future of AC_PREREQ

[Bruno Haible <bruno at clisp dot org>]

Hi,

The automake manual states:

   "any call to `AC_PREREQ' should be done inside
    the defined macro, not at the beginning of the file."

   "a future implementation of `aclocal' (*note Future of aclocal::) will
    have to temporary include all these third party `.m4' files, maybe
    several times, even those which are not actually needed."

Will a package that installs a /usr/share/aclocal/hobbit.m4 with an
AC_PREREQ(3.0) make all versions of autoconf < 3.0 unusable on the system?
This would not be acceptable.

If it applies only to the directories given as -I options to 'aclocal', this
is acceptable, since these always point to directories inside the package
being built, and these normally don't contain unused macros.

Also, how do you want to make the migration? Will an AC_PREREQ outside of any
macro keep its current meaning, or will be become a nop? In the first case,
what is the incentive for a programmer to move the AC_PREREQ into every
macro that is AC_DEFINEd in the .m4 file?

Bruno