10 files changed, 251 insertions, 30 deletions

diff --git a/crates/ra_assists/src/assist_ctx.rs b/crates/ra_assists/src/assist_ctx.rs
index 993aebc47..28152f724 100644
--- a/crates/ra_assists/src/assist_ctx.rs
+++ b/crates/ra_assists/src/assist_ctx.rs
@@ -46,7 +46,7 @@ pub(crate) enum Assist {
 ///
 /// Note, however, that we don't actually use such two-phase logic at the
 /// moment, because the LSP API is pretty awkward in this place, and it's much
-/// easier to just compute the edit eagerly :-)#[derive(Debug, Clone)]
+/// easier to just compute the edit eagerly :-)
 #[derive(Debug)]
 pub(crate) struct AssistCtx<'a, DB> {
     pub(crate) db: &'a DB,
diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index cef669cb5..bc49e71fe 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+
 use hir::{db::HirDatabase, HasSource};
 use ra_syntax::{
     ast::{self, edit, make, AstNode, NameOwner},
@@ -17,26 +19,26 @@ enum AddMissingImplMembersMode {
 // Adds scaffold for required impl members.
 //
 // ```
-// trait T {
+// trait Trait<T> {
 //     Type X;
-//     fn foo(&self);
+//     fn foo(&self) -> T;
 //     fn bar(&self) {}
 // }
 //
-// impl T for () {<|>
+// impl Trait<u32> for () {<|>
 //
 // }
 // ```
 // ->
 // ```
-// trait T {
+// trait Trait<T> {
 //     Type X;
-//     fn foo(&self);
+//     fn foo(&self) -> T;
 //     fn bar(&self) {}
 // }
 //
-// impl T for () {
-//     fn foo(&self) { unimplemented!() }
+// impl Trait<u32> for () {
+//     fn foo(&self) -> u32 { unimplemented!() }
 //
 // }
 // ```
@@ -54,13 +56,13 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Opti
 // Adds scaffold for overriding default impl members.
 //
 // ```
-// trait T {
+// trait Trait {
 //     Type X;
 //     fn foo(&self);
 //     fn bar(&self) {}
 // }
 //
-// impl T for () {
+// impl Trait for () {
 //     Type X = ();
 //     fn foo(&self) {}<|>
 //
@@ -68,13 +70,13 @@ pub(crate) fn add_missing_impl_members(ctx: AssistCtx<impl HirDatabase>) -> Opti
 // ```
 // ->
 // ```
-// trait T {
+// trait Trait {
 //     Type X;
 //     fn foo(&self);
 //     fn bar(&self) {}
 // }
 //
-// impl T for () {
+// impl Trait for () {
 //     Type X = ();
 //     fn foo(&self) {}
 //     fn bar(&self) {}
@@ -99,7 +101,7 @@ fn add_missing_impl_members_inner(
     let impl_node = ctx.find_node_at_offset::<ast::ImplBlock>()?;
     let impl_item_list = impl_node.item_list()?;
 
-    let trait_def = {
+    let (trait_, trait_def) = {
         let analyzer = ctx.source_analyzer(impl_node.syntax(), None);
 
         resolve_target_trait_def(ctx.db, &analyzer, &impl_node)?
@@ -132,10 +134,25 @@ fn add_missing_impl_members_inner(
         return None;
     }
 
+    let file_id = ctx.frange.file_id;
+    let db = ctx.db;
+
     ctx.add_assist(AssistId(assist_id), label, |edit| {
         let n_existing_items = impl_item_list.impl_items().count();
+        let substs = get_syntactic_substs(impl_node).unwrap_or_default();
+        let generic_def: hir::GenericDef = trait_.into();
+        let substs_by_param: HashMap<_, _> = generic_def
+            .params(db)
+            .into_iter()
+            // this is a trait impl, so we need to skip the first type parameter -- this is a bit hacky
+            .skip(1)
+            .zip(substs.into_iter())
+            .collect();
         let items = missing_items
             .into_iter()
+            .map(|it| {
+                substitute_type_params(db, hir::InFile::new(file_id.into(), it), &substs_by_param)
+            })
             .map(|it| match it {
                 ast::ImplItem::FnDef(def) => ast::ImplItem::FnDef(add_body(def)),
                 _ => it,
@@ -160,13 +177,63 @@ fn add_body(fn_def: ast::FnDef) -> ast::FnDef {
     }
 }
 
+// FIXME: It would probably be nicer if we could get this via HIR (i.e. get the
+// trait ref, and then go from the types in the substs back to the syntax)
+// FIXME: This should be a general utility (not even just for assists)
+fn get_syntactic_substs(impl_block: ast::ImplBlock) -> Option<Vec<ast::TypeRef>> {
+    let target_trait = impl_block.target_trait()?;
+    let path_type = match target_trait {
+        ast::TypeRef::PathType(path) => path,
+        _ => return None,
+    };
+    let type_arg_list = path_type.path()?.segment()?.type_arg_list()?;
+    let mut result = Vec::new();
+    for type_arg in type_arg_list.type_args() {
+        let type_arg: ast::TypeArg = type_arg;
+        result.push(type_arg.type_ref()?);
+    }
+    Some(result)
+}
+
+// FIXME: This should be a general utility (not even just for assists)
+fn substitute_type_params<N: AstNode>(
+    db: &impl HirDatabase,
+    node: hir::InFile<N>,
+    substs: &HashMap<hir::TypeParam, ast::TypeRef>,
+) -> N {
+    let type_param_replacements = node
+        .value
+        .syntax()
+        .descendants()
+        .filter_map(ast::TypeRef::cast)
+        .filter_map(|n| {
+            let path = match &n {
+                ast::TypeRef::PathType(path_type) => path_type.path()?,
+                _ => return None,
+            };
+            let analyzer = hir::SourceAnalyzer::new(db, node.with_value(n.syntax()), None);
+            let resolution = analyzer.resolve_path(db, &path)?;
+            match resolution {
+                hir::PathResolution::TypeParam(tp) => Some((n, substs.get(&tp)?.clone())),
+                _ => None,
+            }
+        })
+        .collect::<Vec<_>>();
+
+    if type_param_replacements.is_empty() {
+        node.value
+    } else {
+        edit::replace_descendants(&node.value, type_param_replacements.into_iter())
+    }
+}
+
 /// Given an `ast::ImplBlock`, resolves the target trait (the one being
 /// implemented) to a `ast::TraitDef`.
 fn resolve_target_trait_def(
     db: &impl HirDatabase,
     analyzer: &hir::SourceAnalyzer,
     impl_block: &ast::ImplBlock,
-) -> Option<ast::TraitDef> {
+) -> Option<(hir::Trait, ast::TraitDef)> {
     let ast_path = impl_block
         .target_trait()
         .map(|it| it.syntax().clone())
@@ -174,7 +241,9 @@ fn resolve_target_trait_def(
         .path()?;
 
     match analyzer.resolve_path(db, &ast_path) {
-        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def.source(db).value),
+        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => {
+            Some((def, def.source(db).value))
+        }
         _ => None,
     }
 }
@@ -281,6 +350,40 @@ impl Foo for S {
     }
 
     #[test]
+    fn fill_in_type_params_1() {
+        check_assist(
+            add_missing_impl_members,
+            "
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl Foo<u32> for S { <|> }",
+            "
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl Foo<u32> for S {
+    <|>fn foo(&self, t: u32) -> &u32 { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
+    fn fill_in_type_params_2() {
+        check_assist(
+            add_missing_impl_members,
+            "
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl<U> Foo<U> for S { <|> }",
+            "
+trait Foo<T> { fn foo(&self, t: T) -> &T; }
+struct S;
+impl<U> Foo<U> for S {
+    <|>fn foo(&self, t: U) -> &U { unimplemented!() }
+}",
+        );
+    }
+
+    #[test]
     fn test_cursor_after_empty_impl_block() {
         check_assist(
             add_missing_impl_members,
diff --git a/crates/ra_assists/src/doc_tests/generated.rs b/crates/ra_assists/src/doc_tests/generated.rs
index 4586eeb59..7d84dc8fb 100644
--- a/crates/ra_assists/src/doc_tests/generated.rs
+++ b/crates/ra_assists/src/doc_tests/generated.rs
@@ -101,26 +101,26 @@ fn doctest_add_impl_default_members() {
     check(
         "add_impl_default_members",
         r#####"
-trait T {
+trait Trait {
     Type X;
     fn foo(&self);
     fn bar(&self) {}
 }
 
-impl T for () {
+impl Trait for () {
     Type X = ();
     fn foo(&self) {}<|>
 
 }
 "#####,
         r#####"
-trait T {
+trait Trait {
     Type X;
     fn foo(&self);
     fn bar(&self) {}
 }
 
-impl T for () {
+impl Trait for () {
     Type X = ();
     fn foo(&self) {}
     fn bar(&self) {}
@@ -135,25 +135,25 @@ fn doctest_add_impl_missing_members() {
     check(
         "add_impl_missing_members",
         r#####"
-trait T {
+trait Trait<T> {
     Type X;
-    fn foo(&self);
+    fn foo(&self) -> T;
     fn bar(&self) {}
 }
 
-impl T for () {<|>
+impl Trait<u32> for () {<|>
 
 }
 "#####,
         r#####"
-trait T {
+trait Trait<T> {
     Type X;
-    fn foo(&self);
+    fn foo(&self) -> T;
     fn bar(&self) {}
 }
 
-impl T for () {
-    fn foo(&self) { unimplemented!() }
+impl Trait<u32> for () {
+    fn foo(&self) -> u32 { unimplemented!() }
 
 }
 "#####,
diff --git a/crates/ra_hir/src/code_model.rs b/crates/ra_hir/src/code_model.rs
index bcfc0d03e..76d8f85f1 100644
--- a/crates/ra_hir/src/code_model.rs
+++ b/crates/ra_hir/src/code_model.rs
@@ -644,6 +644,17 @@ impl_froms!(
     Const
 );
 
+impl GenericDef {
+    pub fn params(self, db: &impl HirDatabase) -> Vec<TypeParam> {
+        let generics: Arc<hir_def::generics::GenericParams> = db.generic_params(self.into());
+        generics
+            .types
+            .iter()
+            .map(|(local_id, _)| TypeParam { id: TypeParamId { parent: self.into(), local_id } })
+            .collect()
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub struct Local {
     pub(crate) parent: DefWithBody,
diff --git a/crates/ra_hir_def/src/data.rs b/crates/ra_hir_def/src/data.rs
index 1aa9a9b7d..c900a6a18 100644
--- a/crates/ra_hir_def/src/data.rs
+++ b/crates/ra_hir_def/src/data.rs
@@ -10,8 +10,9 @@ use ra_syntax::ast::{self, AstNode, ImplItem, ModuleItemOwner, NameOwner, TypeAs
 
 use crate::{
     db::DefDatabase,
+    path::{path, GenericArgs, Path},
     src::HasSource,
-    type_ref::{Mutability, TypeRef},
+    type_ref::{Mutability, TypeBound, TypeRef},
     AssocContainerId, AssocItemId, ConstId, ConstLoc, Expander, FunctionId, FunctionLoc, HasModule,
     ImplId, Intern, Lookup, ModuleId, StaticId, TraitId, TypeAliasId, TypeAliasLoc,
 };
@@ -62,11 +63,29 @@ impl FunctionData {
             TypeRef::unit()
         };
 
+        let ret_type = if src.value.is_async() {
+            let future_impl = desugar_future_path(ret_type);
+            let ty_bound = TypeBound::Path(future_impl);
+            TypeRef::ImplTrait(vec![ty_bound])
+        } else {
+            ret_type
+        };
+
         let sig = FunctionData { name, params, ret_type, has_self_param };
         Arc::new(sig)
     }
 }
 
+fn desugar_future_path(orig: TypeRef) -> Path {
+    let path = path![std::future::Future];
+    let mut generic_args: Vec<_> = std::iter::repeat(None).take(path.segments.len() - 1).collect();
+    let mut last = GenericArgs::empty();
+    last.bindings.push((name![Output], orig));
+    generic_args.push(Some(Arc::new(last)));
+
+    Path::from_known_path(path, generic_args)
+}
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct TypeAliasData {
     pub name: Name,
diff --git a/crates/ra_hir_def/src/path.rs b/crates/ra_hir_def/src/path.rs
index 8e1294201..107d2d799 100644
--- a/crates/ra_hir_def/src/path.rs
+++ b/crates/ra_hir_def/src/path.rs
@@ -130,6 +130,14 @@ impl Path {
         Path { type_anchor: None, mod_path: name_ref.as_name().into(), generic_args: vec![None] }
     }
 
+    /// Converts a known mod path to `Path`.
+    pub(crate) fn from_known_path(
+        path: ModPath,
+        generic_args: Vec<Option<Arc<GenericArgs>>>,
+    ) -> Path {
+        Path { type_anchor: None, mod_path: path, generic_args }
+    }
+
     pub fn kind(&self) -> &PathKind {
         &self.mod_path.kind
     }
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index e97b81473..32c0d07a5 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -37,8 +37,8 @@ use test_utils::tested_by;
 use super::{
     primitive::{FloatTy, IntTy},
     traits::{Guidance, Obligation, ProjectionPredicate, Solution},
-    ApplicationTy, InEnvironment, ProjectionTy, Substs, TraitEnvironment, TraitRef, Ty, TypeCtor,
-    TypeWalk, Uncertain,
+    ApplicationTy, GenericPredicate, InEnvironment, ProjectionTy, Substs, TraitEnvironment,
+    TraitRef, Ty, TypeCtor, TypeWalk, Uncertain,
 };
 use crate::{db::HirDatabase, infer::diagnostics::InferenceDiagnostic};
 
@@ -379,6 +379,25 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     ) -> Ty {
         match assoc_ty {
             Some(res_assoc_ty) => {
+                // FIXME:
+                // Check if inner_ty is is `impl Trait` and contained input TypeAlias id
+                // this is a workaround while Chalk assoc type projection doesn't always work yet,
+                // but once that is fixed I don't think we should keep this
+                // (we'll probably change how associated types are resolved anyway)
+                if let Ty::Opaque(ref predicates) = inner_ty {
+                    for p in predicates.iter() {
+                        if let GenericPredicate::Projection(projection) = p {
+                            if projection.projection_ty.associated_ty == res_assoc_ty {
+                                if let ty_app!(_, params) = &projection.ty {
+                                    if params.len() == 0 {
+                                        return projection.ty.clone();
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+
                 let ty = self.table.new_type_var();
                 let builder = Substs::build_for_def(self.db, res_assoc_ty)
                     .push(inner_ty)
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index ae316922b..0bc72644a 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -38,6 +38,63 @@ mod future {
 }
 
 #[test]
+fn infer_async() {
+    let (db, pos) = TestDB::with_position(
+        r#"
+//- /main.rs crate:main deps:std
+
+async fn foo() -> u64 {
+    128
+}
+
+fn test() {
+    let r = foo();
+    let v = r.await;
+    v<|>;
+}
+
+//- /std.rs crate:std
+#[prelude_import] use future::*;
+mod future {
+    trait Future {
+        type Output;
+    }
+}
+
+"#,
+    );
+    assert_eq!("u64", type_at_pos(&db, pos));
+}
+
+#[test]
+fn infer_desugar_async() {
+    let (db, pos) = TestDB::with_position(
+        r#"
+//- /main.rs crate:main deps:std
+
+async fn foo() -> u64 {
+    128
+}
+
+fn test() {
+    let r = foo();
+    r<|>;
+}
+
+//- /std.rs crate:std
+#[prelude_import] use future::*;
+mod future {
+    trait Future {
+        type Output;
+    }
+}
+
+"#,
+    );
+    assert_eq!("impl Future<Output = u64>", type_at_pos(&db, pos));
+}
+
+#[test]
 fn infer_try() {
     let (db, pos) = TestDB::with_position(
         r#"
diff --git a/crates/ra_project_model/src/cargo_workspace.rs b/crates/ra_project_model/src/cargo_workspace.rs
index c862d3912..1b3c246c7 100644
--- a/crates/ra_project_model/src/cargo_workspace.rs
+++ b/crates/ra_project_model/src/cargo_workspace.rs
@@ -165,7 +165,7 @@ impl CargoWorkspace {
             // FIXME: `NoDefaultFeatures` is mutual exclusive with `SomeFeatures`
             // https://github.com/oli-obk/cargo_metadata/issues/79
             meta.features(CargoOpt::NoDefaultFeatures);
-        } else {
+        } else if cargo_features.features.len() > 0 {
             meta.features(CargoOpt::SomeFeatures(cargo_features.features.clone()));
         }
         if let Some(parent) = cargo_toml.parent() {
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index a8f625176..baaef3023 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -221,6 +221,10 @@ impl ast::FnDef {
             .and_then(|it| it.into_token())
             .filter(|it| it.kind() == T![;])
     }
+
+    pub fn is_async(&self) -> bool {
+        self.syntax().children_with_tokens().any(|it| it.kind() == T![async])
+    }
 }
 
 impl ast::LetStmt {