Wonky diagnostics on unsatisfied implicit Sized bounds

[Flying-Toast]

Code

fn main() {
    let _ = std::mem::size_of::<[i32]>();
}

Current output

312 | pub const fn size_of<T>() -> usize {
    |                      ^ required by this bound in `size_of`

The "this bound" doesn't actually point to a bound.

Desired output

Instead of "required by this bound"/"unsatisfied trait bound introduced here" we should say "note: T has an implicit bound of Sized"

Rationale and extra context

No response

Other cases

trait Foo {
    const VAL: usize;
}

impl<T> Foo for T {
    const VAL: usize = std::mem::size_of::<T>();
}

fn main() {
    println!("{}", <[i32] as Foo>::VAL);
}

Produces:

5  | impl<T> Foo for T {
   |      -  ^^^     ^
   |      |
   |      unsatisfied trait bound introduced here

Rust Version

rustc 1.75.0 (82e1608df 2023-12-21)
binary: rustc
commit-hash: 82e1608dfa6e0b5569232559e3d385fea5a93112
commit-date: 2023-12-21
host: x86_64-unknown-linux-gnu
release: 1.75.0
LLVM version: 17.0.6

Anything else?

No response

[fmease]

I've updated the title since Sized is not an auto trait and since this diagnostic issue is specific to Sized only.