From 2e861f3527f2ec97a499d2a223bb1706555eec52 Mon Sep 17 00:00:00 2001
From: manu-sncf <108678139+manu-sncf@users.noreply.github.com>
Date: Tue, 21 Oct 2025 19:04:26 +0200
Subject: [PATCH] Fix SliverMainAxisGroup.cacheOrigin (#175760)

Fix #175759

The fix involves using the same logic for cache calculation on
RenderViewport.

## Pre-launch Checklist

- [X] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [X] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [X] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [X] I signed the [CLA].
- [X] I listed at least one issue that this PR fixes in the description
above.
- [X] I updated/added relevant documentation (doc comments with `///`).
- [X] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [X] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [X] All existing and new tests are passing.
---
 .../lib/src/rendering/sliver_group.dart       | 24 +++++++++++---
 .../widgets/sliver_main_axis_group_test.dart  | 32 +++++++++++++++++++
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/packages/flutter/lib/src/rendering/sliver_group.dart b/packages/flutter/lib/src/rendering/sliver_group.dart
index 190fd295083..f4c01c49ab3 100644
--- a/packages/flutter/lib/src/rendering/sliver_group.dart
+++ b/packages/flutter/lib/src/rendering/sliver_group.dart
@@ -296,6 +296,9 @@ class RenderSliverMainAxisGroup extends RenderSliver
     double paintOffset = constraints.overlap;
     double maxScrollObstructionExtent = 0;
 
+    double cacheOrigin = constraints.cacheOrigin;
+    double remainingCacheExtent = constraints.remainingCacheExtent;
+
     final (
       RenderSliver? leadingChild,
       RenderSliver? Function(RenderSliver child) advance,
@@ -310,17 +313,22 @@ class RenderSliverMainAxisGroup extends RenderSliver
         from: 0.0,
         to: scrollOffset,
       );
+
+      final double childScrollOffset = math.max(0.0, constraints.scrollOffset - scrollOffset);
+      final double correctedCacheOrigin = math.max(cacheOrigin, -childScrollOffset);
+      final double cacheExtentCorrection = cacheOrigin - correctedCacheOrigin;
+
       child.layout(
         constraints.copyWith(
-          scrollOffset: math.max(0.0, constraints.scrollOffset - scrollOffset),
-          cacheOrigin: math.min(0.0, constraints.cacheOrigin + scrollOffset),
+          scrollOffset: childScrollOffset,
+          cacheOrigin: correctedCacheOrigin,
           overlap: math.max(0.0, _fixPrecisionError(paintOffset - beforeOffsetPaintExtent)),
           remainingPaintExtent: _fixPrecisionError(
             constraints.remainingPaintExtent - beforeOffsetPaintExtent,
           ),
-          remainingCacheExtent: _fixPrecisionError(
-            constraints.remainingCacheExtent -
-                calculateCacheOffset(constraints, from: 0.0, to: scrollOffset),
+          remainingCacheExtent: math.max(
+            0.0,
+            _fixPrecisionError(remainingCacheExtent + cacheExtentCorrection),
           ),
           precedingScrollExtent: scrollOffset + constraints.precedingScrollExtent,
         ),
@@ -349,6 +357,12 @@ class RenderSliverMainAxisGroup extends RenderSliver
       maxPaintExtent += childLayoutGeometry.maxPaintExtent;
       maxScrollObstructionExtent += childLayoutGeometry.maxScrollObstructionExtent;
       paintOffset = math.max(childPaintOffset + childLayoutGeometry.paintExtent, paintOffset);
+      if (childLayoutGeometry.cacheExtent != 0.0) {
+        remainingCacheExtent = _fixPrecisionError(
+          remainingCacheExtent - childLayoutGeometry.cacheExtent - cacheExtentCorrection,
+        );
+        cacheOrigin = math.min(correctedCacheOrigin + childLayoutGeometry.cacheExtent, 0.0);
+      }
       child = advance(child);
       assert(() {
         if (child != null && maxPaintExtent.isInfinite) {
diff --git a/packages/flutter/test/widgets/sliver_main_axis_group_test.dart b/packages/flutter/test/widgets/sliver_main_axis_group_test.dart
index 2a110a72384..58896a22f70 100644
--- a/packages/flutter/test/widgets/sliver_main_axis_group_test.dart
+++ b/packages/flutter/test/widgets/sliver_main_axis_group_test.dart
@@ -856,6 +856,38 @@ void main() {
     expect(renderGroup.geometry!.cacheExtent, 850.0);
   });
 
+  testWidgets('SliverMainAxisGroup has consistent cacheOrigin', (WidgetTester tester) async {
+    const Widget item = SizedBox.square(dimension: 50);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: CustomScrollView(
+          slivers: <Widget>[
+            SliverMainAxisGroup(
+              slivers: <Widget>[
+                const PinnedHeaderSliver(child: SizedBox(height: 500)),
+                SliverList.builder(
+                  itemCount: 100,
+                  itemBuilder: (BuildContext context, int index) => item,
+                ),
+                const SliverToBoxAdapter(child: item),
+              ],
+            ),
+          ],
+        ),
+      ),
+    );
+
+    await tester.scrollUntilVisible(find.byType(SliverToBoxAdapter), 500);
+    await tester.pumpAndSettle();
+
+    final RenderSliver sliverList =
+        find.byType(SliverList).evaluate().single.findRenderObject()! as RenderSliver;
+
+    expect(sliverList.constraints.cacheOrigin, -250.0);
+    expect(sliverList.constraints.remainingCacheExtent, 1100);
+  });
+
   testWidgets('SliverMainAxisGroup correctly handles ensureVisible', (WidgetTester tester) async {
     final GlobalKey key = GlobalKey();
     await tester.pumpWidget(