CoroutineScope.future() may trigger global exception handler on cancellation

[frost13it]

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Expected behavior

future coroutine builder delivers all errors via the returned object, just like async.

Actual behavior

future coroutine builder can suddenly trigger global exception handler that may crash the application.

Sample code:

fun main() {
    val future = GlobalScope.future {
        error("foo")
    }
    future.cancel(true)
    Thread.sleep(100)
}

Result: Exception in thread "DefaultDispatcher-worker-1" java.lang.IllegalStateException: foo

[frost13it]

I believe CompletableFutureCorotine should not attempt to handle the exception in any other way than completing the returned CompletableFuture. For now, this is not the case.