Adding upstream version 1:2.39.2.upstream/1%2.39.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2537 insertions, 0 deletions

diff --git a/submodule.c b/submodule.c
new file mode 100644
index 0000000..8ac2fca
--- /dev/null
+++ b/submodule.c
@@ -0,0 +1,2537 @@
+
+#include "cache.h"
+#include "repository.h"
+#include "config.h"
+#include "submodule-config.h"
+#include "submodule.h"
+#include "dir.h"
+#include "diff.h"
+#include "commit.h"
+#include "revision.h"
+#include "run-command.h"
+#include "diffcore.h"
+#include "refs.h"
+#include "string-list.h"
+#include "oid-array.h"
+#include "strvec.h"
+#include "blob.h"
+#include "thread-utils.h"
+#include "quote.h"
+#include "remote.h"
+#include "worktree.h"
+#include "parse-options.h"
+#include "object-store.h"
+#include "commit-reach.h"
+#include "shallow.h"
+
+static int config_update_recurse_submodules = RECURSE_SUBMODULES_OFF;
+static int initialized_fetch_ref_tips;
+static struct oid_array ref_tips_before_fetch;
+static struct oid_array ref_tips_after_fetch;
+
+/*
+ * Check if the .gitmodules file is unmerged. Parsing of the .gitmodules file
+ * will be disabled because we can't guess what might be configured in
+ * .gitmodules unless the user resolves the conflict.
+ */
+int is_gitmodules_unmerged(struct index_state *istate)
+{
+	int pos = index_name_pos(istate, GITMODULES_FILE, strlen(GITMODULES_FILE));
+	if (pos < 0) { /* .gitmodules not found or isn't merged */
+		pos = -1 - pos;
+		if (istate->cache_nr > pos) {  /* there is a .gitmodules */
+			const struct cache_entry *ce = istate->cache[pos];
+			if (ce_namelen(ce) == strlen(GITMODULES_FILE) &&
+			    !strcmp(ce->name, GITMODULES_FILE))
+				return 1;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Check if the .gitmodules file is safe to write.
+ *
+ * Writing to the .gitmodules file requires that the file exists in the
+ * working tree or, if it doesn't, that a brand new .gitmodules file is going
+ * to be created (i.e. it's neither in the index nor in the current branch).
+ *
+ * It is not safe to write to .gitmodules if it's not in the working tree but
+ * it is in the index or in the current branch, because writing new values
+ * (and staging them) would blindly overwrite ALL the old content.
+ */
+int is_writing_gitmodules_ok(void)
+{
+	struct object_id oid;
+	return file_exists(GITMODULES_FILE) ||
+		(get_oid(GITMODULES_INDEX, &oid) < 0 && get_oid(GITMODULES_HEAD, &oid) < 0);
+}
+
+/*
+ * Check if the .gitmodules file has unstaged modifications.  This must be
+ * checked before allowing modifications to the .gitmodules file with the
+ * intention to stage them later, because when continuing we would stage the
+ * modifications the user didn't stage herself too. That might change in a
+ * future version when we learn to stage the changes we do ourselves without
+ * staging any previous modifications.
+ */
+int is_staging_gitmodules_ok(struct index_state *istate)
+{
+	int pos = index_name_pos(istate, GITMODULES_FILE, strlen(GITMODULES_FILE));
+
+	if ((pos >= 0) && (pos < istate->cache_nr)) {
+		struct stat st;
+		if (lstat(GITMODULES_FILE, &st) == 0 &&
+		    ie_modified(istate, istate->cache[pos], &st, 0) & DATA_CHANGED)
+			return 0;
+	}
+
+	return 1;
+}
+
+static int for_each_remote_ref_submodule(const char *submodule,
+					 each_ref_fn fn, void *cb_data)
+{
+	return refs_for_each_remote_ref(get_submodule_ref_store(submodule),
+					fn, cb_data);
+}
+
+/*
+ * Try to update the "path" entry in the "submodule.<name>" section of the
+ * .gitmodules file. Return 0 only if a .gitmodules file was found, a section
+ * with the correct path=<oldpath> setting was found and we could update it.
+ */
+int update_path_in_gitmodules(const char *oldpath, const char *newpath)
+{
+	struct strbuf entry = STRBUF_INIT;
+	const struct submodule *submodule;
+	int ret;
+
+	if (!file_exists(GITMODULES_FILE)) /* Do nothing without .gitmodules */
+		return -1;
+
+	if (is_gitmodules_unmerged(the_repository->index))
+		die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));
+
+	submodule = submodule_from_path(the_repository, null_oid(), oldpath);
+	if (!submodule || !submodule->name) {
+		warning(_("Could not find section in .gitmodules where path=%s"), oldpath);
+		return -1;
+	}
+	strbuf_addstr(&entry, "submodule.");
+	strbuf_addstr(&entry, submodule->name);
+	strbuf_addstr(&entry, ".path");
+	ret = config_set_in_gitmodules_file_gently(entry.buf, newpath);
+	strbuf_release(&entry);
+	return ret;
+}
+
+/*
+ * Try to remove the "submodule.<name>" section from .gitmodules where the given
+ * path is configured. Return 0 only if a .gitmodules file was found, a section
+ * with the correct path=<path> setting was found and we could remove it.
+ */
+int remove_path_from_gitmodules(const char *path)
+{
+	struct strbuf sect = STRBUF_INIT;
+	const struct submodule *submodule;
+
+	if (!file_exists(GITMODULES_FILE)) /* Do nothing without .gitmodules */
+		return -1;
+
+	if (is_gitmodules_unmerged(the_repository->index))
+		die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));
+
+	submodule = submodule_from_path(the_repository, null_oid(), path);
+	if (!submodule || !submodule->name) {
+		warning(_("Could not find section in .gitmodules where path=%s"), path);
+		return -1;
+	}
+	strbuf_addstr(&sect, "submodule.");
+	strbuf_addstr(&sect, submodule->name);
+	if (git_config_rename_section_in_file(GITMODULES_FILE, sect.buf, NULL) < 0) {
+		/* Maybe the user already did that, don't error out here */
+		warning(_("Could not remove .gitmodules entry for %s"), path);
+		strbuf_release(&sect);
+		return -1;
+	}
+	strbuf_release(&sect);
+	return 0;
+}
+
+void stage_updated_gitmodules(struct index_state *istate)
+{
+	if (add_file_to_index(istate, GITMODULES_FILE, 0))
+		die(_("staging updated .gitmodules failed"));
+}
+
+static struct string_list added_submodule_odb_paths = STRING_LIST_INIT_NODUP;
+
+void add_submodule_odb_by_path(const char *path)
+{
+	string_list_insert(&added_submodule_odb_paths, xstrdup(path));
+}
+
+int register_all_submodule_odb_as_alternates(void)
+{
+	int i;
+	int ret = added_submodule_odb_paths.nr;
+
+	for (i = 0; i < added_submodule_odb_paths.nr; i++)
+		add_to_alternates_memory(added_submodule_odb_paths.items[i].string);
+	if (ret) {
+		string_list_clear(&added_submodule_odb_paths, 0);
+		trace2_data_intmax("submodule", the_repository,
+				   "register_all_submodule_odb_as_alternates/registered", ret);
+		if (git_env_bool("GIT_TEST_FATAL_REGISTER_SUBMODULE_ODB", 0))
+			BUG("register_all_submodule_odb_as_alternates() called");
+	}
+	return ret;
+}
+
+void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
+					     const char *path)
+{
+	const struct submodule *submodule = submodule_from_path(the_repository,
+								null_oid(),
+								path);
+	if (submodule) {
+		const char *ignore;
+		char *key;
+
+		key = xstrfmt("submodule.%s.ignore", submodule->name);
+		if (repo_config_get_string_tmp(the_repository, key, &ignore))
+			ignore = submodule->ignore;
+		free(key);
+
+		if (ignore)
+			handle_ignore_submodules_arg(diffopt, ignore);
+		else if (is_gitmodules_unmerged(the_repository->index))
+			diffopt->flags.ignore_submodules = 1;
+	}
+}
+
+/* Cheap function that only determines if we're interested in submodules at all */
+int git_default_submodule_config(const char *var, const char *value,
+				 void *cb UNUSED)
+{
+	if (!strcmp(var, "submodule.recurse")) {
+		int v = git_config_bool(var, value) ?
+			RECURSE_SUBMODULES_ON : RECURSE_SUBMODULES_OFF;
+		config_update_recurse_submodules = v;
+	}
+	return 0;
+}
+
+int option_parse_recurse_submodules_worktree_updater(const struct option *opt,
+						     const char *arg, int unset)
+{
+	if (unset) {
+		config_update_recurse_submodules = RECURSE_SUBMODULES_OFF;
+		return 0;
+	}
+	if (arg)
+		config_update_recurse_submodules =
+			parse_update_recurse_submodules_arg(opt->long_name,
+							    arg);
+	else
+		config_update_recurse_submodules = RECURSE_SUBMODULES_ON;
+
+	return 0;
+}
+
+/*
+ * Determine if a submodule has been initialized at a given 'path'
+ */
+/*
+ * NEEDSWORK: Emit a warning if submodule.active exists, but is valueless,
+ * ie, the config looks like: "[submodule] active\n".
+ * Since that is an invalid pathspec, we should inform the user.
+ */
+int is_tree_submodule_active(struct repository *repo,
+			     const struct object_id *treeish_name,
+			     const char *path)
+{
+	int ret = 0;
+	char *key = NULL;
+	char *value = NULL;
+	const struct string_list *sl;
+	const struct submodule *module;
+
+	module = submodule_from_path(repo, treeish_name, path);
+
+	/* early return if there isn't a path->module mapping */
+	if (!module)
+		return 0;
+
+	/* submodule.<name>.active is set */
+	key = xstrfmt("submodule.%s.active", module->name);
+	if (!repo_config_get_bool(repo, key, &ret)) {
+		free(key);
+		return ret;
+	}
+	free(key);
+
+	/* submodule.active is set */
+	sl = repo_config_get_value_multi(repo, "submodule.active");
+	if (sl) {
+		struct pathspec ps;
+		struct strvec args = STRVEC_INIT;
+		const struct string_list_item *item;
+
+		for_each_string_list_item(item, sl) {
+			strvec_push(&args, item->string);
+		}
+
+		parse_pathspec(&ps, 0, 0, NULL, args.v);
+		ret = match_pathspec(repo->index, &ps, path, strlen(path), 0, NULL, 1);
+
+		strvec_clear(&args);
+		clear_pathspec(&ps);
+		return ret;
+	}
+
+	/* fallback to checking if the URL is set */
+	key = xstrfmt("submodule.%s.url", module->name);
+	ret = !repo_config_get_string(repo, key, &value);
+
+	free(value);
+	free(key);
+	return ret;
+}
+
+int is_submodule_active(struct repository *repo, const char *path)
+{
+	return is_tree_submodule_active(repo, null_oid(), path);
+}
+
+int is_submodule_populated_gently(const char *path, int *return_error_code)
+{
+	int ret = 0;
+	char *gitdir = xstrfmt("%s/.git", path);
+
+	if (resolve_gitdir_gently(gitdir, return_error_code))
+		ret = 1;
+
+	free(gitdir);
+	return ret;
+}
+
+/*
+ * Dies if the provided 'prefix' corresponds to an unpopulated submodule
+ */
+void die_in_unpopulated_submodule(struct index_state *istate,
+				  const char *prefix)
+{
+	int i, prefixlen;
+
+	if (!prefix)
+		return;
+
+	prefixlen = strlen(prefix);
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		int ce_len = ce_namelen(ce);
+
+		if (!S_ISGITLINK(ce->ce_mode))
+			continue;
+		if (prefixlen <= ce_len)
+			continue;
+		if (strncmp(ce->name, prefix, ce_len))
+			continue;
+		if (prefix[ce_len] != '/')
+			continue;
+
+		die(_("in unpopulated submodule '%s'"), ce->name);
+	}
+}
+
+/*
+ * Dies if any paths in the provided pathspec descends into a submodule
+ */
+void die_path_inside_submodule(struct index_state *istate,
+			       const struct pathspec *ps)
+{
+	int i, j;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		int ce_len = ce_namelen(ce);
+
+		if (!S_ISGITLINK(ce->ce_mode))
+			continue;
+
+		for (j = 0; j < ps->nr ; j++) {
+			const struct pathspec_item *item = &ps->items[j];
+
+			if (item->len <= ce_len)
+				continue;
+			if (item->match[ce_len] != '/')
+				continue;
+			if (strncmp(ce->name, item->match, ce_len))
+				continue;
+			if (item->len == ce_len + 1)
+				continue;
+
+			die(_("Pathspec '%s' is in submodule '%.*s'"),
+			    item->original, ce_len, ce->name);
+		}
+	}
+}
+
+enum submodule_update_type parse_submodule_update_type(const char *value)
+{
+	if (!strcmp(value, "none"))
+		return SM_UPDATE_NONE;
+	else if (!strcmp(value, "checkout"))
+		return SM_UPDATE_CHECKOUT;
+	else if (!strcmp(value, "rebase"))
+		return SM_UPDATE_REBASE;
+	else if (!strcmp(value, "merge"))
+		return SM_UPDATE_MERGE;
+	else if (*value == '!')
+		return SM_UPDATE_COMMAND;
+	else
+		return SM_UPDATE_UNSPECIFIED;
+}
+
+int parse_submodule_update_strategy(const char *value,
+		struct submodule_update_strategy *dst)
+{
+	enum submodule_update_type type;
+
+	free((void*)dst->command);
+	dst->command = NULL;
+
+	type = parse_submodule_update_type(value);
+	if (type == SM_UPDATE_UNSPECIFIED)
+		return -1;
+
+	dst->type = type;
+	if (type == SM_UPDATE_COMMAND)
+		dst->command = xstrdup(value + 1);
+
+	return 0;
+}
+
+const char *submodule_update_type_to_string(enum submodule_update_type type)
+{
+	switch (type) {
+	case SM_UPDATE_CHECKOUT:
+		return "checkout";
+	case SM_UPDATE_MERGE:
+		return "merge";
+	case SM_UPDATE_REBASE:
+		return "rebase";
+	case SM_UPDATE_NONE:
+		return "none";
+	case SM_UPDATE_UNSPECIFIED:
+	case SM_UPDATE_COMMAND:
+		BUG("init_submodule() should handle type %d", type);
+	default:
+		BUG("unexpected update strategy type: %d", type);
+	}
+}
+
+void handle_ignore_submodules_arg(struct diff_options *diffopt,
+				  const char *arg)
+{
+	diffopt->flags.ignore_submodule_set = 1;
+	diffopt->flags.ignore_submodules = 0;
+	diffopt->flags.ignore_untracked_in_submodules = 0;
+	diffopt->flags.ignore_dirty_submodules = 0;
+
+	if (!strcmp(arg, "all"))
+		diffopt->flags.ignore_submodules = 1;
+	else if (!strcmp(arg, "untracked"))
+		diffopt->flags.ignore_untracked_in_submodules = 1;
+	else if (!strcmp(arg, "dirty"))
+		diffopt->flags.ignore_dirty_submodules = 1;
+	else if (strcmp(arg, "none"))
+		die(_("bad --ignore-submodules argument: %s"), arg);
+	/*
+	 * Please update _git_status() in git-completion.bash when you
+	 * add new options
+	 */
+}
+
+static int prepare_submodule_diff_summary(struct repository *r, struct rev_info *rev,
+					  const char *path,
+					  struct commit *left, struct commit *right,
+					  struct commit_list *merge_bases)
+{
+	struct commit_list *list;
+
+	repo_init_revisions(r, rev, NULL);
+	setup_revisions(0, NULL, rev, NULL);
+	rev->left_right = 1;
+	rev->first_parent_only = 1;
+	left->object.flags |= SYMMETRIC_LEFT;
+	add_pending_object(rev, &left->object, path);
+	add_pending_object(rev, &right->object, path);
+	for (list = merge_bases; list; list = list->next) {
+		list->item->object.flags |= UNINTERESTING;
+		add_pending_object(rev, &list->item->object,
+			oid_to_hex(&list->item->object.oid));
+	}
+	return prepare_revision_walk(rev);
+}
+
+static void print_submodule_diff_summary(struct repository *r, struct rev_info *rev, struct diff_options *o)
+{
+	static const char format[] = "  %m %s";
+	struct strbuf sb = STRBUF_INIT;
+	struct commit *commit;
+
+	while ((commit = get_revision(rev))) {
+		struct pretty_print_context ctx = {0};
+		ctx.date_mode = rev->date_mode;
+		ctx.output_encoding = get_log_output_encoding();
+		strbuf_setlen(&sb, 0);
+		repo_format_commit_message(r, commit, format, &sb,
+				      &ctx);
+		strbuf_addch(&sb, '\n');
+		if (commit->object.flags & SYMMETRIC_LEFT)
+			diff_emit_submodule_del(o, sb.buf);
+		else
+			diff_emit_submodule_add(o, sb.buf);
+	}
+	strbuf_release(&sb);
+}
+
+void prepare_submodule_repo_env(struct strvec *out)
+{
+	prepare_other_repo_env(out, DEFAULT_GIT_DIR_ENVIRONMENT);
+}
+
+static void prepare_submodule_repo_env_in_gitdir(struct strvec *out)
+{
+	prepare_other_repo_env(out, ".");
+}
+
+/*
+ * Initialize a repository struct for a submodule based on the provided 'path'.
+ *
+ * Returns the repository struct on success,
+ * NULL when the submodule is not present.
+ */
+static struct repository *open_submodule(const char *path)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct repository *out = xmalloc(sizeof(*out));
+
+	if (submodule_to_gitdir(&sb, path) || repo_init(out, sb.buf, NULL)) {
+		strbuf_release(&sb);
+		free(out);
+		return NULL;
+	}
+
+	/* Mark it as a submodule */
+	out->submodule_prefix = xstrdup(path);
+
+	strbuf_release(&sb);
+	return out;
+}
+
+/*
+ * Helper function to display the submodule header line prior to the full
+ * summary output.
+ *
+ * If it can locate the submodule git directory it will create a repository
+ * handle for the submodule and lookup both the left and right commits and
+ * put them into the left and right pointers.
+ */
+static void show_submodule_header(struct diff_options *o,
+		const char *path,
+		struct object_id *one, struct object_id *two,
+		unsigned dirty_submodule,
+		struct repository *sub,
+		struct commit **left, struct commit **right,
+		struct commit_list **merge_bases)
+{
+	const char *message = NULL;
+	struct strbuf sb = STRBUF_INIT;
+	int fast_forward = 0, fast_backward = 0;
+
+	if (dirty_submodule & DIRTY_SUBMODULE_UNTRACKED)
+		diff_emit_submodule_untracked(o, path);
+
+	if (dirty_submodule & DIRTY_SUBMODULE_MODIFIED)
+		diff_emit_submodule_modified(o, path);
+
+	if (is_null_oid(one))
+		message = "(new submodule)";
+	else if (is_null_oid(two))
+		message = "(submodule deleted)";
+
+	if (!sub) {
+		if (!message)
+			message = "(commits not present)";
+		goto output_header;
+	}
+
+	/*
+	 * Attempt to lookup the commit references, and determine if this is
+	 * a fast forward or fast backwards update.
+	 */
+	*left = lookup_commit_reference(sub, one);
+	*right = lookup_commit_reference(sub, two);
+
+	/*
+	 * Warn about missing commits in the submodule project, but only if
+	 * they aren't null.
+	 */
+	if ((!is_null_oid(one) && !*left) ||
+	     (!is_null_oid(two) && !*right))
+		message = "(commits not present)";
+
+	*merge_bases = repo_get_merge_bases(sub, *left, *right);
+	if (*merge_bases) {
+		if ((*merge_bases)->item == *left)
+			fast_forward = 1;
+		else if ((*merge_bases)->item == *right)
+			fast_backward = 1;
+	}
+
+	if (oideq(one, two)) {
+		strbuf_release(&sb);
+		return;
+	}
+
+output_header:
+	strbuf_addf(&sb, "Submodule %s ", path);
+	strbuf_add_unique_abbrev(&sb, one, DEFAULT_ABBREV);
+	strbuf_addstr(&sb, (fast_backward || fast_forward) ? ".." : "...");
+	strbuf_add_unique_abbrev(&sb, two, DEFAULT_ABBREV);
+	if (message)
+		strbuf_addf(&sb, " %s\n", message);
+	else
+		strbuf_addf(&sb, "%s:\n", fast_backward ? " (rewind)" : "");
+	diff_emit_submodule_header(o, sb.buf);
+
+	strbuf_release(&sb);
+}
+
+void show_submodule_diff_summary(struct diff_options *o, const char *path,
+		struct object_id *one, struct object_id *two,
+		unsigned dirty_submodule)
+{
+	struct rev_info rev = REV_INFO_INIT;
+	struct commit *left = NULL, *right = NULL;
+	struct commit_list *merge_bases = NULL;
+	struct repository *sub;
+
+	sub = open_submodule(path);
+	show_submodule_header(o, path, one, two, dirty_submodule,
+			      sub, &left, &right, &merge_bases);
+
+	/*
+	 * If we don't have both a left and a right pointer, there is no
+	 * reason to try and display a summary. The header line should contain
+	 * all the information the user needs.
+	 */
+	if (!left || !right || !sub)
+		goto out;
+
+	/* Treat revision walker failure the same as missing commits */
+	if (prepare_submodule_diff_summary(sub, &rev, path, left, right, merge_bases)) {
+		diff_emit_submodule_error(o, "(revision walker failed)\n");
+		goto out;
+	}
+
+	print_submodule_diff_summary(sub, &rev, o);
+
+out:
+	free_commit_list(merge_bases);
+	release_revisions(&rev);
+	clear_commit_marks(left, ~0);
+	clear_commit_marks(right, ~0);
+	if (sub) {
+		repo_clear(sub);
+		free(sub);
+	}
+}
+
+void show_submodule_inline_diff(struct diff_options *o, const char *path,
+		struct object_id *one, struct object_id *two,
+		unsigned dirty_submodule)
+{
+	const struct object_id *old_oid = the_hash_algo->empty_tree, *new_oid = the_hash_algo->empty_tree;
+	struct commit *left = NULL, *right = NULL;
+	struct commit_list *merge_bases = NULL;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	struct repository *sub;
+
+	sub = open_submodule(path);
+	show_submodule_header(o, path, one, two, dirty_submodule,
+			      sub, &left, &right, &merge_bases);
+
+	/* We need a valid left and right commit to display a difference */
+	if (!(left || is_null_oid(one)) ||
+	    !(right || is_null_oid(two)))
+		goto done;
+
+	if (left)
+		old_oid = one;
+	if (right)
+		new_oid = two;
+
+	cp.git_cmd = 1;
+	cp.dir = path;
+	cp.out = -1;
+	cp.no_stdin = 1;
+
+	/* TODO: other options may need to be passed here. */
+	strvec_pushl(&cp.args, "diff", "--submodule=diff", NULL);
+	strvec_pushf(&cp.args, "--color=%s", want_color(o->use_color) ?
+			 "always" : "never");
+
+	if (o->flags.reverse_diff) {
+		strvec_pushf(&cp.args, "--src-prefix=%s%s/",
+			     o->b_prefix, path);
+		strvec_pushf(&cp.args, "--dst-prefix=%s%s/",
+			     o->a_prefix, path);
+	} else {
+		strvec_pushf(&cp.args, "--src-prefix=%s%s/",
+			     o->a_prefix, path);
+		strvec_pushf(&cp.args, "--dst-prefix=%s%s/",
+			     o->b_prefix, path);
+	}
+	strvec_push(&cp.args, oid_to_hex(old_oid));
+	/*
+	 * If the submodule has modified content, we will diff against the
+	 * work tree, under the assumption that the user has asked for the
+	 * diff format and wishes to actually see all differences even if they
+	 * haven't yet been committed to the submodule yet.
+	 */
+	if (!(dirty_submodule & DIRTY_SUBMODULE_MODIFIED))
+		strvec_push(&cp.args, oid_to_hex(new_oid));
+
+	prepare_submodule_repo_env(&cp.env);
+
+	if (!is_directory(path)) {
+		/* fall back to absorbed git dir, if any */
+		if (!sub)
+			goto done;
+		cp.dir = sub->gitdir;
+		strvec_push(&cp.env, GIT_DIR_ENVIRONMENT "=.");
+		strvec_push(&cp.env, GIT_WORK_TREE_ENVIRONMENT "=.");
+	}
+
+	if (start_command(&cp)) {
+		diff_emit_submodule_error(o, "(diff failed)\n");
+		goto done;
+	}
+
+	while (strbuf_getwholeline_fd(&sb, cp.out, '\n') != EOF)
+		diff_emit_submodule_pipethrough(o, sb.buf, sb.len);
+
+	if (finish_command(&cp))
+		diff_emit_submodule_error(o, "(diff failed)\n");
+
+done:
+	strbuf_release(&sb);
+	free_commit_list(merge_bases);
+	if (left)
+		clear_commit_marks(left, ~0);
+	if (right)
+		clear_commit_marks(right, ~0);
+	if (sub) {
+		repo_clear(sub);
+		free(sub);
+	}
+}
+
+int should_update_submodules(void)
+{
+	return config_update_recurse_submodules == RECURSE_SUBMODULES_ON;
+}
+
+const struct submodule *submodule_from_ce(const struct cache_entry *ce)
+{
+	if (!S_ISGITLINK(ce->ce_mode))
+		return NULL;
+
+	if (!should_update_submodules())
+		return NULL;
+
+	return submodule_from_path(the_repository, null_oid(), ce->name);
+}
+
+
+struct collect_changed_submodules_cb_data {
+	struct repository *repo;
+	struct string_list *changed;
+	const struct object_id *commit_oid;
+};
+
+/*
+ * this would normally be two functions: default_name_from_path() and
+ * path_from_default_name(). Since the default name is the same as
+ * the submodule path we can get away with just one function which only
+ * checks whether there is a submodule in the working directory at that
+ * location.
+ */
+static const char *default_name_or_path(const char *path_or_name)
+{
+	int error_code;
+
+	if (!is_submodule_populated_gently(path_or_name, &error_code))
+		return NULL;
+
+	return path_or_name;
+}
+
+/*
+ * Holds relevant information for a changed submodule. Used as the .util
+ * member of the changed submodule name string_list_item.
+ *
+ * (super_oid, path) allows the submodule config to be read from _some_
+ * .gitmodules file. We store this information the first time we find a
+ * superproject commit that points to the submodule, but this is
+ * arbitrary - we can choose any (super_oid, path) that matches the
+ * submodule's name.
+ *
+ * NEEDSWORK: Storing an arbitrary commit is undesirable because we can't
+ * guarantee that we're reading the commit that the user would expect. A better
+ * scheme would be to just fetch a submodule by its name. This requires two
+ * steps:
+ * - Create a function that behaves like repo_submodule_init(), but accepts a
+ *   submodule name instead of treeish_name and path. This should be easy
+ *   because repo_submodule_init() internally uses the submodule's name.
+ *
+ * - Replace most instances of 'struct submodule' (which is the .gitmodules
+ *   config) with just the submodule name. This is OK because we expect
+ *   submodule settings to be stored in .git/config (via "git submodule init"),
+ *   not .gitmodules. This also lets us delete get_non_gitmodules_submodule(),
+ *   which constructs a bogus 'struct submodule' for the sake of giving a
+ *   placeholder name to a gitlink.
+ */
+struct changed_submodule_data {
+	/*
+	 * The first superproject commit in the rev walk that points to
+	 * the submodule.
+	 */
+	const struct object_id *super_oid;
+	/*
+	 * Path to the submodule in the superproject commit referenced
+	 * by 'super_oid'.
+	 */
+	char *path;
+	/* The submodule commits that have changed in the rev walk. */
+	struct oid_array new_commits;
+};
+
+static void changed_submodule_data_clear(struct changed_submodule_data *cs_data)
+{
+	oid_array_clear(&cs_data->new_commits);
+	free(cs_data->path);
+}
+
+static void collect_changed_submodules_cb(struct diff_queue_struct *q,
+					  struct diff_options *options,
+					  void *data)
+{
+	struct collect_changed_submodules_cb_data *me = data;
+	struct string_list *changed = me->changed;
+	const struct object_id *commit_oid = me->commit_oid;
+	int i;
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+		const struct submodule *submodule;
+		const char *name;
+		struct string_list_item *item;
+		struct changed_submodule_data *cs_data;
+
+		if (!S_ISGITLINK(p->two->mode))
+			continue;
+
+		submodule = submodule_from_path(me->repo,
+						commit_oid, p->two->path);
+		if (submodule)
+			name = submodule->name;
+		else {
+			name = default_name_or_path(p->two->path);
+			/* make sure name does not collide with existing one */
+			if (name)
+				submodule = submodule_from_name(me->repo,
+								commit_oid, name);
+			if (submodule) {
+				warning(_("Submodule in commit %s at path: "
+					"'%s' collides with a submodule named "
+					"the same. Skipping it."),
+					oid_to_hex(commit_oid), p->two->path);
+				name = NULL;
+			}
+		}
+
+		if (!name)
+			continue;
+
+		item = string_list_insert(changed, name);
+		if (item->util)
+			cs_data = item->util;
+		else {
+			item->util = xcalloc(1, sizeof(struct changed_submodule_data));
+			cs_data = item->util;
+			cs_data->super_oid = commit_oid;
+			cs_data->path = xstrdup(p->two->path);
+		}
+		oid_array_append(&cs_data->new_commits, &p->two->oid);
+	}
+}
+
+/*
+ * Collect the paths of submodules in 'changed' which have changed based on
+ * the revisions as specified in 'argv'.  Each entry in 'changed' will also
+ * have a corresponding 'struct oid_array' (in the 'util' field) which lists
+ * what the submodule pointers were updated to during the change.
+ */
+static void collect_changed_submodules(struct repository *r,
+				       struct string_list *changed,
+				       struct strvec *argv)
+{
+	struct rev_info rev;
+	const struct commit *commit;
+	int save_warning;
+	struct setup_revision_opt s_r_opt = {
+		.assume_dashdash = 1,
+	};
+
+	save_warning = warn_on_object_refname_ambiguity;
+	warn_on_object_refname_ambiguity = 0;
+	repo_init_revisions(r, &rev, NULL);
+	setup_revisions(argv->nr, argv->v, &rev, &s_r_opt);
+	warn_on_object_refname_ambiguity = save_warning;
+	if (prepare_revision_walk(&rev))
+		die(_("revision walk setup failed"));
+
+	while ((commit = get_revision(&rev))) {
+		struct rev_info diff_rev;
+		struct collect_changed_submodules_cb_data data;
+		data.repo = r;
+		data.changed = changed;
+		data.commit_oid = &commit->object.oid;
+
+		repo_init_revisions(r, &diff_rev, NULL);
+		diff_rev.diffopt.output_format |= DIFF_FORMAT_CALLBACK;
+		diff_rev.diffopt.format_callback = collect_changed_submodules_cb;
+		diff_rev.diffopt.format_callback_data = &data;
+		diff_rev.dense_combined_merges = 1;
+		diff_tree_combined_merge(commit, &diff_rev);
+		release_revisions(&diff_rev);
+	}
+
+	reset_revision_walk();
+	release_revisions(&rev);
+}
+
+static void free_submodules_data(struct string_list *submodules)
+{
+	struct string_list_item *item;
+	for_each_string_list_item(item, submodules)
+		changed_submodule_data_clear(item->util);
+
+	string_list_clear(submodules, 1);
+}
+
+static int has_remote(const char *refname UNUSED,
+		      const struct object_id *oid UNUSED,
+		      int flags UNUSED, void *cb_data UNUSED)
+{
+	return 1;
+}
+
+static int append_oid_to_argv(const struct object_id *oid, void *data)
+{
+	struct strvec *argv = data;
+	strvec_push(argv, oid_to_hex(oid));
+	return 0;
+}
+
+struct has_commit_data {
+	struct repository *repo;
+	int result;
+	const char *path;
+	const struct object_id *super_oid;
+};
+
+static int check_has_commit(const struct object_id *oid, void *data)
+{
+	struct has_commit_data *cb = data;
+	struct repository subrepo;
+	enum object_type type;
+
+	if (repo_submodule_init(&subrepo, cb->repo, cb->path, cb->super_oid)) {
+		cb->result = 0;
+		/* subrepo failed to init, so don't clean it up. */
+		return 0;
+	}
+
+	type = oid_object_info(&subrepo, oid, NULL);
+
+	switch (type) {
+	case OBJ_COMMIT:
+		goto cleanup;
+	case OBJ_BAD:
+		/*
+		 * Object is missing or invalid. If invalid, an error message
+		 * has already been printed.
+		 */
+		cb->result = 0;
+		goto cleanup;
+	default:
+		die(_("submodule entry '%s' (%s) is a %s, not a commit"),
+		    cb->path, oid_to_hex(oid), type_name(type));
+	}
+cleanup:
+	repo_clear(&subrepo);
+	return 0;
+}
+
+static int submodule_has_commits(struct repository *r,
+				 const char *path,
+				 const struct object_id *super_oid,
+				 struct oid_array *commits)
+{
+	struct has_commit_data has_commit = {
+		.repo = r,
+		.result = 1,
+		.path = path,
+		.super_oid = super_oid
+	};
+
+	oid_array_for_each_unique(commits, check_has_commit, &has_commit);
+
+	if (has_commit.result) {
+		/*
+		 * Even if the submodule is checked out and the commit is
+		 * present, make sure it exists in the submodule's object store
+		 * and that it is reachable from a ref.
+		 */
+		struct child_process cp = CHILD_PROCESS_INIT;
+		struct strbuf out = STRBUF_INIT;
+
+		strvec_pushl(&cp.args, "rev-list", "-n", "1", NULL);
+		oid_array_for_each_unique(commits, append_oid_to_argv, &cp.args);
+		strvec_pushl(&cp.args, "--not", "--all", NULL);
+
+		prepare_submodule_repo_env(&cp.env);
+		cp.git_cmd = 1;
+		cp.no_stdin = 1;
+		cp.dir = path;
+
+		if (capture_command(&cp, &out, GIT_MAX_HEXSZ + 1) || out.len)
+			has_commit.result = 0;
+
+		strbuf_release(&out);
+	}
+
+	return has_commit.result;
+}
+
+static int submodule_needs_pushing(struct repository *r,
+				   const char *path,
+				   struct oid_array *commits)
+{
+	if (!submodule_has_commits(r, path, null_oid(), commits))
+		/*
+		 * NOTE: We do consider it safe to return "no" here. The
+		 * correct answer would be "We do not know" instead of
+		 * "No push needed", but it is quite hard to change
+		 * the submodule pointer without having the submodule
+		 * around. If a user did however change the submodules
+		 * without having the submodule around, this indicates
+		 * an expert who knows what they are doing or a
+		 * maintainer integrating work from other people. In
+		 * both cases it should be safe to skip this check.
+		 */
+		return 0;
+
+	if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
+		struct child_process cp = CHILD_PROCESS_INIT;
+		struct strbuf buf = STRBUF_INIT;
+		int needs_pushing = 0;
+
+		strvec_push(&cp.args, "rev-list");
+		oid_array_for_each_unique(commits, append_oid_to_argv, &cp.args);
+		strvec_pushl(&cp.args, "--not", "--remotes", "-n", "1" , NULL);
+
+		prepare_submodule_repo_env(&cp.env);
+		cp.git_cmd = 1;
+		cp.no_stdin = 1;
+		cp.out = -1;
+		cp.dir = path;
+		if (start_command(&cp))
+			die(_("Could not run 'git rev-list <commits> --not --remotes -n 1' command in submodule %s"),
+					path);
+		if (strbuf_read(&buf, cp.out, the_hash_algo->hexsz + 1))
+			needs_pushing = 1;
+		finish_command(&cp);
+		close(cp.out);
+		strbuf_release(&buf);
+		return needs_pushing;
+	}
+
+	return 0;
+}
+
+int find_unpushed_submodules(struct repository *r,
+			     struct oid_array *commits,
+			     const char *remotes_name,
+			     struct string_list *needs_pushing)
+{
+	struct string_list submodules = STRING_LIST_INIT_DUP;
+	struct string_list_item *name;
+	struct strvec argv = STRVEC_INIT;
+
+	/* argv.v[0] will be ignored by setup_revisions */
+	strvec_push(&argv, "find_unpushed_submodules");
+	oid_array_for_each_unique(commits, append_oid_to_argv, &argv);
+	strvec_push(&argv, "--not");
+	strvec_pushf(&argv, "--remotes=%s", remotes_name);
+
+	collect_changed_submodules(r, &submodules, &argv);
+
+	for_each_string_list_item(name, &submodules) {
+		struct changed_submodule_data *cs_data = name->util;
+		const struct submodule *submodule;
+		const char *path = NULL;
+
+		submodule = submodule_from_name(r, null_oid(), name->string);
+		if (submodule)
+			path = submodule->path;
+		else
+			path = default_name_or_path(name->string);
+
+		if (!path)
+			continue;
+
+		if (submodule_needs_pushing(r, path, &cs_data->new_commits))
+			string_list_insert(needs_pushing, path);
+	}
+
+	free_submodules_data(&submodules);
+	strvec_clear(&argv);
+
+	return needs_pushing->nr;
+}
+
+static int push_submodule(const char *path,
+			  const struct remote *remote,
+			  const struct refspec *rs,
+			  const struct string_list *push_options,
+			  int dry_run)
+{
+	if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
+		struct child_process cp = CHILD_PROCESS_INIT;
+		strvec_push(&cp.args, "push");
+		/*
+		 * When recursing into a submodule, treat any "only" configurations as "on-
+		 * demand", since "only" would not work (we need all submodules to be pushed
+		 * in order to be able to push the superproject).
+		 */
+		strvec_push(&cp.args, "--recurse-submodules=only-is-on-demand");
+		if (dry_run)
+			strvec_push(&cp.args, "--dry-run");
+
+		if (push_options && push_options->nr) {
+			const struct string_list_item *item;
+			for_each_string_list_item(item, push_options)
+				strvec_pushf(&cp.args, "--push-option=%s",
+					     item->string);
+		}
+
+		if (remote->origin != REMOTE_UNCONFIGURED) {
+			int i;
+			strvec_push(&cp.args, remote->name);
+			for (i = 0; i < rs->raw_nr; i++)
+				strvec_push(&cp.args, rs->raw[i]);
+		}
+
+		prepare_submodule_repo_env(&cp.env);
+		cp.git_cmd = 1;
+		cp.no_stdin = 1;
+		cp.dir = path;
+		if (run_command(&cp))
+			return 0;
+		close(cp.out);
+	}
+
+	return 1;
+}
+
+/*
+ * Perform a check in the submodule to see if the remote and refspec work.
+ * Die if the submodule can't be pushed.
+ */
+static void submodule_push_check(const char *path, const char *head,
+				 const struct remote *remote,
+				 const struct refspec *rs)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	int i;
+
+	strvec_push(&cp.args, "submodule--helper");
+	strvec_push(&cp.args, "push-check");
+	strvec_push(&cp.args, head);
+	strvec_push(&cp.args, remote->name);
+
+	for (i = 0; i < rs->raw_nr; i++)
+		strvec_push(&cp.args, rs->raw[i]);
+
+	prepare_submodule_repo_env(&cp.env);
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = path;
+
+	/*
+	 * Simply indicate if 'submodule--helper push-check' failed.
+	 * More detailed error information will be provided by the
+	 * child process.
+	 */
+	if (run_command(&cp))
+		die(_("process for submodule '%s' failed"), path);
+}
+
+int push_unpushed_submodules(struct repository *r,
+			     struct oid_array *commits,
+			     const struct remote *remote,
+			     const struct refspec *rs,
+			     const struct string_list *push_options,
+			     int dry_run)
+{
+	int i, ret = 1;
+	struct string_list needs_pushing = STRING_LIST_INIT_DUP;
+
+	if (!find_unpushed_submodules(r, commits,
+				      remote->name, &needs_pushing))
+		return 1;
+
+	/*
+	 * Verify that the remote and refspec can be propagated to all
+	 * submodules.  This check can be skipped if the remote and refspec
+	 * won't be propagated due to the remote being unconfigured (e.g. a URL
+	 * instead of a remote name).
+	 */
+	if (remote->origin != REMOTE_UNCONFIGURED) {
+		char *head;
+		struct object_id head_oid;
+
+		head = resolve_refdup("HEAD", 0, &head_oid, NULL);
+		if (!head)
+			die(_("Failed to resolve HEAD as a valid ref."));
+
+		for (i = 0; i < needs_pushing.nr; i++)
+			submodule_push_check(needs_pushing.items[i].string,
+					     head, remote, rs);
+		free(head);
+	}
+
+	/* Actually push the submodules */
+	for (i = 0; i < needs_pushing.nr; i++) {
+		const char *path = needs_pushing.items[i].string;
+		fprintf(stderr, _("Pushing submodule '%s'\n"), path);
+		if (!push_submodule(path, remote, rs,
+				    push_options, dry_run)) {
+			fprintf(stderr, _("Unable to push submodule '%s'\n"), path);
+			ret = 0;
+		}
+	}
+
+	string_list_clear(&needs_pushing, 0);
+
+	return ret;
+}
+
+static int append_oid_to_array(const char *ref UNUSED,
+			       const struct object_id *oid,
+			       int flags UNUSED, void *data)
+{
+	struct oid_array *array = data;
+	oid_array_append(array, oid);
+	return 0;
+}
+
+void check_for_new_submodule_commits(struct object_id *oid)
+{
+	if (!initialized_fetch_ref_tips) {
+		for_each_ref(append_oid_to_array, &ref_tips_before_fetch);
+		initialized_fetch_ref_tips = 1;
+	}
+
+	oid_array_append(&ref_tips_after_fetch, oid);
+}
+
+/*
+ * Returns 1 if there is at least one submodule gitdir in
+ * $GIT_DIR/modules and 0 otherwise. This follows
+ * submodule_name_to_gitdir(), which looks for submodules in
+ * $GIT_DIR/modules, not $GIT_COMMON_DIR.
+ *
+ * A submodule can be moved to $GIT_DIR/modules manually by running "git
+ * submodule absorbgitdirs", or it may be initialized there by "git
+ * submodule update".
+ */
+static int repo_has_absorbed_submodules(struct repository *r)
+{
+	int ret;
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_repo_git_path(&buf, r, "modules/");
+	ret = file_exists(buf.buf) && !is_empty_dir(buf.buf);
+	strbuf_release(&buf);
+	return ret;
+}
+
+static void calculate_changed_submodule_paths(struct repository *r,
+		struct string_list *changed_submodule_names)
+{
+	struct strvec argv = STRVEC_INIT;
+	struct string_list_item *name;
+
+	/* No need to check if no submodules would be fetched */
+	if (!submodule_from_path(r, NULL, NULL) &&
+	    !repo_has_absorbed_submodules(r))
+		return;
+
+	strvec_push(&argv, "--"); /* argv[0] program name */
+	oid_array_for_each_unique(&ref_tips_after_fetch,
+				   append_oid_to_argv, &argv);
+	strvec_push(&argv, "--not");
+	oid_array_for_each_unique(&ref_tips_before_fetch,
+				   append_oid_to_argv, &argv);
+
+	/*
+	 * Collect all submodules (whether checked out or not) for which new
+	 * commits have been recorded upstream in "changed_submodule_names".
+	 */
+	collect_changed_submodules(r, changed_submodule_names, &argv);
+
+	for_each_string_list_item(name, changed_submodule_names) {
+		struct changed_submodule_data *cs_data = name->util;
+		const struct submodule *submodule;
+		const char *path = NULL;
+
+		submodule = submodule_from_name(r, null_oid(), name->string);
+		if (submodule)
+			path = submodule->path;
+		else
+			path = default_name_or_path(name->string);
+
+		if (!path)
+			continue;
+
+		if (submodule_has_commits(r, path, null_oid(), &cs_data->new_commits)) {
+			changed_submodule_data_clear(cs_data);
+			*name->string = '\0';
+		}
+	}
+
+	string_list_remove_empty_items(changed_submodule_names, 1);
+
+	strvec_clear(&argv);
+	oid_array_clear(&ref_tips_before_fetch);
+	oid_array_clear(&ref_tips_after_fetch);
+	initialized_fetch_ref_tips = 0;
+}
+
+int submodule_touches_in_range(struct repository *r,
+			       struct object_id *excl_oid,
+			       struct object_id *incl_oid)
+{
+	struct string_list subs = STRING_LIST_INIT_DUP;
+	struct strvec args = STRVEC_INIT;
+	int ret;
+
+	/* No need to check if there are no submodules configured */
+	if (!submodule_from_path(r, NULL, NULL))
+		return 0;
+
+	strvec_push(&args, "--"); /* args[0] program name */
+	strvec_push(&args, oid_to_hex(incl_oid));
+	if (!is_null_oid(excl_oid)) {
+		strvec_push(&args, "--not");
+		strvec_push(&args, oid_to_hex(excl_oid));
+	}
+
+	collect_changed_submodules(r, &subs, &args);
+	ret = subs.nr;
+
+	strvec_clear(&args);
+
+	free_submodules_data(&subs);
+	return ret;
+}
+
+struct submodule_parallel_fetch {
+	/*
+	 * The index of the last index entry processed by
+	 * get_fetch_task_from_index().
+	 */
+	int index_count;
+	/*
+	 * The index of the last string_list entry processed by
+	 * get_fetch_task_from_changed().
+	 */
+	int changed_count;
+	struct strvec args;
+	struct repository *r;
+	const char *prefix;
+	int command_line_option;
+	int default_option;
+	int quiet;
+	int result;
+
+	/*
+	 * Names of submodules that have new commits. Generated by
+	 * walking the newly fetched superproject commits.
+	 */
+	struct string_list changed_submodule_names;
+	/*
+	 * Names of submodules that have already been processed. Lets us
+	 * avoid fetching the same submodule more than once.
+	 */
+	struct string_list seen_submodule_names;
+
+	/* Pending fetches by OIDs */
+	struct fetch_task **oid_fetch_tasks;
+	int oid_fetch_tasks_nr, oid_fetch_tasks_alloc;
+
+	struct strbuf submodules_with_errors;
+};
+#define SPF_INIT { \
+	.args = STRVEC_INIT, \
+	.changed_submodule_names = STRING_LIST_INIT_DUP, \
+	.seen_submodule_names = STRING_LIST_INIT_DUP, \
+	.submodules_with_errors = STRBUF_INIT, \
+}
+
+static int get_fetch_recurse_config(const struct submodule *submodule,
+				    struct submodule_parallel_fetch *spf)
+{
+	if (spf->command_line_option != RECURSE_SUBMODULES_DEFAULT)
+		return spf->command_line_option;
+
+	if (submodule) {
+		char *key;
+		const char *value;
+
+		int fetch_recurse = submodule->fetch_recurse;
+		key = xstrfmt("submodule.%s.fetchRecurseSubmodules", submodule->name);
+		if (!repo_config_get_string_tmp(spf->r, key, &value)) {
+			fetch_recurse = parse_fetch_recurse_submodules_arg(key, value);
+		}
+		free(key);
+
+		if (fetch_recurse != RECURSE_SUBMODULES_NONE)
+			/* local config overrules everything except commandline */
+			return fetch_recurse;
+	}
+
+	return spf->default_option;
+}
+
+/*
+ * Fetch in progress (if callback data) or
+ * pending (if in oid_fetch_tasks in struct submodule_parallel_fetch)
+ */
+struct fetch_task {
+	struct repository *repo;
+	const struct submodule *sub;
+	unsigned free_sub : 1; /* Do we need to free the submodule? */
+	const char *default_argv; /* The default fetch mode. */
+	struct strvec git_args; /* Args for the child git process. */
+
+	struct oid_array *commits; /* Ensure these commits are fetched */
+};
+
+/**
+ * When a submodule is not defined in .gitmodules, we cannot access it
+ * via the regular submodule-config. Create a fake submodule, which we can
+ * work on.
+ */
+static const struct submodule *get_non_gitmodules_submodule(const char *path)
+{
+	struct submodule *ret = NULL;
+	const char *name = default_name_or_path(path);
+
+	if (!name)
+		return NULL;
+
+	ret = xmalloc(sizeof(*ret));
+	memset(ret, 0, sizeof(*ret));
+	ret->path = name;
+	ret->name = name;
+
+	return (const struct submodule *) ret;
+}
+
+static void fetch_task_release(struct fetch_task *p)
+{
+	if (p->free_sub)
+		free((void*)p->sub);
+	p->free_sub = 0;
+	p->sub = NULL;
+
+	if (p->repo)
+		repo_clear(p->repo);
+	FREE_AND_NULL(p->repo);
+
+	strvec_clear(&p->git_args);
+}
+
+static struct repository *get_submodule_repo_for(struct repository *r,
+						 const char *path,
+						 const struct object_id *treeish_name)
+{
+	struct repository *ret = xmalloc(sizeof(*ret));
+
+	if (repo_submodule_init(ret, r, path, treeish_name)) {
+		free(ret);
+		return NULL;
+	}
+
+	return ret;
+}
+
+static struct fetch_task *fetch_task_create(struct submodule_parallel_fetch *spf,
+					    const char *path,
+					    const struct object_id *treeish_name)
+{
+	struct fetch_task *task = xmalloc(sizeof(*task));
+	memset(task, 0, sizeof(*task));
+
+	task->sub = submodule_from_path(spf->r, treeish_name, path);
+
+	if (!task->sub) {
+		/*
+		 * No entry in .gitmodules? Technically not a submodule,
+		 * but historically we supported repositories that happen to be
+		 * in-place where a gitlink is. Keep supporting them.
+		 */
+		task->sub = get_non_gitmodules_submodule(path);
+		if (!task->sub)
+			goto cleanup;
+
+		task->free_sub = 1;
+	}
+
+	if (string_list_lookup(&spf->seen_submodule_names, task->sub->name))
+		goto cleanup;
+
+	switch (get_fetch_recurse_config(task->sub, spf))
+	{
+	default:
+	case RECURSE_SUBMODULES_DEFAULT:
+	case RECURSE_SUBMODULES_ON_DEMAND:
+		if (!task->sub ||
+			!string_list_lookup(
+				&spf->changed_submodule_names,
+				task->sub->name))
+			goto cleanup;
+		task->default_argv = "on-demand";
+		break;
+	case RECURSE_SUBMODULES_ON:
+		task->default_argv = "yes";
+		break;
+	case RECURSE_SUBMODULES_OFF:
+		goto cleanup;
+	}
+
+	task->repo = get_submodule_repo_for(spf->r, path, treeish_name);
+
+	return task;
+
+ cleanup:
+	fetch_task_release(task);
+	free(task);
+	return NULL;
+}
+
+static struct fetch_task *
+get_fetch_task_from_index(struct submodule_parallel_fetch *spf,
+			  struct strbuf *err)
+{
+	for (; spf->index_count < spf->r->index->cache_nr; spf->index_count++) {
+		const struct cache_entry *ce =
+			spf->r->index->cache[spf->index_count];
+		struct fetch_task *task;
+
+		if (!S_ISGITLINK(ce->ce_mode))
+			continue;
+
+		task = fetch_task_create(spf, ce->name, null_oid());
+		if (!task)
+			continue;
+
+		if (task->repo) {
+			if (!spf->quiet)
+				strbuf_addf(err, _("Fetching submodule %s%s\n"),
+					    spf->prefix, ce->name);
+
+			spf->index_count++;
+			return task;
+		} else {
+			struct strbuf empty_submodule_path = STRBUF_INIT;
+
+			fetch_task_release(task);
+			free(task);
+
+			/*
+			 * An empty directory is normal,
+			 * the submodule is not initialized
+			 */
+			strbuf_addf(&empty_submodule_path, "%s/%s/",
+							spf->r->worktree,
+							ce->name);
+			if (S_ISGITLINK(ce->ce_mode) &&
+			    !is_empty_dir(empty_submodule_path.buf)) {
+				spf->result = 1;
+				strbuf_addf(err,
+					    _("Could not access submodule '%s'\n"),
+					    ce->name);
+			}
+			strbuf_release(&empty_submodule_path);
+		}
+	}
+	return NULL;
+}
+
+static struct fetch_task *
+get_fetch_task_from_changed(struct submodule_parallel_fetch *spf,
+			    struct strbuf *err)
+{
+	for (; spf->changed_count < spf->changed_submodule_names.nr;
+	     spf->changed_count++) {
+		struct string_list_item item =
+			spf->changed_submodule_names.items[spf->changed_count];
+		struct changed_submodule_data *cs_data = item.util;
+		struct fetch_task *task;
+
+		if (!is_tree_submodule_active(spf->r, cs_data->super_oid,cs_data->path))
+			continue;
+
+		task = fetch_task_create(spf, cs_data->path,
+					 cs_data->super_oid);
+		if (!task)
+			continue;
+
+		if (!task->repo) {
+			strbuf_addf(err, _("Could not access submodule '%s' at commit %s\n"),
+				    cs_data->path,
+				    find_unique_abbrev(cs_data->super_oid, DEFAULT_ABBREV));
+
+			fetch_task_release(task);
+			free(task);
+			continue;
+		}
+
+		if (!spf->quiet)
+			strbuf_addf(err,
+				    _("Fetching submodule %s%s at commit %s\n"),
+				    spf->prefix, task->sub->path,
+				    find_unique_abbrev(cs_data->super_oid,
+						       DEFAULT_ABBREV));
+
+		spf->changed_count++;
+		/*
+		 * NEEDSWORK: Submodules set/unset a value for
+		 * core.worktree when they are populated/unpopulated by
+		 * "git checkout" (and similar commands, see
+		 * submodule_move_head() and
+		 * connect_work_tree_and_git_dir()), but if the
+		 * submodule is unpopulated in another way (e.g. "git
+		 * rm", "rm -r"), core.worktree will still be set even
+		 * though the directory doesn't exist, and the child
+		 * process will crash while trying to chdir into the
+		 * nonexistent directory.
+		 *
+		 * In this case, we know that the submodule has no
+		 * working tree, so we can work around this by
+		 * setting "--work-tree=." (--bare does not work because
+		 * worktree settings take precedence over bare-ness).
+		 * However, this is not necessarily true in other cases,
+		 * so a generalized solution is still necessary.
+		 *
+		 * Possible solutions:
+		 * - teach "git [add|rm]" to unset core.worktree and
+		 *   discourage users from removing submodules without
+		 *   using a Git command.
+		 * - teach submodule child processes to ignore stale
+		 *   core.worktree values.
+		 */
+		strvec_push(&task->git_args, "--work-tree=.");
+		return task;
+	}
+	return NULL;
+}
+
+static int get_next_submodule(struct child_process *cp, struct strbuf *err,
+			      void *data, void **task_cb)
+{
+	struct submodule_parallel_fetch *spf = data;
+	struct fetch_task *task =
+		get_fetch_task_from_index(spf, err);
+	if (!task)
+		task = get_fetch_task_from_changed(spf, err);
+
+	if (task) {
+		struct strbuf submodule_prefix = STRBUF_INIT;
+
+		child_process_init(cp);
+		cp->dir = task->repo->gitdir;
+		prepare_submodule_repo_env_in_gitdir(&cp->env);
+		cp->git_cmd = 1;
+		strvec_init(&cp->args);
+		if (task->git_args.nr)
+			strvec_pushv(&cp->args, task->git_args.v);
+		strvec_pushv(&cp->args, spf->args.v);
+		strvec_push(&cp->args, task->default_argv);
+		strvec_push(&cp->args, "--submodule-prefix");
+
+		strbuf_addf(&submodule_prefix, "%s%s/",
+						spf->prefix,
+						task->sub->path);
+		strvec_push(&cp->args, submodule_prefix.buf);
+		*task_cb = task;
+
+		strbuf_release(&submodule_prefix);
+		string_list_insert(&spf->seen_submodule_names, task->sub->name);
+		return 1;
+	}
+
+	if (spf->oid_fetch_tasks_nr) {
+		struct fetch_task *task =
+			spf->oid_fetch_tasks[spf->oid_fetch_tasks_nr - 1];
+		struct strbuf submodule_prefix = STRBUF_INIT;
+		spf->oid_fetch_tasks_nr--;
+
+		strbuf_addf(&submodule_prefix, "%s%s/",
+			    spf->prefix, task->sub->path);
+
+		child_process_init(cp);
+		prepare_submodule_repo_env_in_gitdir(&cp->env);
+		cp->git_cmd = 1;
+		cp->dir = task->repo->gitdir;
+
+		strvec_init(&cp->args);
+		strvec_pushv(&cp->args, spf->args.v);
+		strvec_push(&cp->args, "on-demand");
+		strvec_push(&cp->args, "--submodule-prefix");
+		strvec_push(&cp->args, submodule_prefix.buf);
+
+		/* NEEDSWORK: have get_default_remote from submodule--helper */
+		strvec_push(&cp->args, "origin");
+		oid_array_for_each_unique(task->commits,
+					  append_oid_to_argv, &cp->args);
+
+		*task_cb = task;
+		strbuf_release(&submodule_prefix);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int fetch_start_failure(struct strbuf *err,
+			       void *cb, void *task_cb)
+{
+	struct submodule_parallel_fetch *spf = cb;
+	struct fetch_task *task = task_cb;
+
+	spf->result = 1;
+
+	fetch_task_release(task);
+	return 0;
+}
+
+static int commit_missing_in_sub(const struct object_id *oid, void *data)
+{
+	struct repository *subrepo = data;
+
+	enum object_type type = oid_object_info(subrepo, oid, NULL);
+
+	return type != OBJ_COMMIT;
+}
+
+static int fetch_finish(int retvalue, struct strbuf *err,
+			void *cb, void *task_cb)
+{
+	struct submodule_parallel_fetch *spf = cb;
+	struct fetch_task *task = task_cb;
+
+	struct string_list_item *it;
+	struct changed_submodule_data *cs_data;
+
+	if (!task || !task->sub)
+		BUG("callback cookie bogus");
+
+	if (retvalue) {
+		/*
+		 * NEEDSWORK: This indicates that the overall fetch
+		 * failed, even though there may be a subsequent fetch
+		 * by commit hash that might work. It may be a good
+		 * idea to not indicate failure in this case, and only
+		 * indicate failure if the subsequent fetch fails.
+		 */
+		spf->result = 1;
+
+		strbuf_addf(&spf->submodules_with_errors, "\t%s\n",
+			    task->sub->name);
+	}
+
+	/* Is this the second time we process this submodule? */
+	if (task->commits)
+		goto out;
+
+	it = string_list_lookup(&spf->changed_submodule_names, task->sub->name);
+	if (!it)
+		/* Could be an unchanged submodule, not contained in the list */
+		goto out;
+
+	cs_data = it->util;
+	oid_array_filter(&cs_data->new_commits,
+			 commit_missing_in_sub,
+			 task->repo);
+
+	/* Are there commits we want, but do not exist? */
+	if (cs_data->new_commits.nr) {
+		task->commits = &cs_data->new_commits;
+		ALLOC_GROW(spf->oid_fetch_tasks,
+			   spf->oid_fetch_tasks_nr + 1,
+			   spf->oid_fetch_tasks_alloc);
+		spf->oid_fetch_tasks[spf->oid_fetch_tasks_nr] = task;
+		spf->oid_fetch_tasks_nr++;
+		return 0;
+	}
+
+out:
+	fetch_task_release(task);
+
+	return 0;
+}
+
+int fetch_submodules(struct repository *r,
+		     const struct strvec *options,
+		     const char *prefix, int command_line_option,
+		     int default_option,
+		     int quiet, int max_parallel_jobs)
+{
+	int i;
+	struct submodule_parallel_fetch spf = SPF_INIT;
+	const struct run_process_parallel_opts opts = {
+		.tr2_category = "submodule",
+		.tr2_label = "parallel/fetch",
+
+		.processes = max_parallel_jobs,
+
+		.get_next_task = get_next_submodule,
+		.start_failure = fetch_start_failure,
+		.task_finished = fetch_finish,
+		.data = &spf,
+	};
+
+	spf.r = r;
+	spf.command_line_option = command_line_option;
+	spf.default_option = default_option;
+	spf.quiet = quiet;
+	spf.prefix = prefix;
+
+	if (!r->worktree)
+		goto out;
+
+	if (repo_read_index(r) < 0)
+		die(_("index file corrupt"));
+
+	strvec_push(&spf.args, "fetch");
+	for (i = 0; i < options->nr; i++)
+		strvec_push(&spf.args, options->v[i]);
+	strvec_push(&spf.args, "--recurse-submodules-default");
+	/* default value, "--submodule-prefix" and its value are added later */
+
+	calculate_changed_submodule_paths(r, &spf.changed_submodule_names);
+	string_list_sort(&spf.changed_submodule_names);
+	run_processes_parallel(&opts);
+
+	if (spf.submodules_with_errors.len > 0)
+		fprintf(stderr, _("Errors during submodule fetch:\n%s"),
+			spf.submodules_with_errors.buf);
+
+
+	strvec_clear(&spf.args);
+out:
+	free_submodules_data(&spf.changed_submodule_names);
+	return spf.result;
+}
+
+unsigned is_submodule_modified(const char *path, int ignore_untracked)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	FILE *fp;
+	unsigned dirty_submodule = 0;
+	const char *git_dir;
+	int ignore_cp_exit_code = 0;
+
+	strbuf_addf(&buf, "%s/.git", path);
+	git_dir = read_gitfile(buf.buf);
+	if (!git_dir)
+		git_dir = buf.buf;
+	if (!is_git_directory(git_dir)) {
+		if (is_directory(git_dir))
+			die(_("'%s' not recognized as a git repository"), git_dir);
+		strbuf_release(&buf);
+		/* The submodule is not checked out, so it is not modified */
+		return 0;
+	}
+	strbuf_reset(&buf);
+
+	strvec_pushl(&cp.args, "status", "--porcelain=2", NULL);
+	if (ignore_untracked)
+		strvec_push(&cp.args, "-uno");
+
+	prepare_submodule_repo_env(&cp.env);
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.out = -1;
+	cp.dir = path;
+	if (start_command(&cp))
+		die(_("Could not run 'git status --porcelain=2' in submodule %s"), path);
+
+	fp = xfdopen(cp.out, "r");
+	while (strbuf_getwholeline(&buf, fp, '\n') != EOF) {
+		/* regular untracked files */
+		if (buf.buf[0] == '?')
+			dirty_submodule |= DIRTY_SUBMODULE_UNTRACKED;
+
+		if (buf.buf[0] == 'u' ||
+		    buf.buf[0] == '1' ||
+		    buf.buf[0] == '2') {
+			/* T = line type, XY = status, SSSS = submodule state */
+			if (buf.len < strlen("T XY SSSS"))
+				BUG("invalid status --porcelain=2 line %s",
+				    buf.buf);
+
+			if (buf.buf[5] == 'S' && buf.buf[8] == 'U')
+				/* nested untracked file */
+				dirty_submodule |= DIRTY_SUBMODULE_UNTRACKED;
+
+			if (buf.buf[0] == 'u' ||
+			    buf.buf[0] == '2' ||
+			    memcmp(buf.buf + 5, "S..U", 4))
+				/* other change */
+				dirty_submodule |= DIRTY_SUBMODULE_MODIFIED;
+		}
+
+		if ((dirty_submodule & DIRTY_SUBMODULE_MODIFIED) &&
+		    ((dirty_submodule & DIRTY_SUBMODULE_UNTRACKED) ||
+		     ignore_untracked)) {
+			/*
+			 * We're not interested in any further information from
+			 * the child any more, neither output nor its exit code.
+			 */
+			ignore_cp_exit_code = 1;
+			break;
+		}
+	}
+	fclose(fp);
+
+	if (finish_command(&cp) && !ignore_cp_exit_code)
+		die(_("'git status --porcelain=2' failed in submodule %s"), path);
+
+	strbuf_release(&buf);
+	return dirty_submodule;
+}
+
+int submodule_uses_gitfile(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	const char *git_dir;
+
+	strbuf_addf(&buf, "%s/.git", path);
+	git_dir = read_gitfile(buf.buf);
+	if (!git_dir) {
+		strbuf_release(&buf);
+		return 0;
+	}
+	strbuf_release(&buf);
+
+	/* Now test that all nested submodules use a gitfile too */
+	strvec_pushl(&cp.args,
+		     "submodule", "foreach", "--quiet",	"--recursive",
+		     "test -f .git", NULL);
+
+	prepare_submodule_repo_env(&cp.env);
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.no_stderr = 1;
+	cp.no_stdout = 1;
+	cp.dir = path;
+	if (run_command(&cp))
+		return 0;
+
+	return 1;
+}
+
+/*
+ * Check if it is a bad idea to remove a submodule, i.e. if we'd lose data
+ * when doing so.
+ *
+ * Return 1 if we'd lose data, return 0 if the removal is fine,
+ * and negative values for errors.
+ */
+int bad_to_remove_submodule(const char *path, unsigned flags)
+{
+	ssize_t len;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	int ret = 0;
+
+	if (!file_exists(path) || is_empty_dir(path))
+		return 0;
+
+	if (!submodule_uses_gitfile(path))
+		return 1;
+
+	strvec_pushl(&cp.args, "status", "--porcelain",
+		     "--ignore-submodules=none", NULL);
+
+	if (flags & SUBMODULE_REMOVAL_IGNORE_UNTRACKED)
+		strvec_push(&cp.args, "-uno");
+	else
+		strvec_push(&cp.args, "-uall");
+
+	if (!(flags & SUBMODULE_REMOVAL_IGNORE_IGNORED_UNTRACKED))
+		strvec_push(&cp.args, "--ignored");
+
+	prepare_submodule_repo_env(&cp.env);
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.out = -1;
+	cp.dir = path;
+	if (start_command(&cp)) {
+		if (flags & SUBMODULE_REMOVAL_DIE_ON_ERROR)
+			die(_("could not start 'git status' in submodule '%s'"),
+				path);
+		ret = -1;
+		goto out;
+	}
+
+	len = strbuf_read(&buf, cp.out, 1024);
+	if (len > 2)
+		ret = 1;
+	close(cp.out);
+
+	if (finish_command(&cp)) {
+		if (flags & SUBMODULE_REMOVAL_DIE_ON_ERROR)
+			die(_("could not run 'git status' in submodule '%s'"),
+				path);
+		ret = -1;
+	}
+out:
+	strbuf_release(&buf);
+	return ret;
+}
+
+void submodule_unset_core_worktree(const struct submodule *sub)
+{
+	struct strbuf config_path = STRBUF_INIT;
+
+	submodule_name_to_gitdir(&config_path, the_repository, sub->name);
+	strbuf_addstr(&config_path, "/config");
+
+	if (git_config_set_in_file_gently(config_path.buf, "core.worktree", NULL))
+		warning(_("Could not unset core.worktree setting in submodule '%s'"),
+			  sub->path);
+
+	strbuf_release(&config_path);
+}
+
+static const char *get_super_prefix_or_empty(void)
+{
+	const char *s = get_super_prefix();
+	if (!s)
+		s = "";
+	return s;
+}
+
+static int submodule_has_dirty_index(const struct submodule *sub)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	prepare_submodule_repo_env(&cp.env);
+
+	cp.git_cmd = 1;
+	strvec_pushl(&cp.args, "diff-index", "--quiet",
+		     "--cached", "HEAD", NULL);
+	cp.no_stdin = 1;
+	cp.no_stdout = 1;
+	cp.dir = sub->path;
+	if (start_command(&cp))
+		die(_("could not recurse into submodule '%s'"), sub->path);
+
+	return finish_command(&cp);
+}
+
+static void submodule_reset_index(const char *path)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	prepare_submodule_repo_env(&cp.env);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	strvec_pushf(&cp.args, "--super-prefix=%s%s/",
+		     get_super_prefix_or_empty(), path);
+	/* TODO: determine if this might overwright untracked files */
+	strvec_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);
+
+	strvec_push(&cp.args, empty_tree_oid_hex());
+
+	if (run_command(&cp))
+		die(_("could not reset submodule index"));
+}
+
+/**
+ * Moves a submodule at a given path from a given head to another new head.
+ * For edge cases (a submodule coming into existence or removing a submodule)
+ * pass NULL for old or new respectively.
+ */
+int submodule_move_head(const char *path,
+			 const char *old_head,
+			 const char *new_head,
+			 unsigned flags)
+{
+	int ret = 0;
+	struct child_process cp = CHILD_PROCESS_INIT;
+	const struct submodule *sub;
+	int *error_code_ptr, error_code;
+
+	if (!is_submodule_active(the_repository, path))
+		return 0;
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		/*
+		 * Pass non NULL pointer to is_submodule_populated_gently
+		 * to prevent die()-ing. We'll use connect_work_tree_and_git_dir
+		 * to fixup the submodule in the force case later.
+		 */
+		error_code_ptr = &error_code;
+	else
+		error_code_ptr = NULL;
+
+	if (old_head && !is_submodule_populated_gently(path, error_code_ptr))
+		return 0;
+
+	sub = submodule_from_path(the_repository, null_oid(), path);
+
+	if (!sub)
+		BUG("could not get submodule information for '%s'", path);
+
+	if (old_head && !(flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+		/* Check if the submodule has a dirty index. */
+		if (submodule_has_dirty_index(sub))
+			return error(_("submodule '%s' has dirty index"), path);
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (old_head) {
+			if (!submodule_uses_gitfile(path))
+				absorb_git_dir_into_superproject(path);
+		} else {
+			struct strbuf gitdir = STRBUF_INIT;
+			submodule_name_to_gitdir(&gitdir, the_repository,
+						 sub->name);
+			connect_work_tree_and_git_dir(path, gitdir.buf, 0);
+			strbuf_release(&gitdir);
+
+			/* make sure the index is clean as well */
+			submodule_reset_index(path);
+		}
+
+		if (old_head && (flags & SUBMODULE_MOVE_HEAD_FORCE)) {
+			struct strbuf gitdir = STRBUF_INIT;
+			submodule_name_to_gitdir(&gitdir, the_repository,
+						 sub->name);
+			connect_work_tree_and_git_dir(path, gitdir.buf, 1);
+			strbuf_release(&gitdir);
+		}
+	}
+
+	prepare_submodule_repo_env(&cp.env);
+
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	cp.dir = path;
+
+	strvec_pushf(&cp.args, "--super-prefix=%s%s/",
+		     get_super_prefix_or_empty(), path);
+	strvec_pushl(&cp.args, "read-tree", "--recurse-submodules", NULL);
+
+	if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
+		strvec_push(&cp.args, "-n");
+	else
+		strvec_push(&cp.args, "-u");
+
+	if (flags & SUBMODULE_MOVE_HEAD_FORCE)
+		strvec_push(&cp.args, "--reset");
+	else
+		strvec_push(&cp.args, "-m");
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_FORCE))
+		strvec_push(&cp.args, old_head ? old_head : empty_tree_oid_hex());
+
+	strvec_push(&cp.args, new_head ? new_head : empty_tree_oid_hex());
+
+	if (run_command(&cp)) {
+		ret = error(_("Submodule '%s' could not be updated."), path);
+		goto out;
+	}
+
+	if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
+		if (new_head) {
+			child_process_init(&cp);
+			/* also set the HEAD accordingly */
+			cp.git_cmd = 1;
+			cp.no_stdin = 1;
+			cp.dir = path;
+
+			prepare_submodule_repo_env(&cp.env);
+			strvec_pushl(&cp.args, "update-ref", "HEAD",
+				     "--no-deref", new_head, NULL);
+
+			if (run_command(&cp)) {
+				ret = -1;
+				goto out;
+			}
+		} else {
+			struct strbuf sb = STRBUF_INIT;
+
+			strbuf_addf(&sb, "%s/.git", path);
+			unlink_or_warn(sb.buf);
+			strbuf_release(&sb);
+
+			if (is_empty_dir(path))
+				rmdir_or_warn(path);
+
+			submodule_unset_core_worktree(sub);
+		}
+	}
+out:
+	return ret;
+}
+
+int validate_submodule_git_dir(char *git_dir, const char *submodule_name)
+{
+	size_t len = strlen(git_dir), suffix_len = strlen(submodule_name);
+	char *p;
+	int ret = 0;
+
+	if (len <= suffix_len || (p = git_dir + len - suffix_len)[-1] != '/' ||
+	    strcmp(p, submodule_name))
+		BUG("submodule name '%s' not a suffix of git dir '%s'",
+		    submodule_name, git_dir);
+
+	/*
+	 * We prevent the contents of sibling submodules' git directories to
+	 * clash.
+	 *
+	 * Example: having a submodule named `hippo` and another one named
+	 * `hippo/hooks` would result in the git directories
+	 * `.git/modules/hippo/` and `.git/modules/hippo/hooks/`, respectively,
+	 * but the latter directory is already designated to contain the hooks
+	 * of the former.
+	 */
+	for (; *p; p++) {
+		if (is_dir_sep(*p)) {
+			char c = *p;
+
+			*p = '\0';
+			if (is_git_directory(git_dir))
+				ret = -1;
+			*p = c;
+
+			if (ret < 0)
+				return error(_("submodule git dir '%s' is "
+					       "inside git dir '%.*s'"),
+					     git_dir,
+					     (int)(p - git_dir), git_dir);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Embeds a single submodules git directory into the superprojects git dir,
+ * non recursively.
+ */
+static void relocate_single_git_dir_into_superproject(const char *path)
+{
+	char *old_git_dir = NULL, *real_old_git_dir = NULL, *real_new_git_dir = NULL;
+	struct strbuf new_gitdir = STRBUF_INIT;
+	const struct submodule *sub;
+
+	if (submodule_uses_worktrees(path))
+		die(_("relocate_gitdir for submodule '%s' with "
+		      "more than one worktree not supported"), path);
+
+	old_git_dir = xstrfmt("%s/.git", path);
+	if (read_gitfile(old_git_dir))
+		/* If it is an actual gitfile, it doesn't need migration. */
+		return;
+
+	real_old_git_dir = real_pathdup(old_git_dir, 1);
+
+	sub = submodule_from_path(the_repository, null_oid(), path);
+	if (!sub)
+		die(_("could not lookup name for submodule '%s'"), path);
+
+	submodule_name_to_gitdir(&new_gitdir, the_repository, sub->name);
+	if (validate_submodule_git_dir(new_gitdir.buf, sub->name) < 0)
+		die(_("refusing to move '%s' into an existing git dir"),
+		    real_old_git_dir);
+	if (safe_create_leading_directories_const(new_gitdir.buf) < 0)
+		die(_("could not create directory '%s'"), new_gitdir.buf);
+	real_new_git_dir = real_pathdup(new_gitdir.buf, 1);
+
+	fprintf(stderr, _("Migrating git directory of '%s%s' from\n'%s' to\n'%s'\n"),
+		get_super_prefix_or_empty(), path,
+		real_old_git_dir, real_new_git_dir);
+
+	relocate_gitdir(path, real_old_git_dir, real_new_git_dir);
+
+	free(old_git_dir);
+	free(real_old_git_dir);
+	free(real_new_git_dir);
+	strbuf_release(&new_gitdir);
+}
+
+static void absorb_git_dir_into_superproject_recurse(const char *path)
+{
+
+	struct child_process cp = CHILD_PROCESS_INIT;
+
+	cp.dir = path;
+	cp.git_cmd = 1;
+	cp.no_stdin = 1;
+	strvec_pushf(&cp.args, "--super-prefix=%s%s/",
+		     get_super_prefix_or_empty(), path);
+	strvec_pushl(&cp.args, "submodule--helper",
+		     "absorbgitdirs", NULL);
+	prepare_submodule_repo_env(&cp.env);
+	if (run_command(&cp))
+		die(_("could not recurse into submodule '%s'"), path);
+}
+
+/*
+ * Migrate the git directory of the submodule given by path from
+ * having its git directory within the working tree to the git dir nested
+ * in its superprojects git dir under modules/.
+ */
+void absorb_git_dir_into_superproject(const char *path)
+{
+	int err_code;
+	const char *sub_git_dir;
+	struct strbuf gitdir = STRBUF_INIT;
+	strbuf_addf(&gitdir, "%s/.git", path);
+	sub_git_dir = resolve_gitdir_gently(gitdir.buf, &err_code);
+
+	/* Not populated? */
+	if (!sub_git_dir) {
+		const struct submodule *sub;
+		struct strbuf sub_gitdir = STRBUF_INIT;
+
+		if (err_code == READ_GITFILE_ERR_STAT_FAILED) {
+			/* unpopulated as expected */
+			strbuf_release(&gitdir);
+			return;
+		}
+
+		if (err_code != READ_GITFILE_ERR_NOT_A_REPO)
+			/* We don't know what broke here. */
+			read_gitfile_error_die(err_code, path, NULL);
+
+		/*
+		* Maybe populated, but no git directory was found?
+		* This can happen if the superproject is a submodule
+		* itself and was just absorbed. The absorption of the
+		* superproject did not rewrite the git file links yet,
+		* fix it now.
+		*/
+		sub = submodule_from_path(the_repository, null_oid(), path);
+		if (!sub)
+			die(_("could not lookup name for submodule '%s'"), path);
+		submodule_name_to_gitdir(&sub_gitdir, the_repository, sub->name);
+		connect_work_tree_and_git_dir(path, sub_gitdir.buf, 0);
+		strbuf_release(&sub_gitdir);
+	} else {
+		/* Is it already absorbed into the superprojects git dir? */
+		char *real_sub_git_dir = real_pathdup(sub_git_dir, 1);
+		char *real_common_git_dir = real_pathdup(get_git_common_dir(), 1);
+
+		if (!starts_with(real_sub_git_dir, real_common_git_dir))
+			relocate_single_git_dir_into_superproject(path);
+
+		free(real_sub_git_dir);
+		free(real_common_git_dir);
+	}
+	strbuf_release(&gitdir);
+
+	absorb_git_dir_into_superproject_recurse(path);
+}
+
+int get_superproject_working_tree(struct strbuf *buf)
+{
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	struct strbuf one_up = STRBUF_INIT;
+	char *cwd = xgetcwd();
+	int ret = 0;
+	const char *subpath;
+	int code;
+	ssize_t len;
+
+	if (!is_inside_work_tree())
+		/*
+		 * FIXME:
+		 * We might have a superproject, but it is harder
+		 * to determine.
+		 */
+		return 0;
+
+	if (!strbuf_realpath(&one_up, "../", 0))
+		return 0;
+
+	subpath = relative_path(cwd, one_up.buf, &sb);
+	strbuf_release(&one_up);
+
+	prepare_submodule_repo_env(&cp.env);
+	strvec_pop(&cp.env);
+
+	strvec_pushl(&cp.args, "--literal-pathspecs", "-C", "..",
+		     "ls-files", "-z", "--stage", "--full-name", "--",
+		     subpath, NULL);
+	strbuf_reset(&sb);
+
+	cp.no_stdin = 1;
+	cp.no_stderr = 1;
+	cp.out = -1;
+	cp.git_cmd = 1;
+
+	if (start_command(&cp))
+		die(_("could not start ls-files in .."));
+
+	len = strbuf_read(&sb, cp.out, PATH_MAX);
+	close(cp.out);
+
+	if (starts_with(sb.buf, "160000")) {
+		int super_sub_len;
+		int cwd_len = strlen(cwd);
+		char *super_sub, *super_wt;
+
+		/*
+		 * There is a superproject having this repo as a submodule.
+		 * The format is <mode> SP <hash> SP <stage> TAB <full name> \0,
+		 * We're only interested in the name after the tab.
+		 */
+		super_sub = strchr(sb.buf, '\t') + 1;
+		super_sub_len = strlen(super_sub);
+
+		if (super_sub_len > cwd_len ||
+		    strcmp(&cwd[cwd_len - super_sub_len], super_sub))
+			BUG("returned path string doesn't match cwd?");
+
+		super_wt = xstrdup(cwd);
+		super_wt[cwd_len - super_sub_len] = '\0';
+
+		strbuf_realpath(buf, super_wt, 1);
+		ret = 1;
+		free(super_wt);
+	}
+	free(cwd);
+	strbuf_release(&sb);
+
+	code = finish_command(&cp);
+
+	if (code == 128)
+		/* '../' is not a git repository */
+		return 0;
+	if (code == 0 && len == 0)
+		/* There is an unrelated git repository at '../' */
+		return 0;
+	if (code)
+		die(_("ls-tree returned unexpected return code %d"), code);
+
+	return ret;
+}
+
+/*
+ * Put the gitdir for a submodule (given relative to the main
+ * repository worktree) into `buf`, or return -1 on error.
+ */
+int submodule_to_gitdir(struct strbuf *buf, const char *submodule)
+{
+	const struct submodule *sub;
+	const char *git_dir;
+	int ret = 0;
+
+	strbuf_reset(buf);
+	strbuf_addstr(buf, submodule);
+	strbuf_complete(buf, '/');
+	strbuf_addstr(buf, ".git");
+
+	git_dir = read_gitfile(buf->buf);
+	if (git_dir) {
+		strbuf_reset(buf);
+		strbuf_addstr(buf, git_dir);
+	}
+	if (!is_git_directory(buf->buf)) {
+		sub = submodule_from_path(the_repository, null_oid(),
+					  submodule);
+		if (!sub) {
+			ret = -1;
+			goto cleanup;
+		}
+		strbuf_reset(buf);
+		submodule_name_to_gitdir(buf, the_repository, sub->name);
+	}
+
+cleanup:
+	return ret;
+}
+
+void submodule_name_to_gitdir(struct strbuf *buf, struct repository *r,
+			      const char *submodule_name)
+{
+	/*
+	 * NEEDSWORK: The current way of mapping a submodule's name to
+	 * its location in .git/modules/ has problems with some naming
+	 * schemes. For example, if a submodule is named "foo" and
+	 * another is named "foo/bar" (whether present in the same
+	 * superproject commit or not - the problem will arise if both
+	 * superproject commits have been checked out at any point in
+	 * time), or if two submodule names only have different cases in
+	 * a case-insensitive filesystem.
+	 *
+	 * There are several solutions, including encoding the path in
+	 * some way, introducing a submodule.<name>.gitdir config in
+	 * .git/config (not .gitmodules) that allows overriding what the
+	 * gitdir of a submodule would be (and teach Git, upon noticing
+	 * a clash, to automatically determine a non-clashing name and
+	 * to write such a config), or introducing a
+	 * submodule.<name>.gitdir config in .gitmodules that repo
+	 * administrators can explicitly set. Nothing has been decided,
+	 * so for now, just append the name at the end of the path.
+	 */
+	strbuf_repo_git_path(buf, r, "modules/");
+	strbuf_addstr(buf, submodule_name);
+}