1197 Support [ResponseType(typeof(void))] for actions that return an IHttpActionResult with no response content

src/System.Web.Http/Description/ApiExplorer.cs

@@ -362,7 +362,7 @@ namespace System.Web.Http.Description
             // response formatters
             ResponseDescription responseDescription = CreateResponseDescription(actionDescriptor);
             Type returnType = responseDescription.ResponseType ?? responseDescription.DeclaredType;
-            IEnumerable<MediaTypeFormatter> supportedResponseFormatters = returnType != null ?
+            IEnumerable<MediaTypeFormatter> supportedResponseFormatters = (returnType != null && returnType != typeof(void)) ?
                 actionDescriptor.Configuration.Formatters.Where(f => f.CanWriteType(returnType)) :
                 Enumerable.Empty<MediaTypeFormatter>();
 

test/System.Web.Http.Integration.Test/ApiExplorer/Controllers/ResponseTypeController.cs

@@ -24,5 +24,11 @@ namespace System.Web.Http.ApiExplorer
         {
             return "User deleted";
         }
+
+        [ResponseType(typeof(void))]
+        public IHttpActionResult Head()
+        {
+            return StatusCode(HttpStatusCode.OK);
+        }
     }
 }

test/System.Web.Http.Integration.Test/ApiExplorer/ResponseTypeAttributeTest.cs

@@ -12,10 +12,11 @@ namespace System.Web.Http.ApiExplorer
     public class ResponseTypeAttributeTest
     {
         [Theory]
-        [InlineData("Get", typeof(IHttpActionResult), typeof(User))]
-        [InlineData("Post", typeof(HttpResponseMessage), typeof(User))]
-        [InlineData("Delete", typeof(string), null)]
-        public void DeclaredResponseType_AppearsOnApiDescription(string actionName, Type declaredType, Type responseType)
+        [InlineData("Get", typeof(IHttpActionResult), typeof(User), 2)]
+        [InlineData("Post", typeof(HttpResponseMessage), typeof(User), 2)]
+        [InlineData("Delete", typeof(string), null, 2)]
+        [InlineData("Head", typeof(IHttpActionResult), typeof(void), 0)]
+        public void DeclaredResponseType_AppearsOnApiDescription(string actionName, Type declaredType, Type responseType, int responseFormattersCount)
         {
             HttpConfiguration config = new HttpConfiguration();
             config.Routes.MapHttpRoute("Default", "{controller}/{id}", new { id = RouteParameter.Optional });
@@ -29,6 +30,7 @@ namespace System.Web.Http.ApiExplorer
                 api.ResponseDescription.ResponseType == responseType);
 
             Assert.NotNull(expectedApi);
+            Assert.Equal(responseFormattersCount, expectedApi.SupportedResponseFormatters.Count);
         }
     }
 }