[Bug] Type System.String cannot be created without a custom binder.

[rfuzzo]

Hello,
on version 2.0.0-beta4.22272.1 I'm getting a consistent System.ArgumentException: exception.
Please find a minimal working example below:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

	<ItemGroup>
		<PackageReference Include="System.CommandLine.Hosting" Version="0.4.0-alpha.22272.1" />
		<PackageReference Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
	</ItemGroup>

</Project>

using System.CommandLine;
using System.CommandLine.Builder;
using System.CommandLine.NamingConventionBinder;
using System.CommandLine.Parsing;

RootCommand rootCommand = new()
{
    new TestCommand(),
};

Parser parser = new CommandLineBuilder(rootCommand).UseDefaults().Build();
return parser.Invoke(args);

internal class TestCommand : Command
{
    public TestCommand() : base("test", "")
    {
        AddArgument(new Argument<FileSystemInfo[]>("path", "Input path."));

        AddOption(new Option<DirectoryInfo>(new[] { "--outpath", "-o" }, "Output path."));

        Handler = CommandHandler.Create<FileSystemInfo[], DirectoryInfo>(Action);
    }
    private int Action(FileSystemInfo[] path, DirectoryInfo outpath)
    {
        Console.WriteLine("testing");
        return 0;
    }
}

Exception:

Unhandled exception: System.ArgumentException: Type System.String cannot be created without a custom binder.
   at System.CommandLine.Binding.ArgumentConverter.CreateEnumerable(Type type, Type itemType, Int32 capacity)
   at System.CommandLine.Binding.ArgumentConverter.ConvertTokens(Argument argument, Type type, IReadOnlyList`1 tokens, LocalizationResources localizationResources, ArgumentResult argumentResult)
   at System.CommandLine.Binding.ArgumentConverter.ConvertObject(Argument argument, Type type, Object value, LocalizationResources localizationResources)
   at System.CommandLine.Binding.BindingContext.TryBindToScalarValue(IValueDescriptor valueDescriptor, IValueSource valueSource, LocalizationResources localizationResources, Nullable`1& boundValue)
   at System.CommandLine.NamingConventionBinder.ModelBinder.GetBoundValue(IValueSource valueSource, BindingContext bindingContext, IValueDescriptor valueDescriptor, Boolean includeMissingValues, Type parentType)
   at System.CommandLine.NamingConventionBinder.ModelBinder.GetBoundValues(IDictionary`2 bindingSources, BindingContext bindingContext, IReadOnlyList`1 valueDescriptors, Boolean enforceExplicitBinding, Type parentType, Boolean includeMissingValues)
   at System.CommandLine.NamingConventionBinder.ModelBinder.GetBestConstructorAndArgs(BindingContext bindingContext)
   at System.CommandLine.NamingConventionBinder.ModelBinder.CreateInstanceInternal(BindingContext bindingContext)
   at System.CommandLine.NamingConventionBinder.ModelBinder.GetBoundValue(IValueSource valueSource, BindingContext bindingContext, IValueDescriptor valueDescriptor, Boolean includeMissingValues, Type parentType)
   at System.CommandLine.NamingConventionBinder.ModelBinder.GetBoundValues(IDictionary`2 bindingSources, BindingContext bindingContext, IReadOnlyList`1 valueDescriptors, Boolean enforceExplicitBinding, Type parentType, Boolean includeMissingValues)
   at System.CommandLine.NamingConventionBinder.ModelBindingCommandHandler.InvokeAsync(InvocationContext context)
   at System.CommandLine.NamingConventionBinder.ModelBindingCommandHandler.Invoke(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.<>c__DisplayClass4_0.<<BuildInvocationChain>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass17_0.<<UseParseErrorReporting>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass12_0.<<UseHelp>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass22_0.<<UseVersionOption>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass19_0.<<UseTypoCorrections>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseSuggestDirective>b__18_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass16_0.<<UseParseDirective>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<RegisterWithDotnetSuggest>b__5_0>d.MoveNext()
--- End of stack trace from previous location ---
   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass8_0.<<UseExceptionHandler>b__0>d.MoveNext()```

[elgonzo]

I cannot reproduce. What args precisely are you passing?

[rfuzzo]

hmm I was passing test aaa bbb, but also happens with test E:\test E:\test

[elgonzo]

Ah, the -o option is not in your args. If i try without the -o option, i can now also reproduce.