ContextAction.isEnabled needs a context (#127721)

...and lots of things that fall out from that

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

@@ -320,6 +320,10 @@ class Scrollable extends StatefulWidget {
   /// the nearest enclosing [ScrollableState] in that [Axis] is returned, or
   /// null if there is none.
   ///
+  /// This finds the nearest _ancestor_ [Scrollable] of the `context`. This
+  /// means that if the `context` is that of a [Scrollable], it will _not_ find
+  /// _that_ [Scrollable].
+  ///
   /// See also:
   ///
   /// * [Scrollable.of], which is similar to this method, but asserts
@@ -359,6 +363,10 @@ class Scrollable extends StatefulWidget {
   /// target [Scrollable] is not the closest instance. When [axis] is provided,
   /// the nearest enclosing [ScrollableState] in that [Axis] is returned.
   ///
+  /// This finds the nearest _ancestor_ [Scrollable] of the `context`. This
+  /// means that if the `context` is that of a [Scrollable], it will _not_ find
+  /// _that_ [Scrollable].
+  ///
   /// If no [Scrollable] ancestor is found, then this method will assert in
   /// debug mode, and throw an exception in release mode.
   ///
@@ -943,7 +951,6 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin, R
     Widget result = _ScrollableScope(
       scrollable: this,
       position: position,
-      // TODO(ianh): Having all these global keys is sad.
       child: Listener(
         onPointerSignal: _receivedPointerSignal,
         child: RawGestureDetector(

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

@@ -10,7 +10,6 @@ import 'package:flutter/rendering.dart';
 
 import 'actions.dart';
 import 'basic.dart';
-import 'focus_manager.dart';
 import 'framework.dart';
 import 'primary_scroll_controller.dart';
 import 'scroll_configuration.dart';
@@ -377,10 +376,10 @@ class ScrollIntent extends Intent {
   final ScrollIncrementType type;
 }
 
-/// An [Action] that scrolls the [Scrollable] that encloses the current
-/// [primaryFocus] by the amount configured in the [ScrollIntent] given to it.
+/// An [Action] that scrolls the relevant [Scrollable] by the amount configured
+/// in the [ScrollIntent] given to it.
 ///
-/// If a Scrollable cannot be found above the current [primaryFocus], the
+/// If a Scrollable cannot be found above the given [BuildContext], the
 /// [PrimaryScrollController] will be considered for default handling of
 /// [ScrollAction]s.
 ///
@@ -388,21 +387,17 @@ class ScrollIntent extends Intent {
 /// for a [ScrollIntent.type] set to [ScrollIncrementType.page] is 80% of the
 /// size of the scroll window, and for [ScrollIncrementType.line], 50 logical
 /// pixels.
-class ScrollAction extends Action<ScrollIntent> {
+class ScrollAction extends ContextAction<ScrollIntent> {
   @override
-  bool isEnabled(ScrollIntent intent) {
-    final FocusNode? focus = primaryFocus;
-    final bool contextIsValid = focus != null && focus.context != null;
-    if (contextIsValid) {
-      // Check for primary scrollable within the current context
-      if (Scrollable.maybeOf(focus.context!) != null) {
-        return true;
-      }
-      // Check for fallback scrollable with context from PrimaryScrollController
-      final ScrollController? primaryScrollController = PrimaryScrollController.maybeOf(focus.context!);
-      return primaryScrollController != null && primaryScrollController.hasClients;
+  bool isEnabled(ScrollIntent intent, [BuildContext? context]) {
+    if (context == null) {
+      return false;
+    }
+    if (Scrollable.maybeOf(context) != null) {
+      return true;
     }
-    return false;
+    final ScrollController? primaryScrollController = PrimaryScrollController.maybeOf(context);
+    return (primaryScrollController != null) && (primaryScrollController.hasClients);
   }
 
   /// Returns the scroll increment for a single scroll request, for use when
@@ -480,10 +475,11 @@ class ScrollAction extends Action<ScrollIntent> {
   }
 
   @override
-  void invoke(ScrollIntent intent) {
-    ScrollableState? state = Scrollable.maybeOf(primaryFocus!.context!);
+  void invoke(ScrollIntent intent, [BuildContext? context]) {
+    assert(context != null, 'Cannot scroll without a context.');
+    ScrollableState? state = Scrollable.maybeOf(context!);
     if (state == null) {
-      final ScrollController primaryScrollController = PrimaryScrollController.of(primaryFocus!.context!);
+      final ScrollController primaryScrollController = PrimaryScrollController.of(context);
       assert (() {
         if (primaryScrollController.positions.length != 1) {
           throw FlutterError.fromParts(<DiagnosticsNode>[

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

@@ -843,9 +843,13 @@ class ShortcutManager with Diagnosticable, ChangeNotifier {
           primaryContext,
           intent: matchedIntent,
         );
-        if (action != null && action.isEnabled(matchedIntent)) {
-          final Object? invokeResult = Actions.of(primaryContext).invokeAction(action, matchedIntent, primaryContext);
-          return action.toKeyEventResult(matchedIntent, invokeResult);
+        if (action != null) {
+          final (bool enabled, Object? invokeResult) = Actions.of(primaryContext).invokeActionIfEnabled(
+            action, matchedIntent, primaryContext,
+          );
+          if (enabled) {
+            return action.toKeyEventResult(matchedIntent, invokeResult);
+          }
         }
       }
     }

packages/flutter/test/widgets/scrollable_helpers_test.dart

@@ -549,4 +549,33 @@ void main() {
       equals(const Rect.fromLTRB(0.0, 100.0, 800.0, 200.0)),
     );
   }, variant: KeySimulatorTransitModeVariant.all());
+
+  testWidgets('Can scroll using intents only', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      MaterialApp(
+        home: ListView(
+          children: const <Widget>[
+            SizedBox(height: 600.0, child: Text('The cow as white as milk')),
+            SizedBox(height: 600.0, child: Text('The cape as red as blood')),
+            SizedBox(height: 600.0, child: Text('The hair as yellow as corn')),
+          ],
+        ),
+      ),
+    );
+    expect(find.text('The cow as white as milk'), findsOneWidget);
+    expect(find.text('The cape as red as blood'), findsNothing);
+    expect(find.text('The hair as yellow as corn'), findsNothing);
+    Actions.invoke(tester.element(find.byType(SliverList)), const ScrollIntent(direction: AxisDirection.down, type: ScrollIncrementType.page));
+    await tester.pump(); // start scroll
+    await tester.pump(const Duration(milliseconds: 1000)); // end scroll
+    expect(find.text('The cow as white as milk'), findsOneWidget);
+    expect(find.text('The cape as red as blood'), findsOneWidget);
+    expect(find.text('The hair as yellow as corn'), findsNothing);
+    Actions.invoke(tester.element(find.byType(SliverList)), const ScrollIntent(direction: AxisDirection.down, type: ScrollIncrementType.page));
+    await tester.pump(); // start scroll
+    await tester.pump(const Duration(milliseconds: 1000)); // end scroll
+    expect(find.text('The cow as white as milk'), findsNothing);
+    expect(find.text('The cape as red as blood'), findsOneWidget);
+    expect(find.text('The hair as yellow as corn'), findsOneWidget);
+  });
 }