Check if task is currently running one

Task+Current.swift

extension Optional
where Wrapped == Task<Void, Never> {

	public mutating func clearIfCurrent() {
		switch self {
		case .some(let task) where task.isCurrent:
			self = .none

		case _:
			break // noop
		}
	}
}

extension Task {

	public var isCurrent: Bool {
		withUnsafeCurrentTask { (unsafeTask: UnsafeCurrentTask?) -> Bool in
			guard let unsafeTask else { return false }

			return withUnsafePointer(to: self) { (selfPointer: UnsafePointer<Task>) -> Bool in
				selfPointer.withMemoryRebound(to: TaskBox.self, capacity: 1) { (selfBoxPointer: UnsafePointer<TaskBox>) -> Bool in
					withUnsafePointer(to: unsafeTask) { (currentPointer: UnsafePointer<UnsafeCurrentTask>) -> Bool in
						currentPointer.withMemoryRebound(to: TaskBox.self, capacity: 1) { (currentBoxPointer: UnsafePointer<TaskBox>) -> Bool in
							selfBoxPointer.pointee._task == currentBoxPointer.pointee._task
						}
					}
				}
			}
		}
	}
}

// https://github.com/apple/swift/blob/750545774b4505064af1f144a24c1177e8515250/stdlib/public/Concurrency/Task.swift#L81
// https://github.com/apple/swift/blob/750545774b4505064af1f144a24c1177e8515250/stdlib/public/Concurrency/Task.swift#L870
// https://github.com/apple/swift/blob/750545774b4505064af1f144a24c1177e8515250/docs/SIL.rst#ref-to-raw-pointer
fileprivate struct TaskBox {
	// builtin reference (Builtin.RawPointer) uses platform long Int for pointers
	fileprivate let _task: Int
}