More meaningful error message when Option<type> SetDefaultValue mismatched

[PaulFarry]

If I have a Command with a sub command all setup and working, and then I add an extra option, but you've made a typo (copy/paste).

var uploadPrefixOption = new Option<bool>("--uploadprefix", "prefix for the zip file") //Note the incorrect type should be string
{
    IsRequired = false
};
uploadPrefixOption.SetDefaultValue("backup");
backupCommand.AddOption(uploadPrefixOption);

when

return await rootCommand.InvokeAsync(args);

actually runs, I get an error of :

Unhandled exception: System.ArgumentException: The SetHandler call for command 'backup' is missing an Argument or Option for the parameter at position 4. Did you mean to pass one of these?
Option<String> --name

at runtime.

The error is actually coming from the incorrect type being used for uploadPrefixOption.SetDefaultValue("backup").

But the message leads you to the --name parameter, which is actually a bit of a redherring.

Would it be possible to throw the ArgumentException (or similar) on the SetDefaultValue because that's where the error actually is.

[jonsequitur]

You can have a bit more control over this using ParseArgument<T>. There's more information here: https://docs.microsoft.com/en-us/dotnet/standard/commandline/model-binding#custom-validation-and-binding

[PaulFarry]

I understand that you can make the messages better for the consumer, this is more for when a developer is creating them (and they've made a mistake) [which I had], but the error messages took some figuring out because the message I got was unrelated to the actual problem.