add closed/open focus traversal; use open on web (flutter#115961)

* allow focus to leave FlutterView

* fix tests and docs

* small doc update

* fix analysis lint

* use closed loop for dialogs

* add tests for new API

* address comments

* test FocusScopeNode.traversalEdgeBehavior setter; reverse wrap-around

* rename actionResult to invokeResult

* address comments

Author: yjbanov

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

@@ -1238,6 +1238,12 @@ Widget _buildMaterialDialogTransitions(BuildContext context, Animation<double> a
 ///
 /// {@macro flutter.widgets.RestorationManager}
 ///
+/// If not null, `traversalEdgeBehavior` argument specifies the transfer of
+/// focus beyond the first and the last items of the dialog route. By default,
+/// uses [TraversalEdgeBehavior.closedLoop], because it's typical for dialogs
+/// to allow users to cycle through widgets inside it without leaving the
+/// dialog.
+///
 /// ** See code in examples/api/lib/material/dialog/show_dialog.2.dart **
 /// {@end-tool}
 ///
@@ -1263,6 +1269,7 @@ Future<T?> showDialog<T>({
   bool useRootNavigator = true,
   RouteSettings? routeSettings,
   Offset? anchorPoint,
+  TraversalEdgeBehavior? traversalEdgeBehavior,
 }) {
   assert(builder != null);
   assert(barrierDismissible != null);
@@ -1289,6 +1296,7 @@ Future<T?> showDialog<T>({
     settings: routeSettings,
     themes: themes,
     anchorPoint: anchorPoint,
+    traversalEdgeBehavior: traversalEdgeBehavior ?? TraversalEdgeBehavior.closedLoop,
   ));
 }
 
@@ -1367,6 +1375,7 @@ class DialogRoute<T> extends RawDialogRoute<T> {
     bool useSafeArea = true,
     super.settings,
     super.anchorPoint,
+    super.traversalEdgeBehavior,
   }) : assert(barrierDismissible != null),
        super(
          pageBuilder: (BuildContext buildContext, Animation<double> animation, Animation<double> secondaryAnimation) {

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

@@ -794,7 +794,10 @@ class _PopupMenuRoute<T> extends PopupRoute<T> {
     required this.capturedThemes,
     this.constraints,
     required this.clipBehavior,
-  }) : itemSizes = List<Size?>.filled(items.length, null);
+  }) : itemSizes = List<Size?>.filled(items.length, null),
+       // Menus always cycle focus through their items irrespective of the
+       // focus traversal edge behavior set in the Navigator.
+       super(traversalEdgeBehavior: TraversalEdgeBehavior.closedLoop);
 
   final RelativeRect position;
   final List<PopupMenuEntry<T>> items;

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

@@ -251,6 +251,25 @@ abstract class Action<T extends Intent> with Diagnosticable {
   /// The default implementation returns true.
   bool consumesKey(T intent) => true;
 
+  /// Converts the result of [invoke] of this action to a [KeyEventResult].
+  ///
+  /// This is typically used when the action is invoked in response to a keyboard
+  /// shortcut.
+  ///
+  /// The [invokeResult] argument is the value returned by the [invoke] method.
+  ///
+  /// By default, calls [consumesKey] and converts the returned boolean to
+  /// [KeyEventResult.handled] if it's true, and [KeyEventResult.skipRemainingHandlers]
+  /// if it's false.
+  ///
+  /// Concrete implementations may refine the type of [invokeResult], since
+  /// they know the type returned by [invoke].
+  KeyEventResult toKeyEventResult(T intent, covariant Object? invokeResult) {
+    return consumesKey(intent)
+      ? KeyEventResult.handled
+      : KeyEventResult.skipRemainingHandlers;
+  }
+
   /// Called when the action is to be performed.
   ///
   /// This is called by the [ActionDispatcher] when an action is invoked via

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

@@ -1213,6 +1213,7 @@ class FocusScopeNode extends FocusNode {
     super.onKey,
     super.skipTraversal,
     super.canRequestFocus,
+    this.traversalEdgeBehavior = TraversalEdgeBehavior.closedLoop,
   })  : assert(skipTraversal != null),
         assert(canRequestFocus != null),
         super(
@@ -1222,6 +1223,14 @@ class FocusScopeNode extends FocusNode {
   @override
   FocusScopeNode get nearestScope => this;
 
+  /// Controls the transfer of focus beyond the first and the last items of a
+  /// [FocusScopeNode].
+  ///
+  /// Changing this field value has no immediate effect on the UI. Instead, next time
+  /// focus traversal takes place [FocusTraversalPolicy] will read this value
+  /// and apply the new behavior.
+  TraversalEdgeBehavior traversalEdgeBehavior;
+
   /// Returns true if this scope is the focused child of its parent scope.
   bool get isFirstFocus => enclosingScope!.focusedChild == this;
 
@@ -1349,6 +1358,7 @@ class FocusScopeNode extends FocusNode {
       return child.toStringShort();
     }).toList();
     properties.add(IterableProperty<String>('focusedChildren', childList, defaultValue: const Iterable<String>.empty()));
+    properties.add(DiagnosticsProperty<TraversalEdgeBehavior>('traversalEdgeBehavior', traversalEdgeBehavior, defaultValue: TraversalEdgeBehavior.closedLoop));
   }
 }
 

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

@@ -84,8 +84,43 @@ enum TraversalDirection {
   left,
 }
 
-/// An object used to specify a focus traversal policy used for configuring a
-/// [FocusTraversalGroup] widget.
+/// Controls the transfer of focus beyond the first and the last items of a
+/// [FocusScopeNode].
+///
+/// This enumeration only controls the traversal behavior performed by
+/// [FocusTraversalPolicy]. Other methods of focus transfer, such as direct
+/// calls to [FocusNode.requestFocus] and [FocusNode.unfocus], are not affected
+/// by this enumeration.
+///
+/// See also:
+///
+/// * [FocusTraversalPolicy], which implements the logic behind this enum.
+/// * [FocusScopeNode], which is configured by this enum.
+enum TraversalEdgeBehavior {
+  /// Keeps the focus among the items of the focus scope.
+  ///
+  /// Requesting the next focus after the last focusable item will transfer the
+  /// focus to the first item, and requesting focus previous to the first item
+  /// will transfer the focus to the last item, thus forming a closed loop of
+  /// focusable items.
+  closedLoop,
+
+  /// Allows the focus to leave the [FlutterView].
+  ///
+  /// Requesting next focus after the last focusable item or previous to the
+  /// first item will unfocus any focused nodes. If the focus traversal action
+  /// was initiated by the embedder (e.g. the Flutter Engine) the embedder
+  /// receives a result indicating that the focus is no longer within the
+  /// current [FlutterView]. For example, [NextFocusAction] invoked via keyboard
+  /// (typically the TAB key) would receive [KeyEventResult.skipRemainingHandlers]
+  /// allowing the embedder handle the shortcut. On the web, typically the
+  /// control is transfered to the browser, allowing the user to reach the
+  /// address bar, escape an `iframe`, or focus on HTML elements other than
+  /// those managed by Flutter.
+  leaveFlutterView,
+}
+
+/// Determines how focusable widgets are traversed within a [FocusTraversalGroup].
 ///
 /// The focus traversal policy is what determines which widget is "next",
 /// "previous", or in a direction from the widget associated with the currently
@@ -407,12 +442,24 @@ abstract class FocusTraversalPolicy with Diagnosticable {
       return false;
     }
     if (forward && focusedChild == sortedNodes.last) {
-      _focusAndEnsureVisible(sortedNodes.first, alignmentPolicy: ScrollPositionAlignmentPolicy.keepVisibleAtEnd);
-      return true;
+      switch (nearestScope.traversalEdgeBehavior) {
+        case TraversalEdgeBehavior.leaveFlutterView:
+          focusedChild!.unfocus();
+          return false;
+        case TraversalEdgeBehavior.closedLoop:
+          _focusAndEnsureVisible(sortedNodes.first, alignmentPolicy: ScrollPositionAlignmentPolicy.keepVisibleAtEnd);
+          return true;
+      }
     }
     if (!forward && focusedChild == sortedNodes.first) {
-      _focusAndEnsureVisible(sortedNodes.last, alignmentPolicy: ScrollPositionAlignmentPolicy.keepVisibleAtStart);
-      return true;
+      switch (nearestScope.traversalEdgeBehavior) {
+        case TraversalEdgeBehavior.leaveFlutterView:
+          focusedChild!.unfocus();
+          return false;
+        case TraversalEdgeBehavior.closedLoop:
+          _focusAndEnsureVisible(sortedNodes.last, alignmentPolicy: ScrollPositionAlignmentPolicy.keepVisibleAtStart);
+          return true;
+      }
     }
 
     final Iterable<FocusNode> maybeFlipped = forward ? sortedNodes : sortedNodes.reversed;
@@ -1592,7 +1639,7 @@ class _FocusTraversalGroupState extends State<FocusTraversalGroup> {
   // The internal focus node used to collect the children of this node into a
   // group, and to provide a context for the traversal algorithm to sort the
   // group with.
-  FocusNode? focusNode;
+  late final FocusNode focusNode;
 
   @override
   void initState() {
@@ -1606,15 +1653,15 @@ class _FocusTraversalGroupState extends State<FocusTraversalGroup> {
 
   @override
   void dispose() {
-    focusNode?.dispose();
+    focusNode.dispose();
     super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
     return _FocusTraversalGroupMarker(
       policy: widget.policy,
-      focusNode: focusNode!,
+      focusNode: focusNode,
       child: Focus(
         focusNode: focusNode,
         canRequestFocus: false,
@@ -1705,9 +1752,20 @@ class NextFocusIntent extends Intent {
 ///
 /// See [FocusTraversalPolicy] for more information about focus traversal.
 class NextFocusAction extends Action<NextFocusIntent> {
+  /// Attempts to pass the focus to the next widget.
+  ///
+  /// Returns true if a widget was focused as a result of invoking this action.
+  ///
+  /// Returns false when the traversal reached the end and the engine must pass
+  /// focus to platform UI.
+  @override
+  bool invoke(NextFocusIntent intent) {
+    return primaryFocus!.nextFocus();
+  }
+
   @override
-  void invoke(NextFocusIntent intent) {
-    primaryFocus!.nextFocus();
+  KeyEventResult toKeyEventResult(NextFocusIntent intent, bool invokeResult) {
+    return invokeResult ? KeyEventResult.handled : KeyEventResult.skipRemainingHandlers;
   }
 }
 
@@ -1729,9 +1787,20 @@ class PreviousFocusIntent extends Intent {
 ///
 /// See [FocusTraversalPolicy] for more information about focus traversal.
 class PreviousFocusAction extends Action<PreviousFocusIntent> {
+  /// Attempts to pass the focus to the previous widget.
+  ///
+  /// Returns true if a widget was focused as a result of invoking this action.
+  ///
+  /// Returns false when the traversal reached the beginning and the engine must
+  /// pass focus to platform UI.
+  @override
+  bool invoke(PreviousFocusIntent intent) {
+    return primaryFocus!.previousFocus();
+  }
+
   @override
-  void invoke(PreviousFocusIntent intent) {
-    primaryFocus!.previousFocus();
+  KeyEventResult toKeyEventResult(PreviousFocusIntent intent, bool invokeResult) {
+    return invokeResult ? KeyEventResult.handled : KeyEventResult.skipRemainingHandlers;
   }
 }
 

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

@@ -1093,6 +1093,13 @@ class DefaultTransitionDelegate<T> extends TransitionDelegate<T> {
   }
 }
 
+/// The default value of [Navigator.routeTraversalEdgeBehavior].
+///
+/// {@macro flutter.widgets.navigator.routeTraversalEdgeBehavior}
+const TraversalEdgeBehavior kDefaultRouteTraversalEdgeBehavior = kIsWeb
+  ? TraversalEdgeBehavior.leaveFlutterView
+  : TraversalEdgeBehavior.closedLoop;
+
 /// A widget that manages a set of child widgets with a stack discipline.
 ///
 /// Many apps have a navigator near the top of their widget hierarchy in order
@@ -1402,10 +1409,12 @@ class Navigator extends StatefulWidget {
     this.observers = const <NavigatorObserver>[],
     this.requestFocus = true,
     this.restorationScopeId,
+    this.routeTraversalEdgeBehavior = kDefaultRouteTraversalEdgeBehavior,
   }) : assert(pages != null),
        assert(onGenerateInitialRoutes != null),
        assert(transitionDelegate != null),
        assert(observers != null),
+       assert(routeTraversalEdgeBehavior != null),
        assert(reportsRouteUpdateToEngine != null);
 
   /// The list of pages with which to populate the history.
@@ -1513,6 +1522,21 @@ class Navigator extends StatefulWidget {
   /// {@endtemplate}
   final String? restorationScopeId;
 
+  /// Controls the transfer of focus beyond the first and the last items of a
+  /// focus scope that defines focus traversal of widgets within a route.
+  ///
+  /// {@template flutter.widgets.navigator.routeTraversalEdgeBehavior}
+  /// The focus inside routes installed in the top of the app affects how
+  /// the app behaves with respect to the platform content surrounding it.
+  /// For example, on the web, an app is at a minimum surrounded by browser UI,
+  /// such as the address bar, browser tabs, and more. The user should be able
+  /// to reach browser UI using normal focus shortcuts. Similarly, if the app
+  /// is embedded within an `<iframe>` or inside a custom element, it should
+  /// be able to participate in the overall focus traversal, including elements
+  /// not rendered by Flutter.
+  /// {@endtemplate}
+  final TraversalEdgeBehavior routeTraversalEdgeBehavior;
+
   /// The name for the default route of the application.
   ///
   /// See also:

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

@@ -15,6 +15,7 @@ import 'basic.dart';
 import 'display_feature_sub_screen.dart';
 import 'focus_manager.dart';
 import 'focus_scope.dart';
+import 'focus_traversal.dart';
 import 'framework.dart';
 import 'modal_barrier.dart';
 import 'navigator.dart';
@@ -835,24 +836,34 @@ class _ModalScopeState<T> extends State<_ModalScope<T>> {
       if (widget.route.secondaryAnimation != null) widget.route.secondaryAnimation!,
     ];
     _listenable = Listenable.merge(animations);
-    if (widget.route.isCurrent && _shouldRequestFocus) {
-      widget.route.navigator!.focusNode.enclosingScope?.setFirstFocus(focusScopeNode);
-    }
   }
 
   @override
   void didUpdateWidget(_ModalScope<T> oldWidget) {
     super.didUpdateWidget(oldWidget);
     assert(widget.route == oldWidget.route);
-    if (widget.route.isCurrent && _shouldRequestFocus) {
-      widget.route.navigator!.focusNode.enclosingScope?.setFirstFocus(focusScopeNode);
-    }
+    _updateFocusScopeNode();
   }
 
   @override
   void didChangeDependencies() {
     super.didChangeDependencies();
     _page = null;
+    _updateFocusScopeNode();
+  }
+
+  void _updateFocusScopeNode() {
+    final TraversalEdgeBehavior traversalEdgeBehavior;
+    final ModalRoute<T> route = widget.route;
+    if (route.traversalEdgeBehavior != null) {
+      traversalEdgeBehavior = route.traversalEdgeBehavior!;
+    } else {
+      traversalEdgeBehavior = route.navigator!.widget.routeTraversalEdgeBehavior;
+    }
+    focusScopeNode.traversalEdgeBehavior = traversalEdgeBehavior;
+    if (route.isCurrent && _shouldRequestFocus) {
+      route.navigator!.focusNode.enclosingScope?.setFirstFocus(focusScopeNode);
+    }
   }
 
   void _forceRebuildPage() {
@@ -984,6 +995,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   ModalRoute({
     super.settings,
     this.filter,
+    this.traversalEdgeBehavior,
   });
 
   /// The filter to add to the barrier.
@@ -992,6 +1004,12 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   /// [BackdropFilter]. This allows blur effects, for example.
   final ui.ImageFilter? filter;
 
+  /// Controls the transfer of focus beyond the first and the last items of a
+  /// [FocusScopeNode].
+  ///
+  /// If set to null, [Navigator.routeTraversalEdgeBehavior] is used.
+  final TraversalEdgeBehavior? traversalEdgeBehavior;
+
   // The API for general users of this class
 
   /// Returns the modal route most closely associated with the given context.
@@ -1771,6 +1789,7 @@ abstract class PopupRoute<T> extends ModalRoute<T> {
   PopupRoute({
     super.settings,
     super.filter,
+    super.traversalEdgeBehavior,
   });
 
   @override
@@ -2018,6 +2037,7 @@ class RawDialogRoute<T> extends PopupRoute<T> {
     RouteTransitionsBuilder? transitionBuilder,
     super.settings,
     this.anchorPoint,
+    super.traversalEdgeBehavior,
   }) : assert(barrierDismissible != null),
        _pageBuilder = pageBuilder,
        _barrierDismissible = barrierDismissible,