bug#20984: 25.0.50; Combining accents don't display properly in certain fonts

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 9 Jul 2015 22:55:09 +0100
> From: Artur Malabarba <bruce.connor.am@gmail.com>
> Cc: Kenichi Handa <handa@gnu.org>, 20984@debbugs.gnu.org
> 
> > OP (and I guess for you as well) with DejaVu Sans Mono.  I will then
> > try to see what changes were done there since 24.5.
> 
> Just to add information. I built the emacs-24.5 tag today and I still
> see the same issue on it. So don't be surprised if the answer isn't
> there. =/

Yes, I understand.  But walking through the code might be a good
starting point anyway, since the composition data is so completely
broken.

Btw, I wonder why xftfont and libotf don't do the same as Uniscribe,
i.e. instruct Emacs to display the à character.  This is what the
composition data I see here says:

  [0 1 97 231 8 1 7 12 4 nil]

This single vector tells Emacs to display one glyph, and 231 is its
code in the font.

It is strange that libotf doesn't take this shortcut, although I'm
quite sure a glyph for à is available both in DejaVu Sans Mono and in
Source Code Pro.  But I don't know enough about libotf.