bug#34035: 26.1; Arabic shadda-kasrah renders incorrectly

[Basil L. Contovounesios]

Stefan Kangas <stefan@marxist.se> writes:

> So now Emacs 27.1 is released with harfbuzz support.  Could you please
> try this again using that and see if you can still reproduce this issue
> there?

I can still reproduce all of the above on both emacs-27 and master:

0. emacs -Q
1. C-x C-= C-= C-=
2. C-\ arabic RET
3. s ~ A

The kasrah is shown below the sin:

4. C-b
5. C-u C-x =

--8<---------------cut here---------------start------------->8---
             position: 146 of 148 (98%), column: 0
            character: س‎ (displayed as س‎) (codepoint 1587, #o3063, #x633)
              charset: unicode (Unicode (ISO10646))
code point in charset: 0x0633
               script: arabic
               syntax: w        which means: word
             category: .:Base, R:Right-to-left (strong), b:Arabic
             to input: type "s" with arabic input method
          buffer code: #xD8 #xB3
            file code: #xD8 #xB3 (encoded by coding system utf-8-unix)
              display: composed to form "سِّ" (see below)

Composed with the following character(s) "ِّ" using this font:
  xfthb:-PfEd-DejaVu Sans Mono-normal-normal-normal-*-26-*-*-*-m-0-iso10646-1
by these glyphs:
  [0 2 1616 1153 16 4 12 0 4 [0 6 0]]
  [0 2 1617 1154 16 3 12 23 -15 [0 2 0]]
  [0 2 1587 1129 16 -4 15 10 7 nil]

Character code properties: customize what to show
  name: ARABIC LETTER SEEN
  general-category: Lo (Letter, Other)
  decomposition: (1587) ('س')

There are text properties here:
  fontified            nil
--8<---------------cut here---------------end--------------->8---

6. M-x set-frame-font RET symbola RET

The kasrah is shown above the sin:

7. C-u C-x =

--8<---------------cut here---------------start------------->8---
             position: 146 of 148 (98%), column: 0
            character: س‎ (displayed as س‎) (codepoint 1587, #o3063, #x633)
              charset: unicode (Unicode (ISO10646))
code point in charset: 0x0633
               script: arabic
               syntax: w        which means: word
             category: .:Base, R:Right-to-left (strong), b:Arabic
             to input: type "s" with arabic input method
          buffer code: #xD8 #xB3
            file code: #xD8 #xB3 (encoded by coding system utf-8-unix)
              display: composed to form "سِّ" (see below)

Composed with the following character(s) "ِّ" using this font:
  xfthb:-PfEd-DejaVu Sans-normal-normal-semicondensed-*-26-*-*-*-*-0-iso10646-1
by these glyphs:
  [0 2 1616 6022 0 2 10 27 -15 [1 5 0]]
  [0 2 1617 1377 29 1 27 10 7 nil]

Character code properties: customize what to show
  name: ARABIC LETTER SEEN
  general-category: Lo (Letter, Other)
  decomposition: (1587) ('س')

There are text properties here:
  fontified            t
--8<---------------cut here---------------end--------------->8---

My Emacs version details follow.

HTH,

-- 
Basil

In GNU Emacs 27.1.50 (build 1, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars)
 of 2020-08-13 built on tabos
Repository revision: 69568674b3bb5b5f65f2c1342aded205a00f696a
Repository branch: emacs-27
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure 'CC=ccache gcc' 'CFLAGS=-O0 -g3 -ggdb -gdwarf-4'
 --config-cache --prefix=/home/blc/.local --program-suffix=27
 --enable-checking=yes,glyphs --enable-check-lisp-object-type
 --with-x-toolkit=lucid --with-file-notification=yes --with-x'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
XFT ZLIB TOOLKIT_SCROLL_BARS LUCID X11 XDBE XIM MODULES THREADS
LIBSYSTEMD JSON PDUMPER LCMS2 GMP

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

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0, Xaw3d scroll bars)
 of 2020-08-18 built on tabos
Repository revision: 92ec47981acd353658782ce2e094e9f270d8bd8d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure 'CC=ccache gcc' 'CFLAGS=-O2 -march=native' --config-cache
 --prefix=/home/blc/.local --with-x-toolkit=lucid
 --with-file-notification=yes --with-x'

Configured features:
XAW3D 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 LUCID X11 XDBE XIM MODULES THREADS
LIBSYSTEMD JSON PDUMPER LCMS2