--only and ambiguous cop name

[zverok]

Versions: rubocop 1.6.1, rubocop-rspec 2.0.1
This file:

RSpec.describe 'something' do
  let(:field_X) { 1 }
end

...produces (beside others) this offense:

spec/foo_spec.rb:2:7: C: RSpec/VariableName: Use snake_case for variable names.
  let(:field_X) { 1 }
      ^^^^^^^^

...but, when I am trying to use --only RSpec/VariableName (actually, on a large project, checking each cop's impact):

$ rubocop --only RSpec/VariableName spec/
--only option: RSpec/VariableName has the wrong namespace - should be Naming
Inspecting 1 file
.

1 file inspected, no offenses detected

(Notice the warning about namespace)

Shouldn't be this way, I believe :)

[bbatsov]

@dvandersluis can you look into this?

[dvandersluis]

Sure I'll take a look tomorrow (sorry didn't get a notification about this earlier for some reason).

[dvandersluis]

So some context:

$ rubocop --only RSpec/VariableName spec/ --debug

--only option: RSpec/VariableName has the wrong namespace - should be Naming
For /Users/daniel/RubymineProjects/rubocop: configuration from /Users/daniel/RubymineProjects/rubocop/.rubocop.yml
configuration from /Users/daniel/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/rubocop-performance-1.9.1/config/default.yml
configuration from /Users/daniel/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/rubocop-performance-1.9.1/config/default.yml
Default configuration from /Users/daniel/RubymineProjects/rubocop/config/default.yml
configuration from /Users/daniel/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/rubocop-rspec-2.0.1/config/default.yml
configuration from /Users/daniel/.rbenv/versions/2.6.6/lib/ruby/gems/2.6.0/gems/rubocop-rspec-2.0.1/config/default.yml
Inheriting configuration from /Users/daniel/RubymineProjects/rubocop/.rubocop_todo.yml
Inspecting 555 files

What's happening here is:

1. --only triggers Cop::Registry.qualified_cop_name to map the cop names given on the command line to actual cops: https://github.com/rubocop-hq/rubocop/blob/2a4f895dd7eb29246e18f61cb4e3f493cc2005d8/lib/rubocop/options.rb#L100
2. qualified_cop_name tries to match the name against the known registry. If a badge is not found, it accepts it (crucial here). https://github.com/rubocop-hq/rubocop/blob/7989d3ec1f65b9d2a73589cc956d6858742a47d5/lib/rubocop/cop/registry.rb#L106-L114
3. If there is a badge found it resolves it. This is where we're failing. https://github.com/rubocop-hq/rubocop/blob/7989d3ec1f65b9d2a73589cc956d6858742a47d5/lib/rubocop/cop/registry.rb#L270-L278

As you can see from the output above, this check happens before the rubocop-rspec configuration is injected (error message is on line 1 but rubocop-rspec is not loaded until line 6). Therefore, when the Registry tries to find a qualified cop name, it can only find Naming/VariableName (because RSpec/VariableName has not yet been loaded). Then the error message is shown because there's a department mismatch.

So in this case, the error is due to there being a name conflict between cops in different libraries. --only RSpec/Focus for example would work fine, because there is no core RuboCop cop named Focus, so step 2 above will accept the missing badge. Since there is a conflict here, a badge is found, hence the error.

I think the best solution here would be to resolve requires earlier so that the registry is full, I'm going to look into how we can achieve that.

[bquorning]

FYI @pirj