.

wcfs/internal/xbtree/pptreesubset.go

@@ -89,6 +89,8 @@ func (S PPTreeSubSet) Path(oid zodb.Oid) (path []zodb.Oid) {
 }
 
 // AddPath adds path to a node to the set.
+//
+// Note: embedded buckets (leaf node with InvalidOid) are removed from the path.
 func (S PPTreeSubSet) AddPath(path []zodb.Oid) {
 	S.verify()
 	defer S.verify()
@@ -98,6 +100,8 @@ func (S PPTreeSubSet) AddPath(path []zodb.Oid) {
 		panic("empty path")
 	}
 
+	path = normPath(path)
+/*
 	// don't keep track of artificial empty tree
 	if l == 1 && path[0] == zodb.InvalidOid {
 		return
@@ -109,6 +113,7 @@ func (S PPTreeSubSet) AddPath(path []zodb.Oid) {
 	if l == 2 && path[1] == zodb.InvalidOid {
 		path = path[:1]
 	}
+*/
 
 	parent := zodb.InvalidOid
 	var pt *nodeInTree = nil
@@ -137,6 +142,28 @@ func (S PPTreeSubSet) AddPath(path []zodb.Oid) {
 	}
 }
 
+// normPath normalizes path.
+//
+// It removes embedded buckets and artificial empty trees.
+// Returned slice is subslice of path and aliases its memory.
+func normPath(path []zodb.Oid) []zodb.Oid {
+	l := len(path)
+
+	// don't keep track of artificial empty tree
+	if l == 1 && path[0] == zodb.InvalidOid {
+		return nil
+	}
+
+	// don't explicitly keep track of embedded buckets - they all have
+	// InvalidOid, and thus, if kept in S, e.g. T/B1:a and another
+	// T/B2:b would lead to InvalidOid having multiple parents.
+	if l == 2 && path[1] == zodb.InvalidOid {
+		return path[:1]
+	}
+
+	return path
+}
+
 // ---- Union/Difference/Intersetctior ----
 
 // Union returns U = PP(A.leafs | B.leafs)

wcfs/internal/xbtree/δbtail.go

@@ -249,9 +249,16 @@ func (δBtail *ΔBtail) Track(key Key, nodePath []Node) error { // XXX Tree|Buck
 func (δBtail *ΔBtail) track(key Key, path []zodb.Oid) error {
 	// XXX locking
 
-	root := path[0]
+	// first normalize path: remove embedded bucket and check if it was an
+	// empty artificial tree. We need to do the normalization becase we
+	// later check whether leaf path[-1] ∈ trackSet and without
+	// normalization path[-1] can be InvalidOid.
+	path = normPath(path)
+	if len(path) == 0 {
+		return nil // empty tree
+	}
 
-	// XXX first normalize path
+	root := path[0]
 
 	// nothing to do if key is already tracked
 	leaf := path[len(path)-1]