// ISSUE: KT-31191
import kotlin.contracts.*

@OptIn(ExperimentalContracts::class)
fun Any.isString(): Boolean {
    contract { returns(true) implies (this@isString is String) }
    return this is String
}

fun test(x: Any?) {
    if (x != null && <!DEBUG_INFO_SMARTCAST!>x<!>.isString()) {
        x.<!UNRESOLVED_REFERENCE!>length<!>
    }
}