Confusing error with trait with multiple associated types

[apasel422]

I'm not sure if the following should work, but the error message is not helpful:

#![feature(associated_types)]

pub trait Foo {
    type L;
    type R;
}

pub struct Bar<C, D>(C, D);

impl<C: Foo, D: Foo<L = C::L, R = C::R>> Foo for Bar<C, D> {
    type L = C::L;
    type R = C::R;
}

On rustc 0.13.0-nightly (c6c786671 2015-01-04 00:50:59 +0000) this yields:

lib.rs:10:1: 13:2 error: type annotations required: cannot resolve `<D as Foo>::L == <C as Foo>::L`
lib.rs:10 impl<C: Foo, D: Foo<L = C::L, R = C::R>> Foo for Bar<C, D> {
lib.rs:11     type L = C::L;
lib.rs:12     type R = C::R;
lib.rs:13 }

Removing the second associated type from Foo (R) compiles successfully.

[apasel422]

The following also compiles successfully:

#![feature(associated_types)]

pub trait Foo {
    type L;
    type R;
}

pub struct Bar<C, D>(C, D);

impl<C: Foo, D: Foo<L = C::L>> Foo for Bar<C, D> {
    type L = C::L;
    type R = C::R;
}

[apasel422]

This was fixed.