Re: [PATCHv3 3/3] submodule: implement `module-clone` as a builtin helper

> needed for converting `git submodule update` later on, which we want to
> add threading to.
>
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
> +static int module_clone(int argc, const char **argv, const char *prefix)
> +{
> +       const char *path = NULL, *name = NULL, *url = NULL;
> +       const char *reference = NULL, *depth = NULL;
> +       const char *alternative_path = NULL, *p;
> +       int quiet = 0;
> +       FILE *submodule_dot_git;
> +       char *sm_gitdir;
> +       struct strbuf rel_path = STRBUF_INIT;
> +       struct strbuf sb = STRBUF_INIT;
> +
> +       struct option module_update_options[] = {

> +               OPT_STRING(0, "prefix", &alternative_path,
> +                          N_("path"),
> +                          N_("alternative anchor for relative paths")),
> +               OPT_STRING(0, "path", &path,
> +                          N_("path"),
> +                          N_("where the new submodule will be cloned to")),
> +               OPT_STRING(0, "name", &name,
> +                          N_("string"),
> +                          N_("name of the new submodule")),
> +               OPT_STRING(0, "url", &url,
> +                          N_("string"),
> +                          N_("url where to clone the submodule from")),
> +               OPT_STRING(0, "reference", &reference,
> +                          N_("string"),
> +                          N_("reference repository")),
> +               OPT_STRING(0, "depth", &depth,
> +                          N_("string"),
> +                          N_("depth for shallow clones")),
> +               OPT__QUIET(&quiet, "Suppress output for cloning a submodule"),
> +               OPT_END()
> +       };
> +
> +       static const char * const git_submodule_helper_usage[] = {

> +               NULL
> +       };
> +
> +       argc = parse_options(argc, argv, prefix, module_update_options,
> +                            git_submodule_helper_usage, 0);
> +
> +       strbuf_addf(&sb, "%s/modules/%s", get_git_dir(), name);
> +       sm_gitdir = strbuf_detach(&sb, NULL);
> +
> +       if (!file_exists(sm_gitdir)) {
> +               safe_create_leading_directories_const(sm_gitdir);

> +               if (clone_submodule(path, sm_gitdir, url, depth, reference, quiet))
> +                       die(N_("Clone of '%s' into submodule path '%s' failed"),
> +                           url, path);
> +       } else {
> +               safe_create_leading_directories_const(path);
> +               unlink(sm_gitdir);
> +       }
> +
> +       /* Write a .git file in the submodule to redirect to the superproject. */
> +       if (alternative_path && !strcmp(alternative_path, "")) {
> +               p = relative_path(path, alternative_path, &sb);
> +               strbuf_reset(&sb);
> +       } else
> +               p = path;
> +
> +       if (safe_create_leading_directories_const(p) < 0)
> +               die("Could not create directory '%s'", p);
> +
> +       strbuf_addf(&sb, "%s/.git", p);
> +
> +       if (safe_create_leading_directories_const(sb.buf) < 0)
> +               die(_("could not create leading directories of '%s'"), sb.buf);
> +       submodule_dot_git = fopen(sb.buf, "w");
> +       if (!submodule_dot_git)
> +               die ("Cannot open file '%s': %s", sb.buf, strerror(errno));
> +
> +       fprintf(submodule_dot_git, "gitdir: %s\n",
> +               relative_path(sm_gitdir, path, &rel_path));
> +       if (fclose(submodule_dot_git))
> +               die("Could not close file %s", sb.buf);
> +       strbuf_reset(&sb);
> +
> +       /* Redirect the worktree of the submodule in the superprojects config */
> +       if (!is_absolute_path(sm_gitdir)) {
> +               char *s = (char*)sm_gitdir;
> +               if (strbuf_getcwd(&sb))
> +                       die_errno("unable to get current working directory");
> +               strbuf_addf(&sb, "/%s", sm_gitdir);
> +               sm_gitdir = strbuf_detach(&sb, NULL);
> +               free(s);
> +       }
> +
> +       if (strbuf_getcwd(&sb))
> +               die_errno("unable to get current working directory");
> +       strbuf_addf(&sb, "/%s", path);
> +
> +       p = git_pathdup_submodule(path, "config");
> +       if (!p)
> +               die("Could not get submodule directory for '%s'", path);
> +       git_config_set_in_file(p, "core.worktree",
> +                              relative_path(sb.buf, sm_gitdir, &rel_path));
> +       strbuf_release(&sb);
> +       free(sm_gitdir);
> +       return 0;
> +}