Add flag to exclude focus for hidden children in Visibility, maintainFocusability. Set maintainFocusability to false in IndexedStack (#159133)

Fixes: https://github.com/flutter/flutter/issues/114213 and is a
prerequisite for fixing:
https://github.com/flutter/flutter/issues/148405

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we expect every widget to implement].
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- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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

@@ -4242,7 +4242,14 @@ class IndexedStack extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final List<Widget> wrappedChildren = List<Widget>.generate(children.length, (int i) {
-      return Visibility.maintain(visible: i == index, child: children[i]);
+      return Visibility(
+        visible: i == index,
+        maintainInteractivity: true,
+        maintainSize: true,
+        maintainState: true,
+        maintainAnimation: true,
+        child: children[i],
+      );
     });
     return _RawIndexedStack(
       alignment: alignment,

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

@@ -12,6 +12,7 @@ library;
 import 'package:flutter/rendering.dart';
 
 import 'basic.dart';
+import 'focus_scope.dart';
 import 'framework.dart';
 import 'sliver.dart';
 import 'ticker_provider.dart';
@@ -66,6 +67,7 @@ class Visibility extends StatelessWidget {
     this.maintainSize = false,
     this.maintainSemantics = false,
     this.maintainInteractivity = false,
+    this.maintainFocusability = false,
   }) : assert(
          maintainState || !maintainAnimation,
          'Cannot maintain animations if the state is not also maintained.',
@@ -95,6 +97,7 @@ class Visibility extends StatelessWidget {
       maintainSize = true,
       maintainSemantics = true,
       maintainInteractivity = true,
+      maintainFocusability = true,
       replacement = const SizedBox.shrink(); // Unused since maintainState is always true.
 
   /// The widget to show or hide, as controlled by [visible].
@@ -215,6 +218,11 @@ class Visibility extends StatelessWidget {
   /// true, then touch events will nonetheless be passed through.
   final bool maintainInteractivity;
 
+  /// Whether to allow the widget to receive focus when hidden. Only in effect if [visible] is false.
+  ///
+  /// Defaults to false.
+  final bool maintainFocusability;
+
   /// Tells the visibility state of an element in the tree based off its
   /// ancestor [Visibility] elements.
   ///
@@ -245,7 +253,7 @@ class Visibility extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    Widget result = child;
+    Widget result = ExcludeFocus(excluding: !visible && !maintainFocusability, child: child);
     if (maintainSize) {
       result = _Visibility(
         visible: visible,

packages/flutter/test/widgets/stack_test.dart

@@ -489,6 +489,74 @@ void main() {
     }
   });
 
+  testWidgets('IndexedStack excludes focus for hidden children', (WidgetTester tester) async {
+    const List<Widget> children = <Widget>[
+      Focus(child: Text('child 0')),
+      Focus(child: Text('child 1')),
+    ];
+
+    Future<void> pumpIndexedStack(int? activeIndex) async {
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: IndexedStack(index: activeIndex, children: children),
+        ),
+      );
+    }
+
+    Future<void> requestFocusAndPump(FocusNode node) async {
+      node.requestFocus();
+      await tester.pump();
+    }
+
+    await pumpIndexedStack(0);
+
+    final Element child0 = tester.element(find.text('child 0', skipOffstage: false));
+    final Element child1 = tester.element(find.text('child 1', skipOffstage: false));
+    final FocusNode child0FocusNode = Focus.of(child0);
+    final FocusNode child1FocusNode = Focus.of(child1);
+
+    await requestFocusAndPump(child0FocusNode);
+
+    expect(child0FocusNode.hasFocus, true);
+    expect(child1FocusNode.hasFocus, false);
+
+    await requestFocusAndPump(child1FocusNode);
+
+    expect(child0FocusNode.hasFocus, true);
+    expect(child1FocusNode.hasFocus, false);
+
+    await pumpIndexedStack(1);
+    await requestFocusAndPump(child1FocusNode);
+
+    expect(child0FocusNode.hasFocus, false);
+    expect(child1FocusNode.hasFocus, true);
+
+    await requestFocusAndPump(child0FocusNode);
+
+    expect(child0FocusNode.hasFocus, false);
+    expect(child1FocusNode.hasFocus, true);
+  });
+
+  testWidgets('IndexedStack: hidden children can not receive tap events', (
+    WidgetTester tester,
+  ) async {
+    bool tapped = false;
+    final List<Widget> children = <Widget>[
+      const Text('child'),
+      GestureDetector(onTap: () => tapped = true, child: const Text('hiddenChild')),
+    ];
+
+    await tester.pumpWidget(
+      Directionality(textDirection: TextDirection.ltr, child: IndexedStack(children: children)),
+    );
+
+    await tester.tap(find.text('hiddenChild', skipOffstage: false), warnIfMissed: false);
+    await tester.pump();
+
+    expect(tapped, false);
+  });
+
   testWidgets('Stack clip test', (WidgetTester tester) async {
     await tester.pumpWidget(
       const Directionality(

packages/flutter/test/widgets/visibility_test.dart

@@ -396,6 +396,95 @@ void main() {
     semantics.dispose();
   });
 
+  testWidgets('Visibility with maintain* false excludes focus of child when not visible', (
+    WidgetTester tester,
+  ) async {
+    Future<void> pumpVisibility(bool visible) async {
+      await tester.pumpWidget(
+        Visibility(
+          visible: visible,
+          child: const Focus(child: Text('child', textDirection: TextDirection.ltr)),
+        ),
+      );
+    }
+
+    await pumpVisibility(true);
+
+    final Element child = tester.element(find.text('child', skipOffstage: false));
+    final FocusNode childFocusNode = Focus.of(child);
+
+    childFocusNode.requestFocus();
+    await tester.pump();
+
+    expect(childFocusNode.hasFocus, true);
+
+    await pumpVisibility(false);
+    childFocusNode.requestFocus();
+
+    expect(childFocusNode.hasFocus, false);
+  });
+
+  testWidgets('Visibility with maintain* true does not exclude focus of child when not visible', (
+    WidgetTester tester,
+  ) async {
+    Future<void> pumpVisibility(bool visible) async {
+      await tester.pumpWidget(
+        Visibility.maintain(
+          visible: visible,
+          child: const Focus(child: Text('child', textDirection: TextDirection.ltr)),
+        ),
+      );
+    }
+
+    await pumpVisibility(true);
+
+    final Element child = tester.element(find.text('child', skipOffstage: false));
+    final FocusNode childFocusNode = Focus.of(child);
+
+    childFocusNode.requestFocus();
+    await tester.pump();
+
+    expect(childFocusNode.hasFocus, true);
+
+    await pumpVisibility(false);
+
+    expect(childFocusNode.hasFocus, true);
+  });
+
+  testWidgets(
+    'Visibility with maintain* true except maintainFocusability which is false excludes focus of child when not visible',
+    (WidgetTester tester) async {
+      Future<void> pumpVisibility(bool visible) async {
+        await tester.pumpWidget(
+          Visibility(
+            visible: visible,
+            maintainState: true,
+            maintainAnimation: true,
+            maintainInteractivity: true,
+            maintainSemantics: true,
+            maintainSize: true,
+            child: const Focus(child: Text('child', textDirection: TextDirection.ltr)),
+          ),
+        );
+      }
+
+      await pumpVisibility(true);
+
+      final Element child = tester.element(find.text('child', skipOffstage: false));
+      final FocusNode childFocusNode = Focus.of(child);
+
+      childFocusNode.requestFocus();
+      await tester.pump();
+
+      expect(childFocusNode.hasFocus, true);
+
+      await pumpVisibility(false);
+      childFocusNode.requestFocus();
+
+      expect(childFocusNode.hasFocus, false);
+    },
+  );
+
   testWidgets('Visibility does not force compositing when visible and maintain*', (
     WidgetTester tester,
   ) async {