[pigeon] allow empty class

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 27.2.0
+
+* Adds support for empty data classes.
+
 ## 27.1.1
 
 * [dart] Adds usage documentation to generated event channel methods, and

packages/pigeon/lib/src/dart/dart_generator.dart

@@ -222,17 +222,19 @@ class DartGenerator extends StructuredGenerator<InternalDartOptions> {
 
     indent.write('${sealed}class ${classDefinition.name} $implements');
     indent.addScoped('{', '}', () {
-      if (classDefinition.fields.isEmpty) {
+      if (classDefinition.isSealed) {
         return;
       }
       _writeConstructor(indent, classDefinition);
-      indent.newln();
-      for (final NamedType field in getFieldsInSerializationOrder(classDefinition)) {
-        addDocumentationComments(indent, field.documentationComments, docCommentSpec);
-
-        final String datatype = addGenericTypes(field.type);
-        indent.writeln('$datatype ${field.name};');
+      if (classDefinition.fields.isNotEmpty) {
         indent.newln();
+        for (final NamedType field in getFieldsInSerializationOrder(classDefinition)) {
+          addDocumentationComments(indent, field.documentationComments, docCommentSpec);
+
+          final String datatype = addGenericTypes(field.type);
+          indent.writeln('$datatype ${field.name};');
+          indent.newln();
+        }
       }
       _writeToList(indent, classDefinition);
       indent.newln();
@@ -264,6 +266,10 @@ class DartGenerator extends StructuredGenerator<InternalDartOptions> {
 
   void _writeConstructor(Indent indent, Class classDefinition) {
     indent.write(classDefinition.name);
+    if (classDefinition.fields.isEmpty) {
+      indent.addln('();');
+      return;
+    }
     indent.addScoped('({', '});', () {
       for (final NamedType field in getFieldsInSerializationOrder(classDefinition)) {
         final required = !field.type.isNullable && field.defaultValue == null ? 'required ' : '';

packages/pigeon/lib/src/generator_tools.dart

@@ -15,7 +15,7 @@ import 'generator.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '27.1.1';
+const String pigeonVersion = '27.2.0';
 
 /// Default plugin package name.
 const String defaultPluginPackageName = 'dev.flutter.pigeon';

packages/pigeon/lib/src/java/java_generator.dart

@@ -349,7 +349,11 @@ class JavaGenerator extends StructuredGenerator<InternalJavaOptions> {
       final Iterable<String> checks = classDefinition.fields.map((NamedType field) {
         return 'pigeonDeepEquals(${field.name}, that.${field.name})';
       });
-      indent.writeln('return ${checks.join(' && ')};');
+      if (checks.isEmpty) {
+        indent.writeln('return true;');
+      } else {
+        indent.writeln('return ${checks.join(' && ')};');
+      }
     });
     indent.newln();
 

packages/pigeon/lib/src/kotlin/kotlin_generator.dart

@@ -399,24 +399,35 @@ class KotlinGenerator extends StructuredGenerator<InternalKotlinOptions> {
 
   void _writeDataClassSignature(Indent indent, Class classDefinition, {bool private = false}) {
     final privateString = private ? 'private ' : '';
-    final classType = classDefinition.isSealed ? 'sealed' : 'data';
+    final String classType;
+    if (classDefinition.isSealed) {
+      classType = 'sealed ';
+    } else if (classDefinition.fields.isEmpty) {
+      classType = '';
+    } else {
+      classType = 'data ';
+    }
     final inheritance = classDefinition.superClass != null
         ? ' : ${classDefinition.superClassName}()'
         : '';
-    indent.write('$privateString$classType class ${classDefinition.name} ');
+    indent.write('$privateString${classType}class ${classDefinition.name} ');
     if (classDefinition.isSealed) {
       return;
     }
-    indent.addScoped('(', ')$inheritance', () {
-      for (final NamedType element in getFieldsInSerializationOrder(classDefinition)) {
-        _writeClassField(indent, element);
-        if (getFieldsInSerializationOrder(classDefinition).last != element) {
-          indent.addln(',');
-        } else {
-          indent.newln();
+    if (classDefinition.fields.isEmpty) {
+      indent.add(inheritance);
+    } else {
+      indent.addScoped('(', ')$inheritance', () {
+        for (final NamedType element in getFieldsInSerializationOrder(classDefinition)) {
+          _writeClassField(indent, element);
+          if (getFieldsInSerializationOrder(classDefinition).last != element) {
+            indent.addln(',');
+          } else {
+            indent.newln();
+          }
         }
-      }
-    });
+      });
+    }
   }
 
   @override

packages/pigeon/lib/src/objc/objc_generator.dart

@@ -519,7 +519,9 @@ class ObjcSourceGenerator extends StructuredGenerator<InternalObjcOptions> {
     final String className = _className(generatorOptions.prefix, classDefinition.name);
 
     indent.writeln('@implementation $className');
-    _writeObjcSourceClassInitializer(generatorOptions, root, indent, classDefinition, className);
+    if (classDefinition.fields.isNotEmpty) {
+      _writeObjcSourceClassInitializer(generatorOptions, root, indent, classDefinition, className);
+    }
     writeClassDecode(
       generatorOptions,
       root,
@@ -1900,10 +1902,8 @@ void _writeDataClassDeclaration(
   addDocumentationComments(indent, classDefinition.documentationComments, _docCommentSpec);
 
   indent.writeln('@interface ${_className(prefix, classDefinition.name)} : NSObject');
-  if (getFieldsInSerializationOrder(classDefinition).isNotEmpty) {
-    if (getFieldsInSerializationOrder(
-      classDefinition,
-    ).map((NamedType e) => !e.type.isNullable).any((bool e) => e)) {
+  if (classDefinition.fields.isNotEmpty) {
+    if (classDefinition.fields.any((NamedType e) => !e.type.isNullable)) {
       indent.writeln(
         '$_docCommentPrefix `init` unavailable to enforce nonnull fields, see the `make` class method.',
       );

packages/pigeon/pigeons/core_tests.dart

@@ -265,6 +265,7 @@ class AllClassesWrapper {
     this.classMap,
     this.nullableClassList,
     this.nullableClassMap,
+    this.anEmptyClass,
   );
   AllNullableTypes allNullableTypes;
   AllNullableTypesWithoutRecursion? allNullableTypesWithoutRecursion;
@@ -273,6 +274,7 @@ class AllClassesWrapper {
   List<AllNullableTypesWithoutRecursion?>? nullableClassList;
   Map<int?, AllTypes?> classMap;
   Map<int?, AllNullableTypesWithoutRecursion?>? nullableClassMap;
+  AnEmptyClass? anEmptyClass;
 }
 
 /// The core interface that each host language plugin must implement in
@@ -1465,3 +1467,5 @@ class TestMessage {
   // ignore: always_specify_types, strict_raw_type
   List? testList;
 }
+
+class AnEmptyClass {}

packages/pigeon/pigeons/event_channel_tests.dart

@@ -129,6 +129,8 @@ class ClassEvent extends PlatformEvent {
   final EventAllNullableTypes value;
 }
 
+class EmptyEvent extends PlatformEvent {}
+
 @EventChannelApi()
 abstract class EventChannelMethods {
   int streamInts();

packages/pigeon/platform_tests/alternate_language_test_plugin/android/src/main/java/com/example/alternate_language_test_plugin/CoreTests.java

@@ -26,6 +26,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 /** Generated class from Pigeon. */
 @SuppressWarnings({"unused", "unchecked", "CodeBlock2Expr", "RedundantSuppression", "serial"})
@@ -3005,6 +3006,16 @@ public void setNullableClassMap(
       this.nullableClassMap = setterArg;
     }
 
+    private @Nullable AnEmptyClass anEmptyClass;
+
+    public @Nullable AnEmptyClass getAnEmptyClass() {
+      return anEmptyClass;
+    }
+
+    public void setAnEmptyClass(@Nullable AnEmptyClass setterArg) {
+      this.anEmptyClass = setterArg;
+    }
+
     /** Constructor is non-public to enforce null safety; use Builder. */
     AllClassesWrapper() {}
 
@@ -3024,7 +3035,8 @@ && pigeonDeepEquals(allTypes, that.allTypes)
           && pigeonDeepEquals(classList, that.classList)
           && pigeonDeepEquals(nullableClassList, that.nullableClassList)
           && pigeonDeepEquals(classMap, that.classMap)
-          && pigeonDeepEquals(nullableClassMap, that.nullableClassMap);
+          && pigeonDeepEquals(nullableClassMap, that.nullableClassMap)
+          && pigeonDeepEquals(anEmptyClass, that.anEmptyClass);
     }
 
     @Override
@@ -3038,7 +3050,8 @@ public int hashCode() {
             classList,
             nullableClassList,
             classMap,
-            nullableClassMap
+            nullableClassMap,
+            anEmptyClass
           };
       return pigeonDeepHashCode(fields);
     }
@@ -3066,6 +3079,9 @@ public String toString() {
           + ", "
           + "nullableClassMap="
           + nullableClassMap
+          + ", "
+          + "anEmptyClass="
+          + anEmptyClass
           + "}";
     }
 
@@ -3130,6 +3146,14 @@ public static final class Builder {
         return this;
       }
 
+      private @Nullable AnEmptyClass anEmptyClass;
+
+      @CanIgnoreReturnValue
+      public @NonNull Builder setAnEmptyClass(@Nullable AnEmptyClass setterArg) {
+        this.anEmptyClass = setterArg;
+        return this;
+      }
+
       public @NonNull AllClassesWrapper build() {
         AllClassesWrapper pigeonReturn = new AllClassesWrapper();
         pigeonReturn.setAllNullableTypes(allNullableTypes);
@@ -3139,20 +3163,22 @@ public static final class Builder {
         pigeonReturn.setNullableClassList(nullableClassList);
         pigeonReturn.setClassMap(classMap);
         pigeonReturn.setNullableClassMap(nullableClassMap);
+        pigeonReturn.setAnEmptyClass(anEmptyClass);
         return pigeonReturn;
       }
     }
 
     @NonNull
     ArrayList<Object> toList() {
-      ArrayList<Object> toListResult = new ArrayList<>(7);
+      ArrayList<Object> toListResult = new ArrayList<>(8);
       toListResult.add(allNullableTypes);
       toListResult.add(allNullableTypesWithoutRecursion);
       toListResult.add(allTypes);
       toListResult.add(classList);
       toListResult.add(nullableClassList);
       toListResult.add(classMap);
       toListResult.add(nullableClassMap);
+      toListResult.add(anEmptyClass);
       return toListResult;
     }
 
@@ -3174,6 +3200,8 @@ ArrayList<Object> toList() {
       Object nullableClassMap = pigeonVar_list.get(6);
       pigeonResult.setNullableClassMap(
           (Map<Long, AllNullableTypesWithoutRecursion>) nullableClassMap);
+      Object anEmptyClass = pigeonVar_list.get(7);
+      pigeonResult.setAnEmptyClass((AnEmptyClass) anEmptyClass);
       return pigeonResult;
     }
   }
@@ -3249,6 +3277,50 @@ ArrayList<Object> toList() {
     }
   }
 
+  /** Generated class from Pigeon that represents data sent in messages. */
+  public static final class AnEmptyClass {
+    @Override
+    public boolean equals(Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      AnEmptyClass that = (AnEmptyClass) o;
+      return true;
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(getClass());
+    }
+
+    @Override
+    public String toString() {
+      return "AnEmptyClass{}";
+    }
+
+    public static final class Builder {
+
+      public @NonNull AnEmptyClass build() {
+        AnEmptyClass pigeonReturn = new AnEmptyClass();
+        return pigeonReturn;
+      }
+    }
+
+    @NonNull
+    ArrayList<Object> toList() {
+      ArrayList<Object> toListResult = new ArrayList<>(0);
+      return toListResult;
+    }
+
+    static @NonNull AnEmptyClass fromList(@NonNull ArrayList<Object> pigeonVar_list) {
+      AnEmptyClass pigeonResult = new AnEmptyClass();
+      return pigeonResult;
+    }
+  }
+
   private static class PigeonCodec extends StandardMessageCodec {
     public static final PigeonCodec INSTANCE = new PigeonCodec();
 
@@ -3279,6 +3351,8 @@ protected Object readValueOfType(byte type, @NonNull ByteBuffer buffer) {
           return AllClassesWrapper.fromList((ArrayList<Object>) readValue(buffer));
         case (byte) 136:
           return TestMessage.fromList((ArrayList<Object>) readValue(buffer));
+        case (byte) 137:
+          return AnEmptyClass.fromList((ArrayList<Object>) readValue(buffer));
         default:
           return super.readValueOfType(type, buffer);
       }
@@ -3310,6 +3384,9 @@ protected void writeValue(@NonNull ByteArrayOutputStream stream, Object value) {
       } else if (value instanceof TestMessage) {
         stream.write(136);
         writeValue(stream, ((TestMessage) value).toList());
+      } else if (value instanceof AnEmptyClass) {
+        stream.write(137);
+        writeValue(stream, ((AnEmptyClass) value).toList());
       } else {
         super.writeValue(stream, value);
       }