Hi there, After two hours of analysis, it seems that I have found the correct definition for the "node line ID" as required by Julian's move API design:
NodeLineID(Path,Rev) := LastCopyTarget@LastCopyRev where LastCopyRev is the latest copy that involved Path@Rev (or any of its parents). LastCopyTarget is the path to which path got copied to in LastCopyRev. If a node has not been copied, LastCopyRev is the revision that this node got added. Note that possibly LastCopyTarget != Path in case that moves in (LastCopyRev, Rev] changed the path (or any of its parents). Properties of NodeLineID as defined above: * defined for any path@rev in the repository * exactly one IDs for the same path@rev * not defined for any path@rev that does not exist in the repository * is unique for all paths at any one revision * does change [exactly] when path or any of its parents gets copied and only for the copied tree * does *not* change when path or any of its parents gets renamed / moved I.e. LastCopyTarget@LastCopyRev assigns exactly one ID to each line of non-copying node history in the repository. All alternative definitions will should, therefore, be equivalent to the one given here. In particular, the following cannot simply be used: * (nodeId, copyID) since there are usually fewer nodes in the DAG than there are paths @HEAD alone (approx. 1:2 for apache.org) * replacing the current lazy copying with deep copies would create nodes exactly for all LastCopyTarget@LastCopyRev values, i.e. is equivalent but less space-efficient * anything involving parent paths or IDs because a move to a different parent must not change the node line id. The given definition even has nice computational properties: * LastCopyTarget@LastCopyRev can be directly expressed as such in a developer readable string * The code to find the LastCopyRev is part of the standard history following code and relatively efficient * For all entries in the same directory@rev, the effort can be lowered to O(1) in many cases since the respective parents have already been investigated (depends on internal node-ID assignment rules). -- Stefan^2.
