error[E0276]: impl has stricter requirements than trait
  --> $DIR/issue-55872-1.rs:15:5
   |
LL |     fn foo<T>() -> Self::E;
   |     ----------------------- definition of `foo` from trait
...
LL |     fn foo<T: Default>() -> Self::E {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `T: Default`

error[E0277]: the trait bound `S: Copy` is not satisfied in `(S, T)`
  --> $DIR/issue-55872-1.rs:11:14
   |
LL |     type E = impl Copy;
   |              ^^^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `S`
   |
   = note: required because it appears within the type `(S, T)`
help: consider further restricting this bound
   |
LL | impl<S: Default + Copy> Bar for S {
   |                 ^^^^^^

error[E0277]: the trait bound `T: Copy` is not satisfied in `(S, T)`
  --> $DIR/issue-55872-1.rs:11:14
   |
LL |     type E = impl Copy;
   |              ^^^^^^^^^ within `(S, T)`, the trait `Copy` is not implemented for `T`
   |
   = note: required because it appears within the type `(S, T)`
help: consider further restricting this bound
   |
LL |     fn foo<T: Default + Copy>() -> Self::E {
   |                       ^^^^^^

error: type parameter `T` is part of concrete type but not used in parameter list for the `impl Trait` type alias
  --> $DIR/issue-55872-1.rs:15:37
   |
LL |       fn foo<T: Default>() -> Self::E {
   |  _____________________________________^
LL | |
LL | |
LL | |         (S::default(), T::default())
LL | |     }
   | |_____^

error: aborting due to 4 previous errors

Some errors have detailed explanations: E0276, E0277.
For more information about an error, try `rustc --explain E0276`.