src/test/ui/nll/drop-may-dangle.rs

   1 // Basic test for liveness constraints: the region (`R1`) that appears
   2 // in the type of `p` includes the points after `&v[0]` up to (but not
   3 // including) the call to `use_x`. The `else` branch is not included.
   4
   5 // compile-flags:-Zborrowck=mir
   6 // build-pass (FIXME(62277): could be check-pass?)
   7
   8 #![allow(warnings)]
   9 #![feature(dropck_eyepatch)]
  10
  11 fn use_x(_: usize) -> bool { true }
  12
  13 fn main() {
  14     let mut v = [1, 2, 3];
  15     let p: WrapMayDangle<& /* R4 */ usize> = WrapMayDangle { value: &v[0] };
  16     if true {
  17         // `p` will get dropped at end of this block. However, because of
  18         // the `#[may_dangle]` attribute, we do not need to consider R4
  19         // live after this point.
  20         use_x(*p.value);
  21     } else {
  22         v[0] += 1;
  23         use_x(22);
  24     }
  25
  26     v[0] += 1;
  27 }
  28
  29 struct WrapMayDangle<T> {
  30     value: T
  31 }
  32
  33 unsafe impl<#[may_dangle] T> Drop for WrapMayDangle<T> {
  34     fn drop(&mut self) { }
  35 }