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Re: use of (defvar <foo>)

From: Reiner Steib
Subject: Re: use of (defvar <foo>)
Date: Fri, 07 Apr 2006 21:07:48 +0200
User-agent: Gnus/5.110004 (No Gnus v0.4) Emacs/22.0.50 (gnu/linux)

On Fri, Apr 07 2006, Dave Love wrote on address@hidden:

> Reiner Steib <address@hidden> writes:

[ Quote from initial mail added for emacs-devel ]
>> On Thu, Apr 06 2006, Dave Love wrote:
>>> Gnus has lots of instances of `(defvar <foo>)' that aren't protected
>>> by `eval-when-compile' and should be.

>> ,----[ http://article.gmane.org/gmane.emacs.devel/43027 ]
>> | From: Richard M. Stallman
>> | Subject: Re: defvars at compile time
>> |
>> | The only effect of a defvar with no initial value
>> | is to silence the compiler.  So it is superfluous
>> | to put it inside eval-when-compile.
>> `----
> That's certainly not true in Emacs 21:
> (progn
>   (with-temp-file "/tmp/x.el"
>     (insert "(defvar foo)\n"))
>   (byte-compile-file "/tmp/x.el")
>   (with-temp-buffer 
>     (insert-file-contents-literally "/tmp/x.elc")
>     (goto-char (point-max))
>     (delete-region 1 (line-beginning-position 0))
>     (buffer-string)))
>   => "(byte-code \"\\301B\\301\\207\" [current-load-list foo] 2)
> "
> You can completely screw Emacs if you unload a feature that does that
> on important variables.  It also causes confusion with find-function &
> al.  I fixed a fair number of cases in the Emacs source that could
> clobber things like `font-lock-keywords' and documented using
> eval-when-compile in the Lisp manual.  I don't remember what the
> justification was for the one-arg defvar modifying the load history at
> the time; that sort of policy decision often gets reversed.

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

Bye, Reiner.
      (o o)
---ooO-(_)-Ooo---  |  PGP key available  |  http://rsteib.home.pages.de/

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