GNU bug report logs - #63838
28.2; 'wid-edit.el' problems with 'integer' (and 'sexp') widgets.

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From: Mauro Aranda <maurooaranda <at> gmail.com>
To: Marco Antoniotti <marcoxa <at> gmail.com>
Cc: 63838 <at> debbugs.gnu.org
Subject: bug#63838: 28.2; 'wid-edit.el' problems with 'integer' (and 'sexp') widgets.
Date: Sun, 16 Jul 2023 08:50:28 -0300

Marco Antoniotti <marcoxa <at> gmail.com> writes:

> Hi

Thanks for the bug report!

> 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
>   )

The :notify value is kind of necessary, right? I mean, the bug doesn't
manifest as long as code doesn't try to access the value of a
restricted-sexp widget while its empty.

> 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.

I don't think we want to do that.

>  :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))
>     )

I don't think this is a good place to do this.  And there's no
:default-value property in the widget library, just :value.

I think it'd be much better if we specialize the :value-get function for
the restricted-sexp widget, defaulting to return :value when the widget
is empty.

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