Improve robustness of mdate-sh script.

[Ralf Wildenhues]

I managed to get SHELL=.../zsh in some weird configuration of some
unrelated package (m4 on AIX in this case, but I've seen this issue
elsewhere and in other packages before), and it caused mdate-sh to loop
endlessly, trying to shift nonexistent positional parameters in the hope
of finding a date to parse.

This patch fixes both the underlying issue (zsh emulation mode) as
well as making the script a bit more robust and reliable wrt. errors.

Pushing to maint.

Thanks,
Ralf

    Improve robustness of mdate-sh script.
    
    * lib/mdate-sh: Sanitize zsh behavior on startup, to ensure
    $ls_command is word-split properly upon invocation.
    (error): New function.
    (main): Use it.  Improve error checking to avoid endless loop
    in case $ls_command gave bogus output.  Fix eval quotation.
    * tests/mdate6.test: New test, to expose eval quotation error.
    * tests/Makefile.am: Update.

diff --git a/lib/mdate-sh b/lib/mdate-sh
index c477512..60dc485 100755
--- a/lib/mdate-sh
+++ b/lib/mdate-sh
@@ -1,7 +1,7 @@
 #!/bin/sh
 # Get modification time of a file or directory and pretty-print it.
 
-scriptversion=2010-02-22.21; # UTC
+scriptversion=2010-08-21.06; # UTC
 
 # Copyright (C) 1995, 1996, 1997, 2003, 2004, 2005, 2007, 2009, 2010
 # Free Software Foundation, Inc.
@@ -29,6 +29,15 @@ scriptversion=2010-02-22.21; # UTC
 # bugs to <address@hidden> or send patches to
 # <address@hidden>.
 
+if test -n "${ZSH_VERSION+set}" && (emulate sh) >/dev/null 2>&1; then
+  emulate sh
+  NULLCMD=:
+  # Pre-4.2 versions of Zsh do word splitting on ${1+"$@"}, which
+  # is contrary to our usage.  Disable this feature.
+  alias -g '${1+"$@"}'='"$@"'
+  setopt NO_GLOB_SUBST
+fi
+
 case $1 in
   '')
      echo "$0: No file.  Try \`$0 --help' for more information." 1>&2
@@ -51,6 +60,13 @@ EOF
     ;;
 esac
 
+error ()
+{
+  echo "$0: $1" >&2
+  exit 1
+}
+
+
 # Prevent date giving response in another language.
 LANG=C
 export LANG
@@ -100,6 +116,7 @@ month=
 command=
 until test $month
 do
+  test $# -gt 0 || error "failed parsing \`$ls_command /' output"
   shift
   # Add another shift to the command.
   command="$command shift;"
@@ -119,8 +136,10 @@ do
   esac
 done
 
+test -n "$month" || error "failed parsing \`$ls_command /' output"
+
 # Get the extended ls output of the file or directory.
-set dummy x`eval "$ls_command \"\$save_arg1\""`
+set dummy x`eval "$ls_command \"\\\$save_arg1\""`
 
 # Remove all preceding arguments
 eval $command
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 0558149..3ecc341 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -474,6 +474,7 @@ mdate2.test \
 mdate3.test \
 mdate4.test \
 mdate5.test \
+mdate6.test \
 missing.test \
 missing2.test \
 missing3.test \
diff --git a/tests/Makefile.in b/tests/Makefile.in
index a06026e..4671ad0 100644
--- a/tests/Makefile.in
+++ b/tests/Makefile.in
@@ -712,6 +712,7 @@ mdate2.test \
 mdate3.test \
 mdate4.test \
 mdate5.test \
+mdate6.test \
 missing.test \
 missing2.test \
 missing3.test \
diff --git a/tests/mdate6.test b/tests/mdate6.test
new file mode 100755
index 0000000..e7f7d69
--- /dev/null
+++ b/tests/mdate6.test
@@ -0,0 +1,35 @@
+#! /bin/sh
+# Copyright (C) 2010 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/>.
+
+# mdate-sh can work with weird file names, doesn't eval too much.
+
+. ./defs || Exit 1
+
+set -e
+
+a=
+file='file  name $a'
+( : > "$file" ) || Exit 77
+
+cp "$testsrcdir"/../lib/mdate-sh .
+$SHELL ./mdate-sh "$file" >stdout 2>stderr ||
+  { cat stdout; cat stderr >&2; Exit 1; }
+cat stdout
+cat stderr >&2
+grep '[12][0-9]\{3\}' stdout
+test ! -s stderr
+
+: