1 // Test an `exists<'a> { forall<'b> { 'a = 'b } }` pattern -- which should not compile!
3 // In particular, we test this pattern in trait solving, where it is not connected
4 // to any part of the source code.
12 T: Trait<for<'b> fn(Cell<&'b u32>)>,
16 impl<'a> Trait<fn(Cell<&'a u32>)> for () {}
19 // Here, proving that `(): Trait<for<'b> fn(&'b u32)>` uses the impl:
21 // - The impl provides the clause `forall<'a> { (): Trait<fn(&'a u32)> }`
22 // - We instantiate `'a` existentially to get `(): Trait<fn(&?a u32)>`
23 // - We unify `fn(&?a u32)` with `for<'b> fn(&'b u32)`
24 // - This requires (among other things) instantiating `'b` universally,
25 // yielding `fn(&!b u32)`, in a fresh universe U1
26 // - So we get `?a = !b` but the universe U0 assigned to `?a` cannot name `!b`.
28 foo::<()>(); //~ ERROR implementation of `Trait` is not general enough