Confusing #warn(unused_comparisons)

Code

#[allow(overflowing_literals)]
fn bad(c: u8) -> bool {
    if (c as i8) >= 0xFF {
        return true;
    } else {
        return false;
    }
}

fn main() {
    assert!(bad(0));
    assert!(!bad(0xFE));
}

Current output

warning: comparison is useless due to type limits
 --> a.rs:3:8
  |
3 |     if (c as i8) >= 0xFF {
  |        ^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_comparisons)]` on by default

warning: 1 warning emitted

Desired output

Not sure, but possibilities include:
- no warning
- a different warning
- more careful wording of this warning

Rationale and extra context

While the current warning makes sense on the human level (i8 value is always less than 255), it is contrary to the way the code is compiled - the resulting program does not fail any of the assertions, which proves that both branches of the comparison are executed depending on the input argument. So, 0xFF literal is interpreted as -1, in which case it is well within bounds of i8 and the comparison is not useless.

Other cases

Rust Version

$ rustc --version --verbose
rustc 1.91.1 (ed61e7d7e 2025-11-07) (built from a source tarball)
binary: rustc
commit-hash: ed61e7d7e242494fb7057f2657300d9e77bb4fcb
commit-date: 2025-11-07
host: x86_64-unknown-linux-gnu
release: 1.91.1
LLVM version: 21.1.2

Anything else?

No response

Start by compiling the provided Rust example with rustc and compare the unused_comparisons diagnostic with the runtime assertions. Investigate how the warning handles the cast and literal, then determine an agreed warning behavior; done requires a diagnostic that accurately reflects this case.