I think TextMate’s bundle index should include a RuboCop bundle.
Disclaimer: I wrote a RuboCop bundle myself, and there are at least three more that I know about:
1) and 2) seem stale (last commit in Nov resp. Dec 2014). 3) and 4) are actively maintained.
One of the differences between 3) and 4) is that 3) supports different gutter marks for different severities, while 4) only uses a generic warning mark. On the other hand, 3) seems to only ever work on the current file, while 4) uses the filebrowser selection (if any, similar to the Git bundle for example).
In https://github.com/textmate/ruby.tmbundle/pull/99#issuecomment-296400597 ff. there was discussion if the Ruby’s bundle already existing “Validate Syntax” command should be changed / extended to use RuboCop (if present) – this could be an alternative to adding an “official” RuboCop bundle.
Happy to hear your opinions!