/* 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
    }
  }
}