[swift2objc] Support optionals

pkgs/swift2objc/lib/src/ast/_core/interfaces/declaration.dart

@@ -10,6 +10,6 @@ abstract interface class Declaration {
   abstract final String name;
 }
 
-extension AstDeclaredType<T extends Declaration> on T {
+extension AsDeclaredType<T extends Declaration> on T {
   DeclaredType<T> get asDeclaredType => DeclaredType(id: id, declaration: this);
 }

pkgs/swift2objc/lib/src/ast/_core/interfaces/function_declaration.dart

@@ -11,5 +11,5 @@ import 'type_parameterizable.dart';
 /// Describes a function-like entity.
 abstract interface class FunctionDeclaration
     implements Declaration, Parameterizable, Executable, TypeParameterizable {
-  abstract final ReferredType? returnType;
+  abstract final ReferredType returnType;
 }

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

@@ -10,19 +10,19 @@ import '../interfaces/objc_annotatable.dart';
 /// entities (e.g a method return type).
 /// See `DeclaredType` and `GenericType` for concrete implementation.
 sealed class ReferredType {
-  final String id;
-  final String name;
   abstract final bool isObjCRepresentable;
 
-  const ReferredType(this.name, {required this.id});
+  abstract final String swiftType;
+
+  bool sameAs(ReferredType other);
+
+  const ReferredType();
 }
 
 /// Describes a reference of a declared type (user-defined or built-in).
 class DeclaredType<T extends Declaration> implements ReferredType {
-  @override
   final String id;
 
-  @override
   String get name {
     final decl = declaration;
     if (decl is CompoundDeclaration && decl.pathComponents.isNotEmpty) {
@@ -40,6 +40,12 @@ class DeclaredType<T extends Declaration> implements ReferredType {
       declaration is ObjCAnnotatable &&
       (declaration as ObjCAnnotatable).hasObjCAnnotation;
 
+  @override
+  String get swiftType => name;
+
+  @override
+  bool sameAs(ReferredType other) => other is DeclaredType && other.id == id;
+
   const DeclaredType({
     required this.id,
     required this.declaration,
@@ -53,17 +59,44 @@ class DeclaredType<T extends Declaration> implements ReferredType {
 /// Describes a reference of a generic type
 /// (e.g a method return type `T` within a generic class).
 class GenericType implements ReferredType {
-  @override
   final String id;
 
-  @override
   final String name;
 
   @override
   bool get isObjCRepresentable => false;
 
+  @override
+  String get swiftType => name;
+
+  @override
+  bool sameAs(ReferredType other) => other is GenericType && other.id == id;
+
   const GenericType({
     required this.id,
     required this.name,
   });
+
+  @override
+  String toString() => name;
+}
+
+/// An optional type, like Dart's nullable types. Eg `String?`.
+class OptionalType implements ReferredType {
+  final ReferredType child;
+
+  @override
+  bool get isObjCRepresentable => child.isObjCRepresentable;
+
+  @override
+  String get swiftType => '$child?';
+
+  @override
+  bool sameAs(ReferredType other) =>
+      other is OptionalType && child.sameAs(other.child);
+
+  OptionalType(this.child);
+
+  @override
+  String toString() => swiftType;
 }

pkgs/swift2objc/lib/src/ast/declarations/built_in/built_in_declaration.dart

@@ -28,3 +28,10 @@ enum BuiltInDeclaration implements Declaration, ObjCAnnotatable {
     required this.name,
   });
 }
+
+final objectType = BuiltInDeclaration.swiftNSObject.asDeclaredType;
+final stringType = BuiltInDeclaration.swiftString.asDeclaredType;
+final intType = BuiltInDeclaration.swiftInt.asDeclaredType;
+final doubleType = BuiltInDeclaration.swiftDouble.asDeclaredType;
+final boolType = BuiltInDeclaration.swiftBool.asDeclaredType;
+final voidType = BuiltInDeclaration.swiftVoid.asDeclaredType;

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

@@ -34,7 +34,7 @@ class MethodDeclaration
   List<String> statements;
 
   @override
-  ReferredType? returnType;
+  ReferredType returnType;
 
   bool isStatic;
 

pkgs/swift2objc/lib/src/ast/declarations/globals/globals.dart

@@ -34,7 +34,7 @@ class GlobalFunctionDeclaration implements FunctionDeclaration {
   List<GenericType> typeParams;
 
   @override
-  ReferredType? returnType;
+  ReferredType returnType;
 
   @override
   List<String> statements;

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

@@ -11,7 +11,7 @@ String generateParameters(List<Parameter> params) {
       labels = param.name;
     }
 
-    return '$labels: ${param.type.name}';
+    return '$labels: ${param.type.swiftType}';
   }).join(', ');
 }
 

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

@@ -1,4 +1,9 @@
+// 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/_core/shared/referred_type.dart';
+import '../../ast/declarations/built_in/built_in_declaration.dart';
 import '../../ast/declarations/compounds/class_declaration.dart';
 import '../_core/utils.dart';
 
@@ -47,7 +52,7 @@ String? _generateClassWrappedInstance(ClassDeclaration declaration) {
     "Wrapped instance can't have a generic type",
   );
 
-  return 'var ${property.name}: ${property.type.name}';
+  return 'var ${property.name}: ${property.type.swiftType}';
 }
 
 List<String> _generateInitializers(ClassDeclaration declaration) {
@@ -102,8 +107,8 @@ List<String> _generateClassMethods(ClassDeclaration declaration) {
       'public func ${method.name}(${generateParameters(method.params)})',
     );
 
-    if (method.returnType != null) {
-      header.write(' -> ${method.returnType!.name}');
+    if (!method.returnType.sameAs(voidType)) {
+      header.write(' -> ${method.returnType.swiftType}');
     }
 
     return [
@@ -127,7 +132,7 @@ List<String> _generateClassProperties(ClassDeclaration declaration) {
         header.write('static ');
       }
 
-      header.write('public var ${property.name}: ${property.type.name} {');
+      header.write('public var ${property.name}: ${property.type.swiftType} {');
 
       final getterLines = [
         'get {',

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

@@ -0,0 +1,63 @@
+// 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 'json.dart';
+import 'utils.dart';
+
+/// A slicable list of json tokens from the symbolgraph.
+///
+/// These token lists appear in the symbolgraph json under keys like
+/// 'declarationFragments'. They represent things like argument lists, or
+/// variable declarations.
+///
+/// We have to do a little bit of preprocessing on the raw json list before we
+/// can pass it to parseType, because certain tokens get concatenated by the
+/// swift compiler. This class performs that preprocessing, as well as providing
+/// convenience methods for parsing, like slicing.
+class TokenList {
+  final List<Json> _list;
+  final int _start;
+  final int _end;
+
+  TokenList._(this._list, this._start, this._end)
+      : assert(0 <= _start && _start <= _end && _end <= _list.length);
+
+  factory TokenList(Json fragments) {
+    const splits = {
+      '?(': ['?', '('],
+      '?)': ['?', ')'],
+      '?, ': ['?', ', '],
+    };
+
+    final list = <Json>[];
+    for (final token in fragments) {
+      final split = splits[getSpellingForKind(token, 'text')];
+      if (split != null) {
+        for (final sub in split) {
+          list.add(Json({'kind': 'text', 'spelling': sub}));
+        }
+      } else {
+        list.add(token);
+      }
+    }
+    return TokenList._(list, 0, list.length);
+  }
+
+  int get length => _end - _start;
+  bool get isEmpty => length == 0;
+  Json operator [](int index) => _list[index + _start];
+
+  int indexWhere(bool Function(Json element) test) {
+    for (var i = _start; i < _end; ++i) {
+      if (test(_list[i])) return i - _start;
+    }
+    return -1;
+  }
+
+  TokenList slice(int startIndex, [int? endIndex]) => TokenList._(
+      _list, startIndex + _start, endIndex != null ? endIndex + _start : _end);
+
+  @override
+  String toString() => _list.getRange(_start, _end).toString();
+}

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

@@ -10,9 +10,10 @@ import '../../ast/_core/interfaces/declaration.dart';
 import '../../ast/_core/interfaces/enum_declaration.dart';
 import '../../ast/_core/shared/referred_type.dart';
 import '../../ast/declarations/globals/globals.dart';
-import '../parsers/parse_declarations.dart';
+import '../parsers/parse_type.dart';
 import 'json.dart';
 import 'parsed_symbolgraph.dart';
+import 'token_list.dart';
 
 typedef ParsedSymbolsMap = Map<String, ParsedSymbol>;
 typedef ParsedRelationsMap = Map<String, List<ParsedRelation>>;
@@ -22,6 +23,7 @@ Json readJsonFile(String jsonFilePath) {
   return Json(jsonDecode(jsonStr));
 }
 
+// Valid ID characters seen in symbolgraphs: 0-9A-Za-z_():@
 const idDelim = '-';
 
 extension AddIdSuffix on String {
@@ -38,10 +40,16 @@ extension TopLevelOnly<T extends Declaration> on List<T> {
       ).toList();
 }
 
-/// Matches fragments, which look like {"kind": "foo", "spelling": "bar"}.
+/// If `fragment['kind'] == kind`, returns `fragment['spelling']`. Otherwise
+/// returns null.
+String? getSpellingForKind(Json fragment, String kind) =>
+    fragment['kind'].get<String?>() == kind
+        ? fragment['spelling'].get<String?>()
+        : null;
+
+/// Matches fragments, which look like `{"kind": "foo", "spelling": "bar"}`.
 bool matchFragment(Json fragment, String kind, String spelling) =>
-    fragment['kind'].get<String?>() == kind &&
-    fragment['spelling'].get<String?>() == spelling;
+    getSpellingForKind(fragment, kind) == spelling;
 
 String parseSymbolId(Json symbolJson) {
   final idJson = symbolJson['identifier']['precise'];
@@ -70,20 +78,6 @@ bool parseIsOverriding(Json symbolJson) {
       .any((json) => matchFragment(json, 'keyword', 'override'));
 }
 
-ReferredType parseTypeFromId(String typeId, ParsedSymbolgraph symbolgraph) {
-  final paramTypeSymbol = symbolgraph.symbols[typeId];
-
-  if (paramTypeSymbol == null) {
-    throw Exception(
-      'Type with id "$typeId" does not exist among parsed symbols.',
-    );
-  }
-
-  final paramTypeDeclaration = parseDeclaration(paramTypeSymbol, symbolgraph);
-
-  return paramTypeDeclaration.asDeclaredType;
-}
-
 final class ObsoleteException implements Exception {
   final String symbol;
   ObsoleteException(this.symbol);
@@ -107,3 +101,16 @@ extension Deduper<T> on Iterable<T> {
   Iterable<T> dedupeBy<K>(K Function(T) id) =>
       <K, T>{for (final t in this) id(t): t}.values;
 }
+
+ReferredType parseTypeAfterSeparator(
+  TokenList fragments,
+  ParsedSymbolgraph symbolgraph,
+) {
+  // fragments = [..., ': ', type tokens...]
+  final separatorIndex =
+      fragments.indexWhere((token) => matchFragment(token, 'text', ': '));
+  final (type, suffix) =
+      parseType(symbolgraph, fragments.slice(separatorIndex + 1));
+  assert(suffix.isEmpty, '$suffix');
+  return type;
+}

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

@@ -2,15 +2,15 @@
 // 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/_core/interfaces/declaration.dart';
 import '../../../ast/_core/shared/parameter.dart';
 import '../../../ast/_core/shared/referred_type.dart';
 import '../../../ast/declarations/compounds/members/method_declaration.dart';
 import '../../../ast/declarations/globals/globals.dart';
 import '../../_core/json.dart';
 import '../../_core/parsed_symbolgraph.dart';
+import '../../_core/token_list.dart';
 import '../../_core/utils.dart';
-import '../parse_declarations.dart';
+import '../parse_type.dart';
 
 GlobalFunctionDeclaration parseGlobalFunctionDeclaration(
   Json globalFunctionSymbolJson,
@@ -39,34 +39,15 @@ MethodDeclaration parseMethodDeclaration(
   );
 }
 
-ReferredType? _parseFunctionReturnType(
+ReferredType _parseFunctionReturnType(
   Json methodSymbolJson,
   ParsedSymbolgraph symbolgraph,
 ) {
-  final returnJson = methodSymbolJson['functionSignature']['returns'][0];
-
-  // This means there's no return type
-  if (returnJson['spelling'].get<String>() == '()') {
-    return null;
-  }
-
-  final returnTypeId = returnJson['preciseIdentifier'].get<String>();
-
-  final returnTypeSymbol = symbolgraph.symbols[returnTypeId];
-
-  if (returnTypeSymbol == null) {
-    throw Exception(
-      'The method at path "${methodSymbolJson.path}" has a return type that '
-      'does not exist among parsed symbols.',
-    );
-  }
-
-  final returnTypeDeclaration = parseDeclaration(
-    returnTypeSymbol,
-    symbolgraph,
-  );
-
-  return returnTypeDeclaration.asDeclaredType;
+  final returnJson =
+      TokenList(methodSymbolJson['functionSignature']['returns']);
+  final (returnType, unparsed) = parseType(symbolgraph, returnJson);
+  assert(unparsed.isEmpty);
+  return returnType;
 }
 
 List<Parameter> _parseFunctionParams(
@@ -91,12 +72,6 @@ List<Parameter> _parseFunctionParams(
 ReferredType _parseParamType(
   Json paramSymbolJson,
   ParsedSymbolgraph symbolgraph,
-) {
-  final fragments = paramSymbolJson['declarationFragments'];
-
-  final paramTypeId = fragments
-      .firstJsonWhereKey('kind', 'typeIdentifier')['preciseIdentifier']
-      .get<String>();
-
-  return parseTypeFromId(paramTypeId, symbolgraph);
-}
+) =>
+    parseTypeAfterSeparator(
+        TokenList(paramSymbolJson['declarationFragments']), symbolgraph);