Comment by chrismorgan

And I guess it’s 2015 edition, because it’ll fail in 2018 edition Rust: where the 2015 edition has ::u8(0u8), the 2018 edition will need you to write crate::u8(0u8) or self::u8(0u8), since only crates exist at the top level now, rather than the contents of the current crate as well.