Re: m4 macro that would call AAC_INIT

[Eric Blake]

On 09/15/2010 09:21 AM, Vincent Torri wrote:
> Hey,
>
> except AC_PREREQ() (and m4 calls), no macro should be called before
> AC_INIT(). Does this include the call of an m4 macro which itself would
> call AC_INIT. that is, smething like that:
>
> *** my_init.m4 ***
>
> AC_DEFUN([EFL_INIT],
> [
>
> m4_define([v_maj], [$2])
> m4_define([v_min], [$3])
> m4_define([v_mic], [$4])
> m4_define([v_ver], [v_maj.v_min.v_mic])
>
> AC_INIT([$1], [v_ver])
>
> ])
>
> *** configure.ac ***
>
> MY_INIT(foo, 1, 2, 3)

I see no reason why that would not work from the m4 perspective, *as 
long as* my_init.m4 is somehow sourced prior to the MY_INIT line in 
configure.ac.  Generally, when using the autom4te --language=Autoconf 
language, this means that my_init.m4 is included from aclocal.m4 (either 
because aclocal from the Automake package noticed it was a used AC_DEFUN 
macro, or because you did it by hand).  If MY_INIT is defined in time, 
then it will be expanded at m4 time, which in turn calls four instances 
of m4_define (all safe, by your above quote), and finally the call to 
AC_INIT will properly occur as the first autoconf-specific macro.

However, there may be other tools outside of autoconf that grep 
configure.ac (rather than properly relying on autom4te tracing), and 
might get confused by what you've done.  Likewise, I'm not sure whether 
aclocal will succeed at generating aclocal.m4 correctly, since it uses 
autom4te --language=Autoconf-without-aclocal-m4 under the hood, and with 
that particular invocation of autom4te, I don't see how you are going to 
have my_init.m4 included in time to have EFL_INIT defined before it is 
used; AC_INIT _has_ to be expanded even during aclocal for the rest of 
aclocal's magic to work.

If you are having problems getting the definition of MY_INIT seen with 
that cross-file approach, maybe adding m4_include([my_init.m4]) at the 
start of configure.ac will help?

At any rate, rather than just asking about the theory, how about trying 
it out first.  Either it will work, and you are done; or things will 
fail to do what you were hoping, but then you are armed with explicit 
error messages and actual output so that your query to the list can 
contain more details about what you tried vs. what you were hoping.

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