I have written this, which returns 0:

    def _get_attached_docs(self, cr, uid, ids, field_name, arg, context):
        res = {}
        attachment = self.pool.get('ir.attachment')
        for id in ids:
            product_attachments = attachment.search(cr, uid, [('res_model', '=', 'product.template'), ('res_id', '=', id)], context=context, count=True)
            res[id] = product_attachments or 0
        return res

Although, my code to show the actual attachments works:

   def attachment_tree_view(self, cr, uid, ids, context):
        domain = [
             '&', ('res_model', '=', 'product.template'), ('res_id', 'in', ids),
        ]
        res_id = ids and ids[0] or False
        return {
            'name': _('Attachments'),
            'domain': domain,
            'res_model': 'ir.attachment',
            'type': 'ir.actions.act_window',
            'view_id': False,
            'view_mode': 'kanban,tree,form',
            'view_type': 'form',
            'limit': 80,
            'context': "{'default_res_model': '%s','default_res_id': %d}" % (self._name, res_id)
        }

Can anyone see what is wrong with my _get_attached_docs code?  I have verified that the ir.attachment model does contain a record with model = product.template and res_id = product_id from the product I am testing, and I see my attachment in the standard Attachments dropdown menu.  Also, this testing is being done with the Admin user so document locations shouldn't be a problem.