Fixed an issue with overflow exceptions with nested lists inside a reorderable list item. (#84807)

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

@@ -673,7 +673,7 @@ class SliverReorderableListState extends State<SliverReorderableList> with Ticke
     setState(() {
       if (_insertIndex! < widget.itemCount - 1) {
         // Find the location of the item we want to insert before
-        _finalDropPosition = _itemOffsetAt(_insertIndex!);
+        _finalDropPosition = _itemOffsetAt(_insertIndex! + (_reverse ? 1 : 0));
       } else {
         // Inserting into the last spot on the list. If it's the only spot, put
         // it back where it was. Otherwise, grab the second to last and move

packages/flutter/test/widgets/reorderable_list_test.dart

@@ -268,6 +268,49 @@ void main() {
     expect(getItemFadeTransition(), findsNothing);
   });
 
+  testWidgets('SliverReorderableList - properly animates the drop at starting position in a reversed list', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/84625
+    final List<int> items = List<int>.generate(8, (int index) => index);
+
+    Future<void> pressDragRelease(Offset start, Offset delta) async {
+      final TestGesture drag = await tester.startGesture(start);
+      await tester.pump(kPressTimeout);
+      await drag.moveBy(delta);
+      await tester.pumpAndSettle();
+      await drag.up();
+      await tester.pump();
+    }
+
+    // The TestList is 800x600 SliverReorderableList with 8 items 800x100 each.
+    // Each item has a text widget with 'item $index' that can be moved by a
+    // press and drag gesture. For this test we are reversing the order so
+    // the first item is at the bottom.
+    await tester.pumpWidget(TestList(items: items, reverse: true));
+
+    expect(tester.getTopLeft(find.text('item 0')), const Offset(0, 500));
+    expect(tester.getTopLeft(find.text('item 1')), const Offset(0, 400));
+
+    // Drag item 0 downwards off the edge and let it snap back. It should
+    // smoothly animate back up.
+    await pressDragRelease(tester.getCenter(find.text('item 0')), const Offset(0, 50));
+    expect(tester.getTopLeft(find.text('item 0')), const Offset(0, 550));
+    expect(tester.getTopLeft(find.text('item 1')), const Offset(0, 400));
+
+    // After the first several frames we should be moving closer to the final position,
+    // not further away as was the case with the original bug.
+    await tester.pump(const Duration(milliseconds: 10));
+    expect(tester.getTopLeft(find.text('item 0')).dy, lessThan(550));
+
+    // Sample the middle (don't use exact values as it depends on the internal
+    // curve being used).
+    await tester.pump(const Duration(milliseconds: 125));
+    expect(tester.getTopLeft(find.text('item 0')).dy, lessThan(550));
+
+    // Wait for it to finish, it should be back to the original position
+    await tester.pumpAndSettle();
+    expect(tester.getTopLeft(find.text('item 0')), const Offset(0, 500));
+  });
+
   testWidgets('ReorderableList asserts on both non-null itemExtent and prototypeItem', (WidgetTester tester) async {
     final List<int> numbers = <int>[0,1,2];
     expect(() => ReorderableList(
@@ -594,12 +637,14 @@ class TestList extends StatefulWidget {
     this.iconColor,
     this.proxyDecorator,
     required this.items,
+    this.reverse = false,
   }) : super(key: key);
 
   final List<int> items;
   final Color? textColor;
   final Color? iconColor;
   final ReorderItemProxyDecorator? proxyDecorator;
+  final bool reverse;
 
   @override
   State<TestList> createState() => _TestListState();
@@ -618,6 +663,7 @@ class _TestListState extends State<TestList> {
               builder: (BuildContext outerContext, StateSetter setState) {
                 final List<int> items = widget.items;
                 return CustomScrollView(
+                  reverse: widget.reverse,
                   slivers: <Widget>[
                     SliverReorderableList(
                       itemBuilder: (BuildContext context, int index) {