Pluginfy RuboCop Rails

This PR adds support for RuboCop's Plugin feature.

Since RuboCop Rails still supports some older versions of RuboCop,
a conditional check using `RuboCop.const_defined?(:Plugin)` has been added for compatibility.

Once only versions of RuboCop that support the Plugin feature are supported,
the compatibility code and the `RuboCop::Rails::Inject` module will be removed.

This means that the legacy style will gradually become deprecated in the near future.

.rubocop.yml

@@ -1,10 +1,12 @@
 # This is the configuration used to check the rubocop source code.
 
 inherit_from: .rubocop_todo.yml
+plugins:
+  - rubocop-internal_affairs
+  - rubocop-rails
+
 require:
-  - rubocop/cop/internal_affairs
   - rubocop-performance
-  - rubocop-rails
   - rubocop-rspec
 
 AllCops:

README.md

@@ -23,10 +23,48 @@ gem 'rubocop-rails', require: false
 
 ## Usage
 
-You need to tell RuboCop to load the Rails extension. There are three
+You need to tell RuboCop to load the Rails extension. There are some
 ways to do this:
 
-### RuboCop configuration file
+### RuboCop configuration file (Recommended Style)
+
+Put this into your `.rubocop.yml`.
+
+```yaml
+plugins: rubocop-rails
+```
+
+Alternatively, use the following array notation when specifying multiple extensions.
+
+```yaml
+plugins:
+  - rubocop-other-extension
+  - rubocop-rails
+```
+
+Now you can run `rubocop` and it will automatically load the RuboCop Rails
+cops together with the standard cops.
+
+> [!NOTE]
+> The plugin system is supported in RuboCop 1.72+.
+
+### Command line
+
+```sh
+$ rubocop --plugin rubocop-rails
+```
+
+### Rake task
+
+```ruby
+require 'rubocop/rake_task'
+
+RuboCop::RakeTask.new do |task|
+  task.plugins << 'rubocop-rails'
+end
+```
+
+### RuboCop configuration file (Legacy Style)
 
 Put this into your `.rubocop.yml`.
 
@@ -45,15 +83,15 @@ require:
 Now you can run `rubocop` and it will automatically load the RuboCop Rails
 cops together with the standard cops.
 
-### Command line
+### Command line (Legacy Style)
 
 ```sh
 $ rubocop --require rubocop-rails
 ```
 
 Note: `--rails` option is required while `rubocop` command supports `--rails` option.
 
-### Rake task
+### Rake task (Legacy Style)
 
 ```ruby
 require 'rubocop/rake_task'

changelog/new_pluginfy_with_lint_roller.md

@@ -0,0 +1 @@
+* [#1434](https://github.com/rubocop/rubocop-rails/pull/1434): Pluginfy RuboCop Rails. ([@koic][])

docs/modules/ROOT/pages/usage.adoc

@@ -1,15 +1,15 @@
 = Usage
 
-You need to tell RuboCop to load the Rails extension. There are three
+You need to tell RuboCop to load the Rails extension. There are some
 ways to do this:
 
-== RuboCop configuration file
+== RuboCop configuration file (Recommended Style)
 
 Put this into your `.rubocop.yml`.
 
 [source,yaml]
 ----
-require: rubocop-rails
+plugins: rubocop-rails
 ----
 
 Now you can run `rubocop` and it will automatically load the RuboCop Rails
@@ -19,11 +19,41 @@ cops together with the standard cops.
 
 [source,sh]
 ----
-$ rubocop --require rubocop-rails
+$ rubocop --plugin rubocop-rails
 ----
 
 == Rake task
 
+[source,ruby]
+----
+RuboCop::RakeTask.new do |task|
+  task.plugins << 'rubocop-rails'
+end
+----
+
+NOTE: The plugin system is supported in RuboCop 1.72+.
+
+== RuboCop configuration file (Legacy Style)
+
+Put this into your `.rubocop.yml`.
+
+[source,yaml]
+----
+require: rubocop-rails
+----
+
+Now you can run `rubocop` and it will automatically load the RuboCop Rails
+cops together with the standard cops.
+
+== Command line (Legacy Style)
+
+[source,sh]
+----
+$ rubocop --require rubocop-rails
+----
+
+== Rake task (Legacy Style)
+
 [source,ruby]
 ----
 RuboCop::RakeTask.new do |task|

lib/rubocop-rails.rb

@@ -11,7 +11,16 @@
 require_relative 'rubocop/rails/schema_loader'
 require_relative 'rubocop/rails/schema_loader/schema'
 
-RuboCop::Rails::Inject.defaults!
+# FIXME: When RuboCop Rails requires RuboCop 1.72.0+ only, the following compatibility code can be removed.
+if RuboCop.const_defined?(:Plugin)
+  require_relative 'rubocop/rails/plugin'
+else
+  # NOTE: Until the plugin stabilizes, an option to use the older version of RuboCop is provided.
+  # The plugin will be unified in the future.
+  require_relative 'rubocop/rails/inject'
+
+  RuboCop::Rails::Inject.defaults!
+end
 
 require_relative 'rubocop/cop/rails_cops'
 

lib/rubocop/rails.rb

@@ -8,6 +8,6 @@ module Rails
 
     private_constant(:CONFIG_DEFAULT, :PROJECT_ROOT)
 
-    ::RuboCop::ConfigObsoletion.files << PROJECT_ROOT.join('config', 'obsoletion.yml')
+    ConfigObsoletion.files << Pathname("#{__dir__}/../../config/obsoletion.yml")
   end
 end

lib/rubocop/rails/plugin.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'lint_roller'
+
+module RuboCop
+  module Rails
+    # A plugin that integrates RuboCop Rails with RuboCop's plugin system.
+    class Plugin < LintRoller::Plugin
+      def about
+        LintRoller::About.new(
+          name: 'rubocop-rails',
+          version: Version::STRING,
+          homepage: 'https://github.com/rubocop/rubocop-rails',
+          description: 'A RuboCop extension focused on enforcing Rails best practices and coding conventions.'
+        )
+      end
+
+      def supported?(context)
+        context.engine == :rubocop
+      end
+
+      def rules(_context)
+        LintRoller::Rules.new(
+          type: :path,
+          config_format: :rubocop,
+          value: Pathname.new(__dir__).join('../../../config/default.yml')
+        )
+      end
+    end
+  end
+end

rubocop-rails.gemspec

@@ -31,9 +31,12 @@ Gem::Specification.new do |s|
     'rubygems_mfa_required' => 'true'
   }
 
+  s.metadata['default_lint_roller_plugin'] = 'RuboCop::Rails::Plugin'
+
   s.add_dependency 'activesupport', '>= 4.2.0'
   # Rack::Utils::SYMBOL_TO_STATUS_CODE, which is used by HttpStatus cop, was
   # introduced in rack 1.1
+  s.add_dependency 'lint_roller', '~> 1.1'
   s.add_dependency 'rack', '>= 1.1'
   s.add_dependency 'rubocop', '>= 1.52.0', '< 2.0'
   s.add_dependency 'rubocop-ast', '>= 1.38.0', '< 2.0'

spec/spec_helper.rb

@@ -5,6 +5,9 @@
 require_relative 'support/file_helper'
 require_relative 'support/shared_contexts'
 
+# FIXME: Once only RuboCop versions that support plugins remain, please remove the `if` condition.
+RuboCop::ConfigLoader.inject_defaults!("#{__dir__}/../config/default.yml") if RuboCop.const_defined?(:Plugin)
+
 # Requires supporting files with custom matchers and macros, etc,
 # in ./support/ and its subdirectories.
 Dir["#{File.dirname(__FILE__)}/support/**/*.rb"].sort.each { |f| require f }

tasks/cops_documentation.rake

@@ -22,7 +22,7 @@ task update_cops_documentation: :yard_for_generate_documentation do
 
   # NOTE: Update `<<next>>` version for docs/modules/ROOT/pages/cops_rails.adoc
   # when running release tasks.
-  RuboCop::Rails::Inject.defaults!
+  RuboCop::ConfigLoader.inject_defaults!("#{__dir__}/../config/default.yml")
 
   CopsDocumentationGenerator.new(departments: deps, extra_info: extra_info).call
 end