Review

class PeepholeFoldConstants {
  /**
   * Try to fold array-element. e.g [1, 2, 3][10];
   */
  private Node tryFoldGetElem(Node n, Node left, Node right) {
    Preconditions.checkArgument(n.getType() == Token.GETELEM);

    if (left.getType() == Token.ARRAYLIT) {

      if (right.getType() != Token.NUMBER) {
        // Sometimes people like to use complex expressions to index into
        // arrays, or strings to index into array methods.
        return n;
      }

      double index = right.getDouble();
      int intIndex = (int) index;
      if (intIndex != index) {
        error(INVALID_GETELEM_INDEX_ERROR, right);
        return n;
      }

      if (intIndex < 0) {
        error(INDEX_OUT_OF_BOUNDS_ERROR, right);
        return n;
      }

      Node elem = left.getFirstChild();
      for (int i = 0; elem != null && i < intIndex; i++) {
        elem = elem.getNext();
      }

      if (elem == null) {
        error(INDEX_OUT_OF_BOUNDS_ERROR, right);
        return n;
      }

      // Replace the entire GETELEM with the value
      left.removeChild(elem);
      n.getParent().replaceChild(n, elem);
      reportCodeChange();
      return elem;
    }
    return n;
  }

}