[GSoC] [PATCH 0/3] submodule add: partial conversion to C

@@ -196,6 +196,17 @@ test_expect_success 'submodule add to .gitignored path with --force' '
 	)
 '
 
+test_expect_success 'submodule add to path with tracked content fails' '
+	(
+		cd addtest &&
+		echo "'\''dir-tracked'\'' already exists in the index" >expect &&
+		mkdir dir-tracked &&
+		test_commit foo dir-tracked/bar &&
+		test_must_fail git submodule add "$submodurl" dir-tracked >actual 2>&1 &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'submodule add to reconfigure existing submodule with --force' '
 	(
 		cd addtest-ignore &&

@@ -1658,45 +1658,20 @@ static int module_deinit(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
-static int clone_submodule(const char *path, const char *gitdir, const char *url,
-			   const char *depth, struct string_list *reference, int dissociate,
-			   int quiet, int progress, int single_branch)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-
-	strvec_push(&cp.args, "clone");
-	strvec_push(&cp.args, "--no-checkout");
-	if (quiet)
-		strvec_push(&cp.args, "--quiet");
-	if (progress)
-		strvec_push(&cp.args, "--progress");
-	if (depth && *depth)
-		strvec_pushl(&cp.args, "--depth", depth, NULL);
-	if (reference->nr) {
-		struct string_list_item *item;
-		for_each_string_list_item(item, reference)
-			strvec_pushl(&cp.args, "--reference",
-				     item->string, NULL);
-	}
-	if (dissociate)
-		strvec_push(&cp.args, "--dissociate");
-	if (gitdir && *gitdir)
-		strvec_pushl(&cp.args, "--separate-git-dir", gitdir, NULL);
-	if (single_branch >= 0)
-		strvec_push(&cp.args, single_branch ?
-					  "--single-branch" :
-					  "--no-single-branch");
-
-	strvec_push(&cp.args, "--");
-	strvec_push(&cp.args, url);
-	strvec_push(&cp.args, path);
-
-	cp.git_cmd = 1;
-	prepare_submodule_repo_env(&cp.env_array);
-	cp.no_stdin = 1;
-
-	return run_command(&cp);
-}
+struct module_clone_data {
+	const char *prefix;
+	const char *path;
+	const char *name;
+	const char *url;
+	const char *depth;
+	struct string_list reference;
+	unsigned int quiet: 1;
+	unsigned int progress: 1;
+	unsigned int dissociate: 1;
+	unsigned int require_init: 1;
+	int single_branch;
+};
+#define MODULE_CLONE_DATA_INIT { .reference = STRING_LIST_INIT_NODUP, .single_branch = -1 }
 
 struct submodule_alternate_setup {
 	const char *submodule_name;

@@ -1802,37 +1777,128 @@ static void prepare_possible_alternates(const char *sm_name,
 	free(error_strategy);
 }
 
+static int clone_submodule(struct module_clone_data *clone_data)
+{
+	char *p, *sm_gitdir;
+	char *sm_alternate = NULL, *error_strategy = NULL;
+	struct strbuf sb = STRBUF_INIT;
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), clone_data->name);
+	sm_gitdir = absolute_pathdup(sb.buf);
+	strbuf_reset(&sb);
+
+	if (!is_absolute_path(clone_data->path)) {
+		strbuf_addf(&sb, "%s/%s", get_git_work_tree(), clone_data->path);
+		clone_data->path = strbuf_detach(&sb, NULL);
+	} else {
+		clone_data->path = xstrdup(clone_data->path);
+	}
+
+	if (validate_submodule_git_dir(sm_gitdir, clone_data->name) < 0)
+		die(_("refusing to create/use '%s' in another submodule's "
+		      "git dir"), sm_gitdir);
+
+	if (!file_exists(sm_gitdir)) {
+		if (safe_create_leading_directories_const(sm_gitdir) < 0)
+			die(_("could not create directory '%s'"), sm_gitdir);
+
+		prepare_possible_alternates(clone_data->name, &clone_data->reference);
+
+		strvec_push(&cp.args, "clone");
+		strvec_push(&cp.args, "--no-checkout");
+		if (clone_data->quiet)
+			strvec_push(&cp.args, "--quiet");
+		if (clone_data->progress)
+			strvec_push(&cp.args, "--progress");
+		if (clone_data->depth && *(clone_data->depth))
+			strvec_pushl(&cp.args, "--depth", clone_data->depth, NULL);
+		if (clone_data->reference.nr) {
+			struct string_list_item *item;
+			for_each_string_list_item(item, &clone_data->reference)
+				strvec_pushl(&cp.args, "--reference",
+					     item->string, NULL);
+		}
+		if (clone_data->dissociate)
+			strvec_push(&cp.args, "--dissociate");
+		if (sm_gitdir && *sm_gitdir)
+			strvec_pushl(&cp.args, "--separate-git-dir", sm_gitdir, NULL);
+		if (clone_data->single_branch >= 0)
+			strvec_push(&cp.args, clone_data->single_branch ?
+				    "--single-branch" :
+				    "--no-single-branch");
+
+		strvec_push(&cp.args, "--");
+		strvec_push(&cp.args, clone_data->url);
+		strvec_push(&cp.args, clone_data->path);
+
+		cp.git_cmd = 1;
+		prepare_submodule_repo_env(&cp.env_array);
+		cp.no_stdin = 1;
+
+		if(run_command(&cp))
+			die(_("clone of '%s' into submodule path '%s' failed"),
+			    clone_data->url, clone_data->path);
+	} else {
+		if (clone_data->require_init && !access(clone_data->path, X_OK) &&
+		    !is_empty_dir(clone_data->path))
+			die(_("directory not empty: '%s'"), clone_data->path);
+		if (safe_create_leading_directories_const(clone_data->path) < 0)
+			die(_("could not create directory '%s'"), clone_data->path);
+		strbuf_addf(&sb, "%s/index", sm_gitdir);
+		unlink_or_warn(sb.buf);
+		strbuf_reset(&sb);
+	}
+
+	connect_work_tree_and_git_dir(clone_data->path, sm_gitdir, 0);
+
+	p = git_pathdup_submodule(clone_data->path, "config");
+	if (!p)
+		die(_("could not get submodule directory for '%s'"), clone_data->path);
+
+	/* setup alternateLocation and alternateErrorStrategy in the cloned submodule if needed */
+	git_config_get_string("submodule.alternateLocation", &sm_alternate);
+	if (sm_alternate)
+		git_config_set_in_file(p, "submodule.alternateLocation",
+				       sm_alternate);
+	git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);
+	if (error_strategy)
+		git_config_set_in_file(p, "submodule.alternateErrorStrategy",
+				       error_strategy);
+
+	free(sm_alternate);
+	free(error_strategy);
+
+	strbuf_release(&sb);
+	free(sm_gitdir);
+	free(p);
+	return 0;
+}
+
 static int module_clone(int argc, const char **argv, const char *prefix)
 {
-	const char *name = NULL, *url = NULL, *depth = NULL;
-	int quiet = 0;
-	int progress = 0;
-	char *p, *path = NULL, *sm_gitdir;
-	struct strbuf sb = STRBUF_INIT;
-	struct string_list reference = STRING_LIST_INIT_NODUP;
-	int dissociate = 0, require_init = 0;
-	char *sm_alternate = NULL, *error_strategy = NULL;
-	int single_branch = -1;
+	int dissociate = 0, quiet = 0, progress = 0, require_init = 0;
+	struct module_clone_data clone_data = MODULE_CLONE_DATA_INIT;
 
 	struct option module_clone_options[] = {
-		OPT_STRING(0, "prefix", &prefix,
+		OPT_STRING(0, "prefix", &clone_data.prefix,
 			   N_("path"),
 			   N_("alternative anchor for relative paths")),
-		OPT_STRING(0, "path", &path,
+		OPT_STRING(0, "path", &clone_data.path,
 			   N_("path"),
 			   N_("where the new submodule will be cloned to")),
-		OPT_STRING(0, "name", &name,
+		OPT_STRING(0, "name", &clone_data.name,
 			   N_("string"),
 			   N_("name of the new submodule")),
-		OPT_STRING(0, "url", &url,
+		OPT_STRING(0, "url", &clone_data.url,
 			   N_("string"),
 			   N_("url where to clone the submodule from")),
-		OPT_STRING_LIST(0, "reference", &reference,
+		OPT_STRING_LIST(0, "reference", &clone_data.reference,
 			   N_("repo"),
 			   N_("reference repository")),
 		OPT_BOOL(0, "dissociate", &dissociate,
 			   N_("use --reference only while cloning")),
-		OPT_STRING(0, "depth", &depth,
+		OPT_STRING(0, "depth", &clone_data.depth,
 			   N_("string"),
 			   N_("depth for shallow clones")),
 		OPT__QUIET(&quiet, "Suppress output for cloning a submodule"),

@@ -1840,7 +1906,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 			   N_("force cloning progress")),
 		OPT_BOOL(0, "require-init", &require_init,
 			   N_("disallow cloning into non-empty directory")),
-		OPT_BOOL(0, "single-branch", &single_branch,
+		OPT_BOOL(0, "single-branch", &clone_data.single_branch,
 			 N_("clone only one branch, HEAD or --branch")),
 		OPT_END()
 	};

@@ -1856,67 +1922,16 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, module_clone_options,
 			     git_submodule_helper_usage, 0);
 
-	if (argc || !url || !path || !*path)
+	clone_data.dissociate = !!dissociate;
+	clone_data.quiet = !!quiet;
+	clone_data.progress = !!progress;
+	clone_data.require_init = !!require_init;
+
+	if (argc || !clone_data.url || !clone_data.path || !*(clone_data.path))
 		usage_with_options(git_submodule_helper_usage,
 				   module_clone_options);
 
-	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
-	sm_gitdir = absolute_pathdup(sb.buf);
-	strbuf_reset(&sb);
-
-	if (!is_absolute_path(path)) {
-		strbuf_addf(&sb, "%s/%s", get_git_work_tree(), path);
-		path = strbuf_detach(&sb, NULL);
-	} else
-		path = xstrdup(path);
-
-	if (validate_submodule_git_dir(sm_gitdir, name) < 0)
-		die(_("refusing to create/use '%s' in another submodule's "
-			"git dir"), sm_gitdir);
-
-	if (!file_exists(sm_gitdir)) {
-		if (safe_create_leading_directories_const(sm_gitdir) < 0)
-			die(_("could not create directory '%s'"), sm_gitdir);
-
-		prepare_possible_alternates(name, &reference);
-
-		if (clone_submodule(path, sm_gitdir, url, depth, &reference, dissociate,
-				    quiet, progress, single_branch))
-			die(_("clone of '%s' into submodule path '%s' failed"),
-			    url, path);
-	} else {
-		if (require_init && !access(path, X_OK) && !is_empty_dir(path))
-			die(_("directory not empty: '%s'"), path);
-		if (safe_create_leading_directories_const(path) < 0)
-			die(_("could not create directory '%s'"), path);
-		strbuf_addf(&sb, "%s/index", sm_gitdir);
-		unlink_or_warn(sb.buf);
-		strbuf_reset(&sb);
-	}
-
-	connect_work_tree_and_git_dir(path, sm_gitdir, 0);
-
-	p = git_pathdup_submodule(path, "config");
-	if (!p)
-		die(_("could not get submodule directory for '%s'"), path);
-
-	/* setup alternateLocation and alternateErrorStrategy in the cloned submodule if needed */
-	git_config_get_string("submodule.alternateLocation", &sm_alternate);
-	if (sm_alternate)
-		git_config_set_in_file(p, "submodule.alternateLocation",
-					   sm_alternate);
-	git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);
-	if (error_strategy)
-		git_config_set_in_file(p, "submodule.alternateErrorStrategy",
-					   error_strategy);
-
-	free(sm_alternate);
-	free(error_strategy);
-
-	strbuf_release(&sb);
-	free(sm_gitdir);
-	free(path);
-	free(p);
+	clone_submodule(&clone_data);
 	return 0;
 }
 

@@ -30,6 +30,14 @@
 typedef void (*each_submodule_fn)(const struct cache_entry *list_item,
 				  void *cb_data);
 
+static NORETURN void submodule_die(const char *err, va_list params)
+{
+	vfprintf(stderr, err, params);
+	fputc('\n', stderr);
+	fflush(stderr);
+	exit(1);
+}
+
 static char *get_default_remote(void)
 {
 	char *dest = NULL, *ret;

@@ -2760,6 +2768,184 @@ static int module_set_branch(int argc, const char **argv, const char *prefix)
 	return !!ret;
 }
 
+struct add_data {
+	const char *prefix;
+	const char *branch;
+	const char *reference_path;
+	const char *sm_path;
+	const char *sm_name;
+	const char *repo;
+	const char *realrepo;
+	int depth;
+	unsigned int force: 1;
+	unsigned int quiet: 1;
+	unsigned int progress: 1;
+	unsigned int dissociate: 1;
+};
+#define ADD_DATA_INIT { .depth = -1 }
+
+static void show_fetch_remotes(FILE *output, const char *sm_name, const char *git_dir_path)
+{
+	struct child_process cp_remote = CHILD_PROCESS_INIT;
+	struct strbuf sb_remote_out = STRBUF_INIT;
+
+	cp_remote.git_cmd = 1;
+	strvec_pushf(&cp_remote.env_array,
+		     "GIT_DIR=%s", git_dir_path);
+	strvec_push(&cp_remote.env_array, "GIT_WORK_TREE=.");
+	strvec_pushl(&cp_remote.args, "remote", "-v", NULL);
+	if (!capture_command(&cp_remote, &sb_remote_out, 0)) {
+		char *next_line;
+		char *line = sb_remote_out.buf;
+		while ((next_line = strchr(line, '\n')) != NULL) {
+			size_t len = next_line - line;
+			if (strip_suffix_mem(line, &len, " (fetch)"))
+				fprintf(output, "  %.*s\n", (int)len, line);
+			line = next_line + 1;
+		}
+	}
+
+	strbuf_release(&sb_remote_out);
+}
+
+static int add_submodule(const struct add_data *add_data)
+{
+	char *submod_gitdir_path;
+	struct module_clone_data clone_data = MODULE_CLONE_DATA_INIT;
+
+	/* perhaps the path already exists and is already a git repo, else clone it */
+	if (is_directory(add_data->sm_path)) {
+		struct strbuf sm_path = STRBUF_INIT;
+		strbuf_addstr(&sm_path, add_data->sm_path);
+		submod_gitdir_path = xstrfmt("%s/.git", add_data->sm_path);
+		if (is_nonbare_repository_dir(&sm_path))
+			printf(_("Adding existing repo at '%s' to the index\n"),
+			       add_data->sm_path);
+		else
+			die(_("'%s' already exists and is not a valid git repo"),
+			    add_data->sm_path);
+		strbuf_release(&sm_path);
+		free(submod_gitdir_path);
+	} else {
+		struct child_process cp = CHILD_PROCESS_INIT;
+		submod_gitdir_path = xstrfmt(".git/modules/%s", add_data->sm_name);
+
+		if (is_directory(submod_gitdir_path)) {
+			if (!add_data->force) {
+				fprintf(stderr, _("A git directory for '%s' is found "
+						  "locally with remote(s):"),
+					add_data->sm_name);
+				show_fetch_remotes(stderr, add_data->sm_name,
+						   submod_gitdir_path);
+				free(submod_gitdir_path);
+				die(_("If you want to reuse this local git "
+				      "directory instead of cloning again from\n"
+				      "  %s\n"
+				      "use the '--force' option. If the local git "
+				      "directory is not the correct repo\n"
+				      "or if you are unsure what this means, choose "
+				      "another name with the '--name' option.\n"),
+				    add_data->realrepo);
+			} else {
+				printf(_("Reactivating local git directory for "
+					 "submodule '%s'\n"), add_data->sm_name);
+			}
+		}
+		free(submod_gitdir_path);
+
+		clone_data.prefix = add_data->prefix;
+		clone_data.path = add_data->sm_path;
+		clone_data.name = add_data->sm_name;
+		clone_data.url = add_data->realrepo;
+		clone_data.quiet = add_data->quiet;
+		clone_data.progress = add_data->progress;
+		if (add_data->reference_path)
+			string_list_append(&clone_data.reference,
+					   xstrdup(add_data->reference_path));
+		clone_data.dissociate = add_data->dissociate;
+		if (add_data->depth >= 0)
+			clone_data.depth = xstrfmt("%d", add_data->depth);
+
+		if (clone_submodule(&clone_data))
+			return -1;
+
+		prepare_submodule_repo_env(&cp.env_array);
+		cp.git_cmd = 1;
+		cp.dir = add_data->sm_path;
+		strvec_pushl(&cp.args, "checkout", "-f", "-q", NULL);
+
+		if (add_data->branch) {
+			strvec_pushl(&cp.args, "-B", add_data->branch, NULL);
+			strvec_pushf(&cp.args, "origin/%s", add_data->branch);
+		}
+
+		if (run_command(&cp))
+			die(_("unable to checkout submodule '%s'"), add_data->sm_path);
+	}
+	return 0;
+}
+
+static int add_clone(int argc, const char **argv, const char *prefix)
+{
+	int force = 0, quiet = 0, dissociate = 0, progress = 0;
+	struct add_data add_data = ADD_DATA_INIT;
+
+	struct option options[] = {
+		OPT_STRING('b', "branch", &add_data.branch,
+			   N_("branch"),
+			   N_("branch of repository to checkout on cloning")),
+		OPT_STRING(0, "prefix", &prefix,
+			   N_("path"),
+			   N_("alternative anchor for relative paths")),
+		OPT_STRING(0, "path", &add_data.sm_path,
+			   N_("path"),
+			   N_("where the new submodule will be cloned to")),
+		OPT_STRING(0, "name", &add_data.sm_name,
+			   N_("string"),
+			   N_("name of the new submodule")),
+		OPT_STRING(0, "url", &add_data.realrepo,
+			   N_("string"),
+			   N_("url where to clone the submodule from")),
+		OPT_STRING(0, "reference", &add_data.reference_path,
+			   N_("repo"),
+			   N_("reference repository")),
+		OPT_BOOL(0, "dissociate", &dissociate,
+			 N_("use --reference only while cloning")),
+		OPT_INTEGER(0, "depth", &add_data.depth,
+			    N_("depth for shallow clones")),
+		OPT_BOOL(0, "progress", &progress,
+			 N_("force cloning progress")),
+		OPT__FORCE(&force, N_("allow adding an otherwise ignored submodule path"),
+			   PARSE_OPT_NOCOMPLETE),
+		OPT__QUIET(&quiet, "suppress output for cloning a submodule"),
+		OPT_END()
+	};
+
+	const char *const usage[] = {
+		N_("git submodule--helper add-clone [<options>...] "
+		   "--url <url> --path <path> --name <name>"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+
+	if (argc != 0)
+		usage_with_options(usage, options);
+
+	add_data.prefix = prefix;
+	add_data.progress = !!progress;
+	add_data.dissociate = !!dissociate;
+	add_data.force = !!force;
+	add_data.quiet = !!quiet;
+
+	set_die_routine(submodule_die);
+
+	if (add_submodule(&add_data))
+		return 1;
+
+	return 0;
+}
+
 #define SUPPORT_SUPER_PREFIX (1<<0)
 
 struct cmd_struct {

@@ -2772,6 +2958,7 @@ static struct cmd_struct commands[] = {
 	{"list", module_list, 0},
 	{"name", module_name, 0},
 	{"clone", module_clone, 0},
+	{"add-clone", add_clone, 0},
 	{"update-module-mode", module_update_module_mode, 0},
 	{"update-clone", update_clone, 0},
 	{"ensure-core-worktree", ensure_core_worktree, 0},

@@ -241,43 +241,7 @@ cmd_add()
 		die "$(eval_gettext "'$sm_name' is not a valid submodule name")"
 	fi
 
-	# perhaps the path exists and is already a git repo, else clone it
-	if test -e "$sm_path"
-	then
-		if test -d "$sm_path"/.git || test -f "$sm_path"/.git
-		then
-			eval_gettextln "Adding existing repo at '\$sm_path' to the index"
-		else
-			die "$(eval_gettext "'\$sm_path' already exists and is not a valid git repo")"
-		fi
-
-	else
-		if test -d ".git/modules/$sm_name"
-		then
-			if test -z "$force"
-			then
-				eval_gettextln >&2 "A git directory for '\$sm_name' is found locally with remote(s):"
-				GIT_DIR=".git/modules/$sm_name" GIT_WORK_TREE=. git remote -v | grep '(fetch)' | sed -e s,^,"  ", -e s,' (fetch)',, >&2
-				die "$(eval_gettextln "\
-If you want to reuse this local git directory instead of cloning again from
-  \$realrepo
-use the '--force' option. If the local git directory is not the correct repo
-or you are unsure what this means choose another name with the '--name' option.")"
-			else
-				eval_gettextln "Reactivating local git directory for submodule '\$sm_name'."
-			fi
-		fi
-		git submodule--helper clone ${GIT_QUIET:+--quiet} ${progress:+"--progress"} --prefix "$wt_prefix" --path "$sm_path" --name "$sm_name" --url "$realrepo" ${reference:+"$reference"} ${dissociate:+"--dissociate"} ${depth:+"$depth"} || exit
-		(
-			sanitize_submodule_env
-			cd "$sm_path" &&
-			# ash fails to wordsplit ${branch:+-b "$branch"...}
-			case "$branch" in
-			'') git checkout -f -q ;;
-			?*) git checkout -f -q -B "$branch" "origin/$branch" ;;
-			esac
-		) || die "$(eval_gettext "Unable to checkout submodule '\$sm_path'")"
-	fi
+	git submodule--helper add-clone ${GIT_QUIET:+--quiet} ${force:+"--force"} ${progress:+"--progress"} ${branch:+--branch "$branch"} --prefix "$wt_prefix" --path "$sm_path" --name "$sm_name" --url "$realrepo" ${reference:+"$reference"} ${dissociate:+"--dissociate"} ${depth:+"$depth"} || exit
 	git config submodule."$sm_name".url "$realrepo"
 
 	git add --no-warn-embedded-repo $force "$sm_path" ||

@@ -196,6 +196,17 @@ test_expect_success 'submodule add to .gitignored path with --force' '
 	)
 '
 
+test_expect_success 'submodule add to path with tracked content fails' '
+	(
+		cd addtest &&
+		echo "'\''dir-tracked'\'' already exists in the index" >expect &&
+		mkdir dir-tracked &&
+		test_commit foo dir-tracked/bar &&
+		test_must_fail git submodule add "$submodurl" dir-tracked >actual 2>&1 &&
+		test_cmp expect actual
+	)
+'
+
 test_expect_success 'submodule add to reconfigure existing submodule with --force' '
 	(
 		cd addtest-ignore &&

@@ -147,7 +147,7 @@ cmd_add()
 
 	if ! git submodule--helper config --check-writeable >/dev/null 2>&1
 	then
-		 die "$(eval_gettext "please make sure that the .gitmodules file is in the working tree")"
+		 die "$(eval_gettext "fatal: please make sure that the .gitmodules file is in the working tree")"
 	fi
 
 	if test -n "$reference_path"

@@ -176,7 +176,7 @@ cmd_add()
 	case "$repo" in
 	./*|../*)
 		test -z "$wt_prefix" ||
-		die "$(gettext "Relative path can only be used from the toplevel of the working tree")"
+		die "$(gettext "fatal: Relative path can only be used from the toplevel of the working tree")"
 
 		# dereference source url relative to parent's url
 		realrepo=$(git submodule--helper resolve-relative-url "$repo") || exit

@@ -186,7 +186,7 @@ cmd_add()
 		realrepo=$repo
 		;;
 	*)
-		die "$(eval_gettext "repo URL: '\$repo' must be absolute or begin with ./|../")"
+		die "$(eval_gettext "fatal: repo URL: '\$repo' must be absolute or begin with ./|../")"
 	;;
 	esac
 

@@ -205,17 +205,17 @@ cmd_add()
 	if test -z "$force"
 	then
 		git ls-files --error-unmatch "$sm_path" > /dev/null 2>&1 &&
-		die "$(eval_gettext "'\$sm_path' already exists in the index")"
+		die "$(eval_gettext "fatal: '\$sm_path' already exists in the index")"
 	else
 		git ls-files -s "$sm_path" | sane_grep -v "^160000" > /dev/null 2>&1 &&
-		die "$(eval_gettext "'\$sm_path' already exists in the index and is not a submodule")"
+		die "$(eval_gettext "fatal: '\$sm_path' already exists in the index and is not a submodule")"
 	fi
 
 	if test -d "$sm_path" &&
 		test -z $(git -C "$sm_path" rev-parse --show-cdup 2>/dev/null)
 	then
 	    git -C "$sm_path" rev-parse --verify -q HEAD >/dev/null ||
-	    die "$(eval_gettext "'\$sm_path' does not have a commit checked out")"
+	    die "$(eval_gettext "fatal: '\$sm_path' does not have a commit checked out")"
 	fi
 
 	if test -z "$force"

@@ -238,7 +238,7 @@ cmd_add()
 
 	if ! git submodule--helper check-name "$sm_name"
 	then
-		die "$(eval_gettext "'$sm_name' is not a valid submodule name")"
+		die "$(eval_gettext "fatal: '$sm_name' is not a valid submodule name")"
 	fi
 
 	# perhaps the path exists and is already a git repo, else clone it

@@ -281,7 +281,7 @@ or you are unsure what this means choose another name with the '--name' option."
 	git config submodule."$sm_name".url "$realrepo"
 
 	git add --no-warn-embedded-repo $force "$sm_path" ||
-	die "$(eval_gettext "Failed to add submodule '\$sm_path'")"
+	die "$(eval_gettext "fatal: Failed to add submodule '\$sm_path'")"
 
 	git submodule--helper config submodule."$sm_name".path "$sm_path" &&
 	git submodule--helper config submodule."$sm_name".url "$repo" &&

@@ -290,7 +290,7 @@ or you are unsure what this means choose another name with the '--name' option."
 		git submodule--helper config submodule."$sm_name".branch "$branch"
 	fi &&
 	git add --force .gitmodules ||
-	die "$(eval_gettext "Failed to register submodule '\$sm_path'")"
+	die "$(eval_gettext "fatal: Failed to register submodule '\$sm_path'")"
 
 	# NEEDSWORK: In a multi-working-tree world, this needs to be
 	# set in the per-worktree config.

@@ -565,7 +565,7 @@ cmd_update()
 		else
 			subsha1=$(sanitize_submodule_env; cd "$sm_path" &&
 				git rev-parse --verify HEAD) ||
-			die "$(eval_gettext "Unable to find current revision in submodule path '\$displaypath'")"
+			die "$(eval_gettext "fatal: Unable to find current revision in submodule path '\$displaypath'")"
 		fi
 
 		if test -n "$remote"

@@ -575,12 +575,12 @@ cmd_update()
 			then
 				# Fetch remote before determining tracking $sha1
 				fetch_in_submodule "$sm_path" $depth ||
-				die "$(eval_gettext "Unable to fetch in submodule path '\$sm_path'")"
+				die "$(eval_gettext "fatal: Unable to fetch in submodule path '\$sm_path'")"
 			fi
 			remote_name=$(sanitize_submodule_env; cd "$sm_path" && git submodule--helper print-default-remote)
 			sha1=$(sanitize_submodule_env; cd "$sm_path" &&
 				git rev-parse --verify "${remote_name}/${branch}") ||
-			die "$(eval_gettext "Unable to find current \${remote_name}/\${branch} revision in submodule path '\$sm_path'")"
+			die "$(eval_gettext "fatal: Unable to find current \${remote_name}/\${branch} revision in submodule path '\$sm_path'")"
 		fi
 
 		if test "$subsha1" != "$sha1" || test -n "$force"

@@ -604,36 +604,36 @@ cmd_update()
 				# not be reachable from any of the refs
 				is_tip_reachable "$sm_path" "$sha1" ||
 				fetch_in_submodule "$sm_path" "$depth" "$sha1" ||
-				die "$(eval_gettext "Fetched in submodule path '\$displaypath', but it did not contain \$sha1. Direct fetching of that commit failed.")"
+				die "$(eval_gettext "fatal: Fetched in submodule path '\$displaypath', but it did not contain \$sha1. Direct fetching of that commit failed.")"
 			fi
 
 			must_die_on_failure=
 			case "$update_module" in
 			checkout)
 				command="git checkout $subforce -q"
-				die_msg="$(eval_gettext "Unable to checkout '\$sha1' in submodule path '\$displaypath'")"
+				die_msg="$(eval_gettext "fatal: Unable to checkout '\$sha1' in submodule path '\$displaypath'")"
 				say_msg="$(eval_gettext "Submodule path '\$displaypath': checked out '\$sha1'")"
 				;;
 			rebase)
 				command="git rebase ${GIT_QUIET:+--quiet}"
-				die_msg="$(eval_gettext "Unable to rebase '\$sha1' in submodule path '\$displaypath'")"
+				die_msg="$(eval_gettext "fatal: Unable to rebase '\$sha1' in submodule path '\$displaypath'")"
 				say_msg="$(eval_gettext "Submodule path '\$displaypath': rebased into '\$sha1'")"
 				must_die_on_failure=yes
 				;;
 			merge)
 				command="git merge ${GIT_QUIET:+--quiet}"
-				die_msg="$(eval_gettext "Unable to merge '\$sha1' in submodule path '\$displaypath'")"
+				die_msg="$(eval_gettext "fatal: Unable to merge '\$sha1' in submodule path '\$displaypath'")"
 				say_msg="$(eval_gettext "Submodule path '\$displaypath': merged in '\$sha1'")"
 				must_die_on_failure=yes
 				;;
 			!*)
 				command="${update_module#!}"
-				die_msg="$(eval_gettext "Execution of '\$command \$sha1' failed in submodule path '\$displaypath'")"
+				die_msg="$(eval_gettext "fatal: Execution of '\$command \$sha1' failed in submodule path '\$displaypath'")"
 				say_msg="$(eval_gettext "Submodule path '\$displaypath': '\$command \$sha1'")"
 				must_die_on_failure=yes
 				;;
 			*)
-				die "$(eval_gettext "Invalid update mode '$update_module' for submodule path '$path'")"
+				die "$(eval_gettext "fatal: Invalid update mode '$update_module' for submodule path '$path'")"
 			esac
 
 			if (sanitize_submodule_env; cd "$sm_path" && $command "$sha1")

@@ -660,7 +660,7 @@ cmd_update()
 			res=$?
 			if test $res -gt 0
 			then
-				die_msg="$(eval_gettext "Failed to recurse into submodule path '\$displaypath'")"
+				die_msg="$(eval_gettext "fatal: Failed to recurse into submodule path '\$displaypath'")"
 				if test $res -ne 2
 				then
 					err="${err};$die_msg"

@@ -51,7 +51,7 @@ test_expect_success 'submodule update aborts on missing gitmodules url' '
 
 test_expect_success 'add aborts on repository with no commits' '
 	cat >expect <<-\EOF &&
-	'"'repo-no-commits'"' does not have a commit checked out
+	fatal: '"'repo-no-commits'"' does not have a commit checked out
 	EOF
 	git init repo-no-commits &&
 	test_must_fail git submodule add ../a ./repo-no-commits 2>actual &&

@@ -199,7 +199,7 @@ test_expect_success 'submodule add to .gitignored path with --force' '
 test_expect_success 'submodule add to path with tracked content fails' '
 	(
 		cd addtest &&
-		echo "'\''dir-tracked'\'' already exists in the index" >expect &&
+		echo "fatal: '\''dir-tracked'\'' already exists in the index" >expect &&
 		mkdir dir-tracked &&
 		test_commit foo dir-tracked/bar &&
 		test_must_fail git submodule add "$submodurl" dir-tracked >actual 2>&1 &&

@@ -448,7 +448,7 @@ test_expect_success 'fsck detects command in .gitmodules' '
 '
 
 cat << EOF >expect
-Execution of 'false $submodulesha1' failed in submodule path 'submodule'
+fatal: Execution of 'false $submodulesha1' failed in submodule path 'submodule'
 EOF
 
 test_expect_success 'submodule update - command in .git/config catches failure' '

@@ -465,7 +465,7 @@ test_expect_success 'submodule update - command in .git/config catches failure'
 '
 
 cat << EOF >expect
-Execution of 'false $submodulesha1' failed in submodule path '../submodule'
+fatal: Execution of 'false $submodulesha1' failed in submodule path '../submodule'
 EOF
 
 test_expect_success 'submodule update - command in .git/config catches failure -- subdirectory' '

@@ -484,7 +484,7 @@ test_expect_success 'submodule update - command in .git/config catches failure -
 
 test_expect_success 'submodule update - command run for initial population of submodule' '
 	cat >expect <<-EOF &&
-	Execution of '\''false $submodulesha1'\'' failed in submodule path '\''submodule'\''
+	fatal: Execution of '\''false $submodulesha1'\'' failed in submodule path '\''submodule'\''
 	EOF
 	rm -rf super/submodule &&
 	test_must_fail git -C super submodule update 2>actual &&

@@ -493,8 +493,8 @@ test_expect_success 'submodule update - command run for initial population of su
 '
 
 cat << EOF >expect
-Execution of 'false $submodulesha1' failed in submodule path '../super/submodule'
-Failed to recurse into submodule path '../super'
+fatal: Execution of 'false $submodulesha1' failed in submodule path '../super/submodule'
+fatal: Failed to recurse into submodule path '../super'
 EOF
 
 test_expect_success 'recursive submodule update - command in .git/config catches failure -- subdirectory' '

@@ -1658,45 +1658,20 @@ static int module_deinit(int argc, const char **argv, const char *prefix)
 	return 0;
 }
 
-static int clone_submodule(const char *path, const char *gitdir, const char *url,
-			   const char *depth, struct string_list *reference, int dissociate,
-			   int quiet, int progress, int single_branch)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-
-	strvec_push(&cp.args, "clone");
-	strvec_push(&cp.args, "--no-checkout");
-	if (quiet)
-		strvec_push(&cp.args, "--quiet");
-	if (progress)
-		strvec_push(&cp.args, "--progress");
-	if (depth && *depth)
-		strvec_pushl(&cp.args, "--depth", depth, NULL);
-	if (reference->nr) {
-		struct string_list_item *item;
-		for_each_string_list_item(item, reference)
-			strvec_pushl(&cp.args, "--reference",
-				     item->string, NULL);
-	}
-	if (dissociate)
-		strvec_push(&cp.args, "--dissociate");
-	if (gitdir && *gitdir)
-		strvec_pushl(&cp.args, "--separate-git-dir", gitdir, NULL);
-	if (single_branch >= 0)
-		strvec_push(&cp.args, single_branch ?
-					  "--single-branch" :
-					  "--no-single-branch");
-
-	strvec_push(&cp.args, "--");
-	strvec_push(&cp.args, url);
-	strvec_push(&cp.args, path);
-
-	cp.git_cmd = 1;
-	prepare_submodule_repo_env(&cp.env_array);
-	cp.no_stdin = 1;
-
-	return run_command(&cp);
-}
+struct module_clone_data {
+	const char *prefix;
+	const char *path;
+	const char *name;
+	const char *url;
+	const char *depth;
+	struct string_list reference;
+	unsigned int quiet: 1;
+	unsigned int progress: 1;
+	unsigned int dissociate: 1;
+	unsigned int require_init: 1;
+	int single_branch;
+};
+#define MODULE_CLONE_DATA_INIT { .reference = STRING_LIST_INIT_NODUP, .single_branch = -1 }
 
 struct submodule_alternate_setup {
 	const char *submodule_name;

@@ -1802,37 +1777,128 @@ static void prepare_possible_alternates(const char *sm_name,
 	free(error_strategy);
 }
 
+static int clone_submodule(struct module_clone_data *clone_data)
+{
+	char *p, *sm_gitdir;
+	char *sm_alternate = NULL, *error_strategy = NULL;
+	struct strbuf sb = STRBUF_INIT;
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), clone_data->name);
+	sm_gitdir = absolute_pathdup(sb.buf);
+	strbuf_reset(&sb);
+
+	if (!is_absolute_path(clone_data->path)) {
+		strbuf_addf(&sb, "%s/%s", get_git_work_tree(), clone_data->path);
+		clone_data->path = strbuf_detach(&sb, NULL);
+	} else {
+		clone_data->path = xstrdup(clone_data->path);
+	}
+
+	if (validate_submodule_git_dir(sm_gitdir, clone_data->name) < 0)
+		die(_("refusing to create/use '%s' in another submodule's "
+		      "git dir"), sm_gitdir);
+
+	if (!file_exists(sm_gitdir)) {
+		if (safe_create_leading_directories_const(sm_gitdir) < 0)
+			die(_("could not create directory '%s'"), sm_gitdir);
+
+		prepare_possible_alternates(clone_data->name, &clone_data->reference);
+
+		strvec_push(&cp.args, "clone");
+		strvec_push(&cp.args, "--no-checkout");
+		if (clone_data->quiet)
+			strvec_push(&cp.args, "--quiet");
+		if (clone_data->progress)
+			strvec_push(&cp.args, "--progress");
+		if (clone_data->depth && *(clone_data->depth))
+			strvec_pushl(&cp.args, "--depth", clone_data->depth, NULL);
+		if (clone_data->reference.nr) {
+			struct string_list_item *item;
+			for_each_string_list_item(item, &clone_data->reference)
+				strvec_pushl(&cp.args, "--reference",
+					     item->string, NULL);
+		}
+		if (clone_data->dissociate)
+			strvec_push(&cp.args, "--dissociate");
+		if (sm_gitdir && *sm_gitdir)
+			strvec_pushl(&cp.args, "--separate-git-dir", sm_gitdir, NULL);
+		if (clone_data->single_branch >= 0)
+			strvec_push(&cp.args, clone_data->single_branch ?
+				    "--single-branch" :
+				    "--no-single-branch");
+
+		strvec_push(&cp.args, "--");
+		strvec_push(&cp.args, clone_data->url);
+		strvec_push(&cp.args, clone_data->path);
+
+		cp.git_cmd = 1;
+		prepare_submodule_repo_env(&cp.env_array);
+		cp.no_stdin = 1;
+
+		if(run_command(&cp))
+			die(_("clone of '%s' into submodule path '%s' failed"),
+			    clone_data->url, clone_data->path);
+	} else {
+		if (clone_data->require_init && !access(clone_data->path, X_OK) &&
+		    !is_empty_dir(clone_data->path))
+			die(_("directory not empty: '%s'"), clone_data->path);
+		if (safe_create_leading_directories_const(clone_data->path) < 0)
+			die(_("could not create directory '%s'"), clone_data->path);
+		strbuf_addf(&sb, "%s/index", sm_gitdir);
+		unlink_or_warn(sb.buf);
+		strbuf_reset(&sb);
+	}
+
+	connect_work_tree_and_git_dir(clone_data->path, sm_gitdir, 0);
+
+	p = git_pathdup_submodule(clone_data->path, "config");
+	if (!p)
+		die(_("could not get submodule directory for '%s'"), clone_data->path);
+
+	/* setup alternateLocation and alternateErrorStrategy in the cloned submodule if needed */
+	git_config_get_string("submodule.alternateLocation", &sm_alternate);
+	if (sm_alternate)
+		git_config_set_in_file(p, "submodule.alternateLocation",
+				       sm_alternate);
+	git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);
+	if (error_strategy)
+		git_config_set_in_file(p, "submodule.alternateErrorStrategy",
+				       error_strategy);
+
+	free(sm_alternate);
+	free(error_strategy);
+
+	strbuf_release(&sb);
+	free(sm_gitdir);
+	free(p);
+	return 0;
+}
+
 static int module_clone(int argc, const char **argv, const char *prefix)
 {
-	const char *name = NULL, *url = NULL, *depth = NULL;
-	int quiet = 0;
-	int progress = 0;
-	char *p, *path = NULL, *sm_gitdir;
-	struct strbuf sb = STRBUF_INIT;
-	struct string_list reference = STRING_LIST_INIT_NODUP;
-	int dissociate = 0, require_init = 0;
-	char *sm_alternate = NULL, *error_strategy = NULL;
-	int single_branch = -1;
+	int dissociate = 0, quiet = 0, progress = 0, require_init = 0;
+	struct module_clone_data clone_data = MODULE_CLONE_DATA_INIT;
 
 	struct option module_clone_options[] = {
-		OPT_STRING(0, "prefix", &prefix,
+		OPT_STRING(0, "prefix", &clone_data.prefix,
 			   N_("path"),
 			   N_("alternative anchor for relative paths")),
-		OPT_STRING(0, "path", &path,
+		OPT_STRING(0, "path", &clone_data.path,
 			   N_("path"),
 			   N_("where the new submodule will be cloned to")),
-		OPT_STRING(0, "name", &name,
+		OPT_STRING(0, "name", &clone_data.name,
 			   N_("string"),
 			   N_("name of the new submodule")),
-		OPT_STRING(0, "url", &url,
+		OPT_STRING(0, "url", &clone_data.url,
 			   N_("string"),
 			   N_("url where to clone the submodule from")),
-		OPT_STRING_LIST(0, "reference", &reference,
+		OPT_STRING_LIST(0, "reference", &clone_data.reference,
 			   N_("repo"),
 			   N_("reference repository")),
 		OPT_BOOL(0, "dissociate", &dissociate,
 			   N_("use --reference only while cloning")),
-		OPT_STRING(0, "depth", &depth,
+		OPT_STRING(0, "depth", &clone_data.depth,
 			   N_("string"),
 			   N_("depth for shallow clones")),
 		OPT__QUIET(&quiet, "Suppress output for cloning a submodule"),