This article is part of the “Meta Advent 2019” series. I’ve committed to writing a new blog post here every day until Christmas.

Yesterday I wrote about some recent work in RuboCop that resulted in a bunch of breaking changes. Today I’ll share with you a simple strategy for dealing with such changes easily.

Here are the top two problems that people experience on RuboCop upgrades:

  • New offences coming from newly created cops
  • Breaking changes to the configuration (e.g. cops or cop parameter were renamed)

While RuboCop itself mitigates the second problem to some extent (via some deprecation messages) you still have to update your configuration manually, which kind of sucks. Enter mry - a cool little tool by RuboCop Core Team member Masataka “Pocke” Kuwabara. In case you’re wondering - mry stands for “Migrate RuboCop.Yml”.1 Using the tool is super simple:

$ mry .rubocop.yml

That’s going to apply all the necessary changes for the latest RuboCop release. You can also be a bit more specific about the target RuboCop version:

$ mry --target=0.75.0 .rubocop.yml

That’s obviously quite useful if you’re not targeting the latest and greatest RuboCop for some reason. Let’s see mry in action now:


Pretty neat, right?

I guess one obvious question that you might have is why isn’t this in RuboCop itself? Frankly, I don’t have a good answer. We might incorporate the mry functionality down the road, but we’re also planning to really reduce this type of changes after RuboCop 1.0 is out. Anyways, it’d be nice if this was some generic framework in RuboCop that was accessible to all plugins, as currently mry tracks only changes in the main rubocop gem.

That’s all I had for you today. See you again tomorrow!

  1. Naming is hard.