apply: handle Subversion diffs with /dev/null gracefully

[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 "sha1-array.h"
#include "argv-array.h"
#include "blob.h"
#include "thread-utils.h"
#include "quote.h"
#include "remote.h"
#include "worktree.h"
#include "parse-options.h"

static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
static int config_update_recurse_submodules = RECURSE_SUBMODULES_OFF;
static int parallel_jobs = 1;
static struct string_list changed_submodule_paths = STRING_LIST_INIT_DUP;
static int initialized_fetch_ref_tips;
static struct oid_array ref_tips_before_fetch;
static struct oid_array ref_tips_after_fetch;

/*
 * The following flag is set if the .gitmodules file is unmerged. We then
 * disable recursion for all submodules where .git/config doesn't have a
 * matching config entry because we can't guess what might be configured in
 * .gitmodules unless the user resolves the conflict. When a command line
 * option is given (which always overrides configuration) this flag will be
 * ignored.
 */
static int gitmodules_is_unmerged;

/*
 * This flag is set if the .gitmodules file had unstaged modifications on
 * startup. 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.
 */
static int gitmodules_is_modified;

int is_staging_gitmodules_ok(void)
{
        return !gitmodules_is_modified;
}

/*
 * 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;

        if (!file_exists(".gitmodules")) /* Do nothing without .gitmodules */
                return -1;

        if (gitmodules_is_unmerged)
                die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));

        submodule = submodule_from_path(null_sha1, 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");
        if (git_config_set_in_file_gently(".gitmodules", entry.buf, newpath) < 0) {
                /* Maybe the user already did that, don't error out here */
                warning(_("Could not update .gitmodules entry %s"), entry.buf);
                strbuf_release(&entry);
                return -1;
        }
        strbuf_release(&entry);
        return 0;
}

/*
 * 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")) /* Do nothing without .gitmodules */
                return -1;

        if (gitmodules_is_unmerged)
                die(_("Cannot change unmerged .gitmodules, resolve merge conflicts first"));

        submodule = submodule_from_path(null_sha1, 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", 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(void)
{
        if (add_file_to_cache(".gitmodules", 0))
                die(_("staging updated .gitmodules failed"));
}

static int add_submodule_odb(const char *path)
{
        struct strbuf objects_directory = STRBUF_INIT;
        int ret = 0;

        ret = strbuf_git_path_submodule(&objects_directory, path, "objects/");
        if (ret)
                goto done;
        if (!is_directory(objects_directory.buf)) {
                ret = -1;
                goto done;
        }
        add_to_alternates_memory(objects_directory.buf);
done:
        strbuf_release(&objects_directory);
        return ret;
}

void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
                                             const char *path)
{
        const struct submodule *submodule = submodule_from_path(null_sha1, path);
        if (submodule) {
                if (submodule->ignore)
                        handle_ignore_submodules_arg(diffopt, submodule->ignore);
                else if (gitmodules_is_unmerged)
                        DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
        }
}

/* For loading from the .gitmodules file. */
static int git_modules_config(const char *var, const char *value, void *cb)
{
        if (!strcmp(var, "submodule.fetchjobs")) {
                parallel_jobs = git_config_int(var, value);
                if (parallel_jobs < 0)
                        die(_("negative values not allowed for submodule.fetchJobs"));
                return 0;
        } else if (starts_with(var, "submodule."))
                return parse_submodule_config_option(var, value);
        else if (!strcmp(var, "fetch.recursesubmodules")) {
                config_fetch_recurse_submodules = parse_fetch_recurse_submodules_arg(var, value);
                return 0;
        }
        return 0;
}

/* Loads all submodule settings from the config. */
int 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;
        } else {
                return git_modules_config(var, value, cb);
        }
}

/* 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;
}

void load_submodule_cache(void)
{
        if (config_update_recurse_submodules == RECURSE_SUBMODULES_OFF)
                return;

        gitmodules_config();
        git_config(submodule_config, NULL);
}

void gitmodules_config(void)
{
        const char *work_tree = get_git_work_tree();
        if (work_tree) {
                struct strbuf gitmodules_path = STRBUF_INIT;
                int pos;
                strbuf_addstr(&gitmodules_path, work_tree);
                strbuf_addstr(&gitmodules_path, "/.gitmodules");
                if (read_cache() < 0)
                        die("index file corrupt");
                pos = cache_name_pos(".gitmodules", 11);
                if (pos < 0) { /* .gitmodules not found or isn't merged */
                        pos = -1 - pos;
                        if (active_nr > pos) {  /* there is a .gitmodules */
                                const struct cache_entry *ce = active_cache[pos];
                                if (ce_namelen(ce) == 11 &&
                                    !memcmp(ce->name, ".gitmodules", 11))
                                        gitmodules_is_unmerged = 1;
                        }
                } else if (pos < active_nr) {
                        struct stat st;
                        if (lstat(".gitmodules", &st) == 0 &&
                            ce_match_stat(active_cache[pos], &st, 0) & DATA_CHANGED)
                                gitmodules_is_modified = 1;
                }

                if (!gitmodules_is_unmerged)
                        git_config_from_file(git_modules_config,
                                gitmodules_path.buf, NULL);
                strbuf_release(&gitmodules_path);
        }
}

static int gitmodules_cb(const char *var, const char *value, void *data)
{
        struct repository *repo = data;
        return submodule_config_option(repo, var, value);
}

void repo_read_gitmodules(struct repository *repo)
{
        char *gitmodules_path = repo_worktree_path(repo, ".gitmodules");

        git_config_from_file(gitmodules_cb, gitmodules_path, repo);
        free(gitmodules_path);
}

void gitmodules_config_sha1(const unsigned char *commit_sha1)
{
        struct strbuf rev = STRBUF_INIT;
        unsigned char sha1[20];

        if (gitmodule_sha1_from_commit(commit_sha1, sha1, &rev)) {
                git_config_from_blob_sha1(git_modules_config, rev.buf,
                                          sha1, NULL);
        }
        strbuf_release(&rev);
}

/*
 * Determine if a submodule has been initialized at a given 'path'
 */
int is_submodule_active(struct repository *repo, const char *path)
{
        int ret = 0;
        char *key = NULL;
        char *value = NULL;
        const struct string_list *sl;
        const struct submodule *module;

        module = submodule_from_cache(repo, null_sha1, 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 argv_array args = ARGV_ARRAY_INIT;
                const struct string_list_item *item;

                for_each_string_list_item(item, sl) {
                        argv_array_push(&args, item->string);
                }

                parse_pathspec(&ps, 0, 0, NULL, args.argv);
                ret = match_pathspec(&ps, path, strlen(path), 0, NULL, 1);

                argv_array_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_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(const 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(const 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);
                }
        }
}

int parse_submodule_update_strategy(const char *value,
                struct submodule_update_strategy *dst)
{
        free((void*)dst->command);
        dst->command = NULL;
        if (!strcmp(value, "none"))
                dst->type = SM_UPDATE_NONE;
        else if (!strcmp(value, "checkout"))
                dst->type = SM_UPDATE_CHECKOUT;
        else if (!strcmp(value, "rebase"))
                dst->type = SM_UPDATE_REBASE;
        else if (!strcmp(value, "merge"))
                dst->type = SM_UPDATE_MERGE;
        else if (skip_prefix(value, "!", &value)) {
                dst->type = SM_UPDATE_COMMAND;
                dst->command = xstrdup(value);
        } else
                return -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)
{
        DIFF_OPT_CLR(diffopt, IGNORE_SUBMODULES);
        DIFF_OPT_CLR(diffopt, IGNORE_UNTRACKED_IN_SUBMODULES);
        DIFF_OPT_CLR(diffopt, IGNORE_DIRTY_SUBMODULES);

        if (!strcmp(arg, "all"))
                DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
        else if (!strcmp(arg, "untracked"))
                DIFF_OPT_SET(diffopt, IGNORE_UNTRACKED_IN_SUBMODULES);
        else if (!strcmp(arg, "dirty"))
                DIFF_OPT_SET(diffopt, IGNORE_DIRTY_SUBMODULES);
        else if (strcmp(arg, "none"))
                die("bad --ignore-submodules argument: %s", arg);
}

static int prepare_submodule_summary(struct rev_info *rev, const char *path,
                struct commit *left, struct commit *right,
                struct commit_list *merge_bases)
{
        struct commit_list *list;

        init_revisions(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_summary(struct rev_info *rev, FILE *f,
                const char *line_prefix,
                const char *del, const char *add, const char *reset)
{
        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);
                strbuf_addstr(&sb, line_prefix);
                if (commit->object.flags & SYMMETRIC_LEFT) {
                        if (del)
                                strbuf_addstr(&sb, del);
                }
                else if (add)
                        strbuf_addstr(&sb, add);
                format_commit_message(commit, format, &sb, &ctx);
                if (reset)
                        strbuf_addstr(&sb, reset);
                strbuf_addch(&sb, '\n');
                fprintf(f, "%s", sb.buf);
        }
        strbuf_release(&sb);
}

static void prepare_submodule_repo_env_no_git_dir(struct argv_array *out)
{
        const char * const *var;

        for (var = local_repo_env; *var; var++) {
                if (strcmp(*var, CONFIG_DATA_ENVIRONMENT))
                        argv_array_push(out, *var);
        }
}

void prepare_submodule_repo_env(struct argv_array *out)
{
        prepare_submodule_repo_env_no_git_dir(out);
        argv_array_pushf(out, "%s=%s", GIT_DIR_ENVIRONMENT,
                         DEFAULT_GIT_DIR_ENVIRONMENT);
}

/* Helper function to display the submodule header line prior to the full
 * summary output. If it can locate the submodule objects directory it will
 * attempt to lookup both the left and right commits and put them into the
 * left and right pointers.
 */
static void show_submodule_header(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *reset,
                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)
                fprintf(f, "%sSubmodule %s contains untracked content\n",
                        line_prefix, path);
        if (dirty_submodule & DIRTY_SUBMODULE_MODIFIED)
                fprintf(f, "%sSubmodule %s contains modified content\n",
                        line_prefix, path);

        if (is_null_oid(one))
                message = "(new submodule)";
        else if (is_null_oid(two))
                message = "(submodule deleted)";

        if (add_submodule_odb(path)) {
                if (!message)
                        message = "(not initialized)";
                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(one);
        *right = lookup_commit_reference(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 = get_merge_bases(*left, *right);
        if (*merge_bases) {
                if ((*merge_bases)->item == *left)
                        fast_forward = 1;
                else if ((*merge_bases)->item == *right)
                        fast_backward = 1;
        }

        if (!oidcmp(one, two)) {
                strbuf_release(&sb);
                return;
        }

output_header:
        strbuf_addf(&sb, "%s%sSubmodule %s ", line_prefix, meta, path);
        strbuf_add_unique_abbrev(&sb, one->hash, DEFAULT_ABBREV);
        strbuf_addstr(&sb, (fast_backward || fast_forward) ? ".." : "...");
        strbuf_add_unique_abbrev(&sb, two->hash, DEFAULT_ABBREV);
        if (message)
                strbuf_addf(&sb, " %s%s\n", message, reset);
        else
                strbuf_addf(&sb, "%s:%s\n", fast_backward ? " (rewind)" : "", reset);
        fwrite(sb.buf, sb.len, 1, f);

        strbuf_release(&sb);
}

void show_submodule_summary(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *del, const char *add, const char *reset)
{
        struct rev_info rev;
        struct commit *left = NULL, *right = NULL;
        struct commit_list *merge_bases = NULL;

        show_submodule_header(f, path, line_prefix, one, two, dirty_submodule,
                              meta, reset, &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)
                goto out;

        /* Treat revision walker failure the same as missing commits */
        if (prepare_submodule_summary(&rev, path, left, right, merge_bases)) {
                fprintf(f, "%s(revision walker failed)\n", line_prefix);
                goto out;
        }

        print_submodule_summary(&rev, f, line_prefix, del, add, reset);

out:
        if (merge_bases)
                free_commit_list(merge_bases);
        clear_commit_marks(left, ~0);
        clear_commit_marks(right, ~0);
}

void show_submodule_inline_diff(FILE *f, const char *path,
                const char *line_prefix,
                struct object_id *one, struct object_id *two,
                unsigned dirty_submodule, const char *meta,
                const char *del, const char *add, const char *reset,
                const struct diff_options *o)
{
        const struct object_id *old = &empty_tree_oid, *new = &empty_tree_oid;
        struct commit *left = NULL, *right = NULL;
        struct commit_list *merge_bases = NULL;
        struct strbuf submodule_dir = STRBUF_INIT;
        struct child_process cp = CHILD_PROCESS_INIT;

        show_submodule_header(f, path, line_prefix, one, two, dirty_submodule,
                              meta, reset, &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 = one;
        if (right)
                new = two;

        fflush(f);
        cp.git_cmd = 1;
        cp.dir = path;
        cp.out = dup(fileno(f));
        cp.no_stdin = 1;

        /* TODO: other options may need to be passed here. */
        argv_array_pushl(&cp.args, "diff", "--submodule=diff", NULL);

        argv_array_pushf(&cp.args, "--line-prefix=%s", line_prefix);
        if (DIFF_OPT_TST(o, REVERSE_DIFF)) {
                argv_array_pushf(&cp.args, "--src-prefix=%s%s/",
                                 o->b_prefix, path);
                argv_array_pushf(&cp.args, "--dst-prefix=%s%s/",
                                 o->a_prefix, path);
        } else {
                argv_array_pushf(&cp.args, "--src-prefix=%s%s/",
                                 o->a_prefix, path);
                argv_array_pushf(&cp.args, "--dst-prefix=%s%s/",
                                 o->b_prefix, path);
        }
        argv_array_push(&cp.args, oid_to_hex(old));
        /*
         * 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))
                argv_array_push(&cp.args, oid_to_hex(new));

        prepare_submodule_repo_env(&cp.env_array);
        if (run_command(&cp))
                fprintf(f, "(diff failed)\n");

done:
        strbuf_release(&submodule_dir);
        if (merge_bases)
                free_commit_list(merge_bases);
        if (left)
                clear_commit_marks(left, ~0);
        if (right)
                clear_commit_marks(right, ~0);
}

void set_config_fetch_recurse_submodules(int value)
{
        config_fetch_recurse_submodules = value;
}

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(null_sha1, ce->name);
}

static struct oid_array *submodule_commits(struct string_list *submodules,
                                           const char *path)
{
        struct string_list_item *item;

        item = string_list_insert(submodules, path);
        if (item->util)
                return (struct oid_array *) item->util;

        /* NEEDSWORK: should we have oid_array_init()? */
        item->util = xcalloc(1, sizeof(struct oid_array));
        return (struct oid_array *) item->util;
}

static void collect_changed_submodules_cb(struct diff_queue_struct *q,
                                          struct diff_options *options,
                                          void *data)
{
        int i;
        struct string_list *changed = data;

        for (i = 0; i < q->nr; i++) {
                struct diff_filepair *p = q->queue[i];
                struct oid_array *commits;
                if (!S_ISGITLINK(p->two->mode))
                        continue;

                if (S_ISGITLINK(p->one->mode)) {
                        /*
                         * NEEDSWORK: We should honor the name configured in
                         * the .gitmodules file of the commit we are examining
                         * here to be able to correctly follow submodules
                         * being moved around.
                         */
                        commits = submodule_commits(changed, p->two->path);
                        oid_array_append(commits, &p->two->oid);
                } else {
                        /* Submodule is new or was moved here */
                        /*
                         * NEEDSWORK: When the .git directories of submodules
                         * live inside the superprojects .git directory some
                         * day we should fetch new submodules directly into
                         * that location too when config or options request
                         * that so they can be checked out from there.
                         */
                        continue;
                }
        }
}

/*
 * 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 string_list *changed,
                                       struct argv_array *argv)
{
        struct rev_info rev;
        const struct commit *commit;

        init_revisions(&rev, NULL);
        setup_revisions(argv->argc, argv->argv, &rev, NULL);
        if (prepare_revision_walk(&rev))
                die("revision walk setup failed");

        while ((commit = get_revision(&rev))) {
                struct rev_info diff_rev;

                init_revisions(&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 = changed;
                diff_tree_combined_merge(commit, 1, &diff_rev);
        }

        reset_revision_walk();
}

static void free_submodules_oids(struct string_list *submodules)
{
        struct string_list_item *item;
        for_each_string_list_item(item, submodules)
                oid_array_clear((struct oid_array *) 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 argv_array *argv = data;
        argv_array_push(argv, oid_to_hex(oid));
        return 0;
}

static int check_has_commit(const struct object_id *oid, void *data)
{
        int *has_commit = data;

        if (!lookup_commit_reference(oid))
                *has_commit = 0;

        return 0;
}

static int submodule_has_commits(const char *path, struct oid_array *commits)
{
        int has_commit = 1;

        /*
         * Perform a cheap, but incorrect check for the existence of 'commits'.
         * This is done by adding the submodule's object store to the in-core
         * object store, and then querying for each commit's existence.  If we
         * do not have the commit object anywhere, there is no chance we have
         * it in the object store of the correct submodule and have it
         * reachable from a ref, so we can fail early without spawning rev-list
         * which is expensive.
         */
        if (add_submodule_odb(path))
                return 0;

        oid_array_for_each_unique(commits, check_has_commit, &has_commit);

        if (has_commit) {
                /*
                 * 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;

                argv_array_pushl(&cp.args, "rev-list", "-n", "1", NULL);
                oid_array_for_each_unique(commits, append_oid_to_argv, &cp.args);
                argv_array_pushl(&cp.args, "--not", "--all", NULL);

                prepare_submodule_repo_env(&cp.env_array);
                cp.git_cmd = 1;
                cp.no_stdin = 1;
                cp.dir = path;

                if (capture_command(&cp, &out, GIT_MAX_HEXSZ + 1) || out.len)
                        has_commit = 0;

                strbuf_release(&out);
        }

        return has_commit;
}

static int submodule_needs_pushing(const char *path, struct oid_array *commits)
{
        if (!submodule_has_commits(path, 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;

                argv_array_push(&cp.args, "rev-list");
                oid_array_for_each_unique(commits, append_oid_to_argv, &cp.args);
                argv_array_pushl(&cp.args, "--not", "--remotes", "-n", "1" , NULL);

                prepare_submodule_repo_env(&cp.env_array);
                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, 41))
                        needs_pushing = 1;
                finish_command(&cp);
                close(cp.out);
                strbuf_release(&buf);
                return needs_pushing;
        }

        return 0;
}

int find_unpushed_submodules(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 *submodule;
        struct argv_array argv = ARGV_ARRAY_INIT;

        /* argv.argv[0] will be ignored by setup_revisions */
        argv_array_push(&argv, "find_unpushed_submodules");
        oid_array_for_each_unique(commits, append_oid_to_argv, &argv);
        argv_array_push(&argv, "--not");
        argv_array_pushf(&argv, "--remotes=%s", remotes_name);

        collect_changed_submodules(&submodules, &argv);

        for_each_string_list_item(submodule, &submodules) {
                struct oid_array *commits = submodule->util;
                const char *path = submodule->string;

                if (submodule_needs_pushing(path, commits))
                        string_list_insert(needs_pushing, path);
        }

        free_submodules_oids(&submodules);
        argv_array_clear(&argv);

        return needs_pushing->nr;
}

static int push_submodule(const char *path,
                          const struct remote *remote,
                          const char **refspec, int refspec_nr,
                          const struct string_list *push_options,
                          int dry_run)
{
        if (add_submodule_odb(path))
                return 1;

        if (for_each_remote_ref_submodule(path, has_remote, NULL) > 0) {
                struct child_process cp = CHILD_PROCESS_INIT;
                argv_array_push(&cp.args, "push");
                if (dry_run)
                        argv_array_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)
                                argv_array_pushf(&cp.args, "--push-option=%s",
                                                 item->string);
                }

                if (remote->origin != REMOTE_UNCONFIGURED) {
                        int i;
                        argv_array_push(&cp.args, remote->name);
                        for (i = 0; i < refspec_nr; i++)
                                argv_array_push(&cp.args, refspec[i]);
                }

                prepare_submodule_repo_env(&cp.env_array);
                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 char **refspec, int refspec_nr)
{
        struct child_process cp = CHILD_PROCESS_INIT;
        int i;

        argv_array_push(&cp.args, "submodule--helper");
        argv_array_push(&cp.args, "push-check");
        argv_array_push(&cp.args, head);
        argv_array_push(&cp.args, remote->name);

        for (i = 0; i < refspec_nr; i++)
                argv_array_push(&cp.args, refspec[i]);

        prepare_submodule_repo_env(&cp.env_array);
        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 oid_array *commits,
                             const struct remote *remote,
                             const char **refspec, int refspec_nr,
                             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(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.hash, 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,
                                             refspec, refspec_nr);
                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, refspec, refspec_nr,
                                    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);
}

static void calculate_changed_submodule_paths(void)
{
        struct argv_array argv = ARGV_ARRAY_INIT;
        struct string_list changed_submodules = STRING_LIST_INIT_DUP;
        const struct string_list_item *item;

        /* No need to check if there are no submodules configured */
        if (!submodule_from_path(NULL, NULL))
                return;

        argv_array_push(&argv, "--"); /* argv[0] program name */
        oid_array_for_each_unique(&ref_tips_after_fetch,
                                   append_oid_to_argv, &argv);
        argv_array_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_paths".
         */
        collect_changed_submodules(&changed_submodules, &argv);

        for_each_string_list_item(item, &changed_submodules) {
                struct oid_array *commits = item->util;
                const char *path = item->string;

                if (!submodule_has_commits(path, commits))
                        string_list_append(&changed_submodule_paths, path);
        }

        free_submodules_oids(&changed_submodules);
        argv_array_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 object_id *excl_oid,
                               struct object_id *incl_oid)
{
        struct string_list subs = STRING_LIST_INIT_DUP;
        struct argv_array args = ARGV_ARRAY_INIT;
        int ret;

        gitmodules_config();
        /* No need to check if there are no submodules configured */
        if (!submodule_from_path(NULL, NULL))
                return 0;

        argv_array_push(&args, "--"); /* args[0] program name */
        argv_array_push(&args, oid_to_hex(incl_oid));
        argv_array_push(&args, "--not");
        argv_array_push(&args, oid_to_hex(excl_oid));

        collect_changed_submodules(&subs, &args);
        ret = subs.nr;

        argv_array_clear(&args);

        free_submodules_oids(&subs);
        return ret;
}

struct submodule_parallel_fetch {
        int count;
        struct argv_array args;
        const char *work_tree;
        const char *prefix;
        int command_line_option;
        int quiet;
        int result;
};
#define SPF_INIT {0, ARGV_ARRAY_INIT, NULL, NULL, 0, 0, 0}

static int get_next_submodule(struct child_process *cp,
                              struct strbuf *err, void *data, void **task_cb)
{
        int ret = 0;
        struct submodule_parallel_fetch *spf = data;

        for (; spf->count < active_nr; spf->count++) {
                struct strbuf submodule_path = STRBUF_INIT;
                struct strbuf submodule_git_dir = STRBUF_INIT;
                struct strbuf submodule_prefix = STRBUF_INIT;
                const struct cache_entry *ce = active_cache[spf->count];
                const char *git_dir, *default_argv;
                const struct submodule *submodule;

                if (!S_ISGITLINK(ce->ce_mode))
                        continue;

                submodule = submodule_from_path(null_sha1, ce->name);
                if (!submodule)
                        submodule = submodule_from_name(null_sha1, ce->name);

                default_argv = "yes";
                if (spf->command_line_option == RECURSE_SUBMODULES_DEFAULT) {
                        if (submodule &&
                            submodule->fetch_recurse !=
                                                RECURSE_SUBMODULES_NONE) {
                                if (submodule->fetch_recurse ==
                                                RECURSE_SUBMODULES_OFF)
                                        continue;
                                if (submodule->fetch_recurse ==
                                                RECURSE_SUBMODULES_ON_DEMAND) {
                                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                                continue;
                                        default_argv = "on-demand";
                                }
                        } else {
                                if ((config_fetch_recurse_submodules == RECURSE_SUBMODULES_OFF) ||
                                    gitmodules_is_unmerged)
                                        continue;
                                if (config_fetch_recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND) {
                                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                                continue;
                                        default_argv = "on-demand";
                                }
                        }
                } else if (spf->command_line_option == RECURSE_SUBMODULES_ON_DEMAND) {
                        if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))
                                continue;
                        default_argv = "on-demand";
                }

                strbuf_addf(&submodule_path, "%s/%s", spf->work_tree, ce->name);
                strbuf_addf(&submodule_git_dir, "%s/.git", submodule_path.buf);
                strbuf_addf(&submodule_prefix, "%s%s/", spf->prefix, ce->name);
                git_dir = read_gitfile(submodule_git_dir.buf);
                if (!git_dir)
                        git_dir = submodule_git_dir.buf;
                if (is_directory(git_dir)) {
                        child_process_init(cp);
                        cp->dir = strbuf_detach(&submodule_path, NULL);
                        prepare_submodule_repo_env(&cp->env_array);
                        cp->git_cmd = 1;
                        if (!spf->quiet)
                                strbuf_addf(err, "Fetching submodule %s%s\n",
                                            spf->prefix, ce->name);
                        argv_array_init(&cp->args);
                        argv_array_pushv(&cp->args, spf->args.argv);
                        argv_array_push(&cp->args, default_argv);
                        argv_array_push(&cp->args, "--submodule-prefix");
                        argv_array_push(&cp->args, submodule_prefix.buf);
                        ret = 1;
                }
                strbuf_release(&submodule_path);
                strbuf_release(&submodule_git_dir);
                strbuf_release(&submodule_prefix);
                if (ret) {
                        spf->count++;
                        return 1;
                }
        }
        return 0;
}

static int fetch_start_failure(struct strbuf *err,
                               void *cb, void *task_cb)
{
        struct submodule_parallel_fetch *spf = cb;

        spf->result = 1;

        return 0;
}

static int fetch_finish(int retvalue, struct strbuf *err,
                        void *cb, void *task_cb)
{
        struct submodule_parallel_fetch *spf = cb;

        if (retvalue)
                spf->result = 1;

        return 0;
}

int fetch_populated_submodules(const struct argv_array *options,
                               const char *prefix, int command_line_option,
                               int quiet, int max_parallel_jobs)
{
        int i;
        struct submodule_parallel_fetch spf = SPF_INIT;

        spf.work_tree = get_git_work_tree();
        spf.command_line_option = command_line_option;
        spf.quiet = quiet;
        spf.prefix = prefix;

        if (!spf.work_tree)
                goto out;

        if (read_cache() < 0)
                die("index file corrupt");

        argv_array_push(&spf.args, "fetch");
        for (i = 0; i < options->argc; i++)
                argv_array_push(&spf.args, options->argv[i]);
        argv_array_push(&spf.args, "--recurse-submodules-default");
        /* default value, "--submodule-prefix" and its value are added later */

        if (max_parallel_jobs < 0)
                max_parallel_jobs = parallel_jobs;

        calculate_changed_submodule_paths();
        run_processes_parallel(max_parallel_jobs,
                               get_next_submodule,
                               fetch_start_failure,
                               fetch_finish,
                               &spf);

        argv_array_clear(&spf.args);
out:
        string_list_clear(&changed_submodule_paths, 1);
        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);

        argv_array_pushl(&cp.args, "status", "--porcelain=2", NULL);
        if (ignore_untracked)
                argv_array_push(&cp.args, "-uno");

        prepare_submodule_repo_env(&cp.env_array);
        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"))
                                die("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;
        const char *argv[] = {
                "submodule",
                "foreach",
                "--quiet",
                "--recursive",
                "test -f .git",
                NULL,
        };
        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 */
        cp.argv = argv;
        prepare_submodule_repo_env(&cp.env_array);
        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;

        argv_array_pushl(&cp.args, "status", "--porcelain",
                                   "--ignore-submodules=none", NULL);

        if (flags & SUBMODULE_REMOVAL_IGNORE_UNTRACKED)
                argv_array_push(&cp.args, "-uno");
        else
                argv_array_push(&cp.args, "-uall");

        if (!(flags & SUBMODULE_REMOVAL_IGNORE_IGNORED_UNTRACKED))
                argv_array_push(&cp.args, "--ignored");

        prepare_submodule_repo_env(&cp.env_array);
        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;
}

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_array);

        cp.git_cmd = 1;
        argv_array_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_array);

        cp.git_cmd = 1;
        cp.no_stdin = 1;
        cp.dir = path;

        argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
                                   get_super_prefix_or_empty(), path);
        argv_array_pushl(&cp.args, "read-tree", "-u", "--reset", NULL);

        argv_array_push(&cp.args, EMPTY_TREE_SHA1_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,
                         const char *new,
                         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 && !is_submodule_populated_gently(path, error_code_ptr))
                return 0;

        sub = submodule_from_path(null_sha1, path);

        if (!sub)
                die("BUG: could not get submodule information for '%s'", path);

        if (old && !(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) {
                        if (!submodule_uses_gitfile(path))
                                absorb_git_dir_into_superproject("", path,
                                        ABSORB_GITDIR_RECURSE_SUBMODULES);
                } else {
                        char *gitdir = xstrfmt("%s/modules/%s",
                                    get_git_common_dir(), sub->name);
                        connect_work_tree_and_git_dir(path, gitdir);
                        free(gitdir);

                        /* make sure the index is clean as well */
                        submodule_reset_index(path);
                }

                if (old && (flags & SUBMODULE_MOVE_HEAD_FORCE)) {
                        char *gitdir = xstrfmt("%s/modules/%s",
                                    get_git_common_dir(), sub->name);
                        connect_work_tree_and_git_dir(path, gitdir);
                        free(gitdir);
                }
        }

        prepare_submodule_repo_env(&cp.env_array);

        cp.git_cmd = 1;
        cp.no_stdin = 1;
        cp.dir = path;

        argv_array_pushf(&cp.args, "--super-prefix=%s%s/",
                        get_super_prefix_or_empty(), path);
        argv_array_pushl(&cp.args, "read-tree", "--recurse-submodules", NULL);

        if (flags & SUBMODULE_MOVE_HEAD_DRY_RUN)
                argv_array_push(&cp.args, "-n");
        else
                argv_array_push(&cp.args, "-u");

        if (flags & SUBMODULE_MOVE_HEAD_FORCE)
                argv_array_push(&cp.args, "--reset");
        else
                argv_array_push(&cp.args, "-m");

        argv_array_push(&cp.args, old ? old : EMPTY_TREE_SHA1_HEX);
        argv_array_push(&cp.args, new ? new : EMPTY_TREE_SHA1_HEX);

        if (run_command(&cp)) {
                ret = -1;
                goto out;
        }

        if (!(flags & SUBMODULE_MOVE_HEAD_DRY_RUN)) {
                if (new) {
                        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_array);
                        argv_array_pushl(&cp.args, "update-ref", "HEAD", new, 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);
                }
        }
out:
        return ret;
}

static int find_first_merges(struct object_array *result, const char *path,
                struct commit *a, struct commit *b)
{
        int i, j;
        struct object_array merges = OBJECT_ARRAY_INIT;
        struct commit *commit;
        int contains_another;

        char merged_revision[42];
        const char *rev_args[] = { "rev-list", "--merges", "--ancestry-path",
                                   "--all", merged_revision, NULL };
        struct rev_info revs;
        struct setup_revision_opt rev_opts;

        memset(result, 0, sizeof(struct object_array));
        memset(&rev_opts, 0, sizeof(rev_opts));

        /* get all revisions that merge commit a */
        xsnprintf(merged_revision, sizeof(merged_revision), "^%s",
                        oid_to_hex(&a->object.oid));
        init_revisions(&revs, NULL);
        rev_opts.submodule = path;
        setup_revisions(ARRAY_SIZE(rev_args)-1, rev_args, &revs, &rev_opts);

        /* save all revisions from the above list that contain b */
        if (prepare_revision_walk(&revs))
                die("revision walk setup failed");
        while ((commit = get_revision(&revs)) != NULL) {
                struct object *o = &(commit->object);
                if (in_merge_bases(b, commit))
                        add_object_array(o, NULL, &merges);
        }
        reset_revision_walk();

        /* Now we've got all merges that contain a and b. Prune all
         * merges that contain another found merge and save them in
         * result.
         */
        for (i = 0; i < merges.nr; i++) {
                struct commit *m1 = (struct commit *) merges.objects[i].item;

                contains_another = 0;
                for (j = 0; j < merges.nr; j++) {
                        struct commit *m2 = (struct commit *) merges.objects[j].item;
                        if (i != j && in_merge_bases(m2, m1)) {
                                contains_another = 1;
                                break;
                        }
                }

                if (!contains_another)
                        add_object_array(merges.objects[i].item, NULL, result);
        }

        free(merges.objects);
        return result->nr;
}

static void print_commit(struct commit *commit)
{
        struct strbuf sb = STRBUF_INIT;
        struct pretty_print_context ctx = {0};
        ctx.date_mode.type = DATE_NORMAL;
        format_commit_message(commit, " %h: %m %s", &sb, &ctx);
        fprintf(stderr, "%s\n", sb.buf);
        strbuf_release(&sb);
}

#define MERGE_WARNING(path, msg) \
        warning("Failed to merge submodule %s (%s)", path, msg);

int merge_submodule(struct object_id *result, const char *path,
                    const struct object_id *base, const struct object_id *a,
                    const struct object_id *b, int search)
{
        struct commit *commit_base, *commit_a, *commit_b;
        int parent_count;
        struct object_array merges;

        int i;

        /* store a in result in case we fail */
        oidcpy(result, a);

        /* we can not handle deletion conflicts */
        if (is_null_oid(base))
                return 0;
        if (is_null_oid(a))
                return 0;
        if (is_null_oid(b))
                return 0;

        if (add_submodule_odb(path)) {
                MERGE_WARNING(path, "not checked out");
                return 0;
        }

        if (!(commit_base = lookup_commit_reference(base)) ||
            !(commit_a = lookup_commit_reference(a)) ||
            !(commit_b = lookup_commit_reference(b))) {
                MERGE_WARNING(path, "commits not present");
                return 0;
        }

        /* check whether both changes are forward */
        if (!in_merge_bases(commit_base, commit_a) ||
            !in_merge_bases(commit_base, commit_b)) {
                MERGE_WARNING(path, "commits don't follow merge-base");
                return 0;
        }

        /* Case #1: a is contained in b or vice versa */
        if (in_merge_bases(commit_a, commit_b)) {
                oidcpy(result, b);
                return 1;
        }
        if (in_merge_bases(commit_b, commit_a)) {
                oidcpy(result, a);
                return 1;
        }

        /*
         * Case #2: There are one or more merges that contain a and b in
         * the submodule. If there is only one, then present it as a
         * suggestion to the user, but leave it marked unmerged so the
         * user needs to confirm the resolution.
         */

        /* Skip the search if makes no sense to the calling context.  */
        if (!search)
                return 0;

        /* find commit which merges them */
        parent_count = find_first_merges(&merges, path, commit_a, commit_b);
        switch (parent_count) {
        case 0:
                MERGE_WARNING(path, "merge following commits not found");
                break;

        case 1:
                MERGE_WARNING(path, "not fast-forward");
                fprintf(stderr, "Found a possible merge resolution "
                                "for the submodule:\n");
                print_commit((struct commit *) merges.objects[0].item);
                fprintf(stderr,
                        "If this is correct simply add it to the index "
                        "for example\n"
                        "by using:\n\n"
                        "  git update-index --cacheinfo 160000 %s \"%s\"\n\n"
                        "which will accept this suggestion.\n",
                        oid_to_hex(&merges.objects[0].item->oid), path);
                break;

        default:
                MERGE_WARNING(path, "multiple merges found");
                for (i = 0; i < merges.nr; i++)
                        print_commit((struct commit *) merges.objects[i].item);
        }

        free(merges.objects);
        return 0;
}

int parallel_submodules(void)
{
        return parallel_jobs;
}

/*
 * Embeds a single submodules git directory into the superprojects git dir,
 * non recursively.
 */
static void relocate_single_git_dir_into_superproject(const char *prefix,
                                                      const char *path)
{
        char *old_git_dir = NULL, *real_old_git_dir = NULL, *real_new_git_dir = NULL;
        const char *new_git_dir;
        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(null_sha1, path);
        if (!sub)
                die(_("could not lookup name for submodule '%s'"), path);

        new_git_dir = git_path("modules/%s", sub->name);
        if (safe_create_leading_directories_const(new_git_dir) < 0)
                die(_("could not create directory '%s'"), new_git_dir);
        real_new_git_dir = real_pathdup(new_git_dir, 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);
}

/*
 * 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 *prefix,
                                      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;

                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(null_sha1, path);
                if (!sub)
                        die(_("could not lookup name for submodule '%s'"), path);
                connect_work_tree_and_git_dir(path,
                        git_path("modules/%s", sub->name));
        } 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(prefix, 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)
                        die("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;
                argv_array_pushl(&cp.args, "--super-prefix", sb.buf,
                                           "submodule--helper",
                                           "absorb-git-dirs", NULL);
                prepare_submodule_repo_env(&cp.env_array);
                if (run_command(&cp))
                        die(_("could not recurse into submodule '%s'"), path);

                strbuf_release(&sb);
        }
}

const char *get_superproject_working_tree(void)
{
        struct child_process cp = CHILD_PROCESS_INIT;
        struct strbuf sb = STRBUF_INIT;
        const char *one_up = real_path_if_valid("../");
        const char *cwd = xgetcwd();
        const char *ret = NULL;
        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 NULL;

        if (!one_up)
                return NULL;

        subpath = relative_path(cwd, one_up, &sb);

        prepare_submodule_repo_env(&cp.env_array);
        argv_array_pop(&cp.env_array);

        argv_array_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 = sb.buf + sb.len - super_sub - 1;

                if (super_sub_len > cwd_len ||
                    strcmp(&cwd[cwd_len - super_sub_len], super_sub))
                        die (_("BUG: returned path string doesn't match cwd?"));

                super_wt = xstrdup(cwd);
                super_wt[cwd_len - super_sub_len] = '\0';

                ret = real_path(super_wt);
                free(super_wt);
        }
        strbuf_release(&sb);

        code = finish_command(&cp);

        if (code == 128)
                /* '../' is not a git repository */
                return NULL;
        if (code == 0 && len == 0)
                /* There is an unrelated git repository at '../' */
                return NULL;
        if (code)
                die(_("ls-tree returned unexpected return code %d"), code);

        return ret;
}

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)) {
                gitmodules_config();
                sub = submodule_from_path(null_sha1, submodule);
                if (!sub) {
                        ret = -1;
                        goto cleanup;
                }
                strbuf_reset(buf);
                strbuf_git_path(buf, "%s/%s", "modules", sub->name);
        }

cleanup:
        return ret;
}