src/test/ui/lint/dead-code/self-assign.rs

   1 // Test that dead code warnings are issued for superfluous assignments of
   2 // fields or variables to themselves (issue #75356).
   3
   4 // ignore-test FIXME(81658, 83171)
   5
   6 // check-pass
   7 #![allow(unused_assignments)]
   8 #![warn(dead_code)]
   9
  10 fn main() {
  11     let mut x = 0;
  12     x = x;
  13     //~^ WARNING: useless assignment of variable of type `i32` to itself
  14
  15     x = (x);
  16     //~^ WARNING: useless assignment of variable of type `i32` to itself
  17
  18     x = {x};
  19     // block expressions don't count as self-assignments
  20
  21
  22     struct S<'a> { f: &'a str }
  23     let mut s = S { f: "abc" };
  24     s = s;
  25     //~^ WARNING: useless assignment of variable of type `S` to itself
  26
  27     s.f = s.f;
  28     //~^ WARNING: useless assignment of field of type `&str` to itself
  29
  30
  31     struct N0 { x: Box<i32> }
  32     struct N1 { n: N0 }
  33     struct N2(N1);
  34     struct N3 { n: N2 };
  35     let mut n3 = N3 { n: N2(N1 { n: N0 { x: Box::new(42) } }) };
  36     n3.n.0.n.x = n3.n.0.n.x;
  37     //~^ WARNING: useless assignment of field of type `Box<i32>` to itself
  38
  39     let mut t = (1, ((2, 3, (4, 5)),));
  40     t.1.0.2.1 = t.1.0.2.1;
  41     //~^ WARNING: useless assignment of field of type `i32` to itself
  42
  43
  44     let mut y = 0;
  45     macro_rules! assign_to_y {
  46         ($cur:expr) => {{
  47             y = $cur;
  48         }};
  49     }
  50     assign_to_y!(y);
  51     // self-assignments in macro expansions are not reported either
  52 }