+ 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;