Re: [PATCH 1/2] submodule.c: add has_submodules to check if we have any submodules

[Stefan Beller <sbeller@google.com>]

On Thu, Apr 20, 2017 at 3:07 PM, Brandon Williams <bmwill@google.com> wrote:
> On 04/11, Stefan Beller wrote:
>> +int has_submodules(unsigned what_to_check)
>> +{
>> +     if (what_to_check & SUBMODULE_CHECK_ANY_CONFIG) {
>> +             if (submodule_config_reading == SUBMODULE_CONFIG_NOT_READ)
>> +                     load_submodule_config();
>> +             if (submodule_config_reading == SUBMODULE_CONFIG_EXISTS)
>> +                     return 1;
>> +     }
>> +
>> +     if ((what_to_check & SUBMODULE_CHECK_ABSORBED_GIT_DIRS) &&
>> +         file_exists(git_path("modules")))
>> +             return 1;
>> +
>> +     if ((what_to_check & SUBMODULE_CHECK_GITMODULES_IN_WT) &&
>> +         (!is_bare_repository() && file_exists(".gitmodules")))
>> +             return 1;
>> +
>> +     if (what_to_check & SUBMODULE_CHECK_GITLINKS_IN_TREE) {
>> +             int i;
>> +
>> +             if (read_cache() < 0)
>> +                     die(_("index file corrupt"));
>> +
>> +             for (i = 0; i < active_nr; i++)
>> +                     if (S_ISGITLINK(active_cache[i]->ce_mode))
>> +                             return 1;
>> +     }
>> +
>> +     return 0;
>> +}
>
> It may be a good idea to rearrange these by order to correctness.

I arranged by estimated speed, i.e. from fastest to slowest:
* The first check just returns a value from memory in the standard case
  Though the first one may take a hit in performance for the very first time
  as it may need to load the config.
* The next two are an actual stat system call, each having a different
  'defect'. (We may have non-absorbed submodules or non-bare repos)
  -> We could have a check for in-tree as well, not sure if that is desired.

> Correctness may not be the best way to describe it, but which is the
> strongest indicator that there is a submodule or that a repo 'has a
> submodule'.

These indicators differ in strength for different scenarios IMO.
(Just after clone: check for a .gitmodules file instead of a config;
later: rather check for a config as it is fastest and actually catches
active submodules; maybe we do not care about inactive submodules)

>  That way in the future we could have a #define that is
> SUBMODULE_CHECK_ANY or ALL or something....Now that I'm thinking harder
> about that we may not want that, and just require explicitly stating
> which check you want done.
>
> Anyways good looking patch, and I like the idea of consolidating the
> checks into a single function.

Thanks,
Stefan