Sendability warnings / errors disparity for AVFoundation types

Using Swift
,
1

With this setup:

@preconcurrency import AVFoundation

actor A {
    func getSession() -> AVCaptureSession { nonoptionalSession }
    let nonoptionalSession: AVCaptureSession
    let optionalSession: AVCaptureSession!
    
    func getLayer() -> AVCaptureVideoPreviewLayer { nonoptionalLayer }
    let nonoptionalLayer: AVCaptureVideoPreviewLayer
    let optionalLayer: AVCaptureVideoPreviewLayer!
    
    init() { fatalError() }
}

nonisolated class C {}

I am getting expected warnings about lack of sendability here:

extension C {
    func test1(a: A) async {
        _ = await a.getLayer()           // sendability warning (expected)
        _ = await a.nonoptionalLayer     // sendability warning (expected)
    }
}

(expected as if I change @preconcurrency import to normal import the warnings are changed to errors)

unexpected lack of sendability warnings here:

extension C {
    func test2(a: A) async {
        _ = await a.getSession()        // no sendability warning
        _ = await a.nonoptionalSession  // no sendability warning
        _ = await a.optionalSession!    // no sendability warning
    }
}

and somewhat unexpected error here (unexpected because similar code compiles without an error in test2):

extension C {
    func test3(a: A) async {
        // uncomment to see the error
        // _ = await a.optionalLayer!       // sendability error
    }
}

I guess Swift itself is in the clear here, and there's just some difference (in api notes?) for AVCaptureVideoPreviewLayer and AVCaptureSession that'd explain this observable disparity?

2

Not sure what’s happening here, but what’s interesting is that AVCaptureVideoPreviewLayer supposedly conforms to Sendable despite the diagnostic saying otherwise. My guess is that there’s an issue with Objective-C interoperability and sendability. Only my guess though, this all seems very random.

// Kinda expected, except for the methods
import AVFoundation

extension C {
	func test1(a: A) async {
		_ = await a.getSession()
		_ = await a.nonoptionalSession // error: Non-Sendable type
		_ = await a.optionalSession // error: Non-Sendable type

		_ = await a.getLayer()
		_ = await a.nonoptionalLayer // error: Non-Sendable type
		_ = await a.optionalLayer // error: Non-Sendable type
	}
}

// Random warning and error, despite the docs stating that 'AVCaptureVideoPreviewLayer' is Sendable ??
@preconcurrency import AVFoundation

extension C {
	func test1(a: A) async {
		_ = await a.getSession()
		_ = await a.nonoptionalSession
		_ = await a.optionalSession

		_ = await a.getLayer()
		_ = await a.nonoptionalLayer // warning: Non-Sendable type
		_ = await a.optionalLayer // error: Non-Sendable type
	}
}

// All fine as expected.
import AVFoundation

extension C {
	func test1(a: A) async {
		_ = await a.getSession()
		_ = await a.nonoptionalSession
		_ = await a.optionalSession

		_ = await a.getLayer()
		_ = await a.nonoptionalLayer
		_ = await a.optionalLayer
	}
}

extension AVCaptureSession: @retroactive @unchecked Sendable {}

extension AVCaptureVideoPreviewLayer: @retroactive @unchecked Sendable {}