bug#76031: 31.0.50; Switching frames on TTY display doesn't work

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Cc: rudalics@gmx.at,  76031@debbugs.gnu.org
> Date: Wed, 05 Feb 2025 14:43:24 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Thanks, but I'm worried that we will have to special-case TTY frames
> > in Lisp, due to these changes.  I think this again indicates that we
> > use "frame visibility" for several different purposes.  If so, a
> > better way forward would be to make the frame's visibility flag a
> > tristate or maybe even more values, instead of a simple boolean.
> 
> What would the values of such a visibility enum be?

I proposed one possible way in my other messages earlier today.  Other
factoring is, of course, possible.

> I find it easier to have a simple definition in C, and let Lisp decide
> what it wants to do, basically on a use-case basis. For example, if we
> decide other-frame should work with tty root frames that are not
> visible, let other-frame do it. Other function might not want to do the
> same thing.
> 
> An enum, on the other hand, makes things complicated for both C
> internals and Lisp.

We could have two separate flags or a bitmap in C.  For Lisp, I
propose to use predicates and/or teach the likes of next-frame to deal
with these flags internally, in some way that is convenient for Lisp
programs.  Something similar to the possible values of the 2nd
argument of next-frame.