added generation of empty classes in dart

packages/pigeon/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## NEXT
 
 * Updates minimum supported SDK version to Flutter 3.22/Dart 3.4.
+* [dart] fixes [160501](https://github.com/flutter/flutter/issues/160501).
 
 ## 22.7.0
 

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/EventChannelMessages.g.kt

@@ -49,6 +49,19 @@ data class StringEvent(val data: String) : PlatformEvent() {
   }
 }
 
+/** Generated class from Pigeon that represents data sent in messages. */
+class EmptyEvent() : PlatformEvent() {
+  companion object {
+    fun fromList(pigeonVar_list: List<Any?>): EmptyEvent {
+      return EmptyEvent()
+    }
+  }
+
+  fun toList(): List<Any?> {
+    return listOf()
+  }
+}
+
 private open class EventChannelMessagesPigeonCodec : StandardMessageCodec() {
   override fun readValueOfType(type: Byte, buffer: ByteBuffer): Any? {
     return when (type) {
@@ -58,6 +71,9 @@ private open class EventChannelMessagesPigeonCodec : StandardMessageCodec() {
       130.toByte() -> {
         return (readValue(buffer) as? List<Any?>)?.let { StringEvent.fromList(it) }
       }
+      131.toByte() -> {
+        return (readValue(buffer) as? List<Any?>)?.let { EmptyEvent.fromList(it) }
+      }
       else -> super.readValueOfType(type, buffer)
     }
   }
@@ -72,6 +88,10 @@ private open class EventChannelMessagesPigeonCodec : StandardMessageCodec() {
         stream.write(130)
         writeValue(stream, value.toList())
       }
+      is EmptyEvent -> {
+        stream.write(131)
+        writeValue(stream, value.toList())
+      }
       else -> super.writeValue(stream, value)
     }
   }

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/MainActivity.kt

@@ -4,6 +4,7 @@
 
 package dev.flutter.pigeon_example_app
 
+import EmptyEvent
 import ExampleHostApi
 import FlutterError
 import IntEvent
@@ -72,6 +73,10 @@ class EventListener : StreamEventsStreamHandler() {
     eventSink?.success(StringEvent(data = event))
   }
 
+  fun onEmptyEvent() {
+    eventSink?.success(EmptyEvent())
+  }
+
   fun onEventsDone() {
     eventSink?.endOfStream()
     eventSink = null
@@ -93,6 +98,11 @@ fun sendEvents(eventListener: EventListener) {
                 eventListener.onIntEvent(count.toLong())
                 count++
               }
+            } else if (count % 5 == 0) {
+              handler.post {
+                eventListener.onEmptyEvent()
+                count++
+              }
             } else {
               handler.post {
                 eventListener.onStringEvent(count.toString())

packages/pigeon/example/app/ios/Runner/AppDelegate.swift

@@ -66,6 +66,12 @@ class EventListener: StreamEventsStreamHandler {
     }
   }
 
+  func onEmptyEvent() {
+    if let eventSink = eventSink {
+      eventSink.success(EmptyEvent())
+    }
+  }
+
   func onEventsDone() {
     eventSink?.endOfStream()
     eventSink = nil
@@ -84,6 +90,8 @@ func sendEvents(_ eventListener: EventListener) {
       } else {
         if (count % 2) == 0 {
           eventListener.onIntEvent(event: Int64(count))
+        } else if (count % 5) == 0 {
+          eventListener.onEmptyEvent()
         } else {
           eventListener.onStringEvent(event: String(count))
         }

packages/pigeon/example/app/ios/Runner/EventChannelMessages.g.swift

@@ -67,13 +67,28 @@ struct StringEvent: PlatformEvent {
   }
 }
 
+/// Generated class from Pigeon that represents data sent in messages.
+struct EmptyEvent: PlatformEvent {
+
+  // swift-format-ignore: AlwaysUseLowerCamelCase
+  static func fromList(_ pigeonVar_list: [Any?]) -> EmptyEvent? {
+
+    return EmptyEvent()
+  }
+  func toList() -> [Any?] {
+    return []
+  }
+}
+
 private class EventChannelMessagesPigeonCodecReader: FlutterStandardReader {
   override func readValue(ofType type: UInt8) -> Any? {
     switch type {
     case 129:
       return IntEvent.fromList(self.readValue() as! [Any?])
     case 130:
       return StringEvent.fromList(self.readValue() as! [Any?])
+    case 131:
+      return EmptyEvent.fromList(self.readValue() as! [Any?])
     default:
       return super.readValue(ofType: type)
     }
@@ -88,6 +103,9 @@ private class EventChannelMessagesPigeonCodecWriter: FlutterStandardWriter {
     } else if let value = value as? StringEvent {
       super.writeByte(130)
       super.writeValue(value.toList())
+    } else if let value = value as? EmptyEvent {
+      super.writeByte(131)
+      super.writeValue(value.toList())
     } else {
       super.writeValue(value)
     }

packages/pigeon/example/app/lib/main.dart

@@ -99,6 +99,8 @@ class _MyHomePageState extends State<MyHomePage> {
         case StringEvent():
           final String stringData = event.data;
           yield '$stringData, ';
+        case EmptyEvent():
+          yield 'EmptyEvent, ';
       }
     }
   }

packages/pigeon/example/app/lib/src/event_channel_messages.g.dart

@@ -55,6 +55,17 @@ class StringEvent extends PlatformEvent {
   }
 }
 
+class EmptyEvent extends PlatformEvent {
+  Object encode() {
+    return <Object?>[];
+  }
+
+  static EmptyEvent decode(Object result) {
+    result as List<Object?>;
+    return EmptyEvent();
+  }
+}
+
 class _PigeonCodec extends StandardMessageCodec {
   const _PigeonCodec();
   @override
@@ -68,6 +79,9 @@ class _PigeonCodec extends StandardMessageCodec {
     } else if (value is StringEvent) {
       buffer.putUint8(130);
       writeValue(buffer, value.encode());
+    } else if (value is EmptyEvent) {
+      buffer.putUint8(131);
+      writeValue(buffer, value.encode());
     } else {
       super.writeValue(buffer, value);
     }
@@ -80,6 +94,8 @@ class _PigeonCodec extends StandardMessageCodec {
         return IntEvent.decode(readValue(buffer)!);
       case 130:
         return StringEvent.decode(readValue(buffer)!);
+      case 131:
+        return EmptyEvent.decode(readValue(buffer)!);
       default:
         return super.readValueOfType(type, buffer);
     }

packages/pigeon/example/app/pigeons/event_channel_messages.dart

@@ -33,6 +33,9 @@ class StringEvent extends PlatformEvent {
   StringEvent(this.data);
   String data;
 }
+
+class EmptyEvent extends PlatformEvent {}
+
 // #enddocregion sealed-definitions
 
 // #docregion event-definitions

packages/pigeon/lib/dart_generator.dart

@@ -169,20 +169,24 @@ class DartGenerator extends StructuredGenerator<DartOptions> {
         : '';
 
     indent.write('${sealed}class ${classDefinition.name} $implements');
+
     indent.addScoped('{', '}', () {
-      if (classDefinition.fields.isEmpty) {
+      if (classDefinition.isSealed) {
         return;
       }
-      _writeConstructor(indent, classDefinition);
-      indent.newln();
-      for (final NamedType field
-          in getFieldsInSerializationOrder(classDefinition)) {
-        addDocumentationComments(
-            indent, field.documentationComments, _docCommentSpec);
 
-        final String datatype = _addGenericTypesNullable(field.type);
-        indent.writeln('$datatype ${field.name};');
+      if (classDefinition.fields.isNotEmpty) {
+        _writeConstructor(indent, classDefinition);
         indent.newln();
+        for (final NamedType field
+            in getFieldsInSerializationOrder(classDefinition)) {
+          addDocumentationComments(
+              indent, field.documentationComments, _docCommentSpec);
+
+          final String datatype = _addGenericTypesNullable(field.type);
+          indent.writeln('$datatype ${field.name};');
+          indent.newln();
+        }
       }
       writeClassEncode(
         generatorOptions,

packages/pigeon/lib/kotlin_generator.dart

@@ -241,7 +241,11 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
     bool private = false,
   }) {
     final String privateString = private ? 'private ' : '';
-    final String classType = classDefinition.isSealed ? 'sealed' : 'data';
+    final String classType = classDefinition.isSealed
+        ? 'sealed'
+        : classDefinition.fields.isNotEmpty
+            ? 'data'
+            : '';
     final String inheritance = classDefinition.superClass != null
         ? ' : ${classDefinition.superClassName}()'
         : '';

packages/pigeon/test/dart_generator_test.dart

@@ -1807,4 +1807,28 @@ name: foobar
     expect(code, contains('buffer.putUint8(4);'));
     expect(code, contains('buffer.putInt64(value);'));
   });
+
+  // https://github.com/flutter/flutter/issues/160501
+  test('gen one empty class', () {
+    final Class classDefinition = Class(
+      name: 'Foobar',
+      fields: <NamedType>[],
+    );
+    final Root root = Root(
+      apis: <Api>[],
+      classes: <Class>[classDefinition],
+      enums: <Enum>[],
+    );
+    final StringBuffer sink = StringBuffer();
+    const DartGenerator generator = DartGenerator();
+    generator.generate(
+      const DartOptions(),
+      root,
+      sink,
+      dartPackageName: DEFAULT_PACKAGE_NAME,
+    );
+    final String code = sink.toString();
+    expect(code, contains('Object encode()'));
+    expect(code, contains('static Foobar decode(Object result)'));
+  });
 }

packages/pigeon/test/kotlin_generator_test.dart

@@ -1856,4 +1856,30 @@ void main() {
     // There should be only one occurrence of 'is Foo' in the block
     expect(count, 1);
   });
+
+  // https://github.com/flutter/flutter/issues/160501
+  test('gen one empty class', () {
+    final Class classDefinition = Class(
+      name: 'Foobar',
+      fields: <NamedType>[],
+    );
+    final Root root = Root(
+      apis: <Api>[],
+      classes: <Class>[classDefinition],
+      enums: <Enum>[],
+    );
+    final StringBuffer sink = StringBuffer();
+    const KotlinOptions kotlinOptions = KotlinOptions();
+    const KotlinGenerator generator = KotlinGenerator();
+    generator.generate(
+      kotlinOptions,
+      root,
+      sink,
+      dartPackageName: DEFAULT_PACKAGE_NAME,
+    );
+    final String code = sink.toString();
+
+    /// The generated class should not be data class
+    expect(code, isNot(contains('data class')));
+  });
 }

script/tool/lib/src/common/package_looping_command.dart

@@ -340,7 +340,7 @@ abstract class PackageLoopingCommand extends PackageCommand {
     if (minFlutterVersion != null) {
       final Pubspec pubspec = package.parsePubspec();
       final VersionConstraint? flutterConstraint =
-          pubspec.environment?['flutter'];
+          pubspec.environment['flutter'];
       if (flutterConstraint != null &&
           !flutterConstraint.allows(minFlutterVersion)) {
         return PackageResult.skip(
@@ -350,7 +350,7 @@ abstract class PackageLoopingCommand extends PackageCommand {
 
     if (minDartVersion != null) {
       final Pubspec pubspec = package.parsePubspec();
-      final VersionConstraint? dartConstraint = pubspec.environment?['sdk'];
+      final VersionConstraint? dartConstraint = pubspec.environment['sdk'];
       if (dartConstraint != null && !dartConstraint.allows(minDartVersion)) {
         return PackageResult.skip('Does not support Dart $minDartVersion');
       }

script/tool/lib/src/create_all_packages_app_command.dart

@@ -277,7 +277,7 @@ dependencies {}
     final Pubspec originalPubspec = app.parsePubspec();
     const String dartSdkKey = 'sdk';
     final VersionConstraint dartSdkConstraint =
-        originalPubspec.environment?[dartSdkKey] ??
+        originalPubspec.environment[dartSdkKey] ??
             VersionConstraint.compatibleWith(
               Version.parse('3.0.0'),
             );
@@ -342,7 +342,7 @@ publish_to: none
 
 version: ${pubspec.version}
 
-environment:${_pubspecMapString(pubspec.environment!)}
+environment:${_pubspecMapString(pubspec.environment)}
 
 dependencies:${_pubspecMapString(pubspec.dependencies)}
 

script/tool/lib/src/pubspec_check_command.dart

@@ -488,9 +488,9 @@ class PubspecCheckCommand extends PackageLoopingCommand {
     }
 
     final Version? dartConstraintMin =
-        _minimumForConstraint(pubspec.environment?['sdk']);
+        _minimumForConstraint(pubspec.environment['sdk']);
     final Version? flutterConstraintMin =
-        _minimumForConstraint(pubspec.environment?['flutter']);
+        _minimumForConstraint(pubspec.environment['flutter']);
 
     // Validate the Flutter constraint, if any.
     if (flutterConstraintMin != null && minMinFlutterVersion != null) {

script/tool/lib/src/update_min_sdk_command.dart

@@ -87,7 +87,7 @@ class UpdateMinSdkCommand extends PackageLoopingCommand {
   /// Returns the given "environment" section's [key] constraint as a range,
   /// if the key is present and has a range.
   VersionRange? _sdkRange(Pubspec pubspec, String key) {
-    final VersionConstraint? constraint = pubspec.environment?[key];
+    final VersionConstraint? constraint = pubspec.environment[key];
     if (constraint is VersionRange) {
       return constraint;
     }

script/tool/test/create_all_packages_app_command_test.dart

@@ -356,7 +356,7 @@ android {
       final Pubspec generatedPubspec = command.app.parsePubspec();
 
       const String dartSdkKey = 'sdk';
-      expect(generatedPubspec.environment?[dartSdkKey].toString(),
+      expect(generatedPubspec.environment[dartSdkKey].toString(),
           existingSdkConstraint);
     });