The is pattern matching on constraint type

[Meir017]

Version Used:
Visual Studio 2017
Version 15.2 (26430.14) Release

Steps to Reproduce:
The following code works:

public class Person { }
public class Parent : Person { }
public class Program
{
    public static void Test<TPerson>(TPerson person) where TPerson : Person
    {
        if(person is Parent)
        {
             var parent = person as Parent;
        }
    }
}

The following code raises an error An expression of type TPerson cannot be handled by a pattern of type Parent:

public class Person { }
public class Parent : Person { }
public class Program
{
    public static void Test<TPerson>(TPerson person) where TPerson : Person
    {
        if(person is Parent parent)
        {
        }
    }
}

[sharwell]

This looks like a duplicate of #16195. It is my understanding that the restriction on this use case was removed as part of the work on C# 7.1 (which ships with version 15.3).