LL | fn should_not_take_this_arg(m: &mut HashMap<Key, usize>, _n: usize) -> HashSet<Key> {
| ^^^^^^^^^^^^^^^^^^^^^^^^
|
- = note: `#[deny(clippy::mutable_key_type)]` on by default
+ = note: `-D clippy::mutable-key-type` implied by `-D warnings`
error: mutable key type
--> $DIR/mut_key.rs:27:72