warn: allow aclocal to silence m4_require warnings

We introduce a new witness macro, m4_require_silent_probe, for use by
aclocal during the Autoconf-without-aclocal-m4 language.  This will let
aclocal process AC_CONFIG_MACRO_DIRS without emitting spurious warnings.
In fact, if aclocal doesn't suppress require warnings, then, when some macro
expanded in configure.ac calls AC_REQUIRE on another macro that is defined
in one of the local m4 macro dirs specified with AC_CONFIG_MACRO_DIRS, the
*first* autom4te invocation issued by aclocal, not yet being able to "see"
the m4 macro definitions in the local m4 dirs, will print spurious
warnings like:

    configure.ac:4: warning: MY_BAR is m4_require'd but not m4_defun'd
    configure.ac:3: MY_FOO is expanded from...

Expose the use of this macro in our testsuite.

Originally reported by Nick Bowler; see point (4) of:
<http://lists.gnu.org/archive/html/autoconf-patches/2012-11/msg00000.html>

* lib/m4sugar/m4sugar.m4 (_m4_require_call): Make warnings in the
-Wsyntax category depend on the witness macro.
* tests/m4sugar.at (m4@&t@_require: warning message): New test.
* doc/autoconf.texi (Prerequisite Macros): Document how aclocal
can silence AC_REQUIRE (m4_require) warnings.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

0 files changed, 0 insertions, 0 deletions