Subject: bug#26333: 26.0.50; Hang when displaying some special characters for the first time

From: Steven Allen <[email-masked]>
Date: Sun, 02 Apr 2017 10:14:00 -0700

Eli Zaretskii <[email-masked]> writes:
> Is this the only thing one has to do, in "emacs -Q", in order to
> reproduce the problem with these fonts?  Or do you have other
> font-related customizations on your init files?

That's the only thing I have to do. Evaluate that, paste the character
in question, and then wait.

Eli Zaretskii <[email-masked]> writes:
> I meant "normal" as in "Emacs is known to do that sometimes when
> searching for a font".

Emacs is also known to sometimes crash. That doesn't make this behavior
"normal". I'd understand "expected behavior" but I'd disagree (15
seconds is a *really* long time to hang just to lookup a font).

Eli Zaretskii <[email-masked]> writes:
> I'm not sure comparison with other applications is valid, as Emacs
> attempts to solve a more complex problem, and its font-searching
> algorithms are biased in favor of finding fonts which support scripts
> and languages, not symbols.

How are those any different? From a computer's perspective, they're all
just Unicode blocks.

Regardless, if this is the case, one could solve this problem by simply
stacking the algorithms: execute the normal (fast) search first and
fallback on Emacs' complex (slow) search.

However, I kind of doubt this is a fundamental limitation in the current
font search algorithm.

Eli Zaretskii <[email-masked]> writes:
> Is it eventually displayed using Symbola or some other font?

Symbola. However, when the default font is DejaVu, it's displayed with
"DejaVu Math TeX Gyre" (a different font in a different file).