Most of types just derive it using proc_macro directly. Some of value types need manual impl. In my current plan, this new trait will be used in bug 1434130 to expose values as well. Bug: 1455576 Reviewed-by: emilio MozReview-Commit-ID: LI7fy45VkRw
This was generated with: ./mach cargo fmt --package selectors && ./mach cargo fmt --package servo_arc && ./mach cargo fmt --package style Using rustfmt 0.4.1-nightly (a4462d1 2018-03-26)
