Pattern Matching in While Loop

[ChayimFriedman2]

Version Used: 8

Steps to Reproduce:
Type the following code and try to compile:

object o = 8;
while (!(o is int i)) { }
Console.WriteLine(i);

Expected Behavior: The code will emit a loop that run until o is int, then converts it to int as variable i. Just like pattern matching with if:

object o = 8;
if (!(o is int i)) { }
Console.WriteLine(i);

Actual Behavior: The code isn't compiled and strangely the scope of i is inside the loop, instead of outside it.

[HaloFour]

This behavior is intentional:

#15529
https://github.com/dotnet/csharplang/blob/master/meetings/2016/LDM-2016-11-30.md#scope-of-while-condition-expression-variables