ICE with associated type

[Kimundi]

Reproduced by

pub trait Pattern<'a>: Sized {
    type Matcher;
}

struct CharEqMatcher<'a, C>(C, &'a str);

impl<'a, C> Pattern<'a> for C {
    type Matcher = CharEqMatcher<'a, C>;
}

pub struct MatchIndices<'a, P: Pattern<'a>>(P::Matcher);

impl<'a, P: Pattern<'a>> Clone for MatchIndices<'a, P> where P::Matcher: Clone {
    fn clone(&self) -> Self {
        MatchIndices(Clone::clone(&self.0))
    }
}

fn main() {}

error: internal compiler error: Where clause 
`Binder(TraitRef(<P as pattern::Pattern<'a>>::Matcher, core::marker::Sized))` was applicable to
`Obligation(predicate=Binder(TraitPredicate(TraitRef(P, core::marker::Sized))),depth=62)`
but now is not

[Kimundi]

cc @nikomatsakis

[nikomatsakis]

Possible dup of #21212

[nikomatsakis]

I have confirmed this is a dup of #21212