Controllers in entry assembly are not getting discovered automatically in 3.0

[natemcmaster]

Likely the result of #4061.

Controllers are not getting discovered in simple apps, such as dotnet new mvc. Instead, the app fails with 404.

Workaround

        public void ConfigureServices(IServiceCollection services)
        {
			/// ...
            var mvcBuilder = services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
            ConfigureControllers(mvcBuilder.PartManager);
        }

		
        private void ConfigureControllers(ApplicationPartManager applicationPartManager)
        {
            var thisAssembly = typeof(Startup).Assembly;
            var partFactory = ApplicationPartFactory.GetApplicationPartFactory(thisAssembly);
            foreach (var part in partFactory.GetApplicationParts(thisAssembly))
            {
                applicationPartManager.ApplicationParts.Add(part);
            }

            var relatedAssemblies = RelatedAssemblyAttribute.GetRelatedAssemblies(thisAssembly, throwOnError: true);
            foreach (var assembly in relatedAssemblies)
            {
                partFactory = ApplicationPartFactory.GetApplicationPartFactory(assembly);
                foreach (var part in partFactory.GetApplicationParts(assembly))
                {
                    applicationPartManager.ApplicationParts.Add(part);
                }
            }
        }

cc @pranavkm @Eilon @mkArtakMSFT - this seems like a critical bug to fix for preview1

[natemcmaster]

The fix appears to be simple: aspnet/Mvc#8751