Hi

The issue is with the following code that tries to use the Widget
library.  The slots of the widget are actually not necessary to see the
problem.

 (widget-create 'integer
                :help-echo "Enter an integer..."
                :notify (lambda (w1 &rest ws)
                           (ignore ws)
                           (message "WIFT: IF: %s"
                                    (widget-value w1)
                           ))
                :size 4
  )

If you set up a widget buffer, the field will appear as expected with a 0
as initial value.  The problem starts if you try to clear the field and
then enter a new value, say by hitting C-k, and the problem is in the
:value-to-external functions in the in sexp and restricted-sexp widgets
(the number, float and natnum widgets must also be fixed).

The library :value-to-external functions eventually do a (read value) where
value is the widget value; alas, value can be "" if you edit the field in a
pretty standard way, as, as I said above, if you had tried to kill the
field line (C-k); this causes the traditional minor demons to fly out of
the nose, as a 'End of file during parsing' error gets signaled.  After
that, the buffer with the widgets is pretty much in a random state.

Specializing the widget with a hack like the function below fixes the
problem, but a
good solution may need some more work to get all the corner cases.  Note
that setting a "widget buffer" in overwrite mode goes a long way to
mitigate these problems: maybe having widget-setup switch to it would be
another good thing to do.

  :value-to-external
  (lambda (widget value)
    ;; Lifted, and fixed, from `:value-to-external' in
    ;; `restricted-sexp'.

    (unless (stringp value)
      (display-warning
       'widget-bad-default-value
       (format-message
        "\nA widget of type %S has a bad default value.
value: %S
match function: %S
match-alternatives: %S"
        (widget-type widget)
        value
        (widget-get widget :match)
        (widget-get widget :match-alternatives))
       :warning))
    (if (and (stringp value) (string-equal "" value))
        ;; Oooops, we cannot just `read'.
        (widget-get widget :default-value)
      (read value))
    )

Note: this goes back, at least, to 25.x.

Thanks for the attention

Marco Antoniotti





In GNU Emacs 28.2 (build 2, x86_64-w64-mingw32)
 of 2022-09-13 built on AVALON
Windowing system distributor 'Microsoft Corp.', version 10.0.22621
System Description: Microsoft Windows 10 Pro (v10.0.2009.22621.1778)

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Memory information:
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-- 
Marco Antoniotti
Somewhere over the Rainbow