Re: use of (defvar <foo>)

[Stefan Monnier]

> Could people on emacs-devel please comment on this?
> Should we use (defvar <foo>) or (eval-when-compile (defvar <foo>)) in Gnus
> for compatibility with Emacs 21?  (Probably the same holds for MH-E.)

>From the future's point of view (Emacs-22 and up), placing such defvars
inside eval-when-compile is a bad practice (in the future it may even fail
to work since there's nothing that guarantees that the content of
eval-when-compile is actually compiled rather than just eval'd).

In Emacs-21 and older, such a defvar will have some undesirable minor
side-effects (via the load-history) unless it is placed inside an
eval-when-compile *and* the file is byte-compiled.  Indeed placing the
defvar inside the eval-when-compile has no effect if the file is not
byte-compiled.

I'd recommend to not use eval-when-compile since that's what many packages
have been doing for many years without suffering much (if ever) of the
occasional side-effects (which only affect unload-feature and sometimes
C-h v).

But it's your call, really.


        Stefan