On Thu, May 16, 2019 at 09:09:50PM -0400, Jeff King wrote: > - will we ever append a presumed-thin base to the pack, only to later > realize that we already have that object, creating a duplicate > object in the pack? If so, do we handle this correctly when > generating the index (I know we've had issues in the past and have > expressly forbidden duplicates from appearing in the index; even > having a duplicate in the pack stream itself is non-ideal, though, > as it screws up things like on-disk size calculations). > > Because of the sorting in fix_unresolved_deltas(), I think this > could easily be prevented if the non-thin delta is OFS_DELTA (by > just checking for the base in our already-found list of objects > before we call read_object_file(). But for REF_DELTA, I think we > have no way of knowing that appending is the wrong thing (and no > good way of backing it out afterwards). Actually, I think even for REF_DELTA our pack-objects would never produce such a pack, because IIRC we _always_ put bases in the pack before their deltas. But that's a pretty subtle thing to depend on. I'm fine with it if violating it just means things are slightly less optimal. I'm more worried if it means that index-pack silently produces a bogus pack. I think to trigger it you'd have to manually assemble an evil pack as I described (e.g., using the routines in t/lib-pack.sh). I'm going offline for a bit, but I may have a go at it later tonight or tomorrow. -Peff
