Interesting interaction with RSpec let inside a block

[jdickey]

Given the following RSpec spec file (which passes):

require 'spec_helper'

require 'cco/blog_cco2'

# Second-generation CCO for Blogs. Does not (presently) subclass Base.
module CCO
  describe BlogCCO2 do
    let(:from) { BlogCCO2.public_method :from_entity }
    let(:to) { BlogCCO2.public_method :to_entity }

    describe 'has a .from_entity method that' do
      let(:p) { BlogCCO2.public_method :from_entity }

      it 'is a class method' do
        expect(from.receiver).to be BlogCCO2
        expect(p.receiver).to be BlogCCO2
      end

      it 'takes two parameters' do
        expect(p.arity.abs).to eq 2
      end

      describe 'takes two parameters, where' do
        it 'the first parameter is required' do
          param = p.parameters.first
          expect(param[0]).to be :req
        end

        it 'the second parameter is optional' do
          param = p.parameters.second
          expect(param[0]).to be :opt
        end
      end # describe 'takes two parameters, where'
    end # describe 'has a .from_entity method that'

    describe 'has a .to_entity method that' do
      let(:p) { BlogCCO2.public_method :to_entity }

      it 'is a class method' do
        expect(p.receiver).to be BlogCCO2
      end

      it 'takes one required parameter' do
        expect(p.arity).to be 1
        expect(p.parameters.first[0]).to be :req
      end
    end # describe 'has a .to_entity method that'

  end # describe CCO::BlogCCO2
end # module CCO

running RuboCop with the command line rubocop -R spec/models/cco/blog_cco2_spec.rb yields the output

Inspecting 1 file
C

Offenses:

spec/models/cco/blog_cco2_spec.rb:17:16: C: Do not write to stdout. Use Rails' logger if you want to log.
        expect(p.receiver).to be BlogCCO2
               ^
spec/models/cco/blog_cco2_spec.rb:21:16: C: Do not write to stdout. Use Rails' logger if you want to log.
        expect(p.arity.abs).to eq 2
               ^
spec/models/cco/blog_cco2_spec.rb:26:19: C: Do not write to stdout. Use Rails' logger if you want to log.
          param = p.parameters.first
                  ^
spec/models/cco/blog_cco2_spec.rb:31:19: C: Do not write to stdout. Use Rails' logger if you want to log.
          param = p.parameters.second
                  ^
spec/models/cco/blog_cco2_spec.rb:41:16: C: Do not write to stdout. Use Rails' logger if you want to log.
        expect(p.receiver).to be BlogCCO2
               ^
spec/models/cco/blog_cco2_spec.rb:45:16: C: Do not write to stdout. Use Rails' logger if you want to log.
        expect(p.arity).to be 1
               ^
spec/models/cco/blog_cco2_spec.rb:46:16: C: Do not write to stdout. Use Rails' logger if you want to log.
        expect(p.parameters.first[0]).to be :req
               ^

1 file inspected, 7 offenses detected

Note that every reference to p triggers a RuboCop offense, including the first (at line 17), but the expect call at line 16 (which checks from.receiver rather than p.receiver) is not flagged.

Why? Again, RSpec gives me a green bar; no failures.

Behaviour observed in Rubocop 0.23.0 and 0.24.0, with Rails 4.1.2 under Ruby 2.0.0p481. The RSpec version is 2.99.1.

[bbatsov]

That's a bug that we'll have to fix.

[yujinakayama]

I think the underlying problem is that the Output cop (it's a Rails cop) does not have Include option to restrict the target only to app/**/* by default.

• https://github.com/bbatsov/rubocop/blob/v0.24.0/config/default.yml#L494-L522

Also, it's difficult to differentiate Kernel#p and any p defined by user (RSpec's let actually defines an instance method).

[jdickey]

@yujinakayama Good point; I'd forgotten about Kernel#p. I still think it's a Rubocop bug, and I'm glad that @bbatsov apparently agrees.