XHP array specification is stripped

[fredemmott]

<?hh

class bar {
  protected static function __xhpAttributeDeclaration(): array {
    return array();
  }
}

class :foo extends bar {
  const ATTR_TYPE_ARRAY = 4; // :x:composable-element::TYPE_ARRAY
  attribute
    array<int, string> myarray;
  public static function main() {
    $decl = self::__xhpAttributeDeclaration()['myarray'];

    // See https://gist.github.com/fredemmott/cf2d387208463de2cca0

    $type = $decl[0];
    var_dump($type === self::ATTR_TYPE_ARRAY); // bool(true)
    $array_spec= $decl[1];
    /*
     * Actual: NULL
     * Expected:
     *  [
     *    0 => TYPE_INT,
     *    1 => TYPE_STRING,
     *    2 => null,
     *  ]
     */
    var_dump($array_spec);
  }
}

:foo::main();

This means that array attributes are not validated.

[fredemmott]

I'm going to remove the validation from xhp-lib for perf reasons, but ideally this data would still be there for reflection.