Re: [PATCH v2 02/24] pack-bitmap-write.c: gracefully fail to write non-closed bitmaps

> The set of objects covered by a bitmap must be closed under
> reachability, since it must be the case that there is a valid bit
> position assigned for every possible reachable object (otherwise the
> bitmaps would be incomplete).
> 
> Pack bitmaps are never written from 'git repack' unless repacking
> all-into-one, and so we never write non-closed bitmaps (except in the
> case of partial clones where we aren't guaranteed to have all objects).
> 
> But multi-pack bitmaps change this, since it isn't known whether the
> set of objects in the MIDX is closed under reachability until walking
> them. Plumb through a bit that is set when a reachable object isn't
> found.
> 
> As soon as a reachable object isn't found in the set of objects to
> include in the bitmap, bitmap_writer_build() knows that the set is not
> closed, and so it now fails gracefully.

> @@ -463,8 +488,11 @@ void bitmap_writer_build(struct packing_data *to_pack)
>  		struct commit *child;
>  		int reused = 0;
>  
> -		fill_bitmap_commit(ent, commit, &queue, &tree_queue,
> -				   old_bitmap, mapping);
> +		if (fill_bitmap_commit(ent, commit, &queue, &tree_queue,
> +				       old_bitmap, mapping) < 0) {
> +			closed = 0;
> +			break;
> +		}
>  
>  		if (ent->selected) {
>  			store_selected(ent, commit);