IllegalAccessError with package protected java class

[scabug]

A.java

package a;
abstract class A {
    public final void m() { System.out.println("hi"); }
}

Test.scala

package a {
  // A is a class, so W does not conform to A in bytecode. an access (w: W).m() requires a cast to A.
  // If `A` is not accessible, there's no solution, need to issue an error. Currently crashes.
  trait W extends A
  class C extends W
}

object Test {
  def main(args: Array[String]): Unit = {
    val w: a.W = new a.C
    w.m()
  }
}

Crashes

java.lang.IllegalAccessError: tried to access class a.A from class Test$

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-10249?orig=1
Reporter: @lrytz
Affected Versions: 2.12.1
See #4283

[scabug]

@lrytz said:
Related to #4283, it's an example that cannot be solved.