content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.calcite.plan;
  
  import org.apache.calcite.rel.RelNode;
  
  /**
   * Customize the propagation of the {@link org.apache.calcite.rel.hint.RelHint}s
   * from the root relational expression of a rule call {@link RelOptRuleCall} to
   * the new equivalent expression.
   *
   * @see RelOptUtil#propagateRelHints(RelNode, RelNode)
   */
  @FunctionalInterface
  public interface RelHintsPropagator {
  
    /**
     * Propagates the hints from a rule call's root relational expression {@code oriNode}
     * to the new equivalent relational expression {@code equiv}.
     *
     * @param oriNode Root relational expression of a rule call
     * @param equiv   Equivalent expression
     * @return New relational expression that would register into the planner
     */
    RelNode propagate(RelNode oriNode, RelNode equiv);
  }
  