38 files changed, 892 insertions, 625 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 20e6cd540..367ff3f82 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1139,6 +1139,7 @@ dependencies = [
  "jemalloc-ctl",
  "jemallocator",
  "once_cell",
+ "ra_arena",
 ]
 
 [[package]]
diff --git a/crates/ra_arena/src/lib.rs b/crates/ra_arena/src/lib.rs
index ea98d5444..441fbb3cb 100644
--- a/crates/ra_arena/src/lib.rs
+++ b/crates/ra_arena/src/lib.rs
@@ -96,6 +96,9 @@ impl<T> Arena<T> {
     pub const fn new() -> Arena<T> {
         Arena { data: Vec::new() }
     }
+    pub fn clear(&mut self) {
+        self.data.clear();
+    }
 
     pub fn len(&self) -> usize {
         self.data.len()
diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index 3f645a1dd..fb788736d 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -1136,6 +1136,13 @@ impl Type {
         matches!(&self.ty.value, Ty::Apply(ApplicationTy { ctor: TypeCtor::Closure { .. }, .. }))
     }
 
+    pub fn is_fn(&self) -> bool {
+        matches!(&self.ty.value,
+            Ty::Apply(ApplicationTy { ctor: TypeCtor::FnDef(..), .. }) |
+            Ty::Apply(ApplicationTy { ctor: TypeCtor::FnPtr { .. }, .. })
+        )
+    }
+
     pub fn contains_unknown(&self) -> bool {
         return go(&self.ty.value);
 
diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index 3b169440a..890cefcaf 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -27,7 +27,7 @@ use crate::{
     AsMacroCall, DefWithBodyId, HasModule, Lookup, ModuleId,
 };
 
-/// A subser of Exander that only deals with cfg attributes. We only need it to
+/// A subset of Exander that only deals with cfg attributes. We only need it to
 /// avoid cyclic queries in crate def map during enum processing.
 pub(crate) struct CfgExpander {
     cfg_options: CfgOptions,
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index 0caedd8d8..571603854 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -141,6 +141,10 @@ impl ExprCollector<'_> {
 
     fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {
         let syntax_ptr = AstPtr::new(&expr);
+        let attrs = self.expander.parse_attrs(&expr);
+        if !self.expander.is_cfg_enabled(&attrs) {
+            return self.missing_expr();
+        }
         match expr {
             ast::Expr::IfExpr(e) => {
                 let then_branch = self.collect_block_opt(e.then_branch());
diff --git a/crates/ra_hir_expand/src/builtin_derive.rs b/crates/ra_hir_expand/src/builtin_derive.rs
index bb45b0f1d..e60f879a3 100644
--- a/crates/ra_hir_expand/src/builtin_derive.rs
+++ b/crates/ra_hir_expand/src/builtin_derive.rs
@@ -9,7 +9,7 @@ use ra_syntax::{
 };
 
 use crate::db::AstDatabase;
-use crate::{name, quote, LazyMacroId, MacroDefId, MacroDefKind};
+use crate::{name, quote, LazyMacroId, MacroCallId, MacroDefId, MacroDefKind};
 
 macro_rules! register_builtin {
     ( $($trait:ident => $expand:ident),* ) => {
@@ -153,76 +153,113 @@ fn expand_simple_derive(
     Ok(expanded)
 }
 
+fn find_builtin_crate(db: &dyn AstDatabase, id: LazyMacroId) -> tt::TokenTree {
+    // FIXME: make hygiene works for builtin derive macro
+    // such that $crate can be used here.
+
+    let m: MacroCallId = id.into();
+    let file_id = m.as_file().original_file(db);
+    let cg = db.crate_graph();
+    let krates = db.relevant_crates(file_id);
+    let krate = match krates.get(0) {
+        Some(krate) => krate,
+        None => {
+            let tt = quote! { core };
+            return tt.token_trees[0].clone();
+        }
+    };
+
+    // XXX
+    //  All crates except core itself should have a dependency on core,
+    //  We detect `core` by seeing whether it doesn't have such a dependency.
+    let tt = if cg[*krate].dependencies.iter().any(|dep| dep.name == "core") {
+        quote! { core }
+    } else {
+        quote! { crate }
+    };
+
+    tt.token_trees[0].clone()
+}
+
 fn copy_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::marker::Copy })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::marker::Copy })
 }
 
 fn clone_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::clone::Clone })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::clone::Clone })
 }
 
 fn default_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::default::Default })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::default::Default })
 }
 
 fn debug_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::fmt::Debug })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::fmt::Debug })
 }
 
 fn hash_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::hash::Hash })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::hash::Hash })
 }
 
 fn eq_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::cmp::Eq })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::cmp::Eq })
 }
 
 fn partial_eq_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::cmp::PartialEq })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::cmp::PartialEq })
 }
 
 fn ord_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::cmp::Ord })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::cmp::Ord })
 }
 
 fn partial_ord_expand(
-    _db: &dyn AstDatabase,
-    _id: LazyMacroId,
+    db: &dyn AstDatabase,
+    id: LazyMacroId,
     tt: &tt::Subtree,
 ) -> Result<tt::Subtree, mbe::ExpandError> {
-    expand_simple_derive(tt, quote! { std::cmp::PartialOrd })
+    let krate = find_builtin_crate(db, id);
+    expand_simple_derive(tt, quote! { #krate::cmp::PartialOrd })
 }
 
 #[cfg(test)]
@@ -234,8 +271,18 @@ mod tests {
 
     fn expand_builtin_derive(s: &str, name: Name) -> String {
         let def = find_builtin_derive(&name).unwrap();
+        let fixture = format!(
+            r#"//- /main.rs crate:main deps:core
+<|>
+{}
+//- /lib.rs crate:core
+// empty
+"#,
+            s
+        );
 
-        let (db, file_id) = TestDB::with_single_file(&s);
+        let (db, file_pos) = TestDB::with_position(&fixture);
+        let file_id = file_pos.file_id;
         let parsed = db.parse(file_id);
         let items: Vec<_> =
             parsed.syntax_node().descendants().filter_map(ast::ModuleItem::cast).collect();
@@ -264,7 +311,7 @@ mod tests {
             known::Copy,
         );
 
-        assert_eq!(expanded, "impl< >std::marker::CopyforFoo< >{}");
+        assert_eq!(expanded, "impl< >core::marker::CopyforFoo< >{}");
     }
 
     #[test]
@@ -279,7 +326,7 @@ mod tests {
 
         assert_eq!(
             expanded,
-            "impl<T0:std::marker::Copy,T1:std::marker::Copy>std::marker::CopyforFoo<T0,T1>{}"
+            "impl<T0:core::marker::Copy,T1:core::marker::Copy>core::marker::CopyforFoo<T0,T1>{}"
         );
     }
 
@@ -297,7 +344,7 @@ mod tests {
 
         assert_eq!(
             expanded,
-            "impl<T0:std::marker::Copy,T1:std::marker::Copy>std::marker::CopyforFoo<T0,T1>{}"
+            "impl<T0:core::marker::Copy,T1:core::marker::Copy>core::marker::CopyforFoo<T0,T1>{}"
         );
     }
 
@@ -313,7 +360,7 @@ mod tests {
 
         assert_eq!(
             expanded,
-            "impl<T0:std::clone::Clone,T1:std::clone::Clone>std::clone::CloneforFoo<T0,T1>{}"
+            "impl<T0:core::clone::Clone,T1:core::clone::Clone>core::clone::CloneforFoo<T0,T1>{}"
         );
     }
 }
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 6a53be621..bd4ef69a0 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -667,7 +667,7 @@ impl Expectation {
 }
 
 mod diagnostics {
-    use hir_def::{expr::ExprId, src::HasSource, FunctionId, Lookup};
+    use hir_def::{expr::ExprId, FunctionId};
     use hir_expand::diagnostics::DiagnosticSink;
 
     use crate::{db::HirDatabase, diagnostics::NoSuchField};
@@ -686,10 +686,9 @@ mod diagnostics {
         ) {
             match self {
                 InferenceDiagnostic::NoSuchField { expr, field } => {
-                    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: source.file_id, field: field.value })
+                    sink.push(NoSuchField { file: field.file_id, field: field.value })
                 }
             }
         }
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 279c06d65..a8ef32ec5 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -487,6 +487,18 @@ impl<T> Binders<T> {
     pub fn new(num_binders: usize, value: T) -> Self {
         Self { num_binders, value }
     }
+
+    pub fn as_ref(&self) -> Binders<&T> {
+        Binders { num_binders: self.num_binders, value: &self.value }
+    }
+
+    pub fn map<U>(self, f: impl FnOnce(T) -> U) -> Binders<U> {
+        Binders { num_binders: self.num_binders, value: f(self.value) }
+    }
+
+    pub fn filter_map<U>(self, f: impl FnOnce(T) -> Option<U>) -> Option<Binders<U>> {
+        Some(Binders { num_binders: self.num_binders, value: f(self.value)? })
+    }
 }
 
 impl<T: Clone> Binders<&T> {
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index b57214296..a6f893037 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -28,11 +28,11 @@ use crate::{
     db::HirDatabase,
     primitive::{FloatTy, IntTy},
     utils::{
-        all_super_traits, associated_type_by_name_including_super_traits, generics, make_mut_slice,
-        variant_data,
+        all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
+        make_mut_slice, variant_data,
     },
     Binders, BoundVar, DebruijnIndex, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate,
-    ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor,
+    ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor, TypeWalk,
 };
 
 #[derive(Debug)]
@@ -256,7 +256,7 @@ impl Ty {
         if remaining_segments.len() == 1 {
             // resolve unselected assoc types
             let segment = remaining_segments.first().unwrap();
-            (Ty::select_associated_type(ctx, ty, res, segment), None)
+            (Ty::select_associated_type(ctx, res, segment), None)
         } else if remaining_segments.len() > 1 {
             // FIXME report error (ambiguous associated type)
             (Ty::Unknown, None)
@@ -380,21 +380,20 @@ impl Ty {
 
     fn select_associated_type(
         ctx: &TyLoweringContext<'_>,
-        self_ty: Ty,
         res: Option<TypeNs>,
         segment: PathSegment<'_>,
     ) -> Ty {
         let traits_from_env: Vec<_> = match res {
             Some(TypeNs::SelfType(impl_id)) => match ctx.db.impl_trait(impl_id) {
                 None => return Ty::Unknown,
-                Some(trait_ref) => vec![trait_ref.value.trait_],
+                Some(trait_ref) => vec![trait_ref.value],
             },
             Some(TypeNs::GenericParam(param_id)) => {
                 let predicates = ctx.db.generic_predicates_for_param(param_id);
                 let mut traits_: Vec<_> = predicates
                     .iter()
                     .filter_map(|pred| match &pred.value {
-                        GenericPredicate::Implemented(tr) => Some(tr.trait_),
+                        GenericPredicate::Implemented(tr) => Some(tr.clone()),
                         _ => None,
                     })
                     .collect();
@@ -404,20 +403,37 @@ impl Ty {
                     if generics.params.types[param_id.local_id].provenance
                         == TypeParamProvenance::TraitSelf
                     {
-                        traits_.push(trait_id);
+                        let trait_ref = TraitRef {
+                            trait_: trait_id,
+                            substs: Substs::bound_vars(&generics, DebruijnIndex::INNERMOST),
+                        };
+                        traits_.push(trait_ref);
                     }
                 }
                 traits_
             }
             _ => return Ty::Unknown,
         };
-        let traits = traits_from_env.into_iter().flat_map(|t| all_super_traits(ctx.db.upcast(), t));
+        let traits = traits_from_env.into_iter().flat_map(|t| all_super_trait_refs(ctx.db, t));
         for t in traits {
-            if let Some(associated_ty) = ctx.db.trait_data(t).associated_type_by_name(&segment.name)
+            if let Some(associated_ty) =
+                ctx.db.trait_data(t.trait_).associated_type_by_name(&segment.name)
             {
-                let substs =
-                    Substs::build_for_def(ctx.db, t).push(self_ty).fill_with_unknown().build();
-                // FIXME handle type parameters on the segment
+                let substs = match ctx.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => {
+                        // if we're lowering to placeholders, we have to put
+                        // them in now
+                        let s = Substs::type_params(
+                            ctx.db,
+                            ctx.resolver
+                                .generic_def()
+                                .expect("there should be generics if there's a generic param"),
+                        );
+                        t.substs.subst_bound_vars(&s)
+                    }
+                    TypeParamLoweringMode::Variable => t.substs,
+                };
+                // FIXME handle (forbid) type parameters on the segment
                 return Ty::Projection(ProjectionTy { associated_ty, parameters: substs });
             }
         }
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index b6a96bb5c..588d81282 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -391,6 +391,38 @@ fn no_such_field_with_feature_flag_diagnostics_on_struct_lit() {
 }
 
 #[test]
+fn no_such_field_with_feature_flag_diagnostics_on_block_expr() {
+    let diagnostics = TestDB::with_files(
+        r#"
+        //- /lib.rs crate:foo cfg:feature=foo
+        struct S {
+            #[cfg(feature = "foo")]
+            foo: u32,
+            #[cfg(not(feature = "foo"))]
+            bar: u32,
+        }
+
+        impl S {
+            fn new(bar: u32) -> Self {
+                #[cfg(feature = "foo")]
+                {
+                Self { foo: bar }
+                }
+                #[cfg(not(feature = "foo"))]
+                {
+                Self { bar }
+                }
+            }
+        }
+        "#,
+    )
+    .diagnostics()
+    .0;
+
+    assert_snapshot!(diagnostics, @r###""###);
+}
+
+#[test]
 fn no_such_field_with_feature_flag_diagnostics_on_struct_fields() {
     let diagnostics = TestDB::with_files(
         r#"
diff --git a/crates/ra_hir_ty/src/tests/macros.rs b/crates/ra_hir_ty/src/tests/macros.rs
index 6b5267232..5ddecbdc6 100644
--- a/crates/ra_hir_ty/src/tests/macros.rs
+++ b/crates/ra_hir_ty/src/tests/macros.rs
@@ -622,14 +622,14 @@ fn main() {
 fn infer_derive_clone_simple() {
     let (db, pos) = TestDB::with_position(
         r#"
-//- /main.rs crate:main deps:std
+//- /main.rs crate:main deps:core
 #[derive(Clone)]
 struct S;
 fn test() {
     S.clone()<|>;
 }
 
-//- /lib.rs crate:std
+//- /lib.rs crate:core
 #[prelude_import]
 use clone::*;
 mod clone {
@@ -643,10 +643,35 @@ mod clone {
 }
 
 #[test]
+fn infer_derive_clone_in_core() {
+    let (db, pos) = TestDB::with_position(
+        r#"
+//- /lib.rs crate:core
+#[prelude_import]
+use clone::*;
+mod clone {
+    trait Clone {
+        fn clone(&self) -> Self;
+    }
+}
+#[derive(Clone)]
+pub struct S;
+
+//- /main.rs crate:main deps:core
+use core::S;
+fn test() {
+    S.clone()<|>;
+}
+"#,
+    );
+    assert_eq!("S", type_at_pos(&db, pos));
+}
+
+#[test]
 fn infer_derive_clone_with_params() {
     let (db, pos) = TestDB::with_position(
         r#"
-//- /main.rs crate:main deps:std
+//- /main.rs crate:main deps:core
 #[derive(Clone)]
 struct S;
 #[derive(Clone)]
@@ -656,7 +681,7 @@ fn test() {
     (Wrapper(S).clone(), Wrapper(NonClone).clone())<|>;
 }
 
-//- /lib.rs crate:std
+//- /lib.rs crate:core
 #[prelude_import]
 use clone::*;
 mod clone {
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index f51cdd496..e555c879a 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -1898,6 +1898,36 @@ fn test() {
 }
 
 #[test]
+fn unselected_projection_chalk_fold() {
+    let t = type_at(
+        r#"
+//- /main.rs
+trait Interner {}
+trait Fold<I: Interner, TI = I> {
+    type Result;
+}
+
+struct Ty<I: Interner> {}
+impl<I: Interner, TI: Interner> Fold<I, TI> for Ty<I> {
+    type Result = Ty<TI>;
+}
+
+fn fold<I: Interner, T>(interner: &I, t: T) -> T::Result
+where
+    T: Fold<I, I>,
+{
+    loop {}
+}
+
+fn foo<I: Interner>(interner: &I, t: Ty<I>) {
+    fold(interner, t)<|>;
+}
+"#,
+    );
+    assert_eq!(t, "Ty<I>");
+}
+
+#[test]
 fn trait_impl_self_ty() {
     let t = type_at(
         r#"
diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index 1e5022fa4..f98350bf9 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/crates/ra_hir_ty/src/utils.rs
@@ -14,6 +14,8 @@ use hir_def::{
 };
 use hir_expand::name::{name, Name};
 
+use crate::{db::HirDatabase, GenericPredicate, TraitRef};
+
 fn direct_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
     let resolver = trait_.resolver(db);
     // returning the iterator directly doesn't easily work because of
@@ -41,6 +43,28 @@ fn direct_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
         .collect()
 }
 
+fn direct_super_trait_refs(db: &dyn HirDatabase, trait_ref: &TraitRef) -> Vec<TraitRef> {
+    // returning the iterator directly doesn't easily work because of
+    // 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)
+    let generic_params = db.generic_params(trait_ref.trait_.into());
+    let trait_self = match generic_params.find_trait_self_param() {
+        Some(p) => TypeParamId { parent: trait_ref.trait_.into(), local_id: p },
+        None => return Vec::new(),
+    };
+    db.generic_predicates_for_param(trait_self)
+        .iter()
+        .filter_map(|pred| {
+            pred.as_ref().filter_map(|pred| match pred {
+                GenericPredicate::Implemented(tr) => Some(tr.clone()),
+                _ => None,
+            })
+        })
+        .map(|pred| pred.subst(&trait_ref.substs))
+        .collect()
+}
+
 /// Returns an iterator over the whole super trait hierarchy (including the
 /// trait itself).
 pub(super) fn all_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
@@ -62,6 +86,30 @@ pub(super) fn all_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<Tra
     result
 }
 
+/// Given a trait ref (`Self: Trait`), builds all the implied trait refs for
+/// super traits. The original trait ref will be included. So the difference to
+/// `all_super_traits` is that we keep track of type parameters; for example if
+/// we have `Self: Trait<u32, i32>` and `Trait<T, U>: OtherTrait<U>` we'll get
+/// `Self: OtherTrait<i32>`.
+pub(super) fn all_super_trait_refs(db: &dyn HirDatabase, trait_ref: TraitRef) -> Vec<TraitRef> {
+    // we need to take care a bit here to avoid infinite loops in case of cycles
+    // (i.e. if we have `trait A: B; trait B: A;`)
+    let mut result = vec![trait_ref];
+    let mut i = 0;
+    while i < result.len() {
+        let t = &result[i];
+        // yeah this is quadratic, but trait hierarchies should be flat
+        // enough that this doesn't matter
+        for tt in direct_super_trait_refs(db, t) {
+            if !result.iter().any(|tr| tr.trait_ == tt.trait_) {
+                result.push(tt);
+            }
+        }
+        i += 1;
+    }
+    result
+}
+
 /// Finds a path from a trait to one of its super traits. Returns an empty
 /// vector if there is no path.
 pub(super) fn find_super_trait_path(
diff --git a/crates/ra_ide/src/completion/complete_unqualified_path.rs b/crates/ra_ide/src/completion/complete_unqualified_path.rs
index 56cd086c6..f559f2b97 100644
--- a/crates/ra_ide/src/completion/complete_unqualified_path.rs
+++ b/crates/ra_ide/src/completion/complete_unqualified_path.rs
@@ -4,7 +4,7 @@ use hir::ScopeDef;
 use test_utils::tested_by;
 
 use crate::completion::{CompletionContext, Completions};
-use hir::{Adt, ModuleDef};
+use hir::{Adt, ModuleDef, Type};
 use ra_syntax::AstNode;
 
 pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionContext) {
@@ -15,7 +15,9 @@ pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionC
         return;
     }
 
-    complete_enum_variants(acc, ctx);
+    if let Some(ty) = &ctx.expected_type {
+        complete_enum_variants(acc, ctx, ty);
+    }
 
     if ctx.is_pat_binding_or_const {
         return;
@@ -34,26 +36,24 @@ pub(super) fn complete_unqualified_path(acc: &mut Completions, ctx: &CompletionC
     });
 }
 
-fn complete_enum_variants(acc: &mut Completions, ctx: &CompletionContext) {
-    if let Some(ty) = ctx.expected_type_of(&ctx.token.parent()) {
-        if let Some(Adt::Enum(enum_data)) = ty.as_adt() {
-            let variants = enum_data.variants(ctx.db);
-
-            let module = if let Some(module) = ctx.scope().module() {
-                // Compute path from the completion site if available.
-                module
-            } else {
-                // Otherwise fall back to the enum's definition site.
-                enum_data.module(ctx.db)
-            };
-
-            for variant in variants {
-                if let Some(path) = module.find_use_path(ctx.db, ModuleDef::from(variant)) {
-                    // Variants with trivial paths are already added by the existing completion logic,
-                    // so we should avoid adding these twice
-                    if path.segments.len() > 1 {
-                        acc.add_enum_variant(ctx, variant, Some(path.to_string()));
-                    }
+fn complete_enum_variants(acc: &mut Completions, ctx: &CompletionContext, ty: &Type) {
+    if let Some(Adt::Enum(enum_data)) = ty.as_adt() {
+        let variants = enum_data.variants(ctx.db);
+
+        let module = if let Some(module) = ctx.scope().module() {
+            // Compute path from the completion site if available.
+            module
+        } else {
+            // Otherwise fall back to the enum's definition site.
+            enum_data.module(ctx.db)
+        };
+
+        for variant in variants {
+            if let Some(path) = module.find_use_path(ctx.db, ModuleDef::from(variant)) {
+                // Variants with trivial paths are already added by the existing completion logic,
+                // so we should avoid adding these twice
+                if path.segments.len() > 1 {
+                    acc.add_enum_variant(ctx, variant, Some(path.to_string()));
                 }
             }
         }
diff --git a/crates/ra_ide/src/completion/completion_context.rs b/crates/ra_ide/src/completion/completion_context.rs
index 5f2797e41..118fceb2e 100644
--- a/crates/ra_ide/src/completion/completion_context.rs
+++ b/crates/ra_ide/src/completion/completion_context.rs
@@ -5,7 +5,7 @@ use ra_db::SourceDatabase;
 use ra_ide_db::RootDatabase;
 use ra_syntax::{
     algo::{find_covering_element, find_node_at_offset},
-    ast, AstNode,
+    ast, match_ast, AstNode,
     SyntaxKind::*,
     SyntaxNode, SyntaxToken, TextRange, TextSize,
 };
@@ -26,6 +26,7 @@ pub(crate) struct CompletionContext<'a> {
     /// The token before the cursor, in the macro-expanded file.
     pub(super) token: SyntaxToken,
     pub(super) krate: Option<hir::Crate>,
+    pub(super) expected_type: Option<Type>,
     pub(super) name_ref_syntax: Option<ast::NameRef>,
     pub(super) function_syntax: Option<ast::FnDef>,
     pub(super) use_item_syntax: Option<ast::UseItem>,
@@ -93,6 +94,7 @@ impl<'a> CompletionContext<'a> {
             token,
             offset: position.offset,
             krate,
+            expected_type: None,
             name_ref_syntax: None,
             function_syntax: None,
             use_item_syntax: None,
@@ -175,23 +177,30 @@ impl<'a> CompletionContext<'a> {
         self.sema.scope_at_offset(&self.token.parent(), self.offset)
     }
 
-    pub(crate) fn expected_type_of(&self, node: &SyntaxNode) -> Option<Type> {
-        for ancestor in node.ancestors() {
-            if let Some(pat) = ast::Pat::cast(ancestor.clone()) {
-                return self.sema.type_of_pat(&pat);
-            } else if let Some(expr) = ast::Expr::cast(ancestor) {
-                return self.sema.type_of_expr(&expr);
-            }
-        }
-        None
-    }
-
     fn fill(
         &mut self,
         original_file: &SyntaxNode,
         file_with_fake_ident: SyntaxNode,
         offset: TextSize,
     ) {
+        // FIXME: this is wrong in at least two cases:
+        //  * when there's no token `foo(<|>)`
+        //  * when there is a token, but it happens to have type of it's own
+        self.expected_type = self
+            .token
+            .ancestors()
+            .find_map(|node| {
+                let ty = match_ast! {
+                    match node {
+                        ast::Pat(it) => self.sema.type_of_pat(&it),
+                        ast::Expr(it) => self.sema.type_of_expr(&it),
+                        _ => return None,
+                    }
+                };
+                Some(ty)
+            })
+            .flatten();
+
         // First, let's try to complete a reference to some declaration.
         if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(&file_with_fake_ident, offset) {
             // Special case, `trait T { fn foo(i_am_a_name_ref) {} }`.
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index 7633cd7fd..77d354376 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -349,6 +349,14 @@ impl Builder {
         if ctx.use_item_syntax.is_some() || ctx.is_call {
             return self;
         }
+
+        // Don't add parentheses if the expected type is some function reference.
+        if let Some(ty) = &ctx.expected_type {
+            if ty.is_fn() {
+                return self;
+            }
+        }
+
         let cap = match ctx.config.snippet_cap {
             Some(it) => it,
             None => return self,
@@ -749,6 +757,54 @@ mod tests {
     }
 
     #[test]
+    fn no_call_parens_if_fn_ptr_needed() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                fn somefn(with: u8, a: u8, lot: u8, of: u8, args: u8) {}
+
+                struct ManualVtable {
+                    method: fn(u8, u8, u8, u8, u8),
+                }
+
+                fn main() -> ManualVtable {
+                    ManualVtable {
+                        method: some<|>
+                    }
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "ManualVtable",
+                source_range: 295..299,
+                delete: 295..299,
+                insert: "ManualVtable",
+                kind: Struct,
+            },
+            CompletionItem {
+                label: "main",
+                source_range: 295..299,
+                delete: 295..299,
+                insert: "main",
+                kind: Function,
+                detail: "fn main() -> ManualVtable",
+            },
+            CompletionItem {
+                label: "somefn",
+                source_range: 295..299,
+                delete: 295..299,
+                insert: "somefn",
+                kind: Function,
+                detail: "fn somefn(with: u8, a: u8, lot: u8, of: u8, args: u8)",
+            },
+        ]
+        "###
+        );
+    }
+
+    #[test]
     fn arg_snippets_for_method_call() {
         assert_debug_snapshot!(
             do_reference_completion(
@@ -1179,7 +1235,7 @@ mod tests {
 
     #[test]
     fn test_struct_field_completion_in_record_lit() {
-        covers!(test_struct_field_completion_in_func_call);
+        covers!(test_struct_field_completion_in_record_lit);
         assert_debug_snapshot!(
         do_reference_completion(
                 r"
diff --git a/crates/ra_ide/src/snapshots/highlight_injection.html b/crates/ra_ide/src/snapshots/highlight_injection.html
index 6ec13bd80..ea026d7a0 100644
--- a/crates/ra_ide/src/snapshots/highlight_injection.html
+++ b/crates/ra_ide/src/snapshots/highlight_injection.html
@@ -20,6 +20,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 .macro              { color: #94BFF3; }
 .module             { color: #AFD8AF; }
 .variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
 .mutable            { text-decoration: underline; }
 
 .keyword            { color: #F0DFAF; font-weight: bold; }
diff --git a/crates/ra_ide/src/snapshots/highlight_strings.html b/crates/ra_ide/src/snapshots/highlight_strings.html
index 433f2e0c5..de06daf72 100644
--- a/crates/ra_ide/src/snapshots/highlight_strings.html
+++ b/crates/ra_ide/src/snapshots/highlight_strings.html
@@ -20,6 +20,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 .macro              { color: #94BFF3; }
 .module             { color: #AFD8AF; }
 .variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
 .mutable            { text-decoration: underline; }
 
 .keyword            { color: #F0DFAF; font-weight: bold; }
@@ -40,43 +41,43 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 <span class="keyword">fn</span> <span class="function declaration">main</span>() {
     <span class="comment">// from https://doc.rust-lang.org/std/fmt/index.html</span>
     <span class="macro">println!</span>(<span class="string_literal">"Hello"</span>);                 <span class="comment">// =&gt; "Hello"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"Hello, </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"world"</span>);   <span class="comment">// =&gt; "Hello, world!"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"The number is </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>);   <span class="comment">// =&gt; "The number is 1"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">?</span><span class="attribute">}</span><span class="string_literal">"</span>, (<span class="numeric_literal">3</span>, <span class="numeric_literal">4</span>));          <span class="comment">// =&gt; "(3, 4)"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">value</span><span class="attribute">}</span><span class="string_literal">"</span>, value=<span class="numeric_literal">4</span>);      <span class="comment">// =&gt; "4"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, <span class="numeric_literal">2</span>);           <span class="comment">// =&gt; "1 2"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">:</span><span class="numeric_literal">0</span><span class="numeric_literal">4</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">42</span>);             <span class="comment">// =&gt; "0042" with leading zerosV</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="numeric_literal">1</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="numeric_literal">0</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, <span class="numeric_literal">2</span>);   <span class="comment">// =&gt; "2 1 1 2"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">argument</span><span class="attribute">}</span><span class="string_literal">"</span>, argument = <span class="string_literal">"test"</span>);   <span class="comment">// =&gt; "test"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">name</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, name = <span class="numeric_literal">2</span>);          <span class="comment">// =&gt; "2 1"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">a</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="variable">c</span><span class="attribute">}</span><span class="string_literal"> </span><span class="attribute">{</span><span class="variable">b</span><span class="attribute">}</span><span class="string_literal">"</span>, a=<span class="string_literal">"a"</span>, b=<span class="char_literal">'b'</span>, c=<span class="numeric_literal">3</span>);  <span class="comment">// =&gt; "a 3 b"</span>
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="numeric_literal">1</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="numeric_literal">1</span><span class="attribute">:</span><span class="numeric_literal">0</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="variable">width</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>, width = <span class="numeric_literal">5</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">&lt;</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">-</span><span class="attribute">&lt;</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">^</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">&gt;</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">+</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">#</span><span class="variable">x</span><span class="string_literal">}!"</span>, <span class="numeric_literal">27</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">!"</span>, -<span class="numeric_literal">5</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">#</span><span class="numeric_literal">0</span><span class="numeric_literal">10</span><span class="variable">x</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">27</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="numeric_literal">0</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="numeric_literal">1</span><span class="attribute">:</span><span class="attribute">.</span><span class="numeric_literal">5</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="numeric_literal">1</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="numeric_literal">2</span><span class="attribute">:</span><span class="attribute">.</span><span class="numeric_literal">0</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="numeric_literal">5</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="numeric_literal">0</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="numeric_literal">2</span><span class="attribute">:</span><span class="attribute">.</span><span class="numeric_literal">1</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="attribute">:</span><span class="attribute">.</span><span class="attribute">*</span><span class="attribute">}</span><span class="string_literal">"</span>,    <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="numeric_literal">2</span><span class="attribute">:</span><span class="attribute">.</span><span class="attribute">*</span><span class="attribute">}</span><span class="string_literal">"</span>,   <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal"> is </span><span class="attribute">{</span><span class="variable">number</span><span class="attribute">:</span><span class="attribute">.</span><span class="variable">prec</span><span class="attribute">$</span><span class="attribute">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, prec = <span class="numeric_literal">5</span>, number = <span class="numeric_literal">0.01</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">, `</span><span class="attribute">{</span><span class="variable">name</span><span class="attribute">:</span><span class="attribute">.</span><span class="attribute">*</span><span class="attribute">}</span><span class="string_literal">` has 3 fractional digits"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="numeric_literal">1234.56</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">, `</span><span class="attribute">{</span><span class="variable">name</span><span class="attribute">:</span><span class="attribute">.</span><span class="attribute">*</span><span class="attribute">}</span><span class="string_literal">` has 3 characters"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="string_literal">"1234.56"</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">, `</span><span class="attribute">{</span><span class="variable">name</span><span class="attribute">:</span><span class="attribute">&gt;</span><span class="numeric_literal">8</span><span class="attribute">.</span><span class="attribute">*</span><span class="attribute">}</span><span class="string_literal">` has 3 right-aligned characters"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="string_literal">"1234.56"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello, </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"world"</span>);   <span class="comment">// =&gt; "Hello, world!"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"The number is </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>);   <span class="comment">// =&gt; "The number is 1"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">?</span><span class="format_specifier">}</span><span class="string_literal">"</span>, (<span class="numeric_literal">3</span>, <span class="numeric_literal">4</span>));          <span class="comment">// =&gt; "(3, 4)"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">value</span><span class="format_specifier">}</span><span class="string_literal">"</span>, value=<span class="numeric_literal">4</span>);      <span class="comment">// =&gt; "4"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, <span class="numeric_literal">2</span>);           <span class="comment">// =&gt; "1 2"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">4</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">42</span>);             <span class="comment">// =&gt; "0042" with leading zerosV</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, <span class="numeric_literal">2</span>);   <span class="comment">// =&gt; "2 1 1 2"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">argument</span><span class="format_specifier">}</span><span class="string_literal">"</span>, argument = <span class="string_literal">"test"</span>);   <span class="comment">// =&gt; "test"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">1</span>, name = <span class="numeric_literal">2</span>);          <span class="comment">// =&gt; "2 1"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">a</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="variable">c</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="variable">b</span><span class="format_specifier">}</span><span class="string_literal">"</span>, a=<span class="string_literal">"a"</span>, b=<span class="char_literal">'b'</span>, c=<span class="numeric_literal">3</span>);  <span class="comment">// =&gt; "a 3 b"</span>
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">1</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="variable">width</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>, width = <span class="numeric_literal">5</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">&lt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">-</span><span class="format_specifier">&lt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">^</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">&gt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"x"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">+</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">#</span><span class="variable">x</span><span class="string_literal">}!"</span>, <span class="numeric_literal">27</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">5</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, -<span class="numeric_literal">5</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">#</span><span class="numeric_literal">0</span><span class="numeric_literal">10</span><span class="variable">x</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="numeric_literal">27</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">0</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="numeric_literal">5</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">1</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">"</span>,    <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">"</span>,   <span class="string_literal">"x"</span>, <span class="numeric_literal">5</span>, <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="variable">number</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="variable">prec</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span>, <span class="string_literal">"x"</span>, prec = <span class="numeric_literal">5</span>, number = <span class="numeric_literal">0.01</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 fractional digits"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="numeric_literal">1234.56</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 characters"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="string_literal">"1234.56"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">&gt;</span><span class="numeric_literal">8</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 right-aligned characters"</span>, <span class="string_literal">"Hello"</span>, <span class="numeric_literal">3</span>, name=<span class="string_literal">"1234.56"</span>);
     <span class="macro">println!</span>(<span class="string_literal">"Hello {{}}"</span>);
     <span class="macro">println!</span>(<span class="string_literal">"{{ Hello"</span>);
 
-    <span class="macro">println!</span>(<span class="string_literal">r"Hello, </span><span class="attribute">{</span><span class="attribute">}</span><span class="string_literal">!"</span>, <span class="string_literal">"world"</span>);
+    <span class="macro">println!</span>(<span class="string_literal">r"Hello, </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">!"</span>, <span class="string_literal">"world"</span>);
 
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">\x41</span><span class="attribute">}</span><span class="string_literal">"</span>, A = <span class="numeric_literal">92</span>);
-    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="attribute">{</span><span class="variable">ничоси</span><span class="attribute">}</span><span class="string_literal">"</span>, ничоси = <span class="numeric_literal">92</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">\x41</span><span class="format_specifier">}</span><span class="string_literal">"</span>, A = <span class="numeric_literal">92</span>);
+    <span class="macro">println!</span>(<span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">ничоси</span><span class="format_specifier">}</span><span class="string_literal">"</span>, ничоси = <span class="numeric_literal">92</span>);
 }</code></pre>
\ No newline at end of file
diff --git a/crates/ra_ide/src/snapshots/highlighting.html b/crates/ra_ide/src/snapshots/highlighting.html
index ccb1fc751..4b12fe823 100644
--- a/crates/ra_ide/src/snapshots/highlighting.html
+++ b/crates/ra_ide/src/snapshots/highlighting.html
@@ -20,6 +20,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 .macro              { color: #94BFF3; }
 .module             { color: #AFD8AF; }
 .variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
 .mutable            { text-decoration: underline; }
 
 .keyword            { color: #F0DFAF; font-weight: bold; }
diff --git a/crates/ra_ide/src/snapshots/rainbow_highlighting.html b/crates/ra_ide/src/snapshots/rainbow_highlighting.html
index 3df82c45f..11e1f3e44 100644
--- a/crates/ra_ide/src/snapshots/rainbow_highlighting.html
+++ b/crates/ra_ide/src/snapshots/rainbow_highlighting.html
@@ -20,6 +20,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 .macro              { color: #94BFF3; }
 .module             { color: #AFD8AF; }
 .variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
 .mutable            { text-decoration: underline; }
 
 .keyword            { color: #F0DFAF; font-weight: bold; }
diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index be0f8c827..6658c7bb2 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -290,7 +290,7 @@ fn highlight_format_specifier(kind: FormatSpecifier) -> Option<HighlightTag> {
         | FormatSpecifier::DollarSign
         | FormatSpecifier::Dot
         | FormatSpecifier::Asterisk
-        | FormatSpecifier::QuestionMark => HighlightTag::Attribute,
+        | FormatSpecifier::QuestionMark => HighlightTag::FormatSpecifier,
         FormatSpecifier::Integer | FormatSpecifier::Zero => HighlightTag::NumericLiteral,
         FormatSpecifier::Identifier => HighlightTag::Local,
     })
diff --git a/crates/ra_ide/src/syntax_highlighting/html.rs b/crates/ra_ide/src/syntax_highlighting/html.rs
index 010db4017..ff0eeeb52 100644
--- a/crates/ra_ide/src/syntax_highlighting/html.rs
+++ b/crates/ra_ide/src/syntax_highlighting/html.rs
@@ -79,6 +79,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 .macro              { color: #94BFF3; }
 .module             { color: #AFD8AF; }
 .variable           { color: #DCDCCC; }
+.format_specifier   { color: #CC696B; }
 .mutable            { text-decoration: underline; }
 
 .keyword            { color: #F0DFAF; font-weight: bold; }
diff --git a/crates/ra_ide/src/syntax_highlighting/tags.rs b/crates/ra_ide/src/syntax_highlighting/tags.rs
index f2c421654..be1a0f12b 100644
--- a/crates/ra_ide/src/syntax_highlighting/tags.rs
+++ b/crates/ra_ide/src/syntax_highlighting/tags.rs
@@ -39,6 +39,7 @@ pub enum HighlightTag {
     Union,
     Local,
     UnresolvedReference,
+    FormatSpecifier,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
@@ -81,6 +82,7 @@ impl HighlightTag {
             HighlightTag::Union => "union",
             HighlightTag::Local => "variable",
             HighlightTag::UnresolvedReference => "unresolved_reference",
+            HighlightTag::FormatSpecifier => "format_specifier",
         }
     }
 }
diff --git a/crates/ra_prof/Cargo.toml b/crates/ra_prof/Cargo.toml
index d15b08992..c33b5121a 100644
--- a/crates/ra_prof/Cargo.toml
+++ b/crates/ra_prof/Cargo.toml
@@ -9,6 +9,7 @@ publish = false
 doctest = false
 
 [dependencies]
+ra_arena = { path = "../ra_arena" }
 once_cell = "1.3.1"
 backtrace = { version = "0.3.44", optional = true }
 
diff --git a/crates/ra_prof/src/hprof.rs b/crates/ra_prof/src/hprof.rs
new file mode 100644
index 000000000..2b8a90363
--- /dev/null
+++ b/crates/ra_prof/src/hprof.rs
@@ -0,0 +1,246 @@
+//! Simple hierarchical profiler
+use once_cell::sync::Lazy;
+use std::{
+    cell::RefCell,
+    collections::{BTreeMap, HashSet},
+    io::{stderr, Write},
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        RwLock,
+    },
+    time::{Duration, Instant},
+};
+
+use crate::tree::{Idx, Tree};
+
+/// Filtering syntax
+/// env RA_PROFILE=*             // dump everything
+/// env RA_PROFILE=foo|bar|baz   // enabled only selected entries
+/// env RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms
+pub fn init() {
+    let spec = std::env::var("RA_PROFILE").unwrap_or_default();
+    init_from(&spec);
+}
+
+pub fn init_from(spec: &str) {
+    let filter = if spec.is_empty() { Filter::disabled() } else { Filter::from_spec(spec) };
+    filter.install();
+}
+
+pub type Label = &'static str;
+
+/// This function starts a profiling scope in the current execution stack with a given description.
+/// It returns a Profile structure and measure elapsed time between this method invocation and Profile structure drop.
+/// It supports nested profiling scopes in case when this function invoked multiple times at the execution stack. In this case the profiling information will be nested at the output.
+/// Profiling information is being printed in the stderr.
+///
+/// # Example
+/// ```
+/// use ra_prof::{profile, set_filter, Filter};
+///
+/// let f = Filter::from_spec("profile1|profile2@2");
+/// set_filter(f);
+/// profiling_function1();
+///
+/// fn profiling_function1() {
+///     let _p = profile("profile1");
+///     profiling_function2();
+/// }
+///
+/// fn profiling_function2() {
+///     let _p = profile("profile2");
+/// }
+/// ```
+/// This will print in the stderr the following:
+/// ```text
+///  0ms - profile
+///      0ms - profile2
+/// ```
+pub fn profile(label: Label) -> Profiler {
+    assert!(!label.is_empty());
+    let enabled = PROFILING_ENABLED.load(Ordering::Relaxed)
+        && PROFILE_STACK.with(|stack| stack.borrow_mut().push(label));
+    let label = if enabled { Some(label) } else { None };
+    Profiler { label, detail: None }
+}
+
+pub struct Profiler {
+    label: Option<Label>,
+    detail: Option<String>,
+}
+
+impl Profiler {
+    pub fn detail(mut self, detail: impl FnOnce() -> String) -> Profiler {
+        if self.label.is_some() {
+            self.detail = Some(detail())
+        }
+        self
+    }
+}
+
+impl Drop for Profiler {
+    fn drop(&mut self) {
+        match self {
+            Profiler { label: Some(label), detail } => {
+                PROFILE_STACK.with(|stack| {
+                    stack.borrow_mut().pop(label, detail.take());
+                });
+            }
+            Profiler { label: None, .. } => (),
+        }
+    }
+}
+
+static PROFILING_ENABLED: AtomicBool = AtomicBool::new(false);
+static FILTER: Lazy<RwLock<Filter>> = Lazy::new(Default::default);
+thread_local!(static PROFILE_STACK: RefCell<ProfileStack> = RefCell::new(ProfileStack::new()));
+
+#[derive(Default, Clone, Debug)]
+struct Filter {
+    depth: usize,
+    allowed: HashSet<String>,
+    longer_than: Duration,
+    version: usize,
+}
+
+impl Filter {
+    fn disabled() -> Filter {
+        Filter::default()
+    }
+
+    fn from_spec(mut spec: &str) -> Filter {
+        let longer_than = if let Some(idx) = spec.rfind('>') {
+            let longer_than = spec[idx + 1..].parse().expect("invalid profile longer_than");
+            spec = &spec[..idx];
+            Duration::from_millis(longer_than)
+        } else {
+            Duration::new(0, 0)
+        };
+
+        let depth = if let Some(idx) = spec.rfind('@') {
+            let depth: usize = spec[idx + 1..].parse().expect("invalid profile depth");
+            spec = &spec[..idx];
+            depth
+        } else {
+            999
+        };
+        let allowed =
+            if spec == "*" { HashSet::new() } else { spec.split('|').map(String::from).collect() };
+        Filter { depth, allowed, longer_than, version: 0 }
+    }
+
+    fn install(mut self) {
+        PROFILING_ENABLED.store(self.depth > 0, Ordering::SeqCst);
+        let mut old = FILTER.write().unwrap();
+        self.version = old.version + 1;
+        *old = self;
+    }
+}
+
+struct ProfileStack {
+    starts: Vec<Instant>,
+    filter: Filter,
+    messages: Tree<Message>,
+}
+
+#[derive(Default)]
+struct Message {
+    duration: Duration,
+    label: Label,
+    detail: Option<String>,
+}
+
+impl ProfileStack {
+    fn new() -> ProfileStack {
+        ProfileStack { starts: Vec::new(), messages: Tree::default(), filter: Default::default() }
+    }
+
+    fn push(&mut self, label: Label) -> bool {
+        if self.starts.is_empty() {
+            if let Ok(f) = FILTER.try_read() {
+                if f.version > self.filter.version {
+                    self.filter = f.clone();
+                }
+            };
+        }
+        if self.starts.len() > self.filter.depth {
+            return false;
+        }
+        let allowed = &self.filter.allowed;
+        if self.starts.is_empty() && !allowed.is_empty() && !allowed.contains(label) {
+            return false;
+        }
+
+        self.starts.push(Instant::now());
+        self.messages.start();
+        true
+    }
+
+    pub fn pop(&mut self, label: Label, detail: Option<String>) {
+        let start = self.starts.pop().unwrap();
+        let duration = start.elapsed();
+        let level = self.starts.len();
+        self.messages.finish(Message { duration, label, detail });
+        if level == 0 {
+            let longer_than = self.filter.longer_than;
+            // Convert to millis for comparison to avoid problems with rounding
+            // (otherwise we could print `0ms` despite user's `>0` filter when
+            // `duration` is just a few nanos).
+            if duration.as_millis() > longer_than.as_millis() {
+                let stderr = stderr();
+                if let Some(root) = self.messages.root() {
+                    print(&self.messages, root, 0, longer_than, &mut stderr.lock());
+                }
+            }
+            self.messages.clear();
+            assert!(self.starts.is_empty())
+        }
+    }
+}
+
+fn print(
+    tree: &Tree<Message>,
+    curr: Idx<Message>,
+    level: u32,
+    longer_than: Duration,
+    out: &mut impl Write,
+) {
+    let current_indent = "    ".repeat(level as usize);
+    let detail = tree[curr].detail.as_ref().map(|it| format!(" @ {}", it)).unwrap_or_default();
+    writeln!(
+        out,
+        "{}{:5}ms - {}{}",
+        current_indent,
+        tree[curr].duration.as_millis(),
+        tree[curr].label,
+        detail,
+    )
+    .expect("printing profiling info");
+
+    let mut accounted_for = Duration::default();
+    let mut short_children = BTreeMap::new(); // Use `BTreeMap` to get deterministic output.
+    for child in tree.children(curr) {
+        accounted_for += tree[child].duration;
+
+        if tree[child].duration.as_millis() > longer_than.as_millis() {
+            print(tree, child, level + 1, longer_than, out)
+        } else {
+            let (total_duration, cnt) =
+                short_children.entry(tree[child].label).or_insert((Duration::default(), 0));
+            *total_duration += tree[child].duration;
+            *cnt += 1;
+        }
+    }
+
+    for (child_msg, (duration, count)) in short_children.iter() {
+        let millis = duration.as_millis();
+        writeln!(out, "    {}{:5}ms - {} ({} calls)", current_indent, millis, child_msg, count)
+            .expect("printing profiling info");
+    }
+
+    let unaccounted = tree[curr].duration - accounted_for;
+    if tree.children(curr).next().is_some() && unaccounted > longer_than {
+        writeln!(out, "    {}{:5}ms - ???", current_indent, unaccounted.as_millis())
+            .expect("printing profiling info");
+    }
+}
diff --git a/crates/ra_prof/src/lib.rs b/crates/ra_prof/src/lib.rs
index 2d4f68f5e..89df7f04b 100644
--- a/crates/ra_prof/src/lib.rs
+++ b/crates/ra_prof/src/lib.rs
@@ -1,24 +1,17 @@
-//! FIXME: write short doc here
+//! A collection of tools for profiling rust-analyzer.
 
 mod memory_usage;
 #[cfg(feature = "cpu_profiler")]
 mod google_cpu_profiler;
+mod hprof;
+mod tree;
 
-use std::{
-    cell::RefCell,
-    collections::BTreeMap,
-    collections::HashSet,
-    io::{stderr, Write},
-    sync::{
-        atomic::{AtomicBool, Ordering},
-        RwLock,
-    },
-    time::{Duration, Instant},
-};
-
-use once_cell::sync::Lazy;
+use std::cell::RefCell;
 
-pub use crate::memory_usage::{Bytes, MemoryUsage};
+pub use crate::{
+    hprof::{init, init_from, profile},
+    memory_usage::{Bytes, MemoryUsage},
+};
 
 // We use jemalloc mainly to get heap usage statistics, actual performance
 // difference is not measures.
@@ -26,298 +19,6 @@ pub use crate::memory_usage::{Bytes, MemoryUsage};
 #[global_allocator]
 static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 
-pub fn init() {
-    set_filter(match std::env::var("RA_PROFILE") {
-        Ok(spec) => Filter::from_spec(&spec),
-        Err(_) => Filter::disabled(),
-    });
-}
-
-/// Set profiling filter. It specifies descriptions allowed to profile.
-/// This is helpful when call stack has too many nested profiling scopes.
-/// Additionally filter can specify maximum depth of profiling scopes nesting.
-///
-/// #Example
-/// ```
-/// use ra_prof::{set_filter, Filter};
-/// let f = Filter::from_spec("profile1|profile2@2");
-/// set_filter(f);
-/// ```
-pub fn set_filter(f: Filter) {
-    PROFILING_ENABLED.store(f.depth > 0, Ordering::SeqCst);
-    let set: HashSet<_> = f.allowed.iter().cloned().collect();
-    let mut old = FILTER.write().unwrap();
-    let filter_data = FilterData {
-        depth: f.depth,
-        allowed: set,
-        longer_than: f.longer_than,
-        version: old.version + 1,
-    };
-    *old = filter_data;
-}
-
-pub type Label = &'static str;
-
-/// This function starts a profiling scope in the current execution stack with a given description.
-/// It returns a Profile structure and measure elapsed time between this method invocation and Profile structure drop.
-/// It supports nested profiling scopes in case when this function invoked multiple times at the execution stack. In this case the profiling information will be nested at the output.
-/// Profiling information is being printed in the stderr.
-///
-/// # Example
-/// ```
-/// use ra_prof::{profile, set_filter, Filter};
-///
-/// let f = Filter::from_spec("profile1|profile2@2");
-/// set_filter(f);
-/// profiling_function1();
-///
-/// fn profiling_function1() {
-///     let _p = profile("profile1");
-///     profiling_function2();
-/// }
-///
-/// fn profiling_function2() {
-///     let _p = profile("profile2");
-/// }
-/// ```
-/// This will print in the stderr the following:
-/// ```text
-///  0ms - profile
-///      0ms - profile2
-/// ```
-pub fn profile(label: Label) -> Profiler {
-    assert!(!label.is_empty());
-    if !PROFILING_ENABLED.load(Ordering::Relaxed) {
-        return Profiler { label: None, detail: None };
-    }
-
-    PROFILE_STACK.with(|stack| {
-        let mut stack = stack.borrow_mut();
-        if stack.starts.is_empty() {
-            if let Ok(f) = FILTER.try_read() {
-                if f.version > stack.filter_data.version {
-                    stack.filter_data = f.clone();
-                }
-            };
-        }
-        if stack.starts.len() > stack.filter_data.depth {
-            return Profiler { label: None, detail: None };
-        }
-        let allowed = &stack.filter_data.allowed;
-        if stack.starts.is_empty() && !allowed.is_empty() && !allowed.contains(label) {
-            return Profiler { label: None, detail: None };
-        }
-
-        stack.starts.push(Instant::now());
-        Profiler { label: Some(label), detail: None }
-    })
-}
-
-pub struct Profiler {
-    label: Option<Label>,
-    detail: Option<String>,
-}
-
-impl Profiler {
-    pub fn detail(mut self, detail: impl FnOnce() -> String) -> Profiler {
-        if self.label.is_some() {
-            self.detail = Some(detail())
-        }
-        self
-    }
-}
-
-pub struct Filter {
-    depth: usize,
-    allowed: Vec<String>,
-    longer_than: Duration,
-}
-
-impl Filter {
-    // Filtering syntax
-    // env RA_PROFILE=*             // dump everything
-    // env RA_PROFILE=foo|bar|baz   // enabled only selected entries
-    // env RA_PROFILE=*@3>10        // dump everything, up to depth 3, if it takes more than 10 ms
-    pub fn from_spec(mut spec: &str) -> Filter {
-        let longer_than = if let Some(idx) = spec.rfind('>') {
-            let longer_than = spec[idx + 1..].parse().expect("invalid profile longer_than");
-            spec = &spec[..idx];
-            Duration::from_millis(longer_than)
-        } else {
-            Duration::new(0, 0)
-        };
-
-        let depth = if let Some(idx) = spec.rfind('@') {
-            let depth: usize = spec[idx + 1..].parse().expect("invalid profile depth");
-            spec = &spec[..idx];
-            depth
-        } else {
-            999
-        };
-        let allowed =
-            if spec == "*" { Vec::new() } else { spec.split('|').map(String::from).collect() };
-        Filter::new(depth, allowed, longer_than)
-    }
-
-    pub fn disabled() -> Filter {
-        Filter::new(0, Vec::new(), Duration::new(0, 0))
-    }
-
-    pub fn new(depth: usize, allowed: Vec<String>, longer_than: Duration) -> Filter {
-        Filter { depth, allowed, longer_than }
-    }
-}
-
-struct ProfileStack {
-    starts: Vec<Instant>,
-    messages: Vec<Message>,
-    filter_data: FilterData,
-}
-
-struct Message {
-    level: usize,
-    duration: Duration,
-    label: Label,
-    detail: Option<String>,
-}
-
-impl ProfileStack {
-    fn new() -> ProfileStack {
-        ProfileStack { starts: Vec::new(), messages: Vec::new(), filter_data: Default::default() }
-    }
-}
-
-#[derive(Default, Clone)]
-struct FilterData {
-    depth: usize,
-    version: usize,
-    allowed: HashSet<String>,
-    longer_than: Duration,
-}
-
-static PROFILING_ENABLED: AtomicBool = AtomicBool::new(false);
-
-static FILTER: Lazy<RwLock<FilterData>> = Lazy::new(Default::default);
-
-thread_local!(static PROFILE_STACK: RefCell<ProfileStack> = RefCell::new(ProfileStack::new()));
-
-impl Drop for Profiler {
-    fn drop(&mut self) {
-        match self {
-            Profiler { label: Some(label), detail } => {
-                PROFILE_STACK.with(|stack| {
-                    let mut stack = stack.borrow_mut();
-                    let start = stack.starts.pop().unwrap();
-                    let duration = start.elapsed();
-                    let level = stack.starts.len();
-                    stack.messages.push(Message { level, duration, label, detail: detail.take() });
-                    if level == 0 {
-                        let stdout = stderr();
-                        let longer_than = stack.filter_data.longer_than;
-                        // Convert to millis for comparison to avoid problems with rounding
-                        // (otherwise we could print `0ms` despite user's `>0` filter when
-                        // `duration` is just a few nanos).
-                        if duration.as_millis() > longer_than.as_millis() {
-                            print(&stack.messages, longer_than, &mut stdout.lock());
-                        }
-                        stack.messages.clear();
-                    }
-                });
-            }
-            Profiler { label: None, .. } => (),
-        }
-    }
-}
-
-fn print(msgs: &[Message], longer_than: Duration, out: &mut impl Write) {
-    if msgs.is_empty() {
-        return;
-    }
-    let children_map = idx_to_children(msgs);
-    let root_idx = msgs.len() - 1;
-    print_for_idx(root_idx, &children_map, msgs, longer_than, out);
-}
-
-fn print_for_idx(
-    current_idx: usize,
-    children_map: &[Vec<usize>],
-    msgs: &[Message],
-    longer_than: Duration,
-    out: &mut impl Write,
-) {
-    let current = &msgs[current_idx];
-    let current_indent = "    ".repeat(current.level);
-    let detail = current.detail.as_ref().map(|it| format!(" @ {}", it)).unwrap_or_default();
-    writeln!(
-        out,
-        "{}{:5}ms - {}{}",
-        current_indent,
-        current.duration.as_millis(),
-        current.label,
-        detail,
-    )
-    .expect("printing profiling info");
-
-    let longer_than_millis = longer_than.as_millis();
-    let children_indices = &children_map[current_idx];
-    let mut accounted_for = Duration::default();
-    let mut short_children = BTreeMap::new(); // Use `BTreeMap` to get deterministic output.
-
-    for child_idx in children_indices.iter() {
-        let child = &msgs[*child_idx];
-        if child.duration.as_millis() > longer_than_millis {
-            print_for_idx(*child_idx, children_map, msgs, longer_than, out);
-        } else {
-            let pair = short_children.entry(child.label).or_insert((Duration::default(), 0));
-            pair.0 += child.duration;
-            pair.1 += 1;
-        }
-        accounted_for += child.duration;
-    }
-
-    for (child_msg, (duration, count)) in short_children.iter() {
-        let millis = duration.as_millis();
-        writeln!(out, "    {}{:5}ms - {} ({} calls)", current_indent, millis, child_msg, count)
-            .expect("printing profiling info");
-    }
-
-    let unaccounted_millis = (current.duration - accounted_for).as_millis();
-    if !children_indices.is_empty()
-        && unaccounted_millis > 0
-        && unaccounted_millis > longer_than_millis
-    {
-        writeln!(out, "    {}{:5}ms - ???", current_indent, unaccounted_millis)
-            .expect("printing profiling info");
-    }
-}
-
-/// Returns a mapping from an index in the `msgs` to the vector with the indices of its children.
-///
-/// This assumes that the entries in `msgs` are in the order of when the calls to `profile` finish.
-/// In other words, a postorder of the call graph. In particular, the root is the last element of
-/// `msgs`.
-fn idx_to_children(msgs: &[Message]) -> Vec<Vec<usize>> {
-    // Initialize with the index of the root; `msgs` and `ancestors` should be never empty.
-    assert!(!msgs.is_empty());
-    let mut ancestors = vec![msgs.len() - 1];
-    let mut result: Vec<Vec<usize>> = vec![vec![]; msgs.len()];
-    for (idx, msg) in msgs[..msgs.len() - 1].iter().enumerate().rev() {
-        // We need to find the parent of the current message, i.e., the last ancestor that has a
-        // level lower than the current message.
-        while msgs[*ancestors.last().unwrap()].level >= msg.level {
-            ancestors.pop();
-        }
-        result[*ancestors.last().unwrap()].push(idx);
-        ancestors.push(idx);
-    }
-    // Note that above we visited all children from the last to the first one. Let's reverse vectors
-    // to get the more natural order where the first element is the first child.
-    for vec in result.iter_mut() {
-        vec.reverse();
-    }
-    result
-}
-
 /// Prints backtrace to stderr, useful for debugging.
 #[cfg(feature = "backtrace")]
 pub fn print_backtrace() {
@@ -403,86 +104,3 @@ impl Drop for CpuProfiler {
 pub fn memory_usage() -> MemoryUsage {
     MemoryUsage::current()
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_basic_profile() {
-        let s = vec!["profile1".to_string(), "profile2".to_string()];
-        let f = Filter::new(2, s, Duration::new(0, 0));
-        set_filter(f);
-        profiling_function1();
-    }
-
-    fn profiling_function1() {
-        let _p = profile("profile1");
-        profiling_function2();
-    }
-
-    fn profiling_function2() {
-        let _p = profile("profile2");
-    }
-
-    #[test]
-    fn test_longer_than() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 1, duration: Duration::from_nanos(3), label: "bar", detail: None },
-            Message { level: 1, duration: Duration::from_nanos(2), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(1), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        // The calls to `bar` are so short that they'll be rounded to 0ms and should get collapsed
-        // when printing.
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap(),
-            "    1ms - foo\n        0ms - bar (2 calls)\n"
-        );
-    }
-
-    #[test]
-    fn test_unaccounted_for_topmost() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 1, duration: Duration::from_millis(2), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(5), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap().lines().collect::<Vec<_>>(),
-            vec![
-                "    5ms - foo",
-                "        2ms - bar",
-                "        3ms - ???",
-                // Dummy comment to improve formatting
-            ]
-        );
-    }
-
-    #[test]
-    fn test_unaccounted_for_multiple_levels() {
-        let mut result = vec![];
-        let msgs = vec![
-            Message { level: 2, duration: Duration::from_millis(3), label: "baz", detail: None },
-            Message { level: 1, duration: Duration::from_millis(5), label: "bar", detail: None },
-            Message { level: 2, duration: Duration::from_millis(2), label: "baz", detail: None },
-            Message { level: 1, duration: Duration::from_millis(4), label: "bar", detail: None },
-            Message { level: 0, duration: Duration::from_millis(9), label: "foo", detail: None },
-        ];
-        print(&msgs, Duration::from_millis(0), &mut result);
-        assert_eq!(
-            std::str::from_utf8(&result).unwrap().lines().collect::<Vec<_>>(),
-            vec![
-                "    9ms - foo",
-                "        5ms - bar",
-                "            3ms - baz",
-                "            2ms - ???",
-                "        4ms - bar",
-                "            2ms - baz",
-                "            2ms - ???",
-            ]
-        );
-    }
-}
diff --git a/crates/ra_prof/src/tree.rs b/crates/ra_prof/src/tree.rs
new file mode 100644
index 000000000..9ea5b5db8
--- /dev/null
+++ b/crates/ra_prof/src/tree.rs
@@ -0,0 +1,84 @@
+//! A simple tree implementation which tries to not allocate all over the place.
+use std::ops;
+
+use ra_arena::Arena;
+
+#[derive(Default)]
+pub struct Tree<T> {
+    nodes: Arena<Node<T>>,
+    current_path: Vec<(Idx<T>, Option<Idx<T>>)>,
+}
+
+pub type Idx<T> = ra_arena::Idx<Node<T>>;
+
+impl<T> Tree<T> {
+    pub fn start(&mut self)
+    where
+        T: Default,
+    {
+        let me = self.nodes.alloc(Node::new(T::default()));
+        if let Some((parent, last_child)) = self.current_path.last_mut() {
+            let slot = match *last_child {
+                Some(last_child) => &mut self.nodes[last_child].next_sibling,
+                None => &mut self.nodes[*parent].first_child,
+            };
+            let prev = slot.replace(me);
+            assert!(prev.is_none());
+            *last_child = Some(me);
+        }
+
+        self.current_path.push((me, None));
+    }
+
+    pub fn finish(&mut self, data: T) {
+        let (me, _last_child) = self.current_path.pop().unwrap();
+        self.nodes[me].data = data;
+    }
+
+    pub fn root(&self) -> Option<Idx<T>> {
+        self.nodes.iter().next().map(|(idx, _)| idx)
+    }
+
+    pub fn children(&self, idx: Idx<T>) -> impl Iterator<Item = Idx<T>> + '_ {
+        NodeIter { nodes: &self.nodes, next: self.nodes[idx].first_child }
+    }
+    pub fn clear(&mut self) {
+        self.nodes.clear();
+        self.current_path.clear();
+    }
+}
+
+impl<T> ops::Index<Idx<T>> for Tree<T> {
+    type Output = T;
+    fn index(&self, index: Idx<T>) -> &T {
+        &self.nodes[index].data
+    }
+}
+
+pub struct Node<T> {
+    data: T,
+    first_child: Option<Idx<T>>,
+    next_sibling: Option<Idx<T>>,
+}
+
+impl<T> Node<T> {
+    fn new(data: T) -> Node<T> {
+        Node { data, first_child: None, next_sibling: None }
+    }
+}
+
+struct NodeIter<'a, T> {
+    nodes: &'a Arena<Node<T>>,
+    next: Option<Idx<T>>,
+}
+
+impl<'a, T> Iterator for NodeIter<'a, T> {
+    type Item = Idx<T>;
+
+    fn next(&mut self) -> Option<Idx<T>> {
+        self.next.map(|next| {
+            self.next = self.nodes[next].next_sibling;
+            next
+        })
+    }
+}
diff --git a/crates/rust-analyzer/src/cargo_target_spec.rs b/crates/rust-analyzer/src/cargo_target_spec.rs
index c2ece49f4..10c25666a 100644
--- a/crates/rust-analyzer/src/cargo_target_spec.rs
+++ b/crates/rust-analyzer/src/cargo_target_spec.rs
@@ -9,6 +9,7 @@ use crate::{world::WorldSnapshot, Result};
 ///
 /// We use it to cook up the set of cli args we need to pass to Cargo to
 /// build/test/run the target.
+#[derive(Clone)]
 pub(crate) struct CargoTargetSpec {
     pub(crate) package: String,
     pub(crate) target: String,
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 715eddadb..74a63e32a 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -69,6 +69,7 @@ pub enum RustfmtConfig {
 pub struct ClientCapsConfig {
     pub location_link: bool,
     pub line_folding_only: bool,
+    pub hierarchical_symbols: bool,
 }
 
 impl Default for Config {
@@ -215,6 +216,11 @@ impl Config {
         if let Some(value) = caps.folding_range.as_ref().and_then(|it| it.line_folding_only) {
             self.client_caps.line_folding_only = value
         }
+        if let Some(value) =
+            caps.document_symbol.as_ref().and_then(|it| it.hierarchical_document_symbol_support)
+        {
+            self.client_caps.hierarchical_symbols = value
+        }
         self.completion.allow_snippets(false);
         if let Some(completion) = &caps.completion {
             if let Some(completion_item) = &completion.completion_item {
diff --git a/crates/rust-analyzer/src/conv.rs b/crates/rust-analyzer/src/conv.rs
index b0f911f71..ffe3ea84d 100644
--- a/crates/rust-analyzer/src/conv.rs
+++ b/crates/rust-analyzer/src/conv.rs
@@ -25,7 +25,8 @@ use crate::{
     Result,
 };
 use semantic_tokens::{
-    ATTRIBUTE, BUILTIN_TYPE, ENUM_MEMBER, LIFETIME, TYPE_ALIAS, UNION, UNRESOLVED_REFERENCE,
+    ATTRIBUTE, BUILTIN_TYPE, ENUM_MEMBER, FORMAT_SPECIFIER, LIFETIME, TYPE_ALIAS, UNION,
+    UNRESOLVED_REFERENCE,
 };
 
 pub trait Conv {
@@ -381,6 +382,7 @@ impl Conv for Highlight {
             HighlightTag::Attribute => ATTRIBUTE,
             HighlightTag::Keyword => SemanticTokenType::KEYWORD,
             HighlightTag::UnresolvedReference => UNRESOLVED_REFERENCE,
+            HighlightTag::FormatSpecifier => FORMAT_SPECIFIER,
         };
 
         for modifier in self.modifiers.iter() {
diff --git a/crates/rust-analyzer/src/main_loop/handlers.rs b/crates/rust-analyzer/src/main_loop/handlers.rs
index c2c1a23cd..6caaf5f88 100644
--- a/crates/rust-analyzer/src/main_loop/handlers.rs
+++ b/crates/rust-analyzer/src/main_loop/handlers.rs
@@ -16,7 +16,7 @@ use lsp_types::{
     Hover, HoverContents, Location, MarkupContent, MarkupKind, Position, PrepareRenameResponse,
     Range, RenameParams, SemanticTokensParams, SemanticTokensRangeParams,
     SemanticTokensRangeResult, SemanticTokensResult, SymbolInformation, TextDocumentIdentifier,
-    TextEdit, WorkspaceEdit,
+    TextEdit, Url, WorkspaceEdit,
 };
 use ra_ide::{
     Assist, AssistId, FileId, FilePosition, FileRange, Query, RangeInfo, Runnable, RunnableKind,
@@ -219,6 +219,7 @@ pub fn handle_document_symbol(
     let _p = profile("handle_document_symbol");
     let file_id = params.text_document.try_conv_with(&world)?;
     let line_index = world.analysis().file_line_index(file_id)?;
+    let url = file_id.try_conv_with(&world)?;
 
     let mut parents: Vec<(DocumentSymbol, Option<usize>)> = Vec::new();
 
@@ -234,10 +235,10 @@ pub fn handle_document_symbol(
         };
         parents.push((doc_symbol, symbol.parent));
     }
-    let mut res = Vec::new();
+    let mut document_symbols = Vec::new();
     while let Some((node, parent)) = parents.pop() {
         match parent {
-            None => res.push(node),
+            None => document_symbols.push(node),
             Some(i) => {
                 let children = &mut parents[i].0.children;
                 if children.is_none() {
@@ -248,7 +249,35 @@ pub fn handle_document_symbol(
         }
     }
 
-    Ok(Some(res.into()))
+    if world.config.client_caps.hierarchical_symbols {
+        Ok(Some(document_symbols.into()))
+    } else {
+        let mut symbol_information = Vec::<SymbolInformation>::new();
+        for symbol in document_symbols {
+            flatten_document_symbol(&symbol, None, &url, &mut symbol_information);
+        }
+
+        Ok(Some(symbol_information.into()))
+    }
+}
+
+fn flatten_document_symbol(
+    symbol: &DocumentSymbol,
+    container_name: Option<String>,
+    url: &Url,
+    res: &mut Vec<SymbolInformation>,
+) {
+    res.push(SymbolInformation {
+        name: symbol.name.clone(),
+        kind: symbol.kind,
+        deprecated: symbol.deprecated,
+        location: Location::new(url.clone(), symbol.range),
+        container_name: container_name,
+    });
+
+    for child in symbol.children.iter().flatten() {
+        flatten_document_symbol(child, Some(symbol.name.clone()), url, res);
+    }
 }
 
 pub fn handle_workspace_symbol(
@@ -364,28 +393,37 @@ pub fn handle_runnables(
         }
         res.push(to_lsp_runnable(&world, file_id, runnable)?);
     }
-    let mut check_args = vec!["check".to_string()];
-    let label;
+    // Add `cargo check` and `cargo test` for the whole package
     match CargoTargetSpec::for_file(&world, file_id)? {
         Some(spec) => {
-            label = format!("cargo check -p {}", spec.package);
-            spec.push_to(&mut check_args);
+            for &cmd in ["check", "test"].iter() {
+                res.push(req::Runnable {
+                    range: Default::default(),
+                    label: format!("cargo {} -p {}", cmd, spec.package),
+                    bin: "cargo".to_string(),
+                    args: {
+                        let mut args = vec![cmd.to_string()];
+                        spec.clone().push_to(&mut args);
+                        args
+                    },
+                    extra_args: Vec::new(),
+                    env: FxHashMap::default(),
+                    cwd: workspace_root.map(|root| root.to_owned()),
+                })
+            }
         }
         None => {
-            label = "cargo check --all".to_string();
-            check_args.push("--all".to_string())
+            res.push(req::Runnable {
+                range: Default::default(),
+                label: "cargo check --workspace".to_string(),
+                bin: "cargo".to_string(),
+                args: vec!["check".to_string(), "--workspace".to_string()],
+                extra_args: Vec::new(),
+                env: FxHashMap::default(),
+                cwd: workspace_root.map(|root| root.to_owned()),
+            });
         }
     }
-    // Always add `cargo check`.
-    res.push(req::Runnable {
-        range: Default::default(),
-        label,
-        bin: "cargo".to_string(),
-        args: check_args,
-        extra_args: Vec::new(),
-        env: FxHashMap::default(),
-        cwd: workspace_root.map(|root| root.to_owned()),
-    });
     Ok(res)
 }
 
diff --git a/crates/rust-analyzer/src/semantic_tokens.rs b/crates/rust-analyzer/src/semantic_tokens.rs
index 10fe696f6..71f4f58a3 100644
--- a/crates/rust-analyzer/src/semantic_tokens.rs
+++ b/crates/rust-analyzer/src/semantic_tokens.rs
@@ -12,6 +12,7 @@ pub(crate) const TYPE_ALIAS: SemanticTokenType = SemanticTokenType::new("typeAli
 pub(crate) const UNION: SemanticTokenType = SemanticTokenType::new("union");
 pub(crate) const UNRESOLVED_REFERENCE: SemanticTokenType =
     SemanticTokenType::new("unresolvedReference");
+pub(crate) const FORMAT_SPECIFIER: SemanticTokenType = SemanticTokenType::new("formatSpecifier");
 
 pub(crate) const CONSTANT: SemanticTokenModifier = SemanticTokenModifier::new("constant");
 pub(crate) const CONTROL_FLOW: SemanticTokenModifier = SemanticTokenModifier::new("controlFlow");
@@ -46,6 +47,7 @@ pub(crate) const SUPPORTED_TYPES: &[SemanticTokenType] = &[
     TYPE_ALIAS,
     UNION,
     UNRESOLVED_REFERENCE,
+    FORMAT_SPECIFIER,
 ];
 
 pub(crate) const SUPPORTED_MODIFIERS: &[SemanticTokenModifier] = &[
diff --git a/crates/rust-analyzer/tests/heavy_tests/main.rs b/crates/rust-analyzer/tests/heavy_tests/main.rs
index b31533e5e..f6245ddd4 100644
--- a/crates/rust-analyzer/tests/heavy_tests/main.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/main.rs
@@ -87,24 +87,15 @@ fn foo() {
             }
           },
           {
-            "args": [
-              "check",
-              "--all"
-            ],
+            "args": ["check", "--workspace"],
             "extraArgs": [],
             "bin": "cargo",
             "env": {},
             "cwd": null,
-            "label": "cargo check --all",
+            "label": "cargo check --workspace",
             "range": {
-              "end": {
-                "character": 0,
-                "line": 0
-              },
-              "start": {
-                "character": 0,
-                "line": 0
-              }
+              "end": { "character": 0, "line": 0 },
+              "start": { "character": 0, "line": 0 }
             }
           }
         ]),
@@ -145,42 +136,42 @@ fn main() {}
     server.request::<Runnables>(
         RunnablesParams { text_document: server.doc_id("foo/tests/spam.rs"), position: None },
         json!([
-          {
-            "args": [ "test", "--package", "foo", "--test", "spam" ],
-            "extraArgs": [ "test_eggs", "--exact", "--nocapture" ],
-            "bin": "cargo",
-            "env": { "RUST_BACKTRACE": "short" },
-            "label": "test test_eggs",
-            "range": {
-              "end": { "character": 17, "line": 1 },
-              "start": { "character": 0, "line": 0 }
+            {
+              "args": [ "test", "--package", "foo", "--test", "spam" ],
+              "extraArgs": [ "test_eggs", "--exact", "--nocapture" ],
+              "bin": "cargo",
+              "env": { "RUST_BACKTRACE": "short" },
+              "label": "test test_eggs",
+              "range": {
+                "end": { "character": 17, "line": 1 },
+                "start": { "character": 0, "line": 0 }
+              },
+              "cwd": server.path().join("foo")
             },
-            "cwd": server.path().join("foo")
-          },
-          {
-            "args": [
-              "check",
-              "--package",
-              "foo",
-              "--test",
-              "spam"
-            ],
-            "extraArgs": [],
-            "bin": "cargo",
-            "env": {},
-            "cwd": server.path().join("foo"),
-            "label": "cargo check -p foo",
-            "range": {
-              "end": {
-                "character": 0,
-                "line": 0
+            {
+              "args": [ "check", "--package", "foo", "--test", "spam" ],
+              "extraArgs": [],
+              "bin": "cargo",
+              "env": {},
+              "label": "cargo check -p foo",
+              "range": {
+                "end": { "character": 0, "line": 0 },
+                "start": { "character": 0, "line": 0 }
               },
-              "start": {
-                "character": 0,
-                "line": 0
-              }
+              "cwd": server.path().join("foo")
+            },
+            {
+              "args": [ "test", "--package", "foo", "--test", "spam" ],
+              "extraArgs": [],
+              "bin": "cargo",
+              "env": {},
+              "label": "cargo test -p foo",
+              "range": {
+                "end": { "character": 0, "line": 0 },
+                "start": { "character": 0, "line": 0 }
+              },
+              "cwd": server.path().join("foo")
             }
-          }
         ]),
     );
 }
diff --git a/crates/rust-analyzer/tests/heavy_tests/support.rs b/crates/rust-analyzer/tests/heavy_tests/support.rs
index 7eebedff7..e4fe3411a 100644
--- a/crates/rust-analyzer/tests/heavy_tests/support.rs
+++ b/crates/rust-analyzer/tests/heavy_tests/support.rs
@@ -62,11 +62,7 @@ impl<'a> Project<'a> {
         static INIT: Once = Once::new();
         INIT.call_once(|| {
             env_logger::builder().is_test(true).try_init().unwrap();
-            ra_prof::set_filter(if crate::PROFILE.is_empty() {
-                ra_prof::Filter::disabled()
-            } else {
-                ra_prof::Filter::from_spec(&crate::PROFILE)
-            });
+            ra_prof::init_from(crate::PROFILE);
         });
 
         let mut paths = vec![];
diff --git a/docs/dev/architecture.md b/docs/dev/architecture.md
index 0343b6c81..3a337c574 100644
--- a/docs/dev/architecture.md
+++ b/docs/dev/architecture.md
@@ -56,7 +56,7 @@ In particular, `cargo xtask codegen` generates:
 2. [`ast/generated`](https://github.com/rust-analyzer/rust-analyzer/blob/a0be39296d2925972cacd9fbf8b5fb258fad6947/crates/ra_syntax/src/ast/generated.rs)
   -- AST data structure.
 
-.3 [`doc_tests/generated`](https://github.com/rust-analyzer/rust-analyzer/blob/a0be39296d2925972cacd9fbf8b5fb258fad6947/crates/ra_assists/src/doc_tests/generated.rs),
+3. [`doc_tests/generated`](https://github.com/rust-analyzer/rust-analyzer/blob/a0be39296d2925972cacd9fbf8b5fb258fad6947/crates/ra_assists/src/doc_tests/generated.rs),
   [`test_data/parser/inline`](https://github.com/rust-analyzer/rust-analyzer/tree/a0be39296d2925972cacd9fbf8b5fb258fad6947/crates/ra_syntax/test_data/parser/inline)
   -- tests for assists and the parser.
 
diff --git a/docs/user/readme.adoc b/docs/user/readme.adoc
index ce5704836..76d065d35 100644
--- a/docs/user/readme.adoc
+++ b/docs/user/readme.adoc
@@ -23,7 +23,7 @@ https://github.com/rust-analyzer/rust-analyzer/blob/master/docs/user/readme.adoc
 
 == Installation
 
-In theory, one should be able to just install the server binary and have it automatically work with any editor.
+In theory, one should be able to just install the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>> and have it automatically work with any editor.
 We are not there yet, so some editor specific setup is required.
 
 Additionally, rust-analyzer needs the sources of the standard library.
@@ -108,15 +108,26 @@ Here are some useful self-diagnostic commands:
 * To log all LSP requests, add `"rust-analyzer.trace.server": "verbose"` to the settings and look for `Server Trace` in the panel.
 * To enable client-side logging, add `"rust-analyzer.trace.extension": true` to the settings and open the `Console` tab of VS Code developer tools.
 
-=== Language Server Binary
+=== rust-analyzer Language Server Binary
 
 Other editors generally require the `rust-analyzer` binary to be in `$PATH`.
 You can download the pre-built binary from the https://github.com/rust-analyzer/rust-analyzer/releases[releases] page. Typically, you then need to rename the binary for your platform, e.g. `rust-analyzer-mac` if you're on Mac OS, to `rust-analzyer` and make it executable in addition to moving it into a directory in your `$PATH`.
 
+On Linux to install the `rust-analyzer` binary into `~/.local/bin`, this commands could be used
+
+[source,bash]
+----
+$ curl -L https://github.com/rust-analyzer/rust-analyzer/releases/latest/download/rust-analyzer-linux -o ~/.local/bin/rust-analyzer
+$ chmod +x ~/.local/bin/rust-analyzer
+----
+
+Ensure `~/.local/bin` is listed in the `$PATH` variable.
+
 Alternatively, you can install it from source using the following command:
 
 [source,bash]
 ----
+$ git clone https://github.com/rust-analyzer/rust-analyzer.git && cd rust-analyzer
 $ cargo xtask install --server
 ----
 
@@ -139,15 +150,19 @@ $ yay -S rust-analyzer-bin
 
 === Emacs
 
-Emacs support is maintained https://github.com/emacs-lsp/lsp-mode/blob/master/lsp-rust.el[upstream].
+Prerequisites: You have installed the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>>.
 
-1. Install the most recent version of `emacs-lsp` package by following the instructions https://github.com/emacs-lsp/lsp-mode[here].
+Emacs support is maintained as part of the https://github.com/emacs-lsp/lsp-mode[Emacs-LSP] package in https://github.com/emacs-lsp/lsp-mode/blob/master/lsp-rust.el[lsp-rust.el].
+
+1. Install the most recent version of `emacs-lsp` package by following the https://github.com/emacs-lsp/lsp-mode[Emacs-LSP instructions].
 2. Set `lsp-rust-server` to `'rust-analyzer`.
 3. Run `lsp` in a Rust buffer.
 4. (Optionally) bind commands like `lsp-rust-analyzer-join-lines`, `lsp-extend-selection` and `lsp-rust-analyzer-expand-macro` to keys.
 
 === Vim
 
+Prerequisites: You have installed the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>>.
+
 The are several LSP client implementations for vim:
 
 ==== coc-rust-analyzer
@@ -205,7 +220,7 @@ Once `neovim/nvim-lsp` is installed, use `+lua require'nvim_lsp'.rust_analyzer.s
 
 === Sublime Text 3
 
-Prerequisites: You have installed the <<language-server-binary,`rust-analyzer` binary>>.
+Prerequisites: You have installed the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>>.
 
 You also need the `LSP` package. To install it:
 
@@ -218,7 +233,7 @@ Finally, with your Rust project open, in the command palette, run `LSP: Enable L
 
 If it worked, you should see "rust-analzyer, Line X, Column Y" on the left side of the bottom bar, and after waiting a bit, functionality like tooltips on hovering over variables should become available.
 
-If you get an error saying `No such file or directory: 'rust-analyzer'`, see the <<language-server-binary,section on installing the language server binary>>.
+If you get an error saying `No such file or directory: 'rust-analyzer'`, see the <<rust-analyzer-language-server-binary,`rust-analyzer` binary>> section on installing the language server binary.
 
 == Usage
 
diff --git a/editors/code/src/client.ts b/editors/code/src/client.ts
index 0ad4b63ae..cffdcf11a 100644
--- a/editors/code/src/client.ts
+++ b/editors/code/src/client.ts
@@ -4,7 +4,7 @@ import * as vscode from 'vscode';
 import { CallHierarchyFeature } from 'vscode-languageclient/lib/callHierarchy.proposed';
 import { SemanticTokensFeature, DocumentSemanticsTokensSignature } from 'vscode-languageclient/lib/semanticTokens.proposed';
 
-export async function createClient(serverPath: string, cwd: string): Promise<lc.LanguageClient> {
+export function createClient(serverPath: string, cwd: string): lc.LanguageClient {
     // '.' Is the fallback if no folder is open
     // TODO?: Workspace folders support Uri's (eg: file://test.txt).
     // It might be a good idea to test if the uri points to a file.
@@ -42,35 +42,6 @@ export async function createClient(serverPath: string, cwd: string): Promise<lc.
         clientOptions,
     );
 
-    // HACK: This is an awful way of filtering out the decorations notifications
-    // However, pending proper support, this is the most effecitve approach
-    // Proper support for this would entail a change to vscode-languageclient to allow not notifying on certain messages
-    // Or the ability to disable the serverside component of highlighting (but this means that to do tracing we need to disable hihlighting)
-    // This also requires considering our settings strategy, which is work which needs doing
-    // @ts-ignore The tracer is private to vscode-languageclient, but we need access to it to not log publishDecorations requests
-    res._tracer = {
-        log: (messageOrDataObject: string | unknown, data?: string) => {
-            if (typeof messageOrDataObject === 'string') {
-                if (
-                    messageOrDataObject.includes(
-                        'rust-analyzer/publishDecorations',
-                    ) ||
-                    messageOrDataObject.includes(
-                        'rust-analyzer/decorationsRequest',
-                    )
-                ) {
-                    // Don't log publish decorations requests
-                } else {
-                    // @ts-ignore This is just a utility function
-                    res.logTrace(messageOrDataObject, data);
-                }
-            } else {
-                // @ts-ignore
-                res.logObjectTrace(messageOrDataObject);
-            }
-        },
-    };
-
     // To turn on all proposed features use: res.registerProposedFeatures();
     // Here we want to enable CallHierarchyFeature and SemanticTokensFeature
     // since they are available on stable.
diff --git a/editors/code/src/ctx.ts b/editors/code/src/ctx.ts
index f7ed62d03..41df11991 100644
--- a/editors/code/src/ctx.ts
+++ b/editors/code/src/ctx.ts
@@ -21,7 +21,7 @@ export class Ctx {
         serverPath: string,
         cwd: string,
     ): Promise<Ctx> {
-        const client = await createClient(serverPath, cwd);
+        const client = createClient(serverPath, cwd);
         const res = new Ctx(config, extCtx, client, serverPath);
         res.pushCleanup(client.start());
         await client.onReady();