I’m planning to release a 1.0.0 version of failure on March 15. Once this happens, I don’t plan to release any further breaking changes to the failure crate (though maybe someday in the distant future). Breaking changes in 1.0 failure is in a somewhat unique position as being a significant part of the public API of other libraries that depend on it. Whether they use the Error struct or derive Fail for a custom error type, this becomes a part of the API they expose to other users.…