tests/ui/span/issue28498-reject-passed-to-fn.rs

   1 // Demonstrate that a type param in negative position causes dropck to reject code
   2 // that might indirectly access previously dropped value.
   3 //
   4 // Compare with run-pass/issue28498-ugeh-with-passed-to-fn.rs
   5
   6 #[derive(Debug)]
   7 struct ScribbleOnDrop(String);
   8
   9 impl Drop for ScribbleOnDrop {
  10     fn drop(&mut self) {
  11         self.0 = format!("DROPPED");
  12     }
  13 }
  14
  15 struct Foo<T>(u32, T, Box<for <'r> fn(&'r T) -> String>);
  16
  17 impl<T> Drop for Foo<T> {
  18     fn drop(&mut self) {
  19         // Use of `may_dangle` is unsound, because we pass `T` to the callback in `self.2`
  20         // below, and thus potentially read from borrowed data.
  21         println!("Dropping Foo({}, {})", self.0, (self.2)(&self.1));
  22     }
  23 }
  24
  25 fn callback(s: & &ScribbleOnDrop) -> String { format!("{:?}", s) }
  26
  27 fn main() {
  28     let (last_dropped, foo0);
  29     let (foo1, first_dropped);
  30
  31     last_dropped = ScribbleOnDrop(format!("last"));
  32     first_dropped = ScribbleOnDrop(format!("first"));
  33     foo0 = Foo(0, &last_dropped, Box::new(callback)); // OK
  34     foo1 = Foo(1, &first_dropped, Box::new(callback));
  35     //~^ ERROR `first_dropped` does not live long enough
  36
  37     println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
  38 }