Skip cloning Fragments in ListEmptyComponent to avoid onLayout warning (#50833)

Summary:
Fixes https://github.com/facebook/react-native/issues/50817

Using a fragment is very common when rendering elements. We are cloning and adding `onLayout` always to the ListEmptyComponent element, but this would seem to work only when `View` is used for this as a wrapper in this prop. To prevent this unnecessary warning, I think we can easily check whether it is a fragment or not before cloning and adding the extra props – this adds backwards compatibility for those that don't need to use `onLayout`.

## Changelog:

[GENERAL] [FIXED] - Skip cloning Fragments in ListEmptyComponent to avoid onLayout warning

Pull Request resolved: https://github.com/facebook/react-native/pull/50833

Test Plan: Use the code snippet from the linked issue to verify that the warning is not thrown anymore when using a Fragment.

Reviewed By: javache

Differential Revision: D73421503

Pulled By: rshest

fbshipit-source-id: 0da4a38130601943e4704589ac275eba39767191

packages/virtualized-lists/Lists/VirtualizedList.js

@@ -891,6 +891,30 @@ class VirtualizedList extends StateSafePureComponent<
     return key;
   }
 
+  _renderEmptyComponent(
+    element: ExactReactElement_DEPRECATED<any>,
+    inversionStyle: StyleProp<ViewStyle>,
+  ): React.Node {
+    // $FlowFixMe[prop-missing] React.Element internal inspection
+    const isFragment = element.type === React.Fragment;
+
+    if (isFragment) {
+      return element;
+    }
+
+    return React.cloneElement(element, {
+      onLayout: (event: LayoutChangeEvent) => {
+        this._onLayoutEmpty(event);
+        // $FlowFixMe[prop-missing] React.Element internal inspection
+        if (element.props.onLayout) {
+          element.props.onLayout(event);
+        }
+      },
+      // $FlowFixMe[prop-missing] React.Element internal inspection
+      style: StyleSheet.compose(inversionStyle, element.props.style),
+    });
+  }
+
   render(): React.Node {
     this._checkProps(this.props);
     const {ListEmptyComponent, ListFooterComponent, ListHeaderComponent} =
@@ -956,17 +980,7 @@ class VirtualizedList extends StateSafePureComponent<
         <VirtualizedListCellContextProvider
           cellKey={this._getCellKey() + '-empty'}
           key="$empty">
-          {React.cloneElement(element, {
-            onLayout: (event: LayoutChangeEvent) => {
-              this._onLayoutEmpty(event);
-              // $FlowFixMe[prop-missing] React.Element internal inspection
-              if (element.props.onLayout) {
-                element.props.onLayout(event);
-              }
-            },
-            // $FlowFixMe[prop-missing] React.Element internal inspection
-            style: StyleSheet.compose(inversionStyle, element.props.style),
-          })}
+          {this._renderEmptyComponent(element, inversionStyle)}
         </VirtualizedListCellContextProvider>,
       );
     }

packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js

@@ -337,6 +337,95 @@ describe('VirtualizedList', () => {
     });
   });
 
+  it('empty component returns the original element if it is a React.Fragment', () => {
+    const listRef = React.createRef();
+    const fragment = (
+      <React.Fragment>
+        <div>Test</div>
+      </React.Fragment>
+    );
+
+    act(() => {
+      create(
+        <VirtualizedList
+          ref={listRef}
+          data={[]}
+          ListEmptyComponent={fragment}
+          getItem={(data, index) => data[index]}
+          getItemCount={data => data.length}
+          renderItem={({item}) => <item value={item.key} />}
+        />,
+      );
+    });
+
+    const result = listRef.current._renderEmptyComponent(fragment, null);
+    expect(result).toBe(fragment);
+  });
+
+  it('empty component clones the element and adds onLayout and style props if not a Fragment', () => {
+    const listRef = React.createRef();
+    const element = <div>Test</div>;
+    const inversionStyle = {transform: [{scaleY: -1}]};
+
+    act(() => {
+      create(
+        <VirtualizedList
+          ref={listRef}
+          data={[]}
+          ListEmptyComponent={element}
+          getItem={(data, index) => data[index]}
+          getItemCount={data => data.length}
+          renderItem={({item}) => <item value={item.key} />}
+        />,
+      );
+    });
+
+    const result = listRef.current._renderEmptyComponent(
+      element,
+      inversionStyle,
+    );
+
+    // The result should be a cloned element with additional props
+    expect(result).not.toBe(element);
+    expect(result.props).toEqual(
+      expect.objectContaining({
+        onLayout: expect.any(Function),
+        style: inversionStyle,
+      }),
+    );
+  });
+
+  it('empty component preserves original onLayout handler if present', () => {
+    const listRef = React.createRef();
+    const originalOnLayout = jest.fn();
+    const element = <div onLayout={originalOnLayout}>Test</div>;
+    const inversionStyle = {transform: [{scaleY: -1}]};
+
+    act(() => {
+      create(
+        <VirtualizedList
+          ref={listRef}
+          data={[]}
+          ListEmptyComponent={element}
+          getItem={(data, index) => data[index]}
+          getItemCount={data => data.length}
+          renderItem={({item}) => <item value={item.key} />}
+        />,
+      );
+    });
+
+    const result = listRef.current._renderEmptyComponent(
+      element,
+      inversionStyle,
+    );
+
+    // Call the onLayout handler
+    result.props.onLayout({nativeEvent: {layout: {width: 100, height: 100}}});
+
+    // Both the original and the new onLayout should be called
+    expect(originalOnLayout).toHaveBeenCalled();
+  });
+
   it('returns the viewableItems correctly in the onViewableItemsChanged callback after changing the data', async () => {
     const ITEM_HEIGHT = 800;
     let data = [{key: 'i1'}, {key: 'i2'}, {key: 'i3'}];