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