Make Card explicitChildNodes vs container be configurable (#19693)

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

@@ -67,6 +67,7 @@ class Card extends StatelessWidget {
     this.shape,
     this.margin = const EdgeInsets.all(4.0),
     this.child,
+    this.semanticContainer = false,
   }) : super(key: key);
 
   /// The card's background color.
@@ -100,6 +101,19 @@ class Card extends StatelessWidget {
   /// `EdgeInsets.all(4.0)`.
   final EdgeInsetsGeometry margin;
 
+  /// Whether this widget represents a single semantic container, or if false
+  /// a collection of individual semantic nodes.
+  ///
+  /// Defaults to false.
+  ///
+  /// Setting this flag to true will attempt to merge all child semantics into
+  /// this node. Setting this flag to false will force all child semantic nodes
+  /// to be explicit.
+  ///
+  /// This flag should be false if the card contains multiple different types
+  /// of content.
+  final bool semanticContainer;
+
   /// The widget below this widget in the tree.
   ///
   /// {@macro flutter.widgets.child}
@@ -108,7 +122,8 @@ class Card extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return new Semantics(
-      container: true,
+      container: semanticContainer,
+      explicitChildNodes: !semanticContainer,
       child: new Container(
         margin: margin ?? const EdgeInsets.all(4.0),
         child: new Material(

packages/flutter/test/material/card_test.dart

@@ -18,6 +18,7 @@ void main() {
         child: new Material(
           child: new Center(
             child: new Card(
+              semanticContainer: false,
               child: new Column(
                 children: <Widget>[
                   const Text('I am text!'),
@@ -37,13 +38,18 @@ void main() {
     expect(semantics, hasSemantics(
       new TestSemantics.root(
         children: <TestSemantics>[
-          new TestSemantics.rootChild(
+          new TestSemantics(
             id: 1,
-            label: 'I am text!\nMoar text!!1',
+            label: 'I am text!',
             textDirection: TextDirection.ltr,
-            children: <TestSemantics>[
+          ),
           new TestSemantics(
             id: 2,
+            label: 'Moar text!!1',
+             textDirection: TextDirection.ltr,
+          ),
+          new TestSemantics(
+            id: 3,
             label: 'Button',
             textDirection: TextDirection.ltr,
             actions: <SemanticsAction>[
@@ -57,6 +63,44 @@ void main() {
           ),
         ],
       ),
+      ignoreTransform: true,
+      ignoreRect: true,
+    ));
+
+    semantics.dispose();
+  });
+
+  testWidgets('Card merges children when it is a semanticContainer', (WidgetTester tester) async {
+    final SemanticsTester semantics = new SemanticsTester(tester);
+    debugResetSemanticsIdCounter();
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new Material(
+          child: new Center(
+            child: new Card(
+              semanticContainer: true,
+              child: new Column(
+                children: const <Widget>[
+                  Text('First child'),
+                  Text('Second child')
+                ],
+              )
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(semantics, hasSemantics(
+      new TestSemantics.root(
+        children: <TestSemantics>[
+          new TestSemantics(
+            id: 1,
+            label: 'First child\nSecond child',
+            textDirection: TextDirection.ltr,
+          ),
         ],
       ),
       ignoreTransform: true,