Today's weird D edge case

[Petar]

On Sunday, 14 July 2019 at 00:22:10 UTC, Ethan wrote:
> https://run.dlang.io/is/l5Vyn4
>
> Using an is statement inside a template constraint doesn't 
> propagate the is results in to a function. You have to static 
> if with the same is statement to make it work.

I hit the exact same limitation yesterday. It turns out it is a 
known thing from 2011:
https://issues.dlang.org/show_bug.cgi?id=6269