2.x: Zip, CombineLatest, and Amb operators throw when supplied with ObservableSource implementation that doesn't subclass Observable #6753

Issue found in version 2.2.15.

The Zip, CombineLatest, and Amb operators of the Observable class each have an overload that accepts an Iterable<ObservableSource> and a Function<Array<Any>, R> where R is a type parameter. The problem is that the elements of the Iterable are copied into an Observable[] internally by the Observer classes implementing the operators. This causes an ArrayStoreException if one supplies any custom ObservableSource implementation that doesn't subclass Observable.

The equivalent functions for the other stream types don't have this restriction. I.e, the Zip implementation in Maybe copies the source values into a MaybeSource[] and avoids this problem.

Example kotlin code which reproduces the issue:

import io.reactivex.Observable
import io.reactivex.ObservableSource

val sourceA = ObservableSource<String> { Observable.just("A").subscribe(it) }
val sourceB = ObservableSource<String> { Observable.just("b", "B").subscribe(it) }

val combined =
    Observable.combineLatest(
       listOf(sourceA, sourceB),
       { (it[0] as String) + (it[1] as String) }
    )

fun main() {
    combined.subscribe(::println)
}

A simple workaround is to wrap any ObservableSource. To fix the above example pass listOf(sourceA, sourceB).map { Observable.wrap(it) } to combineLatest.