tests/ui/mir/mir_assign_eval_order.rs

   1 // Test evaluation order of assignment expressions is right to left.
   2
   3 // run-pass
   4
   5 // We would previously not finish evaluating borrow and FRU expressions before
   6 // starting on the LHS
   7
   8 struct S(i32);
   9
  10 fn evaluate_reborrow_before_assign() {
  11     let mut x = &1;
  12     let y = &mut &2;
  13     let z = &3;
  14     // There's an implicit reborrow of `x` on the right-hand side of the
  15     // assignment. Note that writing an explicit reborrow would not show this
  16     // bug, as now there would be two reborrows on the right-hand side and at
  17     // least one of them would happen before the left-hand side is evaluated.
  18     *{ x = z; &mut *y } = x;
  19     assert_eq!(*x, 3);
  20     assert_eq!(**y, 1);             // y should be assigned the original value of `x`.
  21 }
  22
  23 fn evaluate_mut_reborrow_before_assign() {
  24     let mut x = &mut 1;
  25     let y = &mut &mut 2;
  26     let z = &mut 3;
  27     *{ x = z; &mut *y } = x;
  28     assert_eq!(*x, 3);
  29     assert_eq!(**y, 1);            // y should be assigned the original value of `x`.
  30 }
  31
  32 // We should evaluate `x[2]` and borrow the value out *before* evaluating the
  33 // LHS and changing its value.
  34 fn evaluate_ref_to_temp_before_assign_slice() {
  35     let mut x = &[S(0), S(1), S(2)][..];
  36     let y = &mut &S(7);
  37     *{ x = &[S(3), S(4), S(5)]; &mut *y } = &x[2];
  38     assert_eq!(2, y.0);
  39     assert_eq!(5, x[2].0);
  40 }
  41
  42 // We should evaluate `x[2]` and copy the value out *before* evaluating the LHS
  43 // and changing its value.
  44 fn evaluate_fru_to_temp_before_assign_slice() {
  45     let mut x = &[S(0), S(1), S(2)][..];
  46     let y = &mut S(7);
  47     *{ x = &[S(3), S(4), S(5)]; &mut *y } = S { ..x[2] };
  48     assert_eq!(2, y.0);
  49     assert_eq!(5, x[2].0);
  50 }
  51
  52 // We should evaluate `*x` and copy the value out *before* evaluating the LHS
  53 // and dropping `x`.
  54 fn evaluate_fru_to_temp_before_assign_box() {
  55     let x = Box::new(S(0));
  56     let y = &mut S(1);
  57     *{ drop(x); &mut *y } = S { ..*x };
  58     assert_eq!(0, y.0);
  59 }
  60
  61 fn main() {
  62     evaluate_reborrow_before_assign();
  63     evaluate_mut_reborrow_before_assign();
  64     evaluate_ref_to_temp_before_assign_slice();
  65     evaluate_fru_to_temp_before_assign_slice();
  66     evaluate_fru_to_temp_before_assign_box();
  67 }