Handle infinite/NaN rects in Hero flights. Less exclamation marks. (#72946)

packages/flutter/test/widgets/heroes_test.dart

@@ -2780,4 +2780,212 @@ Future<void> main() async {
     expect(find.byKey(secondKey), isInCard);
     expect(find.byKey(secondKey), isOnstage);
   });
+
+  testWidgets('kept alive Hero does not throw when the transition begins', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
+    await tester.pumpWidget(
+      MaterialApp(
+        navigatorKey: navigatorKey,
+        home: Scaffold(
+          body: ListView(
+            addAutomaticKeepAlives: false,
+            addRepaintBoundaries: false,
+            addSemanticIndexes: false,
+            children: <Widget>[
+              const KeepAlive(
+                keepAlive: true,
+                child: Hero(
+                  tag: 'a',
+                  child: Placeholder(),
+                ),
+              ),
+              Container(height: 1000.0),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    // Scroll to make the Hero invisible.
+    await tester.drag(find.byType(ListView), const Offset(0.0, -1000.0));
+    await tester.pump();
+
+    expect(find.byType(TextField), findsNothing);
+
+    navigatorKey.currentState?.push(
+      MaterialPageRoute<void>(
+        builder: (BuildContext context) {
+          return const Scaffold(
+            body: Center(
+              child: Hero(
+                tag: 'a',
+                child: Placeholder(),
+              ),
+            ),
+          );
+        },
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    expect(tester.takeException(), isNull);
+    // The Hero on the new route should be visible .
+    expect(find.byType(Placeholder), findsOneWidget);
+  });
+
+  testWidgets('toHero becomes unpaintable after the transition begins', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+    final ScrollController controller = ScrollController();
+
+    RenderOpacity? findRenderOpacity() {
+      AbstractNode? parent = tester.renderObject(find.byType(Placeholder));
+      while (parent is RenderObject && parent is! RenderOpacity) {
+        parent = parent.parent;
+      }
+      return parent is RenderOpacity ? parent : null;
+    }
+
+    await tester.pumpWidget(
+      MaterialApp(
+        navigatorKey: navigatorKey,
+        home: Scaffold(
+          body: ListView(
+            controller: controller,
+            addAutomaticKeepAlives: false,
+            addRepaintBoundaries: false,
+            addSemanticIndexes: false,
+            children: <Widget>[
+              const KeepAlive(
+                keepAlive: true,
+                child: Hero(
+                  tag: 'a',
+                  child: Placeholder(),
+                ),
+              ),
+              Container(height: 1000.0),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    navigatorKey.currentState?.push(
+      MaterialPageRoute<void>(
+        builder: (BuildContext context) {
+          return const Scaffold(
+            body: Center(
+              child: Hero(
+                tag: 'a',
+                child: Placeholder(),
+              ),
+            ),
+          );
+        },
+      ),
+    );
+    await tester.pump();
+    await tester.pumpAndSettle();
+
+    // Pop the new route, and before the animation finishes we scroll the toHero
+    // to make it unpaintable.
+    navigatorKey.currentState?.pop();
+    await tester.pump();
+    controller.jumpTo(1000);
+    // Starts Hero animation and scroll animation almost simutaneously.
+    // Scroll to make the Hero invisible.
+    await tester.pump();
+    expect(findRenderOpacity()?.opacity, anyOf(isNull, 1.0));
+
+    // In this frame the Hero animation finds out the toHero is not paintable,
+    // and starts fading.
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 100));
+
+    expect(findRenderOpacity()?.opacity, lessThan(1.0));
+
+    await tester.pumpAndSettle();
+    // The Hero on the new route should be invisible.
+    expect(find.byType(Placeholder), findsNothing);
+  });
+
+  testWidgets('diverting to a keepalive but unpaintable hero', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();
+
+    await tester.pumpWidget(
+      CupertinoApp(
+        navigatorKey: navigatorKey,
+        home: CupertinoPageScaffold(
+          child: ListView(
+            addAutomaticKeepAlives: false,
+            addRepaintBoundaries: false,
+            addSemanticIndexes: false,
+            children: <Widget>[
+              const KeepAlive(
+                keepAlive: true,
+                child: Hero(
+                  tag: 'a',
+                  child: Placeholder(),
+                ),
+              ),
+              Container(height: 1000.0),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    // Scroll to make the Hero invisible.
+    await tester.drag(find.byType(ListView), const Offset(0.0, -1000.0));
+    await tester.pump();
+
+    expect(find.byType(Placeholder), findsNothing);
+    expect(find.byType(Placeholder, skipOffstage: false), findsOneWidget);
+
+    navigatorKey.currentState?.push(
+      MaterialPageRoute<void>(
+        builder: (BuildContext context) {
+          return const Scaffold(
+            body: Center(
+              child: Hero(
+                tag: 'a',
+                child: Placeholder(),
+              ),
+            ),
+          );
+        },
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    // Yet another route that contains Hero 'a'.
+    navigatorKey.currentState?.push(
+      MaterialPageRoute<void>(
+        builder: (BuildContext context) {
+          return const Scaffold(
+            body: Center(
+              child: Hero(
+                tag: 'a',
+                child: Placeholder(),
+              ),
+            ),
+          );
+        },
+      ),
+    );
+    await tester.pumpAndSettle();
+
+    // Pop both routes.
+    navigatorKey.currentState?.pop();
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 10));
+
+    navigatorKey.currentState?.pop();
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 10));
+    expect(find.byType(Placeholder), findsOneWidget);
+
+    await tester.pumpAndSettle();
+    expect(tester.takeException(), isNull);
+  });
 }