bug#46217: 27.1.91; Configuring certain font ligatures causes Emacs 27 to hang.

[Johannes Grødem]

If configuring for example a "/*" ligature (the font face used doesn't
seem to matter) and opening a C-file or a Java-file or related language
modes, Emacs will hang. (It just rings the bell continuosly, and it's
impossible to interrupt it.)

This seems to be fixed in commit
fe903c5ab7354b97f80ecf1b01ca3ff1027be446 by Eli Zaretskii, which is on
master, but not on emacs-27. I've cherry-picked this on the emacs-27 and
verified that it fixes at least the issue I'm having. Could this be
included in the next 27-release?

I've used Mickey Petersen's ligature.el package to set up ligatures. See
https://github.com/mickeynp/ligature.el/issues/16 for the issue I'm
having.

In GNU Emacs 27.1.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20, cairo 
version 1.16.0)
 of 2021-01-31 built on huglaus
Repository revision: cbeda210835bee9ff3e7f697c7944a10db8b132c
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version 11.0.12009000
System Description: Ubuntu 20.04.2 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
user-error: Beginning of history; no preceding item

Configured using:
 'configure --prefix=/opt/emacs/prerel --with-x-toolkit=yes --with-cairo
 --with-file-notification=yes'

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

Important settings:
  value of $LC_MONETARY: nb_NO.UTF-8
  value of $LC_NUMERIC: nb_NO.UTF-8
  value of $LC_TIME: nb_NO.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
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 elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer cl-generic 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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 44968 8357)
 (symbols 48 6000 1)
 (strings 32 15440 1951)
 (string-bytes 1 503395)
 (vectors 16 10089)
 (vector-slots 8 129969 9846)
 (floats 8 20 40)
 (intervals 56 193 0)
 (buffers 1000 11))