ty_data_query(
     // Lower bounds -- we could/should maybe move this to a separate query in `lower`
     let type_alias_data = db.type_alias_data(type_alias);
     let generic_params = generics(db.upcast(), type_alias.into());
-    let bound_vars = Substs::bound_vars(&generic_params);
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
     let resolver = hir_def::resolver::HasResolver::resolver(type_alias, db.upcast());
     let ctx = crate::TyLoweringContext::new(db, &resolver)
         .with_type_param_mode(crate::lower::TypeParamLoweringMode::Variable);
@@ -849,7 +849,7 @@ pub(crate) fn trait_datum_query(
     let trait_data = db.trait_data(trait_);
     debug!("trait {:?} = {:?}", trait_id, trait_data.name);
     let generic_params = generics(db.upcast(), trait_.into());
-    let bound_vars = Substs::bound_vars(&generic_params);
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
     let flags = chalk_rust_ir::TraitFlags {
         auto: trait_data.auto,
         upstream: trait_.lookup(db.upcast()).container.module(db.upcast()).krate != krate,
@@ -888,7 +888,7 @@ pub(crate) fn struct_datum_query(
         .as_generic_def()
         .map(|generic_def| {
             let generic_params = generics(db.upcast(), generic_def);
-            let bound_vars = Substs::bound_vars(&generic_params);
+            let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
             convert_where_clauses(db, generic_def, &bound_vars)
         })
         .unwrap_or_else(Vec::new);
@@ -934,7 +934,7 @@ fn impl_def_datum(
     let impl_data = db.impl_data(impl_id);
 
     let generic_params = generics(db.upcast(), impl_id.into());
-    let bound_vars = Substs::bound_vars(&generic_params);
+    let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
     let trait_ = trait_ref.trait_;
     let impl_type = if impl_id.lookup(db.upcast()).container.module(db.upcast()).krate == krate {
         chalk_rust_ir::ImplType::Local
diff --git a/crates/ra_ide/src/completion/complete_trait_impl.rs b/crates/ra_ide/src/completion/complete_trait_impl.rs
index fab02945c..2ec0e7ce9 100644
--- a/crates/ra_ide/src/completion/complete_trait_impl.rs
+++ b/crates/ra_ide/src/completion/complete_trait_impl.rs
@@ -142,11 +142,11 @@ fn add_function_impl(
         CompletionItemKind::Function
     };
 
-    let snippet = format!("{} {{}}", display);
+    let snippet = format!("{} {{\n    $0\n}}", display);
 
     let range = TextRange::from_to(fn_def_node.text_range().start(), ctx.source_range().end());
 
-    builder.text_edit(TextEdit::replace(range, snippet)).kind(completion_kind).add_to(acc);
+    builder.snippet_edit(TextEdit::replace(range, snippet)).kind(completion_kind).add_to(acc);
 }
 
 fn add_type_alias_impl(
@@ -217,9 +217,10 @@ fn make_const_compl_syntax(const_: &ast::ConstDef) -> String {
 
 #[cfg(test)]
 mod tests {
-    use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
     use insta::assert_debug_snapshot;
 
+    use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
+
     fn complete(code: &str) -> Vec<CompletionItem> {
         do_completion(code, CompletionKind::Magic)
     }
@@ -255,7 +256,7 @@ mod tests {
                 label: "fn test()",
                 source_range: [209; 210),
                 delete: [209; 210),
-                insert: "fn test() {}",
+                insert: "fn test() {\n    $0\n}",
                 kind: Function,
                 lookup: "test",
             },
@@ -313,7 +314,7 @@ mod tests {
                 label: "fn test()",
                 source_range: [139; 140),
                 delete: [139; 140),
-                insert: "fn test() {}",
+                insert: "fn test() {\n    $0\n}",
                 kind: Function,
                 lookup: "test",
             },
@@ -342,7 +343,7 @@ mod tests {
                 label: "fn foo()",
                 source_range: [141; 142),
                 delete: [138; 142),
-                insert: "fn foo() {}",
+                insert: "fn foo() {\n    $0\n}",
                 kind: Function,
                 lookup: "foo",
             },
@@ -374,7 +375,7 @@ mod tests {
                 label: "fn foo_bar()",
                 source_range: [200; 201),
                 delete: [197; 201),
-                insert: "fn foo_bar() {}",
+                insert: "fn foo_bar() {\n    $0\n}",
                 kind: Function,
                 lookup: "foo_bar",
             },
@@ -425,7 +426,7 @@ mod tests {
                 label: "fn foo()",
                 source_range: [144; 145),
                 delete: [141; 145),
-                insert: "fn foo<T>() {}",
+                insert: "fn foo<T>() {\n    $0\n}",
                 kind: Function,
                 lookup: "foo",
             },
@@ -454,7 +455,7 @@ mod tests {
                 label: "fn foo()",
                 source_range: [166; 167),
                 delete: [163; 167),
-                insert: "fn foo<T>()\nwhere T: Into<String> {}",
+                insert: "fn foo<T>()\nwhere T: Into<String> {\n    $0\n}",
                 kind: Function,
                 lookup: "foo",
             },
diff --git a/crates/ra_ide/src/completion/complete_unqualified_path.rs b/crates/ra_ide/src/completion/complete_unqualified_path.rs
index 2d8e0776c..ad5fdcc4e 100644
--- a/crates/ra_ide/src/completion/complete_unqualified_path.rs
+++ b/crates/ra_ide/src/completion/complete_unqualified_path.rs
@@ -1,6 +1,10 @@
 //! Completion of names from the current scope, e.g. locals and imported items.
 
+use hir::ScopeDef;
+use test_utils::tested_by;
+
 use crate::completion::{CompletionContext, Completions};
+use ra_syntax::AstNode;
 
 pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionContext) {
     if !ctx.is_trivial_path {
@@ -14,12 +18,23 @@ pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionC
         return;
     }
 
-    ctx.scope().process_all_names(&mut |name, res| acc.add_resolution(ctx, name.to_string(), &res));
+    ctx.scope().process_all_names(&mut |name, res| {
+        if ctx.use_item_syntax.is_some() {
+            if let (ScopeDef::Unknown, Some(name_ref)) = (&res, &ctx.name_ref_syntax) {
+                if name_ref.syntax().text() == name.to_string().as_str() {
+                    tested_by!(self_fulfilling_completion);
+                    return;
+                }
+            }
+        }
+        acc.add_resolution(ctx, name.to_string(), &res)
+    });
 }
 
 #[cfg(test)]
 mod tests {
     use insta::assert_debug_snapshot;
+    use test_utils::covers;
 
     use crate::completion::{test_utils::do_completion, CompletionItem, CompletionKind};
 
@@ -28,6 +43,29 @@ mod tests {
     }
 
     #[test]
+    fn self_fulfilling_completion() {
+        covers!(self_fulfilling_completion);
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r#"
+                use foo<|>
+                use std::collections;
+                "#,
+            ),
+            @r###"
+            [
+                CompletionItem {
+                    label: "collections",
+                    source_range: [21; 24),
+                    delete: [21; 24),
+                    insert: "collections",
+                },
+            ]
+            "###
+        );
+    }
+
+    #[test]
     fn bind_pat_and_path_ignore_at() {
         assert_debug_snapshot!(
             do_reference_completion(
diff --git a/crates/ra_ide/src/diagnostics.rs b/crates/ra_ide/src/diagnostics.rs
index 901ad104c..e7e201709 100644
--- a/crates/ra_ide/src/diagnostics.rs
+++ b/crates/ra_ide/src/diagnostics.rs
@@ -1,4 +1,8 @@
-//! FIXME: write short doc here
+//! Collects diagnostics & fixits  for a single file.
+//!
+//! The tricky bit here is that diagnostics are produced by hir in terms of
+//! macro-expanded files, but we need to present them to the users in terms of
+//! original files. So we need to map the ranges.
 
 use std::cell::RefCell;
 
@@ -46,7 +50,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
     let mut sink = DiagnosticSink::new(|d| {
         res.borrow_mut().push(Diagnostic {
             message: d.message(),
-            range: d.highlight_range(),
+            range: sema.diagnostics_range(d).range,
             severity: Severity::Error,
             fix: None,
         })
@@ -62,7 +66,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
         let create_file = FileSystemEdit::CreateFile { source_root, path };
         let fix = SourceChange::file_system_edit("create module", create_file);
         res.borrow_mut().push(Diagnostic {
-            range: d.highlight_range(),
+            range: sema.diagnostics_range(d).range,
             message: d.message(),
             severity: Severity::Error,
             fix: Some(fix),
@@ -95,7 +99,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
         };
 
         res.borrow_mut().push(Diagnostic {
-            range: d.highlight_range(),
+            range: sema.diagnostics_range(d).range,
             message: d.message(),
             severity: Severity::Error,
             fix,
@@ -103,7 +107,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
     })
     .on::<hir::diagnostics::MissingMatchArms, _>(|d| {
         res.borrow_mut().push(Diagnostic {
-            range: d.highlight_range(),
+            range: sema.diagnostics_range(d).range,
             message: d.message(),
             severity: Severity::Error,
             fix: None,
@@ -115,7 +119,7 @@ pub(crate) fn diagnostics(db: &RootDatabase, file_id: FileId) -> Vec<Diagnostic>
         let edit = TextEdit::replace(node.syntax().text_range(), replacement);
         let fix = SourceChange::source_file_edit_from("wrap with ok", file_id, edit);
         res.borrow_mut().push(Diagnostic {
-            range: d.highlight_range(),
+            range: sema.diagnostics_range(d).range,
             message: d.message(),
             severity: Severity::Error,
             fix: Some(fix),
@@ -622,6 +626,62 @@ mod tests {
     }
 
     #[test]
+    fn range_mapping_out_of_macros() {
+        let (analysis, file_id) = single_file(
+            r"
+            fn some() {}
+            fn items() {}
+            fn here() {}
+
+            macro_rules! id {
+                ($($tt:tt)*) => { $($tt)*};
+            }
+
+            fn main() {
+                let _x = id![Foo { a: 42 }];
+            }
+
+            pub struct Foo {
+                pub a: i32,
+                pub b: i32,
+            }
+        ",
+        );
+        let diagnostics = analysis.diagnostics(file_id).unwrap();
+        assert_debug_snapshot!(diagnostics, @r###"
+        [
+            Diagnostic {
+                message: "Missing structure fields:\n- b",
+                range: [224; 233),
+                fix: Some(
+                    SourceChange {
+                        label: "fill struct fields",
+                        source_file_edits: [
+                            SourceFileEdit {
+                                file_id: FileId(
+                                    1,
+                                ),
+                                edit: TextEdit {
+                                    atoms: [
+                                        AtomTextEdit {
+                                            delete: [3; 9),
+                                            insert: "{a:42, b: ()}",
+                                        },
+                                    ],
+                                },
+                            },
+                        ],
+                        file_system_edits: [],
+                        cursor_position: None,
+                    },
+                ),
+                severity: Error,
+            },
+        ]
+        "###);
+    }
+
+    #[test]
     fn test_check_unnecessary_braces_in_use_statement() {
         check_not_applicable(
             "
diff --git a/crates/ra_ide/src/inlay_hints.rs b/crates/ra_ide/src/inlay_hints.rs
index 45b9f7802..0774fa0a1 100644
--- a/crates/ra_ide/src/inlay_hints.rs
+++ b/crates/ra_ide/src/inlay_hints.rs
@@ -237,7 +237,8 @@ fn should_show_param_hint(
 ) -> bool {
     if param_name.is_empty()
         || is_argument_similar_to_param(argument, param_name)
-        || Some(param_name) == fn_signature.name.as_ref().map(String::as_str)
+        || Some(param_name.trim_start_matches('_'))
+            == fn_signature.name.as_ref().map(|s| s.trim_start_matches('_'))
     {
         return false;
     }
@@ -255,6 +256,8 @@ fn should_show_param_hint(
 
 fn is_argument_similar_to_param(argument: &ast::Expr, param_name: &str) -> bool {
     let argument_string = remove_ref(argument.clone()).syntax().to_string();
+    let param_name = param_name.trim_start_matches('_');
+    let argument_string = argument_string.trim_start_matches('_');
     argument_string.starts_with(&param_name) || argument_string.ends_with(&param_name)
 }
 
@@ -1094,8 +1097,10 @@ struct Param {}
 
 fn different_order(param: &Param) {}
 fn different_order_mut(param: &mut Param) {}
+fn has_underscore(_param: bool) {}
 
 fn twiddle(twiddle: bool) {}
+fn doo(_doo: bool) {}
 
 fn main() {
     let container: TestVarContainer = TestVarContainer { test_var: 42 };
@@ -1112,11 +1117,15 @@ fn main() {
     test_processed.frob(false);
 
     twiddle(true);
+    doo(true);
 
     let param_begin: Param = Param {};
     different_order(&param_begin);
     different_order(&mut param_begin);
 
+    let param: bool = true;
+    has_underscore(param);
+
     let a: f64 = 7.0;
     let b: f64 = 4.0;
     let _: f64 = a.div_euclid(b);
diff --git a/crates/ra_ide/src/marks.rs b/crates/ra_ide/src/marks.rs
index 5e1f135c5..eee44e886 100644
--- a/crates/ra_ide/src/marks.rs
+++ b/crates/ra_ide/src/marks.rs
@@ -8,4 +8,5 @@ test_utils::marks!(
     test_resolve_parent_module_on_module_decl
     search_filters_by_range
     dont_insert_macro_call_parens_unncessary
+    self_fulfilling_completion
 );
diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index 83d161f45..7b15b82bd 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -174,7 +174,8 @@ pub(crate) fn highlight(
     }
 
     assert_eq!(res.len(), 1, "after DFS traversal, the stack should only contain a single element");
-    let res = res.pop().unwrap();
+    let mut res = res.pop().unwrap();
+    res.sort_by_key(|range| range.range.start());
     // Check that ranges are sorted and disjoint
     assert!(res
         .iter()
diff --git a/crates/ra_ide/src/syntax_highlighting/tests.rs b/crates/ra_ide/src/syntax_highlighting/tests.rs
index 110887c2a..73611e23a 100644
--- a/crates/ra_ide/src/syntax_highlighting/tests.rs
+++ b/crates/ra_ide/src/syntax_highlighting/tests.rs
@@ -156,3 +156,15 @@ fn main() {
     fs::write(dst_file, &actual_html).unwrap();
     assert_eq_text!(expected_html, actual_html);
 }
+
+#[test]
+fn ranges_sorted() {
+    let (analysis, file_id) = single_file(
+        r#"
+#[foo(bar = "bar")]
+macro_rules! test {}
+}"#
+        .trim(),
+    );
+    let _ = analysis.highlight(file_id).unwrap();
+}
diff --git a/crates/ra_proc_macro_srv/Cargo.toml b/crates/ra_proc_macro_srv/Cargo.toml
index 1e0f50339..ac2d156dc 100644
--- a/crates/ra_proc_macro_srv/Cargo.toml
+++ b/crates/ra_proc_macro_srv/Cargo.toml
@@ -14,6 +14,7 @@ ra_mbe = { path = "../ra_mbe" }
 ra_proc_macro = { path = "../ra_proc_macro" }
 goblin = "0.2.1"
 libloading = "0.6.0"
+memmap = "0.7"
 test_utils = { path = "../test_utils" }
 
 [dev-dependencies]
diff --git a/crates/ra_proc_macro_srv/src/dylib.rs b/crates/ra_proc_macro_srv/src/dylib.rs
index ec63d587b..16bd7466e 100644
--- a/crates/ra_proc_macro_srv/src/dylib.rs
+++ b/crates/ra_proc_macro_srv/src/dylib.rs
@@ -1,10 +1,12 @@
 //! Handles dynamic library loading for proc macro
 
 use crate::{proc_macro::bridge, rustc_server::TokenStream};
+use std::fs::File;
 use std::path::Path;
 
 use goblin::{mach::Mach, Object};
 use libloading::Library;
+use memmap::Mmap;
 use ra_proc_macro::ProcMacroKind;
 
 use std::io::Error as IoError;
@@ -16,55 +18,54 @@ fn invalid_data_err(e: impl Into<Box<dyn std::error::Error + Send + Sync>>) -> I
     IoError::new(IoErrorKind::InvalidData, e)
 }
 
-fn get_symbols_from_lib(file: &Path) -> Result<Vec<String>, IoError> {
-    let buffer = std::fs::read(file)?;
+fn is_derive_registrar_symbol(symbol: &str) -> bool {
+    symbol.contains(NEW_REGISTRAR_SYMBOL)
+}
+
+fn find_registrar_symbol(file: &Path) -> Result<Option<String>, IoError> {
+    let file = File::open(file)?;
+    let buffer = unsafe { Mmap::map(&file)? };
     let object = Object::parse(&buffer).map_err(invalid_data_err)?;
 
     match object {
         Object::Elf(elf) => {
             let symbols = elf.dynstrtab.to_vec().map_err(invalid_data_err)?;
-            let names = symbols.iter().map(|s| s.to_string()).collect();
-            Ok(names)
+            let name =
+                symbols.iter().find(|s| is_derive_registrar_symbol(s)).map(|s| s.to_string());
+            Ok(name)
         }
         Object::PE(pe) => {
-            let symbol_names =
-                pe.exports.iter().flat_map(|s| s.name).map(|n| n.to_string()).collect();
-            Ok(symbol_names)
+            let name = pe
+                .exports
+                .iter()
+                .flat_map(|s| s.name)
+                .find(|s| is_derive_registrar_symbol(s))
+                .map(|s| s.to_string());
+            Ok(name)
         }
-        Object::Mach(mach) => match mach {
-            Mach::Binary(binary) => {
-                let exports = binary.exports().map_err(invalid_data_err)?;
-                let names = exports
-                    .into_iter()
-                    .map(|s| {
-                        // In macos doc:
-                        // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/dlsym.3.html
-                        // Unlike other dyld API's, the symbol name passed to dlsym() must NOT be
-                        // prepended with an underscore.
-                        if s.name.starts_with("_") {
-                            s.name[1..].to_string()
-                        } else {
-                            s.name
-                        }
-                    })
-                    .collect();
-                Ok(names)
-            }
-            Mach::Fat(_) => Ok(vec![]),
-        },
-        Object::Archive(_) | Object::Unknown(_) => Ok(vec![]),
+        Object::Mach(Mach::Binary(binary)) => {
+            let exports = binary.exports().map_err(invalid_data_err)?;
+            let name = exports
+                .iter()
+                .map(|s| {
+                    // In macos doc:
+                    // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/dlsym.3.html
+                    // Unlike other dyld API's, the symbol name passed to dlsym() must NOT be
+                    // prepended with an underscore.
+                    if s.name.starts_with("_") {
+                        &s.name[1..]
+                    } else {
+                        &s.name
+                    }
+                })
+                .find(|s| is_derive_registrar_symbol(s))
+                .map(|s| s.to_string());
+            Ok(name)
+        }
+        _ => Ok(None),
     }
 }
 
-fn is_derive_registrar_symbol(symbol: &str) -> bool {
-    symbol.contains(NEW_REGISTRAR_SYMBOL)
-}
-
-fn find_registrar_symbol(file: &Path) -> Result<Option<String>, IoError> {
-    let symbols = get_symbols_from_lib(file)?;
-    Ok(symbols.into_iter().find(|s| is_derive_registrar_symbol(s)))
-}
-
 /// Loads dynamic library in platform dependent manner.
 ///
 /// For unix, you have to use RTLD_DEEPBIND flag to escape problems described
diff --git a/crates/rust-analyzer/src/cli/load_cargo.rs b/crates/rust-analyzer/src/cli/load_cargo.rs
index eb9ac32c3..762f776fe 100644
--- a/crates/rust-analyzer/src/cli/load_cargo.rs
+++ b/crates/rust-analyzer/src/cli/load_cargo.rs
@@ -75,9 +75,7 @@ pub(crate) fn load_cargo(
     let proc_macro_client = if !with_proc_macro {
         ProcMacroClient::dummy()
     } else {
-        let mut path = std::env::current_exe()?;
-        path.pop();
-        path.push("rust-analyzer");
+        let path = std::env::current_exe()?;
         ProcMacroClient::extern_process(&path, &["proc-macro"]).unwrap()
     };
     let host = load(&source_roots, ws, &mut vfs, receiver, extern_dirs, &proc_macro_client);
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 2b45f1310..3597a14e3 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -134,9 +134,7 @@ impl Config {
 
         match get::<bool>(value, "/procMacro/enabled") {
             Some(true) => {
-                if let Ok(mut path) = std::env::current_exe() {
-                    path.pop();
-                    path.push("rust-analyzer");
+                if let Ok(path) = std::env::current_exe() {
                     self.proc_macro_srv = Some((path.to_string_lossy().to_string(), vec!["proc-macro".to_string()]));
                 }
             }