Added an extra option :render_option which is handed to the nested fields for builder. Also call the correct nested fields builder for each form builder (e.g. semantic_fields_for, simple_fields_for or fields_for).

lib/cocoon/view_helpers.rb

@@ -31,8 +31,9 @@ module Cocoon
     end
 
     # :nodoc:
-    def render_association(association, f, new_object)
-      f.fields_for(association, new_object, :child_index => "new_#{association}") do |builder|
+    def render_association(association, f, new_object, render_options={})
+      method_name = f.respond_to?(:semantic_fields_for) ? :semantic_fields_for : (f.respond_to?(:simple_fields_for) ? :simple_fields_for : :fields_for)
+      f.send(method_name, association, new_object, {:child_index => "new_#{association}"}.merge(render_options)) do |builder|
         render(association.to_s.singularize + "_fields", :f => builder, :dynamic => true)
       end
     end
@@ -57,12 +58,15 @@ module Cocoon
         association  = args[2]
         html_options = args[3] || {}
 
+        render_options = html_options.delete(:render_options)
+        render_options ||={}
+
         html_options[:class] = [html_options[:class], "add_fields"].compact.join(' ')
         html_options[:'data-association'] = association.to_s.singularize
         html_options[:'data-associations'] = association.to_s.pluralize
 
         new_object = f.object.class.reflect_on_association(association).klass.new
-        html_options[:'data-template'] = CGI.escapeHTML(render_association(association, f, new_object)).html_safe
+        html_options[:'data-template'] = CGI.escapeHTML(render_association(association, f, new_object, render_options)).html_safe
 
         link_to(name, '#', html_options )
       end

spec/cocoon_spec.rb

@@ -52,7 +52,48 @@ describe Cocoon do
         result = @tester.link_to_add_association('add something', @form_obj, :people)
         result.to_s.should == '<a href="#" class="add_fields" data-association="person" data-associations="people" data-template="form&lt;tag&gt;">add something</a>'
       end
+    end
 
+    it "tttt" do
+      @post.class.reflect_on_association(:people).klass.new.should be_a(Person)
+    end
+
+    context "with extra render-options for rendering the child relation" do
+      it "should use the correct plural" do
+        @tester.should_receive(:render_association).with(:people, @form_obj, anything, {:wrapper => 'inline'})
+        result = @tester.link_to_add_association('add something', @form_obj, :people, :render_options => {:wrapper => 'inline'})
+        result.to_s.should == '<a href="#" class="add_fields" data-association="person" data-associations="people" data-template="form&lt;tag&gt;">add something</a>'
+      end
+    end
+
+    context "when using formtastic" do
+      before(:each) do
+        @tester.unstub(:render_association)
+        @form_obj.stub(:semantic_fields_for).and_return('form<tagzzz>')
+      end
+      it "calls semantic_fields_for and not fields_for" do
+        @form_obj.should_receive(:semantic_fields_for)
+        @form_obj.should_receive(:fields_for).never
+        result = @tester.link_to_add_association('add something', @form_obj, :people)
+        result.to_s.should == '<a href="#" class="add_fields" data-association="person" data-associations="people" data-template="form&lt;tagzzz&gt;">add something</a>'
+
+      end
+    end
+    context "when using simple_form" do
+      before(:each) do
+        @tester.unstub(:render_association)
+        @form_obj.stub(:simple_fields_for).and_return('form<tagxxx>')
+      end
+      it "responds_to :simple_fields_for" do
+        @form_obj.should respond_to(:simple_fields_for)
+      end
+      it "calls simple_fields_for and not fields_for" do
+        @form_obj.should_receive(:simple_fields_for)
+        @form_obj.should_receive(:fields_for).never
+        result = @tester.link_to_add_association('add something', @form_obj, :people)
+        result.to_s.should == '<a href="#" class="add_fields" data-association="person" data-associations="people" data-template="form&lt;tagxxx&gt;">add something</a>'
+
+      end
     end
 
   end

spec/dummy/app/models/person.rb

@@ -1,2 +1,3 @@
 class Person < ActiveRecord::Base
+  belongs_to :post
 end