If you read my post on running bundle-audit from rake you'll also know I run RuboCop as part of continuous integration in Travis CI. Today I switched a project to run on Travis' new docker infrastructure and something hilarious happened.

Running Travis CI on Docker

This part is super easy. Amazingly easy. Add this to your .travis.yml file:

# Docker Infrastructure
sudo: false
cache: bundler

The sudo key is the magic word to build your project in a Docker container. The cache key will enable bundler caching for your project.

These two lines can speed up your build times by nearly eliminating startup costs. I went from 2.5 minutes to 24 seconds on builds which used the cache and archived images. I'm running bundle-audit, brakeman, rubocop, and rspec in 24 seconds. That is awesome!

The funny thing is…

The first run I had a little hiccup. RuboCop was doing its thing and, on this project, it only has 30 files to inspect. I know that because I just ran it locally and, yep, 30 files. In the Travis environment, however, it was scanning 5320 files. That's probably wrong.

Turns out, by enabling the cache in Travis I caused RuboCop to lose its mind. How? Because of where the cache was stored. Travis put the cache in vendor/bundle which is in my Rails app directory and within sight of RuboCop. That's legit, but I don't actually want RuboCop to check any vendor code.

Why was RuboCop doing that? Because I wanted to Exclude a few things in my Rails app—mostly generated code—so I had a .rubocop.yml file that looked a little like this:

require: rubocop-rspec
inherit_from: .rubocop_todo.yml
AllCops:
  Exclude:
    - 'db/schema.rb'
    - 'bin/**/*'
    - 'config/initializers/devise.rb'
    - 'config/initializers/simple_form*'
    - 'db/migrate/*'
  RunRailsCops: true

The default RuboCop configuration does exclude vendor. I need that, too, but my Exclude above overrides the default, so it was gone.

The simple fix

Lets just add vendor back into the exclusion list:

require: rubocop-rspec
inherit_from: .rubocop_todo.yml
AllCops:
  Exclude:
    - 'db/schema.rb'
    - 'bin/**/*'
    - 'config/initializers/devise.rb'
    - 'config/initializers/simple_form*'
    - 'db/migrate/*'
    - 'vendor/**/*'
  RunRailsCops: true

Voila!

Be careful when modifying RuboCop's configuration that you copy what you need to keep from the defaults, because defining an entry in your project will discard the them, not merge them.