Add RSpec/DuplicatedMetadata cop

[r7kamura]

Looking at RSpec code in some libraries and applications, I see several duplicate metadata. So I think it would be nice to have a Cop that detects such code. What do you think?

For example, the following is the result from rubocop gem:

$ bundle exec rubocop spec
Inspecting 646 files
.................................................................................................................................................................................................................................................................................................................................................................................C....................................................................................................................................................................................................................................................................................

Offenses:

spec/rubocop/cop/style/conditional_assignment_assign_to_condition_spec.rb:3:69: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Style::ConditionalAssignment, :config, :config, :config do
                                                                    ^^^^^^^
spec/rubocop/cop/style/conditional_assignment_assign_to_condition_spec.rb:3:78: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Style::ConditionalAssignment, :config, :config, :config do
                                                                             ^^^^^^^

646 files inspected, 2 offenses detected, 2 offenses autocorrectable

And the following is from rubocop-rails gem:

$ bundle exec rubocop spec
Inspecting 133 files
................CCC..................................C...............................................................................

Offenses:

spec/rubocop/cop/rails/application_job_spec.rb:3:62: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Rails::ApplicationJob, :config, :config do
                                                             ^^^^^^^
spec/rubocop/cop/rails/application_mailer_spec.rb:3:65: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Rails::ApplicationMailer, :config, :config do
                                                                ^^^^^^^
spec/rubocop/cop/rails/application_record_spec.rb:3:65: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Rails::ApplicationRecord, :config, :config do
                                                                ^^^^^^^
spec/rubocop/cop/rails/http_positional_arguments_spec.rb:3:71: C: [Correctable] RSpec/DuplicatedMetadata: Avoid duplicated metadata.
RSpec.describe RuboCop::Cop::Rails::HttpPositionalArguments, :config, :config do
                                                                      ^^^^^^^

133 files inspected, 4 offenses detected, 4 offenses autocorrectable

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• Added the new cop to config/default.yml.
• The cop is configured as Enabled: pending in config/default.yml.
• The cop is configured as Enabled: true in .rubocop.yml.
• The cop documents examples of good and bad code.
• The tests assert both that bad code is reported and that good code is not reported.
• Set VersionAdded in default/config.yml to the next minor version.

If you have modified an existing cop's configuration options:

• Set VersionChanged in config/default.yml to the next major version.

[pirj]

Looks good, thank you!
Did a run on real-world-rspec, no errors.

[Darhazer]

Not a requirement but just wondering - can it also flag :config, config: true duplication?

I’ll do a full review tomorrow

[Darhazer]

❤️

[r7kamura]

Not a requirement but just wondering - can it also flag :config, config: true duplication?

It would be nice to support that case as well 👍
It might be good to do that in this Cop, but it is also a little hard to decide which one should be removed in case of such duplicates. How about we achieve that by having a separate Cop that converts config: true to :config? (Is there already one?)

[pirj]

a separate Cop that converts config: true to :config? (Is there already one?)

There was a PR that initially implemented that, but this part disappeared after a force-push. It remains here in lib/rubocop/cop/rspec/sort_tags.rb around line 187.

[Darhazer]

I agree that :config vs config: true should be separate cop, and that it partially will resolve the question. (:config, config: false will remain an edge case)
Also I was wondering whether a hash metadata should be handled, but since Ruby itself will warn about the overwritten key, I'd say it's a no-goal for a cop.

[Darhazer]

@r7kamura can you please rebase to fix the changelog entry 🙇