// KT-7857: when exhaustiveness does not take previous nullability checks into account
enum class X { A, B }
fun foo(arg: X?): Int {
    if (arg == null) {
        return 0
    }
    else {
        return when (<!DEBUG_INFO_SMARTCAST!>arg<!>) {
            X.A -> 1
            X.B -> 2
            // else or null branch should not be required here!
        }
    } 
}