Improve inspection for Rails/InverseOf

[wata727]

See #5236

Currently, Rails/InverseOf Cop checks associations unspecified inverse_of and included conditions, through, polymorphic, or foreign_key. However, this inspection is incorrect.

For example, for through and polymorphic you have to add inverse_of to the inverse association of them.

# bad
class Physician < ApplicationRecord
  has_many :appointments
  has_many :patients, through: :appointments, inverse_of: :physicians
end

class Appointment < ApplicationRecord
  belongs_to :physician
  belongs_to :patient
end

class Patient < ApplicationRecord
  has_many :appointments
  has_many :physicians, through: :appointments, inverse_of: :patients
end

# good
class Physician < ApplicationRecord
  has_many :appointments
  has_many :patients, through: :appointments
end

class Appointment < ApplicationRecord
  belongs_to :physician, inverse_of: :appointments
  belongs_to :patient, inverse_of: :appointments
end

class Patient < ApplicationRecord
  has_many :appointments
  has_many :physicians, through: :appointments
end

# bad
class Picture < ApplicationRecord
  belongs_to :imageable, polymorphic: true, inverse_of: :pictures
end

class Employee < ApplicationRecord
  has_many :pictures, as: :imageable
end

class Product < ApplicationRecord
  has_many :pictures, as: :imageable
end

# good
class Picture < ApplicationRecord
  belongs_to :imageable, polymorphic: true
end

class Employee < ApplicationRecord
  has_many :pictures, as: :imageable, inverse_of: :imageable
end

class Product < ApplicationRecord
  has_many :pictures, as: :imageable, inverse_of: :imageable
end

Unfortunately, even if this Cop looks at the structure of the send node, it can't check for through associations. So, it ignores them. In the case of polymorphic, this Cop should check on the inverse as associations. In addition, I added the check of class_name option.

This Cop still includes false positives when using Object#with_options. Perhaps I will fix this problem as another pull request.

---

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 rake default or rake parallel. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Thanks for opening PR. #5236 reports on false positives with with_options.

This Cop still includes false positives when using Object#with_options. Perhaps I will fix this problem as another pull request.

If you don't resolve with_options in this PR, you should not write Fixes #5236 in the body of the commit message. Because it closes #5236 unresolved.

[wata727]

Thanks for the advice. I removed Fix #5236 from this pull request and this commit :)

[koic]

You are welcome. I think that writing a link to #5236 in the commit message is good for showing a practical issue. For example, I prefer Refer #5236, Follow up of #5236, and others 😃

In this case it would be better to show the issue without using the following keywords.
https://help.github.com/articles/closing-issues-using-keywords/