IllegalAccessError when calling java method defined in base class

[ohze]

Minimized code

• pk/B.java

package pk;
class B {
    public void hi() { System.out.println("hi"); }
}

• pk/C.java

package pk;
public class C extends B {
    public C() {}
}

• Main.scala

import pk.C
object Main {
  def main(args: Array[String]): Unit = {
    identity(new C).hi()
  }
}

Output

[info] running (fork) Main 
[error] Exception in thread "main" java.lang.IllegalAccessError: tried to access class pk.B from class Main$
[error]         at Main$.main(Main.scala:5)
[error]         at Main.main(Main.scala)

Expectation

run successfully as in scala 2

Notes

In sbt: set Compile/run/fork := true to mute another errors:

[error] java.lang.IllegalAccessError: tried to access class pk.B from class Main$
[error] If using a layered classloader, this can occur if jvm package private classes
 are accessed across layers. This can be fixed by changing to the Flat or
 ScalaInstance class loader layering strategies.

[ohze]

Inspect

Decompile the Main$.class file:

• scala 2:

public final class Main$ ...
    public void main(final String[] args) {
        ((C)Predef$.MODULE$.identity((Object)new C())).hi();
    }

• dotty 0.23.0-RC1 (same for 0.24.0-bin-20200403-2c3212b-NIGHTLY)

public final class Main$ ...
    public void main(final String[] args) {
        ((B)Predef$.MODULE$.identity((Object)new C())).hi();
    }
}

Note the cast (B) in Main$.main!

[odersky]

Good catch!