[Fix #1238] Add new Rails/EnumSyntax cop

[koic]

Fixes #1238.
Based on #1239.

Defining enums with keyword arguments is deprecated and will be removed in Rails 8.0.

---

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.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[Earlopain]

Can you add a test for defining two enums with one method call?

enum enum1: [:active], enum2: [:archived]

I was curious if this syntax works, and it indeed does:

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", "~> 7.0"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :conversations, force: true do |t|
    t.column :enum1, :integer, default: 0
    t.column :enum2, :integer, default: 0
  end
end

class Conversation < ActiveRecord::Base
  enum enum1: [:active], enum2: [:archived]
end

class BugTest < Minitest::Test
  def test_association_stuff
    conversation = Conversation.create!
    assert conversation.active?
    assert conversation.archived?
  end
end

I don't autocorrect is needed for these cases, seems very rare and I don't find documentation for it (though in code, it is pretty explicit https://github.com/rails/rails/blob/914caca2d31bd753f47f9168f2a375921d9e91cc/activerecord/lib/active_record/enum.rb#L160)

[koic]

Yeah, autocorrect might be provided in the future, but for now, let's start by registering an offense only.

[Earlopain]

👍 Looks good