bug#16815: 24.3.50; Provide completion for `describe-font' (enhancement request)

[Eli Zaretskii]

> Date: Fri, 29 Apr 2016 11:39:59 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: 16815@debbugs.gnu.org
> 
> This is what I use, FWIW:
> 
> (let ((fonts        (make-hash-table :test #'equal))
>       (fontset-lst  (fontset-list)))
>   (setq fontset-lst  (delete "-*-*-*-*-*-*-*-*-*-*-*-*-fontset-default"
>                              fontset-lst))
>   (dolist (ft  (append fontset-lst (x-list-fonts "*"))  fonts)
>     (puthash ft t fonts)))

IMO, this is madness: you are bloating the Emacs session with hundreds
of fonts, most of which Emacs will never need to use, or even know
about.  We certainly shouldn't do anything like that in Emacs.

The doc string of describe-font clearly says that the font must be one
which Emacs already loaded, so completing on all the _installed_ fonts
is definitely not TRT.