error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
  --> $DIR/issue-55872.rs:14:28
   |
LL |       fn foo<T>() -> Self::E {
   |  ____________________________^
LL | |
LL | |         || ()
LL | |     }
   | |_____^

error: aborting due to previous error