rust/src/test/ui/lint/lint-unused-mut-variables.rs

// Exercise the unused_mut attribute in some positive and negative cases

#![allow(unused_assignments)]
#![allow(unused_variables)]
#![allow(dead_code)]
#![deny(unused_mut)]


fn main() {
    // negative cases
    let mut a = 3; //~ ERROR: variable does not need to be mutable

    let mut a = 2; //~ ERROR: variable does not need to be mutable

    let mut b = 3; //~ ERROR: variable does not need to be mutable

    let mut a = vec![3]; //~ ERROR: variable does not need to be mutable

    let (mut a, b) = (1, 2); //~ ERROR: variable does not need to be mutable

    let mut a; //~ ERROR: variable does not need to be mutable

    a = 3;

    let mut b; //~ ERROR: variable does not need to be mutable

    if true {
        b = 3;
    } else {
        b = 4;
    }

    match 30 {
        mut x => {} //~ ERROR: variable does not need to be mutable

    }
    match (30, 2) {
      (mut x, 1) | //~ ERROR: variable does not need to be mutable

      (mut x, 2) |
      (mut x, 3) => {
      }
      _ => {}
    }

    let x = |mut y: isize| 10; //~ ERROR: variable does not need to be mutable

    fn what(mut foo: isize) {} //~ ERROR: variable does not need to be mutable


    let mut a = &mut 5; //~ ERROR: variable does not need to be mutable

    *a = 4;

    let mut a = 5;
    let mut b = (&mut a,); //~ ERROR: variable does not need to be mutable
    *b.0 = 4;

    let mut x = &mut 1; //~ ERROR: variable does not need to be mutable

    let mut f = || {
      *x += 1;
    };
    f();

    fn mut_ref_arg(mut arg : &mut [u8]) -> &mut [u8] {
        &mut arg[..] //~^ ERROR: variable does not need to be mutable

    }

    let mut v : &mut Vec<()> = &mut vec![]; //~ ERROR: variable does not need to be mutable

    v.push(());

    // positive cases
    let mut a = 2;
    a = 3;
    let mut a = Vec::new();
    a.push(3);
    let mut a = Vec::new();
    callback(|| {
        a.push(3);
    });
    let mut a = Vec::new();
    callback(|| {
        callback(|| {
            a.push(3);
        });
    });
    let (mut a, b) = (1, 2);
    a = 34;

    match 30 {
        mut x => {
            x = 21;
        }
    }

    match (30, 2) {
      (mut x, 1) |
      (mut x, 2) |
      (mut x, 3) => {
        x = 21
      }
      _ => {}
    }

    // Attribute should be respected on match arms
    match 0 {
        #[allow(unused_mut)]
        mut x => {
            let mut y = 1;
        },
    }

    let x = |mut y: isize| y = 32;
    fn nothing(mut foo: isize) { foo = 37; }

    // leading underscore should avoid the warning, just like the
    // unused variable lint.
    let mut _allowed = 1;
}

fn callback<F>(f: F) where F: FnOnce() {}

// make sure the lint attribute can be turned off
#[allow(unused_mut)]
fn foo(mut a: isize) {
    let mut a = 3;
    let mut b = vec![2];
}

// make sure the lint attribute can be turned off on let statements
#[deny(unused_mut)]
fn bar() {
    #[allow(unused_mut)]
    let mut a = 3;
    let mut b = vec![2]; //~ ERROR: variable does not need to be mutable

}