NS_SWIFT_UI_ACTOR is ignored on block typedefs

[xavierjurado]

Description

NS_SWIFT_UI_ACTOR is not properly recognized on Objective-C block typedefs. This should be possible according to #58150 and #70693, but as far as I can tell it's not working on Xcode 15.4 or the latest Xcode 16 toolchain. Interestingly enough, NS_SWIFT_SENDABLE seems to be working as intended.

Reproduction

typedef void (^MainActorCompletionHandler)(void) NS_SWIFT_UI_ACTOR;
typedef void (^SendableCompletionHandler)(void) NS_SWIFT_SENDABLE;

Is translated as:

@MainActor public typealias MainActorCompletionHandler = () -> Void
public typealias SendableCompletionHandler = @Sendable () -> Void

Notice how the main actor closure has the @MainActor applied before the typedef, which is not valid and seems to be ignored by Swift. The sendable closure, instead, is correctly annotated.

Expected behavior

public typealias MainActorCompletionHandler = @MainActor () -> Void

Environment

swift-driver version: 1.90.11.1 Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)

Additional information

For what is worth, I've tried placing the NS_SWIFT_UI_ACTOR annotation on pretty much every position inside the typedef without any success 😅

NS_SWIFT_UI_ACTOR typedef NS_SWIFT_UI_ACTOR void NS_SWIFT_UI_ACTOR (^ NS_SWIFT_UI_ACTOR MainActorCompletionHandler)(void) NS_SWIFT_UI_ACTOR;

[xavierjurado]

The issue is no longer reproducible in the latest version of Xcode 16 (RC). Closing.

[drodriguez]

There might be something missing in the open source toolchain. With changes like drodriguez@a3c4428 (or even moving the MAIN_ACTOR to just after the block ^) I get the error in that commit message.

[xedin]

I think that might be an issue with how attributes on a typedef declaration are interpreted by the importer, if you move MAIN_ACTOR in the type position (inside of (^)), does that work?

[drodriguez]

@xedin I tested both and got the same results in both cases. I uploaded the second version in drodriguez@7a1032f and when I use check-swift-validation I get those three tests failing with the same error message:

.../test-macosx-arm64/Concurrency/Output/sendable_objc_attr_in_type_context_swift5.swift.tmp/src/main.swift:36:29: error: unexpected error produced: cannot convert value of type '@MainActor () -> Void' to expected argument type 'MainActorCompletionHandler' (aka '(@escaping @Sendable () -> ()) -> ()')
  test.withMainActorHandler(mainFn)

[xedin]

I'm going to take a look at what is going on here!

[xedin]

@drodriguez The type of typedef void (^MainActorCompletionHandler)(void (^ MAIN_ACTOR)(void)); is @Sendable (@MainActor () -> Void) -> Void and mainFn is just @MainActor () -> Void that's why that code is not accepted.

To be able to use mainFn you need to declare your typedef as typedef void (^MAIN_ACTOR MainActorCompletionHandler)(void); that has a type @escaping @MainActor @Sendable () -> Void

The following test-case passes in -swift-version 6 mode:

// RUN: %empty-directory(%t/src)
// RUN: %empty-directory(%t/sdk)
// RUN: split-file %s %t/src

// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck %t/src/main.swift \
// RUN:   -import-objc-header %t/src/Test.h \
// RUN:   -swift-version 6 \
// RUN:   -enable-experimental-feature SendableCompletionHandlers \
// RUN:   -module-name main -I %t -verify

// REQUIRES: objc_interop
// REQUIRES: asserts

//--- Test.h
#define SWIFT_SENDABLE __attribute__((__swift_attr__("@Sendable")))
#define NONSENDABLE __attribute__((__swift_attr__("@_nonSendable")))
#define MAIN_ACTOR __attribute__((__swift_attr__("@MainActor")))

#pragma clang assume_nonnull begin

@import Foundation;

typedef void (^MAIN_ACTOR MainActorCompletionHandler)(void);

@interface Test : NSObject
-(void) withMainActorHandler:(MainActorCompletionHandler)handler;
@end

#pragma clang assume_nonnull end

//--- main.swift

func test_mainactor_attr_on_typealias(test: Test, handler: @escaping @MainActor () -> Void) {
  test.withMainActorHandler(handler)
}