.

wcfs/internal/xbtree/δbtail.go

@@ -329,8 +329,8 @@ func (δTtail *ΔTtail) rebuild(root zodb.Oid, δZtail *zodb.ΔTail, db *zodb.DB
 	// go backwards and merge vδT <- treediff(lo..hi/trackNew)
 	vδZ := δZtail.Data()
 	for {
-		δtkeycov := &RangedKeySet{}     // all keys coming into tracking set during this lo..hi scan
-		trackNewCur := trackNew.Clone() // trackNew adjusted when going to i<- entry
+		δtkeycov := &RangedKeySet{}     // all keys coming into tracking set during this lo<-hi scan
+		trackNewCur := trackNew.Clone() // trackNew adjusted as of when going to i<- entry
 		for i := len(vδZ)-1; i>=0; i-- {
 			δZ := vδZ[i]
 
@@ -576,27 +576,36 @@ if XXX_killWhenRebuildWorks {
 
 		tracefΔBtail("\n-> root<%s>  δkv: %v  δtrack: %v  δtkeycov: %v\n", root, δT, δtrack, δtkeycov)
 
+		δTtail := δBtail.vδTbyRoot[root] // must be there
 		if len(δT) > 0 { // an object might be resaved without change
-			δB.ΔByRoot[root] = δT
-			δTtail, ok := δBtail.vδTbyRoot[root]
-			if !ok {
-				// XXX should not happen (only roots requested to be present are present in δ)
-				// this root was not tracked before -> create δTtail for it with empty changes
-				δTtail = newΔTtail()
-				δBtail.vδTbyRoot[root] = δTtail
-			}
-
+			δB.ΔByRoot[root] = δT	// XXX after rebuild
 			δTtail.vδT = append(δTtail.vδT, ΔTree{Rev: δZ.Tid, ΔKV: δT})
-
-			// XXX rebuild KVAtTail
-			// XXX rebuild lastRevOf
 		}
 
 		δBtail.trackSet.ApplyΔ(δtrack)
-		δTKeyCov.ByRoot[root] = δtkeycov
 
-		// XXX if δtkeycov != ø && len(δZtail) > 1  -> rebuild δTtail
-		// XXX do this
+		// δtkeycov != ø   ->  rebuild δTtail
+		//
+		// XXX NOTE `len(δZtail) > 1` check is not only optimization - it is
+		// important for tests: xverifyΔBTail_Update calls ΔBtail._Update with
+		// only one revision inside δZtail, and this way also directly exercises
+		// treediff. Should we drop `len(δZtail) > 1` check here, that test will
+		// no longer directly exercise treediff behaviour.
+		if !δtkeycov.Empty() && δBtail.δZtail.Len() > 1 {
+			δTtail.trackNew = ... // ~δtkeycov
+			δtrackSet, err := δTtail.rebuild(root, δBtail.δZtail, δBtail.db)
+			if err != nil {
+				return ΔB{}, δTKeyCov, err
+			}
+
+			δBtail.trackSet.UnionInplace(δtrackSet)
+			// XXX Update δTKeyCov? XXX or it is needed only to be returned
+			//     from treediff?
+		}
+
+		δTKeyCov.ByRoot[root] = δtkeycov	// XXX after rebuild
+		// XXX rebuild KVAtTail
+		// XXX rebuild lastRevOf
 	}
 
 	return δB, δTKeyCov, nil
@@ -610,11 +619,6 @@ func (δBtail *ΔBtail) ForgetPast(revCut zodb.Tid) {
 }
 
 
-// update brings .δBtail up to date by recomputing diff XXX and taking new
-// entries in .δZtail into account.
-// func (δBtail *ΔBtail) update()	XXX kill
-
-
 // Get returns root[key] as of @at database state plus revision that changed it.
 //
 // if revExact=False - rev is upper estimate for the revision.