Merge #2661

2661: Implement infer await from async function r=flodiebold a=edwin0cheng

This PR is my attempt for trying to add support for infer `.await` expression from an `async` function, by desugaring its return type to `Impl Future<Output=RetType>`.

Note that I don't know it is supposed to desugaring it in that phase, if it is not suitable in current design, just feel free to reject it :)

r=@flodiebold 

Co-authored-by: Edwin Cheng <[email protected]>

1 files changed, 57 insertions, 0 deletions

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#"