F#/Argu - 如何显示二级命令树的帮助而不引发异常

Question

我有一个两级 F#/Argu 命令树。它的缩写版本如下所示:

[<CliPrefix(CliPrefix.Dash)>]
type RunContGenArgs =
    | [<Unique>] [<EqualsAssignment>] [<AltCommandLine("-ql")>] MaxQueueLength of int

with
    interface IArgParserTemplate with
        member this.Usage =
            match this with
            | MaxQueueLength _ -> "max queue length."
and
    [<CliPrefix(CliPrefix.None)>]
    ContGenArguments =
        | [<Unique>] [<AltCommandLine("run")>]      RunContGen of ParseResults<RunContGenArgs>
    with
        interface IArgParserTemplate with
            member this.Usage =
                match this with
                | RunContGen _ -> "run Continuous Generation."

然后我使用如下:

[<EntryPoint>]
let main argv =
    let parser = ArgumentParser.Create<ContGenArguments>(programName = "ContGen.exe")
    let results = parser.Parse argv

    match results.GetAllResults() |> ContGenTask.tryCreate with
    | Some task -> task.run()
    | None ->
        printfn "%s" (parser.PrintUsage())
        -1

如果我运行 ContGen.exe run help 这样的命令，那么它会正确显示命令 run 的帮助。然而，它随后崩溃并出现丑陋的异常:

Unhandled Exception: Argu.ArguParseException: USAGE: ContGen.exe runcontgen [help] [-maxqueuelength=<int>]
OPTIONS:
    -maxqueuelength, -ql=<int>
                          max queue length.
    help                  display this list of options.
   at Argu.ExceptionExiter.Argu-IExiter-Exit[a](String msg, ErrorCode errorCode) in C:\Users\eirik.tsarpalis\devel\public\Argu\src\Argu\Types.fs:line 62
   at Argu.ArgumentParser\`1.Parse(FSharpOption\`1 inputs, FSharpOption\`1 configurationReader, FSharpOption\`1 ignoreMissing, FSharpOption\`1 ignoreUnrecognized, FSharpOption\`1 raiseOnUsage) in C:\Users\eirik.tsarpalis\devel\public\Argu\src\Argu\ArgumentParser.fs:line 180
   at Program.main(String[] argv) in C:\GitHub\ClmFSharp\Clm\ContGen\Program.fs:line 8

如果我将 let results = parser.Parse argv 更改为 let results = parser.Parse(argv, raiseOnUsage = false)，那么它不会崩溃，但不会崩溃显示任何帮助消息。然后，由于命令 run 可以在没有任何二级参数的情况下运行，因此程序会继续运行，而不是显示帮助并退出。

但是，我需要 ContGen.exe run help 只是显示帮助消息，然后退出。我怎样才能做到这一点？谢谢。

Answer 1

这是阿古的一种有点奇怪的行为；您需要提供自己的退出程序以避免在那里抛出异常。

大致如下:

type NonThrowingExiter() =
    interface IExiter with
        member __.Name = "Exiter" // I don't know what this is used for; I have never seen it appear anywhere
        member __.Exit (msg, code) =
            if code = ErrorCode.HelpText then
                printfn "%s" msg
                exit 0
            else
                printfn "%s" msg // Maybe have code to color the console output red here
                exit 1

To use this, create your `ArgumentParser` like this:

let argumentParser =
    Argu.ArgumentParser.Create<ContGenArguments>(helpTextMessage = "Help requested",
                                                 errorHandler = NonThrowingExiter())

(当然，您实际上不需要为此创建一个类；对象表达式也可以做到这一点。)