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kotlinlang

Hi there! I've recently been experimenting a bit with Kotlin's Contract API but I wasn't able to figure out why some smart casting seemed a little inconsistent. I've added an example in this thread:

Here's an example:

```@OptIn(ExperimentalContracts::class)
fun myTest(foo: String?): String? {
    contract {
        returnsNotNull() implies (foo != null)
    }
    return foo
}

fun myFunction(foo: String?) {
    myTest(foo) ?: return

    foo.length // Error: requires safe or non-null asserted call

    if (myTest(foo) != null) {
        foo.length // No error
    }
}```
In this snippet I have a dummy function `myTest` that which guarantees that if a non-null value is returned, the given parameter is also non-null. This should in theory mean that the first line of `myFunction` "guards" the `foo` value and that `foo` should be guaranteed to be non-null on all lines after that. Instead, this produces an error on the `foo.length` call, implying that no smart cast was possible. If we exlicitly perform this test in an if statement, however, the smart cast succeeds and the compiler seems to know that `foo` can no longer be null.

Does anyone know if this is a limitation in how the compiler treats the `?: return` as opposed to an if statement? Or am I overlooking something?

Thanks for the help!

This is a bug, which is fixed in K2 compiler