Bounds on associated types still ignored

[bgamari]

It seems #20890 may not be entirely resolved. Take this example,

pub trait BitIter {
    type Iter: Iterator<Item=bool>;
    fn bit_iter(self) -> <Self as BitIter>::Iter;
}

fn hi<T>(arg: T) where 
    T: BitIter,
    //<T as BitIter>::Iter: Iterator<Item=bool>
{
    for i in arg.bit_iter() {}
}

rustc 1.0.0-dev (2a51ca0a4 2015-01-25 10:42:41 -0500) fails to compile this with,

hi.rs:9:18: 9:28 error: type mismatch resolving `<<T as BitIter>::Iter as core::iter::Iterator>::Item == bool`:
 expected associated type,
    found bool [E0271]
hi.rs:9     for i in arg.bit_iter() {}
                         ^~~~~~~~~~

Unless, of course, I add the bound.

[huonw]

cc @nikomatsakis

[nikomatsakis]

I think the problem is because we are required to resolve the projection (that is, the result of T::Iter::Item) based on what is declared in the trait, and we don't currently have any logic for doing that.

[carllerche]

cc me

[nikomatsakis]

Fix in #21702

[bgamari]

Confirmed to be fixed.