[pigeon] allow empty class

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 27.2.0
+
+* Adds support for empty data classes.
+
 ## 27.1.2
 
 * Reports a clear error when an input file uses an enhanced enum (one with a

packages/pigeon/lib/src/ast.dart

@@ -803,6 +803,8 @@ class Root extends Node {
     return Root(apis: <Api>[], classes: <Class>[], enums: <Enum>[]);
   }
 
+  // TODO(tarrinneal): Ensure classes are sorted in topological dependency order; see
+  // https://github.com/flutter/flutter/issues/128330.
   /// All the classes contained in the AST.
   List<Class> classes;
 

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);
+      if (classDefinition.fields.isNotEmpty) {
+        for (final NamedType field in getFieldsInSerializationOrder(classDefinition)) {
+          addDocumentationComments(indent, field.documentationComments, docCommentSpec);
 
-        final String datatype = addGenericTypes(field.type);
-        indent.writeln('$datatype ${field.name};');
-        indent.newln();
+          final String datatype = addGenericTypes(field.type);
+          indent.writeln('$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 = '27.1.2';
+const String pigeonVersion = '27.2.0';
 
 /// Default plugin package name.
 const String defaultPluginPackageName = 'dev.flutter.pigeon';

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

@@ -345,11 +345,15 @@ class JavaGenerator extends StructuredGenerator<InternalJavaOptions> {
     indent.writeScoped('public boolean equals(Object o) {', '}', () {
       indent.writeln('if (this == o) { return true; }');
       indent.writeln('if (o == null || getClass() != o.getClass()) { return false; }');
-      indent.writeln('${classDefinition.name} that = (${classDefinition.name}) o;');
-      final Iterable<String> checks = classDefinition.fields.map((NamedType field) {
-        return 'pigeonDeepEquals(${field.name}, that.${field.name})';
-      });
-      indent.writeln('return ${checks.join(' && ')};');
+      if (classDefinition.fields.isEmpty) {
+        indent.writeln('return true;');
+      } else {
+        indent.writeln('${classDefinition.name} that = (${classDefinition.name}) o;');
+        final Iterable<String> checks = classDefinition.fields.map((NamedType field) {
+          return 'pigeonDeepEquals(${field.name}, that.${field.name})';
+        });
+        indent.writeln('return ${checks.join(' && ')};');
+      }
     });
     indent.newln();
 

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

@@ -348,11 +348,11 @@ class KotlinGenerator extends StructuredGenerator<InternalKotlinOptions> {
         indent.writeln('return true');
       });
 
-      indent.writeln('val other = other as ${classDefinition.name}');
       final Iterable<NamedType> fields = getFieldsInSerializationOrder(classDefinition);
       if (fields.isEmpty) {
         indent.writeln('return true');
       } else {
+        indent.writeln('val other = other as ${classDefinition.name}');
         final String utils = _getUtilsClassName(generatorOptions);
         final String comparisons = fields
             .map((NamedType field) => '$utils.deepEquals(this.${field.name}, other.${field.name})')
@@ -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 $className');
-    _writeObjcSourceClassInitializer(generatorOptions, root, indent, classDefinition, className);
+    if (classDefinition.fields.isNotEmpty) {
+      _writeObjcSourceClassInitializer(generatorOptions, root, indent, classDefinition, className);
+    }
     writeClassDecode(
       generatorOptions,
       root,
@@ -554,21 +556,21 @@ class ObjcSourceGenerator extends StructuredGenerator<InternalObjcOptions> {
       indent.writeScoped('if (![object isKindOfClass:[self class]]) {', '}', () {
         indent.writeln('return NO;');
       });
-      indent.writeln('$className *other = ($className *)object;');
-      final Iterable<String> checks = classDefinition.fields.map((NamedType field) {
-        final String name = field.name;
-        if (_usesPrimitive(field.type)) {
-          if (field.type.baseName == 'double') {
-            return '(self.$name == other.$name || (isnan(self.$name) && isnan(other.$name)))';
-          }
-          return 'self.$name == other.$name';
-        } else {
-          return 'FLTPigeonDeepEquals(self.$name, other.$name)';
-        }
-      });
-      if (checks.isEmpty) {
+      if (classDefinition.fields.isEmpty) {
         indent.writeln('return YES;');
       } else {
+        indent.writeln('$className *other = ($className *)object;');
+        final Iterable<String> checks = classDefinition.fields.map((NamedType field) {
+          final String name = field.name;
+          if (_usesPrimitive(field.type)) {
+            if (field.type.baseName == 'double') {
+              return '(self.$name == other.$name || (isnan(self.$name) && isnan(other.$name)))';
+            }
+            return 'self.$name == other.$name';
+          } else {
+            return 'FLTPigeonDeepEquals(self.$name, other.$name)';
+          }
+        });
         indent.writeln('return ${checks.join(' && ')};');
       }
     });
@@ -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

@@ -251,6 +251,9 @@ class AllNullableTypesWithoutRecursion {
   Map<int?, Map<Object?, Object?>?>? mapMap;
 }
 
+/// A data class without fields for testing empty classes.
+class AnEmptyClass {}
+
 /// A class for testing nested class handling.
 ///
 /// This is needed to test nested nullable and non-nullable classes,
@@ -265,6 +268,7 @@ class AllClassesWrapper {
     this.classMap,
     this.nullableClassList,
     this.nullableClassMap,
+    this.anEmptyClass,
   );
   AllNullableTypes allNullableTypes;
   AllNullableTypesWithoutRecursion? allNullableTypesWithoutRecursion;
@@ -273,6 +277,7 @@ 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

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();