init: ensure $ac_aux_dir is defined before being used

Since we use '$ac_aux_dir' to define '$am_aux_dir', we need
to ensure the former has been initialized before we try to
define the latter, otherwise the definition:

   am_aux_dir=`cd $ac_aux_dir && pwd`

will set '$am_aux_dir' to '$HOME', likely causing weird and
unexpected behaviours.

This change fixes automake bug#15981.

* m4/auxdir.m4 (AM_AUX_DIR_EXPAND): AC_REQUIRE expansion
of 'AC_CONFIG_AUX_DIR_DEFAULT'. Fix redundant comment and
AC_PREREQ, add extra quoting around '$ac_aux_dir'.
* t/auxdir-pr15981.sh: New test.
* t/auxdir-cc-pr15981.sh: Likewise.
* t/list-of-tests.mk (handwritten_TESTS): Add them.
* THANKS, NEWS: Update.
* bin/automake.in: Fix a harmless typo in comments, that
I happened to notice while writing this patch.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

7 files changed, 107 insertions, 6 deletions

diff --git a/NEWS b/NEWS
index eb88c17d8..b008a015c 100644
--- a/NEWS
+++ b/NEWS
@@ -97,7 +97,7 @@ New in 1.15:
     extra useless "make all" recursive invocation in some corner cases
     (automake bug#16302).
 
-* Bug fixes:
+* Bugs fixed:
 
   - The user can now extend the special .PRECIOUS target, the same way
     he could already do with the .MAKE .and .PHONY targets.
@@ -105,6 +105,9 @@ New in 1.15:
   - Fixed confusing typos in the manual and in some warning messages
     (automake bug#16827 and bug#16997).
 
+  - We no longer risk to use '$ac_aux_dir' before it's defined.  See
+    automake bug#15981.
+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 New in 1.14.1:
diff --git a/THANKS b/THANKS
index 550b565e8..eef67c353 100644
--- a/THANKS
+++ b/THANKS
@@ -317,6 +317,7 @@ Per Oyvind Hvidsten             poeh@enter.vg
 Peter Breitenlohner             peb@mppmu.mpg.de
 Peter Eisentraut                peter_e@gmx.net
 Peter Gavin                     pgavin@debaser.kicks-ass.org
+Peter Hutterer                  peter.hutterer@who-t.net
 Peter Johansson                 trojkan@gmail.com
 Peter Mattis                    petm@scam.XCF.Berkeley.EDU
 Peter Muir                      iyhi@yahoo.com
diff --git a/bin/automake.in b/bin/automake.in
index 996a9de23..f9cc611a4 100644
--- a/bin/automake.in
+++ b/bin/automake.in
@@ -313,7 +313,7 @@ my $seen_ar = 0;
 # Location of AC_REQUIRE_AUX_FILE calls, indexed by their argument.
 my %required_aux_file = ();
 
-# Where AM_INIT_AUTOMAKE is called;
+# Where AM_INIT_AUTOMAKE is called.
 my $seen_init_automake = 0;
 
 # TRUE if we've seen AM_AUTOMAKE_VERSION.
diff --git a/m4/auxdir.m4 b/m4/auxdir.m4
index 1f8614d47..93fc22521 100644
--- a/m4/auxdir.m4
+++ b/m4/auxdir.m4
@@ -45,8 +45,7 @@
 # configured tree to be moved without reconfiguration.
 
 AC_DEFUN([AM_AUX_DIR_EXPAND],
-[dnl Rely on autoconf to set up CDPATH properly.
-AC_PREREQ([2.50])dnl
-# expand $ac_aux_dir to an absolute path
-am_aux_dir=`cd $ac_aux_dir && pwd`
+[AC_REQUIRE([AC_CONFIG_AUX_DIR_DEFAULT])dnl
+# Expand $ac_aux_dir to an absolute path.
+am_aux_dir=`cd "$ac_aux_dir" && pwd`
 ])
diff --git a/t/auxdir-cc-pr15981.sh b/t/auxdir-cc-pr15981.sh
new file mode 100644
index 000000000..74157cbc1
--- /dev/null
+++ b/t/auxdir-cc-pr15981.sh
@@ -0,0 +1,57 @@
+#! /bin/sh
+# Copyright (C) 2014 Free Software Foundation, Inc.
+#
+# This program 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.
+#
+# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test automake bug#15981: automake 1.14 may use $ac_aux_dir
+# before it is defined, leading to error messages such as:
+# "/bin/sh: /home/david/missing: No such file or directory"
+
+required=cc
+. test-init.sh
+
+cat > configure.ac <<END
+AC_INIT([$me], [0.0])
+AC_USE_SYSTEM_EXTENSIONS
+AM_INIT_AUTOMAKE([1.11 foreign])
+AC_CONFIG_FILES([Makefile])
+AC_SUBST([MISSING])
+AC_OUTPUT
+test -n "\${MISSING}"
+END
+
+echo 'int main (void) { return 0; }' > foo.c
+
+cat > Makefile.am <<'END'
+bin_PROGRAMS = foo
+
+# Without quotes around '--help' and with an empty $(MISSING), make might
+# strip the trailing '--', call Bash's 'help' builtin, and have this test
+# succeed spuriously.  Yes, that has happened in practice :-(
+test:
+	$(MISSING) '--help'
+END
+
+$ACLOCAL
+$AUTOCONF
+$AUTOMAKE
+
+./configure 2>stderr || { cat stderr >&2; exit 1; }
+cat stderr >&2
+$FGREP "missing" stderr && exit 1
+
+$MAKE all
+$MAKE test
+
+:
diff --git a/t/auxdir-pr15981.sh b/t/auxdir-pr15981.sh
new file mode 100644
index 000000000..f09d551fd
--- /dev/null
+++ b/t/auxdir-pr15981.sh
@@ -0,0 +1,39 @@
+#! /bin/sh
+# Copyright (C) 2014 Free Software Foundation, Inc.
+#
+# This program 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.
+#
+# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# AM_AUX_DIR_EXPAND should ensure $ac_aux_dir is properly initialized.
+# Issue revealed by related automake bug#15981.
+
+. test-init.sh
+
+cat > configure.ac <<'END'
+AC_INIT([test], [0.0])
+AM_AUX_DIR_EXPAND
+printf '%s\n' "ac_aux_dir: '$ac_aux_dir'"
+printf '%s\n' "am_aux_dir: '$am_aux_dir'"
+test "$ac_aux_dir" = . || AS_EXIT([1])
+test "$am_aux_dir" = "`pwd`" || AS_EXIT([1])
+AS_EXIT([0])
+END
+
+$ACLOCAL
+$AUTOCONF
+
+test -f install-sh  # sanity check
+
+./configure
+
+:
diff --git a/t/list-of-tests.mk b/t/list-of-tests.mk
index 6b2eebe78..e6ee8569b 100644
--- a/t/list-of-tests.mk
+++ b/t/list-of-tests.mk
@@ -116,6 +116,8 @@ t/aclocal-scan-configure-ac-pr319.sh \
 t/aclocal-serial.sh \
 t/aclocal-underquoted-defun.sh \
 t/aclocal-verbose-install.sh \
+t/auxdir-pr15981.sh \
+t/auxdir-cc-pr15981.sh \
 t/ac-output-old.tap \
 t/acsilent.sh \
 t/acsubst.sh \