bug#70000: 29.2; Grapheme handling incorrect

[Phillip Susi]

I had some terminal breakage the other day when browsing email with
notmuch.  Now a ways down the rabbit hole, it seems this is because
emacs does not correctly handle graphemes.  I found this article here:

https://mitchellh.com/writing/grapheme-clusters-in-terminals

If I paste that gramehe into GUI emacs, it is displayed as two separate
characters, each two columns wide, instead of the correct way: as a
single double wide character.  C-f and C-b move over the character as if
it were one, however, backspace deletes only the second, leaving both
the first and the zero width joiner.  If C-f and C-b treat it as one,
then so should backspace.

Under recent versions of the foot terminal emulator, this character is
displayed as a single, double wide character, but emacs assumes it still
is 4 colums wide, leading to terminal breakage.  Emacs needs to not
assume the width of graphemes are what wcwidth() reports, but instead
need to query the cursor position after printing one to find out how
wide the terminal actually dispalyed it as.



In GNU Emacs 29.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.39,
 cairo version 1.18.0) of 2024-02-26 built on localhost
System Description: Gentoo Linux

Configured using:
 'configure --prefix=/usr --build=x86_64-pc-linux-gnu
 --host=x86_64-pc-linux-gnu --mandir=/usr/share/man
 --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
 --localstatedir=/var/lib --datarootdir=/usr/share
 --disable-silent-rules --docdir=/usr/share/doc/emacs-29.2-r1
 --htmldir=/usr/share/doc/emacs-29.2-r1/html --libdir=/usr/lib64
 --program-suffix=-emacs-29 --includedir=/usr/include/emacs-29
 --infodir=/usr/share/info/emacs-29 --localstatedir=/var
 --enable-locallisppath=/etc/emacs:/usr/share/emacs/site-lisp
 --without-compress-install --without-hesiod --without-pop
 --with-file-notification=inotify --with-pdumper --enable-acl
 --with-dbus --with-modules --without-gameuser --with-libgmp --with-gpm
 --with-native-compilation=aot --without-json --without-kerberos
 --without-kerberos5 --with-lcms2 --without-xml2 --without-mailutils
 --without-selinux --without-sqlite3 --with-gnutls --with-libsystemd
 --with-threads --with-tree-sitter --without-wide-int --with-sound=alsa
 --with-zlib --with-pgtk --without-x --without-ns
 --with-toolkit-scroll-bars --without-gconf --without-gsettings
 --without-harfbuzz --without-libotf --without-m17n-flt
 --without-xwidgets --with-gif --with-jpeg --with-png --with-rsvg
 --with-tiff --without-webp --without-imagemagick --with-dumping=pdumper
 'CFLAGS=-march=native -O2 -pipe' 'LDFLAGS=-Wl,-O1 -Wl,--as-needed''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM JPEG LCMS2 LIBSYSTEMD
MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PGTK PNG RSVG SECCOMP SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER XIM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.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
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: 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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message yank-media puny dired
dired-loaddefs rfc822 mml mml-sec epa derived epg rfc6068 epg-config
gnus-util text-property-search time-date mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils cus-start cus-load
wid-edit descr-text enriched disp-table facemenu comp comp-cstr warnings
icons rx cl-extra help-mode manoj-dark-theme site-gentoo
ranger-autoloads scopeline-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/pgtk-win pgtk-win
term/common-win pgtk-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 dynamic-setting font-render-setting cairo gtk
pgtk lcms2 multi-tty make-network-process native-compile emacs)

Memory information:
((conses 16 121243 14450)
 (symbols 48 22924 0)
 (strings 32 87992 2869)
 (string-bytes 1 2065634)
 (vectors 16 27491)
 (vector-slots 8 1623278 223666)
 (floats 8 58 48)
 (intervals 56 908 0)
 (buffers 984 13))