Re: Suggest installing more fonts?

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: emacs-devel@gnu.org
> Date: Sun, 18 Oct 2020 10:03:25 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Then I really don't understand the goal here, because I think the
> > problems people report are never about "the major fonts" or the
> > "usual" scripts -- those are well covered by our default fontset.
> 
> I was just thinking about listing fonts like DejaVu Sans and Noto (with
> a wide support for many scripts), not smaller language-specific fonts.
> And Symbola?
> 
> > Before we implement something like that, we should be reasonably
> > certain it will not annoy most users (not only power users).  It is
> > entirely legitimate to leave some of the Unicode blocks uncovered by
> > the fonts you have installed, and having Emacs display warnings about
> > that might be annoying.  OTOH, such a feature must be turned on by
> > default, otherwise it will not do its job.  So knowing whether users
> > will welcome this is important, IMO.
> 
> We display a button in warning buffers saying "Click here to switch the
> warning off", so I think the annoyance factor would be somewhat limited.

So what is the proposal in more practical terms?  We want redisplay to
leave some information in a buffer-local variable regarding some
buffer positions where no font could be found, and then we will
display a message saying something like "Characters detected for which
there is no font (buffer positions NN, MM, XX, YY); suggest to install
additional fonts"?  Is that the proposal.

If so, will we also mention specific fonts, and if so, which ones?
Should we also make sure those fonts are not already installed?

Btw, I've looked at browsers, and they just display tofu or an empty
rectangle without any message in this case.