System.CommandLine doesn't work with Wasm

[richlander]

I tried using System.CommandLine with the wasiconsole app type/template

I get this:

Unhandled Exception:
System.PlatformNotSupportedException: Operation is not supported on this platform.
   at System.ConsolePal.IsOutputRedirectedCore()
   at System.Console.<get_IsOutputRedirected>g__EnsureInitialized|36_0()
   at System.Console.get_IsOutputRedirected()
   at System.CommandLine.IO.SystemConsole.get_IsOutputRedirected()
   at System.CommandLine.IO.SystemConsole.GetWindowWidth()
   at System.CommandLine.CommandLineConfiguration.DefaultHelpBuilderFactory(BindingContext context, Nullable`1 requestedMaxWidth)
   at System.CommandLine.Builder.CommandLineBuilder.<GetHelpBuilderFactory>g__CreateHelpBuilder|26_0(BindingContext bindingContext)
   at System.CommandLine.Invocation.ServiceProvider.<>c__DisplayClass1_0.<.ctor>b__3(IServiceProvider _)
   at System.CommandLine.Invocation.ServiceProvider.GetService(Type serviceType)
   at System.CommandLine.Binding.BindingContext.get_HelpBuilder()
   at System.CommandLine.Help.HelpResult.Apply(InvocationContext context)
   at System.CommandLine.Invocation.ParseErrorResult.Apply(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.GetExitCode(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.<Invoke>g__FullInvocationChain|3_0(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.Invoke(IConsole console)
   at System.CommandLine.CommandExtensions.Invoke(Command command, String[] args, IConsole console)
   at Program.<Main>$(String[] args)

[richlander]

This doesn't seem to be a generic issue: https://docs.wasmer.io/integrations/js/wasi/browser/examples/handling-io

This repo is likely the wrong one since it's not likely a SCL issue.

https://github.com/dotnet/runtime/blob/bda1f6c691c6517259a75e969f408e242dbc8103/src/libraries/System.Console/src/System/ConsolePal.Wasi.cs#L108

[richlander]

It's possible we won't fix this. Is it possible for SCL to do a runtime check on the OS and not check for redirected output?

[KalleOlaviNiemitalo]

at System.CommandLine.IO.SystemConsole.get_IsOutputRedirected()
at System.CommandLine.IO.SystemConsole.GetWindowWidth()
at System.CommandLine.CommandLineConfiguration.DefaultHelpBuilderFactory(BindingContext context, Nullable`1 requestedMaxWidth)

SystemConsole was moved from the System.CommandLine package to System.CommandLine.Rendering in #2106; it is not referenced by CliConfiguration, which replaces CommandLineConfiguration.

There is still an IsOutputRedirected check here

command-line-api/src/System.CommandLine/Help/HelpOptionAction.cs

Lines 13 to 17 in 1ad6f51

	public HelpBuilder Builder
	{
	get => _builder ??= new HelpBuilder(Console.IsOutputRedirected ? int.MaxValue : Console.WindowWidth);
	set => _builder = value ?? throw new ArgumentNullException(nameof(value));
	}

but I suppose an application could avoid that by constructing its own HelpBuilder instance and assigning that to the Builder property.

And another here

command-line-api/src/System.CommandLine/ConsoleHelpers.cs

Lines 12 to 21 in 9ebcd90

	private static bool GetColorsAreSupported()
	#if NET7_0_OR_GREATER
	=> !(OperatingSystem.IsBrowser() || OperatingSystem.IsAndroid() || OperatingSystem.IsIOS() || OperatingSystem.IsTvOS())
	#else
	=> !(RuntimeInformation.IsOSPlatform(OSPlatform.Create("BROWSER"))
	|| RuntimeInformation.IsOSPlatform(OSPlatform.Create("ANDROID"))
	|| RuntimeInformation.IsOSPlatform(OSPlatform.Create("IOS"))
	|| RuntimeInformation.IsOSPlatform(OSPlatform.Create("TVOS")))
	#endif
	&& !Console.IsOutputRedirected;

but that one is skipped if OperatingSystem.IsBrowser().

[jkotas]

Is it possible for SCL to do a runtime check on the OS and not check for redirected output?

This would be right thing to do under assumption that wasi is never getting terminal support. Looking at https://github.com/WebAssembly/WASI/issues?q=is%3Aissue+is%3Aopen+terminal , it is likely that wasi is going to get a terminal support at some point.

For now, I think it would be better to fix System.Console in dotnet/runtime to return true from IsOutputRedirected to indicate that the terminal support is not there yet and avoid training the libraries ecosystem to assume that there is not going to be a terminal in wasi.

[richlander]

@pavelsavara

[adamsitnik]

Fixed by dotnet/runtime#87278, thank you all for your feedback and help!