Calculates retaining paths through user fields and ignores VM objects

runtime/observatory/tests/service/get_user_level_retaining_path_rpc_test.dart

+// Copyright (c) 2015, 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.
+// VMOptions=--error_on_bad_type --error_on_bad_override
+
+import 'package:observatory/service_io.dart';
+import 'package:unittest/unittest.dart';
+
+import 'test_helper.dart';
+
+class _TestClass {
+  _TestClass();
+  var x;
+  var y;
+}
+
+class _TestConst {
+  const _TestConst();
+}
+
+_TopLevelClosure() {}
+
+var x;
+var fn;
+
+void warmup() {
+  x = const _TestConst();
+  fn = _TopLevelClosure;
+}
+
+eval(Isolate isolate, String expression) async {
+  Map params = {
+    'targetId': isolate.rootLibrary.id,
+    'expression': expression,
+  };
+  return await isolate.invokeRpcNoUpgrade('evaluate', params);
+}
+
+var tests = [
+  // Expect a simple path through variable x instead of long path filled
+  // with VM objects
+  (Isolate isolate) async {
+    var target1 = await eval(isolate, 'x;');
+    var params = {
+      'targetId': target1['id'],
+      'limit': 100,
+    };
+    var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
+    expect(result['type'], equals('RetainingPath'));
+    expect(result['elements'].length, equals(2));
+    expect(
+        result['elements'][0]['value']['class']['name'], equals('_TestConst'));
+    expect(result['elements'][1]['value']['name'], equals('x'));
+  },
+
+  // Expect a simple path through variable fn instead of long path filled
+  // with VM objects
+  (Isolate isolate) async {
+    var target2 = await eval(isolate, 'fn;');
+    var params = {
+      'targetId': target2['id'],
+      'limit': 100,
+    };
+    var result = await isolate.invokeRpcNoUpgrade('_getRetainingPath', params);
+    expect(result['type'], equals('RetainingPath'));
+    expect(result['elements'].length, equals(2));
+    expect(result['elements'][0]['value']['class']['name'], equals('_Closure'));
+    expect(result['elements'][1]['value']['name'], equals('fn'));
+  }
+];
+
+main(args) async => runIsolateTests(args, tests, testeeBefore: warmup);