Add test

Author: liufengyun

tests/patmat/t11620b.scala

@@ -0,0 +1,16 @@
+sealed abstract class Length
+
+object Length {
+  case class Num(n: Int) extends Length
+  case object StateColumn extends Length
+}
+
+import Length._
+
+case class Indent[T <: Length](length: T)
+
+def withIndent[T <: Length](indent: => Indent[_]): Unit =
+  indent match {
+    case Indent(Num(0)) => println("this")
+    case x              => println(x) // "unreachable"
+  }