submodule--helper: offer a consistent API

In 48308681 (2016-02-29, git submodule update: have a dedicated helper
for cloning), the helper communicated errors back only via exit code,
and dance with printing '#unmatched' in case of error was left to
git-submodule.sh as it uses the output of the helper and pipes it into
shell commands. This change makes the helper consistent by never
printing '#unmatched' in the helper but always handling these piping
issues in the actual shell script.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -287,10 +287,8 @@ static int module_list(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, module_list_options,
 			     git_submodule_helper_usage, 0);
 
-	if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0) {
-		printf("#unmatched\n");
+	if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
 		return 1;
-	}
 
 	for (i = 0; i < list.nr; i++) {
 		const struct cache_entry *ce = list.entries[i];

git-submodule.sh

@@ -345,7 +345,10 @@ cmd_foreach()
 	# command in the subshell (and a recursive call to this function)
 	exec 3<&0
 
-	git submodule--helper list --prefix "$wt_prefix"|
+	{
+		git submodule--helper list --prefix "$wt_prefix" ||
+		echo "#unmatched"
+	} |
 	while read mode sha1 stage sm_path
 	do
 		die_if_unmatched "$mode"
@@ -453,7 +456,10 @@ cmd_deinit()
 		die "$(eval_gettext "Use '--all' if you really want to deinitialize all submodules")"
 	fi
 
-	git submodule--helper list --prefix "$wt_prefix" "$@" |
+	{
+		git submodule--helper list --prefix "$wt_prefix" "$@" ||
+		echo "#unmatched"
+	} |
 	while read mode sha1 stage sm_path
 	do
 		die_if_unmatched "$mode"
@@ -1013,7 +1019,10 @@ cmd_status()
 		shift
 	done
 
-	git submodule--helper list --prefix "$wt_prefix" "$@" |
+	{
+		git submodule--helper list --prefix "$wt_prefix" "$@" ||
+		echo "#unmatched"
+	} |
 	while read mode sha1 stage sm_path
 	do
 		die_if_unmatched "$mode"
@@ -1091,7 +1100,10 @@ cmd_sync()
 		esac
 	done
 	cd_to_toplevel
-	git submodule--helper list --prefix "$wt_prefix" "$@" |
+	{
+		git submodule--helper list --prefix "$wt_prefix" "$@" ||
+		echo "#unmatched"
+	} |
 	while read mode sha1 stage sm_path
 	do
 		die_if_unmatched "$mode"