Swashbuckle/Swagger + ASP.Net Core: "Failed to load API definition"

Question

I develop an ASP.NET Core 2 application and included Swagger. Everything worked fine until I introduced a method without explicitly defining the HTTP action:

public class ErrorController : Controller
{
    [Route("/error")]
    public IActionResult Index()
    {
        return StatusCode(500, new Error("Internal error."));
    }
}

When I started the app with this method, the following message showed up:

Failed to load API definition.

Errors
Fetch error Internal Server Error /swagger/v1/swagger.json

As soon as I explicitly set e.g. [HttpGet] the error disappears. The problem with this is, I need this method to fire for all possible HTTP operations. Of course, I could specify all operations explicitly, but I have the feeling Swagger should be able to handle this correctly.

Why does Swagger behave this way?

Is there any configuration I can use?

services.AddSwaggerGen(c => 
{   
  c.SwaggerDoc("v1", new Info { Title = "My Service", Version = "v1" }); 
});  

app.UseSwagger(c => 
{   
  c.PreSerializeFilters.Add((swagger, httpReq) => swagger.Host = httpReq.Host.Value); 
});  

app.UseSwaggerUI(c => 
{   
  c.RoutePrefix = "swagger"; // serve the UI at root     
  c.SwaggerEndpoint("/swagger/v1/swagger.json", "V1 Docs"); 
})

Answer 1

The option ResolveConflictingActions should be working on this case...

Here is the actual error:

System.NotSupportedException: Ambiguous HTTP method for action

That is coming from: https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/86cc761bc4f5dda796f80ad8dfd8bc205542a6f6/src/Swashbuckle.AspNetCore.SwaggerGen/Generator/SwaggerGenerator.cs#L90

I think this is a bug, if you are truly interested you should report it to the project