nullable

Author: BrennanConroy

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

@@ -218,7 +218,8 @@ private static ParameterDescriptor CreateParameterDescriptor(ParameterInfo param
             else if (parameter.ParameterType == typeof(string) || ParameterBindingMethodCache.HasTryParseMethod(parameter))
             {
                 // complex types will display as strings since they use custom parsing via TryParse on a string
-                var displayType = !parameter.ParameterType.IsPrimitive ? typeof(string) : parameter.ParameterType;
+                var displayType = !parameter.ParameterType.IsPrimitive && Nullable.GetUnderlyingType(parameter.ParameterType)?.IsPrimitive != true
+                    ? typeof(string) : parameter.ParameterType;
                 // Path vs query cannot be determined by RequestDelegateFactory at startup currently because of the layering, but can be done here.
                 if (parameter.Name is { } name && pattern.GetParameter(name) is not null)
                 {

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

@@ -285,7 +285,7 @@ static void AssertPathParameter(ApiDescription apiDescription)
         }
 
         [Fact]
-        public void AddsFromRouteParameterAsPathWithPrimitiveTypeWithTryParse()
+        public void AddsFromRouteParameterAsPathWithPrimitiveType()
         {
             static void AssertPathParameter(ApiDescription apiDescription)
             {
@@ -298,6 +298,20 @@ static void AssertPathParameter(ApiDescription apiDescription)
             AssertPathParameter(GetApiDescription((int foo) => { }, "/{foo}"));
         }
 
+        [Fact]
+        public void AddsFromRouteParameterAsPathWithNullablePrimitiveType()
+        {
+            static void AssertPathParameter(ApiDescription apiDescription)
+            {
+                var param = Assert.Single(apiDescription.ParameterDescriptions);
+                Assert.Equal(typeof(int?), param.Type);
+                Assert.Equal(typeof(int?), param.ModelMetadata.ModelType);
+                Assert.Equal(BindingSource.Path, param.Source);
+            }
+
+            AssertPathParameter(GetApiDescription((int? foo) => { }, "/{foo}"));
+        }
+
         [Fact]
         public void AddsFromRouteParameterAsPathWithStructTypeWithTryParse()
         {