Re: git rebase chokes on directory -> symlink -> directory

Linus Torvalds [off-list ref] writes:

That said, wouldn't it potentially be quite easy in "unpack_trees_rec()" 
to just notice when all the trees are identical, and just not recurse at 
all in that case (or - alternatively - recurse, but on entry, just exit 
quickly?)

In the threeway case, it should be able to notice that the trees
of the ancestor and the other match, which is the only case we
can safely say that the result will be our tree (aka HEAD) and
we won't mess with the index nor worry about local modifications
made only to the working tree.  The case in which all trees
match, regardless of the number of trees involved, should work
the same way.

However, in the threeway case, we still need to make sure that
the index matches the HEAD even when we know the result will be
taken from HEAD, as otherwise we would end up including the
local "git add" made earlier in the merge result.  We need to
make sure the index matches HEAD for such a subdirectory in that
case before skipping it.

What is troublesome is that kind of policy logic is not supposed
to happen in unpack_trees_rec() in the current code structure;
instead, that decision is to be made by o->fn().

So, I am not sure if it is that quite easy.