bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Thamer Mahmoud]

When using ivy.el, some Arabic letters become disconnected. This bug
doesn't affect Emacs 26.3 or any build "--without-harfbuzz".

1. Eval:

(progn
  (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy-overlay.el")
  (load-library "~/.emacs.d/elpa/ivy-0.13.0/colir.el")
  (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy.el")
  (ivy-mode t)
  (run-with-timer .5 nil 'set-input-method "arabic")
  (run-with-timer .5 nil 'insert "السلام عليكم")
  (execute-extended-command nil))

2. While still in the minibuffer, type any Arabic letter. Note the
   AIN(ع) in "عليكم" changes shape from initial to final.

This bug breaks shaping in most buffers, especially after using
swiper.el (ivy-based isearch).


libharfbuzz0b 2.6.7-1 from debian testing
In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.23, cairo version 1.16.0)
 of 2020-11-08, modified by Debian built on x86-ubc-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

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 $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

-- 
Best,
Thamer

bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Eli Zaretskii]

> From: Thamer Mahmoud <thamer.mahmoud@gmail.com>
> Date: Sun, 08 Nov 2020 19:15:37 +0300
> 
> (progn
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy-overlay.el")
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/colir.el")
>   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy.el")
>   (ivy-mode t)
>   (run-with-timer .5 nil 'set-input-method "arabic")
>   (run-with-timer .5 nil 'insert "السلام عليكم")
>   (execute-extended-command nil))
> 
> 2. While still in the minibuffer, type any Arabic letter. Note the
>    AIN(ع) in "عليكم" changes shape from initial to final.
> 
> This bug breaks shaping in most buffers, especially after using
> swiper.el (ivy-based isearch).

I'm not familiar with ivy, but if it writes the text in the minibuffer
in several overlays, then the Arabic text will indeed become
disconnected and generally shaped incorrectly.

I'll try to look into this, but to make this easier and more efficient
I'd appreciate a test case that is less complicated, preferably not
using ivy at all.

Thanks.

bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Eli Zaretskii]

> Date: Sun, 08 Nov 2020 19:20:35 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 44521@debbugs.gnu.org
> 
> > From: Thamer Mahmoud <thamer.mahmoud@gmail.com>
> > Date: Sun, 08 Nov 2020 19:15:37 +0300
> > 
> > (progn
> >   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy-overlay.el")
> >   (load-library "~/.emacs.d/elpa/ivy-0.13.0/colir.el")
> >   (load-library "~/.emacs.d/elpa/ivy-0.13.0/ivy.el")
> >   (ivy-mode t)
> >   (run-with-timer .5 nil 'set-input-method "arabic")
> >   (run-with-timer .5 nil 'insert "السلام عليكم")
> >   (execute-extended-command nil))
> > 
> > 2. While still in the minibuffer, type any Arabic letter. Note the
> >    AIN(ع) in "عليكم" changes shape from initial to final.
> > 
> > This bug breaks shaping in most buffers, especially after using
> > swiper.el (ivy-based isearch).
> 
> I'm not familiar with ivy, but if it writes the text in the minibuffer
> in several overlays, then the Arabic text will indeed become
> disconnected and generally shaped incorrectly.
> 
> I'll try to look into this, but to make this easier and more efficient
> I'd appreciate a test case that is less complicated, preferably not
> using ivy at all.

Actually, it turned out that the reason is very clear, thanks for the
recipe which made it so easy.  So I've now fixed this on the emacs-27
branch for the upcoming Emacs 27.2.

bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Thamer Mahmoud]

Eli Zaretskii <eliz@gnu.org> writes:

> Actually, it turned out that the reason is very clear, thanks for the
> recipe which made it so easy.  So I've now fixed this on the emacs-27
> branch for the upcoming Emacs 27.2.

Confirmed fixed on 27.1.50.

Thanks.

bug#44521: 27.1; ivy.el breaks harfbuzz Arabic shaping

[Eli Zaretskii]

> From: Thamer Mahmoud <thamer.mahmoud@gmail.com>
> Cc: 44521@debbugs.gnu.org
> Date: Tue, 10 Nov 2020 12:19:12 +0300
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Actually, it turned out that the reason is very clear, thanks for the
> > recipe which made it so easy.  So I've now fixed this on the emacs-27
> > branch for the upcoming Emacs 27.2.
> 
> Confirmed fixed on 27.1.50.

Thanks, closing.