undefined method `gem_dir' for nil:NilClass when running the rubocop command on 0.35.0

[roberts1000]

I just upgraded from 0.34.2 to 0.35.0. I'm using the inherit_gem functionality, but I'm getting this error.

undefined method `gem_dir' for nil:NilClass
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:184:in `gem_config_path'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:178:in `block in resolve_inheritance_from_gems'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:176:in `each_pair'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:176:in `resolve_inheritance_from_gems'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:30:in `load_file'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_loader.rb:92:in `configuration_from_file'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/config_store.rb:40:in `for'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/target_finder.rb:112:in `excluded_dirs'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/target_finder.rb:90:in `find_files'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/target_finder.rb:60:in `target_files_in_dir'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/target_finder.rb:31:in `find'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/runner.rb:46:in `find_target_files'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/runner.rb:30:in `run'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/lib/rubocop/cli.rb:26:in `run'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/bin/rubocop:13:in `block in <top (required)>'
/home/user/.rvm/rubies/ruby-2.2.3/lib/ruby/2.2.0/benchmark.rb:303:in `realtime'
/home/user/.rvm/gems/ruby-2.2.3/gems/rubocop-0.35.0/bin/rubocop:12:in `<top (required)>'
/home/user/.rvm/gems/ruby-2.2.3/bin/rubocop:23:in `load'
/home/user/.rvm/gems/ruby-2.2.3/bin/rubocop:23:in `<main>'
/home/user/.rvm/gems/ruby-2.2.3/bin/ruby_executable_hooks:15:in `eval'
/home/user/.rvm/gems/ruby-2.2.3/bin/ruby_executable_hooks:15:in `<main>'

The .rubocop.yml in my application has:

inherit_gem:
  rubocop: config/default.yml
  my_gem: config/.rubocop.yml

Here is what I have observed:

1. If I take the .rubocop.yml out of the gem and overwrite the .rubocop.yml in the application (a.k.a don't load .rubocop.yml from my_gem or use inherit_gem), then rubocop works fine.
2. If I downgrade rubocop and to 0.34.2, and try to use inherit_gem, I get a message about "unrecognized cop inherit_gem".
3. Prior to the release of rubocop 0.35.0, we were loading rubocop HEAD via the :git option in our application's Gemfile. This worked locally; we were able to use the inherit_gem functionality in development. However, our CI pipeline would generate errors during a deploy. We eventually traced it back to "something" with rubocop. If we stopped using :git and just used rubocop 0.34.2 without inherit_gem then our CI deployments worked fine.
4. In my application Gemfile, if I load my_gem via the :path option, the inherit_gem functionality works fine. On my local development machine, I'm able to use inherit_gem to pull the .rubocop.yml out of my_gem. As soon as I drop the :path option in the application's Gemfile, I get the above error.

my_gem doesn't do anything crazy. It's a very simple gem that just holds config/.rubocop.yml file and it installs an executable named rubo which executes the rubocop with specific options so we can have a simple standard command for our team.

[jonas054]

I'm not sure why you get that nilreference and I haven't been able to reproduce it, but either way you should not explicitly inherit from RuboCop's config/default.yml. All configurations are implicitly based on the config/default.yml of the rubocop being run.

[roberts1000]

Thanks for taking a look. I'll do some deeper debugging on my end and see if I can come up with some more specific.

I included config/default.yml because the README section on inherit_gem showed this snippet of code:

inherit_gem:
  rubocop: config/default.yml
  my-shared-gem: .rubocop.yml
  cucumber: conf/rubocop.yml

I thought that mean config/default.yml was needed as a base when using inherit_gem. Thanks for the tip.

[alexdowad]

@roberts1000 Do you still have the same problem after removing config/default.yml?