bug#59057: Emacs 29. Byte compiler sometimes forgets about a defvar.

[Eli Zaretskii]

> Cc: Alan Mackenzie <acm@muc.de>, 59057@debbugs.gnu.org
> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Thu, 24 Nov 2022 11:29:32 -0800
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> >> The basic problem is that defvar is a dog's breakfast of a function.  In
> >> fact, it's two distinct functions sharing a name.  These two functions
> >> have little else to do with eachother.
> >
> > Yup.
> >
> >> And defvar appears to be the only function in Emacs where supplying nil
> >> as an &optional argument has an effect different from omitting it.  This
> >> is bad for anybody trying to learn Emacs Lisp.
> >
> > Not the only one, sadly (`declare-function` comes to mind :-)), but yes,
> > it's unusual.
> 
> I guess defvar will have to stay as it is.  But would it make sense to
> add a new `declare-variable' function, and then document the form
> 
>     (defvar <foo>)
> 
> to be considered deprecated?

It makes no sense to me to deprecate (defvar FOO).  There are only
disadvantages down that path (massive annoyance or breakage of third-party
code, if nothing else).  Please don't.