bug#7860: recursive autoreconf breaks AM_COND_IF conditionalization of AC_CONFIG_FILES

[Dave Hart]

When invoked by autoreconf of a project with nested configure.ac
files, automake does not respect the disabling of AC_CONFIG_FILES by
the top-level configure.ac using AM_COND_IF, resulting in an incorrect
Makefile.  Re-running autoreconf from within the nested project
produces correct output.

http://support.ntp.org/people/hart/am-libopts-subpkg.tar.gz

The layout is:

am-libopts-subpkg/
    configure.ac
    Makefile.am
    top.c
    subproj/
        configure.ac
        Makefile.am
        sub.c
        libopts/
            m4/
            ...

Both top.c and sub.c are libopts clients, sharing the single (patched)
subproj/libopts bundled copy.  The problem is that sometimes
subproj/libopts/Makefile.in is generated correctly by the subproj
machinery, and other times it is generated incorrectly by the
top-level config.status.  The resulting subproj/libopts/Makefile
breaks "make distcheck" using GNU Make, though curiously FreeBSD's
make is able to complete distcheck successfully.  The incorrect
subproj/libopts/Makefile contains "subdir = subproj/libopts" while the
working one has "subdir = libopts".  The distcheck break happens when
subproj/libopts/Makefile attempts to regenerate itself using a missing
automake invocation that contains an extra "subproj/" that makes the
filename non-existent.

I modified our copy of libopts/m4/libopts.m4, originally from Autogen
5.11.2, to add an optional second argument to LIBOPTS_CHECK which can
be used to conditionalize the
AC_CONFIG_FILES([${libopts-dir}/Makefile]) under AM_COND_IF.  The
top-level am-libopts-subpkg/configure.ac uses this facility, so that
the top-level config.status does not generate subproj/libopts/Makefile
as it would otherwise.  Instead, subproj/config.status generates (from
its perspective) libopts/Makefile.

The problem I had was with autoreconf -i from the top level.  After
autoreconf completes, subproj/libopts/Makefile.in was consistently
incorrect.  This can be worked around with, for example:

cd .../am-libopts-subpkg
autoreconf -i -v --no-recursive
cd subproj
autoreconf -i -v
cd ..

After which subproj/libopts/Makefile.in is consistently correct.

The workaround was only temporary, as invariably something triggered
am--refresh and the incorrect subproj/Makefile stopped progress again.

In the end, for the NTP reference implementation, we worked with Bruce
Korb to upstream a split of the former LIBOPTS_CHECK functionality
into a compatible LIBOPTS_CHECK and a new subset
LIBOPTS_CHECK_NOBUILD.  By using the latter in the top-level
configure.ac, we avoid depending on AM_COND_IF correctly
conditionalizing AC_CONFIG_FILES([${libopts-dir}/Makefile]).

See also:
http://lists.gnu.org/archive/html/automake/2010-11/msg00135.html
http://lists.gnu.org/archive/html/automake/2011-01/msg00120.html
http://lists.gnu.org/archive/html/automake/2011-01/msg00122.html