Check overwritten value in parentUpdater callback

Currently, in parentUpdater callback, parent array/map resets same
child value.

Child value ID should match overwritten SlabIDStorable
or Slab.SlabID().

This commit adds check to make sure same child value is being reset.

Author: fxamacker

array.go

@@ -2725,8 +2725,39 @@ func (a *Array) setCallbackWithChild(i uint64, child Value) {
 			return err
 		}
 
-		if existingValueStorable == nil {
-			return NewFatalError(fmt.Errorf("failed to reset child value in parent updater callback because previous value is nil"))
+		// Verify overwritten storable has identical value ID.
+
+		switch x := existingValueStorable.(type) {
+		case SlabIDStorable:
+			sid := SlabID(x)
+			if !vid.equal(sid) {
+				return NewFatalError(
+					fmt.Errorf(
+						"failed to reset child value in parent updater callback: overwritten SlabIDStorable %s != value ID %s",
+						sid,
+						vid))
+			}
+
+		case Slab:
+			sid := x.SlabID()
+			if !vid.equal(sid) {
+				return NewFatalError(
+					fmt.Errorf(
+						"failed to reset child value in parent updater callback: overwritten Slab ID %s != value ID %s",
+						sid,
+						vid))
+			}
+
+		case nil:
+			return NewFatalError(
+				fmt.Errorf(
+					"failed to reset child value in parent updater callback: overwritten value is nil"))
+
+		default:
+			return NewFatalError(
+				fmt.Errorf(
+					"failed to reset child value in parent updater callback: overwritten value is wrong type %T",
+					existingValueStorable))
 		}
 
 		return nil

map.go

@@ -4523,6 +4523,8 @@ func (m *OrderedMap) setCallbackWithChild(
 		return
 	}
 
+	vid := c.ValueID()
+
 	c.setParentUpdater(func() error {
 		// Set child value with parent map using same key.
 		// Set() calls c.Storable() which returns inlined or not-inlined child storable.
@@ -4531,10 +4533,40 @@ func (m *OrderedMap) setCallbackWithChild(
 			return err
 		}
 
-		if existingValueStorable == nil {
-			return NewFatalError(fmt.Errorf("failed to reset child value in parent updater callback because previous value is nil"))
-		}
+		// Verify overwritten storable has identical value ID.
+
+		switch x := existingValueStorable.(type) {
+		case SlabIDStorable:
+			sid := SlabID(x)
+			if !vid.equal(sid) {
+				return NewFatalError(
+					fmt.Errorf(
+						"failed to reset child value in parent updater callback: overwritten SlabIDStorable %s != value ID %s",
+						sid,
+						vid))
+			}
+
+		case Slab:
+			sid := x.SlabID()
+			if !vid.equal(sid) {
+				return NewFatalError(
+					fmt.Errorf(
+						"failed to reset child value in parent updater callback: overwritten Slab ID %s != value ID %s",
+						sid,
+						vid))
+			}
+
+		case nil:
+			return NewFatalError(
+				fmt.Errorf(
+					"failed to reset child value in parent updater callback: overwritten value is nil"))
 
+		default:
+			return NewFatalError(
+				fmt.Errorf(
+					"failed to reset child value in parent updater callback: overwritten value is wrong type %T",
+					existingValueStorable))
+		}
 		return nil
 	})
 }

storage.go

@@ -41,6 +41,19 @@ func slabIDToValueID(sid SlabID) ValueID {
 	return id
 }
 
+func (vid ValueID) equal(sid SlabID) bool {
+	return bytes.Equal(vid[:8], sid.address[:]) &&
+		bytes.Equal(vid[8:], sid.index[:])
+}
+
+func (vid ValueID) String() string {
+	return fmt.Sprintf(
+		"0x%x.%d",
+		binary.BigEndian.Uint64(vid[:8]),
+		binary.BigEndian.Uint64(vid[8:]),
+	)
+}
+
 type (
 	Address   [8]byte
 	SlabIndex [8]byte