Kotlin extension function receiver type inference

ExtFunInf.kt

fun Int.one(x: Int) = this + 1 + x

fun Int.two(x: Int) = this + 2 + x

fun Int.three(x: Int) = this + 3 + x

fun Int.noop(x: Int) = this + x

class Z(val action: Int.() -> Int)

object Test {

    /** OK */
    fun test() {
        val z = Z({one(1)})
    }

    /** OK */
    fun test2() {
        val f: Int.() -> Int = {one(10)}
        val z = Z(f)
    }

    /** Does not compile! */
    fun test3() {
        val choice = Random().nextInt(3)
        // the receiver type does not get inferred with or without the explicit type annotation for `f`
        val f: Int.() -> Int = when(choice) {
            0 -> {one(10)}
            1 -> {two(20)}
            2 -> {three(30)}
            else -> {noop(9000)}
        }
        val z = Z(f)
    }
}