src/test/run-pass/traits/trait-copy-guessing.rs

   1 // run-pass
   2 #![allow(dead_code)]
   3 // "guessing" in trait selection can affect `copy_or_move`. Check that this
   4 // is correctly handled. I am not sure what is the "correct" behaviour,
   5 // but we should at least not ICE.
   6
   7 use std::mem;
   8
   9 struct U([u8; 1337]);
  10
  11 struct S<'a,T:'a>(&'a T);
  12 impl<'a, T> Clone for S<'a, T> { fn clone(&self) -> Self { S(self.0) } }
  13 /// This impl triggers inference "guessing" - S<_>: Copy => _ = U
  14 impl<'a> Copy for S<'a, Option<U>> {}
  15
  16 fn assert_impls_fn<R,T: Fn()->R>(_: &T){}
  17
  18 fn main() {
  19     let n = None;
  20     let e = S(&n);
  21     let f = || {
  22         // S being copy is critical for this to work
  23         drop(e);
  24         mem::size_of_val(e.0)
  25     };
  26     assert_impls_fn(&f);
  27     assert_eq!(f(), 1337+1);
  28
  29     assert_eq!((|| {
  30         // S being Copy is not critical here, but
  31         // we check it anyway.
  32         let n = None;
  33         let e = S(&n);
  34         let ret = mem::size_of_val(e.0);
  35         drop(e);
  36         ret
  37     })(), 1337+1);
  38 }