[ffigen] Direct protocol method implementation using blocks (#2019)

Author: liamappelbe

pkgs/ffigen/test/native_objc_test/protocol_test.dart

@@ -340,6 +340,22 @@ void main() {
         consumer.callBlockingMethodOnRandomThread_(asMyProtocol);
         expect(await listenerCompleter.future, 98765);
       });
+
+      test('Direct method implementation using block', () async {
+        final consumer = ProtocolConsumer.new1();
+
+        final builder = ObjCProtocolBuilder();
+        MyProtocol.instanceMethod_withDouble_.implementWithBlock(
+            builder,
+            ObjCBlock_NSString_ffiVoid_NSString_ffiDouble.fromFunction(
+                (Pointer<Void> _, NSString s, double x) =>
+                    'DirectImpl: ${s.toDartString()}: $x'.toNSString()));
+        final myProtocol = MyProtocol.castFrom(builder.build());
+
+        // Required instance method.
+        final result = consumer.callInstanceMethod_(myProtocol);
+        expect(result.toDartString(), 'DirectImpl: Hello from ObjC: 3.14');
+      });
     });
 
     group('Manual DartProxy implementation', () {

pkgs/objective_c/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 7.0.0-wip
 
 - Use ffigen 18.0.0
+- `ObjCProtocolBuilder` supports implementing protocol methods directly using a
+  block.
 
 ## 6.0.0
 

pkgs/objective_c/lib/src/protocol_builder.dart

@@ -63,10 +63,19 @@ class ObjCProtocolMethod<T extends Function> {
   /// the wrong thread will result in a crash.
   void implement(ObjCProtocolBuilder builder, T? function) {
     if (function != null) {
-      builder.implementMethod(_sel, _sig, _createBlock(function));
+      implementWithBlock(builder, _createBlock(function));
     }
   }
 
+  /// Implement this method on the protocol [builder] using an ObjC [block].
+  ///
+  /// **IMPORTANT**: The [block] must have the same signature as the method,
+  /// but with an extra `void*` argument as the first parameter, before all the
+  /// method parameters. Most users should use one of the other `implement`
+  /// methods, which handles this signature change automatically.
+  void implementWithBlock(ObjCProtocolBuilder builder, ObjCBlockBase block) =>
+      builder.implementMethod(_sel, _sig, block);
+
   bool get isAvailable => _signature != null;
 
   objc.NSMethodSignature get _sig {
@@ -100,7 +109,7 @@ class ObjCProtocolListenableMethod<T extends Function>
   /// See NativeCallable.listener for more details.
   void implementAsListener(ObjCProtocolBuilder builder, T? function) {
     if (function != null) {
-      builder.implementMethod(_sel, _sig, _createListenerBlock(function));
+      implementWithBlock(builder, _createListenerBlock(function));
     }
   }
 
@@ -112,7 +121,7 @@ class ObjCProtocolListenableMethod<T extends Function>
   /// the method. Async functions are not supported.
   void implementAsBlocking(ObjCProtocolBuilder builder, T? function) {
     if (function != null) {
-      builder.implementMethod(_sel, _sig, _createBlockingBlock(function));
+      implementWithBlock(builder, _createBlockingBlock(function));
     }
   }
 }