Re: use-default-font-for-symbols vs. emojis (was: Wrestling with set-fontset-font)

[Eli Zaretskii <eliz@gnu.org>]

> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
> Date: Fri, 27 Dec 2019 19:52:49 +0100
> 
> >          However, these considerations are unlikely to be relevant to
> >          punctuation and other symbols, since the latter generally
> >          aren't specific to any culture, and don't require
> >          sophisticated OTF features.  */
> 
> Do emojis challenge this heuristic, since
> 
> - they can typically use "sophisticated OTF features" such as color,
> - combining sequences[1] are a thing?

We don't yet support these features, so they are largely irrelevant
for Emacs at this point.  And (sadly) I don't see anyone around who
knows enough and has enough motivation and energy to teach Emacs to
support that.

> If so, could/should there be a way to distinguish "emoji" characters
> from the more general "symbol" script, using e.g. data from
> <https://unicode.org/Public/emoji/12.1/>?

If and when we need that, it will be almost trivial.  What's
non-trivial is to add support for color emoji.

> [1] E.g. 🧟‍♂️, 🧟‍♀️, 🐕‍🦺, 🏴‍☠️, from
>     <https://unicode.org/Public/emoji/12.1/emoji-zwj-sequences.txt>, or
>     flag sequences from
>     <https://unicode.org/Public/emoji/12.1/emoji-sequences.txt>; none of
>     which work inside Emacs yet AFAICT.
> 
>     To be more precise: as of commit 9ee5af31, these examples appear
>     "decombined".  I have no idea what controls this (Harfbuzz? Cairo?)…

Could be a simple matter of defining more entries in
composition-function table to support these sequences (assuming the
font supports them).