Generic signatures with value classes are wrong

[Jasper-M]

In the sample below javap says that method b returns a scala.Option<java.lang.String> but the implementation of those methods strongly suggest that the Option contains an instance of class X.

scala> class X(val x: String) extends AnyVal
defined class X

scala> class Foo { def b = Option(new X("minnow")); def get = b.get }
defined class Foo

scala> :javap -filter -cp Foo
Compiled from "<console>"
public class Foo {
  public scala.Option<java.lang.String> b();
    Code:
       0: getstatic     #30                 // Field scala/Option$.MODULE$:Lscala/Option$;
       3: new           #14                 // class X
       6: dup
       7: ldc           #32                 // String minnow
       9: invokespecial #36                 // Method X."<init>":(Ljava/lang/String;)V
      12: invokevirtual #40                 // Method scala/Option$.apply:(Ljava/lang/Object;)Lscala/Option;
      15: areturn

  public java.lang.String get();
    Code:
       0: aload_0
       1: invokevirtual #46                 // Method b:()Lscala/Option;
       4: invokevirtual #51                 // Method scala/Option.get:()Ljava/lang/Object;
       7: checkcast     #14                 // class X
      10: invokevirtual #54                 // Method X.x:()Ljava/lang/String;
      13: areturn

  public Foo();
    Code:
       0: aload_0
       1: invokespecial #57                 // Method java/lang/Object."<init>":()V
       4: return
}

[Jasper-M]

Perhaps a better illustration of why this is a problem:

$ cat XFoo.scala 
class X(val x: String) extends AnyVal
class Foo { def b = Option(new X("minnow")); def get = b.get }

$ cat J.java
public class J {

  public String foo() {
    scala.Option<String> b =  new Foo().b();
    return b.get();
  }

}
$ sbt console

Welcome to Scala 2.13.0-pre-6114bc3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.

scala> new J().foo
java.lang.ClassCastException: X cannot be cast to java.lang.String
  at J.foo(J.java:5)
  ... 38 elided