using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace ThenIncludeIntellisenseBug
{
    class Program
    {
        static void Main(string[] args)
        {
            var registrations = new List<Registration>().AsQueryable();

            // type "a => a." and only ICollection<T> and Enumerable members appear
            var reg = registrations
              .Include(r => r.Activities).ThenInclude(a => a.$$
        }
    }

    internal class Registration
    {
        public ICollection<Activity> Activities { get; set; }
    }

    public class Activity
    {
        public Task Task { get; set; }
    }

    public class Task
    {
        public string Name { get; set; }
    }

    public interface IIncludableQueryable<out TEntity, out TProperty> : IQueryable<TEntity>
    {
    }

    public static class EntityFrameworkQuerybleExtensions
    {
        public static IIncludableQueryable<TEntity, TProperty> Include<TEntity, TProperty>(
         this IQueryable<TEntity> source,
          Expression<Func<TEntity, TProperty>> navigationPropertyPath)
         where TEntity : class
        {
            return default(IIncludableQueryable<TEntity, TProperty>);
        }

        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
        {
            return default(IIncludableQueryable<TEntity, TProperty>);
        }

        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
            this IIncludableQueryable<TEntity, TPreviousProperty> source,
            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
        {
            return default(IIncludableQueryable<TEntity, TProperty>);
        }
    }
}