Skip IResult in metadata if it implements IEndpointMetadataProvider

src/Mvc/Mvc.ApiExplorer/src/ApiResponseTypeProvider.cs

@@ -231,9 +231,10 @@ internal static Dictionary<int, ApiResponseType> ReadResponseMetadata(
 
         foreach (var metadata in responseMetadata)
         {
-            // `IResult` metadata inserted for awaitable types should
-            // not be considered for response metadata.
-            if (typeof(IResult).IsAssignableFrom(metadata.Type))
+            // Skip IResult types that implement IEndpointMetadataProvider (built-in framework types like TypedResults)
+            // since they handle their own metadata population. Custom IResult implementations that don't implement
+            // IEndpointMetadataProvider should be included in response metadata for API documentation.
+            if (typeof(IResult).IsAssignableFrom(metadata.Type) && typeof(IEndpointMetadataProvider).IsAssignableFrom(metadata.Type))
             {
                 continue;
             }

src/Mvc/Mvc.ApiExplorer/test/ApiResponseTypeProviderTest.cs

@@ -811,7 +811,7 @@ public void GetApiResponseTypes_HandlesActionWithMultipleContentTypesAndProduces
     }
 
     [Fact]
-    public void GetApiResponseTypes_ReturnNoResponseTypes_IfActionWithIResultReturnType()
+    public void GetApiResponseTypes_ReturnNoResponseTypes_IfActionWithBuiltIResultReturnType()
     {
         // Arrange
         var actionDescriptor = GetControllerActionDescriptor(typeof(TestController), nameof(TestController.GetIResult));
@@ -824,6 +824,23 @@ public void GetApiResponseTypes_ReturnNoResponseTypes_IfActionWithIResultReturnT
         Assert.False(result.Any());
     }
 
+    [Fact]
+    public void GetApiResponseTypes_ReturnResponseType_IfActionHasCustomIResultReturnTypeInMetadata()
+    {
+        // Arrange
+        var actionDescriptor = GetControllerActionDescriptor(typeof(TestController), nameof(TestController.GetCustomIResult));
+        actionDescriptor.EndpointMetadata = [new ProducesResponseTypeMetadata(200, typeof(MyResponse))];
+        var provider = new ApiResponseTypeProvider(new EmptyModelMetadataProvider(), new ActionResultTypeMapper(), new MvcOptions());
+
+        // Act
+        var result = provider.GetApiResponseTypes(actionDescriptor);
+
+        // Assert
+        var response = Assert.Single(result);
+        Assert.Equal(typeof(MyResponse), response.Type);
+        Assert.Equal(200, response.StatusCode);
+    }
+
     private static ApiResponseTypeProvider GetProvider()
     {
         var mvcOptions = new MvcOptions
@@ -871,6 +888,18 @@ public class TestController
         public ActionResult<DerivedModel> PutModel(string userId, DerivedModel model) => null;
 
         public IResult GetIResult(int id) => null;
+
+        public MyResponse GetCustomIResult() => new MyResponse { Content = "Test Content" };
+    }
+
+    public class MyResponse : IResult
+    {
+        public required string Content { get; set; }
+
+        public Task ExecuteAsync(HttpContext httpContext)
+        {
+            return httpContext.Response.WriteAsJsonAsync(this);
+        }
     }
 
     private class TestOutputFormatter : OutputFormatter

src/Mvc/Mvc.ApiExplorer/test/EndpointMetadataApiDescriptionProviderTest.cs

@@ -628,6 +628,32 @@ async Task<Results<Created<InferredJsonClass>, ProblemHttpResult>> () =>
         Assert.Empty(badRequestResponseType.ApiResponseFormats);
     }
 
+    [Fact]
+    public void ResponseProducesMetadataWithIResultImplementor()
+    {
+        var apiDescription = GetApiDescription(
+            [ProducesResponseType(typeof(CustomIResultImplementor), StatusCodes.Status200OK)] () => new CustomIResultImplementor { Content = "Hello, World!" });
+
+        var okResponseType = Assert.Single(apiDescription.SupportedResponseTypes);
+
+        Assert.Equal(200, okResponseType.StatusCode);
+        Assert.Equal(typeof(CustomIResultImplementor), okResponseType.Type);
+        Assert.Equal(typeof(CustomIResultImplementor), okResponseType.ModelMetadata?.ModelType);
+
+        var okResponseFormat = Assert.Single(okResponseType.ApiResponseFormats);
+        Assert.Equal("application/json", okResponseFormat.MediaType);
+    }
+
+    public class CustomIResultImplementor : IResult
+    {
+        public required string Content { get; set; }
+
+        public Task ExecuteAsync(HttpContext httpContext)
+        {
+            return httpContext.Response.WriteAsJsonAsync(this);
+        }
+    }
+
     [Fact]
     public void AddsFromRouteParameterAsPath()
     {

src/OpenApi/sample/Endpoints/MapSchemasEndpoints.cs

@@ -39,10 +39,20 @@ public static IEndpointRouteBuilder MapSchemasEndpoints(this IEndpointRouteBuild
         schemas.MapPost("/child", (ChildObject child) => Results.Ok(child));
         schemas.MapPatch("/json-patch", (JsonPatchDocument patchDoc) => Results.NoContent());
         schemas.MapPatch("/json-patch-generic", (JsonPatchDocument<ParentObject> patchDoc) => Results.NoContent());
-
+        schemas.MapGet("/custom-iresult", () => new CustomIResultImplementor { Content = "Hello world!" })
+            .Produces<CustomIResultImplementor>(200);
         return endpointRouteBuilder;
     }
 
+    public class CustomIResultImplementor : IResult
+    {
+        public required string Content { get; set; }
+        public Task ExecuteAsync(HttpContext httpContext)
+        {
+            return Task.CompletedTask;
+        }
+    }
+
     public sealed class Category
     {
         public required string Name { get; set; }

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApi3_0/OpenApiDocumentIntegrationTests.VerifyOpenApiDocument_documentName=schemas-by-ref.verified.txt

@@ -551,6 +551,25 @@
           }
         }
       }
+    },
+    "/schemas-by-ref/custom-iresult": {
+      "get": {
+        "tags": [
+          "Sample"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/CustomIResultImplementor"
+                }
+              }
+            }
+          }
+        }
+      }
     }
   },
   "components": {
@@ -631,6 +650,17 @@
           }
         }
       },
+      "CustomIResultImplementor": {
+        "required": [
+          "content"
+        ],
+        "type": "object",
+        "properties": {
+          "content": {
+            "type": "string"
+          }
+        }
+      },
       "Item": {
         "type": "object",
         "properties": {

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApi3_1/OpenApiDocumentIntegrationTests.VerifyOpenApiDocument_documentName=schemas-by-ref.verified.txt

@@ -551,6 +551,25 @@
           }
         }
       }
+    },
+    "/schemas-by-ref/custom-iresult": {
+      "get": {
+        "tags": [
+          "Sample"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/CustomIResultImplementor"
+                }
+              }
+            }
+          }
+        }
+      }
     }
   },
   "components": {
@@ -631,6 +650,17 @@
           }
         }
       },
+      "CustomIResultImplementor": {
+        "required": [
+          "content"
+        ],
+        "type": "object",
+        "properties": {
+          "content": {
+            "type": "string"
+          }
+        }
+      },
       "Item": {
         "type": "object",
         "properties": {

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApiDocumentLocalizationTests.VerifyOpenApiDocumentIsInvariant.verified.txt

@@ -1077,6 +1077,25 @@
         }
       }
     },
+    "/schemas-by-ref/custom-iresult": {
+      "get": {
+        "tags": [
+          "Sample"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/CustomIResultImplementor"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/responses/200-add-xml": {
       "get": {
         "tags": [
@@ -1410,6 +1429,17 @@
           }
         }
       },
+      "CustomIResultImplementor": {
+        "required": [
+          "content"
+        ],
+        "type": "object",
+        "properties": {
+          "content": {
+            "type": "string"
+          }
+        }
+      },
       "IFormFile": {
         "type": "string",
         "format": "binary"