Add support for async/await where available

[sergiocampama]

async/await is useful for writing clean and concise code for building small CLI tools, especially ones that interact with the network or the file system.

Since @main now supports an async variant, I was able to add such support to a prototype with the following code:

// entry.swift

@available(macOS 12.0, *)
protocol AsyncParsableCommand: ParsableCommand {
    mutating func runAsync() async throws
}

extension ParsableCommand {
    static func main(_ arguments: [String]? = nil) async {
        do {
            var command = try parseAsRoot(arguments)
            if #available(macOS 12.0, *), var asyncCommand = command as? AsyncParsableCommand {
                try await asyncCommand.runAsync()
            } else {
                try command.run()
            }
        } catch {
            exit(withError: error)
        }
    }
}

struct MainCommand: AsyncParsableCommand {
    @Option()
    var name: String = "Anon"

    func runAsync() async throws {
        print("Hello, \(name)")
        // await something...
    }
}

@main
struct MainApp {
    static func main() async {
        await MainCommand.main()
    }
}

Having this be officially supported by swift-argument-parser would be ideal.

[Blackjacx]

Today I refactored my App Store Connect API tool with using the async branch and integrating async/await using the async branch of the argument parser was sooooo satisfying. Good job everyone 👍🏼 hope this makes it in the official release soon. It is soo soo great :)

For the interested of you here are some links: https://twitter.com/Blackjacxxx/status/1411730725393555456

[Jerry-Carter]

Curious what the roadmap is for async/await support. Hoping to see it added to the main branch; using the async branch meanwhile.

[Frizlab]

Same here, eagerly waiting for async support to drop officially.

[andyzaharia]

Is there any news on this front? Seems like it should at least work on Monterey / Xcode 13.1... are there any blockers before pushing the async to main?

[Jerry-Carter]

Tried using the async branch in a proof of concept project. Had difficulty with objects in Run() getting deinitialized before the program was done. Not sure whether the error was on my side or intrinsic to the async branch. Either way, dropped back to the main branch and haven't seen any issues.

[Blackjacx]

@Jerry-Carter you could try https://github.com/Blackjacx/swift-argument-parser. It works for me quite well in my CLI application.

[Jerry-Carter]

@natecook1000
Looking at the 'More palatable async command support' changes, wouldn't it just be better to have all commands be async? Async main can contain synchronous code without issue whereas synchronous main cannot invoke async code. This would eliminate the

@main enum Main: AsyncMain {
typealias Command = <#command#>
}

ugliness. You might want to conditionally compile a definition of 'run() async' for Swift 5.5 vs. a synchronous definition for previous versions.

[everlof]

@sergiocampama Does your code work with latests Xcode etc? I just keep getting:
'main' attribute cannot be used in a module that contains top-level code something you've seen?

[Jerry-Carter]

@everlof As I recall @main cannot be used in a file named 'main.swift'. Ensure that the file is named differently and that there is not, in fact, top-level code present.

[everlof]

Ah, of course. Thank you! 🙏🏻

[ffried]

Any news from the team on this? No "official" support for async/await here is the only thing preventing us from migrating our CLI-Tools. I'm aware of the async branch, but this is not an official release and thus doesn't work well with shipping releases in our packages.

Personally, I find the extra type conforming to AsyncMain not really ideal, but if that's what gets us official support, so be it.

[natecook1000]

@ffried I've opened #404 to land async/await support — it will be a part of the 1.1 release once that's ready.

[ffried]

@natecook1000 thank you!

[stherold]

Today I refactored my App Store Connect API tool with using the async branch and integrating async/await using the async branch of the argument parser was sooooo satisfying. Good job everyone 👍🏼 hope this makes it in the official release soon. It is soo soo great :)

For the interested of you here are some links: twitter.com/Blackjacxxx/status/1411730725393555456