bug#27872: 26.0.50; freeze when opening file with emojis

[Alan Third <alan@idiocy.org>]

On Sun, Jul 30, 2017 at 05:27:35PM +0300, Eli Zaretskii wrote:
> > From: Nejc Vivod <nvivod@gmail.com>
> > Date: Sun, 30 Jul 2017 16:19:45 +0200
> > Cc: 27872@debbugs.gnu.org
> > 
> > I thought I did, but I might be mistaken. Re-sending the backtrace.
> 
> Thanks.
> 
> Alan, I don't think I understand how you reached your conclusion: all
> the loops involved in the code shown in the backtrace are fixed-size
> loops, so they've got to end at some point.  Am I missing something?

No, I just saw that the last piece of Emacs code in the backtrace was
macfont_list and figured it was probably something to do with that,
but presumably the loop could be somewhere else.

On macOS there is specific code for displaying colour emojis, but it’s
been disabled. I don’t see any emojis at all, just a blank space the
same size as the colour emoji should be.

I don’t know if Macs come with non‐colour emoji capable fonts by
default, all other Mac apps display the colour ones so I can’t even
see a way to test.

If I call describe-char on the hamburger I get:

             position: 146 of 146 (99%), column: 0
            character: 🍔 (displayed as 🍔) (codepoint 127828, #o371524, #x1f354)
    preferred charset: unicode (Unicode (ISO10646))
code point in charset: 0x1F354
               script: symbol
               syntax: w 	which means: word
             category: .:Base
             to input: type "C-x 8 RET 1f354" or "C-x 8 RET HAMBURGER"
          buffer code: #xF0 #x9F #x8D #x94
            file code: #xF0 #x9F #x8D #x94 (encoded by coding system utf-8-unix)
              display: no font available

Character code properties: customize what to show
  name: HAMBURGER
  general-category: So (Symbol, Other)
  decomposition: (127828) ('🍔')

There are text properties here:
  fontified            nil

I don’t know if any of this is relevant.
-- 
Alan Third