Re: [PATCH 0/5] Store submodules in a hash, not a linked list

[Duy Nguyen <pclouds@gmail.com>]

On Thu, Feb 09, 2017 at 07:40:33PM -0500, Jeff King wrote:
> On Thu, Feb 09, 2017 at 10:23:35PM +0100, Michael Haggerty wrote:
> 
> > >> So push the submodule attribute down to the `files_ref_store` class
> > >> (but continue to let the `ref_store`s be looked up by submodule).
> > > 
> > > I'm not sure I understand all of the ramifications here. It _sounds_ like
> > > pushing this down into the files-backend code would make it harder to
> > > have mixed ref-backends for different submodules. Or is this just
> > > pushing down an implementation detail of the files backend, and future
> > > code is free to have as many different ref_stores as it likes?
> > 
> > I don't understand how this would make it harder, aside from the fact
> > that a new backend class might also need a path member and have to
> > maintain its own copy rather than using one that the base class provides.
> 
> Probably the answer is "I'm really confused".
> 
> But here's how my line of reasoning went:
> 
>   Right now we have a main ref-store that points to the submodule
>   ref-stores. I don't know the current state of it, but in theory those
>   could all use different backends.
> 
>   This seems like it's pushing that submodule linkage down into the
>   backend.
> 
> But I think from your response that the answer is no, the thing that is
> being pushed down is not the right way for the main ref store and the
> submodules to be linked.

I think it's more about "pushing out" than "pushing down". Once files
backend takes a path to .git directory, we could have a submodule
ref_store that resolves submodule path to that .git directory,
files-backend will not need to know anything about submodules.

I imagine in future lookup_ref_store() will take a .git path instead
of a submodule path, then iterate through all backends and call the
backend-specific "probe" function to let the backend figure out if
it's the right backend and whatever parameters it needs (e.g. IP
address or path). There would be submodule_lookup_ref_store() wrapper
that converts submodule path to .git path for lookup_ref_store() to
consume.
--
Duy