Original address

https://github.com/RicoSuter/NSwag/issues/3584

Environment

ASP.NETCore：3.1

NSwag.AspNetCore：13.13.0

Throws an error

System.InvalidOperationException: Method may only be called on a Type for which Type.IsGenericParameter is true.
   at System.RuntimeType.get_GenericParameterPosition()
   at Namotion.Reflection.ContextualType.<get_Properties>b__42_0(PropertyInfo property)
   at System.Linq.Enumerable.SelectArrayIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Namotion.Reflection.ContextualType.get_Properties()
   at Namotion.Reflection.ContextualTypeExtensions.GetContextualProperties(Type type)
   at NJsonSchema.Generation.JsonSchemaGenerator.ApplyAdditionalProperties[TSchemaType](TSchemaType schema, Type type, JsonSchemaResolver schemaResolver)
   at NJsonSchema.Generation.JsonSchemaGenerator.GenerateObject(JsonSchema schema, JsonTypeDescription typeDescription, JsonSchemaResolver schemaResolver)
   at NSwag.Generation.OpenApiSchemaGenerator.GenerateObject(JsonSchema schema, JsonTypeDescription typeDescription, JsonSchemaResolver schemaResolver)
   at NJsonSchema.Generation.JsonSchemaGenerator.Generate[TSchemaType](TSchemaType schema, ContextualType contextualType, JsonSchemaResolver schemaResolver)
   at NJsonSchema.Generation.JsonSchemaGenerator.Generate[TSchemaType](ContextualType contextualType, JsonSchemaResolver schemaResolver)
   at NJsonSchema.Generation.JsonSchemaGenerator.GenerateWithReferenceAndNullability[TSchemaType](ContextualType contextualType, Boolean isNullable, JsonSchemaResolver schemaResolver, Action`2 transformation)
   at NSwag.Generation.OpenApiSchemaGenerator.GenerateWithReferenceAndNullability[TSchemaType](ContextualType contextualType, Boolean isNullable, JsonSchemaResolver schemaResolver, Action`2 transformation)
   at NSwag.Generation.AspNetCore.Processors.OperationResponseProcessor.Process(OperationProcessorContext operationProcessorContext)
   at NSwag.Generation.AspNetCore.AspNetCoreOpenApiDocumentGenerator.RunOperationProcessors(OpenApiDocument document, ApiDescription apiDescription, Type controllerType, MethodInfo methodInfo, OpenApiOperationDescription operationDescription, List`1 allOperations, OpenApiDocumentGenerator swaggerGenerator, OpenApiSchemaResolver schemaResolver)
   at NSwag.Generation.AspNetCore.AspNetCoreOpenApiDocumentGenerator.AddOperationDescriptionsToDocument(OpenApiDocument document, Type controllerType, List`1 operations, OpenApiDocumentGenerator swaggerGenerator, OpenApiSchemaResolver schemaResolver)
   at NSwag.Generation.AspNetCore.AspNetCoreOpenApiDocumentGenerator.GenerateForControllers(OpenApiDocument document, IGrouping`2[] apiGroups, OpenApiSchemaResolver schemaResolver)
   at NSwag.Generation.AspNetCore.AspNetCoreOpenApiDocumentGenerator.GenerateAsync(ApiDescriptionGroupCollection apiDescriptionGroups)
   at NSwag.AspNetCore.Middlewares.OpenApiDocumentMiddleware.GenerateDocumentAsync(HttpContext context)
   at NSwag.AspNetCore.Middlewares.OpenApiDocumentMiddleware.GetDocumentAsync(HttpContext context)
   at NSwag.AspNetCore.Middlewares.OpenApiDocumentMiddleware.Invoke(HttpContext context)
   at NSwag.AspNetCore.Middlewares.SwaggerUiIndexMiddleware.Invoke(HttpContext context)
   at NSwag.AspNetCore.Middlewares.RedirectToIndexMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

Treatment plan

Upgrade NSwag.AspNetCore class library to v13.13.1

Problem description

Before modification

<PackageReference Include=”NSwag.AspNetCore” Version=”13.13.0″ />

Cannot be opened after publishing, and an error is reported when opening locally

(1) Annotated all the methods below the Controller

Then the Swagger page can be opened, but the page has no available interface

(2) In combination with the error prompt type, it is thought that the messagemodel class has a generic t data attribute, and the return value is changed along with it

Now swagger is running normally, and the action is also displayed

(3) It is determined that the exception is caused by the messagemodel generic type, but I haven’t read the specific details

After modification

< PackageReference Include=”NSwag.AspNetCore” Version=”13.13.1″ />

The messagemodel is still returned and runs normally, so it is still a problem with the nswag class library