Imports System.Linq.Expressions

Namespace ThenIncludeIntellisenseBug

    Class Program
        Shared Sub Main(args As String())
            Dim registrations = New List(Of Registration)().AsQueryable()
            Dim reg = registrations.Include(Function(r) r.Activities).ThenInclude(Function(a, b, c) c.F)
        End Sub
    End Class

    Friend Class Registration
        Public Property Activities As ICollection(Of Activity)
    End Class

    Public Class Activity
        Public Property Task As Task
    End Class

    Public Class Task
        Public Property Name As String
    End Class

    Public Interface IIncludableQueryable(Of Out TEntity, Out TProperty)
        Inherits IQueryable(Of TEntity)
    End Interface

    Public Module EntityFrameworkQuerybleExtensions
        <System.Runtime.CompilerServices.Extension>
        Public Function Include(Of TEntity, TProperty)(
                                                      source As IQueryable(Of TEntity),
                                                      navigationPropertyPath As Expression(Of Func(Of TEntity, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
            Return Nothing
        End Function

        <System.Runtime.CompilerServices.Extension>
        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)),
                                                                             navigationPropertyPath As Expression(Of Func(Of String, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
            Return Nothing
        End Function

        <System.Runtime.CompilerServices.Extension>
        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty),
                                                                             navigationPropertyPath As Expression(Of Func(Of String, String, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
            Return Nothing
        End Function

    End Module
End Namespace

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();
            var reg = registrations.Include(r => r.Activities).ThenInclude((a, b, c) => c.F);
        }
    }

    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<string, 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<string, string, TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
        {
            return default(IIncludableQueryable<TEntity, TProperty>);
        }
    }
}