bug#75171: 30.0.50; Checklist widget inside a group does not initialize correctly

[Mauro Aranda <maurooaranda@gmail.com>]

Mauro Aranda <maurooaranda@gmail.com> writes:

 > Al Haji-Ali <abdo.haji.ali@gmail.com> writes:
 >
 >> On 02/01/2025, Mauro Aranda wrote:
 >>
 >>> Al Haji-Ali <abdo.haji.ali@gmail.com> writes:
 >>> This is intended behavior, AFAIU.  The parent can override values for
 >>> the children, and that way we can recreate widgets with new values just
 >>> by changing the values of the parent.
 >>
 >> I was aware of this behaviour for the group, but I didn't twig the
 >> consequence on a checklist.
 >>
 >> I have to say that I find it a bit counter-intuitive. Also the fact
 >> that there is no way to set the value of a checklist without repeating
 >> it in the group is somewhat awkward (certainly it will complicate my
 >> implementation)
 >
 > Note that you don't necessarily need to repeat it in the checklist
 > widget.  In my example, you only need to pass the :value in group:
 >
 > (defun widget-test ()
 >   (let ((items '((item :format "%[One%] " :value 1)
 >                  (item :format "%[Two%] " :value 2)
 >                  (item :format "%[Three%] " :value 3))))
 >     (widget-create
 >      'group
 >      :value '(2 (1 2))
 >      (append '(radio-button-choice
 >                :format "Not inline radio:\n%v\n")
 >              items)
 >      (append '(checklist
 >                :format "Not inline checks:\n%v\n")
 >              items)))
 >   (widget-setup))
 >
 > When created, radio-button-choice will get its :value set to 2 and
 > checklist will get it set to (1 2).
 >
 >> and a bit inconsistent since setting the value of the
 >> checklist after the group creation would override the value of the
 >> group. A fix, or a some way, that would prevents the group from
 >> overriding the values of the children would be useful, IMO.
 >>
 >> With that being said, this issue should probably be closed as "not a
 >> bug".
 >
 > I'd like to take some time to study this and see if there's a way to
 > improve the situation.

Making the group widget create its children with their default
values is easy, by testing if it has a explicit nil value or not.  But
since it has worked this way forever, I wouldn't suggest changing it.

I think that specifying the :value in the group widget is the way that
the group widget it's supposed to work.  There are ways to derive a
widget from it that doesn't enforce it, so I'm inclined to mark this as
notabug.