Respect status given to respond_with when responding with errors

Otherwise we would enforce `422 Unprocessable Entity` even if there was
a `status` provided, now we'll respect that status first, and use `422`
as default/fallback.

lib/action_controller/responder.rb

@@ -238,7 +238,7 @@ def default_render
       if @default_response
         @default_response.call(options)
       elsif !get? && has_errors?
-        controller.render(options.merge(status: :unprocessable_entity))
+        controller.render({ status: :unprocessable_entity }.merge!(options))
       else
         controller.render(options)
       end

test/action_controller/respond_with_test.rb

@@ -10,7 +10,7 @@ def to_json(*); super; end
 
   respond_to :html, :json, :touch
   respond_to :xml, except: :using_resource_with_block
-  respond_to :js,  only: [ :using_resource_with_block, :using_resource, "using_hash_resource" ]
+  respond_to :js,  only: [ :using_resource_with_block, :using_resource, "using_hash_resource", :using_resource_with_status ]
 
   def using_resource
     respond_with(resource)
@@ -20,6 +20,10 @@ def using_hash_resource
     respond_with(result: resource)
   end
 
+  def using_resource_with_status
+    respond_with(resource, status: 418, template: "respond_with/using_resource")
+  end
+
   def using_resource_with_block
     respond_with(resource) do |format|
       format.csv { render body: "CSV", content_type: "text/csv" }
@@ -183,6 +187,16 @@ def test_using_resource_for_post_with_js_renders_the_template_and_yields_unproce
     assert_equal 422, @response.status
   end
 
+  def test_using_resource_for_post_with_js_renders_the_template_and_yields_given_status_on_failure
+    @request.accept = "text/javascript"
+    errors = { name: :invalid }
+    Customer.any_instance.stubs(:errors).returns(errors)
+    post :using_resource_with_status
+    assert_equal "text/javascript", @response.media_type
+    assert_equal "alert(\"Hi\");", @response.body
+    assert_equal 418, @response.status
+  end
+
   def test_using_hash_resource_with_js_raises_an_error_if_template_cant_be_found
     @request.accept = "text/javascript"
     assert_raise ActionView::MissingTemplate do