Re: [PATCH 03/13] list-objects: filter objects in traverse_commit_list

> By adding it to the set of provisionally omitted objects, we
> have the option to capture a little extra information with it
> and refer to that the next time we see the object in the traversal.
> For example, in the sparse-checkout case, the first time we see the
> object we know the pathname and know that it does not need to be
> included.  The second time we see that object, we can see if the
> new pathname is the same as the previous one with a simple strcmp
> and avoid the expensive is_excluded_from_list() computation.  Keep
> in mind that rev-list or pack-objects could be called be on something
> like HEAD~100000..HEAD or that there may be 50,000 tips.  So a file
> that doesn't change across that range will be visited many times
> with the same {pathname, sha}.

> Right now I want to force the tree to be shown the first time it is
> visited (because I don't want to do tree filtering yet).  I don't mark
> it SEEN yet because we may want to revisit blobs within (say, after a
> folder rename like I described previously).
> 
> I do, however, mark the tree object as SEEN (in the _END event) when I
> can verify that I've included ALL of the children.