unused_mut warning gives bad suggestion in a macro

[ehuss]

The following gives a suggestion to remove the mut which will cause the code to fail to compile.

macro_rules! array {
    ($($element:expr),*) => {{
        let mut array = Vec::new();
        $(
            array.push($element);
        )*
        array
    }};
}

fn main() {
    let _x: Vec<i32> = array![];
    let _y: Vec<i32> = array![1,2,3];
}

warning: variable does not need to be mutable
  --> src/main.rs:3:13
   |
3  |         let mut array = Vec::new();
   |             ----^^^^^
   |             |
   |             help: remove this `mut`
...
12 |     let _x: Vec<i32> = array!{};
   |                        -------- in this macro invocation
   |
   = note: #[warn(unused_mut)] on by default

This causes cargo fix to fail.

(Sorry if this is a dupe, I went hunting but couldn't find any issues that were the same.)

[ehuss]

Note: This requires NLL. Using 2015 edition before #59114 does not emit a warning.

[taiki-e]

You probably can avoid this to using variables with names starting with _ in macro.

[mati865]

@rustbot modify labels: +A-NLL

[steveklabnik]

Triage: this still gives the warning, and still fails to compile if you apply the warning.

[estebank]

Triage: no change.