Re: bug#636: Please fix before the release of 23.1

[Alan Mackenzie <acm@muc.de>]

Hi, Ulrich and Yidong!

Thanks for CC'ing me in on this one.

On Mon, Aug 11, 2008 at 09:18:55AM +0200, Ulrich Mueller wrote:
> >>>>> On Sun, 10 Aug 2008, Chong Yidong wrote:

> > In fact, it's apparently not a problem with cc-mode, but with Emacs.
> > Here's a stripped-down recipe:

> > 1. Create a file foo.el in your lisp path with the following contents:

> > (defconst foo
> >   (let ((beginning-of-defun-function
> > 	 (lambda (&optional arg)
> > 	   (not (eq arg nil)))))
> >     (progn
> >       (beginning-of-defun 1))))

> > (provide 'foo)

> Calling beginning-of-defun will move point, right?

> And since beginning-of-defun-function is essentially defined as a
> no-op, point will just be moved to the beginning-of-line. (In fact,
> eval-buffer on foo.el results in an infinite loop.)

> > By the way, replacing `progn' with `save-excursion' makes the bug go
> > away (this makes cc-def.el work too). Why? I don't know.

> Indeed. If we agree that the bug is in cc-defs.el, then the following
> patch should fix it:

> --- progmodes/cc-defs.el	27 Jun 2008 21:12:46 -0000	1.58
> +++ progmodes/cc-defs.el	11 Aug 2008 07:11:04 -0000
> @@ -1445,7 +1445,7 @@
>      (let ((beginning-of-defun-function
>  	   (lambda (&optional arg)
>  	     (not (eq arg nil)))))
> -      (if (beginning-of-defun 1)
> +      (if (save-excursion (beginning-of-defun 1))
>  	  (setq list (cons 'argumentative-bod-function list))))

>      (let ((buf (generate-new-buffer " test"))

I protest against this "fix".  :-)  Not against the fix as such (though
it is somewhat ugly, and would need some comments), just that the bug it
fixes is not understood.  Therefore, it is NOT a fix.  It is still a bug,
which will cause pain somewhere else.

> Ulrich

-- 
Alan Mackenzie (Nuremberg, Germany).