src/test/ui/coherence/coherence-fn-inputs.rs

   1 // Test that we consider these two types completely equal:
   2 //
   3 // * `for<'a, 'b> fn(&'a u32, &'b u32)`
   4 // * `for<'c> fn(&'c u32, &'c u32)`
   5 //
   6 // For a long time we considered these to be distinct types. But in fact they
   7 // are equivalent, if you work through the implications of subtyping -- this is
   8 // because:
   9 //
  10 // * `'c` can be the intersection of `'a` and `'b` (and there is always an intersection)
  11 // * `'a` and `'b` can both be equal to `'c`
  12
  13 trait Trait {}
  14 impl Trait for for<'a, 'b> fn(&'a u32, &'b u32) {}
  15 impl Trait for for<'c> fn(&'c u32, &'c u32) {
  16     //~^ ERROR conflicting implementations
  17     //
  18     // Note in particular that we do NOT get a future-compatibility warning
  19     // here. This is because the new leak-check proposed in [MCP 295] does not
  20     // "error" when these two types are equated.
  21     //
  22     // [MCP 295]: https://github.com/rust-lang/compiler-team/issues/295
  23 }
  24
  25 fn main() {}