Allow ignoring scopes for inverse_of cop

[composerinteralia]

With rails/rails#43358, Rails can now infer
inverse_of for associations with a scope when
config.active_record.automatic_scope_inversing = true.

This commit adds an IgnoreScopes option to the inverse_of cop allowing
us to disable the cop for scopes when the new Rails option is set to
true.

I considered having the default for IgnoreScopes change based on the
Rails version since this is the default for new Rails >= 7.0
applications, but existing applications that upgrade to 7.0 wouldn't
necessarily have the option set and in that case changing the
rubocop-rails default behavior would be a breaking change.

---

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.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[pirj]

automatically detect inverse_of when there is a scope on the association, but not when there is a scope on the potential inverse association

How do we detect that the latter condition is met?

[composerinteralia]

How do we detect that the latter condition is met?

That's not something this Cop currently detects, with or without this change (and I'm not sure there's a good way we could detect it without runtime info).

For example:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post, -> { where("1=0") }
end

Rails is not able to automatically infer the inverse_of for has_many :comments because of the scope on the opposite association. The new config.active_record.automatic_scope_inversing option hasn't changed that behavior.

And regardless of the change in this PR the Rails/InverseOf cop will not report an offense on has_many :comments, even though it doesn't have an inverse_of.

I think this is actually a good thing, since setting inverse_of in cases like this can cause problems. In this contrived example, the post association should never return any records because of the where("1=0") scope, but if we add an inverse_of it could return a record:

class Post < ActiveRecord::Base
  has_many :comments, inverse_of: post
end

class Comment < ActiveRecord::Base
  belongs_to :post, -> { where("1=0") }
end

post = Post.create!
comment = post.comments.create!

# This fails because we use the already loaded inverse record,
# and thus never run the scope.
assert_nil comment.post 

[pirj]

You've right, I've missed the point of Rails/InverseOf cop.
Now, when Rails provides this option, inverse_of becomes redundant.
Looks good to me.
Thanks for the contribution!

[composerinteralia]

🎉 @pirj any chance you have access to approve the workflow so I can verify everything passes?

[pirj]

access to approve the workflow

Unfortunately not, I'm only volunteering here with preliminary assessment of tickets and preliminary code review.
@koic is the sole maintainer as far as I know.

[koic]

Can you update the config/default.yml?

 Rails/InverseOf:
   Description: 'Checks for associations where the inverse cannot be determined automatically.'
   Enabled: true
   VersionAdded: '0.52'
+  IgnoreScopes: false
   Include:
     - app/models/**/*.rb

[koic]

Perhaps the contrast will be more noticeable whether only the differences are extracted as shown below.

      # @example IgnoreScopes: false (default)
      #   # bad
      #   class Blog < ApplicationRecord
      #     has_many :posts, -> { order(published_at: :desc) }
      #   end
      #
      # @example IgnoreScopes: true
      #   # good
      #   class Blog < ApplicationRecord
      #     has_many :posts, -> { order(published_at: :desc) }
      #   end

And can you move this as the bottom example?

[composerinteralia]

Done! Thank you for the review, and hi 👋🏻!

[koic]

Thank you, Daniel!