Re: [PATCH on sb/more-repo-in-api] revision: use commit graph in get_reference()

> > This is on sb/more-repo-in-api because I'm using the repo_parse_commit()
> > function.
> 
> This is a mere nicety, not strictly required.
> Before we had parse_commit(struct commit *) which would accomplish the
> same, (and we'd still have that afterwards as a #define falling back onto
> the_repository). As the function get_reference() is not the_repository safe
> as it contains a call to is_promisor_object() that is repository
> agnostic, I think
> it would be fair game to not depend on that series. I am not
> complaining, though.

> AFAICT oid_object_info doesn't take advantage of the commit graph,
> but just looks up the object header, which is still less than completely
> parsing it. Then lookup_commit is overly strict, as it may return
> NULL as when there still is a type mismatch (I don't think a mismatch
> could happen here, as both rely on just the object store, and not the
> commit graph.), so this would be just defensive programming for
> the sake of it. I dunno.
> 
>     struct commit *c;
> 
>     if (oid_object_info(revs->repo, oid, NULL) == OBJ_COMMIT &&
>         (c = lookup_commit(revs->repo, oid)) &&
>         !repo_parse_commit(revs->repo, c))
>             object = (struct object *) c;
>     else
>         object = parse_object(revs->repo, oid);