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// 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
}
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