bug#63186: 30.0.50; Modeline is not fully repainted when being set to nil then back to having content

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Sun, 30 Apr 2023 10:48:10 -0400
> Cc: 63186-done@debbugs.gnu.org
> 
> On Sun, Apr 30, 2023 at 9:25 AM Eli Zaretskii <eliz@gnu.org> wrote:
> >
> > > (setq mode-line-format "foo")
> > > (setq mode-line-format nil)
> > > (setq mode-line-format "boo")
> > >
> > > After the last line, only the "b" of the mode line will be rendered.
> > > Triggering a repaint with M-x or resizing the window causes the entire
> > > mode line to repaint.
> > >
> > > If the buffer has enough content in it such that there is text where the
> > > mode line is when it is set to `nil', most of that text will remain
> > > painted in place when the mode line is set to "boo".
> >
> > Thanks, should be fixed now on the emacs-29 branch.
> >
> > (This is a regression from Emacs 28, but I have no idea which change
> > caused it.)
> 
> Thanks, confirmed. Fixed when merged into Emacs 30 as well.

Thanks for testing.