unreachable_patterns emitted on _ that matches a local of uninhabited type (that is uninitialized)

[WaffleLapkin]

I tried this code:

enum Void {}

fn main() {
    let void: Void;
    match void {
        _ => (),
    }
}

(playground)

I expected to see this happen: the code compiler without warnings and successfully runs doing nothing.

Instead, this happened: a warning is emitted (the code compiles and runs as expected):

warning: unreachable pattern
 --> src/main.rs:6:9
  |
6 |         _ => (),
  |         ^-------
  |         |
  |         matches no values because `Void` is uninhabited
  |         help: remove the match arm
  |
  = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
  = note: `#[warn(unreachable_patterns)]` on by default

Meta

rustc version: 1.85.0-nightly (2024-12-23 bdc6b3de48646345549f)

[compiler-errors]

This is annoying to fix, b/c while the unreachable patterns lint is in mir-build, we don't actually do the analysis to determine that the variable is uninitialized until borrowck. I'm not totally certain if it's easy or possible to probe whether a variable is initialized in THIR or HIR so that this lint can be suppressed for uninitialized uninhabited variables.