src/test/ui/impl-trait/auto-trait.rs

   1 // Tests that type alias impls traits do not leak auto-traits for
   2 // the purposes of coherence checking
   3 #![feature(type_alias_impl_trait)]
   4
   5 trait OpaqueTrait {}
   6 impl<T> OpaqueTrait for T {}
   7 type OpaqueType = impl OpaqueTrait;
   8 fn mk_opaque() -> OpaqueType {
   9     ()
  10 }
  11
  12 #[derive(Debug)]
  13 struct D<T>(T);
  14
  15 trait AnotherTrait {}
  16 impl<T: Send> AnotherTrait for T {}
  17
  18 // This is in error, because we cannot assume that `OpaqueType: !Send`.
  19 // (We treat opaque types as "foreign types" that could grow more impls
  20 // in the future.)
  21 impl AnotherTrait for D<OpaqueType> {
  22     //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
  23     //~| ERROR cannot implement trait on type alias impl trait
  24 }
  25
  26 fn main() {}