multi-tree-transform

[Aaron Bentley]

(resending-- not sure why it didn't reach the list)
Robert Collins wrote:
> Aaron, you indicated that you thought you'd need to require a single
> file id only turn up once across all trees in a nested tree scenario, to
> let tree transform work correctly. I wonder though, if simply adding the
> tree 'id'(*) to the file_id to get a composite key would be enough for
> you?

Actually applying the transform doesn't require file_ids to be unique.
TreeTransform uses transform_ids, which are unique, for that purpose.

TreeTransform's clients expect there to be a 1:1 mapping between
file_ids and trans_ids, so TreeTransform provides reverse lookup
facilities.  It would break API compatibility if TT's file_id <=>
trans_id facilities started working in terms of tree_ids.

That is what I meant-- not that TT can't function without unique file
ids, but that it can't support its current interface without them.

Aaron