Provide access to named groups of regex match result on JDK8.

#KT-12753 Fixed

libraries/stdlib/jre8/src/kotlin/internal/JRE8PlatformImplementations.kt

@@ -1,5 +1,19 @@
 package kotlin.internal
 
+import java.util.regex.MatchResult
+import java.util.regex.Matcher
+
 @Suppress("INVISIBLE_REFERENCE", "INVISIBLE_MEMBER", "CANNOT_OVERRIDE_INVISIBLE_MEMBER")
 internal open class JRE8PlatformImplementations : JRE7PlatformImplementations() {
+
+    override fun getMatchResultNamedGroup(matchResult: MatchResult, name: String): MatchGroup? {
+        val matcher = matchResult as? Matcher ?: throw UnsupportedOperationException("Retrieving groups by name is not supported on this platform.")
+
+        val range = matcher.start(name)..matcher.end(name)-1
+        return if (range.start >= 0)
+            MatchGroup(matcher.group(name), range)
+        else
+            null
+    }
+
 }

libraries/stdlib/jre8/src/kotlin/text/RegexExtensions.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2010-2016 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.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+@file:JvmName("RegexExtensionsJRE8Kt")
+package kotlin.text
+
+/**
+ * Returns a named group with the specified [name].
+ *
+ * @return An instance of [MatchGroup] if the group with the specified [name] was matched or `null` otherwise.
+ * @throws [UnsupportedOperationException] if getting named groups isn't supported on the current platform.
+ */
+public operator fun MatchGroupCollection.get(name: String): MatchGroup? {
+    val namedGroups = this as? MatchNamedGroupCollection ?:
+            throw UnsupportedOperationException("Retrieving groups by name is not supported on this platform.")
+
+    return namedGroups[name]
+}

libraries/stdlib/jre8/test/text/RegexTest.kt

@@ -0,0 +1,27 @@
+package kotlin.text.test
+
+import org.junit.Test
+import kotlin.test.*
+
+
+class RegexTest {
+    @Test fun namedGroups() {
+        val input = "1a 2b 3c"
+        val regex = "(?<num>\\d)(?<liter>\\w)".toRegex()
+
+        val matches = regex.findAll(input).toList()
+        assertTrue(matches.all { it.groups.size == 3 })
+        val m1 = matches[0]
+
+        assertEquals("1", m1.groups["num"]?.value)
+        assertEquals(0..0, m1.groups["num"]?.range)
+        assertEquals("a", m1.groups["liter"]?.value)
+        assertEquals(1..1, m1.groups["liter"]?.range)
+
+        val m2 = matches[1]
+        assertEquals("2", m2.groups["num"]?.value)
+        assertEquals(3..3, m2.groups["num"]?.range)
+        assertEquals("b", m2.groups["liter"]?.value)
+        assertEquals(4..4, m2.groups["liter"]?.range)
+    }
+}