Merge #7900 #8000

7900: show function params in completion detail r=matklad a=JoshMcguigan

This resolves #7842 by updating the detail for function completions from `-> T` to `fn(T, U) -> V`. I added an expicit unit test for this, `ide_completion::render::fn_detail_includes_args_and_return_type`, which passes.

Lots of other unit tests fail (~60 of them) due to this change, although I believe the failures are purely cosmetic (they were testing the exact format of this output). I'm happy to go update those tests, but before I do that I'd like to make sure this is in fact the format we want for the detail?

edit - I realized `UPDATE_EXPECT=1 cargo test` automatically updates `expect!` tests. Big 👍 to whoever worked on that! So I'll go ahead and update all these tests soon. But I still would like to confirm `fn(T, U) -> V` is the desired content in the `detail` field. 

8000: Use hir formatter for hover text r=matklad a=oxalica

Fix #2765 , (should) fix #4665

Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>
Co-authored-by: oxalica <oxalicc@pm.me>

crates/hir/src/display.rs

@@ -0,0 +1,441 @@
+//! HirDisplay implementations for various hir types.
+use hir_def::{
+    adt::VariantData,
+    generics::{TypeParamProvenance, WherePredicate, WherePredicateTypeTarget},
+    type_ref::{TypeBound, TypeRef},
+    AdtId, GenericDefId,
+};
+use hir_ty::display::{
+    write_bounds_like_dyn_trait_with_prefix, write_visibility, HirDisplay, HirDisplayError,
+    HirFormatter,
+};
+use syntax::ast::{self, NameOwner};
+
+use crate::{
+    Const, ConstParam, Enum, Field, Function, HasVisibility, Module, Static, Struct, Substs, Trait,
+    Type, TypeAlias, TypeParam, Union, Variant,
+};
+
+impl HirDisplay for Function {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        let data = f.db.function_data(self.id);
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        let qual = &data.qualifier;
+        if qual.is_default {
+            write!(f, "default ")?;
+        }
+        if qual.is_const {
+            write!(f, "const ")?;
+        }
+        if qual.is_async {
+            write!(f, "async ")?;
+        }
+        if qual.is_unsafe {
+            write!(f, "unsafe ")?;
+        }
+        if let Some(abi) = &qual.abi {
+            // FIXME: String escape?
+            write!(f, "extern \"{}\" ", abi)?;
+        }
+        write!(f, "fn {}", data.name)?;
+
+        write_generic_params(GenericDefId::FunctionId(self.id), f)?;
+
+        write!(f, "(")?;
+
+        let write_self_param = |ty: &TypeRef, f: &mut HirFormatter| match ty {
+            TypeRef::Path(p) if p.is_self_type() => write!(f, "self"),
+            TypeRef::Reference(inner, lifetime, mut_) if matches!(&**inner,TypeRef::Path(p) if p.is_self_type()) =>
+            {
+                write!(f, "&")?;
+                if let Some(lifetime) = lifetime {
+                    write!(f, "{} ", lifetime.name)?;
+                }
+                if let hir_def::type_ref::Mutability::Mut = mut_ {
+                    write!(f, "mut ")?;
+                }
+                write!(f, "self")
+            }
+            _ => {
+                write!(f, "self: ")?;
+                ty.hir_fmt(f)
+            }
+        };
+
+        let mut first = true;
+        for (param, type_ref) in self.assoc_fn_params(f.db).into_iter().zip(&data.params) {
+            if !first {
+                write!(f, ", ")?;
+            } else {
+                first = false;
+                if data.has_self_param {
+                    write_self_param(type_ref, f)?;
+                    continue;
+                }
+            }
+            match param.pattern_source(f.db) {
+                Some(ast::Pat::IdentPat(p)) if p.name().is_some() => {
+                    write!(f, "{}: ", p.name().unwrap())?
+                }
+                _ => write!(f, "_: ")?,
+            }
+            // FIXME: Use resolved `param.ty` or raw `type_ref`?
+            // The former will ignore lifetime arguments currently.
+            type_ref.hir_fmt(f)?;
+        }
+        write!(f, ")")?;
+
+        // `FunctionData::ret_type` will be `::core::future::Future<Output = ...>` for async fns.
+        // Use ugly pattern match to strip the Future trait.
+        // Better way?
+        let ret_type = if !qual.is_async {
+            &data.ret_type
+        } else {
+            match &data.ret_type {
+                TypeRef::ImplTrait(bounds) => match &bounds[0] {
+                    TypeBound::Path(path) => {
+                        path.segments().iter().last().unwrap().args_and_bindings.unwrap().bindings
+                            [0]
+                        .type_ref
+                        .as_ref()
+                        .unwrap()
+                    }
+                    _ => panic!("Async fn ret_type should be impl Future"),
+                },
+                _ => panic!("Async fn ret_type should be impl Future"),
+            }
+        };
+
+        match ret_type {
+            TypeRef::Tuple(tup) if tup.is_empty() => {}
+            ty => {
+                write!(f, " -> ")?;
+                ty.hir_fmt(f)?;
+            }
+        }
+
+        write_where_clause(GenericDefId::FunctionId(self.id), f)?;
+
+        Ok(())
+    }
+}
+
+impl HirDisplay for Struct {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        write!(f, "struct ")?;
+        write!(f, "{}", self.name(f.db))?;
+        let def_id = GenericDefId::AdtId(AdtId::StructId(self.id));
+        write_generic_params(def_id, f)?;
+        write_where_clause(def_id, f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Enum {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        write!(f, "enum ")?;
+        write!(f, "{}", self.name(f.db))?;
+        let def_id = GenericDefId::AdtId(AdtId::EnumId(self.id));
+        write_generic_params(def_id, f)?;
+        write_where_clause(def_id, f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Union {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        write!(f, "union ")?;
+        write!(f, "{}", self.name(f.db))?;
+        let def_id = GenericDefId::AdtId(AdtId::UnionId(self.id));
+        write_generic_params(def_id, f)?;
+        write_where_clause(def_id, f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Field {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.parent.module(f.db).id, self.visibility(f.db), f)?;
+        write!(f, "{}: ", self.name(f.db))?;
+        self.signature_ty(f.db).hir_fmt(f)
+    }
+}
+
+impl HirDisplay for Variant {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write!(f, "{}", self.name(f.db))?;
+        let data = self.variant_data(f.db);
+        match &*data {
+            VariantData::Unit => {}
+            VariantData::Tuple(fields) => {
+                write!(f, "(")?;
+                let mut first = true;
+                for (_, field) in fields.iter() {
+                    if first {
+                        first = false;
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    // Enum variant fields must be pub.
+                    field.type_ref.hir_fmt(f)?;
+                }
+                write!(f, ")")?;
+            }
+            VariantData::Record(fields) => {
+                write!(f, " {{")?;
+                let mut first = true;
+                for (_, field) in fields.iter() {
+                    if first {
+                        first = false;
+                        write!(f, " ")?;
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    // Enum variant fields must be pub.
+                    write!(f, "{}: ", field.name)?;
+                    field.type_ref.hir_fmt(f)?;
+                }
+                write!(f, " }}")?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for Type {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        self.ty.value.hir_fmt(f)
+    }
+}
+
+impl HirDisplay for TypeParam {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write!(f, "{}", self.name(f.db))?;
+        let bounds = f.db.generic_predicates_for_param(self.id);
+        let substs = Substs::type_params(f.db, self.id.parent);
+        let predicates = bounds.iter().cloned().map(|b| b.subst(&substs)).collect::<Vec<_>>();
+        if !(predicates.is_empty() || f.omit_verbose_types()) {
+            write_bounds_like_dyn_trait_with_prefix(":", &predicates, f)?;
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for ConstParam {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write!(f, "const {}: ", self.name(f.db))?;
+        self.ty(f.db).hir_fmt(f)
+    }
+}
+
+fn write_generic_params(def: GenericDefId, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+    let params = f.db.generic_params(def);
+    if params.lifetimes.is_empty()
+        && params.consts.is_empty()
+        && params
+            .types
+            .iter()
+            .all(|(_, param)| !matches!(param.provenance, TypeParamProvenance::TypeParamList))
+    {
+        return Ok(());
+    }
+    write!(f, "<")?;
+
+    let mut first = true;
+    let mut delim = |f: &mut HirFormatter| {
+        if first {
+            first = false;
+            Ok(())
+        } else {
+            write!(f, ", ")
+        }
+    };
+    for (_, lifetime) in params.lifetimes.iter() {
+        delim(f)?;
+        write!(f, "{}", lifetime.name)?;
+    }
+    for (_, ty) in params.types.iter() {
+        if ty.provenance != TypeParamProvenance::TypeParamList {
+            continue;
+        }
+        if let Some(name) = &ty.name {
+            delim(f)?;
+            write!(f, "{}", name)?;
+            if let Some(default) = &ty.default {
+                write!(f, " = ")?;
+                default.hir_fmt(f)?;
+            }
+        }
+    }
+    for (_, konst) in params.consts.iter() {
+        delim(f)?;
+        write!(f, "const {}: ", konst.name)?;
+        konst.ty.hir_fmt(f)?;
+    }
+
+    write!(f, ">")?;
+    Ok(())
+}
+
+fn write_where_clause(def: GenericDefId, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+    let params = f.db.generic_params(def);
+    if params.where_predicates.is_empty() {
+        return Ok(());
+    }
+
+    let write_target = |target: &WherePredicateTypeTarget, f: &mut HirFormatter| match target {
+        WherePredicateTypeTarget::TypeRef(ty) => ty.hir_fmt(f),
+        WherePredicateTypeTarget::TypeParam(id) => match &params.types[*id].name {
+            Some(name) => write!(f, "{}", name),
+            None => write!(f, "{{unnamed}}"),
+        },
+    };
+
+    write!(f, "\nwhere")?;
+
+    for (pred_idx, pred) in params.where_predicates.iter().enumerate() {
+        let prev_pred =
+            if pred_idx == 0 { None } else { Some(&params.where_predicates[pred_idx - 1]) };
+
+        let new_predicate = |f: &mut HirFormatter| {
+            write!(f, "{}", if pred_idx == 0 { "\n    " } else { ",\n    " })
+        };
+
+        match pred {
+            WherePredicate::TypeBound { target, bound } => {
+                if matches!(prev_pred, Some(WherePredicate::TypeBound { target: target_, .. }) if target_ == target)
+                {
+                    write!(f, " + ")?;
+                } else {
+                    new_predicate(f)?;
+                    write_target(target, f)?;
+                    write!(f, ": ")?;
+                }
+                bound.hir_fmt(f)?;
+            }
+            WherePredicate::Lifetime { target, bound } => {
+                if matches!(prev_pred, Some(WherePredicate::Lifetime { target: target_, .. }) if target_ == target)
+                {
+                    write!(f, " + {}", bound.name)?;
+                } else {
+                    new_predicate(f)?;
+                    write!(f, "{}: {}", target.name, bound.name)?;
+                }
+            }
+            WherePredicate::ForLifetime { lifetimes, target, bound } => {
+                if matches!(
+                    prev_pred,
+                    Some(WherePredicate::ForLifetime { lifetimes: lifetimes_, target: target_, .. })
+                    if lifetimes_ == lifetimes && target_ == target,
+                ) {
+                    write!(f, " + ")?;
+                } else {
+                    new_predicate(f)?;
+                    write!(f, "for<")?;
+                    for (idx, lifetime) in lifetimes.iter().enumerate() {
+                        if idx != 0 {
+                            write!(f, ", ")?;
+                        }
+                        write!(f, "{}", lifetime)?;
+                    }
+                    write!(f, "> ")?;
+                    write_target(target, f)?;
+                    write!(f, ": ")?;
+                }
+                bound.hir_fmt(f)?;
+            }
+        }
+    }
+
+    // End of final predicate. There must be at least one predicate here.
+    write!(f, ",")?;
+
+    Ok(())
+}
+
+impl HirDisplay for Const {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        let data = f.db.const_data(self.id);
+        write!(f, "const ")?;
+        match &data.name {
+            Some(name) => write!(f, "{}: ", name)?,
+            None => write!(f, "_: ")?,
+        }
+        data.type_ref.hir_fmt(f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Static {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        let data = f.db.static_data(self.id);
+        write!(f, "static ")?;
+        if data.mutable {
+            write!(f, "mut ")?;
+        }
+        match &data.name {
+            Some(name) => write!(f, "{}: ", name)?,
+            None => write!(f, "_: ")?,
+        }
+        data.type_ref.hir_fmt(f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for Trait {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        let data = f.db.trait_data(self.id);
+        if data.is_unsafe {
+            write!(f, "unsafe ")?;
+        }
+        if data.is_auto {
+            write!(f, "auto ")?;
+        }
+        write!(f, "trait {}", data.name)?;
+        let def_id = GenericDefId::TraitId(self.id);
+        write_generic_params(def_id, f)?;
+        if !data.bounds.is_empty() {
+            write!(f, ": ")?;
+            f.write_joined(&*data.bounds, " + ")?;
+        }
+        write_where_clause(def_id, f)?;
+        Ok(())
+    }
+}
+
+impl HirDisplay for TypeAlias {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        write_visibility(self.module(f.db).id, self.visibility(f.db), f)?;
+        let data = f.db.type_alias_data(self.id);
+        write!(f, "type {}", data.name)?;
+        if !data.bounds.is_empty() {
+            write!(f, ": ")?;
+            f.write_joined(&data.bounds, " + ")?;
+        }
+        if let Some(ty) = &data.type_ref {
+            write!(f, " = ")?;
+            ty.hir_fmt(f)?;
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for Module {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        // FIXME: Module doesn't have visibility saved in data.
+        match self.name(f.db) {
+            Some(name) => write!(f, "mod {}", name),
+            None if self.crate_root(f.db) == *self => match self.krate().display_name(f.db) {
+                Some(name) => write!(f, "extern crate {}", name),
+                None => write!(f, "extern crate {{unknown}}"),
+            },
+            None => write!(f, "mod {{unnamed}}"),
+        }
+    }
+}

crates/hir/src/lib.rs

@@ -29,6 +29,8 @@ mod has_source;
 pub mod diagnostics;
 pub mod db;
 
+mod display;
+
 use std::{iter, sync::Arc};
 
 use arrayvec::ArrayVec;
@@ -50,7 +52,6 @@ use hir_def::{
 use hir_expand::{diagnostics::DiagnosticSink, name::name, MacroDefKind};
 use hir_ty::{
     autoderef,
-    display::{write_bounds_like_dyn_trait_with_prefix, HirDisplayError, HirFormatter},
     method_resolution::{self, TyFingerprint},
     primitive::UintTy,
     to_assoc_type_id,
@@ -572,6 +573,12 @@ impl Struct {
     }
 }
 
+impl HasVisibility for Struct {
+    fn visibility(&self, db: &dyn HirDatabase) -> Visibility {
+        db.struct_data(self.id).visibility.resolve(db.upcast(), &self.id.resolver(db.upcast()))
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Union {
     pub(crate) id: UnionId,
@@ -604,6 +611,12 @@ impl Union {
     }
 }
 
+impl HasVisibility for Union {
+    fn visibility(&self, db: &dyn HirDatabase) -> Visibility {
+        db.union_data(self.id).visibility.resolve(db.upcast(), &self.id.resolver(db.upcast()))
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Enum {
     pub(crate) id: EnumId,
@@ -631,6 +644,12 @@ impl Enum {
     }
 }
 
+impl HasVisibility for Enum {
+    fn visibility(&self, db: &dyn HirDatabase) -> Visibility {
+        db.enum_data(self.id).visibility.resolve(db.upcast(), &self.id.resolver(db.upcast()))
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Variant {
     pub(crate) parent: Enum,
@@ -822,7 +841,8 @@ impl Function {
         db.function_data(self.id)
             .params
             .iter()
-            .map(|type_ref| {
+            .enumerate()
+            .map(|(idx, type_ref)| {
                 let ty = Type {
                     krate,
                     ty: InEnvironment {
@@ -830,7 +850,7 @@ impl Function {
                         environment: environment.clone(),
                     },
                 };
-                Param { ty }
+                Param { func: self, ty, idx }
             })
             .collect()
     }
@@ -844,7 +864,7 @@ impl Function {
     }
 
     pub fn is_unsafe(self, db: &dyn HirDatabase) -> bool {
-        db.function_data(self.id).is_unsafe
+        db.function_data(self.id).qualifier.is_unsafe
     }
 
     pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
@@ -893,6 +913,9 @@ impl From<hir_ty::Mutability> for Access {
 
 #[derive(Debug)]
 pub struct Param {
+    func: Function,
+    /// The index in parameter list, including self parameter.
+    idx: usize,
     ty: Type,
 }
 
@@ -900,6 +923,15 @@ impl Param {
     pub fn ty(&self) -> &Type {
         &self.ty
     }
+
+    pub fn pattern_source(&self, db: &dyn HirDatabase) -> Option<ast::Pat> {
+        let params = self.func.source(db)?.value.param_list()?;
+        if params.self_param().is_some() {
+            params.params().nth(self.idx.checked_sub(1)?)?.pat()
+        } else {
+            params.params().nth(self.idx)?.pat()
+        }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -922,6 +954,14 @@ impl SelfParam {
             })
             .unwrap_or(Access::Owned)
     }
+
+    pub fn display(self, db: &dyn HirDatabase) -> &'static str {
+        match self.access(db) {
+            Access::Shared => "&self",
+            Access::Exclusive => "&mut self",
+            Access::Owned => "self",
+        }
+    }
 }
 
 impl HasVisibility for Function {
@@ -949,6 +989,10 @@ impl Const {
     pub fn name(self, db: &dyn HirDatabase) -> Option<Name> {
         db.const_data(self.id).name.clone()
     }
+
+    pub fn type_ref(self, db: &dyn HirDatabase) -> TypeRef {
+        db.const_data(self.id).type_ref.clone()
+    }
 }
 
 impl HasVisibility for Const {
@@ -982,6 +1026,12 @@ impl Static {
     }
 }
 
+impl HasVisibility for Static {
+    fn visibility(&self, db: &dyn HirDatabase) -> Visibility {
+        db.static_data(self.id).visibility.resolve(db.upcast(), &self.id.resolver(db.upcast()))
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Trait {
     pub(crate) id: TraitId,
@@ -1001,7 +1051,13 @@ impl Trait {
     }
 
     pub fn is_auto(self, db: &dyn HirDatabase) -> bool {
-        db.trait_data(self.id).auto
+        db.trait_data(self.id).is_auto
+    }
+}
+
+impl HasVisibility for Trait {
+    fn visibility(&self, db: &dyn HirDatabase) -> Visibility {
+        db.trait_data(self.id).visibility.resolve(db.upcast(), &self.id.resolver(db.upcast()))
     }
 }
 
@@ -1413,19 +1469,6 @@ impl TypeParam {
     }
 }
 
-impl HirDisplay for TypeParam {
-    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        write!(f, "{}", self.name(f.db))?;
-        let bounds = f.db.generic_predicates_for_param(self.id);
-        let substs = Substs::type_params(f.db, self.id.parent);
-        let predicates = bounds.iter().cloned().map(|b| b.subst(&substs)).collect::<Vec<_>>();
-        if !(predicates.is_empty() || f.omit_verbose_types()) {
-            write_bounds_like_dyn_trait_with_prefix(":", &predicates, f)?;
-        }
-        Ok(())
-    }
-}
-
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct LifetimeParam {
     pub(crate) id: LifetimeParamId,
@@ -2059,12 +2102,6 @@ impl Type {
     }
 }
 
-impl HirDisplay for Type {
-    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        self.ty.value.hir_fmt(f)
-    }
-}
-
 // FIXME: closures
 #[derive(Debug)]
 pub struct Callable {

crates/hir_def/src/adt.rs

@@ -31,12 +31,14 @@ pub struct StructData {
     pub name: Name,
     pub variant_data: Arc<VariantData>,
     pub repr: Option<ReprKind>,
+    pub visibility: RawVisibility,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct EnumData {
     pub name: Name,
     pub variants: Arena<EnumVariantData>,
+    pub visibility: RawVisibility,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -102,6 +104,7 @@ impl StructData {
             name: strukt.name.clone(),
             variant_data: Arc::new(variant_data),
             repr,
+            visibility: item_tree[strukt.visibility].clone(),
         })
     }
     pub(crate) fn union_data_query(db: &dyn DefDatabase, id: UnionId) -> Arc<StructData> {
@@ -118,6 +121,7 @@ impl StructData {
             name: union.name.clone(),
             variant_data: Arc::new(variant_data),
             repr,
+            visibility: item_tree[union.visibility].clone(),
         })
     }
 }
@@ -150,7 +154,11 @@ impl EnumData {
             }
         }
 
-        Arc::new(EnumData { name: enum_.name.clone(), variants })
+        Arc::new(EnumData {
+            name: enum_.name.clone(),
+            variants,
+            visibility: item_tree[enum_.visibility].clone(),
+        })
     }
 
     pub fn variant(&self, name: &Name) -> Option<LocalEnumVariantId> {

crates/hir_def/src/data.rs

@@ -9,7 +9,7 @@ use crate::{
     attr::Attrs,
     body::Expander,
     db::DefDatabase,
-    item_tree::{AssocItem, ItemTreeId, ModItem},
+    item_tree::{AssocItem, FunctionQualifier, ItemTreeId, ModItem},
     type_ref::{TypeBound, TypeRef},
     visibility::RawVisibility,
     AssocContainerId, AssocItemId, ConstId, ConstLoc, FunctionId, FunctionLoc, HasModule, ImplId,
@@ -26,9 +26,9 @@ pub struct FunctionData {
     /// can be called as a method.
     pub has_self_param: bool,
     pub has_body: bool,
-    pub is_unsafe: bool,
+    pub qualifier: FunctionQualifier,
+    pub is_in_extern_block: bool,
     pub is_varargs: bool,
-    pub is_extern: bool,
     pub visibility: RawVisibility,
 }
 
@@ -46,9 +46,9 @@ impl FunctionData {
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()),
             has_self_param: func.has_self_param,
             has_body: func.has_body,
-            is_unsafe: func.is_unsafe,
+            qualifier: func.qualifier.clone(),
+            is_in_extern_block: func.is_in_extern_block,
             is_varargs: func.is_varargs,
-            is_extern: func.is_extern,
             visibility: item_tree[func.visibility].clone(),
         })
     }
@@ -87,7 +87,10 @@ impl TypeAliasData {
 pub struct TraitData {
     pub name: Name,
     pub items: Vec<(Name, AssocItemId)>,
-    pub auto: bool,
+    pub is_auto: bool,
+    pub is_unsafe: bool,
+    pub visibility: RawVisibility,
+    pub bounds: Box<[TypeBound]>,
 }
 
 impl TraitData {
@@ -96,10 +99,13 @@ impl TraitData {
         let item_tree = db.item_tree(tr_loc.id.file_id);
         let tr_def = &item_tree[tr_loc.id.value];
         let name = tr_def.name.clone();
-        let auto = tr_def.auto;
+        let is_auto = tr_def.is_auto;
+        let is_unsafe = tr_def.is_unsafe;
         let module_id = tr_loc.container;
         let container = AssocContainerId::TraitId(tr);
         let mut expander = Expander::new(db, tr_loc.id.file_id, module_id);
+        let visibility = item_tree[tr_def.visibility].clone();
+        let bounds = tr_def.bounds.clone();
 
         let items = collect_items(
             db,
@@ -111,7 +117,7 @@ impl TraitData {
             100,
         );
 
-        Arc::new(TraitData { name, items, auto })
+        Arc::new(TraitData { name, items, is_auto, is_unsafe, visibility, bounds })
     }
 
     pub fn associated_types(&self) -> impl Iterator<Item = TypeAliasId> + '_ {

crates/hir_def/src/item_tree.rs

@@ -24,7 +24,7 @@ use la_arena::{Arena, Idx, RawIdx};
 use profile::Count;
 use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
-use syntax::{ast, match_ast, SyntaxKind};
+use syntax::{ast, match_ast, SmolStr, SyntaxKind};
 
 use crate::{
     attr::{Attrs, RawAttrs},
@@ -556,16 +556,25 @@ pub struct Function {
     pub generic_params: GenericParamsId,
     pub has_self_param: bool,
     pub has_body: bool,
-    pub is_unsafe: bool,
+    pub qualifier: FunctionQualifier,
     /// Whether the function is located in an `extern` block (*not* whether it is an
     /// `extern "abi" fn`).
-    pub is_extern: bool,
+    pub is_in_extern_block: bool,
     pub params: Box<[Idx<TypeRef>]>,
     pub is_varargs: bool,
     pub ret_type: Idx<TypeRef>,
     pub ast_id: FileAstId<ast::Fn>,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FunctionQualifier {
+    pub is_default: bool,
+    pub is_const: bool,
+    pub is_async: bool,
+    pub is_unsafe: bool,
+    pub abi: Option<SmolStr>,
+}
+
 #[derive(Debug, Clone, Eq, PartialEq)]
 pub struct Struct {
     pub name: Name,
@@ -629,7 +638,9 @@ pub struct Trait {
     pub name: Name,
     pub visibility: RawVisibilityId,
     pub generic_params: GenericParamsId,
-    pub auto: bool,
+    pub is_auto: bool,
+    pub is_unsafe: bool,
+    pub bounds: Box<[TypeBound]>,
     pub items: Box<[AssocItem]>,
     pub ast_id: FileAstId<ast::Trait>,
 }

crates/hir_def/src/item_tree/lower.rs

@@ -391,14 +391,33 @@ impl Ctx {
         let has_body = func.body().is_some();
 
         let ast_id = self.source_ast_id_map.ast_id(func);
+        let qualifier = FunctionQualifier {
+            is_default: func.default_token().is_some(),
+            is_const: func.const_token().is_some(),
+            is_async: func.async_token().is_some(),
+            is_unsafe: func.unsafe_token().is_some(),
+            abi: func.abi().map(|abi| {
+                // FIXME: Abi::abi() -> Option<SyntaxToken>?
+                match abi.syntax().last_token() {
+                    Some(tok) if tok.kind() == SyntaxKind::STRING => {
+                        // FIXME: Better way to unescape?
+                        tok.text().trim_matches('"').into()
+                    }
+                    _ => {
+                        // `extern` default to be `extern "C"`.
+                        "C".into()
+                    }
+                }
+            }),
+        };
         let mut res = Function {
             name,
             visibility,
             generic_params: GenericParamsId::EMPTY,
             has_self_param,
             has_body,
-            is_unsafe: func.unsafe_token().is_some(),
-            is_extern: false,
+            qualifier,
+            is_in_extern_block: false,
             params,
             is_varargs,
             ret_type,
@@ -481,7 +500,9 @@ impl Ctx {
         let visibility = self.lower_visibility(trait_def);
         let generic_params =
             self.lower_generic_params_and_inner_items(GenericsOwner::Trait(trait_def), trait_def);
-        let auto = trait_def.auto_token().is_some();
+        let is_auto = trait_def.auto_token().is_some();
+        let is_unsafe = trait_def.unsafe_token().is_some();
+        let bounds = self.lower_type_bounds(trait_def);
         let items = trait_def.assoc_item_list().map(|list| {
             self.with_inherited_visibility(visibility, |this| {
                 list.assoc_items()
@@ -501,7 +522,9 @@ impl Ctx {
             name,
             visibility,
             generic_params,
-            auto,
+            is_auto,
+            is_unsafe,
+            bounds: bounds.into(),
             items: items.unwrap_or_default(),
             ast_id,
         };
@@ -608,8 +631,8 @@ impl Ctx {
                         ast::ExternItem::Fn(ast) => {
                             let func_id = self.lower_function(&ast)?;
                             let func = &mut self.data().functions[func_id.index];
-                            func.is_unsafe = is_intrinsic_fn_unsafe(&func.name);
-                            func.is_extern = true;
+                            func.qualifier.is_unsafe = is_intrinsic_fn_unsafe(&func.name);
+                            func.is_in_extern_block = true;
                             func_id.into()
                         }
                         ast::ExternItem::Static(ast) => {

crates/hir_def/src/path.rs

@@ -9,7 +9,10 @@ use std::{
 
 use crate::{body::LowerCtx, type_ref::LifetimeRef};
 use base_db::CrateId;
-use hir_expand::{hygiene::Hygiene, name::Name};
+use hir_expand::{
+    hygiene::Hygiene,
+    name::{name, Name},
+};
 use syntax::ast;
 
 use crate::{
@@ -209,6 +212,12 @@ impl Path {
         };
         Some(res)
     }
+
+    pub fn is_self_type(&self) -> bool {
+        self.type_anchor.is_none()
+            && self.generic_args == &[None]
+            && self.mod_path.as_ident() == Some(&name!(Self))
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]

crates/hir_ty/src/diagnostics/decl_check.rs

@@ -91,7 +91,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
     fn validate_func(&mut self, func: FunctionId) {
         let data = self.db.function_data(func);
-        if data.is_extern {
+        if data.is_in_extern_block {
             cov_mark::hit!(extern_func_incorrect_case_ignored);
             return;
         }

crates/hir_ty/src/diagnostics/unsafe_check.rs

@@ -32,7 +32,7 @@ impl<'a, 'b> UnsafeValidator<'a, 'b> {
         let def = self.owner.into();
         let unsafe_expressions = unsafe_expressions(db, self.infer.as_ref(), def);
         let is_unsafe = match self.owner {
-            DefWithBodyId::FunctionId(it) => db.function_data(it).is_unsafe,
+            DefWithBodyId::FunctionId(it) => db.function_data(it).qualifier.is_unsafe,
             DefWithBodyId::StaticId(_) | DefWithBodyId::ConstId(_) => false,
         };
         if is_unsafe
@@ -86,7 +86,7 @@ fn walk_unsafe(
     match expr {
         &Expr::Call { callee, .. } => {
             if let Some(func) = infer[callee].as_fn_def(db) {
-                if db.function_data(func).is_unsafe {
+                if db.function_data(func).qualifier.is_unsafe {
                     unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
             }
@@ -103,7 +103,7 @@ fn walk_unsafe(
         Expr::MethodCall { .. } => {
             if infer
                 .method_resolution(current)
-                .map(|func| db.function_data(func).is_unsafe)
+                .map(|func| db.function_data(func).qualifier.is_unsafe)
                 .unwrap_or(false)
             {
                 unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });

crates/hir_ty/src/display.rs

@@ -5,7 +5,13 @@ use std::{borrow::Cow, fmt};
 use arrayvec::ArrayVec;
 use chalk_ir::Mutability;
 use hir_def::{
-    db::DefDatabase, find_path, generics::TypeParamProvenance, item_scope::ItemInNs,
+    db::DefDatabase,
+    find_path,
+    generics::TypeParamProvenance,
+    item_scope::ItemInNs,
+    path::{GenericArg, Path, PathKind},
+    type_ref::{TypeBound, TypeRef},
+    visibility::Visibility,
     AssocContainerId, Lookup, ModuleId, TraitId,
 };
 use hir_expand::name::Name;
@@ -232,7 +238,7 @@ where
 
 const TYPE_HINT_TRUNCATION: &str = "…";
 
-impl HirDisplay for &Ty {
+impl<T: HirDisplay> HirDisplay for &'_ T {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         HirDisplay::hir_fmt(*self, f)
     }
@@ -761,12 +767,6 @@ impl HirDisplay for TraitRef {
     }
 }
 
-impl HirDisplay for &GenericPredicate {
-    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
-        HirDisplay::hir_fmt(*self, f)
-    }
-}
-
 impl HirDisplay for GenericPredicate {
     fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
         if f.should_truncate() {
@@ -825,3 +825,190 @@ impl HirDisplay for Obligation {
         }
     }
 }
+
+pub fn write_visibility(
+    module_id: ModuleId,
+    vis: Visibility,
+    f: &mut HirFormatter,
+) -> Result<(), HirDisplayError> {
+    match vis {
+        Visibility::Public => write!(f, "pub "),
+        Visibility::Module(vis_id) => {
+            let def_map = module_id.def_map(f.db.upcast());
+            let root_module_id = def_map.module_id(def_map.root());
+            if vis_id == module_id {
+                // pub(self) or omitted
+                Ok(())
+            } else if root_module_id == vis_id {
+                write!(f, "pub(crate) ")
+            } else if module_id.containing_module(f.db.upcast()) == Some(vis_id) {
+                write!(f, "pub(super) ")
+            } else {
+                write!(f, "pub(in ...) ")
+            }
+        }
+    }
+}
+
+impl HirDisplay for TypeRef {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            TypeRef::Never => write!(f, "!")?,
+            TypeRef::Placeholder => write!(f, "_")?,
+            TypeRef::Tuple(elems) => {
+                write!(f, "(")?;
+                f.write_joined(elems, ", ")?;
+                if elems.len() == 1 {
+                    write!(f, ",")?;
+                }
+                write!(f, ")")?;
+            }
+            TypeRef::Path(path) => path.hir_fmt(f)?,
+            TypeRef::RawPtr(inner, mutability) => {
+                let mutability = match mutability {
+                    hir_def::type_ref::Mutability::Shared => "*const ",
+                    hir_def::type_ref::Mutability::Mut => "*mut ",
+                };
+                write!(f, "{}", mutability)?;
+                inner.hir_fmt(f)?;
+            }
+            TypeRef::Reference(inner, lifetime, mutability) => {
+                let mutability = match mutability {
+                    hir_def::type_ref::Mutability::Shared => "",
+                    hir_def::type_ref::Mutability::Mut => "mut ",
+                };
+                write!(f, "&")?;
+                if let Some(lifetime) = lifetime {
+                    write!(f, "{} ", lifetime.name)?;
+                }
+                write!(f, "{}", mutability)?;
+                inner.hir_fmt(f)?;
+            }
+            TypeRef::Array(inner) => {
+                write!(f, "[")?;
+                inner.hir_fmt(f)?;
+                // FIXME: Array length?
+                write!(f, "; _]")?;
+            }
+            TypeRef::Slice(inner) => {
+                write!(f, "[")?;
+                inner.hir_fmt(f)?;
+                write!(f, "]")?;
+            }
+            TypeRef::Fn(tys, is_varargs) => {
+                // FIXME: Function pointer qualifiers.
+                write!(f, "fn(")?;
+                f.write_joined(&tys[..tys.len() - 1], ", ")?;
+                if *is_varargs {
+                    write!(f, "{}...", if tys.len() == 1 { "" } else { ", " })?;
+                }
+                write!(f, ")")?;
+                let ret_ty = tys.last().unwrap();
+                match ret_ty {
+                    TypeRef::Tuple(tup) if tup.is_empty() => {}
+                    _ => {
+                        write!(f, " -> ")?;
+                        ret_ty.hir_fmt(f)?;
+                    }
+                }
+            }
+            TypeRef::ImplTrait(bounds) => {
+                write!(f, "impl ")?;
+                f.write_joined(bounds, " + ")?;
+            }
+            TypeRef::DynTrait(bounds) => {
+                write!(f, "dyn ")?;
+                f.write_joined(bounds, " + ")?;
+            }
+            TypeRef::Error => write!(f, "{{error}}")?,
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for TypeBound {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            TypeBound::Path(path) => path.hir_fmt(f),
+            TypeBound::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
+            TypeBound::Error => write!(f, "{{error}}"),
+        }
+    }
+}
+
+impl HirDisplay for Path {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match (self.type_anchor(), self.kind()) {
+            (Some(anchor), _) => {
+                write!(f, "<")?;
+                anchor.hir_fmt(f)?;
+                write!(f, ">")?;
+            }
+            (_, PathKind::Plain) => {}
+            (_, PathKind::Abs) => write!(f, "::")?,
+            (_, PathKind::Crate) => write!(f, "crate")?,
+            (_, PathKind::Super(0)) => write!(f, "self")?,
+            (_, PathKind::Super(n)) => {
+                write!(f, "super")?;
+                for _ in 0..*n {
+                    write!(f, "::super")?;
+                }
+            }
+            (_, PathKind::DollarCrate(_)) => write!(f, "{{extern_crate}}")?,
+        }
+
+        for (seg_idx, segment) in self.segments().iter().enumerate() {
+            if seg_idx != 0 {
+                write!(f, "::")?;
+            }
+            write!(f, "{}", segment.name)?;
+            if let Some(generic_args) = segment.args_and_bindings {
+                // We should be in type context, so format as `Foo<Bar>` instead of `Foo::<Bar>`.
+                // Do we actually format expressions?
+                write!(f, "<")?;
+                let mut first = true;
+                for arg in &generic_args.args {
+                    if first {
+                        first = false;
+                        if generic_args.has_self_type {
+                            // FIXME: Convert to `<Ty as Trait>` form.
+                            write!(f, "Self = ")?;
+                        }
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    arg.hir_fmt(f)?;
+                }
+                for binding in &generic_args.bindings {
+                    if first {
+                        first = false;
+                    } else {
+                        write!(f, ", ")?;
+                    }
+                    write!(f, "{}", binding.name)?;
+                    match &binding.type_ref {
+                        Some(ty) => {
+                            write!(f, " = ")?;
+                            ty.hir_fmt(f)?
+                        }
+                        None => {
+                            write!(f, ": ")?;
+                            f.write_joined(&binding.bounds, " + ")?;
+                        }
+                    }
+                }
+                write!(f, ">")?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl HirDisplay for GenericArg {
+    fn hir_fmt(&self, f: &mut HirFormatter) -> Result<(), HirDisplayError> {
+        match self {
+            GenericArg::Type(ty) => ty.hir_fmt(f),
+            GenericArg::Lifetime(lifetime) => write!(f, "{}", lifetime.name),
+        }
+    }
+}

crates/hir_ty/src/traits/chalk.rs

@@ -429,7 +429,7 @@ pub(crate) fn trait_datum_query(
     let generic_params = generics(db.upcast(), trait_.into());
     let bound_vars = Substs::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
     let flags = rust_ir::TraitFlags {
-        auto: trait_data.auto,
+        auto: trait_data.is_auto,
         upstream: trait_.lookup(db.upcast()).container.krate() != krate,
         non_enumerable: true,
         coinductive: false, // only relevant for Chalk testing

crates/ide/src/display.rs

@@ -5,6 +5,5 @@ pub(crate) mod navigation_target;
 mod short_label;
 
 pub(crate) use navigation_target::{ToNav, TryToNav};
-pub(crate) use short_label::ShortLabel;
 
 pub(crate) use syntax::display::{function_declaration, macro_label};

crates/ide/src/display/navigation_target.rs

@@ -3,7 +3,9 @@
 use std::fmt;
 
 use either::Either;
-use hir::{AssocItem, Documentation, FieldSource, HasAttrs, HasSource, InFile, ModuleSource};
+use hir::{
+    AssocItem, Documentation, FieldSource, HasAttrs, HasSource, HirDisplay, InFile, ModuleSource,
+};
 use ide_db::{
     base_db::{FileId, FileRange, SourceDatabase},
     symbol_index::FileSymbolKind,
@@ -98,7 +100,7 @@ impl NavigationTarget {
                 SymbolKind::Module,
             );
             res.docs = module.attrs(db).docs();
-            res.description = src.value.short_label();
+            res.description = Some(module.display(db).to_string());
             return res;
         }
         module.to_nav(db)
@@ -251,8 +253,8 @@ impl ToNavFromAst for hir::Trait {
 
 impl<D> TryToNav for D
 where
-    D: HasSource + ToNavFromAst + Copy + HasAttrs,
-    D::Ast: ast::NameOwner + ShortLabel,
+    D: HasSource + ToNavFromAst + Copy + HasAttrs + HirDisplay,
+    D::Ast: ast::NameOwner,
 {
     fn try_to_nav(&self, db: &RootDatabase) -> Option<NavigationTarget> {
         let src = self.source(db)?;
@@ -262,7 +264,7 @@ where
             D::KIND,
         );
         res.docs = self.docs(db);
-        res.description = src.value.short_label();
+        res.description = Some(self.display(db).to_string());
         Some(res)
     }
 }
@@ -317,7 +319,7 @@ impl TryToNav for hir::Field {
                 let mut res =
                     NavigationTarget::from_named(db, src.with_value(it), SymbolKind::Field);
                 res.docs = self.docs(db);
-                res.description = it.short_label();
+                res.description = Some(self.display(db).to_string());
                 res
             }
             FieldSource::Pos(it) => {

crates/ide/src/hover.rs

@@ -1,7 +1,7 @@
 use either::Either;
 use hir::{
-    Adt, AsAssocItem, AssocItemContainer, FieldSource, GenericParam, HasAttrs, HasSource,
-    HirDisplay, Module, ModuleDef, ModuleSource, Semantics,
+    Adt, AsAssocItem, AssocItemContainer, GenericParam, HasAttrs, HasSource, HirDisplay, Module,
+    ModuleDef, Semantics,
 };
 use ide_db::{
     base_db::SourceDatabase,
@@ -14,7 +14,7 @@ use stdx::format_to;
 use syntax::{ast, match_ast, AstNode, SyntaxKind::*, SyntaxToken, TokenAtOffset, T};
 
 use crate::{
-    display::{macro_label, ShortLabel, TryToNav},
+    display::{macro_label, TryToNav},
     doc_links::{remove_links, rewrite_links},
     markdown_remove::remove_markdown,
     markup::Markup,
@@ -335,34 +335,18 @@ fn hover_for_definition(
             let label = macro_label(&it.source(db)?.value);
             from_def_source_labeled(db, it, Some(label), mod_path)
         }
-        Definition::Field(def) => {
-            let src = def.source(db)?.value;
-            if let FieldSource::Named(it) = src {
-                from_def_source_labeled(db, def, it.short_label(), mod_path)
-            } else {
-                None
-            }
-        }
+        Definition::Field(def) => from_hir_fmt(db, def, mod_path),
         Definition::ModuleDef(it) => match it {
-            ModuleDef::Module(it) => from_def_source_labeled(
-                db,
-                it,
-                match it.definition_source(db).value {
-                    ModuleSource::Module(it) => it.short_label(),
-                    ModuleSource::SourceFile(it) => it.short_label(),
-                    ModuleSource::BlockExpr(it) => it.short_label(),
-                },
-                mod_path,
-            ),
-            ModuleDef::Function(it) => from_def_source(db, it, mod_path),
-            ModuleDef::Adt(Adt::Struct(it)) => from_def_source(db, it, mod_path),
-            ModuleDef::Adt(Adt::Union(it)) => from_def_source(db, it, mod_path),
-            ModuleDef::Adt(Adt::Enum(it)) => from_def_source(db, it, mod_path),
-            ModuleDef::Variant(it) => from_def_source(db, it, mod_path),
-            ModuleDef::Const(it) => from_def_source(db, it, mod_path),
-            ModuleDef::Static(it) => from_def_source(db, it, mod_path),
-            ModuleDef::Trait(it) => from_def_source(db, it, mod_path),
-            ModuleDef::TypeAlias(it) => from_def_source(db, it, mod_path),
+            ModuleDef::Module(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Function(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Adt(Adt::Struct(it)) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Adt(Adt::Union(it)) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Adt(Adt::Enum(it)) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Variant(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Const(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Static(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::Trait(it) => from_hir_fmt(db, it, mod_path),
+            ModuleDef::TypeAlias(it) => from_hir_fmt(db, it, mod_path),
             ModuleDef::BuiltinType(it) => famous_defs
                 .and_then(|fd| hover_for_builtin(fd, it))
                 .or_else(|| Some(Markup::fenced_block(&it.name()))),
@@ -370,26 +354,25 @@ fn hover_for_definition(
         Definition::Local(it) => hover_for_local(it, db),
         Definition::SelfType(impl_def) => {
             impl_def.target_ty(db).as_adt().and_then(|adt| match adt {
-                Adt::Struct(it) => from_def_source(db, it, mod_path),
-                Adt::Union(it) => from_def_source(db, it, mod_path),
-                Adt::Enum(it) => from_def_source(db, it, mod_path),
+                Adt::Struct(it) => from_hir_fmt(db, it, mod_path),
+                Adt::Union(it) => from_hir_fmt(db, it, mod_path),
+                Adt::Enum(it) => from_hir_fmt(db, it, mod_path),
             })
         }
         Definition::Label(it) => Some(Markup::fenced_block(&it.name(db))),
         Definition::GenericParam(it) => match it {
             GenericParam::TypeParam(it) => Some(Markup::fenced_block(&it.display(db))),
             GenericParam::LifetimeParam(it) => Some(Markup::fenced_block(&it.name(db))),
-            GenericParam::ConstParam(it) => from_def_source(db, it, None),
+            GenericParam::ConstParam(it) => Some(Markup::fenced_block(&it.display(db))),
         },
     };
 
-    fn from_def_source<A, D>(db: &RootDatabase, def: D, mod_path: Option<String>) -> Option<Markup>
+    fn from_hir_fmt<D>(db: &RootDatabase, def: D, mod_path: Option<String>) -> Option<Markup>
     where
-        D: HasSource<Ast = A> + HasAttrs + Copy,
-        A: ShortLabel,
+        D: HasAttrs + HirDisplay,
     {
-        let short_label = def.source(db)?.value.short_label();
-        from_def_source_labeled(db, def, short_label, mod_path)
+        let label = def.display(db).to_string();
+        from_def_source_labeled(db, def, Some(label), mod_path)
     }
 
     fn from_def_source_labeled<D>(
@@ -670,7 +653,9 @@ fn main() { let foo_test = fo$0o(); }
                 ```
 
                 ```rust
-                pub fn foo<'a, T: AsRef<str>>(b: &'a T) -> &'a str
+                pub fn foo<'a, T>(b: &'a T) -> &'a str
+                where
+                    T: AsRef<str>,
                 ```
             "#]],
         );
@@ -878,7 +863,7 @@ fn main() { So$0me(12); }
                 ```
 
                 ```rust
-                Some
+                Some(T)
                 ```
             "#]],
         );
@@ -944,7 +929,7 @@ fn main() {
                 ```
 
                 ```rust
-                Some
+                Some(T)
                 ```
 
                 ---
@@ -1441,13 +1426,14 @@ fn bar() { fo$0o(); }
                 ```
             "#]],
         );
+        // Top level `pub(crate)` will be displayed as no visibility.
         check(
-            r#"pub(crate) async unsafe extern "C" fn foo$0() {}"#,
+            r#"mod m { pub(crate) async unsafe extern "C" fn foo$0() {} }"#,
             expect![[r#"
                 *foo*
 
                 ```rust
-                test
+                test::m
                 ```
 
                 ```rust
@@ -1489,11 +1475,18 @@ extern crate st$0d;
 //! abc123
             "#,
             expect![[r#"
-            *std*
-            Standard library for this test
+                *std*
 
-            Printed?
-            abc123
+                ```rust
+                extern crate std
+                ```
+
+                ---
+
+                Standard library for this test
+
+                Printed?
+                abc123
             "#]],
         );
         check(
@@ -1507,11 +1500,18 @@ extern crate std as ab$0c;
 //! abc123
             "#,
             expect![[r#"
-            *abc*
-            Standard library for this test
+                *abc*
 
-            Printed?
-            abc123
+                ```rust
+                extern crate std
+                ```
+
+                ---
+
+                Standard library for this test
+
+                Printed?
+                abc123
             "#]],
         );
     }
@@ -2021,7 +2021,7 @@ enum E {
                 ```
 
                 ```rust
-                V
+                V { field: i32 }
                 ```
 
                 ---
@@ -2417,7 +2417,7 @@ fn main() { let s$0t = S{ f1:Arg(0) }; }
                                     focus_range: 24..25,
                                     name: "S",
                                     kind: Struct,
-                                    description: "struct S",
+                                    description: "struct S<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2463,7 +2463,7 @@ fn main() { let s$0t = S{ f1: S{ f1: Arg(0) } }; }
                                     focus_range: 24..25,
                                     name: "S",
                                     kind: Struct,
-                                    description: "struct S",
+                                    description: "struct S<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2605,7 +2605,7 @@ fn main() { let s$0t = foo(); }
                                     focus_range: 6..9,
                                     name: "Foo",
                                     kind: Trait,
-                                    description: "trait Foo",
+                                    description: "trait Foo<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2702,7 +2702,7 @@ fn main() { let s$0t = foo(); }
                                     focus_range: 6..9,
                                     name: "Foo",
                                     kind: Trait,
-                                    description: "trait Foo",
+                                    description: "trait Foo<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2715,7 +2715,7 @@ fn main() { let s$0t = foo(); }
                                     focus_range: 22..25,
                                     name: "Bar",
                                     kind: Trait,
-                                    description: "trait Bar",
+                                    description: "trait Bar<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2819,7 +2819,7 @@ fn foo(ar$0g: &impl Foo + Bar<S>) {}
                                     focus_range: 19..22,
                                     name: "Bar",
                                     kind: Trait,
-                                    description: "trait Bar",
+                                    description: "trait Bar<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2916,7 +2916,7 @@ fn foo(ar$0g: &impl Foo<S>) {}
                                     focus_range: 6..9,
                                     name: "Foo",
                                     kind: Trait,
-                                    description: "trait Foo",
+                                    description: "trait Foo<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -2966,7 +2966,7 @@ fn main() { let s$0t = foo(); }
                                     focus_range: 49..50,
                                     name: "B",
                                     kind: Struct,
-                                    description: "struct B",
+                                    description: "struct B<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -3042,7 +3042,7 @@ fn foo(ar$0g: &dyn Foo<S>) {}
                                     focus_range: 6..9,
                                     name: "Foo",
                                     kind: Trait,
-                                    description: "trait Foo",
+                                    description: "trait Foo<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -3090,7 +3090,7 @@ fn foo(a$0rg: &impl ImplTrait<B<dyn DynTrait<B<S>>>>) {}
                                     focus_range: 6..15,
                                     name: "ImplTrait",
                                     kind: Trait,
-                                    description: "trait ImplTrait",
+                                    description: "trait ImplTrait<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -3103,7 +3103,7 @@ fn foo(a$0rg: &impl ImplTrait<B<dyn DynTrait<B<S>>>>) {}
                                     focus_range: 50..51,
                                     name: "B",
                                     kind: Struct,
-                                    description: "struct B",
+                                    description: "struct B<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -3116,7 +3116,7 @@ fn foo(a$0rg: &impl ImplTrait<B<dyn DynTrait<B<S>>>>) {}
                                     focus_range: 28..36,
                                     name: "DynTrait",
                                     kind: Trait,
-                                    description: "trait DynTrait",
+                                    description: "trait DynTrait<T>",
                                 },
                             },
                             HoverGotoTypeData {
@@ -3582,6 +3582,17 @@ mod foo$0;
 "#,
             expect![[r#"
                 *foo*
+
+                ```rust
+                test
+                ```
+
+                ```rust
+                mod foo
+                ```
+
+                ---
+
                 For the horde!
             "#]],
         );
@@ -3606,7 +3617,7 @@ use foo::bar::{self$0};
                 ```
 
                 ```rust
-                pub mod bar
+                mod bar
                 ```
 
                 ---
@@ -3657,4 +3668,43 @@ cosnt _: &str$0 = ""; }"#;
             "#]],
         );
     }
+
+    #[test]
+    fn hover_macro_expanded_function() {
+        check(
+            r#"
+struct S<'a, T>(&'a T);
+trait Clone {}
+macro_rules! foo {
+    () => {
+        fn bar<'t, T: Clone + 't>(s: &mut S<'t, T>, t: u32) -> *mut u32 where
+            't: 't + 't,
+            for<'a> T: Clone + 'a
+        { 0 as _ }
+    };
+}
+
+foo!();
+
+fn main() {
+    bar$0;
+}
+"#,
+            expect![[r#"
+                *bar*
+
+                ```rust
+                test
+                ```
+
+                ```rust
+                fn bar<'t, T>(s: &mut S<'t, T>, t: u32) -> *mut u32
+                where
+                    T: Clone + 't,
+                    't: 't + 't,
+                    for<'a> T: Clone + 'a,
+                ```
+            "#]],
+        )
+    }
 }

crates/ide_completion/src/completions/dot.rs

@@ -81,7 +81,7 @@ fn foo(s: S) { s.$0 }
 "#,
             expect![[r#"
                 fd foo   u32
-                me bar() -> ()
+                me bar() fn(&self)
             "#]],
         );
     }
@@ -97,7 +97,7 @@ impl S {
 "#,
             expect![[r#"
                 fd the_field (u32,)
-                me foo()     -> ()
+                me foo()     fn(self)
             "#]],
         )
     }
@@ -113,7 +113,7 @@ impl A {
 "#,
             expect![[r#"
                 fd the_field (u32, i32)
-                me foo()     -> ()
+                me foo()     fn(&self)
             "#]],
         )
     }
@@ -163,7 +163,7 @@ mod m {
 fn foo(a: A) { a.$0 }
 "#,
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         );
     }
@@ -196,7 +196,7 @@ impl A<i32> {
 fn foo(a: A<u32>) { a.$0 }
 "#,
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         )
     }
@@ -211,7 +211,7 @@ impl Trait for A {}
 fn foo(a: A) { a.$0 }
 "#,
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         );
     }
@@ -226,7 +226,7 @@ impl<T> Trait for T {}
 fn foo(a: &A) { a.$0 }
 ",
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         );
     }
@@ -244,7 +244,7 @@ impl Trait for A {}
 fn foo(a: A) { a.$0 }
 ",
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         );
     }
@@ -298,7 +298,7 @@ impl T {
 }
 "#,
             expect![[r#"
-                me blah() -> ()
+                me blah() fn(&self)
             "#]],
         );
     }
@@ -407,7 +407,7 @@ fn foo() {
 }
 "#,
             expect![[r#"
-                me the_method() -> ()
+                me the_method() fn(&self)
             "#]],
         );
     }
@@ -422,7 +422,7 @@ macro_rules! make_s { () => { S }; }
 fn main() { make_s!().f$0; }
 "#,
             expect![[r#"
-                me foo() -> ()
+                me foo() fn(&self)
             "#]],
         )
     }
@@ -450,7 +450,7 @@ mod foo {
 }
         "#,
             expect![[r#"
-                me private() -> ()
+                me private() fn(&self)
             "#]],
         );
     }

crates/ide_completion/src/completions/flyimport.rs

@@ -402,7 +402,7 @@ fn main() {
         check(
             fixture,
             expect![[r#"
-                fn weird_function() (dep::test_mod::TestTrait) -> ()
+                fn weird_function() (dep::test_mod::TestTrait) fn()
             "#]],
         );
 
@@ -495,7 +495,7 @@ fn main() {
         check(
             fixture,
             expect![[r#"
-                me random_method() (dep::test_mod::TestTrait) -> ()
+                me random_method() (dep::test_mod::TestTrait) fn(&self)
             "#]],
         );
 
@@ -665,7 +665,7 @@ fn main() {
 }
         "#,
             expect![[r#"
-                me random_method() (dep::test_mod::TestTrait) -> () DEPRECATED
+                me random_method() (dep::test_mod::TestTrait) fn(&self) DEPRECATED
             "#]],
         );
 
@@ -696,7 +696,7 @@ fn main() {
 "#,
             expect![[r#"
                 ct SPECIAL_CONST (dep::test_mod::TestTrait) DEPRECATED
-                fn weird_function() (dep::test_mod::TestTrait) -> () DEPRECATED
+                fn weird_function() (dep::test_mod::TestTrait) fn() DEPRECATED
             "#]],
         );
     }

crates/ide_completion/src/completions/qualified_path.rs

@@ -359,8 +359,8 @@ impl S {
 fn foo() { let _ = S::$0 }
 "#,
             expect![[r#"
-                fn a()  -> ()
-                me b(…) -> ()
+                fn a()  fn()
+                me b(…) fn(&self)
                 ct C    const C: i32 = 42;
                 ta T    type T = i32;
             "#]],
@@ -387,7 +387,7 @@ mod m {
 fn foo() { let _ = S::$0 }
 "#,
             expect![[r#"
-                fn public_method() -> ()
+                fn public_method() fn()
                 ct PUBLIC_CONST    pub(crate) const PUBLIC_CONST: u32 = 1;
                 ta PublicType      pub(crate) type PublicType = u32;
             "#]],
@@ -404,7 +404,7 @@ impl E { fn m() { } }
 fn foo() { let _ = E::$0 }
         "#,
             expect![[r#"
-                fn m() -> ()
+                fn m() fn()
             "#]],
         );
     }
@@ -419,7 +419,7 @@ impl U { fn m() { } }
 fn foo() { let _ = U::$0 }
 "#,
             expect![[r#"
-                fn m() -> ()
+                fn m() fn()
             "#]],
         );
     }
@@ -449,7 +449,7 @@ trait Trait { fn m(); }
 fn foo() { let _ = Trait::$0 }
 "#,
             expect![[r#"
-                fn m() -> ()
+                fn m() fn()
             "#]],
         );
     }
@@ -466,7 +466,7 @@ impl Trait for S {}
 fn foo() { let _ = S::$0 }
 "#,
             expect![[r#"
-                fn m() -> ()
+                fn m() fn()
             "#]],
         );
     }
@@ -483,7 +483,7 @@ impl Trait for S {}
 fn foo() { let _ = <S as Trait>::$0 }
 "#,
             expect![[r#"
-                fn m() -> ()
+                fn m() fn()
             "#]],
         );
     }
@@ -512,11 +512,11 @@ fn foo<T: Sub>() { T::$0 }
                 ta SubTy        type SubTy;
                 ta Ty           type Ty;
                 ct C2           const C2: ();
-                fn subfunc()    -> ()
-                me submethod(…) -> ()
+                fn subfunc()    fn()
+                me submethod(…) fn(&self)
                 ct CONST        const CONST: u8;
-                fn func()       -> ()
-                me method(…)    -> ()
+                fn func()       fn()
+                me method(…)    fn(&self)
             "#]],
         );
     }
@@ -552,11 +552,11 @@ impl<T> Sub for Wrap<T> {
                 ta SubTy        type SubTy;
                 ta Ty           type Ty;
                 ct CONST        const CONST: u8 = 0;
-                fn func()       -> ()
-                me method(…)    -> ()
+                fn func()       fn()
+                me method(…)    fn(&self)
                 ct C2           const C2: () = ();
-                fn subfunc()    -> ()
-                me submethod(…) -> ()
+                fn subfunc()    fn()
+                me submethod(…) fn(&self)
             "#]],
         );
     }
@@ -573,8 +573,8 @@ impl T { fn bar() {} }
 fn main() { T::$0; }
 "#,
             expect![[r#"
-                fn foo() -> ()
-                fn bar() -> ()
+                fn foo() fn()
+                fn bar() fn()
             "#]],
         );
     }
@@ -589,7 +589,7 @@ macro_rules! foo { () => {} }
 fn main() { let _ = crate::$0 }
         "#,
             expect![[r##"
-                fn main()  -> ()
+                fn main()  fn()
                 ma foo!(…) #[macro_export] macro_rules! foo
             "##]],
         );
@@ -633,7 +633,7 @@ mod p {
 "#,
             expect![[r#"
                 ct RIGHT_CONST
-                fn right_fn()  -> ()
+                fn right_fn()  fn()
                 st RightType
             "#]],
         );
@@ -680,8 +680,8 @@ fn main() { m!(self::f$0); }
 fn foo() {}
 "#,
             expect![[r#"
-                fn main() -> ()
-                fn foo()  -> ()
+                fn main() fn()
+                fn foo()  fn()
             "#]],
         );
     }
@@ -699,7 +699,7 @@ mod m {
 "#,
             expect![[r#"
                 md z
-                fn z() -> ()
+                fn z() fn()
             "#]],
         );
     }
@@ -719,7 +719,7 @@ fn foo() {
 }
 "#,
             expect![[r#"
-                fn new() -> HashMap<K, V, RandomState>
+                fn new() fn() -> HashMap<K, V, RandomState>
             "#]],
         );
     }
@@ -752,8 +752,8 @@ fn main() {
 }
 "#,
             expect![[r#"
-                fn main() -> ()
-                fn foo(…) -> ()
+                fn main() fn()
+                fn foo(…) fn(i32, i32)
             "#]],
         );
     }
@@ -776,7 +776,7 @@ impl Foo {
             expect![[r#"
                 ev Bar    ()
                 ev Baz    ()
-                me foo(…) -> ()
+                me foo(…) fn(self)
             "#]],
         );
     }
@@ -800,7 +800,7 @@ impl u8 {
 "#,
             expect![[r#"
                 ct MAX     pub const MAX: Self = 255;
-                me func(…) -> ()
+                me func(…) fn(self)
             "#]],
         );
     }

crates/ide_completion/src/completions/unqualified_path.rs

@@ -135,7 +135,7 @@ fn quux(x: i32) {
             expect![[r#"
                 lc y       i32
                 lc x       i32
-                fn quux(…) -> ()
+                fn quux(…) fn(i32)
             "#]],
         );
     }
@@ -157,7 +157,7 @@ fn quux() {
             expect![[r#"
                 lc b      i32
                 lc a
-                fn quux() -> ()
+                fn quux() fn()
             "#]],
         );
     }
@@ -172,7 +172,7 @@ fn quux() {
 "#,
             expect![[r#"
                 lc x
-                fn quux() -> ()
+                fn quux() fn()
             "#]],
         );
     }
@@ -203,14 +203,14 @@ fn main() {
             r#"fn quux<T>() { $0 }"#,
             expect![[r#"
                 tp T
-                fn quux() -> ()
+                fn quux() fn()
             "#]],
         );
         check(
             r#"fn quux<const C: usize>() { $0 }"#,
             expect![[r#"
                 cp C
-                fn quux() -> ()
+                fn quux() fn()
             "#]],
         );
     }
@@ -221,7 +221,7 @@ fn main() {
         check(
             r#"fn quux<'a>() { $0 }"#,
             expect![[r#"
-                fn quux() -> ()
+                fn quux() fn()
             "#]],
         );
     }
@@ -259,7 +259,7 @@ fn quux() { $0 }
 "#,
             expect![[r#"
                 st S
-                fn quux() -> ()
+                fn quux() fn()
                 en E
             "#]],
         );
@@ -312,7 +312,7 @@ mod m {
 }
 "#,
             expect![[r#"
-                fn quux() -> ()
+                fn quux() fn()
                 st Bar
             "#]],
         );
@@ -327,7 +327,7 @@ fn x() -> $0
 "#,
             expect![[r#"
                 st Foo
-                fn x() -> ()
+                fn x() fn()
             "#]],
         );
     }
@@ -348,7 +348,7 @@ fn foo() {
             expect![[r#"
                 lc bar   i32
                 lc bar   i32
-                fn foo() -> ()
+                fn foo() fn()
             "#]],
         );
     }
@@ -378,7 +378,7 @@ use prelude::*;
 mod prelude { struct Option; }
 "#,
             expect![[r#"
-                fn foo()  -> ()
+                fn foo()  fn()
                 md std
                 st Option
             "#]],
@@ -408,7 +408,7 @@ mod macros {
 }
 "#,
             expect![[r##"
-                fn f()        -> ()
+                fn f()        fn()
                 ma concat!(…) #[macro_export] macro_rules! concat
                 md std
             "##]],
@@ -435,7 +435,7 @@ use prelude::*;
 mod prelude { struct String; }
 "#,
             expect![[r#"
-                fn foo()  -> ()
+                fn foo()  fn()
                 md std
                 md core
                 st String
@@ -466,7 +466,7 @@ fn main() { let v = $0 }
             expect![[r##"
                 md m1
                 ma baz!(…) #[macro_export] macro_rules! baz
-                fn main()  -> ()
+                fn main()  fn()
                 md m2
                 ma bar!(…) macro_rules! bar
                 ma foo!(…) macro_rules! foo
@@ -482,7 +482,7 @@ macro_rules! foo { () => {} }
 fn foo() { $0 }
 "#,
             expect![[r#"
-                fn foo()   -> ()
+                fn foo()   fn()
                 ma foo!(…) macro_rules! foo
             "#]],
         );
@@ -496,7 +496,7 @@ macro_rules! foo { () => {} }
 fn main() { let x: $0 }
 "#,
             expect![[r#"
-                fn main()  -> ()
+                fn main()  fn()
                 ma foo!(…) macro_rules! foo
             "#]],
         );
@@ -510,7 +510,7 @@ macro_rules! foo { () => {} }
 fn main() { $0 }
 "#,
             expect![[r#"
-                fn main()  -> ()
+                fn main()  fn()
                 ma foo!(…) macro_rules! foo
             "#]],
         );
@@ -526,8 +526,8 @@ fn main() {
 }
 "#,
             expect![[r#"
-                fn frobnicate() -> ()
-                fn main()       -> ()
+                fn frobnicate() fn()
+                fn main()       fn()
             "#]],
         );
     }
@@ -545,7 +545,7 @@ fn quux(x: i32) {
             expect![[r#"
                 lc y       i32
                 lc x       i32
-                fn quux(…) -> ()
+                fn quux(…) fn(i32)
                 ma m!(…)   macro_rules! m
             "#]],
         );
@@ -564,7 +564,7 @@ fn quux(x: i32) {
             expect![[r#"
                 lc y       i32
                 lc x       i32
-                fn quux(…) -> ()
+                fn quux(…) fn(i32)
                 ma m!(…)   macro_rules! m
             "#]],
         );
@@ -583,7 +583,7 @@ fn quux(x: i32) {
             expect![[r#"
                 lc y       i32
                 lc x       i32
-                fn quux(…) -> ()
+                fn quux(…) fn(i32)
                 ma m!(…)   macro_rules! m
             "#]],
         );
@@ -598,7 +598,7 @@ use spam::Quux;
 fn main() { $0 }
 "#,
             expect![[r#"
-                fn main() -> ()
+                fn main() fn()
                 ?? Quux
             "#]],
         );
@@ -616,7 +616,7 @@ fn main() { let foo: Foo = Q$0 }
                 ev Foo::Baz  ()
                 ev Foo::Quux ()
                 en Foo
-                fn main()    -> ()
+                fn main()    fn()
             "#]],
         )
     }
@@ -631,7 +631,7 @@ fn f() -> m::E { V$0 }
             expect![[r#"
                 ev m::E::V ()
                 md m
-                fn f()     -> E
+                fn f()     fn() -> E
             "#]],
         )
     }

crates/ide_completion/src/lib.rs

@@ -230,7 +230,7 @@ fn foo() {
     bar.fo$0;
 }
 "#,
-            DetailAndDocumentation { detail: "-> ()", documentation: "Do the foo" },
+            DetailAndDocumentation { detail: "fn(&self)", documentation: "Do the foo" },
         );
     }
 
@@ -255,7 +255,7 @@ fn foo() {
     bar.fo$0;
 }
 "#,
-            DetailAndDocumentation { detail: "-> ()", documentation: " Do the foo" },
+            DetailAndDocumentation { detail: "fn(&self)", documentation: " Do the foo" },
         );
     }
 
@@ -273,7 +273,7 @@ fn bar() {
     for c in fo$0
 }
 "#,
-            DetailAndDocumentation { detail: "-> &str", documentation: "Do the foo" },
+            DetailAndDocumentation { detail: "fn() -> &str", documentation: "Do the foo" },
         );
     }
 }

crates/ide_completion/src/render.rs

@@ -451,6 +451,44 @@ fn main() { Foo::Fo$0 }
         );
     }
 
+    #[test]
+    fn fn_detail_includes_args_and_return_type() {
+        check(
+            r#"
+fn foo<T>(a: u32, b: u32, t: T) -> (u32, T) { (a, t) }
+
+fn main() { fo$0 }
+"#,
+            expect![[r#"
+                [
+                    CompletionItem {
+                        label: "foo(…)",
+                        source_range: 68..70,
+                        delete: 68..70,
+                        insert: "foo(${1:a}, ${2:b}, ${3:t})$0",
+                        kind: SymbolKind(
+                            Function,
+                        ),
+                        lookup: "foo",
+                        detail: "fn(u32, u32, T) -> (u32, T)",
+                        trigger_call_info: true,
+                    },
+                    CompletionItem {
+                        label: "main()",
+                        source_range: 68..70,
+                        delete: 68..70,
+                        insert: "main()$0",
+                        kind: SymbolKind(
+                            Function,
+                        ),
+                        lookup: "main",
+                        detail: "fn()",
+                    },
+                ]
+            "#]],
+        );
+    }
+
     #[test]
     fn enum_detail_just_parentheses_for_unit() {
         check(
@@ -538,7 +576,7 @@ fn main() { let _: m::Spam = S$0 }
                             Function,
                         ),
                         lookup: "main",
-                        detail: "-> ()",
+                        detail: "fn()",
                     },
                 ]
             "#]],
@@ -567,7 +605,7 @@ fn main() { som$0 }
                             Function,
                         ),
                         lookup: "main",
-                        detail: "-> ()",
+                        detail: "fn()",
                     },
                     CompletionItem {
                         label: "something_deprecated()",
@@ -578,7 +616,7 @@ fn main() { som$0 }
                             Function,
                         ),
                         lookup: "something_deprecated",
-                        detail: "-> ()",
+                        detail: "fn()",
                         deprecated: true,
                     },
                     CompletionItem {
@@ -590,7 +628,7 @@ fn main() { som$0 }
                             Function,
                         ),
                         lookup: "something_else_deprecated",
-                        detail: "-> ()",
+                        detail: "fn()",
                         deprecated: true,
                     },
                 ]
@@ -641,7 +679,7 @@ impl S {
                         insert: "bar()$0",
                         kind: Method,
                         lookup: "bar",
-                        detail: "-> ()",
+                        detail: "fn(self)",
                         documentation: Documentation(
                             "Method docs",
                         ),
@@ -741,7 +779,7 @@ fn foo(s: S) { s.$0 }
                         insert: "the_method()$0",
                         kind: Method,
                         lookup: "the_method",
-                        detail: "-> ()",
+                        detail: "fn(&self)",
                     },
                 ]
             "#]],
@@ -1049,7 +1087,7 @@ fn main() {
                             Function,
                         ),
                         lookup: "foo",
-                        detail: "-> ()",
+                        detail: "fn(&mut S)",
                         trigger_call_info: true,
                     },
                     CompletionItem {
@@ -1061,7 +1099,7 @@ fn main() {
                             Function,
                         ),
                         lookup: "main",
-                        detail: "-> ()",
+                        detail: "fn()",
                     },
                     CompletionItem {
                         label: "s",

crates/ide_completion/src/render/function.rs

@@ -2,6 +2,7 @@
 
 use hir::{HasSource, HirDisplay, Type};
 use ide_db::SymbolKind;
+use itertools::Itertools;
 use syntax::ast::Fn;
 
 use crate::{
@@ -73,8 +74,42 @@ impl<'a> FunctionRender<'a> {
     }
 
     fn detail(&self) -> String {
-        let ty = self.func.ret_type(self.ctx.db());
-        format!("-> {}", ty.display(self.ctx.db()))
+        let ret_ty = self.func.ret_type(self.ctx.db());
+        let ret = if ret_ty.is_unit() {
+            // Omit the return type if it is the unit type
+            String::new()
+        } else {
+            format!(" {}", self.ty_display())
+        };
+
+        format!("fn({}){}", self.params_display(), ret)
+    }
+
+    fn params_display(&self) -> String {
+        if let Some(self_param) = self.func.self_param(self.ctx.db()) {
+            let params = self
+                .func
+                .assoc_fn_params(self.ctx.db())
+                .into_iter()
+                .skip(1) // skip the self param because we are manually handling that
+                .map(|p| p.ty().display(self.ctx.db()).to_string());
+
+            std::iter::once(self_param.display(self.ctx.db()).to_owned()).chain(params).join(", ")
+        } else {
+            let params = self
+                .func
+                .assoc_fn_params(self.ctx.db())
+                .into_iter()
+                .map(|p| p.ty().display(self.ctx.db()).to_string())
+                .join(", ");
+            params
+        }
+    }
+
+    fn ty_display(&self) -> String {
+        let ret_ty = self.func.ret_type(self.ctx.db());
+
+        format!("-> {}", ret_ty.display(self.ctx.db()))
     }
 
     fn add_arg(&self, arg: &str, ty: &Type) -> String {