Add child for placeholder widget (#100372)

dev/tracing_tests/test/timeline_test.dart

@@ -120,7 +120,7 @@ void main() {
     args = (events.where((TimelineEvent event) => event.json!['name'] == '$RenderCustomPaint').single.json!['args'] as Map<String, Object?>).cast<String, String>();
     expect(args['creator'], startsWith('CustomPaint'));
     expect(args['creator'], contains('Placeholder'));
-    expect(args['foregroundPainter'], startsWith('_PlaceholderPainter#'));
+    expect(args['painter'], startsWith('_PlaceholderPainter#'));
     debugProfileLayoutsEnabled = false;
 
     debugProfilePaintsEnabled = true;
@@ -133,7 +133,7 @@ void main() {
     args = (events.where((TimelineEvent event) => event.json!['name'] == '$RenderCustomPaint').single.json!['args'] as Map<String, Object?>).cast<String, String>();
     expect(args['creator'], startsWith('CustomPaint'));
     expect(args['creator'], contains('Placeholder'));
-    expect(args['foregroundPainter'], startsWith('_PlaceholderPainter#'));
+    expect(args['painter'], startsWith('_PlaceholderPainter#'));
     debugProfilePaintsEnabled = false;
 
   }, skip: isBrowser); // [intended] uses dart:isolate and io.

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

@@ -59,6 +59,7 @@ class Placeholder extends StatelessWidget {
     this.strokeWidth = 2.0,
     this.fallbackWidth = 400.0,
     this.fallbackHeight = 400.0,
+    this.child
   }) : super(key: key);
 
   /// The color to draw the placeholder box.
@@ -83,6 +84,10 @@ class Placeholder extends StatelessWidget {
   ///  * [fallbackWidth], the same but horizontally.
   final double fallbackHeight;
 
+  /// The [child] contained by the placeholder box.
+  ///
+  /// Defaults to null.
+  final Widget? child;
   @override
   Widget build(BuildContext context) {
     return LimitedBox(
@@ -90,10 +95,11 @@ class Placeholder extends StatelessWidget {
       maxHeight: fallbackHeight,
       child: CustomPaint(
         size: Size.infinite,
-        foregroundPainter: _PlaceholderPainter(
+        painter: _PlaceholderPainter(
           color: color,
           strokeWidth: strokeWidth,
         ),
+        child: child,
       ),
     );
   }
@@ -105,5 +111,6 @@ class Placeholder extends StatelessWidget {
     properties.add(DoubleProperty('strokeWidth', strokeWidth, defaultValue: 2.0));
     properties.add(DoubleProperty('fallbackWidth', fallbackWidth, defaultValue: 400.0));
     properties.add(DoubleProperty('fallbackHeight', fallbackHeight, defaultValue: 400.0));
+    properties.add(DiagnosticsProperty<Widget>('child', child, defaultValue: null));
   }
 }

packages/flutter/test/widgets/keep_alive_test.dart

@@ -327,8 +327,7 @@ void main() {
       '                       │     parentData: <none> (can use size)\n'
       '                       │     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       │     size: Size(800.0, 400.0)\n'
-      '                       │     painter: null\n'
-      '                       │     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       │     painter: _PlaceholderPainter#00000()\n'
       '                       │     preferredSize: Size(Infinity, Infinity)\n'
       '                       │\n'
       '                       ├─child with index 1: RenderLimitedBox#00000\n'                                     // <----- no dashed line starts here
@@ -342,8 +341,7 @@ void main() {
       '                       │     parentData: <none> (can use size)\n'
       '                       │     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       │     size: Size(800.0, 400.0)\n'
-      '                       │     painter: null\n'
-      '                       │     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       │     painter: _PlaceholderPainter#00000()\n'
       '                       │     preferredSize: Size(Infinity, Infinity)\n'
       '                       │\n'
       '                       └─child with index 2: RenderLimitedBox#00000 NEEDS-PAINT\n'
@@ -357,8 +355,7 @@ void main() {
       '                             parentData: <none> (can use size)\n'
       '                             constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                             size: Size(800.0, 400.0)\n'
-      '                             painter: null\n'
-      '                             foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                             painter: _PlaceholderPainter#00000()\n'
       '                             preferredSize: Size(Infinity, Infinity)\n',
     ));
     const GlobalObjectKey<_LeafState>(0).currentState!.setKeepAlive(true);
@@ -490,8 +487,7 @@ void main() {
       '                       │     parentData: <none> (can use size)\n'
       '                       │     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       │     size: Size(800.0, 400.0)\n'
-      '                       │     painter: null\n'
-      '                       │     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       │     painter: _PlaceholderPainter#00000()\n'
       '                       │     preferredSize: Size(Infinity, Infinity)\n'
       '                       │\n'
       '                       ├─child with index 5: RenderLimitedBox#00000\n'                                     // <----- this is index 5, not 0
@@ -505,8 +501,7 @@ void main() {
       '                       │     parentData: <none> (can use size)\n'
       '                       │     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       │     size: Size(800.0, 400.0)\n'
-      '                       │     painter: null\n'
-      '                       │     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       │     painter: _PlaceholderPainter#00000()\n'
       '                       │     preferredSize: Size(Infinity, Infinity)\n'
       '                       │\n'
       '                       ├─child with index 6: RenderLimitedBox#00000\n'
@@ -520,8 +515,7 @@ void main() {
       '                       │     parentData: <none> (can use size)\n'
       '                       │     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       │     size: Size(800.0, 400.0)\n'
-      '                       │     painter: null\n'
-      '                       │     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       │     painter: _PlaceholderPainter#00000()\n'
       '                       │     preferredSize: Size(Infinity, Infinity)\n'
       '                       │\n'
       '                       ├─child with index 7: RenderLimitedBox#00000 NEEDS-PAINT\n'
@@ -535,8 +529,7 @@ void main() {
       '                       ╎     parentData: <none> (can use size)\n'
       '                       ╎     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       ╎     size: Size(800.0, 400.0)\n'
-      '                       ╎     painter: null\n'
-      '                       ╎     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       ╎     painter: _PlaceholderPainter#00000()\n'
       '                       ╎     preferredSize: Size(Infinity, Infinity)\n'
       '                       ╎\n'
       '                       ╎╌child with index 0 (kept alive but not laid out): RenderLimitedBox#00000\n'               // <----- this one is index 0 and is marked as being kept alive but not laid out
@@ -550,8 +543,7 @@ void main() {
       '                       ╎     parentData: <none> (can use size)\n'
       '                       ╎     constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                       ╎     size: Size(800.0, 400.0)\n'
-      '                       ╎     painter: null\n'
-      '                       ╎     foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                       ╎     painter: _PlaceholderPainter#00000()\n'
       '                       ╎     preferredSize: Size(Infinity, Infinity)\n'
       '                       ╎\n'                                                                                // <----- dashed line ends here
       '                       └╌child with index 3 (kept alive but not laid out): RenderLimitedBox#00000\n'
@@ -565,8 +557,7 @@ void main() {
       '                             parentData: <none> (can use size)\n'
       '                             constraints: BoxConstraints(w=800.0, h=400.0)\n'
       '                             size: Size(800.0, 400.0)\n'
-      '                             painter: null\n'
-      '                             foregroundPainter: _PlaceholderPainter#00000()\n'
+      '                             painter: _PlaceholderPainter#00000()\n'
       '                             preferredSize: Size(Infinity, Infinity)\n',
     ));
   }, skip: kIsWeb); // https://github.com/flutter/flutter/issues/87876

packages/flutter/test/widgets/placeholder_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -34,4 +35,11 @@ void main() {
     await tester.pumpWidget(const Placeholder(strokeWidth: 10.0));
     expect(tester.renderObject(find.byType(Placeholder)), paints..path(strokeWidth: 10.0));
   });
+
+   testWidgets('Placeholder child widget', (WidgetTester tester) async {
+    await tester.pumpWidget(const Placeholder());
+    expect(find.text('Label'), findsNothing);
+    await tester.pumpWidget(const MaterialApp(home: Placeholder(child: Text('Label'))));
+    expect(find.text('Label'), findsOneWidget);
+  });
 }