bug#57066: 29.0.50; Complex emoji overlaps with text

[Protesilaos Stavrou]

> From: Eli Zaretskii <eliz@gnu.org>
> Date: Tue, 09 Aug 2022 14:14:54 +0300
>
>> From: Protesilaos Stavrou <info@protesilaos.com>
>> Date: Tue, 09 Aug 2022 12:17:40 +0300
>> 
>> * In the scratch buffer type "Hello "
>> * C-x 8 e s
>> * Search for "sun" and type RET
>> * Now you have: Hello ☀️
>> * C-e
>> * Type something else, like "test".
>> * Notice how "test" is written over the emoji (see attached screenshots).
>
> I cannot reproduce this.
>
> Please go to the Emoji, type "C-u C-x =" and post here everything that
> Emacs shows in the *Help* buffer it pops up.

Right after inserting the "sun" emoji, the 'describe-char' does not
work.  The echo area shows:

    point=154 of 153 (EOB) column=7

Moving the point one character back and retrying returns:

    cl--assertion-failed: Assertion failed: (not (multibyte-string-p str))

Apparently this happens with all emoji.  Even when I insert the first
smiling emoji with the C-x 8 e e s s a sequence I cannot get a Help
buffer out of 'describe-char'.  The point is on the emoji as shown in
the attached screenshot.

-- 
Protesilaos Stavrou
https://protesilaos.com

Screenshot from 2022-08-09 14-26-59.png
Description: PNG image