Subject: bug#69943: 30.0.50; Tabbing through widgets can signal beginning-of-buffer error

From: Stephen Berman <[email-masked]>
Date: Mon, 01 Apr 2024 17:20:04 +0200

On Fri, 22 Mar 2024 17:36:31 +0200 Eli Zaretskii <[email-masked]> wrote:

>> Date: Fri, 22 Mar 2024 15:45:16 +0100
>> From:  Stephen Berman via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <[email-masked]>
>>
>> 0. emacs -Q
>>
>> 1. Evaluate the following sexp:
>>
>> (let ((buf (get-buffer-create "*Widget Test*")))
>>   (switch-to-buffer buf)
>>   (dolist (el '("First" "Second" "Third"))
>>     (widget-create 'push-button el))
>>   (use-local-map widget-keymap)
>>   (widget-setup)
>>   (goto-char (point-min)))
>>
>> Now the current buffer is *Widget Test* containing three push-button
>> widgets labeled "First", "Second", and "Third", and point is at the
>> start of the first widget, at BOB.
>>
>> 2. Hit the TAB key (bound to widget-forward) three times: this moves
>> point successively from "First" to "Second" to "Third" and then back to
>> "First" -- but on returning to the initial position after the third TAB,
>> a beginning-of-buffer error is also signaled.
>>
>> 3. Likewise, hitting S-TAB (bound to widget-backward) three times moves
>> backwards across the widgets, from "Third" to "Second" to "First", again
>> signaling a beginning-of-buffer error after the last S-TAB.
>>
>> These beginning-of-buffer errors are due to widget-move (the workhorse
>> behind widget-forward and widget-backward) calling backward-char in a
>> loop without checking for BOB.  The attached patch fixes this.  The
>> patch also includes additions to widget-test-widget-move (from which
>> most of the above sexp was taken) that test moving to a widget at BOB.
>> (If the patch is acceptable, whoever commits it should use the correct
>> bug# before pushing it, or I can do that myself.)
>
> Mauro, any comments to the proposed patch?

No comments yet, or did I miss them?  If not, any objections to
installing the patch?

Steve Berman