bug#43177: Bug: Emacs 27.1 hangs forever in `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1'

[Alexander Shukaev]

On 03/09/2020 12:06, Robert Pluim wrote:
> > > > > > On Thu, 3 Sep 2020 11:53:05 +0200, Alexander Shukaev 
> > > > > > <emacs@Alexander.Shukaev.name> said:
>
>      Alexander> On 03/09/2020 11:50, Alexander Shukaev wrote:
>      >> On 03/09/2020 11:40, Alexander Shukaev wrote:
>      >>> (gdb) f 7
>      >>> #7  0x0000555555a8d875 in xfont_supported_scripts
>      >>> (display=0x555556594940, fontname=0x55556a79e428 "-misc-trirong
>      >>> medium-medium-i-normal--0-0-0-0-p-0-iso10646-1",
>      >>> props=XIL(0x7ffff27926e5),
>      >>>      encoding=0x7ffff23ab8d0) at xfont.c:266
>      >>> 266          xfont = XLoadQueryFont (display, fontname);
>      >>> (gdb) pp fontname
>      >>> #<INVALID_LISP_OBJECT 0x55556a79e428>
>      >>> (gdb) pp fontname
>      >>> #<INVALID_LISP_OBJECT 0x55556a79e428>
>      >>> (gdb) p fontname
>      >>> $3 = 0x55556a79e428 "-misc-trirong
>      >>> medium-medium-i-normal--0-0-0-0-p-0-iso10646-1"
>      >>> (gdb)
>      >> It appears to always be different `fontname' here as I try multiple
>      >> times to reproduce.  Maybe it's not really hanging but is merely
>      >> ultra-slow somehow in looping over the fonts here.  Any ideas?
>
>      Alexander> Hmm, right, waited for about a minute or so, and the file got 
> opened
>      Alexander> finally.  Reopening it was instant as well as if something got
>      Alexander> cached/loaded already.  So any ideas how to speed things up 
> here?  I
>      Alexander> don't think I've encountered that with 26.3...
>
> You can check easily enough by building emacs-27 --without-cairo, that
> should get you back to emacs-26's font handling.
>
> The issue is: why is Emacs falling back to the 'x' backend?
>
> Robert

The only related font configurations that I can think of are the following:

(defcustom init-font-families
  '("Powerline Consolas"
    "Consolas for Powerline"
    "Consolas"
    ;;
    "Powerline Inconsolata-g"
    "Inconsolata-g for Powerline"
    "Inconsolata-g"
    ;;
    "Powerline Source Code Pro"
    "Source Code Pro for Powerline"
    "Source Code Pro"
    ;;
    "Powerline DejaVu Sans Mono"
    "DejaVu Sans Mono for Powerline"
    "DejaVu Sans Mono"
    ;;
    "Monospace")
  "List of font families."
  :group 'init
  :type 'list)

(defcustom init-font-size
  12
  "Size of font."
  :group 'init
  :type 'integer)

  (defun init-frame-font-setup
      (&optional frame)
    (unless frame (setq frame (selected-frame)))
    (with-selected-frame frame
      (when (and (not noninteractive) (init-display-graphic-p))
        (let ((font (assoc 'font default-frame-alist)))
          (if font
              (when (eq frame frame-initial-frame)
                (set-frame-font font t t)
                (unless noninteractive
                  (message "Font: `%s'" font)))
            (let ((font-family (catch 'break
                                 (dolist (font-family init-font-families)
                                   (when (member font-family
                                                 (font-family-list))
                                     (throw 'break font-family))))))
              (setq font (when font-family
                           (format "%s-%d" font-family init-font-size))))
            (when font
              (add-to-list 'default-frame-alist `(font . ,font))
              (set-frame-font font t t)
              (unless noninteractive
                (message "Font: `%s'" font))))))))

  (unless (or noninteractive (daemonp))
    (when (init-display-graphic-p)
      (init-frame-font-setup)))

  (dolist (hook '(after-make-frame-functions
                  focus-in-hook))
    (add-hook hook #'init-frame-font-setup))

With what I consistently get output

Font: ‘Consolas-12’

for several years already on various Linux systems that I'm using so far.