New Issue: overriden method can return unmanaged subclass but not owned subclass

Notifications Issues
1

17184, "mppf", "overriden method can return unmanaged subclass but not owned subclass", "2021-02-18T17:58:55Z"

It appears that, in an overriden method, we can return a subclass:

class C {
  var x: int;

  proc returnCopyOfMe() {
    return new unmanaged C(x);
  }
}

class D: C {
  var y: int;

  override proc returnCopyOfMe() {
    return new unmanaged D(x,y);
  }
}

proc main() {
  var a = new C(1);
  var b = new D(2,3);
  var c: owned C = new D(4,5);

  writeln(a.returnCopyOfMe());
  writeln(b.returnCopyOfMe());
  writeln(c.returnCopyOfMe());
}

However the equivalent program not using unmanaged but rather owned does not compile:

class C {
  var x: int;

  proc returnCopyOfMe() {
    return new owned C(x);
  }
}

class D: C {
  var y: int;

  override proc returnCopyOfMe() {
    return new owned D(x,y);
  }
}

proc main() {
  var a = new C(1);
  var b = new D(2,3);
  var c: owned C = new D(4,5);

  writeln(a.returnCopyOfMe());
  writeln(b.returnCopyOfMe());
  writeln(c.returnCopyOfMe());
}

It seems like we intend to support covariant return types but have not correctly handled the case when they are owned/shared.