[steveklabnik]

    use self::itertools::join;

This is the free function version; leave it out. I haven't tried this myself, but I'd bet that's what's going on; https://docs.rs/itertools/0.5.6/itertools/trait.Itertools.ht... is different from https://docs.rs/itertools/0.5.6/itertools/fn.join.html, though.