Calling AddError in the DefaultValueFactory will cause exception when showing help

[FMsrAtLapl]

Calling AddError in the DefaultValueFactory will cause an exception when showing help
(provided the condition which triggers the error exists)

Help seemingly tries to create any default value, and in case it needs to call the AddError ( )-method
it tries to add to an internal structure which does not exist in "help-mode"

Probably it is not the best idea to add errors when creating default values
but then I took this example from the
Microsoft Tutorial

Option<FileInfo> fileOption = new("--file")
{
    Description = "An option whose argument is parsed as a FileInfo",
    Required = true,
    DefaultValueFactory = result =>
    {
        if (result.Tokens.Count == 0)
        {
            return new FileInfo("sampleQuotes.txt");

        }
        string filePath = result.Tokens.Single().Value;
        if (!File.Exists(filePath))
        {
            result.AddError("File does not exist");
            return null;
        }
        else
        {
            return new FileInfo(filePath);
        }
    }
};

[jonsequitur]

Can you provide more details or a more complete repro? I wasn't able to reproduce any issue related to AddError here.

[FMsrAtLapl]

Here is a stripped down, but complete version of the program:

1. We have a compare-Copmmand.

2. a. The DefaultValueFactory of the command compare expects a token which it will use for building the default value.
   2.b. If it doesn't find a token, it raises an error.

3. Now when you call help for this command:
   CmdLineDemo compare --help

you get an unhandled exception
when the help system is going to explain the use of the options for the compare command.

Hello, World!
Description:
compares two files

Nutzung:
CmdLineDemo compare [options]

Unhandled exception: System.NullReferenceException: Object reference not set to an instance of an object.
at System.CommandLine.Parsing.ArgumentResult.AddError(String errorMessage)
at CmdLineDemo.CompareCommandCreator.<>c.b__0_1(ArgumentResult result) in C:\Users\XXXXXX.XXXXr\Temp\DemoError\CmdLineDemo\Program.cs:line 43
at System.CommandLine.Argument1.GetDefaultValue(ArgumentResult argumentResult) at System.CommandLine.Argument.GetDefaultValue() at System.CommandLine.Option.GetDefaultValue() at System.CommandLine.Help.HelpBuilder.Default.GetArgumentDefaultValue(Symbol parameter) at System.CommandLine.Help.HelpBuilder.GetArgumentDefaultValue(Symbol parent, Symbol parameter, Boolean displayArgumentName, HelpContext context) at System.CommandLine.Help.HelpBuilder.<>c__DisplayClass21_1.<GetTwoColumnRow>b__4(Symbol argument) at System.Linq.Enumerable.ArraySelectIterator2.MoveNext()
at System.String.Join(String separator, IEnumerable`1 values)
at System.CommandLine.Help.HelpBuilder.<>c__DisplayClass21_0.g__GetSymbolDefaultValue|2(Symbol symbol)
at System.CommandLine.Help.HelpBuilder.<>c__DisplayClass21_0.g__GetOptionOrCommandRow|0()
at System.CommandLine.Help.HelpBuilder.GetTwoColumnRow(Symbol symbol, HelpContext context)
at System.CommandLine.Help.HelpBuilder.Default.<>c.b__11_0(HelpContext ctx)
at System.CommandLine.Help.HelpBuilder.Write(HelpContext context)
at System.CommandLine.Help.HelpAction.Invoke(ParseResult parseResult)
at System.CommandLine.Invocation.InvocationPipeline.Invoke(ParseResult parseResult)

using System.CommandLine;
namespace CmdLineDemo;
internal class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Hello, World!");
        var rootCommand = RootCommandCreator.CreateRootCommand();
        ParseResult parseResult = rootCommand.Parse(args);
        parseResult.Invoke();
    }
}
internal static class RootCommandCreator
{
    public static Command CreateRootCommand()
    {

        RootCommand rootCommand = new("Any Testrunner")
        {
        };
        Command compareCommand = CompareCommandCreator.CreateCommand();
        rootCommand.Subcommands.Add(compareCommand);
        return rootCommand;
    }
}
internal static class CompareCommandCreator
{
    public static Command CreateCommand()
    {
        Option<DirectoryInfo?> excelPathOption = new("--excel-path")
        {
            Description = "Path to Excel",
            Required = false,
            DefaultValueFactory = result =>
            {
                if (result.Tokens.Count == 0)
                {
                    result.AddError("No path given");
                    return null;
                }

                string directoryPath = result.Tokens.Single().Value;
                return new(directoryPath);
            }
        };
        Command compareCommand = new("compare", "compares two files") { excelPathOption };
        compareCommand.SetAction(result => { Console.WriteLine("Command executed"); });
        return compareCommand;
    }
}