error[E0277]: the size for values of type `dyn Future<Output = T> + Unpin` cannot be known at compilation time
  --> $DIR/awaiting-unsized-param.rs:7:17
   |
LL | async fn bug<T>(mut f: dyn Future<Output = T> + Unpin) -> T {
   |                 ^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn Future<Output = T> + Unpin`
   = note: all local variables must have a statically known size

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.