GNU bug report logs - #69384
30.0.50; :align-to and bidi-paragraph-direction interaction

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stephen Berman <stephen.berman <at> gmx.net>
Subject: bug#69384: closed (Re: bug#69384: 30.0.50; :align-to and
 bidi-paragraph-direction interaction)
Date: Tue, 27 Feb 2024 07:48:02 +0000

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Your bug report

#69384: 30.0.50; :align-to and bidi-paragraph-direction interaction

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 69384 <at> debbugs.gnu.org.

-- 
69384: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=69384
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Stephen Berman <stephen.berman <at> gmx.net>
Cc: 69384-done <at> debbugs.gnu.org
Subject: Re: bug#69384: 30.0.50; :align-to and bidi-paragraph-direction
 interaction
Date: Tue, 27 Feb 2024 09:44:36 +0200

> From: Stephen Berman <stephen.berman <at> gmx.net>
> Cc: 69384 <at> debbugs.gnu.org
> Date: Mon, 26 Feb 2024 22:46:50 +0100
> 
> On Mon, 26 Feb 2024 19:28:09 +0200 Eli Zaretskii <eliz <at> gnu.org> wrote:
> 
> >> Cc: 69384 <at> debbugs.gnu.org
> >> Date: Sun, 25 Feb 2024 19:35:22 +0200
> >> From: Eli Zaretskii <eliz <at> gnu.org>
> >>
> >> > Sorry for not being clearer in my report: the bug is the broken shaping
> >> > with the combination of setting bidi-paragraph-direction and using
> >> > :align-to
> >>
> >> OK, I will look into that when I have time.
> >
> > It's a relatively recent regression on the master branch, caused by
> > yours truly.  I hope I've fixed it now.
> 
> I updated and rebuilt, and confirm that with the code I posted that
> resulted in broken Arabic shaping, the shaping is now correct.  Thanks!

Thanks, I'm therefore closing this bug.

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From: Stephen Berman <stephen.berman <at> gmx.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 30.0.50; :align-to and bidi-paragraph-direction interaction
Date: Sun, 25 Feb 2024 17:22:45 +0100

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In a buffer that contains bidirectional text, setting
bidi-paragraph-direction to 'left-to-right aligns the RTL text with the
left margin like the LTR text; see the first sexp below and the top
buffer in the attached screenshot.

Another alternative to get this alignment is to leave
bidi-paragraph-direction at its default value of nil and use a space
display specification with a suitable value for the :align-to property,
but this requires a calculation that seems to depend at least on the
font used and the values of `window-width' and `string-width' for the
string used (or the corresponding pixel-width values); see the second
sexp below and the middle buffer in the attached screenshot.

It's also possible to avoid this calculation and use an :align-to value
of 0 in combination with setting bidi-paragraph-direction to
'left-to-right; see the third sexp below and the bottom buffer in the
attached screenshot.  However, as the screenshot shows, this last
alternative breaks Arabic text shaping, at least for the fonts I tried
(Noto Naskh Arabic, DejaVu Sans and Amiri).  If this is not an Emacs bug
but a limitation of the current display engine or a HarfBuzz bug,
perhaps it should be noted in etc/PROBLEMS.

(let* ((a "السّلام عليكم")
       (b "Hello")
       (buf (get-buffer-create "Test1")))
  (with-current-buffer buf
    (erase-buffer)
    (setq bidi-paragraph-direction 'left-to-right)
    (insert a "\n\n" b)
    (switch-to-buffer buf)))

(let* ((a "السّلام عليكم")
       (wa (+ (- (window-width) (string-width a)) 0.75))
       (b "Hello")
       (buf (get-buffer-create "Test2")))
  (with-current-buffer buf
    (erase-buffer)
    (insert (propertize " " 'display `(space :align-to ,wa)) a "\n\n" b)
    (switch-to-buffer buf)))

(let* ((a "السّلام عليكم")
       (b "Hello")
       (buf (get-buffer-create "Test3")))
  (with-current-buffer buf
    (erase-buffer)
    (setq bidi-paragraph-direction 'left-to-right)
    (insert (propertize " " 'display `(space :align-to 0)) a "\n\n" b)
    (switch-to-buffer buf)))

[Screenshot_2024-02-25_15-28-01.png (image/png, attachment)]

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In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.18.0) of 2024-02-20 built on strobelfs2
Repository revision: d9afa1f30fdf9d00b447fea0a8343397333e172f
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101009
System Description: Linux From Scratch r12.0-112

Configured using:
 'configure -C --with-xwidgets 'CFLAGS=-Og -g3'
 PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER
PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM XWIDGETS GTK3 ZLIB

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