bug#66416: 29.1; Crashes when visiting HELLO file with pgtk on Wayland

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuchen Guo <yguo@posteo.net>
> Cc: 66416@debbugs.gnu.org
> Date: Tue, 10 Oct 2023 05:26:00 +0000
> 
> Besides, in my not so humble opinion, I think Emacs users should have
> the freedom of choosing the preferred font without crashing Emacs,
> regardless of defaults.  Font is a personal matter and one shouldn't be
> dragged by others by the nose, as a Chinese idiom would say.

You do have the freedom, and Emacs gives users more freedom in
customizing fonts than most other GUI apps.  You just need to know
very well what you are doing to exercise that freedom, so we are
trying hard to make the need for that as small and rare as possible.

> > Can you show screenshots of the same text as Emacs displays by
> > default, and as it should display according to your preferences?
> 
> Sure.  Here I made a GIF from the screenshots, hope you can spot the
> difference.
> 
> https://codeberg.org/m0p/ublock-origin-mirror/raw/branch/main/cjk-good-vs-bad.gif

Thanks.  The question is: how can Emacs distinguish between these
fonts and decide that one of them is not suitable.  In general, Emacs
picks up the first font that matches the fontset's spec, so we need to
come up with two things: (a) the way for Emacs to distinguish between
these fonts, and (b) the way to encode the requirements for a "good"
font in our default fontset.  Then Emacs will be able to pick up the
correct font automatically.