Associated const requires trait bounds that are already satisfied

[willglynn]

This code (playpen):

trait Foo {
    const SIZE: usize;
}

struct Container<F: Foo> {
    bytes: [u8; <F as Foo>::SIZE],
}

Fails with:

error[E0277]: the trait bound `F: Foo` is not satisfied
 --> src/main.rs:8:17
  |
8 |     bytes: [u8; <F as Foo>::SIZE],
  |                 ^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `F`
  |
  = help: consider adding a `where F: Foo` bound
  = note: required by `Foo::SIZE`

Changing to struct Container<F: Foo> where F: Foo, as directed, fails with the same message.

[vitalyd]

Probably a dupe of #42863

[Mark-Simulacrum]

I think so, or at least another issue mentioned in that one... closing as a duplicate of #42863.