Allow passing in the serializer class from the render method

lib/action_controller/serialization.rb

@@ -44,7 +44,10 @@ module ActionController
         options[:root] ||= controller_name
       end
 
-      if json.respond_to?(:active_model_serializer) && (serializer = json.active_model_serializer)
+      serializer = options.delete(:serializer) ||
+        (json.respond_to?(:active_model_serializer) && json.active_model_serializer)
+
+      if serializer
         options[:scope] = serialization_scope
 
         if default_options = default_serializer_options

test/serialization_test.rb

@@ -45,6 +45,15 @@ class RenderJsonTest < ActionController::TestCase
     end
   end
 
+  class CustomSerializer
+    def initialize(*)
+    end
+
+    def as_json(*)
+      { :hello => true }
+    end
+  end
+
   class TestController < ActionController::Base
     protect_from_forgery
 
@@ -111,6 +120,10 @@ class RenderJsonTest < ActionController::TestCase
       render :json => JsonSerializable.new(true)
     end
 
+    def render_json_with_custom_serializer
+      render :json => [], :serializer => CustomSerializer
+    end
+
   private
     def default_serializer_options
       if params[:check_defaults]
@@ -211,4 +224,9 @@ class RenderJsonTest < ActionController::TestCase
     get :render_json_with_serializer_api_but_without_serializer
     assert_match '{"serializable_object":true}', @response.body
   end
+
+  def test_render_json_with_custom_serializer
+    get :render_json_with_custom_serializer
+    assert_match '{"hello":true}', @response.body
+  end
 end