X ΔBtail.Clone had bug that it was aliasing klon and orig data

Rebuild tests were "surprisingly" failing when run as part of whole
testsuite, but succeeding when run separately.

wcfs/internal/xbtree/δbtail.go

@@ -188,23 +188,18 @@ func (orig *ΔBtail) Clone() *ΔBtail {
 	}
 
 	// vδBroots
-	klon.vδBroots = append(klon.vδBroots, orig.vδBroots...)
+	for _, origδBroots := range orig.vδBroots {
+		klonδBroots := ΔBroots{
+			Rev:    origδBroots.Rev,
+			ΔRoots: origδBroots.ΔRoots.Clone(),
+		}
+		klon.vδBroots = append(klon.vδBroots, klonδBroots)
+	}
 
 	// vδTbyRoot
 	klon.vδTbyRoot = make(map[zodb.Oid]*ΔTtail, len(orig.vδTbyRoot))
 	for root, origΔTtail := range orig.vδTbyRoot {
-		klonΔTtail := &ΔTtail{}
-		klonΔTtail.vδT = append(klonΔTtail.vδT, origΔTtail.vδT...)
-		klonΔTtail.trackNew = origΔTtail.trackNew.Clone()
-		klonΔTtail.KVAtTail = make(map[Key]Value, len(origΔTtail.KVAtTail))
-		for k, v := range origΔTtail.KVAtTail {
-			klonΔTtail.KVAtTail[k] = v
-		}
-		klonΔTtail.lastRevOf = make(map[Key]zodb.Tid, len(origΔTtail.lastRevOf))
-		for k, rev := range origΔTtail.lastRevOf {
-			klonΔTtail.lastRevOf[k] = rev
-		}
-		klon.vδTbyRoot[root] = klonΔTtail
+		klon.vδTbyRoot[root] = origΔTtail.Clone()
 	}
 
 	// trackSet, trackNewRoots
@@ -214,6 +209,31 @@ func (orig *ΔBtail) Clone() *ΔBtail {
 	return klon
 }
 
+// Clone returns copy of ΔTtail.
+func (orig *ΔTtail) Clone() *ΔTtail {
+	klon := &ΔTtail{}
+	for _, origδT := range orig.vδT {
+		klonδT := ΔTree{
+			Rev: origδT.Rev,
+			ΔKV: make(map[Key]ΔValue, len(origδT.ΔKV)),
+		}
+		for k, δv := range origδT.ΔKV {
+			klonδT.ΔKV[k] = δv
+		}
+		klon.vδT = append(klon.vδT, klonδT)
+	}
+	klon.trackNew = orig.trackNew.Clone()
+	klon.KVAtTail = make(map[Key]Value, len(orig.KVAtTail))
+	for k, v := range orig.KVAtTail {
+		klon.KVAtTail[k] = v
+	}
+	klon.lastRevOf = make(map[Key]zodb.Tid, len(orig.lastRevOf))
+	for k, rev := range orig.lastRevOf {
+		klon.lastRevOf[k] = rev
+	}
+	return klon
+}
+
 // (tail, head] coverage
 func (δBtail *ΔBtail) Head() zodb.Tid { return δBtail.δZtail.Head() }
 func (δBtail *ΔBtail) Tail() zodb.Tid { return δBtail.δZtail.Tail() }

wcfs/internal/xbtree/δbtail_test.go

@@ -929,8 +929,6 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 //	t1 := t2.prev
 //	t0 := t1.prev
 	t.Run(fmt.Sprintf("rebuild/%s→%s", t0.tree, t1.tree), func(t *testing.T) {
-//		t.Skip("TODO") // FIXME rebuild is currently broken
-
 		tAllKeys := allTestKeys(t0, t1, t2)
 		tAllKeyv := tAllKeys.SortedElements()
 
@@ -945,7 +943,6 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 		fmt.Printf("@%s:  %v\n", xat[t1.at], t1.xkv.Flatten())
 		fmt.Printf("@%s:  %v\n", xat[t2.at], t2.xkv.Flatten())
 
-//		kadj01 := KAdj(t0,t1, allTestKeys(t0,t1,t2))
 		kadj10 := KAdj(t1,t0, allTestKeys(t0,t1,t2))
 		kadj21 := KAdj(t2,t1, allTestKeys(t0,t1,t2))
 		kadj12 := KAdj(t1,t2, allTestKeys(t0,t1,t2))
@@ -1086,6 +1083,10 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 								// after rebuild
 								/* trackSet=*/ t2.xkv.trackSet(keys12R2),
 								/*vδT=*/ δkv1_k12R2, δkv2_k12R2)
+
+							// ΔBtail.Clone had bug that aliased klon data to orig
+							assertΔTtail(t, "BUG: after clone check", δbtail, db, t2, treeRoot, xat,
+								/*vδT=*/ δkv1_k1R2, δkv2_k1R2)
 //						})
 					}
 				})