Bounds on associated types ignored

[bgamari]

In,

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

pub fn test_bad<Sym: BitIter>(sym: Sym) {
    let i = sym.bit_iter();
}

pub fn test_good<Sym: BitIter>(sym: Sym)
    where <Sym as BitIter>::Iter: Iterator<Item=bool> {
    let i = sym.bit_iter();
}

pub fn main() {}

test_bad fails to compile, despite the bounds on BitIter::Iter with,

hi.rs:7:17: 7:27 error: type mismatch resolving `<<Sym as BitIter>::Iter as core::iter::Iterator>::Item == bool`: expected associated type, found bool
hi.rs:7     let i = sym.bit_iter();
                        ^~~~~~~~~~

[tomjakubowski]

Is this related to #20890?

[bgamari]

Yep, sounds like the same issue.

[Aatch]

Closing as duplicate of #20890