bug#57066: 29.0.50; Complex emoji overlaps with text

[Protesilaos Stavrou <info@protesilaos.com>]

> From: Eli Zaretskii <eliz@gnu.org>
> Date: Tue, 09 Aug 2022 15:01:44 +0300
>
>> From: Protesilaos Stavrou <info@protesilaos.com>
>> Cc: 57066@debbugs.gnu.org
>> Date: Tue, 09 Aug 2022 14:28:52 +0300
>> 
>> > 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
>
> Are you saying that what describe-char does at EOB means it doesn't
> work?  The above is exactly the expected result at EOB.

Sorry, I meant that I could not produce a Help buffer.

>> Moving the point one character back and retrying returns:
>> 
>>     cl--assertion-failed: Assertion failed: (not (multibyte-string-p str))
>
> I cannot reproduce that, either.  Could you run this under Edebug and
> show the value of 'str' in the above assertion?

I am not sure how to do it with Edebug.  With (setq debug-on-error t) I
get this:

Debugger entered--Lisp error: (cl-assertion-failed ((not (multibyte-string-p str)) nil))
  cl--assertion-failed((not (multibyte-string-p str)))
  encoded-string-description(#("😀" 0 1 (charset unicode)) nil)
  describe-char(146)
  what-cursor-position((4))
  funcall-interactively(what-cursor-position (4))
  call-interactively(what-cursor-position nil nil)
  command-execute(what-cursor-position)

> Someone else reported that this started happening after upgrading
> HarfBuzz to v5.1.0 -- is that the version you are using?

Yes, I am on HarfBuzz v5.1.0 as well.  I will check that thread as well.

-- 
Protesilaos Stavrou
https://protesilaos.com