Move Rails::Rack::Metal to Rails::Application::Metal and just add cascade if any metal was declared.

railties/lib/rails/application.rb

@@ -9,6 +9,7 @@ module Rails
     autoload :Configurable,   'rails/application/configurable'
     autoload :Configuration,  'rails/application/configuration'
     autoload :Finisher,       'rails/application/finisher'
+    autoload :Metal,          'rails/application/metal'
     autoload :Railties,       'rails/application/railties'
     autoload :RoutesReloader, 'rails/application/routes_reloader'
 

railties/lib/rails/application/metal.rb

@@ -1,12 +1,16 @@
 require 'action_dispatch'
 
 module Rails
-  module Rack
+  class Application
     class Metal
       def self.paths
         @paths ||= []
       end
 
+      def self.metals
+        @metals ||= []
+      end
+
       def initialize(list=nil)
         metals = []
         list   = Array(list || :all).map(&:to_sym)
@@ -26,6 +30,7 @@ module Rails
         end
 
         @metals = metals.map { |m| m.to_s.camelize.constantize }
+        self.class.metals.concat(@metals)
       end
 
       def new(app)

railties/lib/rails/configuration.rb

@@ -16,7 +16,7 @@ module Rails
           middleware.use('::ActionDispatch::Cookies')
           middleware.use(lambda { ActionController::Base.session_store }, lambda { ActionController::Base.session_options })
           middleware.use('::ActionDispatch::Flash', :if => lambda { ActionController::Base.session_store })
-          middleware.use(lambda { Rails::Rack::Metal.new(Rails.application.config.metals) })
+          middleware.use(lambda { Rails::Application::Metal.new(Rails.application.config.metals) }, :if => lambda { Rails::Application::Metal.metals.any? })
           middleware.use('ActionDispatch::ParamsParser')
           middleware.use('::Rack::MethodOverride')
           middleware.use('::ActionDispatch::Head')

railties/lib/rails/engine.rb

@@ -99,7 +99,7 @@ module Rails
     end
 
     initializer :add_metals do
-      Rails::Rack::Metal.paths.unshift(*paths.app.metals.to_a)
+      Rails::Application::Metal.paths.unshift(*paths.app.metals.to_a)
     end
 
     initializer :load_application_initializers do

railties/lib/rails/rack.rb

@@ -3,7 +3,6 @@ module Rails
     autoload :Debugger,  "rails/rack/debugger"
     autoload :Logger,    "rails/rack/logger"
     autoload :LogTailer, "rails/rack/log_tailer"
-    autoload :Metal,     "rails/rack/metal"
     autoload :Static,    "rails/rack/static"
   end
 end

railties/test/application/middleware_test.rb

@@ -23,7 +23,6 @@ module ApplicationTests
         "ActionDispatch::Cookies",
         "ActionDispatch::Session::CookieStore",
         "ActionDispatch::Flash",
-        "ActionDispatch::Cascade",
         "ActionDispatch::ParamsParser",
         "Rack::MethodOverride",
         "ActionDispatch::Head",
@@ -70,6 +69,12 @@ module ApplicationTests
       assert_equal "Rack::Config", middleware.first
     end
 
+    test "shows cascade if any metal exists" do
+      app_file "app/metal/foo.rb", "class Foo; end"
+      boot!
+      assert middleware.include?("ActionDispatch::Cascade")
+    end
+
     private
       def boot!
         require "#{app_path}/config/environment"