Use Thor for built-in stats task

Currently, we use both Thor and Rake for `bin/rails` commands.
We eventually want to get all the built-ins task promoted to Thor Commands.
This migrates the `stats` task to Thor.

Author: JuanVqz

railties/lib/rails/commands/stats/stats_command.rb

@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+# While global constants are bad, many 3rd party tools depend on this one (e.g
+# rspec-rails & cucumber-rails). So a deprecation warning is needed if we want
+# to remove it.
+STATS_DIRECTORIES ||= [
+  %w(Controllers        app/controllers),
+  %w(Helpers            app/helpers),
+  %w(Jobs               app/jobs),
+  %w(Models             app/models),
+  %w(Mailers            app/mailers),
+  %w(Mailboxes          app/mailboxes),
+  %w(Channels           app/channels),
+  %w(Views              app/views),
+  %w(JavaScripts        app/assets/javascripts),
+  %w(Stylesheets        app/assets/stylesheets),
+  %w(JavaScript         app/javascript),
+  %w(Libraries          lib/),
+  %w(APIs               app/apis),
+  %w(Controller\ tests  test/controllers),
+  %w(Helper\ tests      test/helpers),
+  %w(Job\ tests         test/jobs),
+  %w(Model\ tests       test/models),
+  %w(Mailer\ tests      test/mailers),
+  %w(Mailbox\ tests     test/mailboxes),
+  %w(Channel\ tests     test/channels),
+  %w(Integration\ tests test/integration),
+  %w(System\ tests      test/system),
+]
+
+module Rails
+  module Command
+    class StatsCommand < Base # :nodoc:
+      desc "stats", "Report code statistics (KLOCs, etc) from the application or engine"
+      def perform
+        require "rails/code_statistics"
+
+        stat_directories = STATS_DIRECTORIES.collect do |name, dir|
+          [name, Rails::Command.application_root.join(dir)]
+        end.select { |name, dir| File.directory?(dir) }
+
+        CodeStatistics.new(*stat_directories).to_s
+      end
+    end
+  end
+end

railties/lib/rails/tasks/statistics.rake

@@ -34,5 +34,11 @@ task :stats do
   stat_directories = STATS_DIRECTORIES.collect do |name, dir|
     [ name, "#{File.dirname(Rake.application.rakefile_location)}/#{dir}" ]
   end.select { |name, dir| File.directory?(dir) }
+
+  $stderr.puts Rails.deprecator.warn(<<~MSG, caller_locations(0..1))
+  `bin/rails stats` as rake task has been deprecated and will be removed in Rails 8.0.
+  Please use `bin/rails stats` as Rails command instead.\n
+  MSG
+
   CodeStatistics.new(*stat_directories).to_s
 end

railties/test/commands/statistics_test.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require "isolation/abstract_unit"
+require "rails/command"
+
+class Rails::Command::StatsTest < ActiveSupport::TestCase
+  include ActiveSupport::Testing::Isolation
+  setup :build_app
+  teardown :teardown_app
+
+  test "`bin/rails stats` handles non-existing directories added by third parties" do
+    app_file "config/initializers/custom.rb", <<~CODE
+      require "rails/code_statistics"
+      ::STATS_DIRECTORIES << ["Non\ Existing", "app/non_existing"]
+    CODE
+
+    assert rails "stats"
+  end
+end