E0392 incorrectly claims generic parameter used in associated type bound is unused

[PatchMixolydic]

Given the following code (playground):

trait Trait<T> {
    type Type;
}

struct X<U, F: Trait<(), Type = U>>(F);
struct Y<T, U, F: Trait<T, Type = U>>(F);

The current output is:

error[E0392]: parameter `T` is never used
 --> src/lib.rs:6:10
  |
6 | struct Y<T, U, F: Trait<T, Type = U>>(F);
  |          ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
  = help: if you intended `T` to be a const parameter, use `const T: usize` instead

error[E0392]: parameter `U` is never used
 --> src/lib.rs:6:13
  |
6 | struct Y<T, U, F: Trait<T, Type = U>>(F);
  |             ^ unused parameter
  |
  = help: consider removing `U`, referring to it in a field, or using a marker such as `PhantomData`
  = help: if you intended `U` to be a const parameter, use `const U: usize` instead

Note that there are no diagnostics for X. Indeed, removing Y causes the build to succeed.

The first instance of E0392 is allegedly correct according to #60214 and #53589. However, the second diagnostic claiming that U is unused seems to be incorrect. Otherwise, E0392 should also complain about X's U parameter.

Ideally, the output should look like:

error[E0392]: parameter `T` is never used
 --> src/lib.rs:6:10
  |
6 | struct Y<T, U, F: Trait<T, Type = U>>(F);
  |          ^ unused parameter
  |
  = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
  = help: if you intended `T` to be a const parameter, use `const T: usize` instead

@rustbot modify labels +A-traits +D-incorrect