src/test/ui/nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs

   1 // Test that the NLL solver cannot find a solution
   2 // for `exists<R1> { forall<R1> { R2: R1 } }`.
   3 //
   4 // In this test, the impl should match `fn(T)` for some `T`,
   5 // but we ask it to match `for<'a> fn(&'a ())`. Due to argument
   6 // contravariance, this effectively requires a `T = &'b ()` where
   7 // `forall<'a> { 'a: 'b }`. Therefore, we get an error.
   8 //
   9 // Note the use of `-Zno-leak-check` here. This is presently required in order
  10 // to skip the leak-check errors.
  11 //
  12 // c.f. Issue #57642.
  13 //
  14 // compile-flags:-Zno-leak-check
  15
  16 trait Y {
  17     type F;
  18     fn make_f() -> Self::F;
  19 }
  20
  21 impl<T> Y for fn(T) {
  22     type F = fn(T);
  23
  24     fn make_f() -> Self::F {
  25         |_| {}
  26     }
  27 }
  28
  29 fn main() {
  30     let _x = <fn(&())>::make_f();
  31     //~^ ERROR implementation of `Y` is not general enough
  32     //~| ERROR implementation of `Y` is not general enough
  33 }