withSideActionAfterDelay.swift

/// Runs a secondary side action concurrently with a primary action.
/// The secondary action only starts after the specified delay.
///
/// Usage example: showing a progress indicator UI only if the primary action
/// takes a significant amount of time.
///
/// The secondary action runs in a child task (structured concurrency).
///
/// - Note: I'd like to provide a default argument for the clock: `clock: C = .continuous`,
///   like `Task.sleep` does. But this doesn't compile in Swift 6.2. Related bug report:
///   [swiftlang/swift issue #67680: Default expression for inference works for static methods but not functions](https://github.com/swiftlang/swift/issues/67680)
@available(macOS 15.0, *)
nonisolated(nonsending)
public func withSideActionAfterDelay<Return, Failure: Error, C: Clock>(
    delay: C.Instant.Duration,
    clock: C,
    _ primary: () async throws(Failure) -> Return,
    delayedAction: sending () async -> Void
) async throws (Failure) -> Return {
    #if compiler(>=6.3)
    #warning("Check if 'clock: C = .continuous' is supported now. See https://github.com/swiftlang/swift/issues/67680")
    #endif
    async let _ = {
        try? await Task.sleep(for: delay, clock: clock)
        if !Task.isCancelled {
            await delayedAction()
        }
    }()
    return try await primary()
}