add task to report code statistics (#2489)

lib/tasks/statistics.rake

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+task stats: 'mastodon:stats'
+
+namespace :mastodon do
+  desc 'Report code statistics (KLOCs, etc)'
+  task :stats do
+    require 'rails/code_statistics'
+    [
+      %w(App\ Libraries app/lib),
+      %w(Presenters app/presenters),
+      %w(Services app/services),
+      %w(Validators app/validators),
+      %w(Workers app/workers),
+    ].each do |name, dir|
+      ::STATS_DIRECTORIES << [name, Rails.root.join(dir)]
+    end
+  end
+end