From bd2d3df94f5868d162a6ff5892f1a2d228744cd9 Mon Sep 17 00:00:00 2001
From: Matej Knopp <matej.knopp@gmail.com>
Date: Sun, 25 Feb 2024 18:29:20 +0100
Subject: [PATCH 1/2] RenderViewport max layout cycles should depend on number
 of children

---
 .../flutter/lib/src/rendering/viewport.dart   |  7 +-
 .../flutter/test/rendering/viewport_test.dart | 83 +++++++++++++++++++
 2 files changed, 87 insertions(+), 3 deletions(-)

diff --git a/packages/flutter/lib/src/rendering/viewport.dart b/packages/flutter/lib/src/rendering/viewport.dart
index e1fa76e479692..45d72611f4149 100644
--- a/packages/flutter/lib/src/rendering/viewport.dart
+++ b/packages/flutter/lib/src/rendering/viewport.dart
@@ -1385,7 +1385,7 @@ class RenderViewport extends RenderViewportBase<SliverPhysicalContainerParentDat
     return constraints.biggest;
   }
 
-  static const int _maxLayoutCycles = 10;
+  static const int _maxLayoutCyclesPerChild = 10;
 
   // Out-of-band data computed during layout.
   late double _minScrollExtent;
@@ -1419,6 +1419,7 @@ class RenderViewport extends RenderViewportBase<SliverPhysicalContainerParentDat
     };
 
     final double centerOffsetAdjustment = center!.centerOffsetAdjustment;
+    final int maxLayoutCycles = _maxLayoutCyclesPerChild * childCount;
 
     double correction;
     int count = 0;
@@ -1435,9 +1436,9 @@ class RenderViewport extends RenderViewportBase<SliverPhysicalContainerParentDat
         }
       }
       count += 1;
-    } while (count < _maxLayoutCycles);
+    } while (count < maxLayoutCycles);
     assert(() {
-      if (count >= _maxLayoutCycles) {
+      if (count >= maxLayoutCycles) {
         assert(count != 1);
         throw FlutterError(
           'A RenderViewport exceeded its maximum number of layout cycles.\n'
diff --git a/packages/flutter/test/rendering/viewport_test.dart b/packages/flutter/test/rendering/viewport_test.dart
index 7013d6dcd183a..563e87cca6d4e 100644
--- a/packages/flutter/test/rendering/viewport_test.dart
+++ b/packages/flutter/test/rendering/viewport_test.dart
@@ -2370,4 +2370,87 @@ void main() {
     );
     errors.clear();
   });
+
+  testWidgets('RenderViewport maxLayoutCycles depends on the number of children',
+      (WidgetTester tester) async {
+    Future<void> expectFlutterError({
+      required Widget widget,
+      required WidgetTester tester,
+    }) async {
+      final List<FlutterErrorDetails> errors = <FlutterErrorDetails>[];
+      final FlutterExceptionHandler? oldHandler = FlutterError.onError;
+      FlutterError.onError = (FlutterErrorDetails error) => errors.add(error);
+      try {
+        await tester.pumpWidget(widget);
+      } finally {
+        FlutterError.onError = oldHandler;
+      }
+      expect(errors, isNotEmpty);
+      expect(errors.first.exception, isFlutterError);
+    }
+
+    Widget buildWidget({required int sliverCount, required int correctionsCount}) {
+      return Directionality(
+        textDirection: TextDirection.ltr,
+        child: CustomScrollView(
+          slivers: List<Widget>.generate(
+              sliverCount,
+              (_) => _ScrollOffsetCorrectionSliver(
+                    correctionsCount: correctionsCount,
+                  )),
+        ),
+      );
+    }
+
+    // 5 correction per child will pass.
+    await tester.pumpWidget(buildWidget(sliverCount: 30, correctionsCount: 5));
+
+    // 15 correction per child will throw exception.
+    await expectFlutterError(
+      widget: buildWidget(sliverCount: 1, correctionsCount: 15),
+      tester: tester,
+    );
+  });
+}
+
+// Simple sliver that applies N scroll offset corrections.
+class _RenderScrollOffsetCorrectionSliver extends RenderSliver {
+  int _correctionCount = 0;
+  @override
+  void performLayout() {
+    if (_correctionCount > 0) {
+      --_correctionCount;
+      geometry = const SliverGeometry(scrollOffsetCorrection: 1.0);
+      return;
+    }
+    const double extent = 5;
+    final double paintedChildSize = calculatePaintOffset(constraints, from: 0.0, to: extent);
+    final double cacheExtent = calculateCacheOffset(constraints, from: 0.0, to: extent);
+
+    geometry = SliverGeometry(
+      scrollExtent: extent,
+      paintExtent: paintedChildSize,
+      maxPaintExtent: extent,
+      cacheExtent: cacheExtent
+    );
+  }
+}
+
+class _ScrollOffsetCorrectionSliver extends SingleChildRenderObjectWidget {
+  const _ScrollOffsetCorrectionSliver({required this.correctionsCount});
+  final int correctionsCount;
+
+  @override
+  _RenderScrollOffsetCorrectionSliver createRenderObject(BuildContext context) {
+    final _RenderScrollOffsetCorrectionSliver sliver = _RenderScrollOffsetCorrectionSliver();
+    sliver._correctionCount = correctionsCount;
+    return sliver;
+  }
+
+  @override
+  void updateRenderObject(BuildContext context, covariant _RenderScrollOffsetCorrectionSliver renderObject) {
+    super.updateRenderObject(context, renderObject);
+    renderObject.markNeedsLayout();
+    renderObject._correctionCount = correctionsCount;
+  }
 }

From ec2cfadc00471b03b0a39680ccabd756af6daa80 Mon Sep 17 00:00:00 2001
From: Matej Knopp <matej.knopp@gmail.com>
Date: Sun, 25 Feb 2024 18:50:12 +0100
Subject: [PATCH 2/2] formatting

---
 packages/flutter/test/rendering/viewport_test.dart | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/packages/flutter/test/rendering/viewport_test.dart b/packages/flutter/test/rendering/viewport_test.dart
index 563e87cca6d4e..8f80cfc301300 100644
--- a/packages/flutter/test/rendering/viewport_test.dart
+++ b/packages/flutter/test/rendering/viewport_test.dart
@@ -2395,9 +2395,7 @@ void main() {
         child: CustomScrollView(
           slivers: List<Widget>.generate(
               sliverCount,
-              (_) => _ScrollOffsetCorrectionSliver(
-                    correctionsCount: correctionsCount,
-                  )),
+              (_) => _ScrollOffsetCorrectionSliver(correctionsCount: correctionsCount)),
         ),
       );
     }