Detect class_variable_set in Style/ClassVars

[biinari]

class_variable_set(:@@name, 2) has the same effect as @@name = 2

This variation can be within the class definition:

class A
  class_variable_set(:@@name, 2)
end

Or it could be called elsewhere, with the class as receiver:

class A; end

class B
  def change(name, value)
    A.class_variable_set(":@@#{name}", value)
  end
end

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Can you add this bad case to the example code?

[koic]

This looks good to me. Can you rebase with the latest master branch for resolve changelog entry?

[biinari]

Thanks for the review @koic. Rebased from master now. Looks like the Changelog has somehow ended up with two Changes sections in the unreleased part. Would you like me to merge those together?

[koic]

Yeah, "Changes" section has been merged on the master branch.
https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md#master-unreleased

[biinari]

Ah thanks. Now I see why it didn't get thrown up as a conflict. That changelog entry should be right now.

[koic]

Thanks 👍