git-submodule summary: --for-status option

The --for-status option is mainly used by builtin-status/commit.
It adds 'Modified submodules:' line at top and  '# ' prefix to all
following lines.
Signed-off-by: NPing Yin <pkufranky@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -342,6 +342,7 @@ set_name_rev () {
 #
 cmd_summary() {
 	summary_limit=-1
+	for_status=
 
 	# parse $args after "submodule ... summary".
 	while test $# -ne 0
@@ -350,6 +351,9 @@ cmd_summary() {
 		--cached)
 			cached="$1"
 			;;
+		--for-status)
+			for_status="$1"
+			;;
 		-n|--summary-limit)
 			if summary_limit=$(($2 + 0)) 2>/dev/null && test "$summary_limit" = "$2"
 			then
@@ -397,7 +401,8 @@ cmd_summary() {
 		done
 	)
 
-	test -n "$modules" &&
+	test -z "$modules" && return
+
 	git diff-index $cached --raw $head -- $modules |
 	grep -e '^:160000' -e '^:[0-7]* 160000' |
 	cut -c2- |
@@ -499,7 +504,14 @@ cmd_summary() {
 			echo
 		fi
 		echo
-	done
+	done |
+	if test -n "$for_status"; then
+		echo "# Modified submodules:"
+		echo "#"
+		sed -e 's|^|# |' -e 's|^# $|#|'
+	else
+		cat
+	fi
 }
 #
 # List all submodules, prefixed with:

t/t7401-submodule-summary.sh

@@ -192,4 +192,17 @@ test_expect_success 'given commit' "
 EOF
 "
 
+test_expect_success '--for-status' "
+    git submodule summary --for-status HEAD^ >actual &&
+    test_cmp actual - <<EOF
+# Modified submodules:
+#
+# * sm1 $head6...0000000:
+#
+# * sm2 0000000...$head7 (2):
+#   > Add foo9
+#
+EOF
+"
+
 test_done