From 79146fd0a6071ef06f4187b5843329cf6d09fcd8 Mon Sep 17 00:00:00 2001
From: Kate Lovett <katelovett@google.com>
Date: Thu, 6 Aug 2020 16:11:16 -0700
Subject: [PATCH] Fix SliverList scrollOffsetCorrection 0 case (#62615)

---
 .../lib/src/rendering/sliver_list.dart        | 18 ++++++++-----
 .../flutter/test/widgets/slivers_test.dart    | 25 +++++++++++++++++++
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/packages/flutter/lib/src/rendering/sliver_list.dart b/packages/flutter/lib/src/rendering/sliver_list.dart
index 5f577b816fa..e47babf7458 100644
--- a/packages/flutter/lib/src/rendering/sliver_list.dart
+++ b/packages/flutter/lib/src/rendering/sliver_list.dart
@@ -169,20 +169,26 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
     // If the scroll offset is at zero, we should make sure we are
     // actually at the beginning of the list.
     if (scrollOffset < precisionErrorTolerance) {
-      if (indexOf(firstChild) > 0) {
+      // We iterate from the firstChild in case the leading child has a 0 paint
+      // extent.
+      while (indexOf(firstChild) > 0) {
         final double earliestScrollOffset = childScrollOffset(firstChild);
         // We correct one child at a time. If there are more children before
         // the earliestUsefulChild, we will correct it once the scroll offset
-        // reach zero again.
+        // reaches zero again.
         earliestUsefulChild = insertAndLayoutLeadingChild(childConstraints, parentUsesSize: true);
         assert(earliestUsefulChild != null);
         final double firstChildScrollOffset = earliestScrollOffset - paintExtentOf(firstChild);
-        geometry = SliverGeometry(
-          scrollOffsetCorrection: -firstChildScrollOffset,
-        );
         final SliverMultiBoxAdaptorParentData childParentData = firstChild.parentData as SliverMultiBoxAdaptorParentData;
         childParentData.layoutOffset = 0.0;
-        return;
+        // We only need to correct if the leading child actually has a
+        // paint extent.
+        if (firstChildScrollOffset < -precisionErrorTolerance) {
+          geometry = SliverGeometry(
+            scrollOffsetCorrection: -firstChildScrollOffset,
+          );
+          return;
+        }
       }
     }
 
diff --git a/packages/flutter/test/widgets/slivers_test.dart b/packages/flutter/test/widgets/slivers_test.dart
index b47d651ba55..c521176698a 100644
--- a/packages/flutter/test/widgets/slivers_test.dart
+++ b/packages/flutter/test/widgets/slivers_test.dart
@@ -814,6 +814,31 @@ void main() {
       expect(events, equals(<String>['tap']));
     });
   });
+
+  testWidgets('SliverList handles 0 scrollOffsetCorrection', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/62198
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        body: CustomScrollView(
+          physics: const BouncingScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
+          slivers: <Widget>[
+            SliverList(
+              delegate: SliverChildListDelegate(
+                const <Widget>[
+                  SizedBox.shrink(),
+                  Text('index 1'),
+                  Text('index 2'),
+                ]
+              ),
+            ),
+          ],
+        )
+      ),
+    ));
+    await tester.fling(find.byType(Scrollable), const Offset(0.0, -500.0), 10000.0);
+    await tester.pumpAndSettle();
+    expect(tester.takeException(), isNull);
+  });
 }
 
 bool isRight(Offset a, Offset b) => b.dx > a.dx;