W1004
W1004 — Unnecessary mutable binding (let mut x where x is never reassigned)
No example yet
No fixture in the test suite asserts this code, so there is no program here that is known to trigger it. That is a gap in our coverage rather than a statement about the code.
Contributing one is a good first change — add a fixture under tests/ with a CHECK line naming W1004, and this page picks it up.