error()

looks good. But we're all in agreement that this is a bit weird, right? Would it be reasonable to file an issue on the compiler, to get some kind of official opinion on whether or not it works as intended?

File an issue. Try it first on 1.2-RC, though, to make sure it is not yet fixed there.

Checked with 1.2-RC over at https://try.kotlinlang.org (very convenient!) -- same error there.

Thanks, writing the issue now...

Just so you know this, the slack link in that issue will die in a couple of weeks when this discussion goes over Slack's 10000 messages limit.

I think all the important info is in the issue anyway, but I'll take an extra look. Thanks for the heads-up, Karel.