Add more structure to errors (continuation of #34684) (#42640)

* Add structured errors in Animations, TabView, ChangeNotifier

* Add structured error on MaterialPageRoute, BoxBorder, DecorationImagePainter, TextSpan

* Add structured errors in Debug

* Fix test errors

* Add structured errors in Scaffold and Stepper

* Add structured errors in part of Rendering Layer

* Fix failing test due to FloatingPoint precision

* Fix failing tests due to precision error and not using final

* Fix failing test due to floating precision error with RegEx instead

* Add structured error in CustomLayout and increase test coverage

* Add structured error & its test in ListBody

* Add structured error in ProxyBox and increase test coverage

* Add structured error message in Viewport

* Fix styles and add more assertions on ErrorHint and DiagnosticProperty

* Add structured error in scheduler/binding and scheduler/ticker

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in AssetBundle and TextInput

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured errors in several widgets flutter#1

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove unused import

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add assertions on hint messages

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix catch spacing

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in several widgets part 2 and increase code coverage

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Add structured error in flutter_test/widget_tester

* Fix floating precision accuracy by using RegExp

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove todo to add tests in Scaffold showBottomSheet

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix reviews by indenting lines and fixing the assertion orders

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Fix failing tests due to renaming class

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Try skipping the NetworkBundleTest

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

* Remove leading space in material/debug error hint

Signed-off-by: Albertus Angga Raharja <albertusangga@google.com>

Author: Albertus Angga Raharja

packages/flutter/lib/src/cupertino/tab_view.dart

@@ -192,29 +192,33 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
   Route<dynamic> _onUnknownRoute(RouteSettings settings) {
     assert(() {
       if (widget.onUnknownRoute == null) {
-        throw FlutterError(
-          'Could not find a generator for route $settings in the $runtimeType.\n'
-          'Generators for routes are searched for in the following order:\n'
-          ' 1. For the "/" route, the "builder" property, if non-null, is used.\n'
-          ' 2. Otherwise, the "routes" table is used, if it has an entry for '
-          'the route.\n'
-          ' 3. Otherwise, onGenerateRoute is called. It should return a '
-          'non-null value for any valid route not handled by "builder" and "routes".\n'
-          ' 4. Finally if all else fails onUnknownRoute is called.\n'
-          'Unfortunately, onUnknownRoute was not set.'
-        );
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('Could not find a generator for route $settings in the $runtimeType.'),
+          ErrorDescription(
+            'Generators for routes are searched for in the following order:\n'
+            ' 1. For the "/" route, the "builder" property, if non-null, is used.\n'
+            ' 2. Otherwise, the "routes" table is used, if it has an entry for '
+            'the route.\n'
+            ' 3. Otherwise, onGenerateRoute is called. It should return a '
+            'non-null value for any valid route not handled by "builder" and "routes".\n'
+            ' 4. Finally if all else fails onUnknownRoute is called.\n'
+            'Unfortunately, onUnknownRoute was not set.'
+          )
+        ]);
       }
       return true;
     }());
     final Route<dynamic> result = widget.onUnknownRoute(settings);
     assert(() {
       if (result == null) {
-        throw FlutterError(
-          'The onUnknownRoute callback returned null.\n'
-          'When the $runtimeType requested the route $settings from its '
-          'onUnknownRoute callback, the callback returned null. Such callbacks '
-          'must never return null.'
-        );
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('The onUnknownRoute callback returned null.'),
+          ErrorDescription(
+            'When the $runtimeType requested the route $settings from its '
+            'onUnknownRoute callback, the callback returned null. Such callbacks '
+            'must never return null.'
+          )
+        ]);
       }
       return true;
     }());

packages/flutter/lib/src/material/debug.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
 import 'material.dart';
@@ -24,45 +25,26 @@ import 'scaffold.dart' show Scaffold;
 bool debugCheckHasMaterial(BuildContext context) {
   assert(() {
     if (context.widget is! Material && context.ancestorWidgetOfExactType(Material) == null) {
-      final StringBuffer message = StringBuffer();
-      message.writeln('No Material widget found.');
-      message.writeln(
-        '${context.widget.runtimeType} widgets require a Material '
-        'widget ancestor.'
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary('No Material widget found.'),
+        ErrorDescription(
+          '${context.widget.runtimeType} widgets require a Material '
+          'widget ancestor.\n'
+          'In material design, most widgets are conceptually "printed" on '
+          'a sheet of material. In Flutter\'s material library, that '
+          'material is represented by the Material widget. It is the '
+          'Material widget that renders ink splashes, for instance. '
+          'Because of this, many material library widgets require that '
+          'there be a Material widget in the tree above them.'
+        ),
+        ErrorHint(
+          'To introduce a Material widget, you can either directly '
+          'include one, or use a widget that contains Material itself, '
+          'such as a Card, Dialog, Drawer, or Scaffold.',
+        ),
+        ...context.describeMissingAncestor(expectedAncestorType: Material)
+      ]
       );
-      message.writeln(
-        'In material design, most widgets are conceptually "printed" on '
-        'a sheet of material. In Flutter\'s material library, that '
-        'material is represented by the Material widget. It is the '
-        'Material widget that renders ink splashes, for instance. '
-        'Because of this, many material library widgets require that '
-        'there be a Material widget in the tree above them.'
-      );
-      message.writeln(
-        'To introduce a Material widget, you can either directly '
-        'include one, or use a widget that contains Material itself, '
-        'such as a Card, Dialog, Drawer, or Scaffold.'
-      );
-      message.writeln(
-        'The specific widget that could not find a Material ancestor was:'
-      );
-      message.writeln('  ${context.widget}');
-      final List<Widget> ancestors = <Widget>[];
-      context.visitAncestorElements((Element element) {
-        ancestors.add(element.widget);
-        return true;
-      });
-      if (ancestors.isNotEmpty) {
-        message.write('The ancestors of this widget were:');
-        for (Widget ancestor in ancestors)
-          message.write('\n  $ancestor');
-      } else {
-        message.writeln(
-          'This widget is the root of the tree, so it has no '
-          'ancestors, let alone a "Material" ancestor.'
-        );
-      }
-      throw FlutterError(message.toString());
     }
     return true;
   }());
@@ -87,42 +69,24 @@ bool debugCheckHasMaterial(BuildContext context) {
 bool debugCheckHasMaterialLocalizations(BuildContext context) {
   assert(() {
     if (Localizations.of<MaterialLocalizations>(context, MaterialLocalizations) == null) {
-      final StringBuffer message = StringBuffer();
-      message.writeln('No MaterialLocalizations found.');
-      message.writeln(
-        '${context.widget.runtimeType} widgets require MaterialLocalizations '
-        'to be provided by a Localizations widget ancestor.'
-      );
-      message.writeln(
-        'Localizations are used to generate many different messages, labels,'
-        'and abbreviations which are used by the material library. '
-      );
-      message.writeln(
-        'To introduce a MaterialLocalizations, either use a '
-        ' MaterialApp at the root of your application to include them '
-        'automatically, or add a Localization widget with a '
-        'MaterialLocalizations delegate.'
-      );
-      message.writeln(
-        'The specific widget that could not find a MaterialLocalizations ancestor was:'
-      );
-      message.writeln('  ${context.widget}');
-      final List<Widget> ancestors = <Widget>[];
-      context.visitAncestorElements((Element element) {
-        ancestors.add(element.widget);
-        return true;
-      });
-      if (ancestors.isNotEmpty) {
-        message.write('The ancestors of this widget were:');
-        for (Widget ancestor in ancestors)
-          message.write('\n  $ancestor');
-      } else {
-        message.writeln(
-          'This widget is the root of the tree, so it has no '
-          'ancestors, let alone a "Localizations" ancestor.'
-        );
-      }
-      throw FlutterError(message.toString());
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary('No MaterialLocalizations found.'),
+        ErrorDescription(
+          '${context.widget.runtimeType} widgets require MaterialLocalizations '
+          'to be provided by a Localizations widget ancestor.'
+        ),
+        ErrorDescription(
+          'Localizations are used to generate many different messages, labels,'
+          'and abbreviations which are used by the material library.'
+        ),
+        ErrorHint(
+          'To introduce a MaterialLocalizations, either use a '
+          'MaterialApp at the root of your application to include them '
+          'automatically, or add a Localization widget with a '
+          'MaterialLocalizations delegate.'
+        ),
+        ...context.describeMissingAncestor(expectedAncestorType: MaterialLocalizations)
+      ]);
     }
     return true;
   }());
@@ -145,17 +109,15 @@ bool debugCheckHasMaterialLocalizations(BuildContext context) {
 bool debugCheckHasScaffold(BuildContext context) {
   assert(() {
     if (context.widget is! Scaffold && context.ancestorWidgetOfExactType(Scaffold) == null) {
-      final Element element = context;
-      throw FlutterError(
-          'No Scaffold widget found.\n'
-          '${context.widget.runtimeType} widgets require a Scaffold widget ancestor.\n'
-          'The Specific widget that could not find a Scaffold ancestor was:\n'
-          '  ${context.widget}\n'
-          'The ownership chain for the affected widget is:\n'
-          '  ${element.debugGetCreatorChain(10)}\n'
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary('No Scaffold widget found.'),
+        ErrorDescription('${context.widget.runtimeType} widgets require a Scaffold widget ancestor.'),
+        ...context.describeMissingAncestor(expectedAncestorType: Scaffold),
+        ErrorHint(
           'Typically, the Scaffold widget is introduced by the MaterialApp or '
           'WidgetsApp widget at the top of your application widget tree.'
-      );
+        )
+      ]);
     }
     return true;
   }());

packages/flutter/lib/src/material/page.dart

@@ -87,10 +87,10 @@ class MaterialPageRoute<T> extends PageRoute<T> {
     final Widget result = builder(context);
     assert(() {
       if (result == null) {
-        throw FlutterError(
-          'The builder for route "${settings.name}" returned null.\n'
-          'Route builders must never return null.'
-        );
+        throw FlutterError.fromParts(<DiagnosticsNode>[
+          ErrorSummary('The builder for route "${settings.name}" returned null.'),
+          ErrorDescription('Route builders must never return null.')
+        ]);
       }
       return true;
     }());

packages/flutter/lib/src/material/scaffold.dart

@@ -1310,25 +1310,32 @@ class Scaffold extends StatefulWidget {
     final ScaffoldState result = context.ancestorStateOfType(const TypeMatcher<ScaffoldState>());
     if (nullOk || result != null)
       return result;
-    throw FlutterError(
-      'Scaffold.of() called with a context that does not contain a Scaffold.\n'
-      'No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). '
-      'This usually happens when the context provided is from the same StatefulWidget as that '
-      'whose build function actually creates the Scaffold widget being sought.\n'
-      'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
-      'context that is "under" the Scaffold. For an example of this, please see the '
-      'documentation for Scaffold.of():\n'
-      '  https://api.flutter.dev/flutter/material/Scaffold/of.html\n'
-      'A more efficient solution is to split your build function into several widgets. This '
-      'introduces a new context from which you can obtain the Scaffold. In this solution, '
-      'you would have an outer widget that creates the Scaffold populated by instances of '
-      'your new inner widgets, and then in these inner widgets you would use Scaffold.of().\n'
-      'A less elegant but more expedient solution is assign a GlobalKey to the Scaffold, '
-      'then use the key.currentState property to obtain the ScaffoldState rather than '
-      'using the Scaffold.of() function.\n'
-      'The context used was:\n'
-      '  $context'
-    );
+    throw FlutterError.fromParts(<DiagnosticsNode>[
+      ErrorSummary(
+        'Scaffold.of() called with a context that does not contain a Scaffold.'
+      ),
+      ErrorDescription(
+        'No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). '
+        'This usually happens when the context provided is from the same StatefulWidget as that '
+        'whose build function actually creates the Scaffold widget being sought.'
+      ),
+      ErrorHint(
+        'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
+        'context that is "under" the Scaffold. For an example of this, please see the '
+        'documentation for Scaffold.of():\n'
+        '  https://api.flutter.dev/flutter/material/Scaffold/of.html'
+      ),
+      ErrorHint(
+        'A more efficient solution is to split your build function into several widgets. This '
+        'introduces a new context from which you can obtain the Scaffold. In this solution, '
+        'you would have an outer widget that creates the Scaffold populated by instances of '
+        'your new inner widgets, and then in these inner widgets you would use Scaffold.of().\n'
+        'A less elegant but more expedient solution is assign a GlobalKey to the Scaffold, '
+        'then use the key.currentState property to obtain the ScaffoldState rather than '
+        'using the Scaffold.of() function.'
+      ),
+      context.describeElement('The context used was')
+    ]);
   }
 
   /// Returns a [ValueListenable] for the [ScaffoldGeometry] for the closest
@@ -1354,22 +1361,28 @@ class Scaffold extends StatefulWidget {
   static ValueListenable<ScaffoldGeometry> geometryOf(BuildContext context) {
     final _ScaffoldScope scaffoldScope = context.inheritFromWidgetOfExactType(_ScaffoldScope);
     if (scaffoldScope == null)
-      throw FlutterError(
-        'Scaffold.geometryOf() called with a context that does not contain a Scaffold.\n'
-        'This usually happens when the context provided is from the same StatefulWidget as that '
-        'whose build function actually creates the Scaffold widget being sought.\n'
-        'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
-        'context that is "under" the Scaffold. For an example of this, please see the '
-        'documentation for Scaffold.of():\n'
-        '  https://api.flutter.dev/flutter/material/Scaffold/of.html\n'
-        'A more efficient solution is to split your build function into several widgets. This '
-        'introduces a new context from which you can obtain the Scaffold. In this solution, '
-        'you would have an outer widget that creates the Scaffold populated by instances of '
-        'your new inner widgets, and then in these inner widgets you would use Scaffold.geometryOf().\n'
-        'The context used was:\n'
-        '  $context'
-      );
-
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary(
+          'Scaffold.geometryOf() called with a context that does not contain a Scaffold.'
+        ),
+        ErrorDescription(
+          'This usually happens when the context provided is from the same StatefulWidget as that '
+          'whose build function actually creates the Scaffold widget being sought.'
+        ),
+        ErrorHint(
+          'There are several ways to avoid this problem. The simplest is to use a Builder to get a '
+          'context that is "under" the Scaffold. For an example of this, please see the '
+          'documentation for Scaffold.of():\n'
+          '  https://api.flutter.dev/flutter/material/Scaffold/of.html'
+        ),
+        ErrorHint(
+          'A more efficient solution is to split your build function into several widgets. This '
+          'introduces a new context from which you can obtain the Scaffold. In this solution, '
+          'you would have an outer widget that creates the Scaffold populated by instances of '
+          'your new inner widgets, and then in these inner widgets you would use Scaffold.geometryOf().',
+        ),
+        context.describeElement('The context used was')
+      ]);
     return scaffoldScope.geometryNotifier;
   }
 
@@ -1679,9 +1692,9 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     assert(() {
       if (widget.bottomSheet != null && isPersistent && _currentBottomSheet != null) {
         throw FlutterError(
-          'Scaffold.bottomSheet cannot be specified while a bottom sheet displayed '
-          'with showBottomSheet() is still visible.\n Rebuild the Scaffold with a null '
-          'bottomSheet before calling showBottomSheet().'
+          'Scaffold.bottomSheet cannot be specified while a bottom sheet'
+          'displayed with showBottomSheet() is still visible.\n'
+          'Rebuild the Scaffold with a null bottomSheet before calling showBottomSheet().'
         );
       }
       return true;
@@ -1818,9 +1831,9 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     assert(() {
       if (widget.bottomSheet != null) {
         throw FlutterError(
-          'Scaffold.bottomSheet cannot be specified while a bottom sheet displayed '
-          'with showBottomSheet() is still visible.\n Rebuild the Scaffold with a null '
-          'bottomSheet before calling showBottomSheet().'
+          'Scaffold.bottomSheet cannot be specified while a bottom sheet'
+          'displayed with showBottomSheet() is still visible.\n'
+          'Rebuild the Scaffold with a null bottomSheet before calling showBottomSheet().'
         );
       }
       return true;
@@ -1952,12 +1965,17 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     if (widget.bottomSheet != oldWidget.bottomSheet) {
       assert(() {
         if (widget.bottomSheet != null && _currentBottomSheet?._isLocalHistoryEntry == true) {
-          throw FlutterError(
-            'Scaffold.bottomSheet cannot be specified while a bottom sheet displayed '
-            'with showBottomSheet() is still visible.\n Use the PersistentBottomSheetController '
-            'returned by showBottomSheet() to close the old bottom sheet before creating '
-            'a Scaffold with a (non null) bottomSheet.'
-          );
+          throw FlutterError.fromParts(<DiagnosticsNode>[
+            ErrorSummary(
+              'Scaffold.bottomSheet cannot be specified while a bottom sheet displayed '
+              'with showBottomSheet() is still visible.'
+            ),
+            ErrorHint(
+              'Use the PersistentBottomSheetController '
+              'returned by showBottomSheet() to close the old bottom sheet before creating '
+              'a Scaffold with a (non null) bottomSheet.'
+            ),
+          ]);
         }
         return true;
       }());

packages/flutter/lib/src/material/stepper.dart

@@ -672,8 +672,9 @@ class _StepperState extends State<Stepper> with TickerProviderStateMixin {
     assert(() {
       if (context.ancestorWidgetOfExactType(Stepper) != null)
         throw FlutterError(
-          'Steppers must not be nested. The material specification advises '
-          'that one should avoid embedding steppers within steppers. '
+          'Steppers must not be nested.\n'
+          'The material specification advises that one should avoid embedding '
+          'steppers within steppers. '
           'https://material.io/archive/guidelines/components/steppers.html#steppers-usage'
         );
       return true;