error[E0038]: the trait `X` cannot be made into an object
  --> $DIR/object-safety-bounds.rs:7:11
   |
LL | trait X {
   |       - this trait cannot be made into an object...
LL |     type U: PartialEq<Self>;
   |             --------------- ...because it uses `Self` as a type parameter in this
...
LL | fn f() -> Box<dyn X<U = u32>> {
   |           ^^^^^^^^^^^^^^^^^^^ the trait `X` cannot be made into an object

error: aborting due to previous error

For more information about this error, try `rustc --explain E0038`.