Test case

This test implements a notNull operation and demonstrates that it works
as required.

Also: Fix repltest

Author: odersky

compiler/test-resources/repl/i5218

@@ -3,4 +3,4 @@ val tuple: (Int, String, Long) = (1,2,3)
 scala> 0.0 *: tuple
 val res0: (Double, Int, String, Long) = (0.0,1,2,3)
 scala> tuple ++ tuple
-val res1: Int *: String *: Long *: scala.Tuple.Concat[Unit, tuple.type] = (1,2,3,1,2,3)
+val res1: Int *: String *: Long *: tuple.type = (1,2,3,1,2,3)

tests/pos/notNull.scala

@@ -0,0 +1,21 @@
+trait Null extends Any
+object Test with
+  def notNull(x: Any): x.type & NotNull =
+    assert(x != null)
+    x.asInstanceOf  // TODO: drop the .asInstanceOf when explicit nulls are implemented
+
+  locally {
+    val x: (Int | Null) = ???
+    val y = x; val _: Int | Null = y
+  }
+  locally {
+    val x: (Int | Null) & NotNull = ???
+    val y = identity(x); val yc: Int = y
+    val z = x; val zc: Int = z
+  }
+  locally {
+    val x: Int | Null = ???
+    val y = notNull(identity(x)); val yc: Int = y
+    val z = notNull(x); val zc: Int = z
+  }
+