bug#20140: 24.4; M17n shaper output rejected

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 16 Feb 2022 19:01:12 +0000
> From: Richard Wordingham <richard.wordingham@ntlworld.com>
> Cc: larsi@gnus.org, 20140@debbugs.gnu.org
> 
> > It sounds like Courier New in Windows 10 was "improved" by removing
> > the capability of ligating those 2 characters.  On Windows XP, their
> > standard Courier New shows the first 2 characters ligate into a single
> > glyph, which looks just like U+FCCA, but on Windows 10 they don't
> > ligate.  I don't know why is that; perhaps Arabic typesetting experts
> > decided these should not ligate?
> > 
> > > I must admit I'm having trouble laying my hand on a font which
> > > does these ligatures.  
> > 
> > Try the Arabic Typesetting font, there I see on Windows 10 that the
> > first 2 characters look like U+FCCA.
> > 
> > IOW, this is a font issue, not an Emacs or HarfBuzz issue.
> 
> Arabic Typesetting seems not to come in an evaluation copy of Windows
> 10.

You can easily install it from the Internet.  I did.

> And yes, the issue is that some fonts probably don't work well with
> Emacs.

??? These issues with fonts have nothing to do with Emacs.  HarfBuzz
will produce the same results outside of Emacs; e.g., try hb-view.  Or
view your message with those characters in a Web browser (by pointing
it to the bug-gnu-emacs archives) -- you will see the same results.
AFAIU, the fonts simply don't want to produce a ligature from those
two characters.  Arabic Typesetting does, so the result is what you
expect, in Emacs and elsewhere.