Silly me! I am sorry to trouble you.
I forgot all that the configure option --with-widgets= is set none.
>>>> In <yosu1zaqmolv.fsf(a)jpl.org>
>>>> Katsumi Yamaoka <yamaoka(a)jpl.org> wrote:
May I bother you? How do I create widget buttons in latest 21.2 CVS?
(widget-create 'push-button
:tag "Hello"
:action (lambda (&rest args) (message "Hello")))
No button appears in *scratch* buffer with this code. :-<
Now it works. :-)