Re: Suggest installing more fonts?

[Eli Zaretskii]

> Date: Fri, 16 Oct 2020 16:09:35 +0000
> From: Gregory Heytings <ghe@sdf.org>
> cc: larsi@gnus.org, emacs-devel@gnu.org
> 
> I think I see what you mean: characters that have no fonts are discovered 
> during redisplay, and at that moment it's too late to add text properties, 
> which are not supposed to change anymore.  It might be possible to add a 
> special help-echo like property that would be added at the moment these 
> characters are discovered, for example in produce_glyphless_glyph().

I don't recommend this, it is tricky and might cause problems.

Instead, it is much easier to have a feature implemented in Lisp that
would detect characters with no font glyphs and put help-echo on them.
We have infrastructure for such features in jit-lock.el.

> I don't think there would be "too many" such properties, it seems safe to 
> assume that in general such characters follow each other and form a 
> "block", and a single text property would be enough for one such block.

It is okay to assume, but I'd still prefer that we also check that the
assumption holds, and if so, do something to keep the number of
properties in check.