.

wcfs/δbtail.go

@@ -765,8 +765,36 @@ func diffT(ctx context.Context, a, b *Tree, δZTC SetOid, trackIdx map[zodb.Oid]
 		for len(aq) > 0 {
 			l := len(aq)
 			arn  := aq[l-1]; aq=aq[:l-1] // arn=aq.pop()
-			err := arn.node.PActivate(ctx);  if err != nil { return nil, err}
-			defer arn.node.PDeactivate()
+			atree := arn.node.(*Tree)    // ok - only trees in aq
+			err = atree.PActivate(ctx);  if err != nil { return nil, err}
+			defer atree.PDeactivate()
+
+			if len(atree.Entryv()) == 0 {
+				// empty tree - do not expand into bucket - only process tracked holes
+				// XXX dup wrt bucket processing?
+				track, ok := trackIdx[atree.POid()]
+				if !ok {
+					panicf("%s ∈ δZTC, but ∉ trackIdx", vnode(atree))
+				}
+				δA := map[Key]ΔValue{}
+				for k := range track.holes {
+					δA[k] = ΔValue{VDEL, VDEL} // ø->ø indicates hole
+				}
+				// δ <- δA
+				err = δMerge(δ, δA)
+				if err != nil {
+					return nil, err
+				}
+
+				// Adone  <- δA
+				// Bqueue <- δA
+				for k := range δA {
+					Adone.Add(k)
+					Bqueue.Add(k)
+				}
+
+				continue
+			}
 
 			children := av.Expand(arn)
 //			fmt.Printf("Y children: %s\n", children)