Rendering errors with root causes in the widget layer should have a reference...

Rendering errors with root causes in the widget layer should have a reference to the widget (#32511)

dev/automated_tests/flutter_test/print_user_created_ancestor_expectation.txt

+<<skip until matching line>>
+══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
+The following assertion was thrown building
+RawGestureDetector-\[LabeledGlobalKey<RawGestureDetectorState>#.+\]\(state:
+RawGestureDetectorState#.+\(gestures: <none>, behavior: opaque\)\):
+'package:flutter\/src\/painting\/basic_types\.dart': Failed assertion: line 223 pos 10: 'textDirection
+!= null': is not true\.
+
+Either the assertion indicates an error in the framework itself, or we should provide substantially
+more information in this error message to help you determine and fix the underlying cause\.
+In either case, please report this assertion by filing a bug on GitHub:
+  https:\/\/github\.com\/flutter\/flutter\/issues\/new\?template=BUG\.md
+
+User-created ancestor of the error-causing widget was:
+  CustomScrollView
+  file:\/\/\/.+print_user_created_ancestor_test\.dart:[0-9]+:7
+
+When the exception was thrown, this was the stack:
+<<skip until matching line>>
+\(elided [0-9]+ frames from .+\)
+════════════════════════════════════════════════════════════════════════════════════════════════════
+.*..:.. \+0 -1: Rendering Error *
+  Test failed\. See exception logs above\.
+  The test description was: Rendering Error
+ *
+.*..:.. \+0 -1: Some tests failed\. *

dev/automated_tests/flutter_test/print_user_created_ancestor_no_flag_expectation.txt

+<<skip until matching line>>
+══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
+The following assertion was thrown building
+RawGestureDetector-\[LabeledGlobalKey<RawGestureDetectorState>#.+\]\(state:
+RawGestureDetectorState#.+\(gestures: <none>, behavior: opaque\)\):
+'package:flutter\/src\/painting\/basic_types\.dart': Failed assertion: line 223 pos 10: 'textDirection
+!= null': is not true\.
+
+Either the assertion indicates an error in the framework itself, or we should provide substantially
+more information in this error message to help you determine and fix the underlying cause\.
+In either case, please report this assertion by filing a bug on GitHub:
+  https:\/\/github\.com\/flutter\/flutter\/issues\/new\?template=BUG\.md
+
+Widget creation tracking is currently disabled. Enabling it enables improved error messages\. It can
+be enabled by passing `--track-widget-creation` to `flutter run` or `flutter test`\.
+
+When the exception was thrown, this was the stack:
+<<skip until matching line>>
+\(elided [0-9]+ frames from .+\)
+════════════════════════════════════════════════════════════════════════════════════════════════════
+.*..:.. \+0 -1: Rendering Error *
+  Test failed\. See exception logs above\.
+  The test description was: Rendering Error
+ *
+.*..:.. \+0 -1: Some tests failed\. *

dev/automated_tests/flutter_test/print_user_created_ancestor_no_flag_test.dart

+// Copyright 2019 The Chromium Authors. 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:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Rendering Error', (WidgetTester tester) async {
+    // this should fail
+    await tester.pumpWidget(
+      CustomScrollView(
+        slivers: <Widget>[
+          SliverToBoxAdapter(child: Container()),
+        ]
+      )
+    );
+  });
+}

dev/automated_tests/flutter_test/print_user_created_ancestor_test.dart

+// Copyright 2019 The Chromium Authors. 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:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Rendering Error', (WidgetTester tester) async {
+    // this should fail
+    await tester.pumpWidget(
+      CustomScrollView(
+        slivers: <Widget>[
+          SliverToBoxAdapter(child: Container()),
+        ]
+      )
+    );
+  });
+}

packages/flutter/lib/src/foundation/assertions.dart

@@ -12,6 +12,9 @@ import 'print.dart';
 /// Signature for [FlutterError.onError] handler.
 typedef FlutterExceptionHandler = void Function(FlutterErrorDetails details);
 
+/// Signature for [DiagnosticPropertiesBuilder] transformer.
+typedef DiagnosticPropertiesTransformer = Iterable<DiagnosticsNode> Function(Iterable<DiagnosticsNode> properties);
+
 /// Signature for [FlutterErrorDetails.informationCollector] callback
 /// and other callbacks that collect information describing an error.
 typedef InformationCollector = Iterable<DiagnosticsNode> Function();
@@ -212,6 +215,20 @@ class FlutterErrorDetails extends Diagnosticable {
     this.silent = false,
   });
 
+  /// Transformers to transform [DiagnosticsNode] in [DiagnosticPropertiesBuilder]
+  /// into a more descriptive form.
+  ///
+  /// There are layers that attach certain [DiagnosticsNode] into
+  /// [FlutterErrorDetails] that require knowledge from other layers to parse.
+  /// To correctly interpret those [DiagnosticsNode], register transformers in
+  /// the layers that possess the knowledge.
+  ///
+  /// See also:
+  ///
+  ///  * [WidgetsBinding.initInstances], which registers its transformer.
+  static final List<DiagnosticPropertiesTransformer> propertiesTransformers =
+    <DiagnosticPropertiesTransformer>[];
+
   /// The exception. Often this will be an [AssertionError], maybe specifically
   /// a [FlutterError]. However, this could be any value at all.
   final dynamic exception;
@@ -449,6 +466,15 @@ class FlutterErrorDetails extends Diagnosticable {
   String toString({DiagnosticLevel minLevel = DiagnosticLevel.debug}) {
     return toDiagnosticsNode(style: DiagnosticsTreeStyle.error).toStringDeep(minLevel: minLevel);
   }
+
+  @override
+  DiagnosticsNode toDiagnosticsNode({ String name, DiagnosticsTreeStyle style }) {
+    return _FlutterErrorDetailsNode(
+      name: name,
+      value: this,
+      style: style,
+    );
+  }
 }
 
 /// Error class used to report Flutter-specific assertion failures and
@@ -777,3 +803,28 @@ class DiagnosticsStackTrace extends DiagnosticsBlock {
     return DiagnosticsNode.message(frame, allowWrap: false);
   }
 }
+
+class _FlutterErrorDetailsNode extends DiagnosticableNode<FlutterErrorDetails> {
+  _FlutterErrorDetailsNode({
+    String name,
+    @required FlutterErrorDetails value,
+    @required DiagnosticsTreeStyle style,
+  }) : super(
+    name: name,
+    value: value,
+    style: style,
+  );
+
+  @override
+  DiagnosticPropertiesBuilder get builder {
+    final DiagnosticPropertiesBuilder builder = super.builder;
+    if (builder == null){
+      return null;
+    }
+    Iterable<DiagnosticsNode> properties = builder.properties;
+    for (DiagnosticPropertiesTransformer transformer in FlutterErrorDetails.propertiesTransformers) {
+      properties = transformer(properties);
+    }
+    return DiagnosticPropertiesBuilder.fromProperties(properties.toList());
+  }
+}

packages/flutter/lib/src/foundation/diagnostics.dart

@@ -2774,7 +2774,10 @@ class DiagnosticableNode<T extends Diagnosticable> extends DiagnosticsNode {
 
   DiagnosticPropertiesBuilder _cachedBuilder;
 
-  DiagnosticPropertiesBuilder get _builder {
+  /// Retrieve the [DiagnosticPropertiesBuilder] of current node.
+  ///
+  /// It will cache the result to prevent duplicate operation.
+  DiagnosticPropertiesBuilder get builder {
     if (kReleaseMode)
       return null;
     if (_cachedBuilder == null) {
@@ -2786,14 +2789,14 @@ class DiagnosticableNode<T extends Diagnosticable> extends DiagnosticsNode {
 
   @override
   DiagnosticsTreeStyle get style {
-    return kReleaseMode ? DiagnosticsTreeStyle.none : super.style ?? _builder.defaultDiagnosticsTreeStyle;
+    return kReleaseMode ? DiagnosticsTreeStyle.none : super.style ?? builder.defaultDiagnosticsTreeStyle;
   }
 
   @override
-  String get emptyBodyDescription => kReleaseMode ? '' : _builder.emptyBodyDescription;
+  String get emptyBodyDescription => kReleaseMode ? '' : builder.emptyBodyDescription;
 
   @override
-  List<DiagnosticsNode> getProperties() => kReleaseMode ? const <DiagnosticsNode>[] : _builder.properties;
+  List<DiagnosticsNode> getProperties() => kReleaseMode ? const <DiagnosticsNode>[] : builder.properties;
 
   @override
   List<DiagnosticsNode> getChildren() {
@@ -2875,6 +2878,13 @@ String describeEnum(Object enumEntry) {
 /// Builder to accumulate properties and configuration used to assemble a
 /// [DiagnosticsNode] from a [Diagnosticable] object.
 class DiagnosticPropertiesBuilder {
+  /// Creates a [DiagnosticPropertiesBuilder] with [properties] initialize to
+  /// an empty array.
+  DiagnosticPropertiesBuilder() : properties = <DiagnosticsNode>[];
+
+  /// Creates a [DiagnosticPropertiesBuilder] with a given [properties].
+  DiagnosticPropertiesBuilder.fromProperties(this.properties);
+
   /// Add a property to the list of properties.
   void add(DiagnosticsNode property) {
     if (!kReleaseMode) {
@@ -2883,7 +2893,7 @@ class DiagnosticPropertiesBuilder {
   }
 
   /// List of properties accumulated so far.
-  final List<DiagnosticsNode> properties = <DiagnosticsNode>[];
+  final List<DiagnosticsNode> properties;
 
   /// Default style to use for the [DiagnosticsNode] if no style is specified.
   DiagnosticsTreeStyle defaultDiagnosticsTreeStyle = DiagnosticsTreeStyle.sparse;

packages/flutter/lib/src/rendering/debug_overflow_indicator.dart

@@ -6,6 +6,7 @@ import 'dart:math' as math;
 import 'dart:ui' as ui;
 
 import 'package:flutter/painting.dart';
+import 'package:flutter/foundation.dart';
 
 import 'object.dart';
 import 'stack.dart';
@@ -248,6 +249,8 @@ mixin DebugOverflowIndicatorMixin on RenderObject {
         context: ErrorDescription('during layout'),
         renderObject: this,
         informationCollector: () sync* {
+          if (debugCreator != null)
+            yield DiagnosticsDebugCreator(debugCreator);
           yield* overflowHints;
           yield describeForError('The specific $runtimeType in question is');
           // TODO(jacobr): this line is ascii art that it would be nice to

packages/flutter/lib/src/rendering/object.dart

@@ -1189,6 +1189,8 @@ abstract class RenderObject extends AbstractNode with DiagnosticableTreeMixin im
       context: ErrorDescription('during $method()'),
       renderObject: this,
       informationCollector: () sync* {
+        if (debugCreator != null)
+          yield DiagnosticsDebugCreator(debugCreator);
         yield describeForError('The following RenderObject was being processed when the exception was fired');
         // TODO(jacobr): this error message has a code smell. Consider whether
         // displaying the truncated children is really useful for command line
@@ -3675,3 +3677,20 @@ class _SemanticsGeometry {
   bool get markAsHidden => _markAsHidden;
   bool _markAsHidden = false;
 }
+
+/// A class that creates [DiagnosticsNode] by wrapping [RenderObject.debugCreator].
+///
+/// Attach a [DiagnosticsDebugCreator] into [FlutterErrorDetails.informationCollector]
+/// when a [RenderObject.debugCreator] is available. This will lead to improved
+/// error message.
+class DiagnosticsDebugCreator extends DiagnosticsProperty<Object> {
+  /// Create a [DiagnosticsProperty] with its [value] initialized to input
+  /// [RenderObject.debugCreator].
+  DiagnosticsDebugCreator(Object value):
+    assert(value != null),
+    super(
+      'debugCreator',
+      value,
+      level: DiagnosticLevel.hidden
+    );
+}

packages/flutter/lib/src/widgets/binding.dart

@@ -256,6 +256,7 @@ mixin WidgetsBinding on BindingBase, SchedulerBinding, GestureBinding, RendererB
     window.onAccessibilityFeaturesChanged = handleAccessibilityFeaturesChanged;
     SystemChannels.navigation.setMethodCallHandler(_handleNavigationInvocation);
     SystemChannels.system.setMessageHandler(_handleSystemMessage);
+    FlutterErrorDetails.propertiesTransformers.add(transformDebugCreator);
   }
 
   /// The current [WidgetsBinding], if one has been created.

packages/flutter/lib/src/widgets/framework.dart

@@ -2344,6 +2344,7 @@ class BuildOwner {
             e,
             stack,
             informationCollector: () sync* {
+              yield DiagnosticsDebugCreator(DebugCreator(_dirtyElements[index]));
               yield _dirtyElements[index].describeElement('The element being rebuilt at the time was index $index of $dirtyCount');
             },
           );
@@ -2771,7 +2772,6 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     return StringProperty(name, debugGetCreatorChain(10));
   }
 
-
   // This is used to verify that Element objects move through life in an
   // orderly fashion.
   _ElementLifecycle _debugLifecycleState = _ElementLifecycle.initial;
@@ -3933,7 +3933,16 @@ abstract class ComponentElement extends Element {
       built = build();
       debugWidgetBuilderValue(widget, built);
     } catch (e, stack) {
-      built = ErrorWidget.builder(_debugReportException(ErrorDescription('building $this'), e, stack));
+      built = ErrorWidget.builder(
+        _debugReportException(
+          ErrorDescription('building $this'),
+          e,
+          stack,
+          informationCollector: () sync* {
+            yield DiagnosticsDebugCreator(DebugCreator(this));
+          },
+        )
+      );
     } finally {
       // We delay marking the element as clean until after calling build() so
       // that attempts to markNeedsBuild() during build() will be ignored.
@@ -3944,7 +3953,16 @@ abstract class ComponentElement extends Element {
       _child = updateChild(_child, built, slot);
       assert(_child != null);
     } catch (e, stack) {
-      built = ErrorWidget.builder(_debugReportException(ErrorDescription('building $this'), e, stack));
+      built = ErrorWidget.builder(
+        _debugReportException(
+          ErrorDescription('building $this'),
+          e,
+          stack,
+          informationCollector: () sync* {
+            yield DiagnosticsDebugCreator(DebugCreator(this));
+          },
+        )
+      );
       _child = updateChild(null, built, slot);
     }
 
@@ -4738,7 +4756,7 @@ abstract class RenderObjectElement extends Element {
 
   void _debugUpdateRenderObjectOwner() {
     assert(() {
-      _renderObject.debugCreator = _DebugCreator(this);
+      _renderObject.debugCreator = DebugCreator(this);
       return true;
     }());
   }
@@ -5219,9 +5237,17 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
   }
 }
 
-class _DebugCreator {
-  _DebugCreator(this.element);
-  final RenderObjectElement element;
+/// A wrapper class for the [Element] that is the creator of a [RenderObject].
+///
+/// Attaching a [DebugCreator] attach the [RenderObject] will lead to better error
+/// message.
+class DebugCreator {
+  /// Create a [DebugCreator] instance with input [Element].
+  DebugCreator(this.element);
+
+  /// The creator of the [RenderObject].
+  final Element element;
+
   @override
   String toString() => element.debugGetCreatorChain(12);
 }

packages/flutter/lib/src/widgets/layout_builder.dart

@@ -113,14 +113,32 @@ class _LayoutBuilderElement extends RenderObjectElement {
           built = widget.builder(this, constraints);
           debugWidgetBuilderValue(widget, built);
         } catch (e, stack) {
-          built = ErrorWidget.builder(_debugReportException(ErrorDescription('building $widget'), e, stack));
+          built = ErrorWidget.builder(
+            _debugReportException(
+              ErrorDescription('building $widget'),
+              e,
+              stack,
+              informationCollector: () sync* {
+                yield DiagnosticsDebugCreator(DebugCreator(this));
+              },
+            )
+          );
         }
       }
       try {
         _child = updateChild(_child, built, null);
         assert(_child != null);
       } catch (e, stack) {
-        built = ErrorWidget.builder(_debugReportException(ErrorDescription('building $widget'), e, stack));
+        built = ErrorWidget.builder(
+          _debugReportException(
+            ErrorDescription('building $widget'),
+            e,
+            stack,
+            informationCollector: () sync* {
+              yield DiagnosticsDebugCreator(DebugCreator(this));
+            },
+          )
+        );
         _child = updateChild(null, built, slot);
       }
     });
@@ -228,13 +246,15 @@ class _RenderLayoutBuilder extends RenderBox with RenderObjectWithChildMixin<Ren
 FlutterErrorDetails _debugReportException(
   DiagnosticsNode context,
   dynamic exception,
-  StackTrace stack,
-) {
+  StackTrace stack, {
+  InformationCollector informationCollector,
+}) {
   final FlutterErrorDetails details = FlutterErrorDetails(
     exception: exception,
     stack: stack,
     library: 'widgets library',
     context: context,
+    informationCollector: informationCollector,
   );
   FlutterError.reportError(details);
   return details;

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -1397,11 +1397,17 @@ mixin WidgetInspectorService {
   }
 
   bool _isLocalCreationLocation(_Location location) {
-    if (_pubRootDirectories == null || location == null || location.file == null) {
+    if (location == null || location.file == null) {
       return false;
     }
-
     final String file = Uri.parse(location.file).path;
+
+    // By default check whether the creation location was within package:flutter.
+    if (_pubRootDirectories == null) {
+      // TODO(chunhtai): Make it more robust once
+      // https://github.com/flutter/flutter/issues/32660 is fixed.
+      return !file.contains('packages/flutter/');
+    }
     for (String directory in _pubRootDirectories) {
       if (file.startsWith(directory)) {
         return true;
@@ -2705,6 +2711,105 @@ class _Location {
   }
 }
 
+bool _isDebugCreator(DiagnosticsNode node) => node is DiagnosticsDebugCreator;
+
+/// Transformer to parse and gather information about [DiagnosticsDebugCreator].
+///
+/// This function will be registered to [FlutterErrorDetails.propertiesTransformers]
+/// in [WidgetsBinding.initInstances].
+Iterable<DiagnosticsNode> transformDebugCreator(Iterable<DiagnosticsNode> properties) sync* {
+  final List<DiagnosticsNode> pending = <DiagnosticsNode>[];
+  bool foundStackTrace = false;
+  for (DiagnosticsNode node in properties) {
+    if (!foundStackTrace && node is DiagnosticsStackTrace)
+      foundStackTrace = true;
+    if (_isDebugCreator(node)) {
+      yield* _parseDiagnosticsNode(node);
+    } else {
+      if (foundStackTrace) {
+        pending.add(node);
+      } else {
+        yield node;
+      }
+    }
+  }
+  yield* pending;
+}
+
+/// Transform the input [DiagnosticsNode].
+///
+/// Return null if input [DiagnosticsNode] is not applicable.
+Iterable<DiagnosticsNode> _parseDiagnosticsNode(DiagnosticsNode node) {
+  if (!_isDebugCreator(node))
+    return null;
+  final DebugCreator debugCreator = node.value;
+  final Element element = debugCreator.element;
+  return _describeRelevantUserCode(element);
+}
+
+Iterable<DiagnosticsNode> _describeRelevantUserCode(Element element) {
+  if (!WidgetInspectorService.instance.isWidgetCreationTracked()) {
+    return <DiagnosticsNode>[
+      ErrorDescription(
+        'Widget creation tracking is currently disabled. Enabling '
+        'it enables improved error messages. It can be enabled by passing '
+        '`--track-widget-creation` to `flutter run` or `flutter test`.',
+      ),
+      ErrorSpacer(),
+    ];
+  }
+  final List<DiagnosticsNode> nodes = <DiagnosticsNode>[];
+  element.visitAncestorElements((Element ancestor) {
+    // TODO(chunhtai): should print out all the widgets that are about to cross
+    // package boundaries.
+    if (_isLocalCreationLocation(ancestor)) {
+      nodes.add(
+        DiagnosticsBlock(
+          name: 'User-created ancestor of the error-causing widget was',
+          children: <DiagnosticsNode>[
+            ErrorDescription('${ancestor.widget.toStringShort()} ${_describeCreationLocation(ancestor)}'),
+          ],
+        )
+      );
+      nodes.add(ErrorSpacer());
+      return false;
+    }
+    return true;
+  });
+  return nodes;
+}
+
+/// Returns if an object is user created.
+///
+/// This function will only work in debug mode builds when
+/// the `--track-widget-creation` flag is passed to `flutter_tool`. Dart 2.0 is
+/// required as injecting creation locations requires a
+/// [Dart Kernel Transformer](https://github.com/dart-lang/sdk/wiki/Kernel-Documentation).
+///
+/// Currently is local creation locations are only available for
+/// [Widget] and [Element].
+bool _isLocalCreationLocation(Object object) {
+  final _Location location = _getCreationLocation(object);
+  if (location == null)
+    return false;
+  return WidgetInspectorService.instance._isLocalCreationLocation(location);
+}
+
+/// Returns the creation location of an object in String format if one is available.
+///
+/// ex: "file:///path/to/main.dart:4:3"
+///
+/// Creation locations are only available for debug mode builds when
+/// the `--track-widget-creation` flag is passed to `flutter_tool`. Dart 2.0 is
+/// required as injecting creation locations requires a
+/// [Dart Kernel Transformer](https://github.com/dart-lang/sdk/wiki/Kernel-Documentation).
+///
+/// Currently creation locations are only available for [Widget] and [Element].
+String _describeCreationLocation(Object object) {
+  final _Location location = _getCreationLocation(object);
+  return location?.toString();
+}
+
 /// Returns the creation location of an object if one is available.
 ///
 /// Creation locations are only available for debug mode builds when
@@ -2712,7 +2817,7 @@ class _Location {
 /// required as injecting creation locations requires a
 /// [Dart Kernel Transformer](https://github.com/dart-lang/sdk/wiki/Kernel-Documentation).
 ///
-/// Currently creation locations are only available for [Widget] and [Element]
+/// Currently creation locations are only available for [Widget] and [Element].
 _Location _getCreationLocation(Object object) {
   final Object candidate =  object is Element ? object.widget : object;
   return candidate is _HasCreationLocation ? candidate._location : null;

packages/flutter/test/material/stepper_test.dart

@@ -527,9 +527,9 @@ void main() {
     final List<String> lines =  errorDetails.toString().split('\n');
     // The lines in the middle of the error message contain the stack trace
     // which will change depending on where the test is run.
-    expect(lines.length, greaterThan(9));
+    expect(lines.length, greaterThan(7));
     expect(
-      lines.take(9).join('\n'),
+      lines.take(7).join('\n'),
       equalsIgnoringHashCodes(
         '══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞════════════════════════\n'
         'The following assertion was thrown building Stepper(dirty,\n'
@@ -537,12 +537,9 @@ void main() {
         '_StepperState#00000):\n'
         'Steppers must not be nested. The material specification advises\n'
         'that one should avoid embedding steppers within steppers.\n'
-        'https://material.io/archive/guidelines/components/steppers.html#steppers-usage\n'
-        '\n'
-        'When the exception was thrown, this was the stack:'
+        'https://material.io/archive/guidelines/components/steppers.html#steppers-usage'
       ),
     );
-
   });
 
   ///https://github.com/flutter/flutter/issues/16920

packages/flutter/test/widgets/widget_inspector_test.dart

@@ -853,6 +853,132 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       expect(paramB2['column'], equals(25));
     }, skip: !WidgetInspectorService.instance.isWidgetCreationTracked()); // Test requires --track-widget-creation flag.
 
+    testWidgets('test transformDebugCreator will re-order if after stack trace', (WidgetTester tester) async {
+      final bool widgetTracked = WidgetInspectorService.instance.isWidgetCreationTracked();
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Stack(
+            children: const <Widget>[
+              Text('a'),
+              Text('b', textDirection: TextDirection.ltr),
+              Text('c', textDirection: TextDirection.ltr),
+            ],
+          ),
+        ),
+      );
+      final Element elementA = find.text('a').evaluate().first;
+      String pubRootTest;
+      if (widgetTracked) {
+        final Map<String, Object> jsonObject = json.decode(
+          service.getSelectedWidget(null, 'my-group'));
+        final Map<String,
+          Object> creationLocation = jsonObject['creationLocation'];
+        expect(creationLocation, isNotNull);
+        final String fileA = creationLocation['file'];
+        expect(fileA, endsWith('widget_inspector_test.dart'));
+        expect(jsonObject, isNot(contains('createdByLocalProject')));
+        final List<String> segments = Uri
+          .parse(fileA)
+          .pathSegments;
+        // Strip a couple subdirectories away to generate a plausible pub root
+        // directory.
+        pubRootTest = '/' +
+          segments.take(segments.length - 2).join('/');
+        service.setPubRootDirectories(<Object>[pubRootTest]);
+      }
+      final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+      builder.add(StringProperty('dummy1', 'value'));
+      builder.add(StringProperty('dummy2', 'value'));
+      builder.add(DiagnosticsStackTrace('When the exception was thrown, this was the stack', null));
+      builder.add(DiagnosticsDebugCreator(DebugCreator(elementA)));
+
+      final List<DiagnosticsNode> nodes = List<DiagnosticsNode>.from(transformDebugCreator(builder.properties));
+      expect(nodes.length, 5);
+      expect(nodes[0].runtimeType, StringProperty);
+      expect(nodes[0].name, 'dummy1');
+      expect(nodes[1].runtimeType, StringProperty);
+      expect(nodes[1].name, 'dummy2');
+      // transformed node should come in front of stack trace.
+      if (widgetTracked) {
+        expect(nodes[2].runtimeType, DiagnosticsBlock);
+        final DiagnosticsBlock node = nodes[2];
+        final List<DiagnosticsNode> children = node.getChildren();
+        expect(children.length, 1);
+        final ErrorDescription child = children[0];
+        expect(child.valueToString().contains(Uri.parse(pubRootTest).path), true);
+      } else {
+        expect(nodes[2].runtimeType, ErrorDescription);
+        final ErrorDescription node = nodes[2];
+        expect(node.valueToString().startsWith('Widget creation tracking is currently disabled.'), true);
+      }
+      expect(nodes[3].runtimeType, ErrorSpacer);
+      expect(nodes[4].runtimeType, DiagnosticsStackTrace);
+    });
+
+    testWidgets('test transformDebugCreator will not re-order if before stack trace', (WidgetTester tester) async {
+      final bool widgetTracked = WidgetInspectorService.instance.isWidgetCreationTracked();
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: Stack(
+            children: const <Widget>[
+              Text('a'),
+              Text('b', textDirection: TextDirection.ltr),
+              Text('c', textDirection: TextDirection.ltr),
+            ],
+          ),
+        ),
+      );
+      final Element elementA = find.text('a').evaluate().first;
+      String pubRootTest;
+      if (widgetTracked) {
+        final Map<String, Object> jsonObject = json.decode(
+          service.getSelectedWidget(null, 'my-group'));
+        final Map<String,
+          Object> creationLocation = jsonObject['creationLocation'];
+        expect(creationLocation, isNotNull);
+        final String fileA = creationLocation['file'];
+        expect(fileA, endsWith('widget_inspector_test.dart'));
+        expect(jsonObject, isNot(contains('createdByLocalProject')));
+        final List<String> segments = Uri
+          .parse(fileA)
+          .pathSegments;
+        // Strip a couple subdirectories away to generate a plausible pub root
+        // directory.
+        pubRootTest = '/' +
+          segments.take(segments.length - 2).join('/');
+        service.setPubRootDirectories(<Object>[pubRootTest]);
+      }
+      final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
+      builder.add(StringProperty('dummy1', 'value'));
+      builder.add(DiagnosticsDebugCreator(DebugCreator(elementA)));
+      builder.add(StringProperty('dummy2', 'value'));
+      builder.add(DiagnosticsStackTrace('When the exception was thrown, this was the stack', null));
+
+      final List<DiagnosticsNode> nodes = List<DiagnosticsNode>.from(transformDebugCreator(builder.properties));
+      expect(nodes.length, 5);
+      expect(nodes[0].runtimeType, StringProperty);
+      expect(nodes[0].name, 'dummy1');
+      // transformed node stays at original place.
+      if (widgetTracked) {
+        expect(nodes[1].runtimeType, DiagnosticsBlock);
+        final DiagnosticsBlock node = nodes[1];
+        final List<DiagnosticsNode> children = node.getChildren();
+        expect(children.length, 1);
+        final ErrorDescription child = children[0];
+        expect(child.valueToString().contains(Uri.parse(pubRootTest).path), true);
+      } else {
+        expect(nodes[1].runtimeType, ErrorDescription);
+        final ErrorDescription node = nodes[1];
+        expect(node.valueToString().startsWith('Widget creation tracking is currently disabled.'), true);
+      }
+      expect(nodes[2].runtimeType, ErrorSpacer);
+      expect(nodes[3].runtimeType, StringProperty);
+      expect(nodes[3].name, 'dummy2');
+      expect(nodes[4].runtimeType, DiagnosticsStackTrace);
+    }, skip: WidgetInspectorService.instance.isWidgetCreationTracked());
+
     testWidgets('WidgetInspectorService setPubRootDirectories', (WidgetTester tester) async {
       await tester.pumpWidget(
         Directionality(

packages/flutter_tools/test/commands/test_test.dart

@@ -31,33 +31,44 @@ void main() {
     testUsingContext('report nice errors for exceptions thrown within testWidgets()', () async {
       Cache.flutterRoot = '../..';
       return _testFile('exception_handling', automatedTestsDirectory, flutterTestDirectory);
-    }, skip: io.Platform.isWindows); // Dart on Windows has trouble with unicode characters in output
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
 
     testUsingContext('report a nice error when a guarded function was called without await', () async {
       Cache.flutterRoot = '../..';
       return _testFile('test_async_utils_guarded', automatedTestsDirectory, flutterTestDirectory);
-    }, skip: io.Platform.isWindows); // Dart on Windows has trouble with unicode characters in output
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
 
     testUsingContext('report a nice error when an async function was called without await', () async {
       Cache.flutterRoot = '../..';
       return _testFile('test_async_utils_unguarded', automatedTestsDirectory, flutterTestDirectory);
-    }, skip: io.Platform.isWindows); // Dart on Windows has trouble with unicode characters in output
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
 
     testUsingContext('report a nice error when a Ticker is left running', () async {
       Cache.flutterRoot = '../..';
       return _testFile('ticker', automatedTestsDirectory, flutterTestDirectory);
-    }, skip: io.Platform.isWindows); // Dart on Windows has trouble with unicode characters in output
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
 
     testUsingContext('report a nice error when a pubspec.yaml is missing a flutter_test dependency', () async {
       final String missingDependencyTests = fs.path.join('..', '..', 'dev', 'missing_dependency_tests');
       Cache.flutterRoot = '../..';
       return _testFile('trivial', missingDependencyTests, missingDependencyTests);
-    }, skip: io.Platform.isWindows); // Dart on Windows has trouble with unicode characters in output
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
+
+    testUsingContext('report which user created widget caused the error', () async {
+      Cache.flutterRoot = '../..';
+      return _testFile('print_user_created_ancestor', automatedTestsDirectory, flutterTestDirectory,
+          extraArguments: const <String>['--track-widget-creation']);
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
+
+    testUsingContext('report which user created widget caused the error - no flag', () async {
+      Cache.flutterRoot = '../..';
+      return _testFile('print_user_created_ancestor_no_flag', automatedTestsDirectory, flutterTestDirectory);
+    }, skip: io.Platform.isWindows); // TODO(chunhtai): Dart on Windows has trouble with unicode characters in output (#35425).
 
     testUsingContext('run a test when its name matches a regexp', () async {
       Cache.flutterRoot = '../..';
       final ProcessResult result = await _runFlutterTest('filtering', automatedTestsDirectory, flutterTestDirectory,
-        extraArgs: const <String>['--name', 'inc.*de']);
+        extraArguments: const <String>['--name', 'inc.*de']);
       if (!result.stdout.contains('+1: All tests passed'))
         fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
       expect(result.exitCode, 0);
@@ -66,7 +77,7 @@ void main() {
     testUsingContext('run a test when its name contains a string', () async {
       Cache.flutterRoot = '../..';
       final ProcessResult result = await _runFlutterTest('filtering', automatedTestsDirectory, flutterTestDirectory,
-        extraArgs: const <String>['--plain-name', 'include']);
+        extraArguments: const <String>['--plain-name', 'include']);
       if (!result.stdout.contains('+1: All tests passed'))
         fail('unexpected output from test:\n\n${result.stdout}\n-- end stdout --\n\n');
       expect(result.exitCode, 0);
@@ -75,7 +86,7 @@ void main() {
     testUsingContext('test runs to completion', () async {
       Cache.flutterRoot = '../..';
       final ProcessResult result = await _runFlutterTest('trivial', automatedTestsDirectory, flutterTestDirectory,
-        extraArgs: const <String>['--verbose']);
+        extraArguments: const <String>['--verbose']);
       if ((!result.stdout.contains('+1: All tests passed')) ||
           (!result.stdout.contains('test 0: starting shell process')) ||
           (!result.stdout.contains('test 0: deleting temporary directory')) ||
@@ -90,7 +101,13 @@ void main() {
   });
 }
 
-Future<void> _testFile(String testName, String workingDirectory, String testDirectory, { Matcher exitCode }) async {
+Future<void> _testFile(
+    String testName,
+    String workingDirectory,
+    String testDirectory, {
+      Matcher exitCode,
+      List<String> extraArguments = const <String>[],
+    }) async {
   exitCode ??= isNonZero;
   final String fullTestExpectation = fs.path.join(testDirectory, '${testName}_expectation.txt');
   final File expectationFile = fs.file(fullTestExpectation);
@@ -100,7 +117,12 @@ Future<void> _testFile(String testName, String workingDirectory, String testDire
   while (_testExclusionLock != null)
     await _testExclusionLock;
 
-  final ProcessResult exec = await _runFlutterTest(testName, workingDirectory, testDirectory);
+  final ProcessResult exec = await _runFlutterTest(
+    testName,
+    workingDirectory,
+    testDirectory,
+    extraArguments: extraArguments,
+  );
 
   expect(exec.exitCode, exitCode);
   final List<String> output = exec.stdout.split('\n');
@@ -164,7 +186,7 @@ Future<ProcessResult> _runFlutterTest(
   String testName,
   String workingDirectory,
   String testDirectory, {
-  List<String> extraArgs = const <String>[],
+  List<String> extraArguments = const <String>[],
 }) async {
 
   final String testFilePath = fs.path.join(testDirectory, '${testName}_test.dart');
@@ -177,7 +199,7 @@ Future<ProcessResult> _runFlutterTest(
     fs.path.absolute(fs.path.join('bin', 'flutter_tools.dart')),
     'test',
     '--no-color',
-    ...extraArgs,
+    ...extraArguments,
     testFilePath
   ];