Toio little error information from widgets

[Lennart Borgman (gmail)]

The following code has an error. This error is however very hard to 
detect. I do not get a traceback, it just behaves very strange.

Try the following:

  emacs -Q
  (eval the code below)
  M-x customize-option RET temp-cust2 RET

Then click INS. It does not work as I expect. (To get it working 
uncomment the line

  ;;(or (eq value 'fundamental-mode)

and the corresponding ")" in the code.

What could be done about this?

Here is the code:

(defun major-modep(value)
  (let ((sym-name (symbol-name value)))
    ;; Do some reasonable test to find out if it is a major mode.
    ;; Load autoloaded mode functions.
    ;;
    ;; Fix-me: Maybe test for minor modes? How was that done?
    (when (and (fboundp value)
               (< 5 (length sym-name))
               (string= "-mode" (substring sym-name (- (length 
sym-name) 5)))
               (if (and (listp (symbol-function value))
                        (eq 'autoload (car (symbol-function value))))
                   (progn
                     (message "loading ")
                     (load (cadr (symbol-function value)) t t))
                 t)
               ;;(or (eq value 'fundamental-mode)
                   (intern-soft (concat sym-name "-hook"))
                   (boundp (intern-soft (concat sym-name "-hook"))))
               ;;)
      t)))

(define-widget 'major-mode-function2 'function
  "A major mode lisp function."
  :complete-function (lambda ()
                       (interactive)
                       (lisp-complete-symbol 'major-modep))
  :prompt-match 'major-modep
  :prompt-history 'widget-function-prompt-value-history
  :match-alternatives '(major-modep)
  :validate (lambda (widget)
              (unless (major-modep (widget-value widget))
                (widget-put widget :error (format "Invalid function: %S"
                                                  (widget-value widget)))
                widget))
  :value 'fundamental-mode
  :tag "Major mode function")

(defcustom temp-cust2 nil
  "doc"
  :type '(alist :key-type major-mode-function2
                :value-type (set
                             (list :tag "Highlighting on" (const hion) 
boolean)
                             (list :tag "Highlighting" (const hili) 
function)
                             (list :tag "Goto" (const goto) function)
                             (list :tag "Next" (const next) function)
                             (list :tag "Prev" (const next) function)
                             )))