OpenAPI: merge multiple body content types into one operation

src/OpenApi/src/Services/OpenApiDocumentService.cs

@@ -278,7 +278,6 @@ private async Task<Dictionary<OperationType, OpenApiOperation>> GetOperationsAsy
             };
 
             _operationTransformerContextCache.TryAdd(description.ActionDescriptor.Id, operationContext);
-            operations[description.GetOperationType()] = operation;
 
             // Use index-based for loop to avoid allocating an enumerator with a foreach.
             for (var i = 0; i < operationTransformers.Length; i++)
@@ -295,6 +294,24 @@ private async Task<Dictionary<OperationType, OpenApiOperation>> GetOperationsAsy
             {
                 await endpointOperationTransformer.TransformAsync(operation, operationContext, cancellationToken);
             }
+
+            var operationType = description.GetOperationType();
+            if (
+                operations.TryGetValue(operationType, out var existingOperation) &&
+                existingOperation.RequestBody?.Content is not null &&
+                operation.RequestBody is { Content.Count: > 0 }
+            )
+            {
+                // Merge additional accepted content types into the existing operation.
+                foreach (var body in operation.RequestBody.Content)
+                {
+                    existingOperation.RequestBody.Content.Add(body);
+                }
+            }
+            else
+            {
+                operations[operationType] = operation;
+            }
         }
         return operations;
     }

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiDocumentService/OpenApiDocumentServiceTests.RequestBody.cs

@@ -259,6 +259,40 @@ await VerifyOpenApiDocument(builder, document =>
         });
     }
 
+    /// <summary>
+    /// Tests documented behavior at https://learn.microsoft.com/en-us/aspnet/core/web-api/?view=aspnetcore-9.0#define-supported-request-content-types-with-the-consumes-attribute-1
+    /// </summary>
+    [Fact]
+    public async Task GetRequestBody_HandlesMultipleAcceptedContentType()
+    {
+        // Arrange
+        var builder = CreateBuilder();
+
+        // Act
+        builder.MapPost("/", [Consumes("application/json")] (TodoWithDueDate name) => { });
+        builder.MapPost("/", [Consumes("application/x-www-form-urlencoded")] ([FromForm] TodoWithDueDate name) => { });
+
+        // Assert
+        await VerifyOpenApiDocument(builder, document =>
+        {
+            var paths = Assert.Single(document.Paths.Values);
+            var operation = paths.Operations[OperationType.Post];
+            Assert.NotNull(operation.RequestBody);
+
+            Assert.Collection(operation.RequestBody.Content,
+                pair =>
+                {
+                    Assert.Equal("application/json", pair.Key);
+                    Assert.Equal("TodoWithDueDate", pair.Value.Schema.Annotations["x-schema-id"]);
+                },
+                pair =>
+                {
+                    Assert.Equal("application/x-www-form-urlencoded", pair.Key);
+                    Assert.Equal("TodoWithDueDate", pair.Value.Schema.Annotations["x-schema-id"]);
+                });
+            });
+    }
+
     [Fact]
     public async Task GetRequestBody_HandlesJsonBody()
     {