generic const exprs in diagnostics aren't printed with substs applied

[BoxyUwU]

Given the following code: link

#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features)]

trait Trait {}
struct HasCastInTraitImpl<const N: usize, const M: usize>;
impl<const M: usize> Trait for HasCastInTraitImpl<M, { M + 1 }> {}
pub struct HasTrait<T: Trait>(T);
fn foo<const N: usize>() -> HasTrait<HasCastInTraitImpl<{ N + 1 }, { N + 1}>> { loop {} }

fn main() {}

The current output is:

error: unconstrained generic constant
 --> src/main.rs:8:29
  |
7 | pub struct HasTrait<T: Trait>(T);
  |                        ----- required by this bound in `HasTrait`
8 | fn foo<const N: usize>() -> HasTrait<HasCastInTraitImpl<{ N + 1 }, { N + 1}>> { loop {} }
  |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: try adding a `where` bound using this expression: `where [(); { M + 1 }]:`
note: required because of the requirements on the impl of `Trait` for `HasCastInTraitImpl<{ N + 1 }, { N + 1}>`
 --> src/main.rs:6:22
  |
6 | impl<const M: usize> Trait for HasCastInTraitImpl<M, { M + 1 }> {}
  |                      ^^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0308]: mismatched types
 --> src/main.rs:8:29
  |
8 | fn foo<const N: usize>() -> HasTrait<HasCastInTraitImpl<{ N + 1 }, { N + 1}>> { loop {} }
  |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{ N + 1}`, found `{ M + 1 }`
  |
  = note: expected type `{ N + 1}`
             found type `{ M + 1 }`

error: aborting due to 2 previous errors

Ideally the output should look like:

error[E0308]: mismatched types
 --> src/main.rs:8:29
  |
8 | fn foo<const N: usize>() -> HasTrait<HasCastInTraitImpl<{ N + 1 }, { N + 1}>> { loop {} }
  |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `{ N + 1}`, found `{ (N + 1) + 1 }`
  |
  = note: expected type `{ N + 1}`
             found type `{ (N + 1) + 1 }`

@rustbot label: +A-const-generics +F-const_generics +F-const_evaluatable_checked