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The aclocal program doesn't have any built-in knowledge of any macros, so it is easy to extend it with your own macros.
This can be used by libraries that want to supply their own Autoconf
macros for use by other programs. For instance, the gettext
library supplies a macro
AM_GNU_GETTEXT that should be used by
any package using gettext. When the library is installed, it
installs this macro so that aclocal will find it.
A macro file's name should end in .m4. Such files should be installed in $(datadir)/aclocal. This is as simple as writing:
aclocaldir = $(datadir)/aclocal aclocal_DATA = mymacro.m4 myothermacro.m4
Please do use $(datadir)/aclocal, and not something based on the result of ‘aclocal --print-ac-dir’ (see Hard-Coded Install Paths, for arguments). It might also be helpful to suggest to the user to add the $(datadir)/aclocal directory to his ACLOCAL_PATH variable (see ACLOCAL_PATH) so that aclocal will find the .m4 files installed by your package automatically.
A file of macros should be a series of properly quoted
AC_DEFUN's (see Macro Definitions). The aclocal programs also understands
AC_REQUIRE (see Prerequisite Macros), so it is safe to put each macro in a separate file.
Each file should have no side effects but macro definitions.
Especially, any call to
AC_PREREQ should be done inside the
defined macro, not at the beginning of the file.
Starting with Automake 1.8, aclocal will warn about all
underquoted calls to
AC_DEFUN. We realize this will annoy a
lot of people, because aclocal was not so strict in the past
and many third party macros are underquoted; and we have to apologize
for this temporary inconvenience. The reason we have to be stricter
is that a future implementation of aclocal (see Future of aclocal) will have to temporarily include all of these third party
.m4 files, maybe several times, including even files that are
not actually needed. Doing so should alleviate many problems of the
current implementation, however it requires a stricter style from the
macro authors. Hopefully it is easy to revise the existing macros.
# bad style AC_PREREQ(2.68) AC_DEFUN(AX_FOOBAR, [AC_REQUIRE([AX_SOMETHING])dnl AX_FOO AX_BAR ])
should be rewritten as
AC_DEFUN([AX_FOOBAR], [AC_PREREQ([2.68])dnl AC_REQUIRE([AX_SOMETHING])dnl AX_FOO AX_BAR ])
AC_PREREQ call inside the macro ensures that
Autoconf 2.68 will not be required if
AX_FOOBAR is not actually
used. Most importantly, quoting the first argument of
allows the macro to be redefined or included twice (otherwise this
first argument would be expanded during the second definition). For
consistency we like to quote even arguments such as
do not require it.
If you have been directed here by the aclocal diagnostic but are not the maintainer of the implicated macro, you will want to contact the maintainer of that macro. Please make sure you have the latest version of the macro and that the problem hasn't already been reported before doing so: people tend to work faster when they aren't flooded by mails.
Another situation where aclocal is commonly used is to manage macros that are used locally by the package, Local Macros.