Re: [PATCH v2] builtin/submodule--helper.c: handle missing submodule URLs

[Eric Sunshine <sunshine@sunshineco.com>]

On Wed, May 24, 2023 at 12:40 PM Taylor Blau <me@ttaylorr.com> wrote:
> In e0a862fdaf (submodule helper: convert relative URL to absolute URL if
> needed, 2018-10-16), `prepare_to_clone_next_submodule()` lost the
> ability to handle URL-less submodules, due to a change from:
>
>     if (repo_get_config_string_const(the_repostiory, sb.buf, &url))
>         url = sub->url;
>
> to
>
>     if (repo_get_config_string_const(the_repostiory, sb.buf, &url)) {
>         if (starts_with_dot_slash(sub->url) ||
>             starts_with_dot_dot_slash(sub->url)) {
>                 /* ... */
>             }
>     }
>
> , which will segfault when `sub->url` is NULL, since both
> `starts_with_dot_slash()` does not guard its arguments as non-NULL.
>
> Guard the checks to both of the above functions by first whether

s/first/first checking/

> `sub->url` is non-NULL. There is no need to check whether `sub` itself
> is NULL, since we already perform this check earlier in
> `prepare_to_clone_next_submodule()`.
>
> By adding a NULL-ness check on `sub->url`, we'll fall into the 'else'
> branch, setting `url` to `sub->url` (which is NULL). Before attempting
> to invoke `git submodule--helper clone`, check whether `url` is NULL,
> and die() if it is.
>
> Reported-by: Tribo Dar <3bodar@gmail.com>
> Signed-off-by: Taylor Blau <me@ttaylorr.com>
> ---
> diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
> @@ -2024,14 +2024,17 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
> -               if (starts_with_dot_slash(sub->url) ||
> -                   starts_with_dot_dot_slash(sub->url)) {
> +               if (sub->url && (starts_with_dot_slash(sub->url) ||
> +                                starts_with_dot_dot_slash(sub->url))) {
>                         url = resolve_relative_url(sub->url, NULL, 0);
>                         need_free_url = 1;
>                 } else
>                         url = sub->url;
>         }
>
> +       if (!url)
> +               die(_("cannot clone submodule '%s' without a URL"), sub->name);

Good. The first version of this patch was more difficult to reason
about due to its "error-at-a-distance" approach. This version is much
cleaner and obvious.

> @@ -2065,11 +2068,11 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
>                 strvec_pushf(&child->args, "--filter=%s",
>                              expand_list_objects_filter_spec(suc->update_data->filter_options));
> +       strvec_pushl(&child->args, "--url", url, NULL);
>         if (suc->update_data->require_init)
>                 strvec_push(&child->args, "--require-init");
>         strvec_pushl(&child->args, "--path", sub->path, NULL);
>         strvec_pushl(&child->args, "--name", sub->name, NULL);
> -       strvec_pushl(&child->args, "--url", url, NULL);

This change is unnecessary now, isn't it? Or is there something
nonobvious going on here?