bug#29837: UTF-16 char display problems and the macOS "character palette"

[Alan Third]

Hi, I’ve had a go at enabling the macOS character palette, which is
just a virtual keyboard that helps you to enter special characters,
emoji’s, etc.

It’s easy enough to bring it up (patch attached) but some special
characters are put into Emacs incorrectly. I think the problem is that
we have multi code‐point UTF‐16 characters, and when they are ‘typed’
into Emacs they are entered as individual 16 bit code‐points and are
therefore displayed as a series of blank spaces.

An example is '🢫' (RIGHTWARDS FRONT-TILTED SHADOWED WHITE ARROW). If I
enter it using C‐x 8 RET, it appears correctly, but if I use the
character palette it shows up as two blank spaces. Describe-char
reveals these to be HIGH SURROGATE-D83E and LOW SURROGATE-DCAB, in
that order.

I can’t work out if Emacs should be able to handle these multi
code‐point characters being entered from a ‘keyboard’ input or not. If
so, does anyone have any idea what I need to do?

(Another minor irritation is that some characters (like pointing
hands) seem to insert the desired character then follow up with
VARIATION SELECTOR-15. I assume this is supposed to tell us what
colour we want the hand? If so should it be displayed?)
-- 
Alan Third

0001-Add-macOS-character-palette.patch
Description: Text document