Poll: what should (note: not, what does) this code...

# compiler

[rocketraman]

Poll: what should (note: not, what does) this code produce? (Hint: it produces 1️⃣ in Kotlin 1.4-dev with new inference enabled)

fun <T> foo(): T? = "abc" as T

fun main() {
  val s: String? = if(false) null else foo()
}

1️⃣ A runtime exception ClassCastException: class java.lang.String cannot be cast to java.lang.Void
2️⃣ A compile-time error due to the type T of foo being ambiguous (could be String? or could be Nothing)
3️⃣ A compile-time warning that the type of T was inferred to Nothing and that is probably not the desired result
4️⃣ An inference of T to be String?, so no compile-time or runtime errors
5️⃣ Other

[rocketraman]

Related fun fact:

fun <T> bar(): T = "abc" as T

fun main() {
  val s: String? = if(false) null else bar()
}

produces a runtime exception 1️⃣, but at least it comes with a compile time warning 3️⃣.

[mikhail.zarechenskiy]

See https://youtrack.jetbrains.com/issue/KT-36776 for more details, I believe we'll end up with the 4️⃣ for cases like that