Cannot compile rethrowing async function

Using Swift
1

Trying to backport NSPersistentContainer.performBackgroundTask for iOS < 15 which has the following signature:

public func performBackgroundTask<T>(_ block: @escaping (NSManagedObjectContext) throws -> T) async rethrows -> T

But getting the following error from compiler (5.8):

Call can throw, but the error is not handled; a function declared 'rethrows' may only throw if its parameter does

Source:

extension NSPersistentContainer {

    @backDeployed(before: iOS 15.0)
    public final func performBackgroundTask<T>(_ block: @escaping (NSManagedObjectContext) throws -> T) async rethrows -> T {
        return try await withCheckedThrowingContinuation { continuation in
            performBackgroundTask { context in
                continuation.resume(with: Result { try block(context) })
            }
        }
    }

}

Is there any way to guarantee that the function is definitely rethrowing or at least silence the compiler?

ps: maybe that's what I am looking for Pitch: Fix rethrows checking and add rethrows(unsafe)