[swift2objc] Support failable initializers (#1734)

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

@@ -29,6 +29,8 @@ class InitializerDeclaration
   @override
   bool isOverriding;
 
+  bool isFailable;
+
   @override
   List<Parameter> params;
 
@@ -41,5 +43,6 @@ class InitializerDeclaration
     this.statements = const [],
     required this.hasObjCAnnotation,
     required this.isOverriding,
+    required this.isFailable,
   });
 }

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

@@ -68,7 +68,13 @@ List<String> _generateInitializers(ClassDeclaration declaration) {
         header.write('override ');
       }
 
-      header.write('init(${generateParameters(initializer.params)})');
+      header.write('init');
+
+      if (initializer.isFailable) {
+        header.write('?');
+      }
+
+      header.write('(${generateParameters(initializer.params)})');
 
       return ['$header {', initializer.statements.join('\n').indent(), '}']
           .join('\n');

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

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:collection';
+import 'dart:convert';
 
 /// This is a helper class that helps with parsing Json values. It supports
 /// accessing the json content using the subscript syntax similar to `List`
@@ -101,6 +102,9 @@ class Json extends IterableBase<Json> {
       ),
     );
   }
+
+  @override
+  String toString() => jsonEncode(_json);
 }
 
 class _JsonIterator implements Iterator<Json> {

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

@@ -38,6 +38,11 @@ extension TopLevelOnly<T extends Declaration> on List<T> {
       ).toList();
 }
 
+/// 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;
+
 String parseSymbolId(Json symbolJson) {
   final idJson = symbolJson['identifier']['precise'];
   final id = idJson.get<String>();
@@ -56,23 +61,13 @@ String parseSymbolName(Json symbolJson) {
 }
 
 bool parseSymbolHasObjcAnnotation(Json symbolJson) {
-  return symbolJson['declarationFragments'].any(
-    (json) =>
-        json['kind'].exists &&
-        json['kind'].get<String>() == 'attribute' &&
-        json['spelling'].exists &&
-        json['spelling'].get<String>() == '@objc',
-  );
+  return symbolJson['declarationFragments']
+      .any((json) => matchFragment(json, 'attribute', '@objc'));
 }
 
 bool parseIsOverriding(Json symbolJson) {
-  return symbolJson['declarationFragments'].any(
-    (json) =>
-        json['kind'].exists &&
-        json['kind'].get<String>() == 'keyword' &&
-        json['spelling'].exists &&
-        json['spelling'].get<String>() == 'override',
-  );
+  return symbolJson['declarationFragments']
+      .any((json) => matchFragment(json, 'keyword', 'override'));
 }
 
 ReferredType parseTypeFromId(String typeId, ParsedSymbolgraph symbolgraph) {

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

@@ -8,22 +8,33 @@ InitializerDeclaration parseInitializerDeclaration(
   Json initializerSymbolJson,
   ParsedSymbolgraph symbolgraph,
 ) {
+  final id = parseSymbolId(initializerSymbolJson);
+
+  // Initializers don't have `functionSignature` field in symbolgraph like
+  // methods do, so we have our only option is to use `declarationFragments`.
+  final declarationFragments = initializerSymbolJson['declarationFragments'];
+
+  // All initializers should start with an `init` keyword.
+  if (!matchFragment(declarationFragments[0], 'keyword', 'init')) {
+    throw Exception('Invalid initializer at ${declarationFragments.path}: $id');
+  }
+
   return InitializerDeclaration(
-    id: parseSymbolId(initializerSymbolJson),
-    params: parseInitializerParams(initializerSymbolJson, symbolgraph),
+    id: id,
+    params: parseInitializerParams(declarationFragments, symbolgraph),
     hasObjCAnnotation: parseSymbolHasObjcAnnotation(initializerSymbolJson),
     isOverriding: parseIsOverriding(initializerSymbolJson),
+    isFailable: parseIsFailableInit(id, declarationFragments),
   );
 }
 
+bool parseIsFailableInit(String id, Json declarationFragments) =>
+    matchFragment(declarationFragments[1], 'text', '?(');
+
 List<Parameter> parseInitializerParams(
-  Json initializerSymbolJson,
+  Json declarationFragments,
   ParsedSymbolgraph symbolgraph,
 ) {
-  // Initializers don't have `functionSignature` field in symbolgraph like
-  // methods do, so we have our only option is to use `declarationFragments`.
-  final fragments = initializerSymbolJson['declarationFragments'];
-
   // `declarationFragments` describes each part of the initializer declaration,
   // things like `init` keyword, brackets, spaces, etc. We only care about the
   // parameter fragments here, and they always appear in this order:
@@ -51,7 +62,7 @@ List<Parameter> parseInitializerParams(
 
   final parameters = <Parameter>[];
 
-  for (final fragmentJson in fragments) {
+  for (final fragmentJson in declarationFragments) {
     final kind = fragmentJson['kind'].get<String>();
     final invalidOrderException = Exception(
       'Invalid fragments order at ${fragmentJson.path}',
@@ -94,7 +105,7 @@ List<Parameter> parseInitializerParams(
   // of `declarationFragments` array.
   if (externalParam != null || internalParam != null || typeId != null) {
     throw Exception(
-      'Missing parameter fragments at the end of ${fragments.path}',
+      'Missing parameter fragments at the end of ${declarationFragments.path}',
     );
   }
 

pkgs/swift2objc/lib/src/transformer/_core/unique_namer.dart

@@ -1,9 +1,14 @@
+// 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/interfaces/compound_declaration.dart';
 
 class UniqueNamer {
   final Set<String> _usedNames;
 
-  UniqueNamer(Iterable<String> usedNames) : _usedNames = usedNames.toSet();
+  UniqueNamer([Iterable<String> usedNames = const <String>[]])
+      : _usedNames = usedNames.toSet();
 
   UniqueNamer.inCompound(CompoundDeclaration compoundDeclaration)
       : _usedNames = {

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

@@ -1,3 +1,7 @@
+// 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/interfaces/declaration.dart';
 import '../../ast/_core/shared/referred_type.dart';
 import '../../ast/declarations/compounds/class_declaration.dart';

pkgs/swift2objc/lib/src/transformer/transformers/transform_compound.dart

@@ -89,6 +89,7 @@ InitializerDeclaration _buildWrapperInitializer(
       )
     ],
     isOverriding: false,
+    isFailable: false,
     statements: ['self.${wrappedClassInstance.name} = wrappedInstance'],
     hasObjCAnnotation: wrappedClassInstance.hasObjCAnnotation,
   );

pkgs/swift2objc/lib/src/transformer/transformers/transform_initializer.dart

@@ -34,6 +34,7 @@ InitializerDeclaration transformInitializer(
       id: originalInitializer.id,
       params: transformedParams,
       hasObjCAnnotation: true,
+      isFailable: originalInitializer.isFailable,
       // Because the wrapper class extends NSObject that has an initializer with
       // no parameters. If we make a similar parameterless initializer we need
       // to add `override` keyword.
@@ -54,13 +55,14 @@ List<String> _generateInitializerStatements(
   InitializerDeclaration transformedInitializer,
 ) {
   final argumentsList = <String>[];
+  final localNamer = UniqueNamer();
 
   for (var i = 0; i < originalInitializer.params.length; i++) {
     final originalParam = originalInitializer.params[i];
     final transformedParam = transformedInitializer.params[i];
 
-    final transformedParamName =
-        transformedParam.internalName ?? transformedParam.name;
+    final transformedParamName = localNamer
+        .makeUnique(transformedParam.internalName ?? transformedParam.name);
 
     final (unwrappedParamValue, unwrappedType) = maybeUnwrapValue(
       transformedParam.type,
@@ -77,5 +79,16 @@ List<String> _generateInitializerStatements(
   final arguments = argumentsList.join(', ');
 
   final instanceConstruction = '${wrappedClassInstance.type.name}($arguments)';
-  return ['${wrappedClassInstance.name} = $instanceConstruction'];
+  if (originalInitializer.isFailable) {
+    final instance = localNamer.makeUnique('instance');
+    return [
+      'if let $instance = $instanceConstruction {',
+      '  ${wrappedClassInstance.name} = $instance',
+      '} else {',
+      '  return nil',
+      '}',
+    ];
+  } else {
+    return ['${wrappedClassInstance.name} = $instanceConstruction'];
+  }
 }

pkgs/swift2objc/test/integration/classes_and_initializers_input.swift

@@ -8,6 +8,15 @@ public class MyClass {
         self.representableProperty = representableProperty
         self.customProperty = customProperty
     }
+
+    public init?(outerLabel x: Int) {
+        if x == 0 {
+            return nil
+        } else {
+            self.representableProperty = x
+            self.customProperty = MyOtherClass()
+        }
+    }
 }
 
 public class MyOtherClass {}

pkgs/swift2objc/test/integration/classes_and_initializers_output.swift

@@ -32,4 +32,12 @@ import Foundation
   @objc init(outerLabel representableProperty: Int, customProperty: MyOtherClassWrapper) {
     wrappedInstance = MyClass(outerLabel: representableProperty, customProperty: customProperty.wrappedInstance)
   }
+
+  @objc init?(outerLabel x: Int) {
+    if let instance = MyClass(outerLabel: x) {
+      wrappedInstance = instance
+    } else {
+      return nil
+    }
+  }
 }

pkgs/swift2objc/test/integration/integration_test.dart

@@ -4,13 +4,18 @@
 
 import 'dart:io';
 
+import 'package:logging/logging.dart';
 import 'package:path/path.dart' as path;
 import 'package:swift2objc/swift2objc.dart';
 import 'package:test/test.dart';
 
 const regenerateExpectedOutputs = false;
 
 void main() {
+  Logger.root.onRecord.listen((record) {
+    stderr.writeln('${record.level.name}: ${record.message}');
+  });
+
   group('Integration tests', () {
     const inputSuffix = '_input.swift';
     const outputSuffix = '_output.swift';

pkgs/swift2objc/test/integration/structs_and_initializers_input.swift

@@ -8,6 +8,15 @@ public class MyStruct {
         self.representableProperty = representableProperty
         self.customProperty = customProperty
     }
+
+    public init?(outerLabel x: Int) {
+        if x == 0 {
+            return nil
+        } else {
+            self.representableProperty = x
+            self.customProperty = MyOtherStruct()
+        }
+    }
 }
 
 public struct MyOtherStruct {}

pkgs/swift2objc/test/integration/structs_and_initializers_output.swift

@@ -20,4 +20,12 @@ import Foundation
   @objc init(outerLabel representableProperty: Int, customProperty: MyOtherStructWrapper) {
     wrappedInstance = MyStruct(outerLabel: representableProperty, customProperty: customProperty.wrappedInstance)
   }
+
+  @objc init?(outerLabel x: Int) {
+    if let instance = MyStruct(outerLabel: x) {
+      wrappedInstance = instance
+    } else {
+      return nil
+    }
+  }
 }