Re: [BUG] two-way read-tree can write null sha1s into index

Jeff King [off-list ref] writes:

Oh, I agree it's insane to try to carry through unmerged entries. I'm
just concerned that not all code paths are careful enough to check.

I would actually be surprised if some code path do assume somebody
might give them an index with conflicting entries in it and guard
against it.  We have been coding under the "index must exactly match
the second tree when three-way unpack_trees() begin" requirement
since day one.  An conflicted entry will appear as "index and HEAD
not matching" and will cause reject_merge() early in threeway_merge()
anyway, no?