CometExpressionSerde.scala

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 * distributed with this work for additional information
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 * 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,
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 */

package org.apache.comet.serde

import org.apache.spark.sql.catalyst.expressions.{Attribute, Expression}

/**
 * Trait for providing serialization logic for expressions.
 */
trait CometExpressionSerde[T <: Expression] {

  /**
   * Get a short name for the expression that can be used as part of a config key related to the
   * expression, such as enabling or disabling that expression.
   *
   * @param expr
   *   The Spark expression.
   * @return
   *   Short name for the expression, defaulting to the Spark class name
   */
  def getExprConfigName(expr: T): String = expr.getClass.getSimpleName

  /**
   * Declarative support conditions for this expression. First match wins.
   *
   * Prefer declaring `conditions` over overriding [[getSupportLevel]]: the list is enumerable for
   * documentation and tests, and each condition carries a stable id and static description.
   *
   * Subclasses should declare `conditions` as a `val` so the list is built once, not on every
   * `getSupportLevel` call.
   */
  def conditions: Seq[SupportCondition[T]] = Seq.empty

  /**
   * Determine the support level of the expression based on its attributes.
   *
   * The default implementation is derived from [[conditions]]. Subclasses may still override this
   * during migration, but new serdes should prefer declaring `conditions`.
   *
   * @param expr
   *   The Spark expression.
   * @return
   *   Support level (Compatible, Incompatible, or Unsupported).
   */
  def getSupportLevel(expr: T): SupportLevel =
    conditions.find(_.fires(expr)) match {
      case Some(c) =>
        val msg = Some(c.message(expr)).filter(_.nonEmpty)
        c.level match {
          case SupportLevelKind.Compatible => Compatible(msg)
          case SupportLevelKind.Incompatible => Incompatible(msg)
          case SupportLevelKind.Unsupported => Unsupported(msg)
        }
      case None => Compatible(None)
    }

  /**
   * Convert a Spark expression into a protocol buffer representation that can be passed into
   * native code.
   *
   * @param expr
   *   The Spark expression.
   * @param inputs
   *   The input attributes.
   * @param binding
   *   Whether the attributes are bound (this is only relevant in aggregate expressions).
   * @return
   *   Protocol buffer representation, or None if the expression could not be converted. In this
   *   case it is expected that the input expression will have been tagged with reasons why it
   *   could not be converted.
   */
  def convert(expr: T, inputs: Seq[Attribute], binding: Boolean): Option[ExprOuterClass.Expr]
}