.Net: Bug: complex function parameter passed as stringified JSON rather than deserialized objects

[adv12]

Describe the bug
Semantic Kernel attempts to call a native function with a typed array for a parameter with the stringified JSON of its content rather than the deserialized array. This only seems to happen if the array type has an enum property.

To Reproduce

Create a Semantic Kernel project with the following Program.cs:

using System.ComponentModel;
using Microsoft.SemanticKernel;
using Microsoft.SemanticKernel.ChatCompletion;
using Microsoft.SemanticKernel.Connectors.OpenAI;

string model = "gpt-4o";

Console.Write("Enter your OpenAI API key: ");
string apiKey = Console.ReadLine();
Console.Write("Enter your OpenAI OrgId: ");
string orgId = Console.ReadLine();

IKernelBuilder builder = Kernel.CreateBuilder();
builder.AddOpenAIChatCompletion(model, apiKey, orgId, null, new HttpClient(new LoggingHttpClientHandler()));
Kernel kernel = builder.Build();

kernel.ImportPluginFromType<MyPlugin>();

OpenAIPromptExecutionSettings settings =
   new() { FunctionChoiceBehavior = FunctionChoiceBehavior.Auto() };

IChatCompletionService chatCompletionService =
   kernel.GetRequiredService<IChatCompletionService>();

ChatHistory chatHistory = [];

chatHistory.AddUserMessage("Set Item1 to 5.");

foreach (var content in await chatCompletionService.GetChatMessageContentsAsync(chatHistory, settings, kernel))
{
   Console.WriteLine(content.Content);
}

enum ItemName
{
   Item1,
   Item2,
   Item3
}

class Item
{
   [Description("The name.")]
   public ItemName Name { get; set; }
   [Description("The value.")]
   public int Value { get; set; }
}

class MyPlugin
{
   [KernelFunction]
   [Description("Sets the values of the specified items.")]
   public Task SetItemValues(Kernel kernel, Item[] items)
   {
      foreach (Item item in items)
      {
         Console.WriteLine($"Setting {item.Name} to {item.Value}!");
      }
      return Task.CompletedTask;
   }
}

class LoggingHttpClientHandler : HttpClientHandler
{
   protected override async Task<HttpResponseMessage> SendAsync(
      HttpRequestMessage request, CancellationToken cancellationToken)
   {
      string content;
      if (request.Content is not null)
      {
         content = await request.Content.ReadAsStringAsync(cancellationToken);
         Console.WriteLine(content);
      }

      HttpResponseMessage response = await base.SendAsync(request, cancellationToken);
      MemoryStream responseStream = new(await response.Content.ReadAsByteArrayAsync(cancellationToken));
      Console.WriteLine(new StreamReader(responseStream).ReadToEnd());
      responseStream.Position = 0;
      response.Content = new StreamContent(responseStream);
      return response;
   }
}

When you run this program, observe that the function parameters from OpenAI are properly formed, but Semantic Kernel tries to call SetItemValues with a stringified version of the JSON rather than the deserialized Item list.

Expected behavior
MyPlugin.SetItemValues gets called with an array of 1 Item

Platform

• Language: C#
• Source: NuGet package version 1.39.0
• AI model: OpenAI:GPT-4o
• IDE: Visual Studio
• OS: Windows, Mac

[adv12]

Found my answer here: https://devblogs.microsoft.com/semantic-kernel/how-to-get-started-using-semantic-kernel-net/

"To be able to fully use this with an AI Model the Enums need to be annotated with a JsonDeserialization converter."