[ffigen] Add selector conversion utils (#1616)

pkgs/ffigen/lib/src/code_generator/objc_built_in_functions.dart

@@ -120,7 +120,7 @@ class ObjCBuiltInFunctions {
       generateForPackageObjectiveC ? null : builtInCompounds[name];
   bool isBuiltInEnum(String name) =>
       !generateForPackageObjectiveC && builtInEnums.contains(name);
-  bool isNSObject(String name) => name == 'NSObject';
+  static bool isNSObject(String name) => name == 'NSObject';
 
   // We need to load a separate instance of objc_msgSend for each signature. If
   // the return type is a struct, we need to use objc_msgSend_stret instead, and

pkgs/ffigen/lib/src/code_generator/objc_interface.dart

@@ -279,8 +279,11 @@ class ObjCInterface extends BindingType with ObjCMethods {
     //  - Methods that return instancetype, because the subclass's copy of the
     //    method needs to return the subclass, not the super class.
     //    Note: instancetype is only allowed as a return type, not an arg type.
+    final isNSObject = ObjCBuiltInFunctions.isNSObject(originalName);
     for (final m in superType!.methods) {
-      if (m.isClassMethod &&
+      if (isNSObject) {
+        addMethod(m);
+      } else if (m.isClassMethod &&
           !_excludedNSObjectMethods.contains(m.originalName)) {
         addMethod(m);
       } else if (ObjCBuiltInFunctions.isInstanceType(m.returnType)) {
@@ -290,8 +293,17 @@ class ObjCInterface extends BindingType with ObjCMethods {
   }
 
   void _copyMethodsFromProtocol(ObjCProtocol proto) {
+    final isNSObject = ObjCBuiltInFunctions.isNSObject(originalName);
     for (final m in proto.methods) {
-      if (!_excludedNSObjectMethods.contains(m.originalName)) {
+      if (isNSObject) {
+        if (m.originalName == 'description' || m.originalName == 'hash') {
+          // TODO(https://github.com/dart-lang/native/issues/1220): Remove this
+          // special case. These methods only clash because they're sometimes
+          // declared as getters and sometimes as normal methods.
+        } else {
+          addMethod(m);
+        }
+      } else if (!_excludedNSObjectMethods.contains(m.originalName)) {
         addMethod(m);
       }
     }

pkgs/ffigen/lib/src/code_generator/objc_protocol.dart

@@ -189,7 +189,7 @@ ${makeDartDoc(dartDoc ?? originalName)}abstract final class $name {
   }
 
   void _copyMethodsFromSuperType(ObjCProtocol superProtocol) {
-    if (builtInFunctions.isNSObject(superProtocol.originalName)) {
+    if (ObjCBuiltInFunctions.isNSObject(superProtocol.originalName)) {
       // When writing a protocol that doesn't inherit from any other protocols,
       // it's typical to have it inherit from NSObject instead. But NSObject has
       // heaps of methods that users are very unlikely to want to implement, so

pkgs/ffigen/test/large_integration_tests/large_objc_test.dart

@@ -47,8 +47,11 @@ void main() {
       'attributedString',
       'cachePolicy',
       'candidateListTouchBarItem',
+      'delegate',
       'hyphenationFactor',
       'image',
+      'isProxy',
+      'objCType',
       'tag',
       'title',
     };

pkgs/ffigen/test/native_objc_test/block_test.dart

@@ -688,7 +688,7 @@ void main() {
       final dummyObject = DummyObject.new1();
       DartObjectListenerBlock? block =
           ObjectListenerBlock.listener((DummyObject obj) {
-        expect(objectRetainCount(obj.ref.pointer), 1);
+        expect(objectRetainCount(obj.ref.pointer), greaterThan(0));
         completer.complete();
         expect(dummyObject, isNotNull);
       });

pkgs/objective_c/CHANGELOG.md

@@ -4,6 +4,7 @@
   bindings if an optional method is invoked, and the instance doesn't implement
   the method.
 - Dispatch all object/block releases to the main thread.
+- Add utils for converting Dart `String`s to Objective-C selectors and back.
 - Require Dart 3.4 or later (due to the use of `dart:ffi`
   `Struct.create` by `package:ffigen`).
 - __Breaking change__: Return structs from ObjC methods by value instead of

pkgs/objective_c/ffigen_c.yaml

@@ -17,6 +17,7 @@ functions:
     - 'objc_.*'
     - 'object_getClass'
     - 'sel_registerName'
+    - 'sel_getName'
     - 'protocol_getMethodDescription'
     - 'disposeObjCBlockWithClosure'
     - 'isValidBlock'
@@ -37,6 +38,7 @@ functions:
       - 'newFinalizableBool'
   rename:
     'sel_registerName': 'registerName'
+    'sel_getName': 'getName'
     'objc_getClass': 'getClass'
     'objc_retain': 'objectRetain'
     'objc_retainBlock': 'blockRetain'

pkgs/objective_c/lib/objective_c.dart

@@ -82,3 +82,4 @@ export 'src/objective_c_bindings_generated.dart'
         NSValue,
         Protocol;
 export 'src/protocol_builder.dart';
+export 'src/selector.dart';

pkgs/objective_c/lib/src/c_bindings_generated.dart

@@ -102,6 +102,12 @@ external ObjCMethodDesc getMethodDescription(
   bool isInstanceMethod,
 );
 
+@ffi.Native<ffi.Pointer<ffi.Char> Function(ffi.Pointer<ObjCSelector>)>(
+    symbol: "sel_getName", isLeaf: true)
+external ffi.Pointer<ffi.Char> getName(
+  ffi.Pointer<ObjCSelector> sel,
+);
+
 @ffi.Native<ffi.Pointer<ObjCObject> Function(ffi.Pointer<ObjCObject>)>(
     symbol: "object_getClass", isLeaf: true)
 external ffi.Pointer<ObjCObject> getObjectClass(

pkgs/objective_c/lib/src/objective_c_bindings_generated.dart

@@ -6338,8 +6338,8 @@ class NSObject extends objc.ObjCObjectBase {
   }
 
   /// class
-  static objc.ObjCObjectBase class1() {
-    final _ret = _objc_msgSend_1unuoxw(_class_NSObject, _sel_class);
+  objc.ObjCObjectBase class1() {
+    final _ret = _objc_msgSend_1unuoxw(this.ref.pointer, _sel_class);
     return objc.ObjCObjectBase(_ret, retain: true, release: true);
   }
 
@@ -6350,9 +6350,9 @@ class NSObject extends objc.ObjCObjectBase {
   }
 
   /// conformsToProtocol:
-  static bool conformsToProtocol_(Protocol protocol) {
+  bool conformsToProtocol_(Protocol aProtocol) {
     return _objc_msgSend_l8lotg(
-        _class_NSObject, _sel_conformsToProtocol_, protocol.ref.pointer);
+        this.ref.pointer, _sel_conformsToProtocol_, aProtocol.ref.pointer);
   }
 
   /// copy
@@ -6374,8 +6374,12 @@ class NSObject extends objc.ObjCObjectBase {
   }
 
   /// debugDescription
-  static NSString debugDescription() {
-    final _ret = _objc_msgSend_1unuoxw(_class_NSObject, _sel_debugDescription);
+  NSString debugDescription() {
+    if (!objc.respondsToSelector(ref.pointer, _sel_debugDescription)) {
+      throw objc.UnimplementedOptionalMethodException(
+          'NSObject', 'debugDescription');
+    }
+    final _ret = _objc_msgSend_1unuoxw(this.ref.pointer, _sel_debugDescription);
     return NSString.castFromPointer(_ret, retain: true, release: true);
   }
 
@@ -6639,6 +6643,12 @@ class NSObject extends objc.ObjCObjectBase {
         _class_NSObject, _sel_resolveInstanceMethod_, sel);
   }
 
+  /// respondsToSelector:
+  bool respondsToSelector_(ffi.Pointer<objc.ObjCSelector> aSelector) {
+    return _objc_msgSend_8d7dvc(
+        this.ref.pointer, _sel_respondsToSelector_, aSelector);
+  }
+
   /// retain
   NSObject retain() {
     final _ret = _objc_msgSend_1unuoxw(this.ref.pointer, _sel_retain);
@@ -6668,8 +6678,8 @@ class NSObject extends objc.ObjCObjectBase {
   }
 
   /// superclass
-  static objc.ObjCObjectBase superclass() {
-    final _ret = _objc_msgSend_1unuoxw(_class_NSObject, _sel_superclass);
+  objc.ObjCObjectBase superclass() {
+    final _ret = _objc_msgSend_1unuoxw(this.ref.pointer, _sel_superclass);
     return objc.ObjCObjectBase(_ret, retain: true, release: true);
   }
 

pkgs/objective_c/lib/src/selector.dart

@@ -0,0 +1,25 @@
+// 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 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+
+import 'c_bindings_generated.dart' as c;
+import 'internal.dart';
+
+extension StringToSelector on String {
+  /// Returns an Objective-C selector (aka `SEL`) for this [String].
+  ///
+  /// This is equivalent to the Objective-C `@selector()` directive, or the
+  /// `NSSelectorFromString` function.
+  Pointer<c.ObjCSelector> toSelector() => registerName(this);
+}
+
+extension SelectorToString on Pointer<c.ObjCSelector> {
+  /// Returns the string that this Objective-C selector represents.
+  ///
+  /// This is equivalent to the Objective-C `NSSelectorFromString` function.
+  String toDartString() => c.getName(this).cast<Utf8>().toDartString();
+}

pkgs/objective_c/pubspec.yaml

@@ -15,7 +15,7 @@ topics:
 
 environment:
   sdk: '>=3.4.0 <4.0.0'
-  flutter: '>=3.3.0'
+  flutter: '>=3.22.0'
 
 dependencies:
   ffi: ^2.1.0

pkgs/objective_c/src/objective_c_runtime.h

@@ -16,6 +16,7 @@ typedef struct _ObjCObject ObjCObject;
 typedef struct _ObjCProtocol ObjCProtocol;
 
 ObjCSelector *sel_registerName(const char *name);
+const char * sel_getName(ObjCSelector* sel);
 ObjCObject *objc_getClass(const char *name);
 ObjCObject *objc_retain(ObjCObject *object);
 ObjCObject *objc_retainBlock(const ObjCObject *object);

pkgs/objective_c/test/selector_test.dart

@@ -0,0 +1,37 @@
+// 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.
+
+// Objective C support is only available on mac.
+@TestOn('mac-os')
+library;
+
+import 'dart:ffi';
+
+import 'package:objective_c/objective_c.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Selector', () {
+    setUpAll(() {
+      // TODO(https://github.com/dart-lang/native/issues/1068): Remove this.
+      DynamicLibrary.open('test/objective_c.dylib');
+    });
+
+    test('from String and back', () {
+      expect('hello'.toSelector().toDartString(), 'hello');
+      expect(''.toSelector().toDartString(), '');
+      expect('foo:with:args:'.toSelector().toDartString(), 'foo:with:args:');
+    });
+
+    test('responds to selector', () {
+      final sel1 = 'addObserver:forKeyPath:options:context:'.toSelector();
+      expect(NSObject.new1().respondsToSelector_(sel1), isTrue);
+      expect(NSObject.new1().respondsToSelector_('foo'.toSelector()), isFalse);
+
+      final sel2 = 'canBeConvertedToEncoding:'.toSelector();
+      expect(NSString.new1().respondsToSelector_(sel2), isTrue);
+      expect(NSString.new1().respondsToSelector_('bar'.toSelector()), isFalse);
+    });
+  });
+}