Function only used in const assert is treated as dead code

[clarfonthey]

I tried this code: playground link

const fn is_nonzero(x: u8) -> bool {
    x != 0
}
const _: () = {
    assert!(is_nonzero(2));
};

I expected to compile without any warnings.

Instead, it indicates that is_nonzero is dead code:

warning: function `is_nonzero` is never used
 --> src/lib.rs:1:10
  |
1 | const fn is_nonzero(x: u8) -> bool {
  |          ^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (5d707b07e 2025-06-02)
binary: rustc
commit-hash: 5d707b07e42766c080c5012869c9988a18dcbb83
commit-date: 2025-06-02
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.5

[Noratrieb]

Constants with the name _ should be seen as live for the dead code analysis.

[hanna-kruppe]

Some previous discussion in #142075

[DoubleHyphen]

I swear, myself and @clarfonthey are completely different people.