exposing copy is not safe about contraband HOT 2 CLOSED

class A; object A1 extends A
class B; object B1 extends B; object B2 extends B
class C; object C1 extends C

object T {
  def t = {
    val x = new Foo(A1, B1)
    x.copy(b = B2)
  }
}

final class Foo(a: A, b: B) {
  def copy(a: A = a , b: B = b) = new Foo(a, b)
}

<synthetic> def copy$default$1(): A = Foo.this.a;
<synthetic> def copy$default$2(): B = Foo.this.b;

def t(): Foo = {
  val x: Foo = new Foo(A1, B1);
  {
    <artifact> val x$1: B2.type = B2;
    <artifact> val x$2: A = x.copy$default$1();
    x.copy(x$2, x$1)
  }
};

final class Foo(c: C, a: A, b: B) {
  def this(a: A, b: B) = this(C1, a, b)
  def copy(a: A, b: B) = new Foo(c, a, b)
  def copy(c: C = c, a: A = a, b: B = b) = new Foo(c, a, b)
}

<synthetic> def copy$default$1(): C = Foo.this.c;
<synthetic> def copy$default$2(): A = Foo.this.a;
<synthetic> def copy$default$3(): B = Foo.this.b;

def t(): Foo = {
  val x: Foo = new Foo(A1, B1);
  {
    <artifact> val x$1: B2.type = B2;
    <artifact> val x$2: C = x.copy$default$1();
    <artifact> val x$3: A = x.copy$default$2();
    x.copy(x$2, x$3, x$1)
  }
};