Re: [PATCH v3 2/3] config: add hashtable for config parsing & retrieval

[Ramsay Jones <ramsay@ramsay1.demon.co.uk>]

On 24/06/14 00:25, Junio C Hamano wrote:
> Ramsay Jones <ramsay@ramsay1.demon.co.uk> writes:
> 
>>> +static struct hashmap *get_config_cache(void)
>>> +{
>>> +	static struct hashmap config_cache;
>>> +	if (!hashmap_initialized) {
>>> +		config_cache_init(&config_cache);
>>> +		hashmap_initialized = 1;
>>> +		git_config(config_cache_callback, NULL);
>>> +	}
>>> +	return &config_cache;
>>> +}
>>
>> [I have not been following this series at all (sorry I haven't had
>> the time to spare), so take these comments with a very big pinch of
>> salt! ie just ignore me if it's already been discussed etc. ;-) ]
>>
>> The 'git config' command can be used to read arbitrary files (so long
>> as they conform to the config syntax). For example, see the --file and
>> --blob options to git-config. At present, I think only scripted commands
>> use this facility (eg git-submodule). Noting the singleton config_cache,
>> what happens when git-submodule becomes a C builtin, or indeed any other
>> C builtin wants to take advantage of the new code when processing a non-
>> standard config file?
> 
> Yup, that is a very good point.  There needs an infrastructure to
> tie a set of files (i.e. the standard one being the chain of
> system-global /etc/gitconfig to repo-specific .git/config, and any
> custom one that can be specified by the caller like submodule code)
> to a separate hashmap; a future built-in submodule code would use
> two hashmaps aka "config-caches", one to manage the usual
> "configuration" and the other to manage the contents of the
> .gitmodules file.
> 

I had expected to see one hash table per file/blob, with the three
standard config hash tables linked together to implement the scope/
priority rules. (Well, these could be merged into one, as the current
code does, since that makes handling "multi" keys slightly easier).

ie when looking up a symbol in the .git/config, if not found then
follow the link to parent scope (~/.gitconfig) and search there ...

Of course, other uses (I think) represent only a single scope, so they
would not have any parent scopes to link to.

> When we are operating across repositories (think "recursive
> checkout"), we somehow have to deal with multiple sets of
> configuration, one that applies to the top-level superproject and
> others that apply to individual submodule repositories.
> 

Here, you could push the new .git/config onto a stack while linking
to the parent (~/.gitconfig) scope. So, the lookup code starts from
the stack top, etc, ...

> Even there is currently one caller, the "git config" command
> implementation, if one is designing the new API, the design
> shouldn't be tied to a singleton limitation, I would have to say, so
> that future callers do not have to throw away everything done in
> this series and start from scratch.
> .

I would like to stress that, despite the above, I have not given
any great thought to this project. So please take my comments with
a big pinch of salt. I was just scrolling through the patch in my
email client and was surprised to see the singleton ...

ATB,
Ramsay Jones