Add new Lint/DuplicateRegexpCharacterClassElement cop

[owst]

Cop documentation:

      # This cop checks for duplicate elements in Regexp character classes.
      #
      # @example
      #
      #   # bad
      #   r = /[xyx]/
      #
      #   # bad
      #   r = /[0-9x0-9]/
      #
      #   # good
      #   r = /[xy]/
      #
      #   # good
      #   r = /[0-9x]/

---

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.

[marcandre]

Looks good. Only thing I can see is I think this would trigger a false positive on repeated space:

hex = /[
  a-f  # lowercase letter
  0-9 # digit
]+/x

[bbatsov]

After rebasing update this to 1.1. :-)

[owst]

🎉 amazing - 1.0! Great news @bbatsov - thank you for all of your and the core team's hard work!

[owst]

@marcandre regarding your comment:

Looks good. Only thing I can see is I think this would trigger a false positive on repeated space:

hex = /[
  a-f  # lowercase letter
  0-9 # digit
]+/x

Indeed, I thought the same would happen, but actually, it appears that Ruby's free-space mode doesn't support comments inside characters classes (at least on 2.6.6):

[1] pry(main)> hex = /[
[1] pry(main)*   a-f  # lowercase letter
[1] pry(main)*   0-9 # digit
[1] pry(main)* ]+/x
=> /[
  a-f  # lowercase letter
  0-9 # digit
]+/x
[2] pry(main)> hex.match('loot')
=> #<MatchData "loot">

We shouldn't be able to match loot unless # lowercase letter is not a comment.

[marcandre]

Awesome, thanks!