Suggest return type for async function without return type

2 files changed, 57 insertions, 0 deletions

diff --git a/tests/ui/typeck/issue-90027-async-fn-return-suggestion.rs b/tests/ui/typeck/issue-90027-async-fn-return-suggestion.rs
new file mode 100644
index 00000000000..8ccb15ca48a
--- /dev/null
+++ b/tests/ui/typeck/issue-90027-async-fn-return-suggestion.rs
@@ -0,0 +1,21 @@
+// edition:2018
+
+async fn hello() { //~ HELP try adding a return type
+    0
+    //~^ ERROR [E0308]
+}
+
+async fn world() -> () {
+    0
+    //~^ ERROR [E0308]
+}
+
+async fn suggest_await_in_async_fn_return() {
+    hello()
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider `await`ing on the `Future`
+    //~| HELP consider using a semicolon here
+    //~| SUGGESTION .await
+}
+
+fn main() {}
diff --git a/tests/ui/typeck/issue-90027-async-fn-return-suggestion.stderr b/tests/ui/typeck/issue-90027-async-fn-return-suggestion.stderr
new file mode 100644
index 00000000000..6a1a9f45bc6
--- /dev/null
+++ b/tests/ui/typeck/issue-90027-async-fn-return-suggestion.stderr
@@ -0,0 +1,36 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-90027-async-fn-return-suggestion.rs:4:5
+   |
+LL | async fn hello() {
+   |                  - help: try adding a return type: `-> i32`
+LL |     0
+   |     ^ expected `()`, found integer
+
+error[E0308]: mismatched types
+  --> $DIR/issue-90027-async-fn-return-suggestion.rs:9:5
+   |
+LL | async fn world() -> () {
+   |                     -- expected `()` because of return type
+LL |     0
+   |     ^ expected `()`, found integer
+
+error[E0308]: mismatched types
+  --> $DIR/issue-90027-async-fn-return-suggestion.rs:14:5
+   |
+LL |     hello()
+   |     ^^^^^^^ expected `()`, found opaque type
+   |
+   = note: expected unit type `()`
+            found opaque type `impl Future<Output = ()>`
+help: consider `await`ing on the `Future`
+   |
+LL |     hello().await
+   |            ++++++
+help: consider using a semicolon here
+   |
+LL |     hello();
+   |            +
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.