See https://github.com/sdroege/rust-associated-types-from-other-crate-projection-bug

The following are the relevant parts of the code:

https://github.com/sdroege/rust-associated-types-from-other-crate-projection-bug/blob/5586433d247734d0efdb73cf51f9b8b9ecde1852/bar/src/lib.rs#L7-L16

https://github.com/sdroege/rust-associated-types-from-other-crate-projection-bug/blob/5586433d247734d0efdb73cf51f9b8b9ecde1852/bar/src/lib.rs#L28-L38

In summary it seems like impl Something<<Foo as Mapper>::OtherType> for Baz {} works fine as long as Foo is defined in the same crate, otherwise it maps the Foo (for whatever reason) to Baz itself.

@alexcrichton