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

[Stefan Kangas]

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?