[ package:vm_service ] Fix issue where null was returned instead of @Instance of type Null

Also includes some cleanup for next release.

Fixes https://github.com/dart-lang/sdk/issues/44842

TEST=pkg/vm_service/test/regress_44842_test.dart

Change-Id: I250fac7c52d6d5344bd5c3ec1c143deaa97419d9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182369
Reviewed-by: Gary Roumanis <grouma@google.com>

pkg/vm_service/CHANGELOG.md

@@ -6,6 +6,7 @@
 - Added `successors` iterable to `HeapSnapshotObject`, which provides a convenient way to
   access children of a given object.
 - Added `klass` getter to `HeapSnapshotObject`.
+- Fixed issue where `null` could be returned instead of `InstanceRef` of type `Null`.
 
 ## 6.0.1
 - Stable null-safe release.

pkg/vm_service/lib/src/vm_service.dart

@@ -55,7 +55,8 @@ Object? createServiceObject(dynamic json, List<String> expectedTypes) {
       } else {
         return null;
       }
-    } else if (_isNullInstance(json) && (!expectedTypes.contains(type))) {
+    } else if (_isNullInstance(json) &&
+        (!expectedTypes.contains('InstanceRef'))) {
       // Replace null instances with null when we don't expect an instance to
       // be returned.
       return null;

pkg/vm_service/test/regress_44842_test.dart

@@ -0,0 +1,24 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:vm_service/vm_service.dart';
+import 'package:test/test.dart';
+
+const Map<String, dynamic> kNullInstance = {
+  'type': '@Instance',
+  'id': 'instance/123',
+  'kind': 'Null',
+  'class': {
+    'type': '@Class',
+    'id': 'object/0',
+    'name': 'Null',
+  }
+};
+
+void main() {
+  test('Ensure createServiceObject handles Null @Instances properly', () {
+    expect(createServiceObject(kNullInstance, ['InstanceRef']), isNotNull);
+    expect(createServiceObject(kNullInstance, ['ClassRef']), isNull);
+  });
+}

pkg/vm_service/tool/dart/generate_dart.dart

@@ -535,7 +535,7 @@ Object? createServiceObject(dynamic json, List<String> expectedTypes) {
       } else {
         return null;
       }
-    } else if (_isNullInstance(json) && (!expectedTypes.contains(type))) {
+    } else if (_isNullInstance(json) && (!expectedTypes.contains('InstanceRef'))) {
       // Replace null instances with null when we don't expect an instance to
       // be returned.
       return null;

runtime/observatory/tests/service/get_version_rpc_test.dart

@@ -12,7 +12,7 @@ var tests = <VMTest>[
     final result = await vm.invokeRpcNoUpgrade('getVersion', {});
     expect(result['type'], 'Version');
     expect(result['major'], 3);
-    expect(result['minor'], 42);
+    expect(result['minor'], 43);
     expect(result['_privateMajor'], 0);
     expect(result['_privateMinor'], 0);
   },

runtime/observatory_2/tests/service_2/get_version_rpc_test.dart

@@ -12,7 +12,7 @@ var tests = <VMTest>[
     var result = await vm.invokeRpcNoUpgrade('getVersion', {});
     expect(result['type'], equals('Version'));
     expect(result['major'], equals(3));
-    expect(result['minor'], equals(42));
+    expect(result['minor'], equals(43));
     expect(result['_privateMajor'], equals(0));
     expect(result['_privateMinor'], equals(0));
   },

runtime/vm/service.h

@@ -15,7 +15,7 @@
 namespace dart {
 
 #define SERVICE_PROTOCOL_MAJOR_VERSION 3
-#define SERVICE_PROTOCOL_MINOR_VERSION 42
+#define SERVICE_PROTOCOL_MINOR_VERSION 43
 
 class Array;
 class EmbedderServiceHandler;

runtime/vm/service/service.md

@@ -1,8 +1,8 @@
-# Dart VM Service Protocol 3.42
+# Dart VM Service Protocol 3.43
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
-This document describes of _version 3.42_ of the Dart VM Service Protocol. This
+This document describes of _version 3.43_ of the Dart VM Service Protocol. This
 protocol is used to communicate with a running Dart Virtual Machine.
 
 To use the Service Protocol, start the VM with the *--observe* flag.
@@ -3948,5 +3948,6 @@ version | comments
 3.40 | Added `IsolateFlag` object and `isolateFlags` property to `Isolate`.
 3.41 | Added `PortList` object, `ReceivePort` `InstanceKind`, and `getPorts` RPC.
 3.42 | Added `limit` optional parameter to `getStack` RPC.
+3.43 | Updated heap snapshot format to include identity hash codes.
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss