Update Highlight mode initial value calculation. (#52990)

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

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:io';
 import 'dart:ui';
 
 import 'package:flutter/foundation.dart';
@@ -1368,7 +1367,34 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
   /// the [WidgetsBinding] instance.
   static FocusManager get instance => WidgetsBinding.instance.focusManager;
 
-  bool _lastInteractionWasTouch = true;
+  bool get _lastInteractionWasTouch {
+    // Assume that if we're on one of these mobile platforms, or if there's no
+    // mouse connected, that the initial interaction will be touch-based, and
+    // that it's traditional mouse and keyboard on all others.
+    //
+    // This only affects the initial value: the ongoing value is updated to a
+    // known correct value as soon as any pointer events are received.
+    if (_lastInteractionWasTouchValue == null) {
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.android:
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.iOS:
+          _lastInteractionWasTouchValue = !WidgetsBinding.instance.mouseTracker.mouseIsConnected;
+          break;
+        case TargetPlatform.linux:
+        case TargetPlatform.macOS:
+        case TargetPlatform.windows:
+          _lastInteractionWasTouchValue = false;
+          break;
+      }
+    }
+    return _lastInteractionWasTouchValue;
+  }
+  bool _lastInteractionWasTouchValue;
+  set _lastInteractionWasTouch(bool value) {
+    _lastInteractionWasTouchValue = value;
+  }
+
 
   /// Sets the strategy by which [highlightMode] is determined.
   ///
@@ -1418,13 +1444,6 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
   // Update function to be called whenever the state relating to highlightMode
   // changes.
   void _updateHighlightMode() {
-    // Assume that if we're on one of these mobile platforms, or if there's no
-    // mouse connected, that the initial interaction will be touch-based, and
-    // that it's traditional mouse and keyboard on all others.
-    //
-    // This only affects the initial value: the ongoing value is updated as soon
-    // as any input events are received.
-    _lastInteractionWasTouch ??= Platform.isAndroid || Platform.isIOS || !WidgetsBinding.instance.mouseTracker.mouseIsConnected;
     FocusHighlightMode newMode;
     switch (highlightStrategy) {
       case FocusHighlightStrategy.automatic:

packages/flutter/test/widgets/focus_manager_test.dart

@@ -828,6 +828,21 @@ void main() {
       // receive it.
       expect(receivedAnEvent, isEmpty);
     });
+    testWidgets('Initial highlight mode guesses correctly.', (WidgetTester tester) async {
+      FocusManager.instance.highlightStrategy = FocusHighlightStrategy.automatic;
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.fuchsia:
+        case TargetPlatform.android:
+        case TargetPlatform.iOS:
+          expect(FocusManager.instance.highlightMode, equals(FocusHighlightMode.touch));
+          break;
+        case TargetPlatform.linux:
+        case TargetPlatform.macOS:
+        case TargetPlatform.windows:
+          expect(FocusManager.instance.highlightMode, equals(FocusHighlightMode.traditional));
+          break;
+      }
+    }, variant: TargetPlatformVariant.all());
     testWidgets('Events change focus highlight mode.', (WidgetTester tester) async {
       await setupWidget(tester);
       int callCount = 0;