Maintaining ACLOCAL_AMFLAGS in the Makefile.am to pass extra flags
to aclocal is (and have always been) quite of an hack. For example,
autoreconf is forced to grep Makefile.am to honour those flags. But
this is a bad obsolescent behaviour; in fact, the autotools have moved
consistently in the past years from custom grepping of Makefile.am and
configure.ac to tracing of m4 macro calls, which is more consistent,
more reliable and more flexible.
And when autoreconf is not used, the developer is forced to add *by hand*
the flags specified by ACLOCAL_AMFLAGS to the aclocal calls not triggered
by make rebuild rules; here lie again more duplication and more chances
for errors.
Moreover, ACLOCAL_AMFLAGS has only two typical use cases:
- to instruct aclocal to look for extra macro definition in a local
directory (as with "ACLOCAL_AMFLAGS = -I m4"); and
- to further instruct aclocal to copy in that local directory the
required third-party .m4 files found in the system-wide directory
(as with "ACLOCAL_AMFLAGS = -I m4 --install").
The first use case can be better covered if aclocal can instead trace and
honours call to the AC_CONFIG_MACRO_DIR autoconf macro; and the second
use case shouldn't be considered really legitimate, as it is quite (and
subtly) brittle (see automake bug#9037).