allow (sub)packages to share files in subpackages

[Ralf Wildenhues]

[ Please remove libtool-patches from followups; this is merely to
  make them aware of this discussion ]

This proposed patch is short, but requires some more explanation:
In CVS Libtool, libltdl may be used as a subpackage within third-
party packages; this is nothing new: 1.5.x has this, too[1].
New is that we now actively encourage such users to set
  AC_CONFIG_AUX_DIR([libltdl/config])
  AC_CONFIG_MACRO_DIR([libltdl/m4])

in order to avoid some duplication[2].  For simple packages, this
works fine.  But now suppose the toplevel package needs `mdate-sh'
or some other auxiliary script not needed by libltdl itself.
  automake --add-missing
will install this into libltdl/config, but `make dist' will fail,
because the libltdl part of the `distdir' target will remove the
previously copied file `libltdl/config/mdate-sh': the toplevel
`distdir' target simply does the copying before calling the sub-
package target, which then removes its `$(distdir)'.

The proposed patch below now allows[3] this to work: subpackages
will not clean their `$(distdir)' any more before populating it.
(Changing the order is not feasible for other reasons.)

This change would also facilitate manual sharing of m4 macro files
within subpackage trees: since you're far more likely to have to
modify the toplevel package for the tree anyway, you can now
  m4_include([subpkg/m4/foo.m4])
in toplevel acinclude.m4, and everything will Just Work[tm]. :-)

This is very useful for easily building package trees where the
top level package is merely glue.

Cheers,
Ralf

[1] New in CVS Libtool is that libltdl may also be used in a non-
subpackage fashion.  This is not the topic of this message.

[2] We are aware that this suggestion is not scalable, and to some
extent an artifact of the way libltdl is created.  It is not a
requirement of the toplevel package to do the sharing, so we still
think it's useful for some packages.

[3] The $(MAKE) invocation for the subpackage `distdir' is not
portable to all `make' implementation (as not all allow to override
set macros from the command line); this requirement does not change
with the patch.


        Allow package trees (packages with subpackages) to share
        common distributed auxiliary files (and directories) that
        reside within a subpackage.

        * lib/am/distdir.am (distdir %?TOPDIR_P%): Do not fail if
        `$(distdir)' already exists.
        (%?SUBDIRS%): Set `am__remove_distdir' to `:' to prevent
        removal of subpackage trees for distribution.
        * tests/subpkg3.test: New test.
        * tests/Makefile.am: Updated.

Index: lib/am/distdir.am
===================================================================
RCS file: /cvs/automake/automake/lib/am/distdir.am,v
retrieving revision 1.62
diff -u -r1.62 distdir.am
--- lib/am/distdir.am   3 Oct 2005 20:48:59 -0000       1.62
+++ lib/am/distdir.am   12 Jan 2006 20:21:07 -0000
@@ -50,7 +50,7 @@
 ##
 if %?TOPDIR_P%
        $(am__remove_distdir)
-       mkdir $(distdir)
+       test -d $(distdir) || mkdir $(distdir)
 endif %?TOPDIR_P%
 ##
 ##
@@ -175,6 +175,7 @@
              $(MAKE) $(AM_MAKEFLAGS) \
                top_distdir="$$top_distdir" \
                distdir="$$distdir/$$subdir" \
+               am__remove_distdir=: \
                distdir) \
              || exit 1; \
          fi; \
Index: tests/Makefile.am
===================================================================
RCS file: /cvs/automake/automake/tests/Makefile.am,v
retrieving revision 1.591
diff -u -r1.591 Makefile.am
--- tests/Makefile.am   30 Jun 2005 21:19:47 -0000      1.591
+++ tests/Makefile.am   12 Jan 2006 20:29:27 -0000
@@ -497,6 +497,7 @@
 subobjname.test \
 subpkg.test \
 subpkg2.test \
+subpkg3.test \
 subst.test \
 subst2.test \
 substref.test \
--- /dev/null   1970-01-01 00:00:01.000000000 +0000
+++ tests/subpkg3.test  2006-01-12 20:51:15.000000000 +0100
@@ -0,0 +1,64 @@
+#! /bin/sh
+# Copyright (C) 2006  Free Software Foundation, Inc.
+#
+# This file is part of GNU Automake.
+#
+# GNU Automake is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2, or (at your option)
+# any later version.
+#
+# GNU Automake is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Automake; see the file COPYING.  If not, write to
+# the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+# Boston, MA 02110-1301, USA.
+
+# make sure different subpackages may share files and directories.
+
+. ./defs || exit 1
+
+set -e
+
+cat >Makefile.am <<'END'
+SUBDIRS = subpkg
+EXTRA_DIST = subpkg/foobar
+END
+
+cat >>configure.in <<'END'
+AC_CONFIG_SUBDIRS([subpkg])
+AC_OUTPUT
+END
+
+mkdir subpkg
+
+cat >subpkg/foobar <<'END'
+foobar
+END
+
+cat >subpkg/Makefile.am <<'END'
+SUBDIRS =
+END
+cat >subpkg/configure.in <<'END'
+AC_INIT([subpkg], [1.0])
+AM_INIT_AUTOMAKE
+AC_CONFIG_FILES([Makefile])
+AC_OUTPUT
+END
+
+$ACLOCAL
+$AUTOMAKE
+$AUTOCONF
+
+cd subpkg
+$ACLOCAL
+$AUTOMAKE
+$AUTOCONF
+cd ..
+
+./configure
+$MAKE distcheck