In Factorial, we had the need to know during the CI analysis which pull request were introducing new Rubocop offenses in our source code.

The requirement was a bit tricky. We didn’t want existing offenses in our source code, only the new ones. This let us to set an starting point as a threshold of offenses to start decreasing it to zero.

There are similar projects out there, like rubocop-git, diffcop, nexocop, but not all of them offer differences at line level. Only rubocop-git offer this nice feature but you have to craft the commit id to get the proper fork point of your pull request.

For this reason, I created rubocop-changes. Also, I was a bit curious to play with git diff and Rubocop output. The idea was to cross both outputs to know exactly in which line there were new offenses.

This is just an example of a failing pull request with one offense:

== components/importer/app/services/workbook.rb ==
C:145: 28: Style/TrailingCommaInArguments: Avoid comma after the last parameter of a method call.

12 files inspected, 1 offense detected

If you want to play with it, you have it available as a gem in RubyGems.