Incorrect "function is never used" for function only used in a const assertion

[RalfJung]

Code

const fn black_box<T>(x: T) -> T { x }

const _: () = {
    assert!(black_box(5) == 5);
};

Current output

warning: function `black_box` is never used
 --> src/lib.rs:1:10
  |
1 | const fn black_box<T>(x: T) -> T { x }
  |          ^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

Desired output

(none)

Rationale and extra context

The function is used in a const assertion -- that can have a side-effect so it should be considered a "use".

Other cases

No response

Rust Version

Current nightly

Anything else?

No response

[CastilloDel]

Hey! I would like to tackle this. Could you give some pointers on where to look? I'm still unfamiliar with the codebase. EDIT: I guess most of it will be in compiler/rustc_passes/src/dead.rs, but any extra pointer is appreciated!

@rustbot claim

[RalfJung]

Sorry, I got no idea. Maybe try the t-compiler/help stream on Zulip.

[zachs18]

Related #118424

[RalfJung]

Ah indeed, this is a duplicate.