[swift2objc] Support Swift extension declarations

pkgs/swift2objc/lib/src/ast/declarations/compounds/extension_declaration.dart

@@ -0,0 +1,60 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../../../config.dart';
+import '../../_core/interfaces/availability.dart';
+import '../../_core/interfaces/declaration.dart';
+import '../../_core/shared/referred_type.dart';
+import '../../ast_node.dart';
+import 'members/initializer_declaration.dart';
+import 'members/method_declaration.dart';
+import 'members/property_declaration.dart';
+
+class ExtensionDeclaration extends AstNode implements Declaration {
+  @override
+  String id;
+
+  @override
+  String name;
+
+  @override
+  InputConfig? source;
+
+  @override
+  List<AvailabilityInfo> availability;
+
+  @override
+  final int? lineNumber;
+
+  DeclaredType<Declaration> extendedType;
+
+  List<PropertyDeclaration> properties;
+  List<MethodDeclaration> methods;
+  List<InitializerDeclaration> initializers;
+
+  ExtensionDeclaration({
+    required this.id,
+    required this.name,
+    required this.source,
+    required this.availability,
+    required this.extendedType,
+    this.lineNumber,
+    this.properties = const [],
+    this.methods = const [],
+    this.initializers = const [],
+  });
+
+  @override
+  void visit(Visitation visitation) =>
+      visitation.visitExtensionDeclaration(this);
+
+  @override
+  void visitChildren(Visitor visitor) {
+    super.visitChildren(visitor);
+    visitor.visit(extendedType);
+    visitor.visitAll(properties);
+    visitor.visitAll(methods);
+    visitor.visitAll(initializers);
+  }
+}

pkgs/swift2objc/lib/src/ast/declarations/compounds/members/initializer_declaration.dart

@@ -52,6 +52,7 @@ class InitializerDeclaration extends AstNode
   bool async;
 
   bool isFailable;
+  bool isExtensionMember;
 
   @override
   List<Parameter> params;
@@ -73,6 +74,7 @@ class InitializerDeclaration extends AstNode
     required this.throws,
     required this.async,
     required this.isFailable,
+    this.isExtensionMember = false,
   });
 
   @override

pkgs/swift2objc/lib/src/ast/declarations/compounds/members/method_declaration.dart

@@ -58,6 +58,7 @@ class MethodDeclaration extends AstNode
 
   bool mutating;
   bool isOperator = false;
+  bool isExtensionMember;
 
   String get fullName => [name, for (final p in params) p.name].join(':');
 
@@ -78,6 +79,7 @@ class MethodDeclaration extends AstNode
     this.async = false,
     this.mutating = false,
     this.isOperator = false,
+    this.isExtensionMember = false,
   }) : assert(!isStatic || !isOverriding);
 
   @override

pkgs/swift2objc/lib/src/ast/declarations/compounds/members/property_declaration.dart

@@ -60,6 +60,7 @@ class PropertyDeclaration extends AstNode
   bool lazy;
 
   bool isStatic;
+  bool isExtensionMember;
 
   PropertyDeclaration({
     required this.id,
@@ -75,6 +76,7 @@ class PropertyDeclaration extends AstNode
     this.setter,
     this.hasExplicitGetter = false,
     this.isStatic = false,
+    this.isExtensionMember = false,
     this.throws = false,
     this.async = false,
     this.unowned = false,

pkgs/swift2objc/lib/src/ast/visitor.dart

@@ -12,6 +12,7 @@ import 'ast_node.dart';
 import 'declarations/built_in/built_in_declaration.dart';
 import 'declarations/compounds/class_declaration.dart';
 import 'declarations/compounds/enum_declaration.dart';
+import 'declarations/compounds/extension_declaration.dart';
 import 'declarations/compounds/members/initializer_declaration.dart';
 import 'declarations/compounds/members/method_declaration.dart';
 import 'declarations/compounds/members/property_declaration.dart';
@@ -109,6 +110,8 @@ abstract class Visitation {
   void visitTypealiasDeclaration(TypealiasDeclaration node) =>
       visitDeclaration(node);
   void visitTupleType(TupleType node) => visitReferredType(node);
+  void visitExtensionDeclaration(ExtensionDeclaration node) =>
+      visitDeclaration(node);
 
   /// Default behavior for all visit methods.
   void visitAstNode(AstNode node) => node.visitChildren(visitor);

pkgs/swift2objc/lib/src/generator/generator.dart

@@ -4,7 +4,9 @@
 
 import '../ast/_core/interfaces/declaration.dart';
 import '../ast/declarations/compounds/class_declaration.dart';
+import '../ast/declarations/compounds/extension_declaration.dart';
 import 'generators/class_generator.dart';
+import 'generators/extension_generator.dart';
 
 String generate(
   List<Declaration> declarations, {
@@ -22,6 +24,7 @@ String generate(
 List<String> generateDeclaration(Declaration declaration) {
   return switch (declaration) {
     ClassDeclaration() => generateClass(declaration),
+    ExtensionDeclaration() => generateExtension(declaration),
     _ => throw UnimplementedError(
       "$declaration generation isn't implemented yet",
     ),

pkgs/swift2objc/lib/src/generator/generators/class_generator.dart

@@ -73,21 +73,23 @@ String? _generateClassWrappedInstance(ClassDeclaration declaration) {
 
 List<String> _generateInitializers(ClassDeclaration declaration) {
   return [
-    ..._generateInitializer(declaration.wrapperInitializer, isPublic: false),
+    ...generateInitializer(declaration.wrapperInitializer, isPublic: false),
     for (final init in declaration.initializers)
-      ..._generateInitializer(init, isPublic: true),
+      ...generateInitializer(init, isPublic: true),
   ];
 }
 
-List<String> _generateInitializer(
+List<String> generateInitializer(
   InitializerDeclaration? initializer, {
   required bool isPublic,
+  bool isConvenience = false,
 }) {
   if (initializer == null) return [];
   final header = [
     if (initializer.hasObjCAnnotation) '@objc ',
     if (initializer.isOverriding) 'override ',
     if (isPublic) 'public ',
+    if (isConvenience) 'convenience ',
     'init',
     if (initializer.isFailable) '?',
     '(${generateParameters(initializer.params)}) ',
@@ -103,10 +105,10 @@ List<String> _generateInitializer(
 }
 
 List<String> _generateClassMethods(ClassDeclaration declaration) => [
-  for (final method in declaration.methods) ..._generateClassMethod(method),
+  for (final method in declaration.methods) ...generateClassMethod(method),
 ];
 
-List<String> _generateClassMethod(MethodDeclaration method) {
+List<String> generateClassMethod(MethodDeclaration method) {
   final header = StringBuffer();
 
   if (method.hasObjCAnnotation) {
@@ -141,10 +143,10 @@ List<String> _generateClassMethod(MethodDeclaration method) {
 
 List<String> _generateClassProperties(ClassDeclaration declaration) => [
   for (final property in declaration.properties)
-    ..._generateClassProperty(property),
+    ...generateClassProperty(property),
 ];
 
-List<String> _generateClassProperty(PropertyDeclaration property) {
+List<String> generateClassProperty(PropertyDeclaration property) {
   final header = StringBuffer();
 
   if (property.hasObjCAnnotation) {

pkgs/swift2objc/lib/src/generator/generators/extension_generator.dart

@@ -0,0 +1,22 @@
+// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../../ast/declarations/compounds/extension_declaration.dart';
+import '../_core/utils.dart';
+import 'class_generator.dart';
+
+List<String> generateExtension(ExtensionDeclaration declaration) {
+  return [
+    ...generateAvailability(declaration),
+    '@objc extension ${declaration.extendedType.declaration.name} {',
+    ...[
+      for (final method in declaration.methods) ...generateClassMethod(method),
+      for (final property in declaration.properties)
+        ...generateClassProperty(property),
+      for (final init in declaration.initializers)
+        ...generateInitializer(init, isPublic: true, isConvenience: true),
+    ].indent(),
+    '}\n',
+  ];
+}

pkgs/swift2objc/lib/src/parser/_core/parsed_symbolgraph.dart

@@ -4,6 +4,7 @@
 
 import '../../ast/_core/interfaces/declaration.dart';
 import '../../ast/declarations/built_in/built_in_declaration.dart';
+import '../../ast/declarations/compounds/extension_declaration.dart';
 import '../../config.dart';
 import 'json.dart';
 
@@ -66,6 +67,7 @@ class ParsedSymbol {
   final InputConfig? source;
   final Json json;
   Declaration? declaration;
+  ExtensionDeclaration? extension;
 
   ParsedSymbol({required this.source, required this.json, this.declaration});
 }

pkgs/swift2objc/lib/src/parser/_core/utils.dart

@@ -9,6 +9,7 @@ import '../../ast/_core/interfaces/availability.dart';
 import '../../ast/_core/interfaces/declaration.dart';
 import '../../ast/_core/interfaces/nestable_declaration.dart';
 import '../../ast/_core/shared/referred_type.dart';
+import '../../ast/declarations/compounds/extension_declaration.dart';
 import '../../ast/declarations/globals/globals.dart';
 import '../../context.dart';
 import '../parsers/parse_type.dart';
@@ -34,7 +35,8 @@ extension TopLevelOnly<T extends Declaration> on List<T> {
       return declaration.nestingParent == null;
     }
     return declaration is GlobalVariableDeclaration ||
-        declaration is GlobalFunctionDeclaration;
+        declaration is GlobalFunctionDeclaration ||
+        declaration is ExtensionDeclaration;
   }).toList();
 }
 

pkgs/swift2objc/lib/src/parser/parsers/declaration_parsers/parse_compound_declaration.dart

@@ -7,6 +7,7 @@ import '../../../ast/_core/interfaces/compound_declaration.dart';
 import '../../../ast/_core/interfaces/declaration.dart';
 import '../../../ast/_core/interfaces/nestable_declaration.dart';
 import '../../../ast/declarations/compounds/class_declaration.dart';
+import '../../../ast/declarations/compounds/extension_declaration.dart';
 import '../../../ast/declarations/compounds/members/initializer_declaration.dart';
 import '../../../ast/declarations/compounds/members/method_declaration.dart';
 import '../../../ast/declarations/compounds/members/property_declaration.dart';
@@ -65,26 +66,81 @@ ParsedCompound<T> parseCompoundDeclaration<T extends CompoundDeclaration>(
       .dedupeBy((decl) => decl.id)
       .toList();
 
+  // Separate extension members from regular members
+  final extensionMethods = memberDeclarations
+      .whereType<MethodDeclaration>()
+      .where((m) => m.isExtensionMember)
+      .toList();
+  final extensionProperties = memberDeclarations
+      .whereType<PropertyDeclaration>()
+      .where((p) => p.isExtensionMember)
+      .toList();
+  final extensionInitializers = memberDeclarations
+      .whereType<InitializerDeclaration>()
+      .where((i) => i.isExtensionMember)
+      .toList();
+
+  final firstExtMember = extensionMethods.isNotEmpty
+      ? extensionMethods.first
+      : extensionProperties.isNotEmpty
+      ? extensionProperties.first
+      : extensionInitializers.isNotEmpty
+      ? extensionInitializers.first
+      : null;
+
+  if (firstExtMember != null) {
+    final isExternal =
+        symbolgraph.symbols[firstExtMember.id]?.source == builtInInputConfig;
+
+    if (isExternal) {
+      // TODO(https://github.com/dart-lang/native/issues/3228): Support
+      // extensions on external types.
+      context.logger.warning(
+        'Extension on external type ${compound.name} is not '
+        'supported yet.',
+      );
+    } else {
+      symbol.extension = ExtensionDeclaration(
+        id: compoundId.addIdSuffix('extension'),
+        name: compound.name,
+        source: compound.source,
+        availability: compound.availability,
+        extendedType: compound.asDeclaredType,
+        methods: extensionMethods,
+        properties: extensionProperties,
+        initializers: extensionInitializers,
+      );
+    }
+  }
+
+  // Only add non-extension members to the compound
+  final regularMembers = memberDeclarations.where((d) {
+    if (d is MethodDeclaration) return !d.isExtensionMember;
+    if (d is PropertyDeclaration) return !d.isExtensionMember;
+    if (d is InitializerDeclaration) return !d.isExtensionMember;
+    return true;
+  }).toList();
+
   compound.methods.addAll(
-    memberDeclarations.removeWhereType<MethodDeclaration>().dedupeBy(
+    regularMembers.removeWhereType<MethodDeclaration>().dedupeBy(
       (m) => m.fullName,
     ),
   );
   compound.properties.addAll(
-    memberDeclarations.removeWhereType<PropertyDeclaration>(),
+    regularMembers.removeWhereType<PropertyDeclaration>(),
   );
   compound.initializers.addAll(
-    memberDeclarations.removeWhereType<InitializerDeclaration>().dedupeBy(
+    regularMembers.removeWhereType<InitializerDeclaration>().dedupeBy(
       (m) => m.fullName,
     ),
   );
   compound.nestedDeclarations.addAll(
-    memberDeclarations.removeWhereType<InnerNestableDeclaration>(),
+    regularMembers.removeWhereType<InnerNestableDeclaration>(),
   );
 
   compound.nestedDeclarations.fillNestingParents(compound);
 
-  return (compound: compound, excessMembers: memberDeclarations);
+  return (compound: compound, excessMembers: regularMembers);
 }
 
 ClassDeclaration parseClassDeclaration(

pkgs/swift2objc/lib/src/parser/parsers/declaration_parsers/parse_function_declaration.dart

@@ -62,6 +62,7 @@ MethodDeclaration parseMethodDeclaration(
     async: info.async,
     mutating: info.mutating,
     isOperator: isOperator,
+    isExtensionMember: symbol.json['swiftExtension'].exists,
   );
 }
 

pkgs/swift2objc/lib/src/parser/parsers/declaration_parsers/parse_initializer_declaration.dart

@@ -38,6 +38,7 @@ InitializerDeclaration parseInitializerDeclaration(
     isFailable: parseIsFailableInit(id, declarationFragments),
     throws: info.throws,
     async: info.async,
+    isExtensionMember: symbol.json['swiftExtension'].exists,
   );
 }
 

pkgs/swift2objc/lib/src/parser/parsers/declaration_parsers/parse_variable_declaration.dart

@@ -36,6 +36,7 @@ PropertyDeclaration parsePropertyDeclaration(
     lazy: info.lazy,
     hasSetter: info.constant ? false : (info.getter ? info.setter : true),
     hasExplicitGetter: info.getter,
+    isExtensionMember: symbol.json['swiftExtension'].exists,
   );
 }
 

pkgs/swift2objc/lib/src/parser/parsers/parse_declarations.dart

@@ -37,10 +37,17 @@ List<Declaration> parseDeclarations(
     }
   }
 
+  // Collect ExtensionDeclarations that were created during compound parsing
+  // and stored on their symbols.
+  final extensions = symbolgraph.symbols.values
+      .map((s) => s.extension)
+      .nonNulls
+      .toList();
+
+  declarations.addAll(extensions);
   return declarations.topLevelOnly;
 }
 
-// TODO(https://github.com/dart-lang/native/issues/1815): Support for extensions
 Declaration parseDeclaration(
   Context context,
   ParsedSymbol parsedSymbol,