Add logging for OpenAPI schema default value type mismatches

src/OpenApi/src/Extensions/JsonNodeSchemaExtensions.cs

@@ -15,6 +15,7 @@
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Constraints;
+using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.OpenApi;
 
@@ -170,7 +171,8 @@ internal static void ApplyValidationAttributes(this JsonNode schema, IEnumerable
     /// <param name="schema">The <see cref="JsonNode"/> produced by the underlying schema generator.</param>
     /// <param name="defaultValue">An object representing the <see cref="object"/> associated with the default value.</param>
     /// <param name="jsonTypeInfo">The <see cref="JsonTypeInfo"/> associated with the target type.</param>
-    internal static void ApplyDefaultValue(this JsonNode schema, object? defaultValue, JsonTypeInfo? jsonTypeInfo)
+    /// <param name="logger">The logger to use for warning messages when default value type mismatches occur.</param>
+    internal static void ApplyDefaultValue(this JsonNode schema, object? defaultValue, JsonTypeInfo? jsonTypeInfo, ILogger? logger = null)
     {
         if (jsonTypeInfo is null)
         {
@@ -183,7 +185,16 @@ internal static void ApplyDefaultValue(this JsonNode schema, object? defaultValu
         }
         else
         {
-            schema[OpenApiSchemaKeywords.DefaultKeyword] = JsonSerializer.SerializeToNode(defaultValue, jsonTypeInfo);
+            try
+            {
+                schema[OpenApiSchemaKeywords.DefaultKeyword] = JsonSerializer.SerializeToNode(defaultValue, jsonTypeInfo);
+            }
+            catch (Exception ex) when (ex is InvalidCastException or NotSupportedException or InvalidOperationException)
+            {
+                // Log warning when there's a type mismatch that prevents serialization
+                logger?.DefaultValueTypeMismatch(defaultValue.GetType().Name, jsonTypeInfo.Type.Name);
+                // Do not apply the default value when there's a type mismatch
+            }
         }
     }
 
@@ -305,7 +316,8 @@ internal static void ApplyRouteConstraints(this JsonNode schema, IEnumerable<IRo
     /// <param name="schema">The <see cref="JsonNode"/> produced by the underlying schema generator.</param>
     /// <param name="parameterDescription">The <see cref="ApiParameterDescription"/> associated with the <see paramref="schema"/>.</param>
     /// <param name="jsonTypeInfo">The <see cref="JsonTypeInfo"/> associated with the <see paramref="schema"/>.</param>
-    internal static void ApplyParameterInfo(this JsonNode schema, ApiParameterDescription parameterDescription, JsonTypeInfo? jsonTypeInfo)
+    /// <param name="logger">The logger to use for warning messages when default value type mismatches occur.</param>
+    internal static void ApplyParameterInfo(this JsonNode schema, ApiParameterDescription parameterDescription, JsonTypeInfo? jsonTypeInfo, ILogger? logger = null)
     {
         // This is special handling for parameters that are not bound from the body but represented in a complex type.
         // For example:
@@ -338,11 +350,11 @@ internal static void ApplyParameterInfo(this JsonNode schema, ApiParameterDescri
         {
             if (parameterInfo.HasDefaultValue)
             {
-                schema.ApplyDefaultValue(parameterInfo.DefaultValue, jsonTypeInfo);
+                schema.ApplyDefaultValue(parameterInfo.DefaultValue, jsonTypeInfo, logger);
             }
             else if (parameterInfo.GetCustomAttributes<DefaultValueAttribute>().LastOrDefault() is { } defaultValueAttribute)
             {
-                schema.ApplyDefaultValue(defaultValueAttribute.Value, jsonTypeInfo);
+                schema.ApplyDefaultValue(defaultValueAttribute.Value, jsonTypeInfo, logger);
             }
 
             if (parameterInfo.GetCustomAttributes<ValidationAttribute>() is { } validationAttributes)

src/OpenApi/src/Extensions/OpenApiLoggingExtensions.cs

@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.AspNetCore.OpenApi;
+
+internal static partial class OpenApiLoggingExtensions
+{
+    [LoggerMessage(1, LogLevel.Warning, "Failed to apply default value for parameter due to type mismatch. Default value type: '{DefaultValueType}', Parameter type: '{ParameterType}'. Default value will be omitted from the OpenAPI schema.", EventName = "DefaultValueTypeMismatch")]
+    public static partial void DefaultValueTypeMismatch(this ILogger logger, string defaultValueType, string parameterType);
+}

src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs

@@ -16,6 +16,7 @@
 using Microsoft.AspNetCore.Mvc.ApiExplorer;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 
 namespace Microsoft.AspNetCore.OpenApi;
@@ -28,7 +29,8 @@ namespace Microsoft.AspNetCore.OpenApi;
 internal sealed class OpenApiSchemaService(
     [ServiceKey] string documentName,
     IOptions<JsonOptions> jsonOptions,
-    IOptionsMonitor<OpenApiOptions> optionsMonitor)
+    IOptionsMonitor<OpenApiOptions> optionsMonitor,
+    ILogger<OpenApiSchemaService>? logger = null)
 {
     private readonly ConcurrentDictionary<Type, string?> _schemaIdCache = new();
     private readonly OpenApiJsonSchemaContext _jsonSchemaContext = new(new(jsonOptions.Value.SerializerOptions));
@@ -105,7 +107,7 @@ internal sealed class OpenApiSchemaService(
                 }
                 if (attributeProvider.GetCustomAttributes(inherit: false).OfType<DefaultValueAttribute>().LastOrDefault() is DefaultValueAttribute defaultValueAttribute)
                 {
-                    schema.ApplyDefaultValue(defaultValueAttribute.Value, context.TypeInfo);
+                    schema.ApplyDefaultValue(defaultValueAttribute.Value, context.TypeInfo, logger);
                 }
                 if (attributeProvider.GetCustomAttributes(inherit: false).OfType<DescriptionAttribute>().LastOrDefault() is DescriptionAttribute descriptionAttribute)
                 {
@@ -125,7 +127,7 @@ internal async Task<OpenApiSchema> GetOrCreateUnresolvedSchemaAsync(OpenApiDocum
         var schemaAsJsonObject = CreateSchema(key);
         if (parameterDescription is not null)
         {
-            schemaAsJsonObject.ApplyParameterInfo(parameterDescription, _jsonSerializerOptions.GetTypeInfo(type));
+            schemaAsJsonObject.ApplyParameterInfo(parameterDescription, _jsonSerializerOptions.GetTypeInfo(type), logger);
         }
         // Use _jsonSchemaContext constructed from _jsonSerializerOptions to respect shared config set by end-user,
         // particularly in the case of maxDepth.

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiDocumentServiceTestsBase.cs

@@ -20,6 +20,8 @@
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Constraints;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using Microsoft.Net.Http.Headers;
 using Moq;
@@ -88,7 +90,8 @@ internal static OpenApiDocumentService CreateDocumentService(IEndpointRouteBuild
         // Set strict number handling by default to make integer type checks more straightforward
         jsonOptions.SerializerOptions.NumberHandling = System.Text.Json.Serialization.JsonNumberHandling.Strict;
 
-        var schemaService = new OpenApiSchemaService("Test", Options.Create(jsonOptions), openApiOptions.Object);
+        var logger = builder.ServiceProvider.GetService<ILogger<OpenApiSchemaService>>() ?? NullLogger<OpenApiSchemaService>.Instance;
+        var schemaService = new OpenApiSchemaService("Test", Options.Create(jsonOptions), openApiOptions.Object, logger);
         ((TestServiceProvider)builder.ServiceProvider).TestSchemaService = schemaService;
         var documentService = new OpenApiDocumentService("Test", apiDescriptionGroupCollectionProvider, hostEnvironment, openApiOptions.Object, builder.ServiceProvider, new OpenApiTestServer());
         ((TestServiceProvider)builder.ServiceProvider).TestDocumentService = documentService;
@@ -134,7 +137,8 @@ internal static OpenApiDocumentService CreateDocumentService(IEndpointRouteBuild
         defaultJsonOptions.SerializerOptions.NumberHandling = System.Text.Json.Serialization.JsonNumberHandling.Strict;
         var jsonOptions = builder.ServiceProvider.GetService<IOptions<Microsoft.AspNetCore.Http.Json.JsonOptions>>() ?? Options.Create(defaultJsonOptions);
 
-        var schemaService = new OpenApiSchemaService("Test", jsonOptions, options.Object);
+        var logger = builder.ServiceProvider.GetService<ILogger<OpenApiSchemaService>>() ?? NullLogger<OpenApiSchemaService>.Instance;
+        var schemaService = new OpenApiSchemaService("Test", jsonOptions, options.Object, logger);
         ((TestServiceProvider)builder.ServiceProvider).TestSchemaService = schemaService;
         var documentService = new OpenApiDocumentService("Test", apiDescriptionGroupCollectionProvider, hostEnvironment, options.Object, builder.ServiceProvider, new OpenApiTestServer());
         ((TestServiceProvider)builder.ServiceProvider).TestDocumentService = documentService;

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs

@@ -14,6 +14,7 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
 
 public partial class OpenApiSchemaServiceTests : OpenApiDocumentServiceTestBase
 {
@@ -642,6 +643,50 @@ await VerifyOpenApiDocument(builder, document =>
         });
     }
 
+    public static object[][] RouteParametersWithDefaultValueTypeMismatch =>
+    [
+        // F# scenarios where type mismatch causes InvalidCastException and logging should occur
+        [([DefaultValue(10)] ulong id) => { }, (Action<string[]>)((logMessages) => 
+        {
+            Assert.Single(logMessages);
+            Assert.Contains("Failed to apply default value for parameter due to type mismatch", logMessages[0]);
+            Assert.Contains("Default value type: 'Int32', Parameter type: 'UInt64'", logMessages[0]);
+        })],
+        [([DefaultValue(10u)] ulong id) => { }, (Action<string[]>)((logMessages) => 
+        {
+            Assert.Single(logMessages);
+            Assert.Contains("Failed to apply default value for parameter due to type mismatch", logMessages[0]);
+            Assert.Contains("Default value type: 'UInt32', Parameter type: 'UInt64'", logMessages[0]);
+        })],
+    ];
+
+    [Theory]
+    [MemberData(nameof(RouteParametersWithDefaultValueTypeMismatch))]
+    public async Task GetOpenApiParameters_LogsWarningForDefaultValueTypeMismatch(Delegate requestHandler, Action<string[]> assertLogMessages)
+    {
+        // Arrange
+        var logMessages = new List<string>();
+        var serviceCollection = new ServiceCollection();
+        serviceCollection.AddSingleton<ILoggerProvider>(new TestLoggerProvider(logMessages));
+        serviceCollection.AddLogging();
+
+        var builder = CreateBuilder(serviceCollection);
+        builder.MapGet("/api/{id}", requestHandler);
+
+        // Act & Assert
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var operation = document.Paths["/api/{id}"].Operations[HttpMethod.Get];
+            var parameter = Assert.Single(operation.Parameters);
+
+            // Verify that no default value is set when there's a type mismatch
+            Assert.Null(parameter.Schema.Default);
+
+            // Verify the warning log was emitted
+            assertLogMessages(logMessages.ToArray());
+        });
+    }
+
     public struct CustomType { }
 
     public class CustomTypeConverter : JsonConverter<CustomType>
@@ -890,6 +935,48 @@ public override void Write(Utf8JsonWriter writer, EnumArrayType value, JsonSeria
         }
     }
 
+    public class TestLoggerProvider : ILoggerProvider
+    {
+        private readonly List<string> _logMessages;
+
+        public TestLoggerProvider(List<string> logMessages)
+        {
+            _logMessages = logMessages;
+        }
+
+        public ILogger CreateLogger(string categoryName)
+        {
+            return new TestLogger(_logMessages);
+        }
+
+        public void Dispose() { }
+    }
+
+    public class TestLogger : ILogger
+    {
+        private readonly List<string> _logMessages;
+
+        public TestLogger(List<string> logMessages)
+        {
+            _logMessages = logMessages;
+        }
+
+        public IDisposable BeginScope<TState>(TState state) => NullScope.Instance;
+
+        public bool IsEnabled(LogLevel logLevel) => true;
+
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+        {
+            _logMessages.Add(formatter(state, exception));
+        }
+
+        private class NullScope : IDisposable
+        {
+            public static NullScope Instance { get; } = new();
+            public void Dispose() { }
+        }
+    }
+
     [ApiController]
     [Route("[controller]/[action]")]
     private class TestFromQueryController : ControllerBase