Remove the extra options-hash for the partial, instead use the same html_options hash. Is less confusing, and matches the documentation (I was under the impression it was already like that --ooops).

lib/cocoon/view_helpers.rb

@@ -32,7 +32,7 @@ module Cocoon
 
     # :nodoc:
     def render_association(association, f, new_object, render_options={}, custom_partial=nil)
-      partial = setup_partial(custom_partial, association)
+      partial = get_partial_path(custom_partial, association)
       locals =  render_options.delete(:locals) || {}
       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|
@@ -57,24 +57,23 @@ module Cocoon
         f            = args[0]
         association  = args[1]
         html_options = args[2] || {}
-        options      = args[3] || {}
+        link_to_add_association(capture(&block), f, association, html_options)
-        link_to_add_association(capture(&block), f, association, html_options, options)
       else
         name         = args[0]
         f            = args[1]
         association  = args[2]
         html_options = args[3] || {}
-        options      = args[4] || {}
 
         render_options   = html_options.delete(:render_options)
         render_options ||= {}
+        override_partial = html_options.delete(:partial)
 
         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 = create_object(f, association)
-        html_options[:'data-template'] = CGI.escapeHTML(render_association(association, f, new_object, render_options, options[:partial])).html_safe
+        html_options[:'data-template'] = CGI.escapeHTML(render_association(association, f, new_object, render_options, override_partial)).html_safe
 
         link_to(name, '#', html_options )
       end
@@ -90,12 +89,8 @@ module Cocoon
       new_object = assoc.klass.new(*conditions)
     end
 
-    def setup_partial(partial, association)
+    def get_partial_path(partial, association)
-      if partial
+      partial ? partial : association.to_s.singularize + "_fields"
-        partial
-      else
-        association.to_s.singularize + "_fields"
-      end
     end
 
   end

spec/cocoon_spec.rb

@@ -28,6 +28,13 @@ describe Cocoon do
         result = @tester.link_to_add_association('add something', @form_obj, :comments, {:class => 'something silly'})
         result.to_s.should == '<a href="#" class="something silly add_fields" data-association="comment" data-associations="comments" data-template="form&lt;tag&gt;">add something</a>'
       end
+
+      it "allows to explicitly hand the wanted partial" do
+        @tester.unstub(:render_association)
+        @tester.should_receive(:render_association).with(anything(), anything(), anything(), anything(), "shared/partial").and_return('partiallll')
+        result = @tester.link_to_add_association('add something', @form_obj, :comments, :partial => "shared/partial")
+        result.to_s.should == '<a href="#" class="add_fields" data-association="comment" data-associations="comments" data-template="partiallll">add something</a>'
+      end
     end
 
     context "with a block" do
@@ -45,10 +52,10 @@ describe Cocoon do
         result.to_s.should == '<a href="#" class="floppy disk add_fields" data-association="comment" data-associations="comments" data-template="form&lt;tag&gt;">some long name</a>'
       end
 
-      it "accepts options and passes them to link_to" do
+      it "allows to explicitly hand the wanted partial" do
         @tester.unstub(:render_association)
         @tester.should_receive(:render_association).with(anything(), anything(), anything(), anything(), "shared/partial").and_return('partiallll')
-        result = @tester.link_to_add_association( @form_obj, :comments, {:class => 'floppy disk'}, {:partial => "shared/partial"}) do
+        result = @tester.link_to_add_association( @form_obj, :comments, :class => 'floppy disk', :partial => "shared/partial") do
           "some long name"
         end
         result.to_s.should == '<a href="#" class="floppy disk add_fields" data-association="comment" data-associations="comments" data-template="partiallll">some long name</a>'
@@ -175,13 +182,13 @@ describe Cocoon do
       end
     end
 
-    context "setup_partial" do
+    context "get_partial_path" do
       it "generates the default partial name if no partial given" do
-        result = @tester.setup_partial(nil, :admin_comments)
+        result = @tester.get_partial_path(nil, :admin_comments)
         result.should == "admin_comment_fields"
       end
       it "uses the given partial name" do
-        result = @tester.setup_partial("comment_fields", :admin_comments)
+        result = @tester.get_partial_path("comment_fields", :admin_comments)
         result.should == "comment_fields"
       end
     end