.Net: Fix 5796 function calling enum params (#5998)

### Motivation and Context

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Fixes #5796

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

Type for enum wasn't correctly set in JsonSchemaMapper, it didn't matter
for OpenAI but gemini was throwing exception if type isn't specified.
Fixed that with `string` type.
Added new unit tests for Gemini and OpenAI. Both passed.

@RogerBarreto 
@SergeyMenshykh

DataHelper and BertOnyx was updated automatically by formatter.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Roger Barreto <19890735+RogerBarreto@users.noreply.github.com>

dotnet/samples/GettingStarted/Step7_Observability.cs

@@ -77,7 +77,7 @@ void MyInvokedHandler(object? sender, FunctionInvokedEventArgs e)
         {
             if (e.Result.Metadata is not null && e.Result.Metadata.ContainsKey("Usage"))
             {
-                Console.WriteLine($"Token usage: {e.Result.Metadata?["Usage"]?.AsJson()}");
+                Console.WriteLine("Token usage: {0}", e.Result.Metadata?["Usage"]?.AsJson());
             }
         }
 

dotnet/src/Connectors/Connectors.Google.UnitTests/Extensions/KernelFunctionMetadataExtensionsTests.cs

@@ -200,7 +200,7 @@ public void ItCanCreateValidGeminiFunctionManualForPlugin()
         // Assert
         Assert.NotNull(result);
         Assert.Equal(
-            """{"type":"object","required":["parameter1","parameter2","parameter3"],"properties":{"parameter1":{"type":"string","description":"String parameter"},"parameter2":{"enum":["Value1","Value2"],"description":"Enum parameter"},"parameter3":{"type":"string","format":"date-time","description":"DateTime parameter"}}}""",
+            """{"type":"object","required":["parameter1","parameter2","parameter3"],"properties":{"parameter1":{"type":"string","description":"String parameter"},"parameter2":{"type":"string","enum":["Value1","Value2"],"description":"Enum parameter"},"parameter3":{"type":"string","format":"date-time","description":"DateTime parameter"}}}""",
             JsonSerializer.Serialize(result.Parameters)
         );
     }

dotnet/src/Connectors/Connectors.UnitTests/OpenAI/FunctionCalling/KernelFunctionMetadataExtensionsTests.cs

@@ -196,7 +196,7 @@ public void ItCanCreateValidOpenAIFunctionManualForPlugin()
         // Assert
         Assert.NotNull(result);
         Assert.Equal(
-            """{"type":"object","required":["parameter1","parameter2","parameter3"],"properties":{"parameter1":{"type":"string","description":"String parameter"},"parameter2":{"enum":["Value1","Value2"],"description":"Enum parameter"},"parameter3":{"type":"string","format":"date-time","description":"DateTime parameter"}}}""",
+            """{"type":"object","required":["parameter1","parameter2","parameter3"],"properties":{"parameter1":{"type":"string","description":"String parameter"},"parameter2":{"type":"string","enum":["Value1","Value2"],"description":"Enum parameter"},"parameter3":{"type":"string","format":"date-time","description":"DateTime parameter"}}}""",
             result.Parameters.ToString()
         );
     }

dotnet/src/IntegrationTests/Connectors/GoogleVertexAI/EmbeddingGenerationTests.cs → dotnet/src/IntegrationTests/Connectors/Google/EmbeddingGenerationTests.cs

@@ -6,7 +6,7 @@
 using Xunit;
 using Xunit.Abstractions;
 
-namespace SemanticKernel.IntegrationTests.Connectors.GoogleVertexAI;
+namespace SemanticKernel.IntegrationTests.Connectors.Google;
 
 public sealed class EmbeddingGenerationTests(ITestOutputHelper output) : TestsBase(output)
 {

dotnet/src/IntegrationTests/Connectors/GoogleVertexAI/Gemini/GeminiChatCompletionTests.cs → dotnet/src/IntegrationTests/Connectors/Google/Gemini/GeminiChatCompletionTests.cs

@@ -12,7 +12,7 @@
 using Xunit;
 using Xunit.Abstractions;
 
-namespace SemanticKernel.IntegrationTests.Connectors.GoogleVertexAI.Gemini;
+namespace SemanticKernel.IntegrationTests.Connectors.Google.Gemini;
 
 public sealed class GeminiChatCompletionTests(ITestOutputHelper output) : TestsBase(output)
 {

dotnet/src/IntegrationTests/Connectors/GoogleVertexAI/Gemini/GeminiFunctionCallingTests.cs → dotnet/src/IntegrationTests/Connectors/Google/Gemini/GeminiFunctionCallingTests.cs

@@ -4,14 +4,15 @@
 using System.ComponentModel;
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.Extensions.Time.Testing;
 using Microsoft.SemanticKernel;
 using Microsoft.SemanticKernel.ChatCompletion;
 using Microsoft.SemanticKernel.Connectors.Google;
 using xRetry;
 using Xunit;
 using Xunit.Abstractions;
 
-namespace SemanticKernel.IntegrationTests.Connectors.GoogleVertexAI.Gemini;
+namespace SemanticKernel.IntegrationTests.Connectors.Google.Gemini;
 
 public sealed class GeminiFunctionCallingTests(ITestOutputHelper output) : TestsBase(output)
 {
@@ -291,6 +292,64 @@ public async Task ChatStreamingAutoInvokeTwoPluginsShouldGetDateAndReturnTasksBy
         Assert.Contains("5", content, StringComparison.OrdinalIgnoreCase);
     }
 
+    [RetryTheory]
+    [InlineData(ServiceType.GoogleAI, Skip = "This test is for manual verification.")]
+    [InlineData(ServiceType.VertexAI, Skip = "This test is for manual verification.")]
+    public async Task ChatGenerationAutoInvokeShouldCallFunctionWithEnumParameterAndReturnResponseAsync(ServiceType serviceType)
+    {
+        // Arrange
+        var kernel = new Kernel();
+        var timeProvider = new FakeTimeProvider();
+        timeProvider.SetUtcNow(new DateTimeOffset(new DateTime(2024, 4, 24))); // Wednesday
+        var timePlugin = new TimePlugin(timeProvider);
+        kernel.ImportPluginFromObject(timePlugin, nameof(TimePlugin));
+        var sut = this.GetChatService(serviceType);
+        var chatHistory = new ChatHistory();
+        chatHistory.AddUserMessage("When was last friday? Show the date in format DD.MM.YYYY for example: 15.07.2019");
+        var executionSettings = new GeminiPromptExecutionSettings()
+        {
+            MaxTokens = 2000,
+            ToolCallBehavior = GeminiToolCallBehavior.AutoInvokeKernelFunctions,
+        };
+
+        // Act
+        var response = await sut.GetChatMessageContentAsync(chatHistory, executionSettings, kernel);
+
+        // Assert
+        this.Output.WriteLine(response.Content);
+        Assert.Contains("19.04.2024", response.Content, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [RetryTheory]
+    [InlineData(ServiceType.GoogleAI, Skip = "This test is for manual verification.")]
+    [InlineData(ServiceType.VertexAI, Skip = "This test is for manual verification.")]
+    public async Task ChatStreamingAutoInvokeShouldCallFunctionWithEnumParameterAndReturnResponseAsync(ServiceType serviceType)
+    {
+        // Arrange
+        var kernel = new Kernel();
+        var timeProvider = new FakeTimeProvider();
+        timeProvider.SetUtcNow(new DateTimeOffset(new DateTime(2024, 4, 24))); // Wednesday
+        var timePlugin = new TimePlugin(timeProvider);
+        kernel.ImportPluginFromObject(timePlugin, nameof(TimePlugin));
+        var sut = this.GetChatService(serviceType);
+        var chatHistory = new ChatHistory();
+        chatHistory.AddUserMessage("When was last friday? Show the date in format DD.MM.YYYY for example: 15.07.2019");
+        var executionSettings = new GeminiPromptExecutionSettings()
+        {
+            MaxTokens = 2000,
+            ToolCallBehavior = GeminiToolCallBehavior.AutoInvokeKernelFunctions,
+        };
+
+        // Act
+        var responses = await sut.GetStreamingChatMessageContentsAsync(chatHistory, executionSettings, kernel)
+            .ToListAsync();
+
+        // Assert
+        string content = string.Concat(responses.Select(c => c.Content));
+        this.Output.WriteLine(content);
+        Assert.Contains("19.04.2024", content, StringComparison.OrdinalIgnoreCase);
+    }
+
     public sealed class CustomerPlugin
     {
         [KernelFunction(nameof(GetCustomers))]
@@ -343,6 +402,37 @@ public DateTime GetDate()
         }
     }
 
+    public sealed class TimePlugin
+    {
+        private readonly TimeProvider _timeProvider;
+
+        public TimePlugin(TimeProvider timeProvider)
+        {
+            this._timeProvider = timeProvider;
+        }
+
+        [KernelFunction]
+        [Description("Get the date of the last day matching the supplied week day name in English. Example: Che giorno era 'Martedi' scorso -> dateMatchingLastDayName 'Tuesday' => Tuesday, 16 May, 2023")]
+        public string DateMatchingLastDayName(
+            [Description("The day name to match")] DayOfWeek input,
+            IFormatProvider? formatProvider = null)
+        {
+            DateTimeOffset dateTime = this._timeProvider.GetUtcNow();
+
+            // Walk backwards from the previous day for up to a week to find the matching day
+            for (int i = 1; i <= 7; ++i)
+            {
+                dateTime = dateTime.AddDays(-1);
+                if (dateTime.DayOfWeek == input)
+                {
+                    break;
+                }
+            }
+
+            return dateTime.ToString("D", formatProvider);
+        }
+    }
+
     public sealed class MathPlugin
     {
         [KernelFunction(nameof(Sum))]

dotnet/src/IntegrationTests/Connectors/GoogleVertexAI/TestsBase.cs → dotnet/src/IntegrationTests/Connectors/Google/TestsBase.cs

@@ -7,7 +7,7 @@
 using Microsoft.SemanticKernel.Embeddings;
 using Xunit.Abstractions;
 
-namespace SemanticKernel.IntegrationTests.Connectors.GoogleVertexAI;
+namespace SemanticKernel.IntegrationTests.Connectors.Google;
 
 public abstract class TestsBase(ITestOutputHelper output)
 {

dotnet/src/IntegrationTests/Connectors/OpenAI/OpenAIToolsTests.cs

@@ -9,6 +9,7 @@
 using System.Threading.Tasks;
 using Azure.AI.OpenAI;
 using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Time.Testing;
 using Microsoft.SemanticKernel;
 using Microsoft.SemanticKernel.ChatCompletion;
 using Microsoft.SemanticKernel.Connectors.OpenAI;
@@ -112,6 +113,27 @@ public async Task CanAutoInvokeKernelFunctionsWithPrimitiveTypeParametersAsync()
         Assert.Contains("10", result.GetValue<string>(), StringComparison.InvariantCulture);
     }
 
+    [Fact(Skip = "OpenAI is throttling requests. Switch this test to use Azure OpenAI.")]
+    public async Task CanAutoInvokeKernelFunctionsWithEnumTypeParametersAsync()
+    {
+        // Arrange
+        Kernel kernel = this.InitializeKernel();
+        var timeProvider = new FakeTimeProvider();
+        timeProvider.SetUtcNow(new DateTimeOffset(new DateTime(2024, 4, 24))); // Wednesday
+        var timePlugin = new TimePlugin(timeProvider);
+        kernel.ImportPluginFromObject(timePlugin, nameof(TimePlugin));
+
+        // Act
+        OpenAIPromptExecutionSettings settings = new() { ToolCallBehavior = ToolCallBehavior.AutoInvokeKernelFunctions };
+        var result = await kernel.InvokePromptAsync(
+            "When was last friday? Show the date in format DD.MM.YYYY for example: 15.07.2019",
+            new(settings));
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.Contains("19.04.2024", result.GetValue<string>(), StringComparison.OrdinalIgnoreCase);
+    }
+
     [Fact]
     public async Task CanAutoInvokeKernelFunctionFromPromptAsync()
     {
@@ -550,4 +572,35 @@ public Task OnFunctionInvocationAsync(FunctionInvocationContext context, Func<Fu
     }
 
     #endregion
+
+    public sealed class TimePlugin
+    {
+        private readonly TimeProvider _timeProvider;
+
+        public TimePlugin(TimeProvider timeProvider)
+        {
+            this._timeProvider = timeProvider;
+        }
+
+        [KernelFunction]
+        [Description("Get the date of the last day matching the supplied week day name in English. Example: Che giorno era 'Martedi' scorso -> dateMatchingLastDayName 'Tuesday' => Tuesday, 16 May, 2023")]
+        public string DateMatchingLastDayName(
+            [Description("The day name to match")] DayOfWeek input,
+            IFormatProvider? formatProvider = null)
+        {
+            DateTimeOffset dateTime = this._timeProvider.GetUtcNow();
+
+            // Walk backwards from the previous day for up to a week to find the matching day
+            for (int i = 1; i <= 7; ++i)
+            {
+                dateTime = dateTime.AddDays(-1);
+                if (dateTime.DayOfWeek == input)
+                {
+                    break;
+                }
+            }
+
+            return dateTime.ToString("D", formatProvider);
+        }
+    }
 }

dotnet/src/IntegrationTests/IntegrationTests.csproj

@@ -32,6 +32,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" />
     <PackageReference Include="Microsoft.Extensions.Http" />
     <PackageReference Include="Microsoft.Extensions.Http.Resilience" />
+    <PackageReference Include="Microsoft.Extensions.TimeProvider.Testing" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="System.Linq.Async" />
     <PackageReference Include="xRetry" />

dotnet/src/InternalUtilities/src/Schema/JsonSchemaMapper.cs

@@ -173,6 +173,7 @@ private static JsonObject MapJsonSchemaCore(
         string? title = null,
         string? description = null,
         bool isNullableReferenceType = false,
+        bool isNullableOfTElement = false,
         JsonConverter? customConverter = null,
         bool hasDefaultValue = false,
         JsonNode? defaultValue = null,
@@ -186,7 +187,7 @@ private static JsonObject MapJsonSchemaCore(
         JsonConverter effectiveConverter = customConverter ?? typeInfo.Converter;
         JsonNumberHandling? effectiveNumberHandling = customNumberHandling ?? typeInfo.NumberHandling;
         bool emitsTypeDiscriminator = derivedTypeDiscriminator?.Value is not null;
-        bool isCacheable = !emitsTypeDiscriminator && description is null && !hasDefaultValue;
+        bool isCacheable = !emitsTypeDiscriminator && description is null && !hasDefaultValue && !isNullableOfTElement;
 
         if (!IsBuiltInConverter(effectiveConverter))
         {
@@ -220,7 +221,8 @@ private static JsonObject MapJsonSchemaCore(
                 defaultValue: defaultValue,
                 customNumberHandling: customNumberHandling,
                 customConverter: customConverter,
-                parentNullableOfT: type);
+                parentNullableOfT: type,
+                isNullableOfTElement: true);
         }
 
         if (isCacheable && typeInfo.Kind != JsonTypeInfoKind.None)
@@ -319,23 +321,15 @@ private static JsonObject MapJsonSchemaCore(
                 }
                 else if (type.IsEnum)
                 {
-                    if (TryGetStringEnumConverterValues(typeInfo, effectiveConverter, out JsonArray? values))
+                    if (TryGetStringEnumConverterValues(typeInfo, effectiveConverter, out enumValues))
                     {
-                        if (values is null)
-                        {
-                            // enum declared with the flags attribute -- do not surface enum values in the JSON schema.
-                            schemaType = JsonSchemaType.String;
-                        }
-                        else
+                        schemaType = JsonSchemaType.String;
+
+                        if (enumValues != null && isNullableOfTElement)
                         {
-                            if (parentNullableOfT is not null)
-                            {
-                                // We're generating the schema for a nullable
-                                // enum type. Append null to the "enum" array.
-                                values.Add(null);
-                            }
-
-                            enumValues = values;
+                            // We're generating the schema for a nullable
+                            // enum type. Append null to the "enum" array.
+                            enumValues.Add(null);
                         }
                     }
                     else
@@ -417,15 +411,15 @@ private static JsonObject MapJsonSchemaCore(
 
                     state.Push(property.Name);
                     JsonObject propertySchema = MapJsonSchemaCore(
-                        propertyTypeInfo,
-                        ref state,
+                        typeInfo: propertyTypeInfo,
+                        state: ref state,
                         title: null,
-                        propertyDescription,
-                        isPropertyNullableReferenceType,
-                        property.CustomConverter,
-                        propertyHasDefaultValue,
-                        propertyDefaultValue,
-                        propertyNumberHandling);
+                        description: propertyDescription,
+                        isNullableReferenceType: isPropertyNullableReferenceType,
+                        customConverter: property.CustomConverter,
+                        hasDefaultValue: propertyHasDefaultValue,
+                        defaultValue: propertyDefaultValue,
+                        customNumberHandling: propertyNumberHandling);
 
                     state.Pop();