Added rethrowError to FutureBuilder (#84308)

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

@@ -737,6 +737,14 @@ class FutureBuilder<T> extends StatefulWidget {
   /// [AsyncSnapshot.hasError] will be true.)
   final T? initialData;
 
+  /// Whether the latest error received by the asynchronous computation should
+  /// be rethrown or swallowed. This property is useful for debugging purposes.
+  ///
+  /// When set to true, will rethrow the latest error only in debug mode.
+  ///
+  /// Defaults to `false`, resulting in swallowing of errors.
+  static bool debugRethrowError = false;
+
   @override
   State<FutureBuilder<T>> createState() => _FutureBuilderState<T>();
 }
@@ -795,6 +803,13 @@ class _FutureBuilderState<T> extends State<FutureBuilder<T>> {
             _snapshot = AsyncSnapshot<T>.withError(ConnectionState.done, error, stackTrace);
           });
         }
+        assert(() {
+          if(FutureBuilder.debugRethrowError) {
+            Future<Object>.error(error, stackTrace);
+          }
+          return true;
+        }());
+
       });
       _snapshot = _snapshot.inState(ConnectionState.waiting);
     }

packages/flutter/test/widgets/async_test.dart

@@ -165,6 +165,24 @@ void main() {
       ));
       expect(find.text('AsyncSnapshot<String>(ConnectionState.waiting, I, null, null)'), findsOneWidget);
     });
+    testWidgets('debugRethrowError rethrows caught error', (WidgetTester tester) async {
+      FutureBuilder.debugRethrowError = true;
+      final Completer<void> caughtError = Completer<void>();
+      await runZonedGuarded(() async {
+        final Completer<String> completer = Completer<String>();
+        await tester.pumpWidget(FutureBuilder<String>(
+          future: completer.future,
+          builder: snapshotText,
+        ), const Duration(seconds: 1));
+        completer.completeError('bad');
+      }, (Object error, StackTrace stack) {
+        expectSync(error, equals('bad'));
+        caughtError.complete();
+      });
+      await tester.pumpAndSettle();
+      expectSync(caughtError.isCompleted, isTrue);
+      FutureBuilder.debugRethrowError = false;
+    });
   });
   group('StreamBuilder', () {
     testWidgets('gracefully handles transition from null stream', (WidgetTester tester) async {