bug#67810: 29.1; fonts use synthetic bold on Linux / pgtk

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Tim Ruffing <crypto@timruffing.de>
>> Cc: 67810@debbugs.gnu.org
>> Date: Thu, 14 Dec 2023 10:54:45 +0100
>> 
>> So I think whether overstriking is performed should ideally be a
>> property of the font. Having some variable similar to the existing 
>> vertical-centering-font-regexp would be great, and this would also make
>> it possible to turn off overstriking globally.
>> 
>> Do you think that's a reasonable thing to add?

The only existing variable which controls font display through matching
fonts against a regexp has been effectively abandoned over the years,
and is nonfunctional on all systems besides X and Android.
(Grep for Vvertical_centering_font_regexp: only sfntfont.c and xfont.c
consult it.)

A compelling reason for us _not_ to introduce more such variables, as
they will soon fall into disuse and neglect.

> What are the chances of someone wanting to disable this feature only
> for some fonts?  If we want to allow disabling it globally, it should
> be a simple matter of adding a boolean variable exposed to Lisp, and
> then performing this only when the variable doesn't inhibit that.
>
> Adding a font property, or a regexp for matching fonts which are
> exempt from this, are by contrast much more complex and require more
> changes.  For a feature that was so far requested by a single user,
> I'm not sure this is justified.
>
> As for your example: if Doom uses this for icons, why cannot Doom
> refrain from using bold face for these cases?

Yes, and don't these packages require using their own specialized icon
fonts to begin with?