Re: [PATCH 2/9] pack-objects: add `--print-filtered` to print omitted objects

> > Makes sense.  It is a bit sad that we have to accumulate everything
> > until the end at which time we have to dump the accumulated in bulk,
> > but that is a current limitation of list-objects-filter API and not
> > within the scope of this change.  We may in the longer term want to
> > see if we can make the collection of filtered-out objects streamable
> > by replacing the .omits object array with a callback function, or do
> > something along that line.
>
> Hmm. I think it is possible to use something like `git pack-objects`'s
> `--stdin-packs` mode to accomplish this without needing to keep track of
> the set of discarded objects (i.e. those which don't match the filter).
>
> IIUC, the set of objects which don't match the filter is the same as the
> set of all objects in packs beforehand, differenced with the set of
> objects that shows up in the pack containing objects which *do* match
> the filter.
>
> If you mark all of the "before" packs with `-` in the input to
> `--stdin-packs`, and then pass along the pack containing the filtered
> set without `-` (to indicate that the resulting pack should not contain
> any objects which appear in that pack), I think you would end up with
> the set of non-matching objects.