Is this a known IDE bug? I’m told the when case is not exhaustive, but the missing branch was already handled. If I do add the branch, I get a different error that the branch is unreachable, so there is no way to make the IDE happy.

Make it sealed class or you can use class outside of sealed interface & there you can implement

Yes there are many ways to workaround it, but it doesn’t change the fact it’s a bug.

I don't think it's strictly a bug, more like a missing feature: The compiler just isn't smart enough to figure out that the cases not handled in the

if

are enough to make the

when

exhaustive. And TBH, if I saw this code in a review, I would tell you to use either an

if

or a

when

here, but not both…

This is a minimal example which makes using both

if

and

when

useless. The real code needs it.

Lint errors should not be ignored, but warnings can and very well should be suppressed in such cases

There is now: https://youtrack.jetbrains.com/issue/KT-62514/False-positive-for-when-expression-must-be-exhaustive-for-cases-that-were-already-handled

Thanks, added as a comment on my issue

What is the

new *

source annotation in the screenshot?