[ReorderableListView] remove extra margin added after picking up the item (#65080)

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

@@ -206,9 +206,6 @@ class _ReorderableListContentState extends State<_ReorderableListContent> with T
   // the currently dragging widget, such as when it first builds.
   static const double _defaultDropAreaExtent = 100.0;
 
-  // The additional margin to place around a computed drop area.
-  static const double _dropAreaMargin = 8.0;
-
   // How long an animation to reorder an element in the list takes.
   static const Duration _reorderAnimationDuration = Duration(milliseconds: 200);
 
@@ -264,7 +261,7 @@ class _ReorderableListContentState extends State<_ReorderableListContent> with T
         dropAreaWithoutMargin = _draggingFeedbackSize.height;
         break;
     }
-    return dropAreaWithoutMargin + _dropAreaMargin;
+    return dropAreaWithoutMargin;
   }
 
   @override

packages/flutter/test/material/reorderable_list_test.dart

@@ -177,11 +177,9 @@ void main() {
           return contentElement;
         }
 
-        const double kNonDraggingListHeight = 292.0;
-        // The list view pads the drop area by 8dp.
-        const double kDraggingListHeight = 300.0;
+        const double kDraggingListHeight = 292.0;
         // Drag a normal text item
-        expect(getContentElement().size.height, kNonDraggingListHeight);
+        expect(getContentElement().size.height, kDraggingListHeight);
         TestGesture drag = await tester.startGesture(tester.getCenter(find.text('Normal item')));
         await tester.pump(kLongPressTimeout + kPressTimeout);
         await tester.pumpAndSettle();
@@ -195,7 +193,7 @@ void main() {
         // Drop it
         await drag.up();
         await tester.pumpAndSettle();
-        expect(getContentElement().size.height, kNonDraggingListHeight);
+        expect(getContentElement().size.height, kDraggingListHeight);
 
         // Drag a tall item
         drag = await tester.startGesture(tester.getCenter(find.text('Tall item')));
@@ -210,7 +208,48 @@ void main() {
         // Drop it
         await drag.up();
         await tester.pumpAndSettle();
-        expect(getContentElement().size.height, kNonDraggingListHeight);
+        expect(getContentElement().size.height, kDraggingListHeight);
+      });
+
+      testWidgets('Vertical drop area golden', (WidgetTester tester) async {
+        final Widget reorderableListView = ReorderableListView(
+          children: <Widget>[
+            Container(
+              key: const Key('pink'),
+              width: double.infinity,
+              height: itemHeight,
+              color: Colors.pink,
+            ),
+            Container(
+              key: const Key('blue'),
+              width: double.infinity,
+              height: itemHeight,
+              color: Colors.blue,
+            ),
+            Container(
+              key: const Key('green'),
+              width: double.infinity,
+              height: itemHeight,
+              color: Colors.green,
+            ),
+          ],
+          scrollDirection: Axis.vertical,
+          onReorder: (int oldIndex, int newIndex) { },
+        );
+        await tester.pumpWidget(MaterialApp(
+          home: SizedBox(
+            height: itemHeight * 3,
+            child: reorderableListView,
+          ),
+        ));
+
+        await tester.startGesture(tester.getCenter(find.byKey(const Key('blue'))));
+        await tester.pump(kLongPressTimeout + kPressTimeout);
+        await tester.pumpAndSettle();
+        await expectLater(
+          find.byKey(const Key('blue')),
+          matchesGoldenFile('reorderable_list_test.vertical.drop_area.png'),
+        );
       });
 
       testWidgets('Preserves children states when the list parent changes the order', (WidgetTester tester) async {
@@ -721,11 +760,9 @@ void main() {
           return contentElement;
         }
 
-        const double kNonDraggingListWidth = 292.0;
-        // The list view pads the drop area by 8dp.
-        const double kDraggingListWidth = 300.0;
+        const double kDraggingListWidth = 292.0;
         // Drag a normal text item
-        expect(getContentElement().size.width, kNonDraggingListWidth);
+        expect(getContentElement().size.width, kDraggingListWidth);
         TestGesture drag = await tester.startGesture(tester.getCenter(find.text('Normal item')));
         await tester.pump(kLongPressTimeout + kPressTimeout);
         await tester.pumpAndSettle();
@@ -739,7 +776,7 @@ void main() {
         // Drop it
         await drag.up();
         await tester.pumpAndSettle();
-        expect(getContentElement().size.width, kNonDraggingListWidth);
+        expect(getContentElement().size.width, kDraggingListWidth);
 
         // Drag a tall item
         drag = await tester.startGesture(tester.getCenter(find.text('Tall item')));
@@ -754,9 +791,49 @@ void main() {
         // Drop it
         await drag.up();
         await tester.pumpAndSettle();
-        expect(getContentElement().size.width, kNonDraggingListWidth);
+        expect(getContentElement().size.width, kDraggingListWidth);
       });
 
+      testWidgets('Horizontal drop area golden', (WidgetTester tester) async {
+        final Widget reorderableListView = ReorderableListView(
+          children: <Widget>[
+            Container(
+              key: const Key('pink'),
+              height: double.infinity,
+              width: itemHeight,
+              color: Colors.pink,
+            ),
+            Container(
+              key: const Key('blue'),
+              height: double.infinity,
+              width: itemHeight,
+              color: Colors.blue,
+            ),
+            Container(
+              key: const Key('green'),
+              height: double.infinity,
+              width: itemHeight,
+              color: Colors.green,
+            ),
+          ],
+          scrollDirection: Axis.horizontal,
+          onReorder: (int oldIndex, int newIndex) { },
+        );
+        await tester.pumpWidget(MaterialApp(
+          home: SizedBox(
+            width: itemHeight * 3,
+            child: reorderableListView,
+          ),
+        ));
+
+        await tester.startGesture(tester.getCenter(find.byKey(const Key('blue'))));
+        await tester.pump(kLongPressTimeout + kPressTimeout);
+        await tester.pumpAndSettle();
+        await expectLater(
+          find.byKey(const Key('blue')),
+          matchesGoldenFile('reorderable_list_test.horizontal.drop_area.png'),
+        );
+      });
 
       testWidgets('Preserves children states when the list parent changes the order', (WidgetTester tester) async {
         _StatefulState findState(Key key) {