bug#70594: 30.0.50; Error when tabbing with only one active widget

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: maurooaranda@gmail.com,  70594@debbugs.gnu.org
> Date: Sat, 25 May 2024 11:30:01 +0200
> 
> On Sat, 25 May 2024 10:42:33 +0300 Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > Ping! Ping!  Can we please make some progress here?
> 
> Since the patch fixes (according to me testing) a clear bug, either the
> patch should be installed (or a better one, if someone comes up with
> one) or commit 91333dacfa1, which introduced the bug, should be
> reverted; my preference is to install the patch.

Mauro, what do you prefer?

> >> Cc: 70594@debbugs.gnu.org
> >> Date: Thu, 09 May 2024 10:23:13 +0300
> >> From: Eli Zaretskii <eliz@gnu.org>
> >>
> >> Ping!
> >>
> >> > Cc: 70594@debbugs.gnu.org
> >> > Date: Fri, 26 Apr 2024 18:02:13 +0300
> >> > From: Eli Zaretskii <eliz@gnu.org>
> >> >
> >> > > Date: Fri, 26 Apr 2024 14:43:42 +0200
> >> > > From:  Stephen Berman via "Bug reports for GNU Emacs,
> >> > >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> >> > >
> >> > > Commit 91333dacfa1, which adds the feature of optionally skipping over
> >> > > inactive widgets when tabbing (bug#70413), fails to handle buffers that
> >> > > contain only one active widget; in that case, pressing TAB or S-TAB
> >> > > raises the error "No buttons or fields found".  To reproduce:
> >> > >
> >> > > 0. emacs -Q
> >> > > 1. Load the attached file widget-test.el and then type `M-x
> >> > >    my-widget-test'.
> >> > > 2. In the buffer "*My Widget Test*" repeatedly press TAB and S-TAB and
> >> > >    observe that point moves successively between the active radio
> >> > >    buttons labelled "One" and "Two" and the active push button "Submit",
> >> > >    but skips the inactive push button "Reset", since the user option
> >> > >    widget-skip-inactive is enabled.
> >> > > 3. Now press (via RET or mouse-click) the "Submit" button, which makes
> >> > >    the radio buttons and the "Submit" button inactive and the "Reset"
> >> > >    button active.
> >> > > 4. Pressing TAB once moves point to the "Reset" button, then pressing
> >> > >    TAB again moves point to BOB and raises the error "No buttons or
> >> > >    fields found".  Likewise, pressing S-TAB once moves point to "Reset",
> >> > >    then pressing S-TAB again moves to EOB and raises the same error.
> >> > >
> >> > > The attached patched fixes this bug.  In addition, when only one widget
> >> > > is active and point is on it, since pressing TAB or S-TAB does not move
> >> > > point, the informational message "Only one tabable widget" is displayed.
> >> > >
> >> > > The original code in widget-move contained separate loops to handle
> >> > > forward and backward movement and this involved some code duplication.
> >> > > The changes to this code to fix the bug would have required further
> >> > > duplication, so I took the opportunity to parameterize the
> >> > > directionality, allowing handling both directions in a single loop.
> >> > > This shortens the code and IMO makes the similarities and differences in
> >> > > the handling easier to see.
> >> >
> >> > Adding Mauro to the discussion.
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >>
>