src/test/ui/span/issue28498-reject-trait-bound.rs

   1 // Demonstrate that having a trait bound causes dropck to reject code
   2 // that might indirectly access previously dropped value.
   3 //
   4 // Compare with run-pass/issue28498-ugeh-with-trait-bound.rs
   5
   6 use std::fmt;
   7
   8 #[derive(Debug)]
   9 struct ScribbleOnDrop(String);
  10
  11 impl Drop for ScribbleOnDrop {
  12     fn drop(&mut self) {
  13         self.0 = format!("DROPPED");
  14     }
  15 }
  16
  17 struct Foo<T: fmt::Debug>(u32, T);
  18
  19 impl<T: fmt::Debug> Drop for Foo<T> {
  20     fn drop(&mut self) {
  21         // Use of `may_dangle` is unsound, because we access `T` fmt method when we pass
  22         // `self.1` below, and thus potentially read from borrowed data.
  23         println!("Dropping Foo({}, {:?})", self.0, self.1);
  24     }
  25 }
  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); // OK
  34     foo1 = Foo(1, &first_dropped);
  35     //~^ ERROR `first_dropped` does not live long enough
  36
  37     println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
  38 }