unsized coercion: select vs trait goal mismatch

[lcnr]

trait Super<'a> {}
trait Trait<'a>: Super<'a> + for<'hr> Super<'hr> {}

fn foo<'a>(x: Box<dyn Trait<'a>>) -> Box<dyn Super<'a>> {
    x
}

ICEs in the new solver: using select in HIR typeck arbitrarily prefers the earlier super trait bound, proving the CoerceUnsized trait goal in MIR typeck fails with ambiguity

the above is ambig in the old solver, this one is pass -> fail:

trait Super<T> {}
trait Trait<T>: Super<T> + for<'hr> Super<&'hr ()> {}

fn foo<'a>(x: Box<dyn Trait<&'a ()>>) -> Box<dyn Super<&'a ()>> {
    x
}

[lcnr]

both this issue and #238 would get fixed by rust-lang/rust#141926