Duplicate results shown in OData route debug view for conventional and attribute routed routes

• Latest affected version: Microsoft.AspNetCore.OData v8.0.5

The OData route debug view currently show matches for all conventions, regardless if they are duplicates. Let's take the default Weather Forecast sample for this.

If we have:

[Route("Forecasts")]
public class ForecastsController : ODataController
{
    [HttpGet]
    public IQueryable<WeatherForecast> Whatever()
    {
        return this.repository.GetForecasts();
    }

Then the debug view correctly lists GET Forecasts only once:

However, if I change the method name from Whatever to Get, it will now show the exact same route twice (due to now matching both via convention, and attribute routing):

[Route("Forecasts")]
public class ForecastsController : ODataController
{
    [HttpGet]
    public IQueryable<WeatherForecast> Get()
    {
        return this.repository.GetForecasts();
    }

The application works correctly in both cases, resolving the GET action to the same method. The way the routes are displayed in the debug view, however, is fairly confusing. IMHO, this should be fixed in one of 2 ways:

1. Remove duplicate entries from the table and only show the first matches for each route (like what the convention priority itself does normally, which will hit the attribute route and skip other conventions)
2. Add a third column to the table, to indicate which convention resulted in the route's inclusion.

1 seems simpler to me, but 2 might be of help for debugging purposes.

FYI, the exact same behavior is present for all other route types and verbs: as long as they are attribute routed and match the naming convention at the same time, they appear twice. I used the GET entityset here as an example only.