Re: [PATCH v2 1/2] setup.c: make bare repo discovery optional

>>> +static int check_bare_repo_allowed(void)
>>> +{
>>> +	if (discovery_bare_config == DISCOVERY_BARE_UNKNOWN) {
>>> +		read_very_early_config(discovery_bare_cb, NULL);
>>
>> This will add the third place where we use read_very_early_config(),
>> adding to the existing calls in tr2_sysenv_load() and
>> ensure_valid_ownership(). If I understand it correctly, that means
>> that every Git execution in a bare repository will now parse the
>> system and global config three times.
>>
>> This doesn't count the check for uploadpack.packobjectshook in
>> upload-pack.c that uses current_config_scope() to restrict its
>> value to the system and global config.
>>
>> We are probably at the point where we need to instead create a
>> configset that stores this "protected config" and allow us to
>> lookup config keys directly from that configset instead of
>> iterating through these config files repeatedly.
>
> Looking at all of the read_very_early_config() calls,
>
> - check_bare_repo_allowed() can use git_configset_get_string()
> - ensure_valid_ownership() can use git_configset_get_value_multi()
> - tr2_sysenv_load() reads every value with the "trace2." prefix. AFAICT
>   configsets only support exact key lookups and I don't see an easy way
>   teach configsets to support prefix lookups.
>
> (I didn't look too closely at uploadpack.packobjectshook because I don't
> know enough about config scopes to comment.)
>
> So using a configset, we'll still need to read the config files at least
> twice. That's better than thrice, but it doesn't cover the
> tr2_sysenv_load() use case, and we'll run into this yet again if add
> function that reads all config values with a given prefix.
>
> An hacky alternative that covers all of these use cases would be to read
> all protected config in a single pass, e.g.
>
>   static struct protected_config {
>          struct safe_directory_data safe_directory_data;
>          const char *discovery_bare;
>          struct string_list tr2_sysenv;
>   };
>
>   static int protected_config_cb()
>   {
>     /* Parse EVERYTHING that belongs in protected_config. */
>   }
>
> but protected_config_cb() would have to parse too many unrelated things
> for my liking.
>
> So I'll use the configset for the cases where the key is known, and
> perhaps we'll punt on tr2_sysenv_load().