Add new Style/MagicCommentFormat cop

[mattbearman]

Magic comments in Ruby are underscore/hyphen agnostic, this can lead to codebases having inconsistent case style in the frozen string literal comment (# frozen_string_literal: true and # frozen-string-literal: true)

This cop allows the enforcement of either snake case (underscore separated) or kebab case (hyphen separated).

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Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

I think it'd better is this was a cop covering all such pragmas. One cop per pragma seems like a massive overkill to me.

[mattbearman]

That's a great point, I'll see about extending this to all magic comments 👍

[bbatsov]

@mattbearman ping :-)

[dvandersluis]

@mattbearman are you still interested in completing this?

[dvandersluis]

@bbatsov I have updated this PR to complete it.

The cop is now called Style/MagicComments, and it enforces consistency on all magic comments, not just frozen-string-literal. I also added the ability to keep capitalization consistent, for both the comment directives and values independently.

[dvandersluis]

Some tests are failing randomly and I haven't been able to repro yet. Looking into it.

[dvandersluis]

Ah, figured it out, filter_map isn't available in all rubies 😁 Fixed it now.

[bbatsov]

Seems to me this can simply be a boolean.

[dvandersluis]

There are three options - upper (all uppercase), lower (all lowercase) and nil (ignore capitalization)

[bbatsov]

Yeah, I saw this, but was on the fence for whether it makes sense for someone to disable this. I've yet to see someone not writing lowercase magic comments, but I guess they exist. :D

[dvandersluis]

I figured that since it's easy, having options is better 😄

[koic]

Style/MagicComments may be abstract. A somewhat concreted name like Style/MagicCommentFormat, Style/MagicCommentShape, or more better name looks user friendly.

[dvandersluis]

Style/MagicComments may be abstract. A somewhat concreted name like Style/MagicCommentFormat, Style/MagicCommentShape, or more better name looks user friendly.

Sure, MagicCommentFormat works for me.

[bbatsov]

I think I like DirectiveCase a bit better as capitalization and lowercase don't mix very well IMO. :-) Perhaps spelling out fully lowercase and uppercase would be best.

[dvandersluis]

I had DirectiveCase first but I found it confusing with snake case and kebab case. I'll change it to the full lowercase and uppercase, good suggestion!

[dvandersluis]

Updated!