rubocop-rails

rubocop 0.72.0 removes all Rails cops, since they “[…] want RuboCop to be focused just on Ruby […]” (and I agree with them), see PR #5976.

In order to use the Rails cops after rubocop 0.72.0, we need to add rubocop-rails gem and require it as a dependency in .rubocop.yml:

require:
  - rubocop-rails