Temporary workaround due to KT-7502.

Correct usage of joinToString.
Test for passing multiple options.

js/js.libraries/src/core/regex.kt

@@ -50,7 +50,7 @@ public class Regex(pattern: String, options: Set<RegexOption>) {
     public val pattern: String = pattern
     /** The set of options that were used to create this regular expression. */
     public val options: Set<RegexOption> = options.toSet()
-    private val nativePattern: RegExp = RegExp(pattern, options.map { it.value }.joinToString() + "g")
+    private val nativePattern: RegExp = RegExp(pattern, options.map { it.value }.joinToString(separator = "") + "g")
 
     /** Indicates whether the regular expression matches the entire [input]. */
     public fun matches(input: CharSequence): Boolean {
@@ -115,8 +115,10 @@ public class Regex(pattern: String, options: Set<RegexOption>) {
      *
      * @param replacement A replacement expression that can include substitutions. See [Matcher.appendReplacement] for details.
      */
-    public fun replaceFirst(input: CharSequence, replacement: String): String =
-            input.toString().nativeReplace(RegExp(pattern, options.map { it.value }.joinToString()), replacement)
+    public fun replaceFirst(input: CharSequence, replacement: String): String {
+        val nonGlobalOptions = options.map { it.value }.joinToString(separator = "")
+        return input.toString().nativeReplace(RegExp(pattern, nonGlobalOptions), replacement)
+    }
 
     /**
      * Splits this string around matches of the given regular expression.

libraries/stdlib/test/text/RegexTest.kt

@@ -84,6 +84,12 @@ class RegexTest {
         assertEquals("bye", m2.groups[2]?.value)
     }
 
+    test fun matchMultiline() {
+        val regex = "^[a-z]*$".toRegex(setOf(RegexOption.IGNORE_CASE, RegexOption.MULTILINE))
+        val matchedValues = regex.matchAll("test\r\nLine").map { it.value }.toList()
+        assertEquals(listOf("test", "Line"), matchedValues)
+    }
+
     test fun escapeLiteral() {
         val literal = """[-\/\\^$*+?.()|[\]{}]"""
         assertTrue(Regex.fromLiteral(literal).matches(literal))