FeatureProviders

 /// <summary>
        /// Adds the minimum essential MVC services to the specified <see cref="IServiceCollection" />. Additional services
        /// including MVC's support for authorization, formatters, and validation must be added separately using the
        /// <see cref="IMvcCoreBuilder"/> returned from this method.
        /// </summary>
        /// <param name="services">The <see cref="IServiceCollection" /> to add services to.</param>
        /// <returns>An <see cref="IMvcCoreBuilder"/> that can be used to further configure the MVC services.</returns>
        /// <remarks>
        /// The <see cref="MvcCoreServiceCollectionExtensions.AddMvcCore(IServiceCollection)"/> approach for configuring
        /// MVC is provided for experienced MVC developers who wish to have full control over the set of default services
        /// registered. <see cref="MvcCoreServiceCollectionExtensions.AddMvcCore(IServiceCollection)"/> will register
        /// the minimum set of services necessary to route requests and invoke controllers. It is not expected that any
        /// application will satisfy its requirements with just a call to
        /// <see cref="MvcCoreServiceCollectionExtensions.AddMvcCore(IServiceCollection)"/>. Additional configuration using the
        /// <see cref="IMvcCoreBuilder"/> will be required.
        /// </remarks>
        public static IMvcCoreBuilder AddMvcCore(this IServiceCollection services)
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            var partManager = GetApplicationPartManager(services);
            services.TryAddSingleton(partManager);

            ConfigureDefaultFeatureProviders(partManager);
            ConfigureDefaultServices(services);
            AddMvcCoreServices(services);

            var builder = new MvcCoreBuilder(services, partManager);

            return builder;
        }

        private static void ConfigureDefaultFeatureProviders(ApplicationPartManager manager)
        {
            if (!manager.FeatureProviders.OfType<ControllerFeatureProvider>().Any())
            {
                manager.FeatureProviders.Add(new ControllerFeatureProvider());
            }
        }