Re: Strange merge failure (would be overwritten by merge / cannot merge)

Linus Torvalds [off-list ref] writes:

The index case is slightly easier, as we can go back-and-forth in the 
source index (we do try to avoid it right now, but that's a small 
optimization rather than anything fundamental),...

Almost true, but there is the final "Any left-over entries in the index?"
phase in unpack_trees() that relies on o->pos being correct.