.Net: Add RetainArgumentTypes support to FunctionCallContentBuilder

Before this patch, the `FunctionCallContentBuilder` did not support retaining the
argument types. We need this to support retained argument types when not using auto
invoke function choices.

Author: ioshm

dotnet/src/SemanticKernel.Abstractions/Contents/FunctionCallContentBuilder.cs

@@ -18,7 +18,8 @@ public sealed class FunctionCallContentBuilder
     private Dictionary<string, string>? _functionCallIdsByIndex = null;
     private Dictionary<string, string>? _functionNamesByIndex = null;
     private Dictionary<string, StringBuilder>? _functionArgumentBuildersByIndex = null;
-    private readonly JsonSerializerOptions? _jsonSerializerOptions;
+    private readonly JsonSerializerOptions? _jsonSerializerOptions = null;
+    private readonly bool _retainArgumentTypes = false;
 
     /// <summary>
     /// Creates a new instance of the <see cref="FunctionCallContentBuilder"/> class.
@@ -33,10 +34,12 @@ public FunctionCallContentBuilder()
     /// Creates a new instance of the <see cref="FunctionCallContentBuilder"/> class.
     /// </summary>
     /// <param name="jsonSerializerOptions">The <see cref="JsonSerializerOptions"/> to use for deserializing function arguments.</param>
+    /// <param name="retainArgumentTypes">A value indicating whether the types of function arguments provided by the AI model are retained by SK or not. By default <see langword="false"/>.</param>
     [Experimental("SKEXP0120")]
-    public FunctionCallContentBuilder(JsonSerializerOptions jsonSerializerOptions)
+    public FunctionCallContentBuilder(JsonSerializerOptions? jsonSerializerOptions = null, bool retainArgumentTypes = false)
     {
         this._jsonSerializerOptions = jsonSerializerOptions;
+        this._retainArgumentTypes = retainArgumentTypes;
     }
 
     /// <summary>
@@ -146,7 +149,7 @@ public IReadOnlyList<FunctionCallContent> Build()
                 arguments = JsonSerializer.Deserialize<KernelArguments>(argumentsString);
             }
 
-            if (arguments is { Count: > 0 })
+            if (arguments is { Count: > 0 } && !this._retainArgumentTypes)
             {
                 var names = arguments.Names.ToArray();
                 foreach (var name in names)

dotnet/src/SemanticKernel.UnitTests/Contents/FunctionCallBuilder/FunctionCallContentBuilderTests.cs

@@ -212,6 +212,60 @@ public void ItShouldCaptureArgumentsDeserializationException(JsonSerializerOptio
         Assert.NotNull(functionCall.Exception);
     }
 
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public void ItShouldRetainArgumentTypesIfSpecified(bool retain)
+    {
+        // Arrange
+        var sut = new FunctionCallContentBuilder(null, retainArgumentTypes: retain);
+
+        // Act
+        var update1 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: "f_101", name: null, arguments: null);
+        sut.Append(update1);
+
+        var update2 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: "WeatherUtils-GetTemperature", arguments: null);
+        sut.Append(update2);
+
+        var update3 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: null, arguments: "{\"city\":");
+        sut.Append(update3);
+
+        var update4 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: null, arguments: "\"Seattle\",");
+        sut.Append(update4);
+
+        var update5 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: null, arguments: "\"temperature\":");
+        sut.Append(update5);
+
+        var update6 = CreateStreamingContentWithFunctionCallUpdate(choiceIndex: 1, functionCallIndex: 2, callId: null, name: null, arguments: "20}");
+        sut.Append(update6);
+
+        var functionCalls = sut.Build();
+
+        // Assert
+        var functionCall = Assert.Single(functionCalls);
+
+        Assert.Equal("f_101", functionCall.Id);
+        Assert.Equal("WeatherUtils", functionCall.PluginName);
+        Assert.Equal("GetTemperature", functionCall.FunctionName);
+        Assert.NotNull(functionCall.Arguments);
+
+        if (retain)
+        {
+            var city = Assert.IsType<JsonElement>(functionCall.Arguments?["city"]);
+            Assert.Equal(JsonValueKind.String, city.ValueKind);
+            Assert.Equal("Seattle", city.GetString());
+
+            var temperature = Assert.IsType<JsonElement>(functionCall.Arguments?["temperature"]);
+            Assert.Equal(JsonValueKind.Number, temperature.ValueKind);
+            Assert.Equal(20, temperature.GetInt32());
+        }
+        else
+        {
+            Assert.Equal("Seattle", functionCall.Arguments?["city"]);
+            Assert.Equal("20", functionCall.Arguments?["temperature"]);
+        }
+    }
+
     private static StreamingChatMessageContent CreateStreamingContentWithFunctionCallUpdate(int choiceIndex, int functionCallIndex, string? callId, string? name, string? arguments, int requestIndex = 0)
     {
         var content = new StreamingChatMessageContent(AuthorRole.Assistant, null);