error[E0277]: the trait bound `impl Future<Output = ()>: Copy` is not satisfied
  --> $DIR/issue-55872-3.rs:14:20
   |
LL |     fn foo<T>() -> Self::E {
   |                    ^^^^^^^ the trait `Copy` is not implemented for `impl Future<Output = ()>`

error: aborting due to previous error

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