Git 2.37.7

[git.git] / submodule.c

#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)
{
        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_strategy_to_string(const struct submodule_update_strategy *s)
{
        struct strbuf sb = STRBUF_INIT;
        switch (s->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:
                return NULL;
        case SM_UPDATE_COMMAND:
                strbuf_addf(&sb, "!%s", s->command);
                return strbuf_detach(&sb, NULL);
        }
        return NULL;
}

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, const struct object_id *oid,
                      int flags, void *cb_data)
{
        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");
                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, const struct object_id *oid,
                               int flags, 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;

        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_tr2(max_parallel_jobs,
                                   get_next_submodule,
                                   fetch_start_failure,
                                   fetch_finish,
                                   &spf,
                                   "submodule", "parallel/fetch");

        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,
                                        ABSORB_GITDIR_RECURSE_SUBMODULES);
                } 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);
}

/*
 * 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,
                                      unsigned flags)
{
        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);

        if (flags & ABSORB_GITDIR_RECURSE_SUBMODULES) {
                struct child_process cp = CHILD_PROCESS_INIT;
                struct strbuf sb = STRBUF_INIT;

                if (flags & ~ABSORB_GITDIR_RECURSE_SUBMODULES)
                        BUG("we don't know how to pass the flags down?");

                strbuf_addstr(&sb, get_super_prefix_or_empty());
                strbuf_addstr(&sb, path);
                strbuf_addch(&sb, '/');

                cp.dir = path;
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                strvec_pushl(&cp.args, "--super-prefix", sb.buf,
                             "submodule--helper",
                             "absorb-git-dirs", NULL);
                prepare_submodule_repo_env(&cp.env);
                if (run_command(&cp))
                        die(_("could not recurse into submodule '%s'"), path);

                strbuf_release(&sb);
        }
}

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;
        const 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);
        }
        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);
}