Disallow taking a class tag of Nothing or Null.

It seems in most cases this leads to weird behavior and cause
confusing error messages later.

It also means we cannot create an Array[Nothing], except by
passing the classtag explicitly.

3 files changed, 14 insertions, 2 deletions

diff --git a/tests/neg/i1802.scala b/tests/neg/i1802.scala
index 56da672a8..93e790f18 100644
--- a/tests/neg/i1802.scala
+++ b/tests/neg/i1802.scala
@@ -14,8 +14,8 @@ object Exception {
     def apply(x: Throwable): T = f(downcast(x).get)
   }
 
-  def mkThrowableCatcher[T](isDef: Throwable => Boolean, f: Throwable => T) = mkCatcher(isDef, f)
+  def mkThrowableCatcher[T](isDef: Throwable => Boolean, f: Throwable => T) = mkCatcher(isDef, f) // error: undetermined ClassTag
 
-  implicit def throwableSubtypeToCatcher[Ex <: Throwable: ClassTag, T](pf: PartialFunction[Ex, T]) = // error: cyclic reference
+  implicit def throwableSubtypeToCatcher[Ex <: Throwable: ClassTag, T](pf: PartialFunction[Ex, T]) =
     mkCatcher(pf.isDefinedAt _, pf.apply _)
 }
diff --git a/tests/neg/i1907.scala b/tests/neg/i1907.scala
new file mode 100644
index 000000000..6bc3bb56f
--- /dev/null
+++ b/tests/neg/i1907.scala
@@ -0,0 +1,7 @@
+import java.io.File
+
+object Test {
+  Some(new File("."))
+    .map(_.listFiles).getOrElse(Array.empty) // error: undetermined ClassTag
+    .map(_.listFiles)
+}
diff --git a/tests/neg/undet-classtag.scala b/tests/neg/undet-classtag.scala
new file mode 100644
index 000000000..563596d14
--- /dev/null
+++ b/tests/neg/undet-classtag.scala
@@ -0,0 +1,5 @@
+object Test {
+  def f[T: reflect.ClassTag](x: T) = ???
+
+  f(???) // error: undetermined ClassTag
+}