warnings: more precise category and message for one warning

If automake detected an usage like "AC_CONFIG_FILES([./Makefile])"
in configure.ac, it warned that such an usage was unportable to
non-GNU make implementations.  But the truth is actually worse:
that is actually *unportable to GNU make* itself, since it breaks
the automatic remake rules in subtle ways.

So we now reveal this breakage in a new test case, and enhance
the warning by giving it a more precise and correct wording, and
by moving it from the category 'portability' to the category
'unsupported'.

* automake.in (scan_autoconf_config_files): Improve the warning.
* tests/conffile-leading-dot.test: New test.
* tests/list-of-tests.mk: Add it.

3 files changed, 68 insertions, 4 deletions

diff --git a/automake.in b/automake.in
index abca23de1..cdbb820b2 100644
--- a/automake.in
+++ b/automake.in
@@ -5253,10 +5253,11 @@ sub scan_autoconf_config_files ($$)
       # Handle $local:$input syntax.
       my ($local, @rest) = split (/:/);
       @rest = ("$local.in",) unless @rest;
-      msg ('portability', $where,
-	  "Omit leading `./' from config file names such as `$local',"
-	  . "\nas not all make implementations treat `file' and `./file' equally.")
-	if ($local =~ /^\.\//);
+      # Keep in sync with 'conffile-leading-dot.test'.
+      msg ('unsupported', $where,
+           "omit leading './' from config file names such as '$local';"
+           . "\nremake rules might be subtly broken otherwise")
+        if ($local =~ /^\.\//);
       my $input = locate_am @rest;
       if ($input)
 	{
diff --git a/tests/conffile-leading-dot.test b/tests/conffile-leading-dot.test
new file mode 100755
index 000000000..1d3d12fab
--- /dev/null
+++ b/tests/conffile-leading-dot.test
@@ -0,0 +1,62 @@
+#! /bin/sh
+# Copyright (C) 2012 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/>.
+
+# Automake must complain if AC_CONFIG_FILES is passed something starting
+# with a dot (like "./Makefile"), since the remake rules might be subtly
+# broken in that case.
+
+required=GNUmake
+. ./defs || Exit 1
+
+set -e
+
+cat > configure.in << END
+AC_INIT([$me], [1.0])
+AM_INIT_AUTOMAKE
+AC_CONFIG_FILES([./Makefile])
+AC_CONFIG_FILES([./foo:a.in:b.in:c.in])
+AC_OUTPUT
+END
+
+echo foo = barbarbar > Makefile.am
+
+touch a.in b.in c.in
+
+$ACLOCAL
+
+AUTOMAKE_fails -Wnone -Wunsupported
+grep "^configure\.in:3:.*'\\./Makefile'" stderr
+grep "^configure\.in:3:.* omit leading '\\./'" stderr
+grep "^configure\.in:3:.*remake rules might be subtly broken" stderr
+grep "^configure\.in:4:.*'\\./foo'" stderr
+grep "^configure\.in:4:.* omit leading '\\./'" stderr
+grep "^configure\.in:4:.*remake rules might be subtly broken" stderr
+
+# Check that our warning was actually justified.
+$AUTOCONF
+$AUTOMAKE -Wall -Wno-unsupported
+./configure
+$MAKE
+grep barbarbar Makefile
+# No need to sleep here, configure did that for us already.
+echo foo = bazbazbaz > Makefile.am
+# Check that remake rules do truly break -- otherwise automake is
+# giving a bogus warning.
+$MAKE 2>stderr && { cat stderr >&2 Exit 1; }
+cat stderr >&2
+grep "config\\.status:.*invalid argument.*[\`\"']Makefile[\`\"']" stderr
+
+:
diff --git a/tests/list-of-tests.mk b/tests/list-of-tests.mk
index 556989ea0..c35589f15 100644
--- a/tests/list-of-tests.mk
+++ b/tests/list-of-tests.mk
@@ -244,6 +244,7 @@ configure.test \
 confdeps.test \
 conff.test \
 conff2.test \
+conffile-leading-dot.test \
 confh.test \
 confh4.test \
 confh5.test \