Cleanup junk metal and revise API

API Change: Returning a "X-Cascade: pass" header triggers the cascade
instead of a 404 response.

actionpack/lib/action_controller/railtie.rb

@@ -37,11 +37,33 @@ class Railtie < Rails::Railtie
       ActionController::Base.view_paths = view_path if ActionController::Base.view_paths.blank?
     end
 
+    class MetalMiddlewareBuilder
+      def initialize(metals)
+        @metals = metals
+      end
+
+      def new(app)
+        ActionDispatch::Cascade.new(@metals, app)
+      end
+
+      def name
+        ActionDispatch::Cascade.name
+      end
+      alias_method :to_s, :name
+    end
+
     initializer "action_controller.initialize_metal" do |app|
-      Rails::Rack::Metal.requested_metals = app.config.metals
+      metal_root = "#{Rails.root}/app/metal"
+      load_list = app.config.metals || Dir["#{metal_root}/**/*.rb"]
+
+      metals = load_list.map { |metal|
+        metal = File.basename(metal.gsub("#{metal_root}/", ''), '.rb')
+        require_dependency metal
+        metal.camelize.constantize
+      }.compact
 
-      app.config.middleware.insert_before(:"ActionDispatch::ParamsParser",
-        Rails::Rack::Metal, :if => Rails::Rack::Metal.metals.any?)
+      middleware = MetalMiddlewareBuilder.new(metals)
+      app.config.middleware.insert_before(:"ActionDispatch::ParamsParser", middleware)
     end
 
     # # Prepare dispatcher callbacks and run 'prepare' callbacks

railties/lib/rails/rack.rb

@@ -2,7 +2,6 @@ module Rails
   module Rack
     autoload :Debugger, "rails/rack/debugger"
     autoload :LogTailer, "rails/rack/log_tailer"
-    autoload :Metal, "rails/rack/metal"
     autoload :Static, "rails/rack/static"
   end
 end

railties/test/application/metal_test.rb

@@ -37,7 +37,7 @@ def self.call(env)
       app_file 'app/metal/metal_a.rb', <<-RUBY
         class MetalA
           def self.call(env)
-            [404, { "Content-Type" => "text/html"}, ["Metal A"]]
+            [404, { "Content-Type" => "text/html", "X-Cascade" => "pass" }, ["Metal A"]]
           end
         end
       RUBY
@@ -59,7 +59,7 @@ def self.call(env)
       app_file 'app/metal/foo_metal.rb', <<-RUBY
         class FooMetal
           def self.call(env)
-            [404, { "Content-Type" => "text/html"}, ["Not Found"]]
+            [404, { "Content-Type" => "text/html", "X-Cascade" => "pass" }, ["Not Found"]]
           end
         end
       RUBY

railties/test/application/middleware_test.rb

@@ -20,6 +20,7 @@ def setup
         "ActionDispatch::ShowExceptions",
         "ActionDispatch::Callbacks",
         "ActionDispatch::Session::CookieStore",
+        "ActionDispatch::Cascade",
         "ActionDispatch::ParamsParser",
         "Rack::MethodOverride",
         "Rack::Head",