Provide java.util.Collections#shuffle as extensions for collections in JS

#KT-2460

js/js.libraries/src/core/collections.kt

@@ -17,6 +17,7 @@
 package kotlin.collections
 
 import kotlin.comparisons.naturalOrder
+import kotlin.js.Math
 
 /** Returns the array if it's not `null`, or an empty array otherwise. */
 @kotlin.internal.InlineOnly
@@ -85,12 +86,38 @@ public fun <K, V> mapOf(pair: Pair<K, V>): Map<K, V> = hashMapOf(pair)
  * Each element in the list gets replaced with the [value].
  */
 @SinceKotlin("1.2")
-public fun <T> MutableList<T>.fill(value: T) {
+public fun <T> MutableList<T>.fill(value: T): Unit {
     for (index in 0..lastIndex) {
         this[index] = value
     }
 }
 
+/**
+ * Randomly shuffles elements in this list.
+ *
+ * See: https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_modern_algorithm
+ */
+@SinceKotlin("1.2")
+public fun <T> MutableList<T>.shuffle(): Unit {
+    for (i in lastIndex downTo 1) {
+        rand(i + 1).let { j ->
+            swap(this, i, j)
+        }
+}
+private fun rand(upperBound: Int) = Math.floor(Math.random() * upperBound)
+private fun swap(list: MutableList<T>, i: Int, j: Int): Unit {
+    val copy = list[i]
+    list[i] = list[j]
+    list[j] = copy
+}
+
+
+/**
+ * Returns a new list with the elements of this list randomly shuffled.
+ */
+@SinceKotlin("1.2")
+public fun <T> Iterable<T>.shuffled(): List<T> = toMutableList().apply { shuffle() }
+
 /**
  * Sorts elements in the list in-place according to their natural sort order.
  */
@@ -112,7 +139,7 @@ private fun <T> collectionsSort(list: MutableList<T>, comparator: Comparator<in
 
     array.asDynamic().sort(comparator.asDynamic().compare.bind(comparator))
 
-    for (i in 0..array.size - 1) {
+    for (i in 0..array.lastIndex) {
         list[i] = array[i]
     }
 }

libraries/stdlib/common/src/kotlin/CollectionsH.kt

@@ -149,10 +149,12 @@ expect inline fun <reified T> Array<out T>?.orEmpty(): Array<out T>
 
 expect inline fun <reified T> Collection<T>.toTypedArray(): Array<T>
 
-@SinceKotlin("1.2")
+@SinceKotlin("1.2") header fun <T> MutableList<T>.fill(value: T): Unit
-expect fun <T> MutableList<T>.fill(value: T): Unit
+@SinceKotlin("1.2") header fun <T> MutableList<T>.shuffle(): Unit
-expect fun <T : Comparable<T>> MutableList<T>.sort(): Unit
+@SinceKotlin("1.2") header fun <T> Iterable<T>.shuffled(): List<T>
-expect fun <T> MutableList<T>.sortWith(comparator: Comparator<in T>): Unit
+
+header fun <T : Comparable<T>> MutableList<T>.sort(): Unit
+header fun <T> MutableList<T>.sortWith(comparator: Comparator<in T>): Unit
 
 
 // from Grouping.kt

libraries/stdlib/test/collections/MutableCollectionsTest.kt

@@ -101,7 +101,6 @@ class MutableCollectionTest {
         assertEquals(listOf(42, 42, 42), list)
     }
 
-    @JvmVersion
     @Test fun shuffled() {
         val list = MutableList(100) { it }
         val shuffled = list.shuffled()
@@ -127,6 +126,4 @@ class MutableCollectionTest {
 
         assertEquals(shuffled1, shuffled2)
     }
-
-
 }