[ffigen] Migrate to ARC (#1441)

.github/workflows/objective_c.yaml

@@ -75,3 +75,20 @@ jobs:
           carryforward: "ffigen,jni,jnigen,native_assets_builder_macos,native_assets_builder_ubuntu,native_assets_builder_windows,native_assets_cli_macos,native_assets_cli_ubuntu,native_assets_cli_windows,native_toolchain_c_macos,native_toolchain_c_ubuntu,native_toolchain_c_windows,objective_c,swift2objc"
           github-token: ${{ secrets.GITHUB_TOKEN }}
           parallel-finished: true
+
+  build-example:
+    needs: analyze
+    runs-on: 'macos-latest'
+    defaults:
+      run:
+        working-directory: pkgs/objective_c/example/
+    steps:
+      - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332
+      - uses: subosito/flutter-action@44ac965b96f18d999802d4b807e3256d5a3f9fa1
+        with:
+          flutter-version: 3.19.0
+          channel: 'stable'
+      - name: Install dependencies
+        run: flutter pub get
+      - name: Build the example app
+        run: flutter build macos

.gitignore

@@ -97,6 +97,7 @@ coverage/
 *.jar
 *.class
 *.exe
+*.o
 
 # Visual Studio user-specific files.
 *.suo

pkgs/ffigen/CHANGELOG.md

@@ -13,7 +13,11 @@
   `ObjCBlock<Ret Function(Args...)>`, instead of the codegenned
   `ObjCBlock_...` wrapper. The wrapper is now a non-constructible set of util
   methods for constructing `ObjCBlock`.
-
+- __Breaking change__: Generated ObjC code has been migrated to ARC (Automatic
+  Reference Counting), and must now be compiled with ARC enabled. For example,
+  if you had a line like `s.requires_arc = []` in your podspec, this should
+  either be removed, or you should add the ffigen generated ObjC code to the
+  list. If you're compiling directly with clang, add the `-fobjc-arc` flag.
 
 ## 13.0.0
 

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

@@ -193,6 +193,8 @@ abstract final class $name {
           objCRetain: true);
       final listenerConvFn =
           '($paramsFfiDartType) => $listenerConvFnInvocation';
+      final wrapFn = _wrapListenerBlock?.name;
+      final releaseFn = ObjCBuiltInFunctions.objectRelease.gen(w);
 
       s.write('''
 
@@ -205,12 +207,22 @@ abstract final class $name {
   ///
   /// Note that unlike the default behavior of NativeCallable.listener, listener
   /// blocks do not keep the isolate alive.
-  static $blockType listener($funcDartType fn) =>
-      $blockType(${_wrapListenerBlock?.name ?? ''}($newClosureBlock(
-          (_dartFuncListenerTrampoline ??= $nativeCallableType.listener(
-              $closureTrampoline $exceptionalReturn)..keepIsolateAlive =
-                  false).nativeFunction.cast(), $listenerConvFn)),
-          retain: false, release: true);
+  static $blockType listener($funcDartType fn) {
+    final raw = $newClosureBlock(
+        (_dartFuncListenerTrampoline ??= $nativeCallableType.listener(
+            $closureTrampoline $exceptionalReturn)..keepIsolateAlive =
+                false).nativeFunction.cast(), $listenerConvFn);''');
+      if (wrapFn != null) {
+        s.write('''
+    final wrapper = $wrapFn(raw);
+    $releaseFn(raw.cast());
+    return $blockType(wrapper, retain: false, release: true);''');
+      } else {
+        s.write('''
+    return $blockType(raw, retain: false, release: true);''');
+      }
+      s.write('''
+  }
   static $nativeCallableType? _dartFuncListenerTrampoline;
 ''');
     }
@@ -256,12 +268,10 @@ pointer.ref.invoke.cast<$natTrampFnType>().asFunction<$trampFuncFfiDartType>()(
     s.write('''
 
 typedef ${getNativeType(varName: blockTypedef)};
-$blockTypedef $fnName($blockTypedef block) {
-  $blockTypedef wrapper = [^void(${argsReceived.join(', ')}) {
+$blockTypedef $fnName($blockTypedef block) NS_RETURNS_RETAINED {
+  return ^void(${argsReceived.join(', ')}) {
     block(${retains.join(', ')});
-  } copy];
-  [block release];
-  return wrapper;
+  };
 }
 ''');
     return BindingString(
@@ -337,7 +347,7 @@ $blockTypedef $fnName($blockTypedef block) {
       ObjCInterface.generateConstructor(name, value, objCRetain);
 
   @override
-  String? generateRetain(String value) => '[$value copy]';
+  String? generateRetain(String value) => 'objc_retainBlock($value)';
 
   @override
   String toString() => '($returnType (^)(${argTypes.join(', ')}))';

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

@@ -25,6 +25,7 @@ class ObjCBuiltInFunctions {
   static const getProtocolMethodSignature =
       ObjCImport('getProtocolMethodSignature');
   static const getProtocol = ObjCImport('getProtocol');
+  static const objectRelease = ObjCImport('objectRelease');
   static const objectBase = ObjCImport('ObjCObjectBase');
   static const blockType = ObjCImport('ObjCBlock');
   static const protocolMethod = ObjCImport('ObjCProtocolMethod');

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

@@ -341,7 +341,7 @@ class ObjCInterface extends BindingType with ObjCMethods {
   }
 
   @override
-  String? generateRetain(String value) => '[$value retain]';
+  String? generateRetain(String value) => 'objc_retain($value)';
 
   String _getConvertedType(Type type, Writer w, String enclosingClass) {
     if (type is ObjCInstanceType) return enclosingClass;

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

@@ -135,5 +135,5 @@ class ObjCObjectPointer extends PointerType {
       '${getDartType(w)}($value, retain: $objCRetain, release: true)';
 
   @override
-  String? generateRetain(String value) => '[$value retain]';
+  String? generateRetain(String value) => 'objc_retain($value)';
 }

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

@@ -418,12 +418,20 @@ class Writer {
     final s = StringBuffer();
     s.write('''
 #include <stdint.h>
-
 ''');
 
     for (final entryPoint in nativeEntryPoints) {
       s.write(_objcImport(entryPoint, outDir));
     }
+    s.write('''
+
+#if !__has_feature(objc_arc)
+#error "This file must be compiled with ARC enabled"
+#endif
+
+id objc_retain(id);
+id objc_retainBlock(id);
+''');
 
     var empty = true;
     for (final binding in _allBindings) {

pkgs/ffigen/test/native_objc_test/arc_config.yaml

@@ -0,0 +1,17 @@
+name: ArcTestObjCLibrary
+description: 'Tests ARC'
+language: objc
+output: 'arc_bindings.dart'
+exclude-all-by-default: true
+functions:
+  include:
+    - objc_autoreleasePoolPop
+    - objc_autoreleasePoolPush
+objc-interfaces:
+  include:
+    - ArcTestObject
+headers:
+  entry-points:
+    - 'arc_test.m'
+preamble: |
+  // ignore_for_file: camel_case_types, non_constant_identifier_names, unnecessary_non_null_assertion, unused_element, unused_field