Fix ModelMetadata for TryParse-parameters in ApiExplorer

src/OpenApi/src/Services/OpenApiDocumentService.cs

@@ -686,10 +686,17 @@ private static Type GetTargetType(ApiDescription description, ApiParameterDescri
         var parameterType = parameter.Type is not null
             ? Nullable.GetUnderlyingType(parameter.Type) ?? parameter.Type
             : parameter.Type;
-        var requiresModelMetadataFallback = parameterType == typeof(string) && parameter.ModelMetadata.ModelType != parameter.Type;
+
+        // parameter.Type = typeof(string)
+        // parameter.ModelMetadata.Type = typeof(TEnum)
+        var requiresModelMetadataFallbackForEnum = parameterType == typeof(string)
+            && parameter.ModelMetadata.ModelType != parameter.Type
+            && parameter.ModelMetadata.ModelType.IsEnum;
         // Enums are exempt because we want to set the OpenApiSchema.Enum field when feasible.
+        // parameter.Type = typeof(TEnum), typeof(Student), typeof(ITryParse)
+        // parameter.ModelMetadata.Type = typeof(string)
         var hasTryParse = bindingMetadata?.HasTryParse == true && parameterType is not null && !parameterType.IsEnum;
-        var targetType = requiresModelMetadataFallback || hasTryParse
+        var targetType = requiresModelMetadataFallbackForEnum || hasTryParse
             ? parameter.ModelMetadata.ModelType
             : parameter.Type;
         targetType ??= typeof(string);

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

@@ -604,26 +604,35 @@ await VerifyOpenApiDocument(action, document =>
     [Route("/api/with-ambient-route-param/{versionId}")]
     private void AmbientRouteParameter() { }
 
-    [Fact]
-    public async Task SupportsRouteParameterWithCustomTryParse()
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task SupportsRouteParameterWithCustomTryParse(bool useAction)
     {
         // Arrange
         var builder = CreateBuilder();
 
         // Act
-        builder.MapGet("/api/{student}", (Student student) => { });
-        builder.MapGet("/api", () => new Student("Tester"));
+        if (!useAction)
+        {
+            builder.MapGet("/api/{student}", (Student student) => student);
+            await VerifyOpenApiDocument(builder, AssertOpenApiDocument);
+        }
+        else
+        {
+            var action = CreateActionDescriptor(nameof(GetStudent));
+            await VerifyOpenApiDocument(action, AssertOpenApiDocument);
+        }
 
         // Assert
-        await VerifyOpenApiDocument(builder, document =>
+        static void AssertOpenApiDocument(OpenApiDocument document)
         {
             // Parameter is a plain-old string when it comes from the route or query
             var operation = document.Paths["/api/{student}"].Operations[OperationType.Get];
             var parameter = Assert.Single(operation.Parameters);
             Assert.Equal("string", parameter.Schema.Type);
 
             // Type is fully serialized in the response
-            operation = document.Paths["/api"].Operations[OperationType.Get];
             var response = Assert.Single(operation.Responses).Value;
             Assert.True(response.Content.TryGetValue("application/json", out var mediaType));
             var schema = mediaType.Schema.GetEffective(document);
@@ -633,9 +642,12 @@ await VerifyOpenApiDocument(builder, document =>
                 Assert.Equal("name", property.Key);
                 Assert.Equal("string", property.Value.Type);
             });
-        });
+        }
     }
 
+    [Route("/api/{student}")]
+    private Student GetStudent(Student student) => student;
+
     public record Student(string Name)
     {
         public static bool TryParse(string value, out Student result)