bug#56691: outline-minor-mode displays navigation arrow buttons as emojis

[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: Po Lu <luangruo@yahoo.com>
>> Cc: Lars Ingebrigtsen <larsi@gnus.org>,  rpluim@gmail.com,
>>   56691@debbugs.gnu.org,  hello@paulwrankin.com
>> Date: Tue, 02 Aug 2022 19:57:55 +0800
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> > Yes, but is it reasonable to expect such a system?  I mean, if someone
>> > builds an Emacs capable of displaying color Emoji, isn't it reasonable
>> > to expect him/her to install a suitable font as well?  Color Emoji are
>> > a "hot" feature, so I'd expect that.
>> 
>> The problem is that Emacs is built with color Emoji support by default.
>> Most people do not know the necessary compile-time options to turn that
>> support off.
>> 
>> > Also, do distros come without a color Emoji font nowadays?  Because
>> > Symbola AFAIK needs to be installed, it isn't by default, so if a
>> > color Emoji font _is_ available OOTB, I think the chances for the
>> > problems you mention are very small, and/or are easily fixed.
>> 
>> Symbola comes with most systems OOTB.  I remember Firefox displaying
>> Emoji using that font not too long ago, on a fresh install of RHEL 7.9.
>
> <Shrug> I still feel it's wrong for a capability predicate to load
> fonts etc., and generally be potentially very slow and expensive.

Maybe we could only look for fonts once (on each terminal), and then
cache the result?