src/test/ui/nll/issue-27282-mutate-before-diverging-arm-2.rs

   1 // This is testing an attempt to corrupt the discriminant of the match
   2 // arm in a guard, followed by an attempt to continue matching on that
   3 // corrupted discriminant in the remaining match arms.
   4 //
   5 // Basically this is testing that our new NLL feature of emitting a
   6 // fake read on each match arm is catching cases like this.
   7 //
   8 // This case is interesting because it includes a guard that
   9 // diverges, and therefore a single final fake-read at the very end
  10 // after the final match arm would not suffice.
  11 //
  12 // It is also interesting because the access to the corrupted data
  13 // occurs in the pattern-match itself, and not in the guard
  14 // expression.
  15
  16 struct ForceFnOnce;
  17
  18 fn main() {
  19     let mut x = &mut Some(&2);
  20     let force_fn_once = ForceFnOnce;
  21     match x {
  22         &mut None => panic!("unreachable"),
  23         &mut Some(&_)
  24             if {
  25                 // ForceFnOnce needed to exploit #27282
  26                 (|| { *x = None; drop(force_fn_once); })();
  27                 //~^ ERROR cannot mutably borrow `x` in match guard [E0510]
  28                 false
  29             } => {}
  30
  31         // this segfaults if we corrupted the discriminant, because
  32         // the compiler gets to *assume* that it cannot be the `None`
  33         // case, even though that was the effect of the guard.
  34         &mut Some(&2)
  35             if {
  36                 panic!()
  37             } => {}
  38         _ => panic!("unreachable"),
  39     }
  40 }