1 files changed, 50 insertions, 0 deletions
diff --git a/railties/lib/rails/application/metal_loader.rb b/railties/lib/rails/application/metal_loader.rb
new file mode 100644
index 0000000000..c0f2e4f948
--- /dev/null
+++ b/railties/lib/rails/application/metal_loader.rb
@@ -0,0 +1,50 @@
+require 'action_dispatch'
+
+module Rails
+  class Application
+    class MetalLoader
+      attr_reader :paths, :metals
+
+      def initialize
+        @paths, @metals = [], []
+      end
+
+      def build_middleware(list=nil)
+        load_metals!(list)
+        self
+      end
+
+      def new(app)
+        ActionDispatch::Cascade.new(@metals, app)
+      end
+
+      def name
+        ActionDispatch::Cascade.name
+      end
+      alias :to_s :name
+
+    protected
+
+      def load_metals!(list)
+        metals = []
+        list = Array(list || :all).map(&:to_sym)
+
+        paths.each do |path|
+          matcher = /\A#{Regexp.escape(path)}\/(.*)\.rb\Z/
+          Dir.glob("#{path}/**/*.rb").sort.each do |metal_path|
+            metal = metal_path.sub(matcher, '\1').to_sym
+            next unless list.include?(metal) || list.include?(:all)
+            require_dependency metal
+            metals << metal
+          end
+        end
+
+        metals = metals.sort_by do |m|
+          [list.index(m) || list.index(:all), m.to_s]
+        end
+
+        @metals = metals.map { |m| m.to_s.camelize.constantize }
+      end
+    end
+  end
+end