+ | ^
+ | |
+ | checked the `Output` of this `async fn`, found opaque type
+ | expected `()`, found opaque type
+ |
+ = note: while checking the return type of the `async fn`
+note: type in trait
+ --> $DIR/fn-header-semantic-fail.rs:21:47
+ |
+LL | const async unsafe extern "C" fn ft5();
+ | ^
+ = note: expected fn pointer `unsafe extern "C" fn()`
+ found fn pointer `unsafe extern "C" fn() -> impl Future<Output = ()>`