Suggest more impl Trait on -> _

Author: compiler-errors

core/src/future/future.rs

@@ -37,6 +37,7 @@ use crate::task::{Context, Poll};
 pub trait Future {
     /// The type of value produced on completion.
     #[stable(feature = "futures_api", since = "1.36.0")]
+    #[rustc_diagnostic_item = "FutureOutput"]
     type Output;
 
     /// Attempt to resolve the future to a final value, registering