2 files changed, 30 insertions, 2 deletions

diff --git a/crates/ra_hir_def/src/data.rs b/crates/ra_hir_def/src/data.rs
index 1aa9a9b7d..0a282f31b 100644
--- a/crates/ra_hir_def/src/data.rs
+++ b/crates/ra_hir_def/src/data.rs
@@ -6,12 +6,15 @@ use hir_expand::{
     name::{name, AsName, Name},
     AstId, InFile,
 };
-use ra_syntax::ast::{self, AstNode, ImplItem, ModuleItemOwner, NameOwner, TypeAscriptionOwner};
+use ra_syntax::ast::{
+    self, AstNode, AsyncOwner, ImplItem, ModuleItemOwner, NameOwner, TypeAscriptionOwner,
+};
 
 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 +65,31 @@ 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..bf401df35 100644
--- a/crates/ra_hir_def/src/path.rs
+++ b/crates/ra_hir_def/src/path.rs
@@ -130,6 +130,11 @@ 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
     }