Replace WidgetError and RenderingError with FlutterError

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

@@ -11,7 +11,7 @@ bool debugCheckHasMaterial(BuildContext context) {
   assert(() {
     if (context.widget is! Material && context.ancestorWidgetOfExactType(Material) == null) {
       Element element = context;
-      throw new WidgetError(
+      throw new FlutterError(
         'No Material widget found.\n'
         '${context.widget.runtimeType} widgets require a Material widget ancestor.\n'
         'In material design, most widgets are conceptually "printed" on a sheet of material. In Flutter\'s material library, '
@@ -35,7 +35,7 @@ bool debugCheckHasScaffold(BuildContext context) {
   assert(() {
     if (Scaffold.of(context) == null) {
       Element element = context;
-      throw new WidgetError(
+      throw new FlutterError(
         'No Scaffold widget found.\n'
         '${context.widget.runtimeType} widgets require a Scaffold widget ancestor.\n'
         'The specific widget that could not find a Scaffold ancestor was:\n'

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

@@ -306,17 +306,17 @@ class BoxConstraints extends Constraints {
   bool get debugAssertIsNormalized {
     assert(() {
       if (minWidth < 0.0 && minHeight < 0.0)
-        throw new RenderingError('BoxConstraints has both a negative minimum width and a negative minimum height.\n$this');
+        throw new FlutterError('BoxConstraints has both a negative minimum width and a negative minimum height.\n$this');
       if (minWidth < 0.0)
-        throw new RenderingError('BoxConstraints has a negative minimum width.\n$this');
+        throw new FlutterError('BoxConstraints has a negative minimum width.\n$this');
       if (minHeight < 0.0)
-        throw new RenderingError('BoxConstraints has a negative minimum height.\n$this');
+        throw new FlutterError('BoxConstraints has a negative minimum height.\n$this');
       if (maxWidth < minWidth && maxHeight < minHeight)
-        throw new RenderingError('BoxConstraints has both width and height constraints non-normalized.\n$this');
+        throw new FlutterError('BoxConstraints has both width and height constraints non-normalized.\n$this');
       if (maxWidth < minWidth)
-        throw new RenderingError('BoxConstraints has non-normalized width constraints.\n$this');
+        throw new FlutterError('BoxConstraints has non-normalized width constraints.\n$this');
       if (maxHeight < minHeight)
-        throw new RenderingError('BoxConstraints has non-normalized height constraints.\n$this');
+        throw new FlutterError('BoxConstraints has non-normalized height constraints.\n$this');
       return isNormalized;
     });
     return isNormalized;
@@ -636,7 +636,7 @@ abstract class RenderBox extends RenderObject {
         for (String line in description)
         information.writeln('  $line');
       }
-      throw new RenderingError(
+      throw new FlutterError(
         '$runtimeType object was given an infinite size during layout.\n'
         'This probably means that it is a render object that tries to be\n'
         'as big as possible, but it was put inside another render object\n'
@@ -647,7 +647,7 @@ abstract class RenderBox extends RenderObject {
     }
     // verify that the size is within the constraints
     if (!constraints.isSatisfiedBy(_size)) {
-      throw new RenderingError(
+      throw new FlutterError(
         '$runtimeType does not meet its constraints.\n'
         'Constraints: $constraints\n'
         'Size: $_size\n'
@@ -684,7 +684,7 @@ abstract class RenderBox extends RenderObject {
     RenderObject.debugCheckingIntrinsics = false;
     if (failures.isNotEmpty) {
       assert(failureCount > 0);
-      throw new RenderingError(
+      throw new FlutterError(
         'The intrinsic dimension methods of the $runtimeType class returned values that violate the given constraints.\n'
         'The constraints were: $constraints\n'
         'The following method${failureCount > 1 ? "s" : ""} returned values outside of those constraints:\n'

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

@@ -45,13 +45,13 @@ abstract class MultiChildLayoutDelegate {
     final RenderBox child = _idToChild[childId];
     assert(() {
       if (child == null) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $this custom multichild layout delegate tried to lay out a non-existent child:\n'
           'There is no child with the id "$childId".'
         );
       }
       if (!_debugChildrenNeedingLayout.remove(child)) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $this custom multichild layout delegate tried to lay out the child with id "$childId" more than once.\n'
           'Each child must be laid out exactly once.'
         );
@@ -59,7 +59,7 @@ abstract class MultiChildLayoutDelegate {
       try {
         assert(constraints.debugAssertIsNormalized);
       } on AssertionError catch (exception) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $this custom multichild layout delegate provided invalid box constraints for the child with id "$childId":\n'
           '$exception\n'
           'The minimum width and height must be greater than or equal to zero.\n'
@@ -83,13 +83,13 @@ abstract class MultiChildLayoutDelegate {
     final RenderBox child = _idToChild[childId];
     assert(() {
       if (child == null) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $this custom multichild layout delegate tried to position out a non-existent child:\n'
           'There is no child with the id "$childId".'
         );
       }
       if (offset == null) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $this custom multichild layout delegate provided a null position for the child with id "$childId".'
         );
       }
@@ -124,7 +124,7 @@ abstract class MultiChildLayoutDelegate {
         final MultiChildLayoutParentData childParentData = child.parentData;
         assert(() {
           if (childParentData.id == null) {
-            throw new RenderingError(
+            throw new FlutterError(
               'The following child has no ID:\n'
               '  $child\n'
               'Every child of a RenderCustomMultiChildLayoutBox must have an ID in its parent data.'
@@ -143,13 +143,13 @@ abstract class MultiChildLayoutDelegate {
       assert(() {
         if (_debugChildrenNeedingLayout.isNotEmpty) {
           if (_debugChildrenNeedingLayout.length > 1) {
-            throw new RenderingError(
+            throw new FlutterError(
               'The $this custom multichild layout delegate forgot to lay out the following children:\n'
               '  ${_debugChildrenNeedingLayout.map(_debugDescribeChild).join("\n  ")}\n'
               'Each child must be laid out exactly once.'
             );
           } else {
-            throw new RenderingError(
+            throw new FlutterError(
               'The $this custom multichild layout delegate forgot to lay out the following child:\n'
               '  ${_debugDescribeChild(_debugChildrenNeedingLayout.single)}\n'
               'Each child must be laid out exactly once.'

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

@@ -399,7 +399,7 @@ class RenderGrid extends RenderVirtualViewport<GridParentData> {
   void set mainAxis(Axis value) {
     assert(() {
       if (value != Axis.vertical)
-        throw new RenderingError('RenderGrid doesn\'t yet support horizontal scrolling.');
+        throw new FlutterError('RenderGrid doesn\'t yet support horizontal scrolling.');
       return true;
     });
     super.mainAxis = value;

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

@@ -20,6 +20,7 @@ import 'binding.dart';
 
 export 'package:flutter/gestures.dart' show HitTestEntry, HitTestResult;
 export 'package:flutter/painting.dart';
+export 'package:flutter/services.dart' show FlutterError;
 
 /// Base class for data associated with a [RenderObject] by its parent.
 ///
@@ -2089,13 +2090,3 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
     return result;
   }
 }
-
-/// Error thrown when the rendering library encounters a contract violation.
-class RenderingError extends AssertionError {
-  RenderingError(this.message);
-
-  final String message;
-
-  @override
-  String toString() => message;
-}

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

@@ -441,7 +441,7 @@ class RenderAspectRatio extends RenderProxyBox {
     assert(constraints.debugAssertIsNormalized);
     assert(() {
       if (!constraints.hasBoundedWidth && !constraints.hasBoundedHeight) {
-        throw new RenderingError(
+        throw new FlutterError(
           '$runtimeType has unbounded constraints.\n'
           'This $runtimeType was given an aspect ratio of $aspectRatio but was given '
           'both unbounded width and unbounded height constraints. Because both '
@@ -1386,7 +1386,7 @@ class RenderCustomPaint extends RenderProxyBox {
       // below that number.
       int debugNewCanvasSaveCount = canvas.getSaveCount();
       if (debugNewCanvasSaveCount > debugPreviousCanvasSaveCount) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $painter custom painter called canvas.save() or canvas.saveLayer() at least '
           '${debugNewCanvasSaveCount - debugPreviousCanvasSaveCount} more '
           'time${debugNewCanvasSaveCount - debugPreviousCanvasSaveCount == 1 ? '' : 's' } '
@@ -1396,7 +1396,7 @@ class RenderCustomPaint extends RenderProxyBox {
         );
       }
       if (debugNewCanvasSaveCount < debugPreviousCanvasSaveCount) {
-        throw new RenderingError(
+        throw new FlutterError(
           'The $painter custom painter called canvas.restore() '
           '${debugPreviousCanvasSaveCount - debugNewCanvasSaveCount} more '
           'time${debugPreviousCanvasSaveCount - debugNewCanvasSaveCount == 1 ? '' : 's' } '

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

@@ -2,9 +2,32 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+/// Error class used to report Flutter-specific assertion failures and
+/// contract violations.
 class FlutterError extends AssertionError {
+  /// Creates a [FlutterError].
+  ///
+  /// See [message] for details on the format that the message should
+  /// take.
+  ///
+  /// Include as much detail as possible in the full error message,
+  /// including specifics about the state of the app that might be
+  /// relevant to debugging the error.
   FlutterError(this.message);
 
+  /// The message associated with this error.
+  ///
+  /// The message may have newlines in it. The first line should be a
+  /// terse description of the error, e.g. "Incorrect GlobalKey usage"
+  /// or "setState() or markNeedsBuild() called during build".
+  /// Subsequent lines can then contain more information. In some
+  /// cases, when a FlutterError is reported to the user, only the
+  /// first line is included. For example, Flutter will typically only
+  /// fully report the first exception at runtime, displaying only the
+  /// first line of subsequent errors.
+  ///
+  /// All sentences in the error should be correctly punctuated (i.e.,
+  /// do end the error message with a period).
   final String message;
 
   @override

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

@@ -291,7 +291,7 @@ class _DismissableState extends State<Dismissable> {
       assert(() {
         if (_resizeAnimation.status != AnimationStatus.forward) {
           assert(_resizeAnimation.status == AnimationStatus.completed);
-          throw new WidgetError(
+          throw new FlutterError(
             'A dismissed Dismissable widget is still part of the tree.\n' +
             'Make sure to implement the onDismissed handler and to immediately remove the Dismissable\n' +
             'widget from the application once that handler has fired.'

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

@@ -9,6 +9,7 @@ import 'package:flutter/rendering.dart';
 
 export 'dart:ui' show hashValues, hashList;
 export 'package:flutter/rendering.dart' show RenderObject, RenderBox, debugPrint;
+export 'package:flutter/services.dart' show FlutterError;
 
 // KEYS
 
@@ -178,7 +179,7 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
       message += 'The most recently registered instance is: ${_registry[key]}\n';
     }
     if (_debugDuplicates.isNotEmpty) {
-      throw new WidgetError(
+      throw new FlutterError(
         'Incorrect GlobalKey usage.\n'
         '$message'
       );
@@ -380,7 +381,7 @@ abstract class State<T extends StatefulWidget> {
   void setState(VoidCallback fn) {
     assert(() {
       if (_debugLifecycleState == _StateLifecycle.defunct) {
-        throw new WidgetError(
+        throw new FlutterError(
           'setState() called after dipose(): $this\n'
           'This error happens if you call setState() on State object for a widget that\n'
           'no longer appears in the widget tree (e.g., whose parent widget no longer\n'
@@ -1197,7 +1198,7 @@ abstract class BuildableElement extends Element {
           return true;
       }
       if (_debugStateLocked && (!_debugAllowIgnoredCallsToMarkNeedsBuild || !dirty)) {
-        throw new WidgetError(
+        throw new FlutterError(
           'setState() or markNeedsBuild() called during build.\n'
           'This widget cannot be marked as needing to build because the framework '
           'is already in the process of building widgets. A widget can be marked as '
@@ -1296,7 +1297,7 @@ abstract class ComponentElement extends BuildableElement {
       built = _builder(this);
       assert(() {
         if (built == null) {
-          throw new WidgetError(
+          throw new FlutterError(
             'A build function returned null.\n'
             'The offending widget is: $widget\n'
             'Build functions must never return null. '
@@ -1388,7 +1389,7 @@ class StatefulElement extends ComponentElement {
     assert(() {
       if (_state._debugLifecycleState == _StateLifecycle.initialized)
         return true;
-      throw new WidgetError(
+      throw new FlutterError(
         '${_state.runtimeType}.initState failed to call super.initState.\n'
         'initState() implementations must always call their superclass initState() method, to ensure '
         'that the entire widget is initialized correctly.'
@@ -1430,7 +1431,7 @@ class StatefulElement extends ComponentElement {
     assert(() {
       if (_state._debugLifecycleState == _StateLifecycle.defunct)
         return true;
-      throw new WidgetError(
+      throw new FlutterError(
         '${_state.runtimeType}.dispose failed to call super.dispose.\n'
         'dispose() implementations must always call their superclass dispose() method, to ensure '
         'that all the resources used by the widget are fully released.'
@@ -1503,7 +1504,7 @@ class ParentDataElement<T extends RenderObjectWidget> extends _ProxyElement {
       }
       if (ancestor != null && badAncestors.isEmpty)
         return true;
-      throw new WidgetError(
+      throw new FlutterError(
         'Incorrect use of ParentDataWidget.\n' +
         widget.debugDescribeInvalidAncestorChain(
           description: "$this",
@@ -1975,7 +1976,7 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
         continue; // when these nodes are reordered, we just reassign the data
 
       if (!idSet.add(child.key)) {
-        throw new WidgetError(
+        throw new FlutterError(
           'Duplicate keys found.\n'
           'If multiple keyed nodes exist as children of another node, they must have unique keys.\n'
           '$widget has multiple children with key "${child.key}".'
@@ -2021,14 +2022,6 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
   }
 }
 
-class WidgetError extends AssertionError {
-  WidgetError(this.message);
-  final String message;
-
-  @override
-  String toString() => message;
-}
-
 typedef void WidgetsExceptionHandler(String context, dynamic exception, StackTrace stack);
 /// This callback is invoked whenever an exception is caught by the widget
 /// system. The 'context' argument is a description of what was happening when

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

@@ -79,14 +79,14 @@ class GestureDetector extends StatelessWidget {
       bool haveScale = onScaleStart != null || onScaleUpdate != null || onScaleEnd != null;
       if (havePan || haveScale) {
         if (havePan && haveScale) {
-          throw new WidgetError(
+          throw new FlutterError(
             'Incorrect GestureDetector arguments.\n'
             'Having both a pan gesture recognizer and a scale gesture recognizer is redundant; scale is a superset of pan. Just use the scale gesture recognizer.'
           );
         }
         String recognizer = havePan ? 'pan' : 'scale';
         if (haveVerticalDrag && haveHorizontalDrag) {
-          throw new WidgetError(
+          throw new FlutterError(
             'Incorrect GestureDetector arguments.\n'
             'Simultaneously having a vertical drag gesture recognizer, a horizontal drag gesture recognizer, and a $recognizer gesture recognizer '
             'will result in the $recognizer gesture recognizer being ignored, since the other two will catch all drags.'
@@ -336,7 +336,7 @@ class RawGestureDetectorState extends State<RawGestureDetector> {
   void replaceGestureRecognizers(Map<Type, GestureRecognizerFactory> gestures) {
     assert(() {
       if (!RenderObject.debugDoingLayout) {
-        throw new WidgetError(
+        throw new FlutterError(
           'Unexpected call to replaceGestureRecognizers() method of RawGestureDetectorState.\n'
           'The replaceGestureRecognizers() method can only be called during the layout phase. '
           'To set the gesture recognisers at other times, trigger a new build using setState() '

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

@@ -115,7 +115,7 @@ class Hero extends StatefulWidget {
         final Map<Key, HeroState> tagHeroes = heroes.putIfAbsent(tag, () => <Key, HeroState>{});
         assert(() {
           if (tagHeroes.containsKey(key)) {
-            new WidgetError(
+            new FlutterError(
               'There are multiple heroes that share the same key within the same subtree.\n'
               'Within each subtree for which heroes are to be animated (typically a PageRoute subtree), '
               'either each Hero must have a unique tag, or, all the heroes with a particular tag must '

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

@@ -181,7 +181,7 @@ class MimicableState extends State<Mimicable> {
   MimicableHandle startMimic() {
     assert(() {
       if (_placeholderSize != null) {
-        throw new WidgetError(
+        throw new FlutterError(
           'Mimicable started while already active.\n'
           'When startMimic() or liftToOverlay() is called on a MimicableState, the mimic becomes active. '
           'While active, it cannot be reactivated until it is stopped. '

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

@@ -262,7 +262,7 @@ class Navigator extends StatefulWidget {
     NavigatorState navigator = context.ancestorStateOfType(const TypeMatcher<NavigatorState>());
     assert(() {
       if (navigator == null) {
-        throw new WidgetError(
+        throw new FlutterError(
           'openTransaction called with a context that does not include a Navigator.\n'
           'The context passed to the Navigator.openTransaction() method must be that of a widget that is a descendant of a Navigator widget.'
         );

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

@@ -90,7 +90,7 @@ class Overlay extends StatefulWidget {
         String additional = context.widget != debugRequiredFor
           ? '\nThe context from which that widget was searching for an overlay was:\n  $context'
           : '';
-        throw new WidgetError(
+        throw new FlutterError(
           'No Overlay widget found.\n'
           '${debugRequiredFor.runtimeType} widgets require an Overlay widget ancestor for correct operation.\n'
           'The most common way to add an Overlay to an application is to include a MaterialApp or Navigator widget in the runApp() call.\n'

packages/flutter/test/widget/navigator_test.dart

@@ -113,7 +113,7 @@ void main() {
       );
       tester.pumpWidget(widget);
       tester.tap(tester.findElementByKey(targetKey));
-      expect(exception, new isInstanceOf<WidgetError>());
+      expect(exception, new isInstanceOf<FlutterError>());
       expect('$exception', startsWith('openTransaction called with a context'));
     });
   });