1 files changed, 986 insertions, 72 deletions

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index f4c3eff179..85aafe46a4 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -9,6 +9,215 @@
 #include "submodule-config.h"
 #include "string-list.h"
 #include "run-command.h"
+#include "remote.h"
+#include "refs.h"
+#include "connect.h"
+
+static char *get_default_remote(void)
+{
+	char *dest = NULL, *ret;
+	unsigned char sha1[20];
+	struct strbuf sb = STRBUF_INIT;
+	const char *refname = resolve_ref_unsafe("HEAD", 0, sha1, NULL);
+
+	if (!refname)
+		die(_("No such ref: %s"), "HEAD");
+
+	/* detached HEAD */
+	if (!strcmp(refname, "HEAD"))
+		return xstrdup("origin");
+
+	if (!skip_prefix(refname, "refs/heads/", &refname))
+		die(_("Expecting a full ref name, got %s"), refname);
+
+	strbuf_addf(&sb, "branch.%s.remote", refname);
+	if (git_config_get_string(sb.buf, &dest))
+		ret = xstrdup("origin");
+	else
+		ret = dest;
+
+	strbuf_release(&sb);
+	return ret;
+}
+
+static int starts_with_dot_slash(const char *str)
+{
+	return str[0] == '.' && is_dir_sep(str[1]);
+}
+
+static int starts_with_dot_dot_slash(const char *str)
+{
+	return str[0] == '.' && str[1] == '.' && is_dir_sep(str[2]);
+}
+
+/*
+ * Returns 1 if it was the last chop before ':'.
+ */
+static int chop_last_dir(char **remoteurl, int is_relative)
+{
+	char *rfind = find_last_dir_sep(*remoteurl);
+	if (rfind) {
+		*rfind = '\0';
+		return 0;
+	}
+
+	rfind = strrchr(*remoteurl, ':');
+	if (rfind) {
+		*rfind = '\0';
+		return 1;
+	}
+
+	if (is_relative || !strcmp(".", *remoteurl))
+		die(_("cannot strip one component off url '%s'"),
+			*remoteurl);
+
+	free(*remoteurl);
+	*remoteurl = xstrdup(".");
+	return 0;
+}
+
+/*
+ * The `url` argument is the URL that navigates to the submodule origin
+ * repo. When relative, this URL is relative to the superproject origin
+ * URL repo. The `up_path` argument, if specified, is the relative
+ * path that navigates from the submodule working tree to the superproject
+ * working tree. Returns the origin URL of the submodule.
+ *
+ * Return either an absolute URL or filesystem path (if the superproject
+ * origin URL is an absolute URL or filesystem path, respectively) or a
+ * relative file system path (if the superproject origin URL is a relative
+ * file system path).
+ *
+ * When the output is a relative file system path, the path is either
+ * relative to the submodule working tree, if up_path is specified, or to
+ * the superproject working tree otherwise.
+ *
+ * NEEDSWORK: This works incorrectly on the domain and protocol part.
+ * remote_url      url              outcome          expectation
+ * http://a.com/b  ../c             http://a.com/c   as is
+ * http://a.com/b/ ../c             http://a.com/c   same as previous line, but
+ *                                                   ignore trailing slash in url
+ * http://a.com/b  ../../c          http://c         error out
+ * http://a.com/b  ../../../c       http:/c          error out
+ * http://a.com/b  ../../../../c    http:c           error out
+ * http://a.com/b  ../../../../../c    .:c           error out
+ * NEEDSWORK: Given how chop_last_dir() works, this function is broken
+ * when a local part has a colon in its path component, too.
+ */
+static char *relative_url(const char *remote_url,
+				const char *url,
+				const char *up_path)
+{
+	int is_relative = 0;
+	int colonsep = 0;
+	char *out;
+	char *remoteurl = xstrdup(remote_url);
+	struct strbuf sb = STRBUF_INIT;
+	size_t len = strlen(remoteurl);
+
+	if (is_dir_sep(remoteurl[len-1]))
+		remoteurl[len-1] = '\0';
+
+	if (!url_is_local_not_ssh(remoteurl) || is_absolute_path(remoteurl))
+		is_relative = 0;
+	else {
+		is_relative = 1;
+		/*
+		 * Prepend a './' to ensure all relative
+		 * remoteurls start with './' or '../'
+		 */
+		if (!starts_with_dot_slash(remoteurl) &&
+		    !starts_with_dot_dot_slash(remoteurl)) {
+			strbuf_reset(&sb);
+			strbuf_addf(&sb, "./%s", remoteurl);
+			free(remoteurl);
+			remoteurl = strbuf_detach(&sb, NULL);
+		}
+	}
+	/*
+	 * When the url starts with '../', remove that and the
+	 * last directory in remoteurl.
+	 */
+	while (url) {
+		if (starts_with_dot_dot_slash(url)) {
+			url += 3;
+			colonsep |= chop_last_dir(&remoteurl, is_relative);
+		} else if (starts_with_dot_slash(url))
+			url += 2;
+		else
+			break;
+	}
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s%s%s", remoteurl, colonsep ? ":" : "/", url);
+	if (ends_with(url, "/"))
+		strbuf_setlen(&sb, sb.len - 1);
+	free(remoteurl);
+
+	if (starts_with_dot_slash(sb.buf))
+		out = xstrdup(sb.buf + 2);
+	else
+		out = xstrdup(sb.buf);
+	strbuf_reset(&sb);
+
+	if (!up_path || !is_relative)
+		return out;
+
+	strbuf_addf(&sb, "%s%s", up_path, out);
+	free(out);
+	return strbuf_detach(&sb, NULL);
+}
+
+static int resolve_relative_url(int argc, const char **argv, const char *prefix)
+{
+	char *remoteurl = NULL;
+	char *remote = get_default_remote();
+	const char *up_path = NULL;
+	char *res;
+	const char *url;
+	struct strbuf sb = STRBUF_INIT;
+
+	if (argc != 2 && argc != 3)
+		die("resolve-relative-url only accepts one or two arguments");
+
+	url = argv[1];
+	strbuf_addf(&sb, "remote.%s.url", remote);
+	free(remote);
+
+	if (git_config_get_string(sb.buf, &remoteurl))
+		/* the repository is its own authoritative upstream */
+		remoteurl = xgetcwd();
+
+	if (argc == 3)
+		up_path = argv[2];
+
+	res = relative_url(remoteurl, url, up_path);
+	puts(res);
+	free(res);
+	free(remoteurl);
+	return 0;
+}
+
+static int resolve_relative_url_test(int argc, const char **argv, const char *prefix)
+{
+	char *remoteurl, *res;
+	const char *up_path, *url;
+
+	if (argc != 4)
+		die("resolve-relative-url-test only accepts three arguments: <up_path> <remoteurl> <url>");
+
+	up_path = argv[1];
+	remoteurl = xstrdup(argv[2]);
+	url = argv[3];
+
+	if (!strcmp(up_path, "(null)"))
+		up_path = NULL;
+
+	res = relative_url(remoteurl, url, up_path);
+	puts(res);
+	free(res);
+	free(remoteurl);
+	return 0;
+}
 
 struct module_list {
 	const struct cache_entry **entries;
@@ -22,17 +231,12 @@ static int module_list_compute(int argc, const char **argv,
 			       struct module_list *list)
 {
 	int i, result = 0;
-	char *max_prefix, *ps_matched = NULL;
-	int max_prefix_len;
+	char *ps_matched = NULL;
 	parse_pathspec(pathspec, 0,
 		       PATHSPEC_PREFER_FULL |
 		       PATHSPEC_STRIP_SUBMODULE_SLASH_CHEAP,
 		       prefix, argv);
 
-	/* Find common prefix for all pathspec's */
-	max_prefix = common_prefix(pathspec);
-	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
-
 	if (pathspec->nr)
 		ps_matched = xcalloc(pathspec->nr, 1);
 
@@ -42,9 +246,9 @@ static int module_list_compute(int argc, const char **argv,
 	for (i = 0; i < active_nr; i++) {
 		const struct cache_entry *ce = active_cache[i];
 
-		if (!S_ISGITLINK(ce->ce_mode) ||
-		    !match_pathspec(pathspec, ce->name, ce_namelen(ce),
-				    max_prefix_len, ps_matched, 1))
+		if (!match_pathspec(pathspec, ce->name, ce_namelen(ce),
+				    0, ps_matched, 1) ||
+		    !S_ISGITLINK(ce->ce_mode))
 			continue;
 
 		ALLOC_GROW(list->entries, list->nr + 1, list->alloc);
@@ -57,7 +261,6 @@ static int module_list_compute(int argc, const char **argv,
 			 */
 			i++;
 	}
-	free(max_prefix);
 
 	if (ps_matched && report_path_error(ps_matched, pathspec, prefix))
 		result = -1;
@@ -67,6 +270,29 @@ static int module_list_compute(int argc, const char **argv,
 	return result;
 }
 
+static void module_list_active(struct module_list *list)
+{
+	int i;
+	struct module_list active_modules = MODULE_LIST_INIT;
+
+	gitmodules_config();
+
+	for (i = 0; i < list->nr; i++) {
+		const struct cache_entry *ce = list->entries[i];
+
+		if (!is_submodule_initialized(ce->name))
+			continue;
+
+		ALLOC_GROW(active_modules.entries,
+			   active_modules.nr + 1,
+			   active_modules.alloc);
+		active_modules.entries[active_modules.nr++] = ce;
+	}
+
+	free(list->entries);
+	*list = active_modules;
+}
+
 static int module_list(int argc, const char **argv, const char *prefix)
 {
 	int i;
@@ -88,10 +314,8 @@ 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];
@@ -99,13 +323,151 @@ static int module_list(int argc, const char **argv, const char *prefix)
 		if (ce_stage(ce))
 			printf("%06o %s U\t", ce->ce_mode, sha1_to_hex(null_sha1));
 		else
-			printf("%06o %s %d\t", ce->ce_mode, sha1_to_hex(ce->sha1), ce_stage(ce));
+			printf("%06o %s %d\t", ce->ce_mode,
+			       oid_to_hex(&ce->oid), ce_stage(ce));
 
 		utf8_fprintf(stdout, "%s\n", ce->name);
 	}
 	return 0;
 }
 
+static void init_submodule(const char *path, const char *prefix, int quiet)
+{
+	const struct submodule *sub;
+	struct strbuf sb = STRBUF_INIT;
+	char *upd = NULL, *url = NULL, *displaypath;
+
+	/* Only loads from .gitmodules, no overlay with .git/config */
+	gitmodules_config();
+
+	if (prefix && get_super_prefix())
+		die("BUG: cannot have prefix and superprefix");
+	else if (prefix)
+		displaypath = xstrdup(relative_path(path, prefix, &sb));
+	else if (get_super_prefix()) {
+		strbuf_addf(&sb, "%s%s", get_super_prefix(), path);
+		displaypath = strbuf_detach(&sb, NULL);
+	} else
+		displaypath = xstrdup(path);
+
+	sub = submodule_from_path(null_sha1, path);
+
+	if (!sub)
+		die(_("No url found for submodule path '%s' in .gitmodules"),
+			displaypath);
+
+	/*
+	 * NEEDSWORK: In a multi-working-tree world, this needs to be
+	 * set in the per-worktree config.
+	 *
+	 * Set active flag for the submodule being initialized
+	 */
+	if (!is_submodule_initialized(path)) {
+		strbuf_reset(&sb);
+		strbuf_addf(&sb, "submodule.%s.active", sub->name);
+		git_config_set_gently(sb.buf, "true");
+	}
+
+	/*
+	 * Copy url setting when it is not set yet.
+	 * To look up the url in .git/config, we must not fall back to
+	 * .gitmodules, so look it up directly.
+	 */
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "submodule.%s.url", sub->name);
+	if (git_config_get_string(sb.buf, &url)) {
+		url = xstrdup(sub->url);
+
+		if (!url)
+			die(_("No url found for submodule path '%s' in .gitmodules"),
+				displaypath);
+
+		/* Possibly a url relative to parent */
+		if (starts_with_dot_dot_slash(url) ||
+		    starts_with_dot_slash(url)) {
+			char *remoteurl, *relurl;
+			char *remote = get_default_remote();
+			struct strbuf remotesb = STRBUF_INIT;
+			strbuf_addf(&remotesb, "remote.%s.url", remote);
+			free(remote);
+
+			if (git_config_get_string(remotesb.buf, &remoteurl)) {
+				warning(_("could not lookup configuration '%s'. Assuming this repository is its own authoritative upstream."), remotesb.buf);
+				remoteurl = xgetcwd();
+			}
+			relurl = relative_url(remoteurl, url, NULL);
+			strbuf_release(&remotesb);
+			free(remoteurl);
+			free(url);
+			url = relurl;
+		}
+
+		if (git_config_set_gently(sb.buf, url))
+			die(_("Failed to register url for submodule path '%s'"),
+			    displaypath);
+		if (!quiet)
+			fprintf(stderr,
+				_("Submodule '%s' (%s) registered for path '%s'\n"),
+				sub->name, url, displaypath);
+	}
+
+	/* Copy "update" setting when it is not set yet */
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "submodule.%s.update", sub->name);
+	if (git_config_get_string(sb.buf, &upd) &&
+	    sub->update_strategy.type != SM_UPDATE_UNSPECIFIED) {
+		if (sub->update_strategy.type == SM_UPDATE_COMMAND) {
+			fprintf(stderr, _("warning: command update mode suggested for submodule '%s'\n"),
+				sub->name);
+			upd = xstrdup("none");
+		} else
+			upd = xstrdup(submodule_strategy_to_string(&sub->update_strategy));
+
+		if (git_config_set_gently(sb.buf, upd))
+			die(_("Failed to register update mode for submodule path '%s'"), displaypath);
+	}
+	strbuf_release(&sb);
+	free(displaypath);
+	free(url);
+	free(upd);
+}
+
+static int module_init(int argc, const char **argv, const char *prefix)
+{
+	struct pathspec pathspec;
+	struct module_list list = MODULE_LIST_INIT;
+	int quiet = 0;
+	int i;
+
+	struct option module_init_options[] = {
+		OPT__QUIET(&quiet, N_("Suppress output for initializing a submodule")),
+		OPT_END()
+	};
+
+	const char *const git_submodule_helper_usage[] = {
+		N_("git submodule--helper init [<path>]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, module_init_options,
+			     git_submodule_helper_usage, 0);
+
+	if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
+		return 1;
+
+	/*
+	 * If there are no path args and submodule.active is set then,
+	 * by default, only initialize 'active' modules.
+	 */
+	if (!argc && git_config_get_value_multi("submodule.active"))
+		module_list_active(&list);
+
+	for (i = 0; i < list.nr; i++)
+		init_submodule(list.entries[i]->name, prefix, quiet);
+
+	return 0;
+}
+
 static int module_name(int argc, const char **argv, const char *prefix)
 {
 	const struct submodule *sub;
@@ -124,20 +486,27 @@ static int module_name(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, const char *reference, int quiet)
+			   const char *depth, struct string_list *reference,
+			   int quiet, int progress)
 {
-	struct child_process cp;
-	child_process_init(&cp);
+	struct child_process cp = CHILD_PROCESS_INIT;
 
 	argv_array_push(&cp.args, "clone");
 	argv_array_push(&cp.args, "--no-checkout");
 	if (quiet)
 		argv_array_push(&cp.args, "--quiet");
+	if (progress)
+		argv_array_push(&cp.args, "--progress");
 	if (depth && *depth)
 		argv_array_pushl(&cp.args, "--depth", depth, NULL);
-	if (reference && *reference)
-		argv_array_pushl(&cp.args, "--reference", reference, NULL);
+	if (reference->nr) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, reference)
+			argv_array_pushl(&cp.args, "--reference",
+					 item->string, NULL);
+	}
 	if (gitdir && *gitdir)
 		argv_array_pushl(&cp.args, "--separate-git-dir", gitdir, NULL);
 
@@ -145,21 +514,115 @@ static int clone_submodule(const char *path, const char *gitdir, const char *url
 	argv_array_push(&cp.args, path);
 
 	cp.git_cmd = 1;
-	cp.env = local_repo_env;
+	prepare_submodule_repo_env(&cp.env_array);
 	cp.no_stdin = 1;
 
 	return run_command(&cp);
 }
 
+struct submodule_alternate_setup {
+	const char *submodule_name;
+	enum SUBMODULE_ALTERNATE_ERROR_MODE {
+		SUBMODULE_ALTERNATE_ERROR_DIE,
+		SUBMODULE_ALTERNATE_ERROR_INFO,
+		SUBMODULE_ALTERNATE_ERROR_IGNORE
+	} error_mode;
+	struct string_list *reference;
+};
+#define SUBMODULE_ALTERNATE_SETUP_INIT { NULL, \
+	SUBMODULE_ALTERNATE_ERROR_IGNORE, NULL }
+
+static int add_possible_reference_from_superproject(
+		struct alternate_object_database *alt, void *sas_cb)
+{
+	struct submodule_alternate_setup *sas = sas_cb;
+
+	/*
+	 * If the alternate object store is another repository, try the
+	 * standard layout with .git/(modules/<name>)+/objects
+	 */
+	if (ends_with(alt->path, "/objects")) {
+		char *sm_alternate;
+		struct strbuf sb = STRBUF_INIT;
+		struct strbuf err = STRBUF_INIT;
+		strbuf_add(&sb, alt->path, strlen(alt->path) - strlen("objects"));
+
+		/*
+		 * We need to end the new path with '/' to mark it as a dir,
+		 * otherwise a submodule name containing '/' will be broken
+		 * as the last part of a missing submodule reference would
+		 * be taken as a file name.
+		 */
+		strbuf_addf(&sb, "modules/%s/", sas->submodule_name);
+
+		sm_alternate = compute_alternate_path(sb.buf, &err);
+		if (sm_alternate) {
+			string_list_append(sas->reference, xstrdup(sb.buf));
+			free(sm_alternate);
+		} else {
+			switch (sas->error_mode) {
+			case SUBMODULE_ALTERNATE_ERROR_DIE:
+				die(_("submodule '%s' cannot add alternate: %s"),
+				    sas->submodule_name, err.buf);
+			case SUBMODULE_ALTERNATE_ERROR_INFO:
+				fprintf(stderr, _("submodule '%s' cannot add alternate: %s"),
+					sas->submodule_name, err.buf);
+			case SUBMODULE_ALTERNATE_ERROR_IGNORE:
+				; /* nothing */
+			}
+		}
+		strbuf_release(&sb);
+	}
+
+	return 0;
+}
+
+static void prepare_possible_alternates(const char *sm_name,
+		struct string_list *reference)
+{
+	char *sm_alternate = NULL, *error_strategy = NULL;
+	struct submodule_alternate_setup sas = SUBMODULE_ALTERNATE_SETUP_INIT;
+
+	git_config_get_string("submodule.alternateLocation", &sm_alternate);
+	if (!sm_alternate)
+		return;
+
+	git_config_get_string("submodule.alternateErrorStrategy", &error_strategy);
+
+	if (!error_strategy)
+		error_strategy = xstrdup("die");
+
+	sas.submodule_name = sm_name;
+	sas.reference = reference;
+	if (!strcmp(error_strategy, "die"))
+		sas.error_mode = SUBMODULE_ALTERNATE_ERROR_DIE;
+	else if (!strcmp(error_strategy, "info"))
+		sas.error_mode = SUBMODULE_ALTERNATE_ERROR_INFO;
+	else if (!strcmp(error_strategy, "ignore"))
+		sas.error_mode = SUBMODULE_ALTERNATE_ERROR_IGNORE;
+	else
+		die(_("Value '%s' for submodule.alternateErrorStrategy is not recognized"), error_strategy);
+
+	if (!strcmp(sm_alternate, "superproject"))
+		foreach_alt_odb(add_possible_reference_from_superproject, &sas);
+	else if (!strcmp(sm_alternate, "no"))
+		; /* do nothing */
+	else
+		die(_("Value '%s' for submodule.alternateLocation is not recognized"), sm_alternate);
+
+	free(sm_alternate);
+	free(error_strategy);
+}
+
 static int module_clone(int argc, const char **argv, const char *prefix)
 {
-	const char *path = NULL, *name = NULL, *url = NULL;
-	const char *reference = NULL, *depth = NULL;
+	const char *name = NULL, *url = NULL, *depth = NULL;
 	int quiet = 0;
-	FILE *submodule_dot_git;
-	char *sm_gitdir, *cwd, *p;
-	struct strbuf rel_path = STRBUF_INIT;
+	int progress = 0;
+	char *p, *path = NULL, *sm_gitdir;
 	struct strbuf sb = STRBUF_INIT;
+	struct string_list reference = STRING_LIST_INIT_NODUP;
+	char *sm_alternate = NULL, *error_strategy = NULL;
 
 	struct option module_clone_options[] = {
 		OPT_STRING(0, "prefix", &prefix,
@@ -174,33 +637,50 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "url", &url,
 			   N_("string"),
 			   N_("url where to clone the submodule from")),
-		OPT_STRING(0, "reference", &reference,
-			   N_("string"),
+		OPT_STRING_LIST(0, "reference", &reference,
+			   N_("repo"),
 			   N_("reference repository")),
 		OPT_STRING(0, "depth", &depth,
 			   N_("string"),
 			   N_("depth for shallow clones")),
 		OPT__QUIET(&quiet, "Suppress output for cloning a submodule"),
+		OPT_BOOL(0, "progress", &progress,
+			   N_("force cloning progress")),
 		OPT_END()
 	};
 
 	const char *const git_submodule_helper_usage[] = {
 		N_("git submodule--helper clone [--prefix=<path>] [--quiet] "
-		   "[--reference <repository>] [--name <name>] [--url <url>]"
-		   "[--depth <depth>] [--] [<path>...]"),
+		   "[--reference <repository>] [--name <name>] [--depth <depth>] "
+		   "--url <url> --path <path>"),
 		NULL
 	};
 
 	argc = parse_options(argc, argv, prefix, module_clone_options,
 			     git_submodule_helper_usage, 0);
 
+	if (argc || !url || !path || !*path)
+		usage_with_options(git_submodule_helper_usage,
+				   module_clone_options);
+
 	strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
-	sm_gitdir = strbuf_detach(&sb, NULL);
+	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 (!file_exists(sm_gitdir)) {
 		if (safe_create_leading_directories_const(sm_gitdir) < 0)
 			die(_("could not create directory '%s'"), sm_gitdir);
-		if (clone_submodule(path, sm_gitdir, url, depth, reference, quiet))
+
+		prepare_possible_alternates(name, &reference);
+
+		if (clone_submodule(path, sm_gitdir, url, depth, &reference,
+				    quiet, progress))
 			die(_("clone of '%s' into submodule path '%s' failed"),
 			    url, path);
 	} else {
@@ -211,72 +691,506 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		strbuf_reset(&sb);
 	}
 
-	/* Write a .git file in the submodule to redirect to the superproject. */
-	if (safe_create_leading_directories_const(path) < 0)
-		die(_("could not create directory '%s'"), path);
+	/* Connect module worktree and git dir */
+	connect_work_tree_and_git_dir(path, sm_gitdir);
 
-	if (path && *path)
-		strbuf_addf(&sb, "%s/.git", path);
-	else
-		strbuf_addstr(&sb, ".git");
-
-	if (safe_create_leading_directories_const(sb.buf) < 0)
-		die(_("could not create leading directories of '%s'"), sb.buf);
-	submodule_dot_git = fopen(sb.buf, "w");
-	if (!submodule_dot_git)
-		die_errno(_("cannot open file '%s'"), sb.buf);
-
-	fprintf(submodule_dot_git, "gitdir: %s\n",
-		relative_path(sm_gitdir, path, &rel_path));
-	if (fclose(submodule_dot_git))
-		die(_("could not close file %s"), sb.buf);
-	strbuf_reset(&sb);
-	strbuf_reset(&rel_path);
-
-	cwd = xgetcwd();
-	/* Redirect the worktree of the submodule in the superproject's config */
-	if (!is_absolute_path(sm_gitdir)) {
-		strbuf_addf(&sb, "%s/%s", cwd, sm_gitdir);
-		free(sm_gitdir);
-		sm_gitdir = strbuf_detach(&sb, NULL);
-	}
-
-	strbuf_addf(&sb, "%s/%s", cwd, path);
 	p = git_pathdup_submodule(path, "config");
 	if (!p)
 		die(_("could not get submodule directory for '%s'"), path);
-	git_config_set_in_file(p, "core.worktree",
-			       relative_path(sb.buf, sm_gitdir, &rel_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);
-	strbuf_release(&rel_path);
 	free(sm_gitdir);
-	free(cwd);
+	free(path);
 	free(p);
 	return 0;
 }
 
+struct submodule_update_clone {
+	/* index into 'list', the list of submodules to look into for cloning */
+	int current;
+	struct module_list list;
+	unsigned warn_if_uninitialized : 1;
+
+	/* update parameter passed via commandline */
+	struct submodule_update_strategy update;
+
+	/* configuration parameters which are passed on to the children */
+	int progress;
+	int quiet;
+	int recommend_shallow;
+	struct string_list references;
+	const char *depth;
+	const char *recursive_prefix;
+	const char *prefix;
+
+	/* Machine-readable status lines to be consumed by git-submodule.sh */
+	struct string_list projectlines;
+
+	/* If we want to stop as fast as possible and return an error */
+	unsigned quickstop : 1;
+
+	/* failed clones to be retried again */
+	const struct cache_entry **failed_clones;
+	int failed_clones_nr, failed_clones_alloc;
+};
+#define SUBMODULE_UPDATE_CLONE_INIT {0, MODULE_LIST_INIT, 0, \
+	SUBMODULE_UPDATE_STRATEGY_INIT, 0, 0, -1, STRING_LIST_INIT_DUP, \
+	NULL, NULL, NULL, \
+	STRING_LIST_INIT_DUP, 0, NULL, 0, 0}
+
+
+static void next_submodule_warn_missing(struct submodule_update_clone *suc,
+		struct strbuf *out, const char *displaypath)
+{
+	/*
+	 * Only mention uninitialized submodules when their
+	 * paths have been specified.
+	 */
+	if (suc->warn_if_uninitialized) {
+		strbuf_addf(out,
+			_("Submodule path '%s' not initialized"),
+			displaypath);
+		strbuf_addch(out, '\n');
+		strbuf_addstr(out,
+			_("Maybe you want to use 'update --init'?"));
+		strbuf_addch(out, '\n');
+	}
+}
+
+/**
+ * Determine whether 'ce' needs to be cloned. If so, prepare the 'child' to
+ * run the clone. Returns 1 if 'ce' needs to be cloned, 0 otherwise.
+ */
+static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
+					   struct child_process *child,
+					   struct submodule_update_clone *suc,
+					   struct strbuf *out)
+{
+	const struct submodule *sub = NULL;
+	struct strbuf displaypath_sb = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	const char *displaypath = NULL;
+	int needs_cloning = 0;
+
+	if (ce_stage(ce)) {
+		if (suc->recursive_prefix)
+			strbuf_addf(&sb, "%s/%s", suc->recursive_prefix, ce->name);
+		else
+			strbuf_addstr(&sb, ce->name);
+		strbuf_addf(out, _("Skipping unmerged submodule %s"), sb.buf);
+		strbuf_addch(out, '\n');
+		goto cleanup;
+	}
+
+	sub = submodule_from_path(null_sha1, ce->name);
+
+	if (suc->recursive_prefix)
+		displaypath = relative_path(suc->recursive_prefix,
+					    ce->name, &displaypath_sb);
+	else
+		displaypath = ce->name;
+
+	if (!sub) {
+		next_submodule_warn_missing(suc, out, displaypath);
+		goto cleanup;
+	}
+
+	if (suc->update.type == SM_UPDATE_NONE
+	    || (suc->update.type == SM_UPDATE_UNSPECIFIED
+		&& sub->update_strategy.type == SM_UPDATE_NONE)) {
+		strbuf_addf(out, _("Skipping submodule '%s'"), displaypath);
+		strbuf_addch(out, '\n');
+		goto cleanup;
+	}
+
+	/* Check if the submodule has been initialized. */
+	if (!is_submodule_initialized(ce->name)) {
+		next_submodule_warn_missing(suc, out, displaypath);
+		goto cleanup;
+	}
+
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s/.git", ce->name);
+	needs_cloning = !file_exists(sb.buf);
+
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%06o %s %d %d\t%s\n", ce->ce_mode,
+			oid_to_hex(&ce->oid), ce_stage(ce),
+			needs_cloning, ce->name);
+	string_list_append(&suc->projectlines, sb.buf);
+
+	if (!needs_cloning)
+		goto cleanup;
+
+	child->git_cmd = 1;
+	child->no_stdin = 1;
+	child->stdout_to_stderr = 1;
+	child->err = -1;
+	argv_array_push(&child->args, "submodule--helper");
+	argv_array_push(&child->args, "clone");
+	if (suc->progress)
+		argv_array_push(&child->args, "--progress");
+	if (suc->quiet)
+		argv_array_push(&child->args, "--quiet");
+	if (suc->prefix)
+		argv_array_pushl(&child->args, "--prefix", suc->prefix, NULL);
+	if (suc->recommend_shallow && sub->recommend_shallow == 1)
+		argv_array_push(&child->args, "--depth=1");
+	argv_array_pushl(&child->args, "--path", sub->path, NULL);
+	argv_array_pushl(&child->args, "--name", sub->name, NULL);
+	argv_array_pushl(&child->args, "--url", sub->url, NULL);
+	if (suc->references.nr) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, &suc->references)
+			argv_array_pushl(&child->args, "--reference", item->string, NULL);
+	}
+	if (suc->depth)
+		argv_array_push(&child->args, suc->depth);
+
+cleanup:
+	strbuf_reset(&displaypath_sb);
+	strbuf_reset(&sb);
+
+	return needs_cloning;
+}
+
+static int update_clone_get_next_task(struct child_process *child,
+				      struct strbuf *err,
+				      void *suc_cb,
+				      void **idx_task_cb)
+{
+	struct submodule_update_clone *suc = suc_cb;
+	const struct cache_entry *ce;
+	int index;
+
+	for (; suc->current < suc->list.nr; suc->current++) {
+		ce = suc->list.entries[suc->current];
+		if (prepare_to_clone_next_submodule(ce, child, suc, err)) {
+			int *p = xmalloc(sizeof(*p));
+			*p = suc->current;
+			*idx_task_cb = p;
+			suc->current++;
+			return 1;
+		}
+	}
+
+	/*
+	 * The loop above tried cloning each submodule once, now try the
+	 * stragglers again, which we can imagine as an extension of the
+	 * entry list.
+	 */
+	index = suc->current - suc->list.nr;
+	if (index < suc->failed_clones_nr) {
+		int *p;
+		ce = suc->failed_clones[index];
+		if (!prepare_to_clone_next_submodule(ce, child, suc, err)) {
+			suc->current ++;
+			strbuf_addstr(err, "BUG: submodule considered for "
+					   "cloning, doesn't need cloning "
+					   "any more?\n");
+			return 0;
+		}
+		p = xmalloc(sizeof(*p));
+		*p = suc->current;
+		*idx_task_cb = p;
+		suc->current ++;
+		return 1;
+	}
+
+	return 0;
+}
+
+static int update_clone_start_failure(struct strbuf *err,
+				      void *suc_cb,
+				      void *idx_task_cb)
+{
+	struct submodule_update_clone *suc = suc_cb;
+	suc->quickstop = 1;
+	return 1;
+}
+
+static int update_clone_task_finished(int result,
+				      struct strbuf *err,
+				      void *suc_cb,
+				      void *idx_task_cb)
+{
+	const struct cache_entry *ce;
+	struct submodule_update_clone *suc = suc_cb;
+
+	int *idxP = *(int**)idx_task_cb;
+	int idx = *idxP;
+	free(idxP);
+
+	if (!result)
+		return 0;
+
+	if (idx < suc->list.nr) {
+		ce  = suc->list.entries[idx];
+		strbuf_addf(err, _("Failed to clone '%s'. Retry scheduled"),
+			    ce->name);
+		strbuf_addch(err, '\n');
+		ALLOC_GROW(suc->failed_clones,
+			   suc->failed_clones_nr + 1,
+			   suc->failed_clones_alloc);
+		suc->failed_clones[suc->failed_clones_nr++] = ce;
+		return 0;
+	} else {
+		idx -= suc->list.nr;
+		ce  = suc->failed_clones[idx];
+		strbuf_addf(err, _("Failed to clone '%s' a second time, aborting"),
+			    ce->name);
+		strbuf_addch(err, '\n');
+		suc->quickstop = 1;
+		return 1;
+	}
+
+	return 0;
+}
+
+static int update_clone(int argc, const char **argv, const char *prefix)
+{
+	const char *update = NULL;
+	int max_jobs = -1;
+	struct string_list_item *item;
+	struct pathspec pathspec;
+	struct submodule_update_clone suc = SUBMODULE_UPDATE_CLONE_INIT;
+
+	struct option module_update_clone_options[] = {
+		OPT_STRING(0, "prefix", &prefix,
+			   N_("path"),
+			   N_("path into the working tree")),
+		OPT_STRING(0, "recursive-prefix", &suc.recursive_prefix,
+			   N_("path"),
+			   N_("path into the working tree, across nested "
+			      "submodule boundaries")),
+		OPT_STRING(0, "update", &update,
+			   N_("string"),
+			   N_("rebase, merge, checkout or none")),
+		OPT_STRING_LIST(0, "reference", &suc.references, N_("repo"),
+			   N_("reference repository")),
+		OPT_STRING(0, "depth", &suc.depth, "<depth>",
+			   N_("Create a shallow clone truncated to the "
+			      "specified number of revisions")),
+		OPT_INTEGER('j', "jobs", &max_jobs,
+			    N_("parallel jobs")),
+		OPT_BOOL(0, "recommend-shallow", &suc.recommend_shallow,
+			    N_("whether the initial clone should follow the shallow recommendation")),
+		OPT__QUIET(&suc.quiet, N_("don't print cloning progress")),
+		OPT_BOOL(0, "progress", &suc.progress,
+			    N_("force cloning progress")),
+		OPT_END()
+	};
+
+	const char *const git_submodule_helper_usage[] = {
+		N_("git submodule--helper update_clone [--prefix=<path>] [<path>...]"),
+		NULL
+	};
+	suc.prefix = prefix;
+
+	argc = parse_options(argc, argv, prefix, module_update_clone_options,
+			     git_submodule_helper_usage, 0);
+
+	if (update)
+		if (parse_submodule_update_strategy(update, &suc.update) < 0)
+			die(_("bad value for update parameter"));
+
+	if (module_list_compute(argc, argv, prefix, &pathspec, &suc.list) < 0)
+		return 1;
+
+	if (pathspec.nr)
+		suc.warn_if_uninitialized = 1;
+
+	/* Overlay the parsed .gitmodules file with .git/config */
+	gitmodules_config();
+	git_config(submodule_config, NULL);
+
+	if (max_jobs < 0)
+		max_jobs = parallel_submodules();
+
+	run_processes_parallel(max_jobs,
+			       update_clone_get_next_task,
+			       update_clone_start_failure,
+			       update_clone_task_finished,
+			       &suc);
+
+	/*
+	 * We saved the output and put it out all at once now.
+	 * That means:
+	 * - the listener does not have to interleave their (checkout)
+	 *   work with our fetching.  The writes involved in a
+	 *   checkout involve more straightforward sequential I/O.
+	 * - the listener can avoid doing any work if fetching failed.
+	 */
+	if (suc.quickstop)
+		return 1;
+
+	for_each_string_list_item(item, &suc.projectlines)
+		utf8_fprintf(stdout, "%s", item->string);
+
+	return 0;
+}
+
+static int resolve_relative_path(int argc, const char **argv, const char *prefix)
+{
+	struct strbuf sb = STRBUF_INIT;
+	if (argc != 3)
+		die("submodule--helper relative-path takes exactly 2 arguments, got %d", argc);
+
+	printf("%s", relative_path(argv[1], argv[2], &sb));
+	strbuf_release(&sb);
+	return 0;
+}
+
+static const char *remote_submodule_branch(const char *path)
+{
+	const struct submodule *sub;
+	gitmodules_config();
+	git_config(submodule_config, NULL);
+
+	sub = submodule_from_path(null_sha1, path);
+	if (!sub)
+		return NULL;
+
+	if (!sub->branch)
+		return "master";
+
+	if (!strcmp(sub->branch, ".")) {
+		unsigned char sha1[20];
+		const char *refname = resolve_ref_unsafe("HEAD", 0, sha1, NULL);
+
+		if (!refname)
+			die(_("No such ref: %s"), "HEAD");
+
+		/* detached HEAD */
+		if (!strcmp(refname, "HEAD"))
+			die(_("Submodule (%s) branch configured to inherit "
+			      "branch from superproject, but the superproject "
+			      "is not on any branch"), sub->name);
+
+		if (!skip_prefix(refname, "refs/heads/", &refname))
+			die(_("Expecting a full ref name, got %s"), refname);
+		return refname;
+	}
+
+	return sub->branch;
+}
+
+static int resolve_remote_submodule_branch(int argc, const char **argv,
+		const char *prefix)
+{
+	const char *ret;
+	struct strbuf sb = STRBUF_INIT;
+	if (argc != 2)
+		die("submodule--helper remote-branch takes exactly one arguments, got %d", argc);
+
+	ret = remote_submodule_branch(argv[1]);
+	if (!ret)
+		die("submodule %s doesn't exist", argv[1]);
+
+	printf("%s", ret);
+	strbuf_release(&sb);
+	return 0;
+}
+
+static int absorb_git_dirs(int argc, const char **argv, const char *prefix)
+{
+	int i;
+	struct pathspec pathspec;
+	struct module_list list = MODULE_LIST_INIT;
+	unsigned flags = ABSORB_GITDIR_RECURSE_SUBMODULES;
+
+	struct option embed_gitdir_options[] = {
+		OPT_STRING(0, "prefix", &prefix,
+			   N_("path"),
+			   N_("path into the working tree")),
+		OPT_BIT(0, "--recursive", &flags, N_("recurse into submodules"),
+			ABSORB_GITDIR_RECURSE_SUBMODULES),
+		OPT_END()
+	};
+
+	const char *const git_submodule_helper_usage[] = {
+		N_("git submodule--helper embed-git-dir [<path>...]"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, embed_gitdir_options,
+			     git_submodule_helper_usage, 0);
+
+	gitmodules_config();
+	git_config(submodule_config, NULL);
+
+	if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
+		return 1;
+
+	for (i = 0; i < list.nr; i++)
+		absorb_git_dir_into_superproject(prefix,
+				list.entries[i]->name, flags);
+
+	return 0;
+}
+
+static int is_active(int argc, const char **argv, const char *prefix)
+{
+	if (argc != 2)
+		die("submodule--helper is-active takes exactly 1 arguments");
+
+	gitmodules_config();
+
+	return !is_submodule_initialized(argv[1]);
+}
+
+#define SUPPORT_SUPER_PREFIX (1<<0)
+
 struct cmd_struct {
 	const char *cmd;
 	int (*fn)(int, const char **, const char *);
+	unsigned option;
 };
 
 static struct cmd_struct commands[] = {
-	{"list", module_list},
-	{"name", module_name},
-	{"clone", module_clone},
+	{"list", module_list, 0},
+	{"name", module_name, 0},
+	{"clone", module_clone, 0},
+	{"update-clone", update_clone, 0},
+	{"relative-path", resolve_relative_path, 0},
+	{"resolve-relative-url", resolve_relative_url, 0},
+	{"resolve-relative-url-test", resolve_relative_url_test, 0},
+	{"init", module_init, SUPPORT_SUPER_PREFIX},
+	{"remote-branch", resolve_remote_submodule_branch, 0},
+	{"absorb-git-dirs", absorb_git_dirs, SUPPORT_SUPER_PREFIX},
+	{"is-active", is_active, 0},
 };
 
 int cmd_submodule__helper(int argc, const char **argv, const char *prefix)
 {
 	int i;
 	if (argc < 2)
-		die(_("fatal: submodule--helper subcommand must be "
+		die(_("submodule--helper subcommand must be "
 		      "called with a subcommand"));
 
-	for (i = 0; i < ARRAY_SIZE(commands); i++)
-		if (!strcmp(argv[1], commands[i].cmd))
+	for (i = 0; i < ARRAY_SIZE(commands); i++) {
+		if (!strcmp(argv[1], commands[i].cmd)) {
+			if (get_super_prefix() &&
+			    !(commands[i].option & SUPPORT_SUPER_PREFIX))
+				die(_("%s doesn't support --super-prefix"),
+				    commands[i].cmd);
 			return commands[i].fn(argc - 1, argv + 1, prefix);
+		}
+	}
 
-	die(_("fatal: '%s' is not a valid submodule--helper "
+	die(_("'%s' is not a valid submodule--helper "
 	      "subcommand"), argv[1]);
 }