Re: [RFC PATCH 1/2] refs: make _advance() check struct repo, not flag

[Jonathan Tan <jonathantanmy@google.com>]

> The answer to whether or not a ref store should refer to a certain
> object store seems unresolved because a ref store is trying to do two
> separate things. Perhaps it is reasonable to associate a ref database
> with an object store (so that it can validate its refs), but we would
> prefer to dissociate the physical ref storage layer from the object
> store. (I'm paraphrasing Johnathan Nieder here, this isn't an original
> thought).
> 
> Perhaps this is a question we want to resolve when considering reftable
> and other ref databases.

Either adding an explicit dependency on an object store to a ref store
or dissociating it would be an improvement over what we have now, which
is an implicit dependency on the_repository's object store. Of the two,
I also prefer dissociating it. In practice, if I remember correctly, the
part that checks object existence during ref writing is the last
dependency, so if we can eliminate that without a convoluted design, I
think it's worth dissociating.