.

wcfs/internal/xbtree/δbtail.go

@@ -579,8 +579,8 @@ func (δBtail *ΔBtail) Update(δZ *zodb.EventCommit) (_ ΔB, err error) {
 			}
 			δTtail.trackNew = trackNew
 
-			// XXX vvv we can skip computing diff for HEAD~..HEAD (we just
-			//     computed it in _Update1)? (or not - trackNew is as of @head ?)
+			// NOTE we cannot skip computing diff for HEAD~..HEAD
+			// even after _Update1 because _Update1 was working with different trackNew.
 			δtrackSet, δrevSet, err := δTtail.rebuild(root, δBtail.δZtail, δBtail.db)
 			if err != nil {
 				return ΔB{}, err