Turns out you need to call MapControllerRoute instead of MapControllers for the endpoint-routing-based link generation to work.

If a controller doesn't have attributes on it, then a controller route needs to be specified with the map controller call.

Is there a test for a controller with attributes?

Is there a test for a controller with attributes?

No. I tried to add one as follows (without any groups first this time):

<a id="route-attribute-link" asp-action="Get" asp-controller="EndpointRoutingController" asp-route-id="10">Test</a>

But it generates a link to /EndpointRoutingController/Get/10 instead of /endpoint-routing/10 like expected. It appears to just be going with the MapCotrollerRoute pattern rather than using the [Route] attributes as it should, so the generated link 404s. Do you know why that happens?

I don't know exactly why. My guess is the controller has two routes, and MapCotrollerRoute is taking precedence, so the link generator is going with it.

I recommend using MapControllers with the attribute route test. Mixing the two together (convention routes and attribute routes) is a weird thing to do.