kotlin-fork/compiler/testData/diagnostics/tests/smartCasts/propertyToNotNull.fir.kt

class Immutable(val x: String?) {
    fun foo(): String {
        if (x != null) return x
        return ""
    }
}

class Mutable(var y: String?) {
    fun foo(): String {
        if (y != null) return <!RETURN_TYPE_MISMATCH!>y<!>
        return ""
    }
}