Map all true schemas to empty object schemas in OpenAPI (#57067)

* Map all true schemas to empty object schemas in OpenAPI

* Address feedback

Author: captainsafia

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

@@ -82,9 +82,9 @@ internal sealed class OpenApiSchemaService(
                 };
             }
             // STJ uses `true` in place of an empty object to represent a schema that matches
-            // anything. We override this default behavior here to match the style traditionally
-            // expected in OpenAPI documents.
-            if (type == typeof(object))
+            // anything (like the `object` type) or types with user-defined converters. We override
+            // this default behavior here to match the format expected in OpenAPI v3.
+            if (schema.GetValueKind() == JsonValueKind.True)
             {
                 schema = new JsonObject();
             }

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

@@ -3,9 +3,13 @@
 
 using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.OpenApi.Any;
 using Microsoft.OpenApi.Models;
 
@@ -462,4 +466,70 @@ private class RouteParamsWithValidationsContainer
         [MaxLength(5)]
         public string Name { get; set; }
     }
+
+    [Fact]
+    public async Task SupportsParametersWithTypeConverter()
+    {
+        // Arrange
+        var serviceCollection = new ServiceCollection();
+        serviceCollection.ConfigureHttpJsonOptions(options =>
+        {
+            options.SerializerOptions.Converters.Add(new CustomTypeConverter());
+        });
+        var builder = CreateBuilder(serviceCollection);
+
+        // Act
+        builder.MapPost("/api", (CustomType id) => { });
+
+        // Assert
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var operation = document.Paths["/api"].Operations[OperationType.Post];
+            Assert.NotNull(operation.RequestBody);
+            Assert.NotNull(operation.RequestBody.Content);
+            Assert.NotNull(operation.RequestBody.Content["application/json"]);
+            Assert.NotNull(operation.RequestBody.Content["application/json"].Schema);
+            // Type is null, it's up to the user to configure this via a custom schema
+            // transformer for types with a converter.
+            Assert.Null(operation.RequestBody.Content["application/json"].Schema.Type);
+        });
+    }
+
+    public struct CustomType { }
+
+    public class CustomTypeConverter : JsonConverter<CustomType>
+    {
+        public override CustomType Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            return new CustomType();
+        }
+
+        public override void Write(Utf8JsonWriter writer, CustomType value, JsonSerializerOptions options)
+        {
+            throw new NotImplementedException();
+        }
+    }
+
+    [Fact]
+    public async Task SupportsParameterWithDynamicType()
+    {
+        // Arrange
+        var builder = CreateBuilder();
+
+        // Act
+        builder.MapPost("/api", (dynamic id) => { });
+
+        // Assert
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var operation = document.Paths["/api"].Operations[OperationType.Post];
+            Assert.NotNull(operation.RequestBody);
+            Assert.NotNull(operation.RequestBody.Content);
+            Assert.NotNull(operation.RequestBody.Content["application/json"]);
+            Assert.NotNull(operation.RequestBody.Content["application/json"].Schema);
+            // Type is null, it's up to the user to configure this via a custom schema
+            // transformer for types with a converter.
+            Assert.Null(operation.RequestBody.Content["application/json"].Schema.Type);
+        });
+    }
 }