SI-8314 Prevent SI-8314 by adding a test

The original issue was fixed already. This test is just for make sure.
Or `root._class("A").comment foreach println`.

So it could run under `-Ywarn-value-discard`.  If it had to. Maybe easier to read, etc.  Half-point reduction for each paren, full points for braces and underscores.

I just made up that scoring system. Or underscoring system.