Experimental code for configuring an ASP.NET Core app using KDL rather than JSON

AspnetCoreKdlConfiguration.cs

// NOTE: This requires you to have a reference to KDL for .NET, and import the kdl-net namespace
// https://github.com/borland/kdl-net
//
// Highly experimental, but it works.
//
// NOTE: Once you have this code in your project, you can use 
//
// var config = new ConfigurationBuilder()
//    .AddKdlFile("appsettings.kdl", optional: false, reloadOnChange: false)
//
// in the same way you would for JSON

public static class KdlConfigurationExtensions
{
    public static IConfigurationBuilder AddKdlFile(this IConfigurationBuilder builder, string path, bool optional, bool reloadOnChange)
        => AddKdlFile(builder, null, path, optional, reloadOnChange);

    public static IConfigurationBuilder AddKdlFile(this IConfigurationBuilder builder, IFileProvider provider, string path, bool optional, bool reloadOnChange)
    {
        return builder.AddKdlFile(s => {
            s.FileProvider = provider;
            s.Path = path;
            s.Optional = optional;
            s.ReloadOnChange = reloadOnChange;
            s.ResolveFileProvider();
        });
    }

    public static IConfigurationBuilder AddKdlFile(this IConfigurationBuilder builder, Action<KdlConfigurationSource> configureSource)
        => builder.Add(configureSource);

    class KdlConfigurationProvider : FileConfigurationProvider
    {
        public KdlConfigurationProvider(KdlConfigurationSource source) :  base(source) { }

        public override void Load(Stream stream)
        {
            try
            {
                Data = KdlConfigurationFileParser.Parse(stream);
            }
            catch (KDLParseException e)
            {
                 throw new FormatException("Invalid KDL file", e);
            }
        }
    }

    public class KdlConfigurationSource : FileConfigurationSource
    {
        public override IConfigurationProvider Build(IConfigurationBuilder builder)
        {
            EnsureDefaults(builder);
            return new KdlConfigurationProvider(this);
        }
    }

    static class KdlConfigurationFileParser
    {
        public static Dictionary<string, string> Parse(Stream stream)
        {
            var doc = new KDLParser().Parse(stream);
            var context = new Stack<string>();
            var result = new Dictionary<string, string>();

            VisitKdlDoc(doc, context, result);

            return result;
        }

        public static void VisitKdlDoc(KDLDocument doc, Stack<string> context, Dictionary<string, string> result)
        {
            foreach (var node in doc.Nodes)
            {
                context.Push(node.Identifier);

                if (node.Child != null)
                {
                    VisitKdlDoc(node.Child, context, result);
                }
                else if (node.Args.Count > 0) // we only support really basic trivial KDL of [key value] or key { subkey value }, nothing else fancier or multiple args, props etc
                {
                    result[string.Join(':', context)] = node.Args[0].AsString().Value;
                }

                context.Pop();
            }
        }
    }
}