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

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: Stefan Kangas <stefankangas@gmail.com>, yantar92@gmail.com,
>  57693@debbugs.gnu.org
> Date: Sat, 18 Feb 2023 11:35:33 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > 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.
> 
> I am not sure if it is relevant, but I see
> https://unix.stackexchange.com/questions/184345/detect-how-much-of-unicode-my-terminal-supports-even-through-screen
> 
> May it be something of use for Emacs?

If you are asking about the Linux console, then we already have a way
of asking it whether it supports a given character.

If you are asking about the kludges they suggest for other terminals,
where we are supposed to deduce support fro a character by counting
columns, then that is both unreliable and extremely cumbersome (we'd
need to try to actually display a character in order to know whether
its displayable).