[widget] defining a widget that propagates a property to its children

[Oliver Scholz]

I am trying to define some rather complex combined widgets that
(among other things) shall propagate some of their properties to
their children. 

A simple case is a cons widget consisting of two editable fields. If
I create this modified cons widget with the :size property specified,
this :size property shall apply to the editable fields.

This task is as simple as getting the :size property from the parent
widget and putting it on all children somewhere in the creation
process of the widget without modifying anything else.

But, alas, I couldn't find out how to do this.

I first tried to do it in a function specified with the
:convert-widget property, but at this time there is not enough
information available (come to think of it, I guess that I don't
really understand what the :convert-widget function is supposed to
do).

I was able to come close with this kludge:

(define-widget 'cus-fontset-cons 'cons
  "FIXME"
  :format "%v"
  :args '((editable-field
           :format "%v\n"
           :create cus-fontset-create-cons-item
           )
          (editable-field
           :format "%v\n"
           :create cus-fontset-create-cons-item
           )))

(defun cus-fontset-create-cons-item (wid)
  (setq wid (widget-convert wid))
  (widget-put wid :size 
              (widget-get (widget-get wid :parent) 
                          :size))
  (widget-default-create wid))

(defvar egoge-test-widget nil)
(make-variable-buffer-local 'egoge-test-widget)

(progn (switch-to-buffer (generate-new-buffer "*test*"))
       (setq egoge-test-widget
             (widget-create 'cus-fontset-cons 
                            :size 40          
                            :value
                            '("lirum" . "larum")))
       (widget-setup)
       (use-local-map widget-keymap))


Unfortunately this wreaks havoc with the editable fields: edit one of
those fields and type 

`M-: (widget-value egoge-test-widget) RET'

The value is not updated to the actual content of the editable field
in the buffer.

What can I do?

    Oliver
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