Error message suggests using "ref mut mut" which is invalid

[upsuper]

See the following code:

enum TestEnum {
    Item(i32),
}

fn test(_: &mut i32) {
}

fn main() {
    let mut x = TestEnum::Item(10);
    match x {
        TestEnum::Item(ref mut x) => {
            test(&mut x);
        }
    }
}

The compiler raises error and suggests that:

error: cannot borrow immutable local variable `x` as mutable
  --> <anon>:12:23
   |
11 |         TestEnum::Item(ref mut x) => {
   |                        --------- use `ref mut mut x` here to make mutable
12 |             test(&mut x);
   |                       ^ cannot borrow mutably

which doesn't make sense, because ref mut mut is invalid.

The correct code here is actually using test(x) directly as x itself is already a mutable reference there.

[nagisa]

Similar #34337