use concat instead of returned string in fields_for

lib/nested_form/builder.rb

@@ -4,8 +4,9 @@ def link_to_add(name, association)
       @fields ||= {}
       @template.after_nested_form do
         model_object = object.class.reflect_on_association(association).klass.new
-        fields = fields_for(association, model_object, :child_index => "new_#{association}", &@fields[association])
-        @template.content_tag(:div, fields, :style => "display: none")
+        @template.concat('<div style="display: none">')
+        fields_for(association, model_object, :child_index => "new_#{association}", &@fields[association])
+        @template.concat('</div>')
       end
       @template.link_to(name, "javascript:void(0)", :class => "add_nested_fields", "data-association" => association)
     end
@@ -22,7 +23,9 @@ def fields_for_with_nested_attributes(association, args, block)
 
 
     def fields_for_nested_model(name, association, args, block)
-      @template.content_tag(:div, super, :class => "fields")
+      @template.concat('<div class="fields">')
+      super
+      @template.concat('</div>')
     end
   end
 end

lib/nested_form/view_helper.rb

@@ -3,7 +3,7 @@ module ViewHelper
     def nested_form_for(*args, &block)
       options = args.extract_options!.reverse_merge(:builder => NestedForm::Builder)
       form_for(*(args << options), &block) 
-      concat(@after_nested_form_callback.call) if @after_nested_form_callback
+      @after_nested_form_callback.call if @after_nested_form_callback
     end
 
     def after_nested_form(&block)

spec/nested_form/builder_spec.rb

@@ -20,16 +20,16 @@
     it "should wrap nested fields each in a div with class" do
       2.times { @project.tasks.build }
       @builder.fields_for(:tasks) do
-        "Task"
-      end.should == '<div class="fields">Task</div><div class="fields">Task</div>'
+        @template.concat("Task")
+      end
+      @template.output_buffer.should == '<div class="fields">Task</div><div class="fields">Task</div>'
     end
 
     it "should add task fields to hidden div after form" do
-      content = nil
-      mock(@template).after_nested_form { |block| content = block.call }
-      @builder.fields_for(:tasks) { "Task" }
+      mock(@template).after_nested_form { |block| block.call }
+      @builder.fields_for(:tasks) { @template.concat("Task") }
       @builder.link_to_add("Add", :tasks)
-      content.should == '<div style="display: none"><div class="fields">Task</div></div>'
+      @template.output_buffer.should == '<div style="display: none"><div class="fields">Task</div></div>'
     end
   end
 end