add tests

Author: noti0na1

tests/explicit-nulls/neg/basic.scala

@@ -0,0 +1,18 @@
+// Test that reference types are no longer nullable.
+
+class Foo {
+  val s: String = null // error
+  val s1: String | Null = null
+  val s2: String | Null = ""
+
+  val b: Boolean = null // error
+  val c: Int | Null = null
+
+  val ar1: AnyRef = null // error
+  val ar2: AnyRef | Null = null
+  val ob: Object = null // error
+
+  val av: AnyVal = null // error
+  val a: Any  = null
+  val n: Null = null
+}

tests/explicit-nulls/neg/default.scala

@@ -0,0 +1,12 @@
+class Foo {
+  val x: String = null // error: String is non-nullable
+
+  def foo(x: String): String = "x"
+
+  val y = foo(null) // error: String argument is non-nullable
+
+  val z: String = foo("hello")
+
+  class Bar
+  val b: Bar = null // error: user-created classes are also non-nullable
+}

tests/explicit-nulls/run/unsafe-nulls.scala

@@ -2,12 +2,21 @@
 // Enabling unsafeNulls allows this kind of unsafe operations,
 // but could cause exception during runtime.
 
-import scala.language.unsafeNulls
+object F {
+  def apply(x: String): String = x
+}
+
+object G {
+  def h(f: String | Null => String, x: String | Null): String | Null =
+    f(x)
+}
 
 object Test {
+  import scala.language.unsafeNulls
+
   def main(args: Array[String]): Unit = {
-    val s: String | Null = "hello"
-    assert(s.length == 5)
+    val s1: String | Null = "hello"
+    assert(s1.length == 5)
 
     val s2: String | Null = null
     try {
@@ -17,5 +26,11 @@ object Test {
       case e: NullPointerException =>
         // ok: Selecting on a null value would throw NullPointerException.
     }
+
+    val s3: String = F(s1)
+    assert(s3.length == 5)
+
+    val s4: String = G.h(F.apply, s1)
+    assert(s4.length == 5)
   }
 }