anchor.diff:                       ;; TODO(cgay): this should probably refer to the external field name but I'll
                        ;; wait since I've no idea if that slot is bound at this point.
                        (proto-internal-field-name field) (proto-class msg-desc))
  -             ;; todo(benkuehnert: What does this do?
  -             (setq index idx)
                (when slot
                  (collect-slot slot))
                (push field (proto-fields msg-desc))))))
  
positive.code:                     :options   (remove-options options "default" "packed")
                      :message-type :group                ;this message is a group
                      :documentation documentation))
           (index 0)
           (field-offset 0)
           (bool-count (count-if #'non-repeated-bool-field fields))
           (bool-index -1)
  
negative.code:              (assert (index-within-extensions-p idx message) ()
                       "The index ~D is not in range for extending ~S"
                       idx (proto-class message))
               (when slot
                 (let* (;; The slot name which is the %field-name
                        (sname  (field-data-internal-slot-name slot))
  