Make Regex class serializable on JVM

#KT-16447 Fixed

Refactor helper functions for serialization tests.

libraries/stdlib/src/kotlin/text/regex/Regex.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -95,7 +95,7 @@ public data class MatchGroup(public val value: String, public val range: IntRang
  */
 public class Regex
 @PublishedApi
-internal constructor(private val nativePattern: Pattern) {
+internal constructor(private val nativePattern: Pattern) : Serializable {
 
 
     /** Creates a regular expression from the specified [pattern] string and the default options.  */
@@ -112,8 +112,9 @@ internal constructor(private val nativePattern: Pattern) {
     public val pattern: String
         get() = nativePattern.pattern()
 
+    private var _options: Set<RegexOption>? = null
     /** The set of options that were used to create this regular expression.  */
-    public val options: Set<RegexOption> = fromInt(nativePattern.flags())
+    public val options: Set<RegexOption> get() = _options ?: fromInt<RegexOption>(nativePattern.flags()).also { _options = it }
 
     /** Indicates whether the regular expression matches the entire [input]. */
     public infix fun matches(input: CharSequence): Boolean = nativePattern.matcher(input).matches()
@@ -203,6 +204,16 @@ internal constructor(private val nativePattern: Pattern) {
      */
     public fun toPattern(): Pattern = nativePattern
 
+    private fun writeReplace(): Any = Serialized(nativePattern.pattern(), nativePattern.flags())
+
+    private class Serialized(val pattern: String, val flags: Int) : Serializable {
+        companion object {
+            private const val serialVersionUID: Long = 0L
+        }
+
+        private fun readResolve(): Any = Regex(Pattern.compile(pattern, flags))
+    }
+
     companion object {
         /** Returns a literal regex for the specified [literal] string. */
         public fun fromLiteral(literal: String): Regex = literal.toRegex(RegexOption.LITERAL)