GAT's + const generics error yields Invalid suggestion

[DutchGhost]

The following code errors, and the error contains a suggestion how to fix the error:

#![feature(generic_associated_types)]
#![feature(const_generics)]
#![feature(const_evaluatable_checked)]

trait Funk<const P: usize> {
    type Item<const N: usize>: Funk<{core::mem::size_of::<Self>()}>;
}

The error message states:

error[E0277]: the size for values of type `Self` cannot be known at compilation time
   --> src/lib.rs:6:59
    |
6   |     type Item<const N: usize>: Funk<{core::mem::size_of::<Self>()}>;
    |                                                           ^^^^ doesn't have a size known at compile-time
    |
help: consider further restricting `Self`
    |
5   | trait Funk: Sized<const P: usize> {
    |           ^^^^^^^

error: aborting due to previous error; 3 warnings emitted

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground`

Obviously, writing trait Funk: Sized<const P: usize> { is invalid syntax.

[camelid]

It seems the issue is that it's inserting the suggestion after the trait name and before the generics, rather than after the generics.

[SNCPlay42]

No-nightly-features code that exhibits the same problem:

trait Foo<T> {
    const SIZE: usize = core::mem::size_of::<Self>();
}

error[E0277]: the size for values of type `Self` cannot be known at compilation time
   --> src/lib.rs:2:46
    |
2   |     const SIZE: usize = core::mem::size_of::<Self>();
    |                                              ^^^^ doesn't have a size known at compile-time
    |
help: consider further restricting `Self`
    |
1   | trait Foo: Sized<T> {
    |          ^^^^^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground`

@rustbot label -requires-nightly

(should the F-labels go as well?)