bug#38569: 27.0.50; Certain emoji crashes with "X protocol error: BadLength"

[Robert Pluim]

>>>>> On Fri, 13 Dec 2019 08:50:04 +0200, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Cochran <robert@cochranmail.com>
    >> Date: Thu, 12 Dec 2019 13:34:46 -0800
    >> Cc: Shelvacu <shelvacu@gmail.com>, 38569@debbugs.gnu.org,
    >> Robert Cochran <robert-emacs@cochranmail.com>
    >> 
    >> The easier thing is to add another exception to face-ignored-fonts, but
    >> at this point it'd be a better idea to deal with it at the font renderer
    >> level. IMO it's not scalable for the solution to be "ok, also add this
    >> font to the exception list", especially as frequently as Emacs has
    >> releases.

    Eli> The problem is that AFAIR the "font renderer" that is to blame in this
    Eli> case is XFT, and it doesn't seem to be actively maintained lately.
    Eli> (Robert Pluim will correct me if I'm wrong.)  That's why we are using
    Eli> the face-ignored-fonts workaround.

Thatʼs correct. The real solution is 'stop using XFT', but I donʼt
think we can require cairo just yet, much as Iʼd like to do so.

Eli, we could install my patch to filter out all colour fonts (see
<https://lists.gnu.org/archive/html/bug-gnu-emacs/2019-11/msg00409.html>),
that should reduce the amount of whack-a-mole required.

Robert