[swift2objc] Support Protocols

pkgs/swift2objc/lib/src/ast/_core/shared/referred_type.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import '../../ast_node.dart';
+import '../../declarations/compounds/protocol_declaration.dart';
 import '../interfaces/declaration.dart';
 import '../interfaces/nestable_declaration.dart';
 import '../interfaces/objc_annotatable.dart';
@@ -97,6 +98,33 @@ class GenericType extends AstNode implements ReferredType {
   void visit(Visitation visitation) => visitation.visitGenericType(this);
 }
 
+/// Associated Types are similar to Generics, but in the context of protocols. 
+/// They are declared with an `associatedType` keyword inside a protocol.
+/// 
+/// For more information: https://docs.swift.org/swift-book/documentation/the-swift-programming-language/generics/#Associated-Types
+class AssociatedType extends AstNode implements ReferredType {
+  final String id;
+
+  final String name;
+
+  @override
+  bool get isObjCRepresentable => false;
+
+  @override
+  String get swiftType => name;
+
+  List<DeclaredType<ProtocolDeclaration>> conformedProtocols;
+
+  @override
+  bool sameAs(ReferredType other) => other is AssociatedType && other.id == id;
+
+  AssociatedType(
+      {required this.id, required this.name, required this.conformedProtocols});
+
+  @override
+  String toString() => name;
+}
+
 /// An optional type, like Dart's nullable types. Eg `String?`.
 class OptionalType extends AstNode implements ReferredType {
   final ReferredType child;

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

@@ -0,0 +1,22 @@
+import '../../../_core/interfaces/declaration.dart';
+import '../../../_core/shared/referred_type.dart';
+import '../../../ast_node.dart';
+import '../protocol_declaration.dart';
+
+class AssociatedTypeDeclaration extends AstNode implements Declaration {
+  @override
+  String id;
+
+  @override
+  String name;
+
+  List<DeclaredType<ProtocolDeclaration>> conformedProtocols;
+
+  AssociatedTypeDeclaration(
+      {required this.id, required this.name, required this.conformedProtocols});
+}
+
+extension AsAssociatedType<T extends AssociatedTypeDeclaration> on T {
+  AssociatedType asType() => AssociatedType(
+      id: id, name: name, conformedProtocols: conformedProtocols);
+}

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

@@ -13,6 +13,7 @@ import '../../../_core/shared/parameter.dart';
 import '../../../ast_node.dart';
 
 /// Describes an initializer for a Swift compound entity (e.g, class, structs)
+/// TODO(https://github.com/dart-lang/native/issues/2048): Convenience and Required Initializers
 class InitializerDeclaration extends AstNode
     implements
         Declaration,

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

@@ -11,6 +11,7 @@ import '../../../ast_node.dart';
 
 /// Describes a method declaration for a Swift compound entity
 /// (e.g, class, structs)
+/// TODO(https://github.com/dart-lang/native/issues/2049): Add support for private(set) functions
 class MethodDeclaration extends AstNode
     implements FunctionDeclaration, ObjCAnnotatable, Overridable {
   @override
@@ -45,13 +46,16 @@ class MethodDeclaration extends AstNode
 
   bool isStatic;
 
+  bool public;
+
   bool mutating;
 
   String get fullName => [
         name,
         for (final p in params) p.name,
       ].join(':');
 
+
   MethodDeclaration(
       {required this.id,
       required this.name,
@@ -64,6 +68,7 @@ class MethodDeclaration extends AstNode
       this.isOverriding = false,
       this.throws = false,
       this.async = false,
+      this.public = false,
       this.mutating = false})
       : assert(!isStatic || !isOverriding);
 

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

@@ -4,14 +4,16 @@
 
 import '../../_core/interfaces/compound_declaration.dart';
 import '../../_core/interfaces/nestable_declaration.dart';
+import '../../_core/interfaces/objc_annotatable.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';
 
 /// Describes the declaration of a Swift protocol.
-class ProtocolDeclaration extends AstNode implements CompoundDeclaration {
+class ProtocolDeclaration extends AstNode
+    implements CompoundDeclaration, ObjCAnnotatable {
   @override
   String id;
 
@@ -24,11 +26,21 @@ class ProtocolDeclaration extends AstNode implements CompoundDeclaration {
   @override
   covariant List<MethodDeclaration> methods;
 
+  /// Only present if indicated with `@objc`
+  List<PropertyDeclaration> optionalProperties;
+
+  /// Only present if indicated with `@objc`
+  List<MethodDeclaration> optionalMethods;
+
+  /// Associated types used with this declaration. They are similar to generic 
+  /// types, but only designated for protocol declarations.
+  List<AssociatedType> associatedTypes;
+
   @override
   List<DeclaredType<ProtocolDeclaration>> conformedProtocols;
 
   @override
-  List<GenericType> typeParams;
+  bool hasObjCAnnotation;
 
   @override
   List<InitializerDeclaration> initializers;
@@ -46,10 +58,12 @@ class ProtocolDeclaration extends AstNode implements CompoundDeclaration {
     required this.methods,
     required this.initializers,
     required this.conformedProtocols,
-    required this.typeParams,
+    this.hasObjCAnnotation = false,
     this.nestingParent,
-    this.nestedDeclarations = const [],
-  });
+  })  : associatedTypes = [],
+        nestedDeclarations = [],
+        optionalMethods = [],
+        optionalProperties = [];
 
   @override
   void visit(Visitation visitation) =>
@@ -61,9 +75,13 @@ class ProtocolDeclaration extends AstNode implements CompoundDeclaration {
     visitor.visitAll(properties);
     visitor.visitAll(methods);
     visitor.visitAll(conformedProtocols);
-    visitor.visitAll(typeParams);
     visitor.visitAll(initializers);
     visitor.visit(nestingParent);
     visitor.visitAll(nestedDeclarations);
   }
+
+  @override
+  List<GenericType> get typeParams =>
+      throw Exception('Protocols do not have type params: '
+          'Did you mean to use `associatedTypes` instead?');
 }

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

@@ -1,6 +1,8 @@
 import '../ast/_core/interfaces/declaration.dart';
 import '../ast/declarations/compounds/class_declaration.dart';
+import '../ast/declarations/compounds/protocol_declaration.dart';
 import 'generators/class_generator.dart';
+import 'generators/protocol_generator.dart';
 
 String generate(
   List<Declaration> declarations, {
@@ -19,6 +21,7 @@ String generate(
 List<String> generateDeclaration(Declaration declaration) {
   return switch (declaration) {
     ClassDeclaration() => generateClass(declaration),
+    ProtocolDeclaration() => generateProtocol(declaration),
     _ => throw UnimplementedError(
         "$declaration generation isn't implemented yet",
       ),

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

@@ -134,6 +134,7 @@ List<String> _generateClassProperties(ClassDeclaration declaration) => [
         ..._generateClassProperty(property),
     ];
 
+// TODO(https://github.com/dart-lang/native/pull/2056): Generate Class properties for constants (i.e let)
 List<String> _generateClassProperty(PropertyDeclaration property) {
   final header = StringBuffer();
 

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

@@ -0,0 +1,123 @@
+import '../../ast/declarations/built_in/built_in_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';
+import '../../ast/declarations/compounds/protocol_declaration.dart';
+import '../_core/utils.dart';
+
+List<String> generateProtocol(ProtocolDeclaration declaration) {
+  return [
+    '${_generateProtocolHeader(declaration)} {',
+    ...<String>[
+      ..._generateProtocolProperties(declaration),
+      ..._generateInitializers(declaration),
+      ..._generateProtocolMethods(declaration)
+    ].nonNulls.indent(),
+    '}\n',
+  ];
+}
+
+String _generateProtocolHeader(ProtocolDeclaration declaration) {
+  final header = StringBuffer();
+
+  if (declaration.hasObjCAnnotation) {
+    header.write('@objc ');
+  }
+
+  header.write('public protocol ${declaration.name}');
+
+  final superClassAndProtocols = [
+    ...declaration.conformedProtocols
+        .map((protocol) => protocol.declaration.name),
+  ].nonNulls;
+
+  if (superClassAndProtocols.isNotEmpty) {
+    header.write(': ${superClassAndProtocols.join(", ")}');
+  }
+
+  return header.toString();
+}
+
+List<String> _generateProtocolMethods(ProtocolDeclaration declaration) => [
+      for (final method in declaration.methods)
+        ..._generateProtocolMethod(method)
+    ];
+
+List<String> _generateProtocolMethod(MethodDeclaration method) {
+  final header = StringBuffer();
+
+  if (method.hasObjCAnnotation) {
+    header.write('@objc ');
+  }
+
+  if (method.isStatic) {
+    header.write('static ');
+  }
+
+  header.write(
+    'func ${method.name}(${generateParameters(method.params)}) ',
+  );
+
+  header.write(generateAnnotations(method));
+
+  if (!method.returnType.sameAs(voidType)) {
+    header.write('-> ${method.returnType.swiftType} ');
+  }
+
+  return ['$header'];
+}
+
+List<String> _generateProtocolProperties(ProtocolDeclaration declaration) => [
+      for (final property in declaration.properties)
+        ..._generateProtocolProperty(property),
+    ];
+
+List<String> _generateProtocolProperty(PropertyDeclaration property) {
+  final header = StringBuffer();
+
+  if (property.hasObjCAnnotation) {
+    header.write('@objc ');
+  }
+
+  if (property.isStatic) {
+    header.write('static ');
+  }
+
+  header.write(property.isConstant ? 'let' : 'var');
+  header.write(' ${property.name}: ${property.type.swiftType}');
+  header.write(' { ${[
+    if (property.getter != null) 'get',
+    if (property.setter != null) 'set'
+  ].join(' ')} }');
+
+  return [
+    header.toString(),
+  ];
+}
+
+List<String> _generateInitializers(ProtocolDeclaration declaration) {
+  final initializers = [
+    ...declaration.initializers,
+  ].nonNulls;
+  return [for (final init in initializers) ..._generateInitializer(init)];
+}
+
+List<String> _generateInitializer(InitializerDeclaration initializer) {
+  final header = StringBuffer();
+
+  if (initializer.hasObjCAnnotation) {
+    header.write('@objc ');
+  }
+
+  header.write('init');
+
+  if (initializer.isFailable) {
+    header.write('?');
+  }
+
+  header.write('(${generateParameters(initializer.params)})');
+
+  return [
+    '$header ${generateAnnotations(initializer)}',
+  ];
+}

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

@@ -35,6 +35,10 @@ class ParsedRelation {
 }
 
 enum ParsedRelationKind {
+  requirementOf,
+  defaultImplementationOf,
+  optionalRequirementOf,
+  conformsTo,
   memberOf;
 
   static final _supportedRelationKindsMap = {