error[E0277]: the trait bound `impl Future: Copy` is not satisfied
  --> $DIR/issue-55872-2.rs:13:20
   |
LL |     fn foo<T>() -> Self::E {
   |                    ^^^^^^^ the trait `Copy` is not implemented for `impl Future`

error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
  --> $DIR/issue-55872-2.rs:13:28
   |
LL |       fn foo<T>() -> Self::E {
   |  ____________________________^
LL | |
LL | |
LL | |         async {}
LL | |     }
   | |_____^

error: aborting due to 2 previous errors

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