bug#36914: Font Ligatures

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 03 Aug 2019 20:34:14 +0000
> From: Charles Jackson <charles.b.jackson@protonmail.com>
> 
> I am requesting that GNU Emacs supports ligatures out of the box. I know
> about pretty-symbols-mode, and it is great, but it is not font
> ligatures.
> 
> Take my case for example: I just found the a new (new to me) font called
> Monoid (https://larsenwork.com/monoid/). It provides ligatures for
> various programming symbols That I would like to use. The ligatures are
> provided as actual True Type Font ligatures rather than Unicode symbols
> used by pretty-symbols-mode. Thus I couldn't use them at all. I even
> tried to look at the source code for the font to find the character
> code, but the codes for the ligature glyphs were not correct or did not
> exist.
> 
> I am asking you to provide font ligatures out of the box (emacs -Q) by
> using whatever fancy system that True Type Fonts use. This has become a
> feature that most text editors and word processors have by
> default. Emacs has no excuse.

Please be more specific about the feature you'd like to see: how would
Emacs support the ligatures? should it, for example, automatically
produce ff when you type "ff" and ffi when you type "ffi"?  Or do you
want the ligation to happen only on-demand?

IOW, we need a user-level specification to make this happen.  Because
the infrastructure for supporting ligatures already exist, since we
started supporting the HarfBuzz shaping engine in Emacs.

Thanks.