.Net: New Feature: Support DateTime parameters in tools for Assistants API

[joeyj]

---

name: Support DateTime parameter in tool definition for Assistants API

DateTime is currently converted to object which prevents the model from generating proper tool calls in Assistants API as object is defined as a dictionary or property bag in JSON Schema: https://json-schema.org/understanding-json-schema/reference/object

Current logic:

semantic-kernel/dotnet/src/Agents/OpenAI/Extensions/KernelFunctionExtensions.cs

Lines 62 to 94 in 43235b8

	private static string ConvertType(Type? type)
	{
	if (type is null || type == typeof(string))
	{
	return "string";
	}
	if (type == typeof(bool))
	{
	return "boolean";
	}
	if (type.IsEnum)
	{
	return "enum";
	}
	if (type.IsArray)
	{
	return "array";
	}
	return Type.GetTypeCode(type) switch
	{
	TypeCode.SByte or TypeCode.Byte or
	TypeCode.Int16 or TypeCode.UInt16 or
	TypeCode.Int32 or TypeCode.UInt32 or
	TypeCode.Int64 or TypeCode.UInt64 or
	TypeCode.Single or TypeCode.Double or TypeCode.Decimal => "number",
	_ => "object",
	};
	}

This can be worked around by changing the kernel function parameter type to string and handling type conversion manually.

By contrast, tool definitions generated for Chat Completion API are higher fidelity. For example, it converts DateTime to

{
  "type" : "string",
  "format": "date-time"
}