Scala example source code file (InfoTransform.scala)

This example Scala source code file (InfoTransform.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

compiler, infotransform, infotransformer, nsc, phase, stdphase, symbol, transform, type

The InfoTransform.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author
 */

package scala.tools.nsc
package transform

/**
 * An InfoTransform contains a compiler phase that transforms trees and symbol infos -- making sure they stay consistent.
 * The symbol info is transformed assuming it is consistent right before this phase.
 * The info transformation is triggered by Symbol::rawInfo, which caches the results in the symbol's type history.
 * This way sym.info (during an enteringPhase(p)) can look up what the symbol's info should look like at the beginning of phase p.
 * (If the transformed info had not been stored yet, rawInfo will compute the info by composing the info-transformers
 *  of the most recent phase before p, up to the transformer of the phase right before p.)
 *
 * Concretely, enteringPhase(p) { sym.info } yields the info *before* phase p has transformed it. Imagine you're a phase and it all makes sense.
 */
trait InfoTransform extends Transform {
  import global.{Symbol, Type, InfoTransformer, infoTransformers}

  def transformInfo(sym: Symbol, tpe: Type): Type

  override def newPhase(prev: scala.tools.nsc.Phase): StdPhase =
    new Phase(prev)

  protected def changesBaseClasses = true
  protected def keepsTypeParams = true

  class Phase(prev: scala.tools.nsc.Phase) extends super.Phase(prev) {
    override val keepsTypeParams = InfoTransform.this.keepsTypeParams

    if (infoTransformers.nextFrom(id).pid != id) {
      // this phase is not yet in the infoTransformers
      val infoTransformer = new InfoTransformer {
        val pid = id
        val changesBaseClasses = InfoTransform.this.changesBaseClasses
        def transform(sym: Symbol, tpe: Type): Type = transformInfo(sym, tpe)
      }
      infoTransformers insert infoTransformer
    }
  }
}