Accessing error messages in a custom FormBuilder

Hi there,

I'm trying to create a FormBuilder called LabellingBuilder, to implement Simply Accessible's form error messages strategy:

http://simplyaccessible.org/article/form-error-messages

The problem is that ActionView::Helpers::ActiveRecordHelper#error_messages_on isn't available in subclasses of ActionView::Helpers::FormBuilder.

So I tried to write my own little error fetcher and was stunned by the results -- while @object_name is correctly set, @object is nil, as indicated by the XXX comment in the code below.

Can anyone help me with this code?