src/test/compile-fail/lint-unused-mut-variables.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Exercise the unused_mut attribute in some positive and negative cases
  12
  13 #![allow(unused_assignments)]
  14 #![allow(unused_variables)]
  15 #![allow(dead_code)]
  16 #![deny(unused_mut)]
  17
  18
  19 fn main() {
  20     // negative cases
  21     let mut a = 3; //~ ERROR: variable does not need to be mutable
  22     let mut a = 2; //~ ERROR: variable does not need to be mutable
  23     let mut b = 3; //~ ERROR: variable does not need to be mutable
  24     let mut a = vec!(3); //~ ERROR: variable does not need to be mutable
  25     let (mut a, b) = (1, 2); //~ ERROR: variable does not need to be mutable
  26     let mut a; //~ ERROR: variable does not need to be mutable
  27     a = 3;
  28
  29     let mut b; //~ ERROR: variable does not need to be mutable
  30     if true {
  31         b = 3;
  32     } else {
  33         b = 4;
  34     }
  35
  36     match 30 {
  37         mut x => {} //~ ERROR: variable does not need to be mutable
  38     }
  39     match (30, 2) {
  40       (mut x, 1) | //~ ERROR: variable does not need to be mutable
  41       (mut x, 2) |
  42       (mut x, 3) => {
  43       }
  44       _ => {}
  45     }
  46
  47     let x = |mut y: isize| 10; //~ ERROR: variable does not need to be mutable
  48     fn what(mut foo: isize) {} //~ ERROR: variable does not need to be mutable
  49
  50     // positive cases
  51     let mut a = 2;
  52     a = 3;
  53     let mut a = Vec::new();
  54     a.push(3);
  55     let mut a = Vec::new();
  56     callback(|| {
  57         a.push(3);
  58     });
  59     let (mut a, b) = (1, 2);
  60     a = 34;
  61
  62     match 30 {
  63         mut x => {
  64             x = 21;
  65         }
  66     }
  67
  68     match (30, 2) {
  69       (mut x, 1) |
  70       (mut x, 2) |
  71       (mut x, 3) => {
  72         x = 21
  73       }
  74       _ => {}
  75     }
  76
  77     let x = |mut y: isize| y = 32;
  78     fn nothing(mut foo: isize) { foo = 37; }
  79
  80     // leading underscore should avoid the warning, just like the
  81     // unused variable lint.
  82     let mut _allowed = 1;
  83 }
  84
  85 fn callback<F>(f: F) where F: FnOnce() {}
  86
  87 // make sure the lint attribute can be turned off
  88 #[allow(unused_mut)]
  89 fn foo(mut a: isize) {
  90     let mut a = 3;
  91     let mut b = vec!(2);
  92 }