bug#57693: 29.0.50; Is there a more reliable version of `char-displayable-p'?

[Eli Zaretskii]

> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Fri, 17 Feb 2023 14:31:49 -0800
> Cc: yantar92@gmail.com, 57693@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Something like what?  If you want to suggest some specific function,
> > please show the proposed code, and let's take it from there.
> > Otherwise, this bug discussion was long and considered several issues,
> > and it is hard to know what you have in mind.
> 
> The code is here:
> 
>     https://debbugs.gnu.org/cgi/bugreport.cgi?bug=57693#71

That's for GUI displays only.  And it's for strings, not characters.
To test a single character, you don't need a separate function, IMO,
you just need to use the test that is the core of that code.

> > And what is the problem with using char-displayable-p in that case?
> 
> My concern is that `char-displayable-p' will return t even if the
> character is not displayable.

If you need to care for TTY frames, that problem has no known solution
that works for all terminal emulators.  So using fancy characters in
general-purpose Emacs features is a problem that cannot be solved
programmatically, or at least we don't currently know how to do that.