bug#71866: 30.0.50; [macOS] Cursor hiding char behind it with certain theme customization

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Stefan Kangas <stefankangas@gmail.com>, 71866@debbugs.gnu.org
> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Date: Thu, 25 Jul 2024 05:03:03 +0200
> 
> Dmitry Gutov <dmitry@gutov.dev> writes:
> 
> > On 24/07/2024 06:48, Gerd Möllmann wrote:
> >>>> And now to my pet peeve 🙂. Dmitry could you please comment out the
> >>>> calls to redisplay (2 of them) in nsterm.m and try again?
> >>> I've tried that now, but it didn't seem to help. Does it make a
> >>> difference on your system?
> >> Yes, without the calls to redisplay, I can no longer reproduce it 🤷
> >> That's on a MBP with M1 Pro chip, macOS 14.5.
> >
> > Oh well. I've tried re-bootstrapping with that change applied, but the
> > problem remains.
> >
> > M3 Pro, macOS 14.5.
> >
> > Or maybe this is about the slightly different font files:
> >
> >> ls -l ~/Library/Fonts/
> > total 3352
> > ...  290368 Dec 13  2021 CascadiaMono-Bold.otf
> > ...  273200 Dec 13  2021 CascadiaMono-ExtraLight.otf
> > ...  282548 Dec 13  2021 CascadiaMono-Light.otf
> > ...  285336 Dec 13  2021 CascadiaMono-Regular.otf
> > ...  292316 Dec 13  2021 CascadiaMono-SemiBold.otf
> > ...  285944 Dec 13  2021 CascadiaMono-SemiLight.otf
> 
> The fonts from Homebrew are .ttf files
> 
> -rw-r--r--@ 1 gerd  admin  715000 Apr 26 02:49 CascadiaMono.ttf
> -rw-r--r--@ 1 gerd  admin  524508 Apr 26 02:49 CascadiaMonoItalic.ttf

Given the latest information from Dmitry, I very much doubt that fonts
are related to this.

> The ASAN bug I was referring to is bug#58334. I think there's some chance
> that this is also timing dependent, so maybe it's your faster CPU 🤷

If the other ideas I just described prove fruitless, then yes, I would
claim that the weird things the NS display does with its async nature
(which no other platform I'm familiar with does) could cause ASAN
bugs, and are the only explanation that is left un-rebuffed.

In general, as long as we don't have on board an active developer who
has a good grip on the intricacies of the NS redisplay in Emacs, we
will continue hearing about display problems like this one, and
there's nothing that can be done about it except stop using macOS.