Fix FlutterError.onError in debug mode (#53843)

* Fix FlutterError.onError in debug mode

* update

* fix comments

* add license header

* fix analyzer

* update

* another attempt

* fix test

* fix comment

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

@@ -715,7 +715,7 @@ class FlutterError extends Error with DiagnosticableTreeMixin implements Asserti
 
   /// Called whenever the Flutter framework catches an error.
   ///
-  /// The default behavior is to call [dumpErrorToConsole].
+  /// The default behavior is to call [presentError].
   ///
   /// You can set this to your own function to override this default behavior.
   /// For example, you could report all errors to your server.
@@ -725,7 +725,18 @@ class FlutterError extends Error with DiagnosticableTreeMixin implements Asserti
   ///
   /// Set this to null to silently catch and ignore errors. This is not
   /// recommended.
-  static FlutterExceptionHandler onError = dumpErrorToConsole;
+  static FlutterExceptionHandler onError = (FlutterErrorDetails details) => presentError(details);
+
+  /// Called whenever the Flutter framework wants to present an error to the
+  /// users.
+  ///
+  /// The default behavior is to call [dumpErrorToConsole].
+  ///
+  /// Plugins can override how an error is to be presented to the user. For
+  /// example, the structured errors service extension sets its own method when
+  /// the extension is enabled. If you want to change how Flutter responds to an
+  /// error, use [onError] instead.
+  static FlutterExceptionHandler presentError = dumpErrorToConsole;
 
   static int _errorCount = 0;
 

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

@@ -959,13 +959,13 @@ mixin WidgetInspectorService {
     SchedulerBinding.instance.addPersistentFrameCallback(_onFrameStart);
 
     final FlutterExceptionHandler structuredExceptionHandler = _reportError;
-    final FlutterExceptionHandler defaultExceptionHandler = FlutterError.onError;
+    final FlutterExceptionHandler defaultExceptionHandler = FlutterError.presentError;
 
     _registerBoolServiceExtension(
       name: 'structuredErrors',
-      getter: () async => FlutterError.onError == structuredExceptionHandler,
+      getter: () async => FlutterError.presentError == structuredExceptionHandler,
       setter: (bool value) {
-        FlutterError.onError = value ? structuredExceptionHandler : defaultExceptionHandler;
+        FlutterError.presentError = value ? structuredExceptionHandler : defaultExceptionHandler;
         return Future<void>.value();
       },
     );

packages/flutter/test/material/scaffold_test.dart

@@ -1840,7 +1840,7 @@ void main() {
         final GlobalKey<ScaffoldState> key = GlobalKey<ScaffoldState>();
         const Key buttonKey = Key('button');
         final List<FlutterErrorDetails> errors = <FlutterErrorDetails>[];
-        FlutterError.onError = (FlutterErrorDetails error) => errors.add(error);
+        FlutterError.presentError = (FlutterErrorDetails error) => errors.add(error);
         int state = 0;
         await tester.pumpWidget(
           MaterialApp(

packages/flutter/test/widgets/image_test.dart

@@ -528,6 +528,7 @@ void main() {
     final ImageListener listener = (ImageInfo info, bool synchronous) {
       capturedImage = info;
     };
+    final FlutterExceptionHandler oldHandler = FlutterError.onError;
     FlutterError.onError = (FlutterErrorDetails flutterError) {
       reportedException = flutterError.exception;
       reportedStackTrace = flutterError.stack;
@@ -564,6 +565,7 @@ void main() {
     // The image stream error handler should have the original exception.
     expect(capturedException, testException);
     expect(capturedStackTrace, testStack);
+    FlutterError.onError = oldHandler;
   });
 
   testWidgets('Duplicate listener registration does not affect error listeners', (WidgetTester tester) async {

packages/flutter/test/widgets/widget_inspector_structure_error_test.dart

@@ -0,0 +1,91 @@
+// Copyright 2014 The Flutter 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 'dart:async';
+import 'dart:convert';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  StructureErrorTestWidgetInspectorService.runTests();
+}
+
+typedef InspectorServiceExtensionCallback = FutureOr<Map<String, Object>> Function(Map<String, String> parameters);
+
+class StructureErrorTestWidgetInspectorService extends Object with WidgetInspectorService {
+  final Map<String, InspectorServiceExtensionCallback> extensions = <String, InspectorServiceExtensionCallback>{};
+
+  final Map<String, List<Map<Object, Object>>> eventsDispatched = <String, List<Map<Object, Object>>>{};
+
+  @override
+  void registerServiceExtension({
+    @required String name,
+    @required FutureOr<Map<String, Object>> callback(Map<String, String> parameters),
+  }) {
+    assert(!extensions.containsKey(name));
+    extensions[name] = callback;
+  }
+
+  @override
+  void postEvent(String eventKind, Map<Object, Object> eventData) {
+    getEventsDispatched(eventKind).add(eventData);
+  }
+
+  List<Map<Object, Object>> getEventsDispatched(String eventKind) {
+    return eventsDispatched.putIfAbsent(eventKind, () => <Map<Object, Object>>[]);
+  }
+
+  Iterable<Map<Object, Object>> getServiceExtensionStateChangedEvents(String extensionName) {
+    return getEventsDispatched('Flutter.ServiceExtensionStateChanged')
+      .where((Map<Object, Object> event) => event['extension'] == extensionName);
+  }
+
+  Future<String> testBoolExtension(String name, Map<String, String> arguments) async {
+    expect(extensions, contains(name));
+    // Encode and decode to JSON to match behavior using a real service
+    // extension where only JSON is allowed.
+    return json.decode(json.encode(await extensions[name](arguments)))['enabled'] as String;
+  }
+
+
+  static void runTests() {
+    final StructureErrorTestWidgetInspectorService service = StructureErrorTestWidgetInspectorService();
+    WidgetInspectorService.instance = service;
+
+    test('ext.flutter.inspector.structuredErrors still report error to original on error', () async {
+      final FlutterExceptionHandler oldHandler = FlutterError.onError;
+
+      FlutterErrorDetails actualError;
+      // Creates a spy onError. This spy needs to be set before widgets binding
+      // initializes.
+      FlutterError.onError = (FlutterErrorDetails details) {
+        actualError = details;
+      };
+
+      WidgetsFlutterBinding.ensureInitialized();
+      try {
+        // Enables structured errors.
+        expect(await service.testBoolExtension(
+          'structuredErrors', <String, String>{'enabled': 'true'}),
+          equals('true'));
+
+        // Creates an error.
+        final FlutterErrorDetails expectedError = FlutterErrorDetailsForRendering(
+          library: 'rendering library',
+          context: ErrorDescription('during layout'),
+          exception: StackTrace.current,
+        );
+        FlutterError.reportError(expectedError);
+
+        // Validates the spy still received an error.
+        expect(actualError, expectedError);
+      } finally {
+        FlutterError.onError = oldHandler;
+      }
+    });
+  }
+}

packages/flutter/test/widgets/widget_inspector_test.dart

@@ -2280,7 +2280,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       List<Map<Object, Object>> flutterErrorEvents = service.getEventsDispatched('Flutter.Error');
       expect(flutterErrorEvents, isEmpty);
 
-      final FlutterExceptionHandler oldHandler = FlutterError.onError;
+      final FlutterExceptionHandler oldHandler = FlutterError.presentError;
 
       try {
         // Enable structured errors.
@@ -2337,7 +2337,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
         error = flutterErrorEvents.last;
         expect(error['errorsSinceReload'], 0);
       } finally {
-        FlutterError.onError = oldHandler;
+        FlutterError.presentError = oldHandler;
       }
     });
 

packages/flutter_test/lib/src/binding.dart

@@ -572,9 +572,9 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   }) {
     assert(description != null);
     assert(inTest);
-    _oldExceptionHandler = FlutterError.onError;
+    _oldExceptionHandler = FlutterError.presentError;
     int _exceptionCount = 0; // number of un-taken exceptions
-    FlutterError.onError = (FlutterErrorDetails details) {
+    FlutterError.presentError = (FlutterErrorDetails details) {
       if (_pendingExceptionDetails != null) {
         debugPrint = debugPrintOverride; // just in case the test overrides it -- otherwise we won't see the errors!
         if (_exceptionCount == 0) {
@@ -800,7 +800,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   /// Called by the [testWidgets] function after a test is executed.
   void postTest() {
     assert(inTest);
-    FlutterError.onError = _oldExceptionHandler;
+    FlutterError.presentError = _oldExceptionHandler;
     _pendingExceptionDetails = null;
     _parentZone = null;
     buildOwner.focusManager = FocusManager();