bug#64024: 29.0.91; `emoji-insert` shows me confusing empty lists

[Stefan Monnier]

Package: Emacs
Version: 29.0.91


    % src/emacs -Q
    M-x emoji-insert RET
    s s

I expect at this point to see a list of "smiling Smiley" emojis
displayed in the small bottom window, but instead that window is empty
(there's just a one-pixel-thick line about one-char wide at the very
top-left) and it sits there.  At this point I get the impression that
this bottom window is actually gone and I'm now looking at an unusually
high empty echo area.  But if I try to type characters, I'm met with
messages like:

    Unbound suffix: 'a' (Use 'C-g' to abort, '?' for help) [self-insert-command]

if I hit `?` I get:

    Error in post-command-hook (transient--post-command): (error "Invalid 
search bound (wrong side of point)")

There are several bugs here (probably parts in `emoji.el` and parts in
`transient.el`):

1- The list shouldn't be empty, right?
2- If really the list should be empty, then it would be better after the
   first `s` not to offer me a second `s` choice if that choice leads nowhere.
3- Once I get to this empty list, the state is quite confusing.
   It would be desirable to emit a message about the fact that there's
   no valid choice at this point and that `C-g` and `?` are the only
   options (assuming these are really the only options).
4- The search-bound error, of course.

Side note: during this `emoji-insert` interaction, I only see
black&white emojis, so maybe this is linked to some compilation option
I used which prevents the use of color emojis, tho I don't know what
that option would be.


        Stefan


In GNU Emacs 29.0.91 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw3d scroll bars) of 2023-06-12 built on pastel
Repository revision: 36aa9bd818334bba56b0fdd6e10d7dc05ba4bbd4
Repository branch: emacs-29
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure -C --enable-checking --enable-check-lisp-object-type
 --with-modules --with-cairo --with-tiff=ifavailable 'CFLAGS=-Wall -g3
 -Og -Wno-pointer-sign' PKG_CONFIG_PATH=/home/monnier/lib/pkgconfig'

Configured features:
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LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND
THREADS TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XAW3D XDBE XIM XINPUT2
XPM LUCID ZLIB

Important settings:
  value of $LANG: fr_CH.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
emoji-labels emoji generate-lisp-file multisession sqlite transient
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tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors
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cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
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code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting cairo x-toolkit xinput2 x multi-tty
make-network-process emacs)

Memory information:
((conses 16 64058 6337)
 (symbols 48 7321 0)
 (strings 32 36137 2055)
 (string-bytes 1 857492)
 (vectors 16 16552)
 (vector-slots 8 362576 16685)
 (floats 8 33 138)
 (intervals 56 617 0)
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