bug#69941: 30.0.50; Faulty fontification of radio button widgets

[Eli Zaretskii <eliz@gnu.org>]

Ping!  Any comments?  Or should we install the proposed patch?

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: Mauro Aranda <maurooaranda@gmail.com>,  69941@debbugs.gnu.org,
>   monnier@iro.umontreal.ca
> Date: Fri, 26 Apr 2024 14:45:54 +0200
> 
> On Sun, 21 Apr 2024 21:45:59 +0200 Stephen Berman <stephen.berman@gmx.net> wrote:
> 
> > On Thu, 18 Apr 2024 15:38:33 +0200 Stephen Berman <stephen.berman@gmx.net> wrote:
> >
> >> On Thu, 18 Apr 2024 14:33:57 +0300 Eli Zaretskii <eliz@gnu.org> wrote:
> >>
> >>>> Date: Thu, 18 Apr 2024 07:18:29 -0300
> >>>> Cc: Eli Zaretskii <eliz@gnu.org>, 69941@debbugs.gnu.org,
> >>>>  Stefan Monnier <monnier@iro.umontreal.ca>
> >>>> From: Mauro Aranda <maurooaranda@gmail.com>
> >>>> 
> >>>>  > To fix this bug, do you have a preference between this patch for
> >>>>  > widget-specify-inactive and the attached patch for
> >>>>  > widget-default-create?  Or do you have a better fix?
> >>>>  >
> >>>>  > Steve Berman
> >>>> 
> >>>> I don't really have a better fix.  I mean, ideally, we'd find the reason
> >>>> why the setting behaves differently for the radio-button-choice widget,
> >>>> and only for the first one in a radio widget, as it seems to me. But
> >>>> I'll need more time to be able to look into that.
> >>>> 
> >>>> That said, if Eli is OK with installing a minor hack (with a FIXME,
> >>>> please), I don't have problems.  And since it's a hack (and hopefully
> >>>> temporary), it's better if we keep it at widget-default-create then.
> >>>
> >>> My opinion doesn't matter much in this case.  If you two agree on a
> >>> solution, feel free to install it, even if it is not 110% clean.
> >>
> >> I've been using the patch for for widget-specify-inactive in an
> >> application I'm developing that exercises radio-button-choice widgets,
> >> but I'll switch to using the patch for widget-default-create instead.
> >> I've been encountering inconsistent behavior in combination with the use
> >> of widget-unselected face that I haven't tracked down the cause of yet.
> >> I don't expect using the patch for widget-default-create will improve
> >> this issue, but I'll find out.  I also plan to test that patch in
> >> combination with widget-unselected face with checklist widgets, which my
> >> application currently does not use.  I'll report back here before
> >> committing the patch for widget-default-create (or something else,
> >> depending on the outcome of further testing).
> >
> > Just a brief status report: My testing does indeed indicate that the
> > fontification problem with radio-button-choice also occurs with
> > checklist widgets, though the pattern appears not to be identical; I
> > need to do more testing and debugging.
> 
> Further testing confirms that checklists are subject to this problem, so
> I've added them to the attached patch.  The rest of this post reports
> results from and speculations based on my debugging efforts, which
> remain somewhat inconclusive.
> 
> According to my tests, checklists and radio-button-choice widgets do
> indeed display the same problem with the first checkbox or radio-button,
> respectively: if it's selected and then the parent widget is
> deactivated, then the button/checkbox incorrectly does not have
> widget-inactive face.  I think the reason for this is that selecting
> inserts "[X]" for the checkbox and "(*)" for the radio-button, and since
> the parent widget's :from property has marker insertion type `t', its
> position advances to after the insertion (I guess this is because the
> starting position of the first checkbox/button coincides with the parent
> widget's :from), so the overlay with the widget-inactive face beginning
> at :from does not cover the checkbox/button.
> 
> But checklists and radio-button-choice widgets differ when a non-initial
> checkbox/button is selected.  With checklists, multiple checkboxes can
> be selected, and selecting the second checkbox does not advance the
> parent widget's :from position, unlike with radio-button-choice widget's
> when selecting the second radio-button, as I reported in my OP.  I think
> this is because in radio-button-choice widgets only one radio-button can
> be selected, so selecting any one triggers the :from marker's advancing.
> I could not verify this hypothesis through debugging because I was
> unable to find out exactly when this happens.  The marker advance is
> done in the C code, I think at adjust_markers_for_insert in insdel.c; I
> set a gdb breakpoint there and this triggers when I select a radio
> button, but it's too early: a lot happens in wid-edit.el between
> selecting a button and the selection becoming visible, and the
> breakpoint triggered so often that I gave up.  Is there a way to make a
> breakpoint in the C code trigger only when a specific part of
> wid-edit.el is evaluated?
> 
> Nevertheless, by assigning the :from marker the insertion type nil in
> widget-default-create when the widget is either a checklist or
> radio-button-choice, does result in the correct fontification of the
> first checkbox/radio-button in all tests I've conducted with varying the
> selection.  And conceptually it seems to me correct that :from should
> not advance with these widgets: selecting a checkbox or button is
> operationally quite different from inserting text (e.g. in an
> editable-field widget), even though the implementation technically
> involves insertion.  So I think the attached patch is at least a viable
> stopgap, until a better (or at least less ad hoc) fix is found.
> 
> Steve Berman