false negative unused_mut: if let x .. = &mut

[matthiaskrgr]

fn main() {
   let mut word = "hello".to_string();
   if let Some(_) = &mut word.chars().last() { // here
       word.push_str(" word");
   }
   
   println!("{}", word);
}

In this example, the mut in if let Some(char) = &mut word.chars().last() { is redundant but the compiler issued no warning.

rustc 1.43.0-nightly (4ad624882 2020-03-03)

[cuviper]

Does unused_mut ever trigger for &mut? I thought that was only for mut bindings.

fn main() {
    let x = &mut 42;
    println!("{}", *x);
}

No warning there...

[jeremystucki]

I’ll try to implement this

[jeremystucki]

Okay it is way harder than I thought, so I won't be able to get it to work