submodule--helper: add a new 'config' subcommand

Add a new 'config' subcommand to 'submodule--helper', this extra level
of indirection makes it possible to add some flexibility to how the
submodules configuration is handled.

Signed-off-by: Antonio Ospite <ao2@ao2.it>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -2003,6 +2003,19 @@ static int check_name(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
+static int module_config(int argc, const char **argv, const char *prefix)
+{
+	/* Equivalent to ACTION_GET in builtin/config.c */
+	if (argc == 2)
+		return print_config_from_gitmodules(the_repository, argv[1]);
+
+	/* Equivalent to ACTION_SET in builtin/config.c */
+	if (argc == 3)
+		return config_set_in_gitmodules_file_gently(argv[1], argv[2]);
+
+	die("submodule--helper config takes 1 or 2 arguments: name [value]");
+}
+
 #define SUPPORT_SUPER_PREFIX (1<<0)
 
 struct cmd_struct {
@@ -2030,6 +2043,7 @@ static struct cmd_struct commands[] = {
 	{"absorb-git-dirs", absorb_git_dirs, SUPPORT_SUPER_PREFIX},
 	{"is-active", is_active, 0},
 	{"check-name", check_name, 0},
+	{"config", module_config, 0},
 };
 
 int cmd_submodule__helper(int argc, const char **argv, const char *prefix)

t/t7411-submodule-config.sh

@@ -134,4 +134,31 @@ test_expect_success 'error in history in fetchrecursesubmodule lets continue' '
 	)
 '
 
+test_expect_success 'reading submodules config with "submodule--helper config"' '
+	(cd super &&
+		echo "../submodule" >expect &&
+		git submodule--helper config submodule.submodule.url >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'writing submodules config with "submodule--helper config"' '
+	(cd super &&
+		echo "new_url" >expect &&
+		git submodule--helper config submodule.submodule.url "new_url" &&
+		git submodule--helper config submodule.submodule.url >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'overwriting unstaged submodules config with "submodule--helper config"' '
+	test_when_finished "git -C super checkout .gitmodules" &&
+	(cd super &&
+		echo "newer_url" >expect &&
+		git submodule--helper config submodule.submodule.url "newer_url" &&
+		git submodule--helper config submodule.submodule.url >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_done