tests/ui/dropck/issue-28498-ugeh-with-passed-to-fn.rs

   1 // run-pass
   2
   3 // Demonstrate the use of the unguarded escape hatch with a type param in negative position
   4 // to assert that destructor will not access any dead data.
   5 //
   6 // Compare with ui/span/issue28498-reject-lifetime-param.rs
   7
   8 // Demonstrate that a type param in negative position causes dropck to reject code
   9 // that might indirectly access previously dropped value.
  10 //
  11 // Compare with run-pass/issue28498-ugeh-with-passed-to-fn.rs
  12
  13 #![feature(dropck_eyepatch)]
  14
  15 #[derive(Debug)]
  16 struct ScribbleOnDrop(String);
  17
  18 impl Drop for ScribbleOnDrop {
  19     fn drop(&mut self) {
  20         self.0 = format!("DROPPED");
  21     }
  22 }
  23
  24 struct Foo<T>(u32, T, #[allow(unused_tuple_struct_fields)] Box<for <'r> fn(&'r T) -> String>);
  25
  26 unsafe impl<#[may_dangle] T> Drop for Foo<T> {
  27     fn drop(&mut self) {
  28         // Use of `may_dangle` is sound, because destructor never passes a `self.1`
  29         // to the callback (in `self.2`) despite having it available.
  30         println!("Dropping Foo({}, _)", self.0);
  31     }
  32 }
  33
  34 fn callback(s: & &ScribbleOnDrop) -> String { format!("{:?}", s) }
  35
  36 fn main() {
  37     let (last_dropped, foo0);
  38     let (foo1, first_dropped);
  39
  40     last_dropped = ScribbleOnDrop(format!("last"));
  41     first_dropped = ScribbleOnDrop(format!("first"));
  42     foo0 = Foo(0, &last_dropped, Box::new(callback));
  43     foo1 = Foo(1, &first_dropped, Box::new(callback));
  44
  45     println!("foo0.1: {:?} foo1.1: {:?}", foo0.1, foo1.1);
  46 }