error[E0277]: the trait bound `{async block@$DIR/issue-55872-3.rs:17:9: 17:14}: Copy` is not satisfied
  --> $DIR/issue-55872-3.rs:14:20
   |
LL |     fn foo<T>() -> Self::E {
   |                    ^^^^^^^ the trait `Copy` is not implemented for `{async block@$DIR/issue-55872-3.rs:17:9: 17:14}`
...
LL |         async {}
   |         -------- return type was inferred to be `{async block@$DIR/issue-55872-3.rs:17:9: 17:14}` here

error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
  --> $DIR/issue-55872-3.rs:14:20
   |
LL |     fn foo<T>() -> Self::E {
   |                    ^^^^^^^

error: aborting due to 2 previous errors

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