scala 2.12.1 ClassNotFoundException Product$class

Question

I recently updated scala from v2.11.8 to 2.12.1 and got a CNF exception:

java.lang.ClassNotFoundException: scala.Product$class

I saw the class is shipped by scala-library.jar. The error happens when running a scalatest (the project is still at a very early stage so I have only tests).

Do you have any idea? I found nothing on the release notes.

Answer 1

libraries are not binary compatible between 2.11 and 2.12, most likely one of your libraries has to be recompiled with scala 2.12

Answer 2

In particular, trait implementations are no longer provided in classes named with the $class suffix. You'll find the notice about "trait encoding" in the release notes.

Probably you want to use sbt or ammonite if experimenting with any dependencies besides built-ins. One day they will have a tidy "platform" to help you.

$ cat notraitclass.scala

package notraitclass

trait T {
  def t: Int = 42
}
$ scalac211 notraitclass.scala
$ ls notraitclass
T.class  T$class.class
$ rm -rf notraitclass
$ scalac notraitclass.scala
$ ls notraitclass
T.class