More null-safety fixes for flutter_driver (#75343)

packages/flutter_driver/lib/src/common/find.dart

@@ -64,20 +64,6 @@ class WaitFor extends CommandWithTarget {
   String get kind => 'waitFor';
 }
 
-/// The result of a [WaitFor] command.
-class WaitForResult extends Result {
-  /// Creates a [WaitForResult].
-  const WaitForResult();
-
-  /// Deserializes the result from JSON.
-  static WaitForResult fromJson(Map<String, dynamic> json) {
-    return const WaitForResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => <String, dynamic>{};
-}
-
 /// A Flutter Driver command that waits until [finder] can no longer locate the target.
 class WaitForAbsent extends CommandWithTarget {
   /// Creates a command that waits for the widget identified by [finder] to
@@ -94,20 +80,6 @@ class WaitForAbsent extends CommandWithTarget {
   String get kind => 'waitForAbsent';
 }
 
-/// The result of a [WaitForAbsent] command.
-class WaitForAbsentResult extends Result {
-  /// Creates a [WaitForAbsentResult].
-  const WaitForAbsentResult();
-
-  /// Deserializes the result from JSON.
-  static WaitForAbsentResult fromJson(Map<String, dynamic> json) {
-    return const WaitForAbsentResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => <String, dynamic>{};
-}
-
 /// Base class for Flutter Driver finders, objects that describe how the driver
 /// should search for elements.
 abstract class SerializableFinder {

packages/flutter_driver/lib/src/common/frame_sync.dart

@@ -25,17 +25,3 @@ class SetFrameSync extends Command {
     'enabled': '$enabled',
   });
 }
-
-/// The result of a [SetFrameSync] command.
-class SetFrameSyncResult extends Result {
-  /// Creates a [SetFrameSyncResult].
-  const SetFrameSyncResult();
-
-  /// Deserializes this result from JSON.
-  static SetFrameSyncResult fromJson(Map<String, dynamic> json) {
-    return const SetFrameSyncResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => <String, dynamic>{};
-}

packages/flutter_driver/lib/src/common/gesture.dart

@@ -4,7 +4,6 @@
 
 import 'deserialization_factory.dart';
 import 'find.dart';
-import 'message.dart';
 
 /// A Flutter Driver command that taps on a target widget located by [finder].
 class Tap extends CommandWithTarget {
@@ -18,21 +17,6 @@ class Tap extends CommandWithTarget {
   String get kind => 'tap';
 }
 
-/// The result of a [Tap] command.
-class TapResult extends Result {
-  /// Creates a [TapResult].
-  const TapResult();
-
-  /// Deserializes this result from JSON.
-  static TapResult fromJson(Map<String, dynamic> json) {
-    return const TapResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => <String, dynamic>{};
-}
-
-
 /// A Flutter Driver command that commands the driver to perform a scrolling action.
 class Scroll extends CommandWithTarget {
   /// Creates a scroll command that will attempt to scroll a scrollable view by
@@ -78,20 +62,6 @@ class Scroll extends CommandWithTarget {
   });
 }
 
-/// The result of a [Scroll] command.
-class ScrollResult extends Result {
-  /// Creates a [ScrollResult].
-  const ScrollResult();
-
-  /// Deserializes this result from JSON.
-  static ScrollResult fromJson(Map<String, dynamic> json) {
-    return const ScrollResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => <String, dynamic>{};
-}
-
 /// A Flutter Driver command that commands the driver to ensure that the element
 /// represented by [finder] has been scrolled completely into view.
 class ScrollIntoView extends CommandWithTarget {

packages/flutter_driver/lib/src/common/handler_factory.dart

@@ -154,7 +154,7 @@ mixin CommandHandlerFactory {
   final TestTextInput _testTextInput = TestTextInput();
 
   /// Deserializes the finder from JSON generated by [Command.serialize] or [CommandWithTarget.serialize].
-  Future<Result?> handleCommand(Command command, WidgetController prober, CreateFinderFactory finderFactory) {
+  Future<Result> handleCommand(Command command, WidgetController prober, CreateFinderFactory finderFactory) {
     switch(command.kind) {
       case 'get_health': return _getHealth(command);
       case 'get_layer_tree': return _getLayerTree(command);
@@ -192,14 +192,14 @@ mixin CommandHandlerFactory {
     return RenderTree(RendererBinding.instance?.renderView.toStringDeep());
   }
 
-  Future<EnterTextResult> _enterText(Command command) async {
+  Future<Result> _enterText(Command command) async {
     if (!_testTextInput.isRegistered) {
       throw 'Unable to fulfill `FlutterDriver.enterText`. Text emulation is '
             'disabled. You can enable it using `FlutterDriver.setTextEntryEmulation`.';
     }
     final EnterText enterTextCommand = command as EnterText;
     _testTextInput.enterText(enterTextCommand.text);
-    return const EnterTextResult();
+    return Result.empty;
   }
 
   Future<RequestDataResult> _requestData(Command command) async {
@@ -210,49 +210,49 @@ mixin CommandHandlerFactory {
       : await dataHandler(requestDataCommand.message));
   }
 
-  Future<SetFrameSyncResult> _setFrameSync(Command command) async {
+  Future<Result> _setFrameSync(Command command) async {
     final SetFrameSync setFrameSyncCommand = command as SetFrameSync;
     _frameSync = setFrameSyncCommand.enabled;
-    return const SetFrameSyncResult();
+    return Result.empty;
   }
 
-  Future<TapResult> _tap(Command command, WidgetController prober, CreateFinderFactory finderFactory) async {
+  Future<Result> _tap(Command command, WidgetController prober, CreateFinderFactory finderFactory) async {
     final Tap tapCommand = command as Tap;
     final Finder computedFinder = await waitForElement(
       finderFactory.createFinder(tapCommand.finder).hitTestable(),
     );
     await prober.tap(computedFinder);
-    return const TapResult();
+    return Result.empty;
   }
 
-  Future<WaitForResult> _waitFor(Command command, CreateFinderFactory finderFactory) async {
+  Future<Result> _waitFor(Command command, CreateFinderFactory finderFactory) async {
     final WaitFor waitForCommand = command as WaitFor;
     await waitForElement(finderFactory.createFinder(waitForCommand.finder));
-    return const WaitForResult();
+    return Result.empty;
   }
 
-  Future<WaitForAbsentResult> _waitForAbsent(Command command, CreateFinderFactory finderFactory) async {
+  Future<Result> _waitForAbsent(Command command, CreateFinderFactory finderFactory) async {
     final WaitForAbsent waitForAbsentCommand = command as WaitForAbsent;
     await waitForAbsentElement(finderFactory.createFinder(waitForAbsentCommand.finder));
-    return const WaitForAbsentResult();
+    return Result.empty;
   }
 
-  Future<Result?> _waitForCondition(Command command) async {
+  Future<Result> _waitForCondition(Command command) async {
     assert(command != null);
     final WaitForCondition waitForConditionCommand = command as WaitForCondition;
     final WaitCondition condition = deserializeCondition(waitForConditionCommand.condition);
     await condition.wait();
-    return null;
+    return Result.empty;
   }
 
   @Deprecated(
     'This method has been deprecated in favor of _waitForCondition. '
     'This feature was deprecated after v1.9.3.'
   )
-  Future<Result?> _waitUntilNoTransientCallbacks(Command command) async {
+  Future<Result> _waitUntilNoTransientCallbacks(Command command) async {
     if (SchedulerBinding.instance!.transientCallbackCount != 0)
       await _waitUntilFrame(() => SchedulerBinding.instance!.transientCallbackCount == 0);
-    return null;
+    return Result.empty;
   }
 
   /// Returns a future that waits until no pending frame is scheduled (frame is synced).
@@ -278,12 +278,12 @@ mixin CommandHandlerFactory {
     'This method has been deprecated in favor of _waitForCondition. '
     'This feature was deprecated after v1.9.3.'
   )
-  Future<Result?> _waitUntilNoPendingFrame(Command command) async {
+  Future<Result> _waitUntilNoPendingFrame(Command command) async {
     await _waitUntilFrame(() {
       return SchedulerBinding.instance!.transientCallbackCount == 0
           && !SchedulerBinding.instance!.hasScheduledFrame;
     });
-    return null;
+    return Result.empty;
   }
 
   Future<GetSemanticsIdResult> _getSemanticsId(Command command, CreateFinderFactory finderFactory) async {
@@ -351,7 +351,7 @@ mixin CommandHandlerFactory {
     )));
   }
 
-  Future<ScrollResult> _scroll(Command command, WidgetController _prober, CreateFinderFactory finderFactory) async {
+  Future<Result> _scroll(Command command, WidgetController _prober, CreateFinderFactory finderFactory) async {
     final Scroll scrollCommand = command as Scroll;
     final Finder target = await waitForElement(finderFactory.createFinder(scrollCommand.finder));
     final int totalMoves = scrollCommand.duration.inMicroseconds * scrollCommand.frequency ~/ Duration.microsecondsPerSecond;
@@ -369,14 +369,14 @@ mixin CommandHandlerFactory {
     }
     _prober.binding.handlePointerEvent(pointer.up());
 
-    return const ScrollResult();
+    return Result.empty;
   }
 
-  Future<ScrollResult> _scrollIntoView(Command command, CreateFinderFactory finderFactory) async {
+  Future<Result> _scrollIntoView(Command command, CreateFinderFactory finderFactory) async {
     final ScrollIntoView scrollIntoViewCommand = command as ScrollIntoView;
     final Finder target = await waitForElement(finderFactory.createFinder(scrollIntoViewCommand.finder));
     await Scrollable.ensureVisible(target.evaluate().single, duration: const Duration(milliseconds: 100), alignment: scrollIntoViewCommand.alignment);
-    return const ScrollResult();
+    return Result.empty;
   }
 
   Future<GetTextResult> _getText(Command command, CreateFinderFactory finderFactory) async {
@@ -408,14 +408,14 @@ mixin CommandHandlerFactory {
     return GetTextResult(text);
   }
 
-  Future<SetTextEntryEmulationResult> _setTextEntryEmulation(Command command) async {
+  Future<Result> _setTextEntryEmulation(Command command) async {
     final SetTextEntryEmulation setTextEntryEmulationCommand = command as SetTextEntryEmulation;
     if (setTextEntryEmulationCommand.enabled) {
       _testTextInput.register();
     } else {
       _testTextInput.unregister();
     }
-    return const SetTextEntryEmulationResult();
+    return Result.empty;
   }
 
   SemanticsHandle? _semantics;
@@ -446,9 +446,9 @@ mixin CommandHandlerFactory {
     'This method has been deprecated in favor of _waitForCondition. '
     'This feature was deprecated after v1.9.3.'
   )
-  Future<Result?> _waitUntilFirstFrameRasterized(Command command) async {
+  Future<Result> _waitUntilFirstFrameRasterized(Command command) async {
     await WidgetsBinding.instance!.waitUntilFirstFrameRasterized;
-    return null;
+    return Result.empty;
   }
 
   /// Runs `finder` repeatedly until it finds one or more [Element]s.

packages/flutter_driver/lib/src/common/message.dart

@@ -64,6 +64,19 @@ abstract class Result {
   /// A const constructor to allow subclasses to be const.
   const Result();
 
+  /// An empty responds that does not include any result data.
+  ///
+  /// Consider using this object as a result for [Command]s that do not return
+  /// any data.
+  static const Result empty = _EmptyResult();
+
   /// Serializes this message to a JSON map.
   Map<String, dynamic> toJson();
 }
+
+class _EmptyResult extends Result {
+  const _EmptyResult();
+
+  @override
+  Map<String, dynamic> toJson() => <String, dynamic>{};
+}

packages/flutter_driver/lib/src/common/text.dart

@@ -59,20 +59,6 @@ class EnterText extends Command {
   });
 }
 
-/// The result of the [EnterText] command.
-class EnterTextResult extends Result {
-  /// Creates a successful result of entering the text.
-  const EnterTextResult();
-
-  /// Deserializes the result from JSON.
-  static EnterTextResult fromJson(Map<String, dynamic> json) {
-    return const EnterTextResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => const <String, String>{};
-}
-
 /// A Flutter Driver command that enables and disables text entry emulation.
 class SetTextEntryEmulation extends Command {
   /// Creates a command that enables and disables text entry emulation.
@@ -94,17 +80,3 @@ class SetTextEntryEmulation extends Command {
     'enabled': '$enabled',
   });
 }
-
-/// The result of the [SetTextEntryEmulation] command.
-class SetTextEntryEmulationResult extends Result {
-  /// Creates a successful result.
-  const SetTextEntryEmulationResult();
-
-  /// Deserializes the result from JSON.
-  static SetTextEntryEmulationResult fromJson(Map<String, dynamic> json) {
-    return const SetTextEntryEmulationResult();
-  }
-
-  @override
-  Map<String, dynamic> toJson() => const <String, String>{};
-}

packages/flutter_driver/lib/src/extension/extension.dart

@@ -433,7 +433,7 @@ class FlutterDriverExtension with DeserializeFinderFactory, CreateFinderFactory,
   }
 
   @override
-  Future<Result?> handleCommand(Command command, WidgetController prober, CreateFinderFactory finderFactory) {
+  Future<Result> handleCommand(Command command, WidgetController prober, CreateFinderFactory finderFactory) {
     final String kind = command.kind;
     if(_commandExtensions.containsKey(kind)) {
       return _commandExtensions[kind]!.call(command, prober, finderFactory, this);

packages/flutter_driver/test/src/real_tests/extension_test.dart

@@ -56,7 +56,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -81,7 +81,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -117,7 +117,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -142,7 +142,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -159,7 +159,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -182,7 +182,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -201,7 +201,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -230,7 +230,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -259,7 +259,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -277,7 +277,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -310,7 +310,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -359,7 +359,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -410,7 +410,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -460,7 +460,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -1145,7 +1145,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -1171,7 +1171,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });
@@ -1195,7 +1195,7 @@ void main() {
         result,
         <String, dynamic>{
           'isError': false,
-          'response': null,
+          'response': <String, dynamic>{},
         },
       );
     });