bug#69860: 29.2; ERC 5.6-git: erc: Incorrect face formatting applied for fg=99 bg=x (irccontrols module with erc-interpret-mirc-color=t)

[Alcor]

On Emacs 29.2, using erc-5.6snapshot0.20240310.61129:

1. Enable the irccontrols module (for erc)
2. Enable `erc-interpret-mirc-color'
3. Login onto any IRC network, any channel, or perform a /query session
4. Either send, or have someone send you the string ^C99,4Text with a
red background^C (Key sequence: C-q C-c 99,4Text with a red background
C-q C-c)

According to https://modern.ircdocs.horse/formatting.html the text
*should* get formatted with a default foreground, and a red background. The
observed behavior - however - is that the text is formatted with multiple
background "bg" faces: (erc-control-default-bg bg:erc-color-face4
erc-input-face).

A screenshot illustrating the issue is attached to this message.


In GNU Emacs 29.2 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
 cairo version 1.16.0) of 2024-03-13 built on lcy02-amd64-051
Repository revision: 900dc1b4bf3011e685a1ec7d7ce4dcd0262ec880
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12201001
System Description: Ubuntu 22.04.4 LTS

Configured using:
 'configure --prefix=/snap/emacs/current/usr --with-x-toolkit=gtk3
 --without-xaw3d --with-modules --with-cairo
 --with-native-compilation=aot --without-pgtk --with-xinput2
 --with-tree-sitter --with-json
 'CFLAGS=-isystem/build/emacs/parts/emacs/install/usr/include
 -isystem/build/emacs/parts/emacs/install/usr/include/x86_64-linux-gnu
 -isystem/build/emacs/stage/usr/include -O2'
 'CPPFLAGS=-isystem/build/emacs/parts/emacs/install/usr/include
 -isystem/build/emacs/parts/emacs/install/usr/include/x86_64-linux-gnu
 -isystem/build/emacs/stage/usr/include'
 'LDFLAGS=-L/build/emacs/parts/emacs/install/lib
 -L/build/emacs/parts/emacs/install/usr/lib
 -L/build/emacs/parts/emacs/install/lib/x86_64-linux-gnu
 -L/build/emacs/parts/emacs/install/usr/lib/x86_64-linux-gnu
 -L/build/emacs/stage/usr/lib''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER X11 XDBE XIM XINPUT2 XPM
GTK3 ZLIB

Important settings:
  value of $LANG: de_DE.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Group

Minor modes in effect:
  gnus-undo-mode: t
  shell-dirtrack-mode: t
  erc-ring-mode: t
  erc-notifications-mode: t
  erc-netsplit-mode: t
  erc-menu-mode: t
  erc-list-mode: t
  erc-irccontrols-mode: t
  erc-keep-place-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  erc-scrolltobottom-mode: t
  erc-imenu-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-bufbar-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-autojoin-mode: t
  erc-autoaway-mode: t
  recentf-mode: t
  pixel-scroll-precision-mode: t
  minibuffer-depth-indicate-mode: t
  global-whitespace-mode: t
  global-goto-address-mode: t
  goto-address-mode: t
  global-auto-revert-mode: t
  fido-vertical-mode: t
  icomplete-vertical-mode: t
  icomplete-mode: t
  fido-mode: t
  erc-networks-mode: t
  desktop-save-mode: t
  windmove-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  column-number-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

Features:
(shadow emacsbug mailalias smtpmail ispell cl-print help-fns radix-tree
sort smiley gnus-cite mail-extr textsec uni-scripts idna-mapping
ucs-normalize uni-confusable textsec-check gnus-bcklg gnus-async gnus-ml
nndraft nnmh nnfolder utf-7 rfc2104 network-stream nsm gnus-agent
gnus-srvr gnus-score score-mode nnvirtual gnus-msg nntp gnus-cache
display-line-numbers org-element org-persist org-id org-refile avl-tree
generator oc-basic ol-eww eww url-queue mm-url ol-rmail ol-mhe ol-irc
ol-info ol-gnus nnselect gnus-art mm-uu mml2015 mm-view mml-smime smime
gnutls dig gnus-sum shr pixel-fill kinsoku url-file svg dom gnus-group
gnus-undo gnus-start gnus-dbus gnus-cloud nnimap nnmail mail-source utf7
nnoo gnus-spec gnus-int gnus-range message sendmail yank-media puny
rfc822 mml mml-sec epa epg rfc6068 epg-config mm-decode mm-bodies
mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mailabbrev
gmm-utils mailheader gnus-win gnus nnheader gnus-util
text-property-search mail-utils range mm-util mail-prsvr ol-docview
doc-view jka-compr image-mode exif dired dired-loaddefs ol-bibtex bibtex
ol-bbdb ol-w3m ol-doi org-link-doi org ob ob-tangle ob-ref ob-lob
ob-table ob-exp org-macro org-src ob-comint org-pcomplete org-list
org-footnote org-faces org-entities noutline outline ob-emacs-lisp
ob-core ob-eval org-cycle org-table ol org-fold org-fold-core org-keys
oc org-loaddefs find-func cal-menu calendar cal-loaddefs org-version
org-compat org-macs tramp-cache time-stamp tramp-sh tramp tramp-loaddefs
trampver tramp-integration files-x tramp-compat shell parse-time iso8601
disp-table erc-ring erc-desktop-notifications notifications dbus xml
erc-nicks color erc-netsplit erc-menu erc-list erc-goodies erc-imenu
imenu erc-pcomplete time-date pcomplete comint ansi-osc ansi-color
erc-button erc-fill erc-stamp erc-status-sidebar erc-track erc-match
erc-join erc-autoaway leuven-dark-theme recentf tree-widget wid-edit
pixel-scroll cua-base ring mb-depth whitespace goto-addr thingatpt
autorevert filenotify icomplete erc derived format-spec erc-backend
erc-networks easy-mmode erc-common inline erc-compat pcase compat
erc-loaddefs desktop frameset cus-load windmove xdg site-start comp
comp-cstr warnings icons rx cl-extra help-mode erc-autoloads info
compat-autoloads markdown-mode-autoloads package browse-url url
url-proxy url-privacy url-expand url-methods url-history url-cookie
generate-lisp-file url-domsuf url-util mailcap url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs password-cache json subr-x
map byte-opt gv bytecomp byte-compile url-vars cl-loaddefs cl-lib rmc
iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
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
frame minibuffer nadvice seq simple cl-generic indonesian philippine
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp
files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify lcms2 dynamic-setting system-font-setting
font-render-setting cairo move-toolbar gtk x-toolkit xinput2 x multi-tty
make-network-process native-compile emacs)

Memory information:
((conses 16 615423 61113)
 (symbols 48 32158 26)
 (strings 32 117195 5131)
 (string-bytes 1 3518684)
 (vectors 16 71836)
 (vector-slots 8 1268576 98438)
 (floats 8 591 755)
 (intervals 56 1811 223)
 (buffers 984 22))

c99x-describe-char.png
Description: Screenshot demonstrating the issue