EndpointDataSource empty with top-level route registrations?

[RichardD2]

I have a unit test project to ensure that all of the routes used in my API client library can be resolved to actual endpoints in the API project.

To do that, I use the registered EndpointDataSource instance(s) to list the registered endpoints, TemplateParser / TemplateMatcher to match the path, HttpMethodMetadata to check the method, IRouteConstraint to match the parameters, and EndpointSelector to select the endpoint from the matching endpoints.

ApiRouteTester.cs

If I use app.UseEndpoints(e => { ... }) to configure the endpoints, then everything works as expected. But I get an ASP0014 warning telling me I should be using top-level route registrations.

app.UseRouting();
app.UseEndpoints(e =>
{
    e.MapControllers();
    e.MapMyMinimalApis(); // Custom extension method
});

If I switch to using top-level route registrations, then the EndpointDataSource is completely empty.

app.UseRouting();
app.MapControllers();
app.MapMyMinimalApis();

Is this expected? Is the EndpointDataSource now obsolete with top-level route registrations? And if so, is there a replacement I can use to find a matching Endpoint given an HTTP method and route path?