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

[Stephen Berman]

On Fri, 11 Jan 2019 11:30:56 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: "Peter" <craven@gmx.net>,  34035@debbugs.gnu.org
>> Date: Fri, 11 Jan 2019 10:24:45 +0100
>> 
>> > Thanks.  On my system, this is displayed correctly, with kasrah above
>> > the letter.  So I don't think it's Emacs, I think it's the shaping
>> > engine you are using.  As you didn't provide the information collected
>> > by "M-x report-emacs-bug", I can only guess what is that shaping
>> > engine: XFT and libflt, right?  Maybe you could try building the
>> > harfbazz branch, which uses HarfBazz for shaping, I'd expect this
>> > problem not to exist there.
>> 
>> I believe the problem is not with the shaping engine but with the font:
>
> The OP did say he tried different fonts, to no avail.  It would be
> interesting to know which fonts were those.
>
>> I see the same problem on both builds from current master (with libotf)
>> and from the current harfbuzz branch using my default font, DejaVu Sans
>> Mono.  But when I switch the font to Symbola, the kasrah is correctly
>> displayed between the sin and the shadda, both on master and on
>> harfbuzz.  (Nevertheless, on both branches, after switching to Symbola,
>> describe-char surprisingly says this:
>> 
>> Composed with the following character(s) "ِّ" using this font:
>>   xft:-PfEd-DejaVu Sans-normal-normal-semicondensed-*-15-*-*-*-*-0-iso10646-1
>> 
>> Is this expected?)
>
> Please show the entire output of "C-x =" 

I assume you meant `C-u C-x ='

>                                          (I presume you invoke it on
> the position of sin?).

Yes.  Here's the output on master:

==============================================================================
             position: 1 of 3 (0%), 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:
  xft:-PfEd-DejaVu Sans-normal-normal-semicondensed-*-15-*-*-*-*-0-iso10646-1
by these glyphs:
  [0 2 1587 1377 16 0 16 6 4 nil]
  [0 2 0 6022 0 -15 -10 13 -11 [-16 2 0]]

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

On the harfbuzz branch the output is the same except for the glyphs:

  [0 2 1587 6022 0 1 6 16 -8 [0 3 0]]
  [0 2 1587 1377 16 0 16 6 4 nil]

Note the second line here is identical to the first line of glyphs on
master.

Steve Berman