VM: const constructor allowed to call non-const superconstructor, enables side-effects before main()

[rakudrama]

class I {
  I() { print('xxx'); }
  const I._();
}

class U extends I {
  const U();
}

const x = const U();

main() {
  print('Hello');
  print(x);
  print(const U());
}

$ sdk/bin/dart ~/play1/bug6K.dart
xxx
xxx
Hello
Instance of 'U'
Instance of 'U'
$

Removing the private const I._() gives the expected error 'superclass 'I' must be const'.
I would expect to need to change U's constructor to the following:

  const U() : super._();

The superconstructor call is implicit but there is no error for an explicit non-const superconstuctor, i.e.

  const U() : super();

[iposva-google]

Removed this from the M6 milestone.

[iposva-google]

This is a duplicate of issue #392: Need to verify that the expressions in the initializer list are all potentially const. The I.super() call in this case isn't.

---

Added Duplicate label.
Marked as being merged into #392.