Error message improvements (#58204)
diff --git a/packages/flutter/lib/src/painting/alignment.dart b/packages/flutter/lib/src/painting/alignment.dart
index 3a72983..b5d6bc3 100644
--- a/packages/flutter/lib/src/painting/alignment.dart
+++ b/packages/flutter/lib/src/painting/alignment.dart
@@ -525,7 +525,7 @@
@override
Alignment resolve(TextDirection direction) {
- assert(direction != null);
+ assert(direction != null, 'Cannot resolve $runtimeType without a TextDirection.');
switch (direction) {
case TextDirection.rtl:
return Alignment(-start, y);
@@ -621,7 +621,7 @@
@override
Alignment resolve(TextDirection direction) {
- assert(direction != null);
+ assert(direction != null, 'Cannot resolve $runtimeType without a TextDirection.');
switch (direction) {
case TextDirection.rtl:
return Alignment(_x - _start, _y);
diff --git a/packages/flutter/lib/src/widgets/framework.dart b/packages/flutter/lib/src/widgets/framework.dart
index 7fe0ccf..2c895b7 100644
--- a/packages/flutter/lib/src/widgets/framework.dart
+++ b/packages/flutter/lib/src/widgets/framework.dart
@@ -2627,7 +2627,34 @@
while (index < dirtyCount) {
assert(_dirtyElements[index] != null);
assert(_dirtyElements[index]._inDirtyList);
- assert(!_dirtyElements[index]._active || _dirtyElements[index]._debugIsInScope(context));
+ assert(() {
+ if (_dirtyElements[index]._active && !_dirtyElements[index]._debugIsInScope(context)) {
+ throw FlutterError.fromParts(<DiagnosticsNode>[
+ ErrorSummary('Tried to build dirty widget in the wrong build scope.'),
+ ErrorDescription(
+ 'A widget which was marked as dirty and is still active was scheduled to be built, '
+ 'but the current build scope unexpectedly does not contain that widget.',
+ ),
+ ErrorHint(
+ 'Sometimes this is detected when an element is removed from the widget tree, but the '
+ 'element somehow did not get marked as inactive. In that case, it might be caused by '
+ 'an ancestor element failing to implement visitChildren correctly, thus preventing '
+ 'some or all of its descendants from being correctly deactivated.',
+ ),
+ DiagnosticsProperty<Element>(
+ 'The root of the build scope was',
+ context,
+ style: DiagnosticsTreeStyle.errorProperty,
+ ),
+ DiagnosticsProperty<Element>(
+ 'The offending element (which does not appear to be a descendant of the root of the build scope) was',
+ _dirtyElements[index],
+ style: DiagnosticsTreeStyle.errorProperty,
+ ),
+ ]);
+ }
+ return true;
+ }());
try {
_dirtyElements[index].rebuild();
} catch (e, stack) {
diff --git a/packages/flutter/test/widgets/framework_test.dart b/packages/flutter/test/widgets/framework_test.dart
index 68bb488..80c890d 100644
--- a/packages/flutter/test/widgets/framework_test.dart
+++ b/packages/flutter/test/widgets/framework_test.dart
@@ -1427,6 +1427,74 @@
expect(debugDoingBuildOnDidUnmountRenderObject, isFalse);
});
});
+
+ testWidgets('A widget whose element has an invalid visitChildren implementation triggers a useful error message', (WidgetTester tester) async {
+ final GlobalKey key = GlobalKey();
+ await tester.pumpWidget(Container(child: _WidgetWithNoVisitChildren(_StatefulLeaf(key: key))));
+ (key.currentState as _StatefulLeafState).markNeedsBuild();
+ await tester.pumpWidget(Container());
+ final dynamic exception = tester.takeException();
+ expect(
+ exception.message,
+ equalsIgnoringHashCodes(
+ 'Tried to build dirty widget in the wrong build scope.\n'
+ 'A widget which was marked as dirty and is still active was scheduled to be built, '
+ 'but the current build scope unexpectedly does not contain that widget.\n'
+ 'Sometimes this is detected when an element is removed from the widget tree, but '
+ 'the element somehow did not get marked as inactive. In that case, it might be '
+ 'caused by an ancestor element failing to implement visitChildren correctly, thus '
+ 'preventing some or all of its descendants from being correctly deactivated.\n'
+ 'The root of the build scope was:\n'
+ ' [root]\n'
+ 'The offending element (which does not appear to be a descendant of the root of '
+ 'the build scope) was:\n'
+ ' _StatefulLeaf-[GlobalKey#00000]'
+ )
+ );
+ });
+}
+
+class _WidgetWithNoVisitChildren extends StatelessWidget {
+ const _WidgetWithNoVisitChildren(this.child, { Key key }) :
+ super(key: key);
+
+ final Widget child;
+
+ @override
+ Widget build(BuildContext context) => child;
+
+ @override
+ _WidgetWithNoVisitChildrenElement createElement() => _WidgetWithNoVisitChildrenElement(this);
+}
+
+class _WidgetWithNoVisitChildrenElement extends StatelessElement {
+ _WidgetWithNoVisitChildrenElement(_WidgetWithNoVisitChildren widget): super(widget);
+
+ @override
+ void visitChildren(ElementVisitor visitor) {
+ // This implementation is intentionally buggy, to test that an error message is
+ // shown when this situation occurs.
+ // The superclass has the correct implementation (calling `visitor(_child)`), so
+ // we don't call it here.
+ }
+}
+
+class _StatefulLeaf extends StatefulWidget {
+ const _StatefulLeaf({ Key key }) : super(key: key);
+
+ @override
+ State<_StatefulLeaf> createState() => _StatefulLeafState();
+}
+
+class _StatefulLeafState extends State<_StatefulLeaf> {
+ void markNeedsBuild() {
+ setState(() { });
+ }
+
+ @override
+ Widget build(BuildContext context) {
+ return const SizedBox.shrink();
+ }
}
class Decorate extends StatefulWidget {
@@ -1503,7 +1571,6 @@
bool get debugDoingBuild => throw UnimplementedError();
}
-
class DirtyElementWithCustomBuildOwner extends Element {
DirtyElementWithCustomBuildOwner(BuildOwner buildOwner, Widget widget)
: _owner = buildOwner, super(widget);
