bug#31316: Emacs hangs in `font_open_entity'

[Werner LEMBERG <wl@gnu.org>]

Eli, thanks for the `pp' tip.

>> Sort of, thanks.  After waiting a few seconds, Emacs now displays
>> three characters, but navigation is hard: it takes a few seconds to
>> move from character to character (I guess Emacs tries to reload the
>> missing glyph again and again).
> 
> Well, maybe I went overboard with the 100 figure, and we should use
> a much smaller number, like 10 or 20?

Maybe, yes.  I don't know enough of Emacs code to have an opinion on
that.

> And anyway, some delays are better than an infloop, yes?

Certainly.  However, I wonder why Emacs doesn't cache this...

>> >> Both `average_width' and `height' are always zero for `font'
>> >> regardless of `psize'; this effectively makes the above code an
>> >> endless loop.
>>
>> > What kind of strange font has both of these always zero?

I have to correct me: Only `average_width' is zero, not value
`height'.

The font is called `emmentaler-brace.otf' (part of lilypond,
containing system braces for musical scores).  However, I wonder how
this font can ever be considered as a fallback, since its SFNT (3,1)
Unicode cmap contains only PUA character codes in the range
0xe100-0xe33f (and `fc-list -v' correctly lists that).  In other
words, this font definitely doesn't contain anything relevant to the
CJK character codes originally reported.


    Werner