[pigeon]: added generation of empty classes in dart

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 22.7.3
+
+* Adds support for empty data classes.
+
 ## 22.7.2
 
 * Updates README to discuss best practices for using Pigeon-generated code.

packages/pigeon/example/README.md

@@ -390,6 +390,8 @@ Stream<String> getEventStream() async* {
       case StringEvent():
         final String stringData = event.data;
         yield '$stringData, ';
+      case EmptyEvent():
+        yield 'EmptyEvent, ';
     }
   }
 }
@@ -420,6 +422,12 @@ class EventListener: StreamEventsStreamHandler {
     }
   }
 
+  func onEmptyEvent() {
+    if let eventSink = eventSink {
+      eventSink.success(EmptyEvent())
+    }
+  }
+
   func onEventsDone() {
     eventSink?.endOfStream()
     eventSink = nil
@@ -457,6 +465,10 @@ class EventListener : StreamEventsStreamHandler() {
     eventSink?.success(StringEvent(data = event))
   }
 
+  fun onEmptyEvent() {
+    eventSink?.success(EmptyEvent())
+  }
+
   fun onEventsDone() {
     eventSink?.endOfStream()
     eventSink = null

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

@@ -49,6 +49,20 @@ data class StringEvent(val data: String) : PlatformEvent() {
   }
 }
 
+/** Generated class from Pigeon that represents data sent in messages. */
+class EmptyEvent() : PlatformEvent() {
+  companion object {
+    @Suppress("UNUSED_PARAMETER")
+    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 +72,9 @@ 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 +89,10 @@ 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/generator_tools.dart

@@ -14,7 +14,7 @@ import 'ast.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '22.7.2';
+const String pigeonVersion = '22.7.3';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {

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}()'
         : '';
@@ -295,6 +299,10 @@ class KotlinGenerator extends StructuredGenerator<KotlinOptions> {
 
     indent.write('companion object ');
     indent.addScoped('{', '}', () {
+      if (getFieldsInSerializationOrder(classDefinition).isEmpty) {
+        indent.write('@Suppress("UNUSED_PARAMETER")');
+      }
+
       indent
           .write('fun fromList(${varNamePrefix}list: List<Any?>): $className ');
 

packages/pigeon/pigeons/event_channel_tests.dart

@@ -137,6 +137,8 @@ class ClassEvent extends PlatformEvent {
   final EventAllNullableTypes value;
 }
 
+class EmptyEvent extends PlatformEvent {}
+
 @EventChannelApi()
 abstract class EventChannelMethods {
   int streamInts();

packages/pigeon/platform_tests/shared_test_plugin_code/lib/integration_tests.dart

@@ -2907,6 +2907,9 @@ void runPigeonIntegrationTests(TargetGenerator targetGenerator) {
           expect(event.value.aNullableInt, 0);
           expect(count, 6);
           count++;
+        case EmptyEvent():
+          expect(count, 7);
+          count++;
           completer.complete();
       }
     });

packages/pigeon/platform_tests/shared_test_plugin_code/lib/src/generated/event_channel_tests.gen.dart

@@ -352,6 +352,17 @@ class ClassEvent 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
@@ -389,6 +400,9 @@ class _PigeonCodec extends StandardMessageCodec {
     } else if (value is ClassEvent) {
       buffer.putUint8(138);
       writeValue(buffer, value.encode());
+    } else if (value is EmptyEvent) {
+      buffer.putUint8(139);
+      writeValue(buffer, value.encode());
     } else {
       super.writeValue(buffer, value);
     }
@@ -419,6 +433,8 @@ class _PigeonCodec extends StandardMessageCodec {
         return EnumEvent.decode(readValue(buffer)!);
       case 138:
         return ClassEvent.decode(readValue(buffer)!);
+      case 139:
+        return EmptyEvent.decode(readValue(buffer)!);
       default:
         return super.readValueOfType(type, buffer);
     }

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/EventChannelTests.gen.kt

@@ -312,6 +312,20 @@ data class ClassEvent(val value: EventAllNullableTypes) : PlatformEvent() {
   }
 }
 
+/** Generated class from Pigeon that represents data sent in messages. */
+class EmptyEvent() : PlatformEvent() {
+  companion object {
+    @Suppress("UNUSED_PARAMETER")
+    fun fromList(pigeonVar_list: List<Any?>): EmptyEvent {
+      return EmptyEvent()
+    }
+  }
+
+  fun toList(): List<Any?> {
+    return listOf()
+  }
+}
+
 private open class EventChannelTestsPigeonCodec : StandardMessageCodec() {
   override fun readValueOfType(type: Byte, buffer: ByteBuffer): Any? {
     return when (type) {
@@ -345,6 +359,9 @@ private open class EventChannelTestsPigeonCodec : StandardMessageCodec() {
       138.toByte() -> {
         return (readValue(buffer) as? List<Any?>)?.let { ClassEvent.fromList(it) }
       }
+      139.toByte() -> {
+        return (readValue(buffer) as? List<Any?>)?.let { EmptyEvent.fromList(it) }
+      }
       else -> super.readValueOfType(type, buffer)
     }
   }
@@ -391,6 +408,10 @@ private open class EventChannelTestsPigeonCodec : StandardMessageCodec() {
         stream.write(138)
         writeValue(stream, value.toList())
       }
+      is EmptyEvent -> {
+        stream.write(139)
+        writeValue(stream, value.toList())
+      }
       else -> super.writeValue(stream, value)
     }
   }