[aspnetcore] Implement c# server through inheritance and abstract override

Description

I want to write a yaml OpenAPI specification and generate a c# client and server from it (I do not want to generate the yaml for the c# server code.).

The code generator generates something similar to this:

  [ApiController]
    public class PetApiController : ControllerBase, IPetApiController
    { 
        /// <summary>
        /// Deletes a pet
        /// </summary>
        /// <param name="petId">Pet id to delete</param>
        /// <param name="apiKey"></param>
        /// <response code="400">Invalid ID supplied</response>
        /// <response code="404">Pet not found</response>
        [HttpDelete]
        [Route("/v2/pet/{petId}")]
        [ValidateModelState]
        [SwaggerOperation("DeletePet")]
        public virtual IActionResult DeletePet([FromRoute][Required]long? petId, [FromHeader]string apiKey)
        { 
            //TODO: Uncomment the next line to return response 400 or use other options such as return this.NotFound(), return this.BadRequest(..), ...
            // return StatusCode(400);

            //TODO: Uncomment the next line to return response 404 or use other options such as return this.NotFound(), return this.BadRequest(..), ...
            // return StatusCode(404);

            throw new NotImplementedException();
        }
}

What I want to do is to Not touch anything of the generated code, inherit this class and implement it:

    public class TestController : PetApiController
    {
        public override IActionResult DeletePet(long? petId, string apiKey)
        {
            // TODO my new implementation goes here.
            throw new NotImplementedException();
        }
    }

But I will get an error, that the path/route is used twice:

Exception thrown: 'System.IO.FileNotFoundException' in System.Private.CoreLib.dll
'dotnet.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.2.5\System.Reflection.Emit.dll'. 
'dotnet.exe' (CoreCLR: clrhost): Loaded 'Microsoft.GeneratedCode'. 
'dotnet.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.2.5\System.Reflection.Extensions.dll'. 
'dotnet.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.2.5\System.Reflection.TypeExtensions.dll'. 
Exception thrown: 'System.NotSupportedException' in Swashbuckle.AspNetCore.SwaggerGen.dll
Exception thrown: 'System.NotSupportedException' in System.Private.CoreLib.dll
Exception thrown: 'System.NotSupportedException' in System.Private.CoreLib.dll
Exception thrown: 'System.NotSupportedException' in System.Private.CoreLib.dll
Exception thrown: 'System.NotSupportedException' in System.Private.CoreLib.dll
'dotnet.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.2.5\System.Diagnostics.StackTrace.dll'. 
'dotnet.exe' (CoreCLR: clrhost): Loaded 'C:\Program Files\dotnet\shared\Microsoft.NETCore.App\2.2.5\System.Reflection.Metadata.dll'. 
Microsoft.AspNetCore.Server.Kestrel:Error: Connection id "0HLSKRN7E1EUJ", Request id "0HLSKRN7E1EUJ:00000002": An unhandled exception was thrown by the application.

System.NotSupportedException: HTTP method "GET" & path "v2/pet/{petId}" overloaded by actions - IO.Swagger.Controllers.TestController.GetPetById (IO.Swagger),IO.Swagger.Controllers.TestController.GetPetById2 (IO.Swagger). Actions require unique method/path combination for Swagger 2.0. Use ConflictingActionsResolver as a workaround
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.CreatePathItem(IEnumerable`1 apiDescriptions, ISchemaRegistry schemaRegistry)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.CreatePathItems(IEnumerable`1 apiDescriptions, ISchemaRegistry schemaRegistry)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwagger(String documentName, String host, String basePath, String[] schemes)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Server.IISIntegration.IISMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)
Microsoft.AspNetCore.Hosting.Internal.WebHost:Information: Request finished in 336.3171ms 500 
The thread 0x5560 has exited with code 0 (0x0).
The thread 0x56cc has exited with code 0 (0x0).
The thread 0x904 has exited with code 0 (0x0).

Now my Question is: How can I properly override those methods without getting this error? If I change the methods from virtual to abstract, remove the (not relevant, generated) "implementation", the error disappears.

Swagger-codegen version

3.0.15 Windows

Command line used for generation

java -jar swagger-codegen-cli-3.0.15.jar generate -i petstore.yaml -l aspnetcore

Suggest a fix/enhancement

There is very likely something I am not aware of yet, but if that is not the case, we could maybe also provide an abstract option to generate. The interface-only option does not contain any path definitions, so that is not a suitable option.

Start with the aspnetcore generator entry point and templates used by the swagger-codegen-cli command, then reproduce the duplicate-route error with petstore.yaml and the generated PetApiController/TestController. Done means the generated server can be inherited and overridden without duplicate routes, or an abstract-generation option is clearly supported and documented.