SI-7737 Regex matches Char

Enables Char extraction by regex.

```
val r = """(\p{Lower})""".r
"cat"(0) match { case r(x) => true }
val nc = """\p{Lower}""".r
"cat"(0) match { case nc() => true }
```

1 files changed, 58 insertions, 0 deletions

diff --git a/test/junit/scala/util/matching/regextract-char.scala b/test/junit/scala/util/matching/regextract-char.scala
new file mode 100644
index 0000000000..50fdcd9d46
--- /dev/null
+++ b/test/junit/scala/util/matching/regextract-char.scala
@@ -0,0 +1,58 @@
+
+package scala.util.matching
+
+import org.junit.Assert._
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+
+import PartialFunction._
+
+/** Regex can match a Char.
+ *  If the pattern includes a group,
+ *  always return a single char.
+ */
+@RunWith(classOf[JUnit4])
+class CharRegexTest {
+  implicit class Averrable(val b: Boolean) /*extends AnyVal*/ {
+    def yes = assert(b)
+    def no = assert(!b)
+  }
+  val c: Char = 'c'  // "cat"(0)
+  val d: Char = 'D'  // "Dog"(0)
+
+  @Test def comparesGroupCorrectly(): Unit = {
+    val r = """(\p{Lower})""".r
+    cond(c) { case r(x) => true } .yes
+    cond(c) { case r(_) => true } .yes
+    cond(c) { case r(_*) => true } .yes
+    cond(c) { case r() => true } .no
+
+    cond(d) { case r(x) => true } .no
+    cond(d) { case r(_) => true } .no
+    cond(d) { case r(_*) => true } .no
+    cond(d) { case r() => true } .no
+  }
+
+  @Test def comparesNoGroupCorrectly(): Unit = {
+    val rnc = """\p{Lower}""".r
+    cond(c) { case rnc(x) => true } .no
+    cond(c) { case rnc(_) => true } .no
+    cond(c) { case rnc(_*) => true } .yes
+    cond(c) { case rnc() => true } .yes
+
+    cond(d) { case rnc(x) => true } .no
+    cond(d) { case rnc(_) => true } .no
+    cond(d) { case rnc(_*) => true } .no
+    cond(d) { case rnc() => true } .no
+  }
+
+  @Test(expected = classOf[MatchError])
+  def failCorrectly(): Unit = {
+    val headAndTail = """(\p{Lower})([a-z]+)""".r
+    val n = "cat"(0) match {
+      case headAndTail(ht @ _*) => ht.size
+    }
+    assert(false, s"Match size $n")
+  }
+}