How to make the compile time red color warning ?

[MrSmith]

On Wednesday, 3 June 2020 at 11:48:27 UTC, Виталий Фадеев wrote:
> Use case:
> I have class for Windows OS.
> I not implement class for Linux.
> I want message about it. When code compiled under Linux.

You could use `static assert(false, "Message");` to make it an 
error.