TODO(@lcnr): why fail

[lcnr]

//@ check-pass
//@ revisions: current next
//@[next] compile-flags: -Znext-solver
//@ ignore-compare-mode-next-solver (explicit revisions)

trait Sup {
    type As;
}
trait Trait<'d>: Sup {}
fn foo3<T>()
where
    for<'i> T: Trait<'i, As: Trait<'i, As: Sup>>,
{
}

fn main() {}

This test fails with https://github.com/lcnr/rust/pull/new/no-region-unification. I have to figure out whether that's a fundamental issue or not.