If a user wants json output then try best to render json output. In such cases...

If a user wants json output then try best to render json output. In such cases prefer kind_of(String) over respond_to?(to_str)

[#5841 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

actionpack/lib/action_controller/metal/renderers.rb

@@ -55,7 +55,7 @@ module All
     end
 
     add :json do |json, options|
-      json = json.to_json(options) unless json.respond_to?(:to_str)
+      json = json.to_json(options) unless json.kind_of?(String)
       json = "#{options[:callback]}(#{json})" unless options[:callback].blank?
       self.content_type ||= Mime::JSON
       self.response_body  = json

actionpack/test/controller/mime_responds_test.rb

@@ -599,6 +599,17 @@ def index
   end
 end
 
+class RenderJsonRespondWithController < RespondWithController
+  clear_respond_to
+  respond_to :json
+
+  def index
+    respond_with(resource) do |format|
+      format.json { render :json => RenderJsonTestException.new('boom') }
+    end
+  end
+end
+
 class EmptyRespondWithController < ActionController::Base
   def index
     respond_with(Customer.new("david", 13))
@@ -914,6 +925,13 @@ def test_block_inside_respond_with_is_rendered
     assert_equal "JSON", @response.body
   end
 
+  def test_render_json_object_responds_to_str_still_produce_json
+    @controller = RenderJsonRespondWithController.new
+    @request.accept = "application/json"
+    get :index, :format => :json
+    assert_equal %Q{{"message":"boom","error":"RenderJsonTestException"}}, @response.body
+  end
+
   def test_no_double_render_is_raised
     @request.accept = "text/html"
     assert_raise ActionView::MissingTemplate do

actionpack/test/lib/controller/fake_models.rb

@@ -194,3 +194,9 @@ def each
     a.each { |i| yield i }
   end
 end
+
+class RenderJsonTestException < Exception
+  def to_json(options = nil)
+    return { :error => self.class.name, :message => self.to_str }.to_json
+  end
+end