Using strings or symbols for middleware class names is deprecated.

Convert things like this:

  middleware.use "Foo::Bar"

to this:

  middleware.use Foo::Bar

actionpack/CHANGELOG.md

@@ -1,3 +1,12 @@
+*   Using strings or symbols for middleware class names is deprecated.  Convert
+    things like this:
+
+      middleware.use "Foo::Bar"
+
+    to this:
+
+      middleware.use Foo::Bar
+
 *   ActionController::TestSession now accepts a default value as well as
     a block for generating a default value based off the key provided.
 

actionpack/lib/action_controller/metal.rb

@@ -53,8 +53,7 @@ def build_middleware(klass, args, block)
         list     = except
       end
 
-
-      Middleware.new(klass, args, list, strategy, block)
+      Middleware.new(get_class(klass), args, list, strategy, block)
     end
   end
 

actionpack/lib/action_dispatch/middleware/stack.rb

@@ -4,25 +4,15 @@
 module ActionDispatch
   class MiddlewareStack
     class Middleware
-      attr_reader :args, :block, :name, :classcache
+      attr_reader :args, :block, :klass
 
-      def initialize(klass_or_name, args, block)
-        @klass = nil
-
-        if klass_or_name.respond_to?(:name)
-          @klass = klass_or_name
-          @name  = @klass.name
-        else
-          @name  = klass_or_name.to_s
-        end
-
-        @classcache = ActiveSupport::Dependencies::Reference
-        @args, @block = args, block
+      def initialize(klass, args, block)
+        @klass = klass
+        @args  = args
+        @block = block
       end
 
-      def klass
-        @klass || classcache[@name]
-      end
+      def name; klass.name; end
 
       def ==(middleware)
         case middleware
@@ -31,7 +21,7 @@ def ==(middleware)
         when Class
           klass == middleware
         else
-          normalize(@name) == normalize(middleware)
+          normalize(name) == normalize(middleware)
         end
       end
 
@@ -123,8 +113,25 @@ def assert_index(index, where)
 
     private
 
+    def get_class(klass)
+      if klass.is_a?(String) || klass.is_a?(Symbol)
+        classcache = ActiveSupport::Dependencies::Reference
+        converted_klass = classcache[klass.to_s]
+        ActiveSupport::Deprecation.warn <<-eowarn
+Passing strings or symbols to the middleware builder is deprecated, please change
+them to actual class references.  For example:
+
+  "#{klass}" => #{converted_klass}
+
+        eowarn
+        converted_klass
+      else
+        klass
+      end
+    end
+
     def build_middleware(klass, args, block)
-      Middleware.new(klass, args, block)
+      Middleware.new(get_class(klass), args, block)
     end
   end
 end

actionpack/test/abstract_unit.rb

@@ -123,13 +123,13 @@ class ActionDispatch::IntegrationTest < ActiveSupport::TestCase
 
   def self.build_app(routes = nil)
     RoutedRackApp.new(routes || ActionDispatch::Routing::RouteSet.new) do |middleware|
-      middleware.use "ActionDispatch::ShowExceptions", ActionDispatch::PublicExceptions.new("#{FIXTURE_LOAD_PATH}/public")
-      middleware.use "ActionDispatch::DebugExceptions"
-      middleware.use "ActionDispatch::Callbacks"
-      middleware.use "ActionDispatch::ParamsParser"
-      middleware.use "ActionDispatch::Cookies"
-      middleware.use "ActionDispatch::Flash"
-      middleware.use "Rack::Head"
+      middleware.use ActionDispatch::ShowExceptions, ActionDispatch::PublicExceptions.new("#{FIXTURE_LOAD_PATH}/public")
+      middleware.use ActionDispatch::DebugExceptions
+      middleware.use ActionDispatch::Callbacks
+      middleware.use ActionDispatch::ParamsParser
+      middleware.use ActionDispatch::Cookies
+      middleware.use ActionDispatch::Flash
+      middleware.use Rack::Head
       yield(middleware) if block_given?
     end
   end

actionpack/test/dispatch/middleware_stack/middleware_test.rb

@@ -33,12 +33,6 @@ def setup
         @stack = ActionDispatch::MiddlewareStack.new
       end
 
-      def test_string_class
-        stack = ActionDispatch::MiddlewareStack.new
-        stack.use Omg.name
-        assert_equal Omg, stack.first.klass
-      end
-
       def test_double_equal_works_with_classes
         k = Class.new
         stack.use k

actionpack/test/dispatch/middleware_stack_test.rb

@@ -25,17 +25,21 @@ def setup
   end
 
   test "use should push middleware as a string onto the stack" do
-    assert_difference "@stack.size" do
-      @stack.use "MiddlewareStackTest::BazMiddleware"
+    assert_deprecated do
+      assert_difference "@stack.size" do
+        @stack.use "MiddlewareStackTest::BazMiddleware"
+      end
+      assert_equal BazMiddleware, @stack.last.klass
     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"
+    assert_deprecated do
+      assert_difference "@stack.size" do
+        @stack.use :"MiddlewareStackTest::BazMiddleware"
+      end
+      assert_equal BazMiddleware, @stack.last.klass
     end
-    assert_equal BazMiddleware, @stack.last.klass
   end
 
   test "use should push middleware class with arguments onto the stack" do
@@ -88,8 +92,10 @@ def setup
   end
 
   test "unshift adds a new middleware at the beginning of the stack" do
-    @stack.unshift :"MiddlewareStackTest::BazMiddleware"
-    assert_equal BazMiddleware, @stack.first.klass
+    assert_deprecated do
+      @stack.unshift :"MiddlewareStackTest::BazMiddleware"
+      assert_equal BazMiddleware, @stack.first.klass
+    end
   end
 
   test "raise an error on invalid index" do
@@ -103,15 +109,11 @@ def setup
   end
 
   test "lazy evaluates middleware class" do
-    assert_difference "@stack.size" do
-      @stack.use "MiddlewareStackTest::BazMiddleware"
+    assert_deprecated do
+      assert_difference "@stack.size" do
+        @stack.use "MiddlewareStackTest::BazMiddleware"
+      end
+      assert_equal BazMiddleware, @stack.last.klass
     end
-    assert_equal BazMiddleware, @stack.last.klass
-  end
-
-  test "lazy compares so unloaded constants are not loaded" do
-    @stack.use "UnknownMiddleware"
-    @stack.use :"MiddlewareStackTest::BazMiddleware"
-    assert @stack.include?("::MiddlewareStackTest::BazMiddleware")
   end
 end