Re: Warnings for excessive macro arguments

[Eric Blake]

On 08/23/2010 11:02 AM, Yavor Doganov wrote:
> I was wondering if it is possible (and whether it is a good idea in
> general) autoconf to print warnings for extra macro arguments instead
> of silently ignoring them.

I have to wonder if there are cases where rejecting extra arguments 
might not be advisable, because it hampers future extensions that assign 
meaning to those extra arguments while still being backwards compatible 
with earlier versions.  That is, if 2.67 supports macro ABC(arg), then 
in 2.68 we add support for ABC(arg1, arg2), there is the question of 
whether the person calling ABC(arg1, arg2) will get sane semantics even 
if they use 2.67, by silently ignoring arg2.

On the other hand, any good extension is one where leaving the argument 
blank achieves the same behavior as the old version.  And since the 
older version knows that it doesn't handle extra arguments, checking for 
a maximum $# (or, perhaps more robustly, checking that any arguments 
after a maximum $# are blank) may be feasible.  But it would take a lot 
of work to add that to all the existing autoconf macros.

> AC_CHECK_ALIGNOF(pthread_mutex_t,,[AC_INCLUDES_DEFAULT
> #include<pthread.h>])
>
> The generated configure script fails on OpenBSD and Woe32, because
> <pthread.h>  is not #include'd in the test program.
>
> It took me some time to spot where the problem is :-)

At any rate, this is an interesting feature request.  Maybe the thing to 
do now is add mention of it in TODO, if we don't come up with a patch 
right away?

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org