Avoid using FlutterError.fromParts when possible (#43696)

This PR is a follow up of https://github.com/flutter/flutter/pull/42640
Some changes of that PR includes redundant changes using FlutterError.fromParts constructor even though it's not necessary.

Some minor changes are:

- Remove one unnecessary todo
- Fix indent consistencies

packages/flutter/lib/src/animation/animations.dart

@@ -439,14 +439,12 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
         final double transformedValue = activeCurve.transform(t);
         final double roundedTransformedValue = transformedValue.round().toDouble();
         if (roundedTransformedValue != t) {
-          throw FlutterError.fromParts(<DiagnosticsNode>[
-            ErrorSummary('Invalid curve endpoint at $t.'),
-            ErrorDescription(
-              'Curves must map 0.0 to near zero and 1.0 to near one but '
-              '${activeCurve.runtimeType} mapped $t to $transformedValue, which '
-              'is near $roundedTransformedValue.'
-            )
-          ]);
+          throw FlutterError(
+            'Invalid curve endpoint at $t.\n'
+            'Curves must map 0.0 to near zero and 1.0 to near one but '
+            '${activeCurve.runtimeType} mapped $t to $transformedValue, which '
+            'is near $roundedTransformedValue.'
+          );
         }
         return true;
       }());

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

@@ -192,33 +192,29 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
   Route<dynamic> _onUnknownRoute(RouteSettings settings) {
     assert(() {
       if (widget.onUnknownRoute == null) {
-        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.'
-          )
-        ]);
+        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.'
+        );
       }
       return true;
     }());
     final Route<dynamic> result = widget.onUnknownRoute(settings);
     assert(() {
       if (result == 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.'
-          )
-        ]);
+        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.'
+        );
       }
       return true;
     }());

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

@@ -102,10 +102,10 @@ class ChangeNotifier implements Listenable {
   bool _debugAssertNotDisposed() {
     assert(() {
       if (_listeners == null) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('A $runtimeType was used after being disposed.'),
-          ErrorDescription('Once you have called dispose() on a $runtimeType, it can no longer be used.')
-        ]);
+        throw FlutterError(
+          'A $runtimeType was used after being disposed.\n'
+          'Once you have called dispose() on a $runtimeType, it can no longer be used.'
+        );
       }
       return true;
     }());

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

@@ -82,10 +82,10 @@ class MaterialPageRoute<T> extends PageRoute<T> {
     final Widget result = builder(context);
     assert(() {
       if (result == null) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('The builder for route "${settings.name}" returned null.'),
-          ErrorDescription('Route builders must never return null.')
-        ]);
+        throw FlutterError(
+          'The builder for route "${settings.name}" returned null.\n'
+          'Route builders must never return null.'
+        );
       }
       return true;
     }());

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

@@ -142,16 +142,16 @@ abstract class MultiChildLayoutDelegate {
     final RenderBox child = _idToChild[childId];
     assert(() {
       if (child == null) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('The $this custom multichild layout delegate tried to lay out a non-existent child.'),
-          ErrorDescription('There is no child with the id "$childId".')
-        ]);
+        throw 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 FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('The $this custom multichild layout delegate tried to lay out the child with id "$childId" more than once.'),
-          ErrorDescription('Each child must be laid out exactly once.')
-        ]);
+        throw 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.'
+        );
       }
       try {
         assert(constraints.debugAssertIsValid(isAppliedConstraint: true));
@@ -182,15 +182,15 @@ abstract class MultiChildLayoutDelegate {
     final RenderBox child = _idToChild[childId];
     assert(() {
       if (child == null) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('The $this custom multichild layout delegate tried to position out a non-existent child:'),
-          ErrorDescription('There is no child with the id "$childId".')
-        ]);
+        throw 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 FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('The $this custom multichild layout delegate provided a null position for the child with id "$childId".')
-        ]);
+        throw FlutterError(
+          'The $this custom multichild layout delegate provided a null position for the child with id "$childId".'
+        );
       }
       return true;
     }());

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

@@ -318,13 +318,11 @@ class RenderFlow extends RenderBox
     final FlowParentData childParentData = child.parentData as FlowParentData;
     assert(() {
       if (childParentData._transform != null) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('Cannot call paintChild twice for the same child.'),
-          ErrorDescription(
-            'The flow delegate of type ${_delegate.runtimeType} attempted to '
-            'paint child $i multiple times, which is not permitted.'
-          )
-        ]);
+        throw FlutterError(
+          'Cannot call paintChild twice for the same child.\n'
+          'The flow delegate of type ${_delegate.runtimeType} attempted to '
+          'paint child $i multiple times, which is not permitted.'
+        );
       }
       return true;
     }());

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

@@ -461,15 +461,13 @@ class RenderAspectRatio extends RenderProxyBox {
     assert(constraints.debugAssertIsValid());
     assert(() {
       if (!constraints.hasBoundedWidth && !constraints.hasBoundedHeight) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('$runtimeType has unbounded constraints.'),
-          ErrorDescription(
-            'This $runtimeType was given an aspect ratio of $aspectRatio but was given '
-            'both unbounded width and unbounded height constraints. Because both '
-            "constraints were unbounded, this render object doesn't know how much "
-            'size to consume.'
-          )
-        ]);
+        throw FlutterError(
+          '$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 '
+          'constraints were unbounded, this render object doesn\'t know how much '
+          'size to consume.'
+        );
       }
       return true;
     }());

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

@@ -1018,14 +1018,12 @@ class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
     final Route<dynamic> result = widget.onUnknownRoute(settings);
     assert(() {
       if (result == 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.'
-          )
-        ]);
+        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.'
+        );
       }
       return true;
     }());

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

@@ -136,13 +136,11 @@ bool debugChildrenHaveDuplicateKeys(Widget parent, Iterable<Widget> children) {
   assert(() {
     final Key nonUniqueKey = _firstNonUniqueKey(children);
     if (nonUniqueKey != null) {
-      throw FlutterError.fromParts(<DiagnosticsNode>[
-        ErrorSummary('Duplicate keys found.'),
-        ErrorDescription(
-          'If multiple keyed nodes exist as children of another node, they must have unique keys.\n'
-          '$parent has multiple children with key $nonUniqueKey.'
-        ),
-      ]);
+      throw FlutterError(
+        'Duplicate keys found.\n'
+        'If multiple keyed nodes exist as children of another node, they must have unique keys.\n'
+        '$parent has multiple children with key $nonUniqueKey.'
+      );
     }
     return true;
   }());
@@ -165,9 +163,7 @@ bool debugItemsHaveDuplicateKeys(Iterable<Widget> items) {
   assert(() {
     final Key nonUniqueKey = _firstNonUniqueKey(items);
     if (nonUniqueKey != null)
-      throw FlutterError.fromParts(<DiagnosticsNode>[
-        ErrorSummary('Duplicate key found: $nonUniqueKey.'),
-      ]);
+      throw FlutterError('Duplicate key found: $nonUniqueKey.');
     return true;
   }());
   return false;
@@ -315,7 +311,7 @@ bool debugAssertAllWidgetVarsUnset(String reason) {
         debugPrintGlobalKeyedWidgetLifecycle ||
         debugProfileBuildsEnabled ||
         debugHighlightDeprecatedWidgets) {
-      throw FlutterError.fromParts(<DiagnosticsNode>[ErrorSummary(reason)]);
+      throw FlutterError(reason);
     }
     return true;
   }());

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

@@ -190,7 +190,7 @@ class TextEditingController extends ValueNotifier<TextEditingValue> {
   /// change the controller's [value].
   set selection(TextSelection newSelection) {
     if (newSelection.start > text.length || newSelection.end > text.length)
-      throw FlutterError.fromParts(<DiagnosticsNode>[ErrorSummary('invalid text selection: $newSelection')]);
+      throw FlutterError('invalid text selection: $newSelection');
     value = value.copyWith(selection: newSelection, composing: TextRange.empty);
   }
 

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

@@ -242,13 +242,11 @@ class GestureDetector extends StatelessWidget {
            }
            final String recognizer = havePan ? 'pan' : 'scale';
            if (haveVerticalDrag && haveHorizontalDrag) {
-             throw FlutterError.fromParts(<DiagnosticsNode>[
-               ErrorSummary('Incorrect GestureDetector arguments.'),
-               ErrorDescription(
-                 '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.'
-               )
-             ]);
+             throw 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.'
+             );
            }
          }
          return true;

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

@@ -229,14 +229,12 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
       assert(() {
         final double delta = newPixels - pixels;
         if (overscroll.abs() > delta.abs()) {
-          throw FlutterError.fromParts(<DiagnosticsNode>[
-            ErrorSummary('$runtimeType.applyBoundaryConditions returned invalid overscroll value.'),
-            ErrorDescription(
-              'setPixels() was called to change the scroll offset from $pixels to $newPixels.\n'
-              'That is a delta of $delta units.\n'
-              '$runtimeType.applyBoundaryConditions reported an overscroll of $overscroll units.'
-            )
-          ]);
+          throw FlutterError(
+            '$runtimeType.applyBoundaryConditions returned invalid overscroll value.\n'
+            'setPixels() was called to change the scroll offset from $pixels to $newPixels.\n'
+            'That is a delta of $delta units.\n'
+            '$runtimeType.applyBoundaryConditions reported an overscroll of $overscroll units.'
+          );
         }
         return true;
       }());
@@ -402,18 +400,16 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     assert(() {
       final double delta = value - pixels;
       if (result.abs() > delta.abs()) {
-        throw FlutterError.fromParts(<DiagnosticsNode>[
-          ErrorSummary('${physics.runtimeType}.applyBoundaryConditions returned invalid overscroll value.'),
-          ErrorDescription(
-            'The method was called to consider a change from $pixels to $value, which is a '
-            'delta of ${delta.toStringAsFixed(1)} units. However, it returned an overscroll of '
-            '${result.toStringAsFixed(1)} units, which has a greater magnitude than the delta. '
-            'The applyBoundaryConditions method is only supposed to reduce the possible range '
-            'of movement, not increase it.\n'
-            'The scroll extents are $minScrollExtent .. $maxScrollExtent, and the '
-            'viewport dimension is $viewportDimension.'
-          )
-        ]);
+        throw FlutterError(
+          '${physics.runtimeType}.applyBoundaryConditions returned invalid overscroll value.\n'
+          'The method was called to consider a change from $pixels to $value, which is a '
+          'delta of ${delta.toStringAsFixed(1)} units. However, it returned an overscroll of '
+          '${result.toStringAsFixed(1)} units, which has a greater magnitude than the delta. '
+          'The applyBoundaryConditions method is only supposed to reduce the possible range '
+          'of movement, not increase it.\n'
+          'The scroll extents are $minScrollExtent .. $maxScrollExtent, and the '
+          'viewport dimension is $viewportDimension.'
+        );
       }
       return true;
     }());

packages/flutter_test/lib/src/widget_tester.dart

@@ -780,8 +780,6 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
   void _verifySemanticsHandlesWereDisposed() {
     assert(_lastRecordedSemanticsHandles != null);
     if (binding.pipelineOwner.debugOutstandingSemanticsHandles > _lastRecordedSemanticsHandles) {
-      // TODO(jacobr): The hint for this one causes a change in line breaks but
-      // I think it is for the best.
       throw FlutterError.fromParts(<DiagnosticsNode>[
         ErrorSummary('A SemanticsHandle was active at the end of the test.'),
         ErrorDescription(