Move metal above method piggybacking middleware and add some test coverage

actionpack/lib/action_controller/middleware_stack.rb

 module ActionController
   class MiddlewareStack < Array
     class Middleware
+      def self.new(klass, *args, &block)
+        if klass.is_a?(self)
+          klass
+        else
+          super
+        end
+      end
+
       attr_reader :args, :block
 
       def initialize(klass, *args, &block)
@@ -65,6 +73,19 @@ def initialize(*args, &block)
       block.call(self) if block_given?
     end
 
+    def insert(index, *objs)
+      index = self.index(index) unless index.is_a?(Integer)
+      objs = objs.map { |obj| Middleware.new(obj) }
+      super(index, *objs)
+    end
+
+    alias_method :insert_before, :insert
+
+    def insert_after(index, *objs)
+      index = self.index(index) unless index.is_a?(Integer)
+      insert(index + 1, *objs)
+    end
+
     def use(*args, &block)
       middleware = Middleware.new(*args, &block)
       push(middleware)

actionpack/test/controller/middleware_stack_test.rb

+require 'abstract_unit'
+
+class MiddlewareStackTest < ActiveSupport::TestCase
+  class FooMiddleware; end
+  class BarMiddleware; end
+  class BazMiddleware; end
+
+  def setup
+    @stack = ActionController::MiddlewareStack.new
+    @stack.use FooMiddleware
+    @stack.use BarMiddleware
+  end
+
+  test "use should push middleware as class onto the stack" do
+    assert_difference "@stack.size" do
+      @stack.use BazMiddleware
+    end
+    assert_equal BazMiddleware, @stack.last.klass
+  end
+
+  test "use should push middleware as a string onto the stack" do
+    assert_difference "@stack.size" do
+      @stack.use "MiddlewareStackTest::BazMiddleware"
+    end
+    assert_equal BazMiddleware, @stack.last.klass
+  end
+
+  test "use should push middleware as a symbol onto the stack" do
+    assert_difference "@stack.size" do
+      @stack.use :"MiddlewareStackTest::BazMiddleware"
+    end
+    assert_equal BazMiddleware, @stack.last.klass
+  end
+
+  test "use should push middleware class with arguments onto the stack" do
+    assert_difference "@stack.size" do
+      @stack.use BazMiddleware, true, :foo => "bar"
+    end
+    assert_equal BazMiddleware, @stack.last.klass
+    assert_equal([true, {:foo => "bar"}], @stack.last.args)
+  end
+
+  test "insert inserts middleware at the integer index" do
+    @stack.insert(1, BazMiddleware)
+    assert_equal BazMiddleware, @stack[1].klass
+  end
+
+  test "insert_after inserts middleware after the integer index" do
+    @stack.insert_after(1, BazMiddleware)
+    assert_equal BazMiddleware, @stack[2].klass
+  end
+
+  test "insert_before inserts middleware before another middleware class" do
+    @stack.insert_before(BarMiddleware, BazMiddleware)
+    assert_equal BazMiddleware, @stack[1].klass
+  end
+
+  test "insert_after inserts middleware after another middleware class" do
+    @stack.insert_after(BarMiddleware, BazMiddleware)
+    assert_equal BazMiddleware, @stack[2].klass
+  end
+
+  test "active returns all only enabled middleware" do
+    assert_no_difference "@stack.active.size" do
+      assert_difference "@stack.size" do
+        @stack.use BazMiddleware, :if => lambda { false }
+      end
+    end
+  end
+end

railties/lib/initializer.rb

@@ -537,7 +537,7 @@ def initialize_i18n
     end
 
     def initialize_metal
-      configuration.middleware.use Rails::Rack::Metal
+      configuration.middleware.insert_before(:"ActionController::VerbPiggybacking", Rails::Rack::Metal)
     end
 
     # Initializes framework-specific settings for each of the loaded frameworks