bug#57141: 29.0.50; Most emoji not displaying in PGTK emacs

[Michael Eliachevitch]

> This is not an Emoji character, this is NBSP.

Upps, my bad, obviously, seems that `(emoji-list)' skips those unrenderable 
emoji.
For describe-char on "😊", I get

--8<---------------cut here---------------start------------->8---
               position: 523 of 1964 (27%), restriction: <103-1965>, column: 0
               character: 😊 (displayed as 😊) (codepoint 128522, #o373012, 
#x1f60a)
               charset: unicode (Unicode (ISO10646))
   code point in charset: 0x1F60A
               script: emoji
               syntax: w        which means: word
               category: .:Base
               to input: type "C-x 8 RET 1f60a" or "C-x 8 RET SMILING FACE WITH 
SMILING EYES"
           buffer code: #xF0 #x9F #x98 #x8A
               file code: #xF0 #x9F #x98 #x8A (encoded by coding system 
utf-8-unix)
               display: no font available

   Character code properties: customize what to show
   name: SMILING FACE WITH SMILING EYES
   general-category: So (Symbol, Other)
   decomposition: (128522) ('😊')

   There are text properties here:
   fontified            t
   wrap-prefix          ""
   ws-butler-chg        chg
--8<---------------cut here---------------end--------------->8---

I now also attached some screenshots of the emoji-list and also of the 
completion-buffer when I press <tab> in emoji-search, which shows the unicode 
placeholders that I get, so it might be more clear what my problem is.

> Do you have Color Note Emoji font installed?

"Noto Color Emoji" is in the output of '(font-family-list) ` and it's also installed via my system 
package manager. Weirdly, if try to change the frame font to "Noto Color Emoji", which I did via the 
menu-bar "options->set default font", I get the error message

   set-frame-font: Font not available: #<font-spec nil nil Noto\ Color\ Emoji nil 
nil normal normal nil 10.0 nil nil nil nil>

I get this for all other emoji fonts that I have installed, but maybe this is 
normal for an emoji font because setting it as font for the entire frame 
doesn't make much sense, but I don't know if this is not a hint of an 
underlying font-config issue.

> Could this be bug#57066?  Does the patch posted there fix the problem?

I agree this is likely to be an issue with harfbuzz, even though the symptoms 
of this bug look different from bug#57066, as I just don't get any rendered 
emoji instead of overlapping emoji (see attached screenshots). I will try this 
patch anyway after this mail.

I also saw bug#56789 which seemed similar in symptoms, but I just checked that 
my archlinux installation has harfbuzz 5.1.0, where the bug causing #56789 is 
should be fixed as far as I understood. I tried a clean rebuild to make sure I 
use that harfbuzz version and also I tried downgrading harfbuzz to 4.4.1 and 
rebuilding emacs and neither solved my rendering issues. I also tried the 
command

   hb-view  --output-file=foo.svg --font-size=13 \
   /usr/share/fonts/noto/NotoColorEmoji.ttf \
   -u 1f469,200d,2764,fe0f,200d,1f468

and it works, producing a nice SVG emoji image. So it's not that harfbuzz in 
general is broken.

Thanks for the help,
Michael

emoji-list.png
Description: PNG image

emoji-completion.png
Description: PNG image