Fix exit status of "xzdiff foo.xz bar.xz".

xzdiff was clobbering the exit status from diff in a case
statement used to analyze the exit statuses from "xz" when
its operands were two compressed files. Save and restore
diff's exit status to fix this.

The bug is inherited from zdiff in GNU gzip and was fixed
there on 2009-10-09.

Thanks to Jonathan Nieder for the patch and
to Peter Pallinger for reporting the bug.

src/scripts/xzdiff.in

@@ -126,10 +126,12 @@ elif test $# -eq 2; then
                 ( ($xz2 -cdfq -- "$2" 4>&-; echo $? >&4) 3>&- 5<&- </dev/null |
                 eval "$cmp" /dev/fd/5 - >&3) 5<&0
             )
+            cmp_status=$?
             case $xz_status in
               *[1-9]*) xz_status=1;;
               *) xz_status=0;;
             esac
+            (exit $cmp_status)
           else
             F=`expr "/$2" : '.*/\(.*\)[-.][ablmotxz2]*$'` || F=$prog
             tmp=

tests/Makefile.am

@@ -10,6 +10,7 @@ EXTRA_DIST = \
 	tests.h \
 	test_files.sh \
 	test_compress.sh \
+	test_scripts.sh \
 	bcj_test.c \
 	compress_prepared_bcj_sparc \
 	compress_prepared_bcj_x86
@@ -42,7 +43,8 @@ TESTS = \
 	test_block_header \
 	test_index \
 	test_files.sh \
-	test_compress.sh
+	test_compress.sh \
+	test_scripts.sh
 
 clean-local:
 	-rm -f compress_generated_*

tests/test_scripts.sh

@@ -0,0 +1,54 @@
+#!/bin/sh
+
+###############################################################################
+#
+# Author: Jonathan Nieder
+#
+# This file has been put into the public domain.
+# You can do whatever you want with this file.
+#
+###############################################################################
+
+# If scripts weren't built, this test is skipped.
+XZ=../src/xz/xz
+XZDIFF=../src/scripts/xzdiff
+test -x "$XZ" || XZ=
+test -r "$XZDIFF" || XZDIFF=
+if test -z "$XZ" || test -z "$XZDIFF"; then
+	(exit 77)
+	exit 77
+fi
+
+PATH=`pwd`/../src/xz:$PATH
+export PATH
+
+preimage=$srcdir/files/good-1-check-crc32.xz
+samepostimage=$srcdir/files/good-1-check-crc64.xz
+otherpostimage=$srcdir/files/good-1-lzma2-1.xz
+
+sh "$XZDIFF" "$preimage" "$samepostimage" >/dev/null
+status=$?
+if test "$status" != 0 ; then
+	echo "xzdiff with no changes exited with status $status != 0"
+	(exit 1)
+	exit 1
+fi
+
+sh "$XZDIFF" "$preimage" "$otherpostimage" >/dev/null
+status=$?
+if test "$status" != 1 ; then
+	echo "xzdiff with changes exited with status $status != 1"
+	(exit 1)
+	exit 1
+fi
+
+sh "$XZDIFF" "$preimage" "$srcdir/files/missing.xz" >/dev/null 2>&1
+status=$?
+if test "$status" != 2 ; then
+	echo "xzdiff with missing operand exited with status $status != 2"
+	(exit 1)
+	exit 1
+fi
+
+(exit 0)
+exit 0