Add new Rails/RedundantReceiverInWithOptions cop

[koic]

Feature

This cop checks for redundant receiver in with_options.
Receiver is implicit from Rails 4.2 or higher.

Bad case

class Account < ApplicationRecord
  with_options dependent: :destroy do |assoc|
    assoc.has_many :customers
    assoc.has_many :products
    assoc.has_many :invoices
    assoc.has_many :expenses
  end
end

Good case

class Account < ApplicationRecord
  with_options dependent: :destroy do
    has_many :customers
    has_many :products
    has_many :invoices
    has_many :expenses
  end
end

How to use

% cat app/models/account.rb
# frozen_string_literal: true

class Account < ApplicationRecord
  with_options dependent: :destroy do |assoc|
    assoc.has_many :customers
    assoc.has_many :products
    assoc.has_many :invoices
    assoc.has_many :expenses
  end
end

% rubocop /tmp/app/models/account.rb --only Rails/RedundantReceiverInWithOptions
Inspecting 1 file
C

Offenses:

/tmp/app/models/account.rb:5:5: C: Rails/RedundantReceiverInWithOptions: Redundant receiver in with_options.
    assoc.has_many :customers
    ^^^^^
/tmp/app/models/account.rb:6:5: C: Rails/RedundantReceiverInWithOptions: Redundant receiver in with_options.
    assoc.has_many :products
    ^^^^^
/tmp/app/models/account.rb:7:5: C: Rails/RedundantReceiverInWithOptions: Redundant receiver in with_options.
    assoc.has_many :invoices
    ^^^^^
/tmp/app/models/account.rb:8:5: C: Rails/RedundantReceiverInWithOptions: Redundant receiver in with_options.
    assoc.has_many :expenses
    ^^^^^

1 file inspected, 4 offenses detected

Other Information

API documentation
http://api.rubyonrails.org/?q=with_options

---

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).
• Used the same coding conventions as the rest of the project.
• 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.
• All tests(rake spec) are passing.
• The new code doesn't generate RuboCop offenses that are checked by rake internal_investigation.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[bbatsov]

Usually in English the word redundant would be used instead of unneeded.

[koic]

Thanks for the review. Code comment, cop name, offense message, commit message and so on in this PR were all replaced with redundant.

[bbatsov]

👍