bug#53625: 28.0.91; Incorrect Malayalam font rendering

[Sameer Singh]

Emacs is unable to properly render a Malayalam font when a Virama is
applied to a consonant with a diacritic. Instead of appearing with the
consonant, it is displayed separately.
Steps to Reproduce:
1. emacs -Q
2. In the scratch buffer type any malayalam consonant with a diacritic
and a virama. e.g. : കാ്, കെ്, കൈ്
3. Instead of appearing on the consonant, the Virama appears separately
with a dotted circle

I am using the "Baloo Chettan 2" font, but the issue is appearing with other
fonts also.
I have attached the correct render from "hb-view" in the file "mal.png", and the incorrect
render from emacs in the file "mal-emacs.png"


In GNU Emacs 28.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.31, cairo version 1.17.4)
 of 2022-01-20 built on baf2fb08a9c3
Repository revision: 4445f200b7c0bf11e412ca300de00e2988922ba0
Repository branch: pgtk-nativecomp
Windowing system distributor 'System Description: Arch Linux

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
 --with-sound=alsa --with-modules --with-x-toolkit=gtk3 --with-cairo
 --with-xwidgets --with-native-compilation --with-pgtk
 --without-compress-install --without-gconf --without-gsettings
 --without-m17n-flt --enable-autodepend --enable-link-time-optimization
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions
 -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security
 -fstack-clash-protection -fcf-protection -g -flto'
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM HARFBUZZ JPEG JSON LCMS2
LIBOTF LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PGTK PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS XIM
XWIDGETS GTK3 ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
  text-scale-mode: t
  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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util rmail
rmail-loaddefs auth-source eieio eieio-core eieio-loaddefs
password-cache json map text-property-search mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
comp comp-cstr warnings rx cl-seq cl-macs cl-extra seq byte-opt gv
bytecomp byte-compile cconv rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils time-date subr-x pp wid-edit descr-text help-mode
cl-loaddefs cl-lib face-remap iso-transl tooltip eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/pgtk-win pgtk-win term/common-win 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 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 emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads xwidget-internal dbusbind
inotify dynamic-setting font-render-setting cairo move-toolbar gtk
x-toolkit pgtk lcms2 multi-tty make-network-process native-compile
emacs)

Memory information:
((conses 16 94063 23351)
 (symbols 48 20847 1)
 (strings 32 81418 4452)
 (string-bytes 1 1988002)
 (vectors 16 24062)
 (vector-slots 8 1453075 134979)
 (floats 8 38 87)
 (intervals 56 372 0)
 (buffers 992 13))

mal-emacs.png
Description: PNG image

mal.png
Description: PNG image