text: /**
   * Copyright (C) 2017 MongoDB Inc.
   *
   * This program is free software: you can redistribute it and/or  modify
   * it under the terms of the GNU Affero General Public License, version 3,
   * as published by the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Affero General Public License for more details.
   *
   * You should have received a copy of the GNU Affero General Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   *
   * As a special exception, the copyright holders give permission to link the
   * code of portions of this program with the OpenSSL library under certain
   * conditions as described in each individual source file and distribute
   * linked combinations including the program with the OpenSSL library. You
   * must comply with the GNU Affero General Public License in all respects
   * for all of the code used other than as permitted herein. If you modify
   * file(s) with this exception, you may extend this exception to your
   * version of the file(s), but you are not obligated to do so. If you do not
   * wish to do so, delete this exception statement from your version. If you
   * delete this exception statement from all source files in the program,
   * then also delete it in the license file.
   */
  
  #pragma once
  
  #include "mongo/db/update/update_leaf_node.h"
  #include "mongo/stdx/memory.h"
  
  namespace mongo {
  
  /**
   * Represents a placeholder update that generates conflicts with other updates on the same path but
   * has no effect of its own (i.e., its apply() function does nothing).
   *
   * We use the ConflictPlaceholderNode to ensure that the "from" path of a $rename does not conflict
   * with any other updates. A {$rename: {'from': 'to'}} results in a ConflictPlaceholderNode on the
   * "from" path and a RenameNode on the "to" path. The actual rename operation executes with
   * RenameNode::apply().
   */
  class ConflictPlaceholderNode : public UpdateLeafNode {
  public:
      Status init(BSONElement modExpr, const boost::intrusive_ptr<ExpressionContext>& expCtx) final {
          return Status::OK();
      }
  
      std::unique_ptr<UpdateNode> clone() const final {
          return stdx::make_unique<ConflictPlaceholderNode>(*this);
      }
  
      void setCollator(const CollatorInterface* collator) final {}
  
      ApplyResult apply(ApplyParams applyParams) const final {
          return ApplyResult::noopResult();
      }
  };
  
  }  // namespace mongo
  