Scala example source code file (Flatten.scala)

This example Scala source code file (Flatten.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

classinfotype, collection, compiler, flattener, lifted, list, listbuffer, mutable, nsc, polytype, symbol, transformer, tree, type

The Flatten.scala Scala example source code

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

package scala.tools.nsc
package transform

import symtab._
import Flags._
import scala.collection.mutable.ListBuffer

abstract class Flatten extends InfoTransform {
  import global._
  import treeInfo.isQualifierSafeToElide

  /** the following two members override abstract members in Transform */
  val phaseName: String = "flatten"

  /** Updates the owning scope with the given symbol, unlinking any others.
   */
  private def replaceSymbolInCurrentScope(sym: Symbol): Unit = exitingFlatten {
    removeSymbolInCurrentScope(sym)
    sym.owner.info.decls enter sym
  }

  private def removeSymbolInCurrentScope(sym: Symbol): Unit = exitingFlatten {
    val scope = sym.owner.info.decls
    val old   = (scope lookupUnshadowedEntries sym.name).toList
    old foreach (scope unlink _)
    def old_s = old map (_.sym) mkString ", "
    if (old.nonEmpty) debuglog(s"In scope of ${sym.owner}, unlinked $old_s")
  }

  private def liftClass(sym: Symbol) {
    if (!sym.isLifted) {
      sym setFlag LIFTED
      debuglog("re-enter " + sym.fullLocationString)
      replaceSymbolInCurrentScope(sym)
    }
  }
  private def liftSymbol(sym: Symbol) {
    liftClass(sym)
    if (sym.needsImplClass)
      liftClass(erasure implClass sym)
  }
  // This is a short-term measure partially working around objects being
  // lifted out of parameterized classes, leaving them referencing
  // invisible type parameters.
  private def isFlattenablePrefix(pre: Type) = {
    val clazz = pre.typeSymbol
    clazz.isClass && !clazz.isPackageClass && {
      // Cannot flatten here: class A[T] { object B }
      // was "at erasurePhase.prev"
      enteringErasure(clazz.typeParams.isEmpty)
    }
  }

  private val flattened = new TypeMap {
    def apply(tp: Type): Type = tp match {
      case TypeRef(pre, sym, args) if isFlattenablePrefix(pre) =>
        assert(args.isEmpty && sym.enclosingTopLevelClass != NoSymbol, sym.ownerChain)
        typeRef(sym.enclosingTopLevelClass.owner.thisType, sym, Nil)
      case ClassInfoType(parents, decls, clazz) =>
        var parents1 = parents
        val decls1 = scopeTransform(clazz) {
          val decls1 = newScope
          if (clazz.isPackageClass) {
            exitingFlatten { decls foreach (decls1 enter _) }
          }
          else {
            val oldowner = clazz.owner
            exitingFlatten { oldowner.info }
            parents1 = parents mapConserve (this)

            for (sym <- decls) {
              if (sym.isTerm && !sym.isStaticModule) {
                decls1 enter sym
                if (sym.isModule)
                  sym.moduleClass setFlag LIFTED
              } else if (sym.isClass)
                liftSymbol(sym)
            }
          }
          decls1
        }
        ClassInfoType(parents1, decls1, clazz)
      case MethodType(params, restp) =>
        val restp1 = apply(restp)
        if (restp1 eq restp) tp else copyMethodType(tp, params, restp1)
      case PolyType(tparams, restp) =>
        val restp1 = apply(restp)
        if (restp1 eq restp) tp else PolyType(tparams, restp1)
      case _ =>
        mapOver(tp)
    }
  }

  def transformInfo(sym: Symbol, tp: Type): Type = flattened(tp)

  protected def newTransformer(unit: CompilationUnit): Transformer = new Flattener

  class Flattener extends Transformer {
    /** Buffers for lifted out classes */
    private val liftedDefs = perRunCaches.newMap[Symbol, ListBuffer[Tree]]()

    override def transform(tree: Tree): Tree = postTransform {
      tree match {
        case PackageDef(_, _) =>
          liftedDefs(tree.symbol.moduleClass) = new ListBuffer
          super.transform(tree)
        case Template(_, _, _) if tree.symbol.isDefinedInPackage =>
          liftedDefs(tree.symbol.owner) = new ListBuffer
          super.transform(tree)
        case ClassDef(_, _, _, _) if tree.symbol.isNestedClass =>
          // SI-5508 Ordering important. In `object O { trait A { trait B } }`, we want `B` to appear after `A` in
          //         the sequence of lifted trees in the enclosing package. Why does this matter? Currently, mixin
          //         needs to transform `A` first to a chance to create accessors for private[this] trait fields
          //         *before* it transforms inner classes that refer to them. This also fixes SI-6231.
          //
          //         Alternative solutions
          //            - create the private[this] accessors eagerly in Namer (but would this cover private[this] fields
          //              added later phases in compilation?)
          //            - move the accessor creation to the Mixin info transformer
          val liftedBuffer = liftedDefs(tree.symbol.enclosingTopLevelClass.owner)
          val index = liftedBuffer.length
          liftedBuffer.insert(index, super.transform(tree))
          if (tree.symbol.sourceModule.isStaticModule)
            removeSymbolInCurrentScope(tree.symbol.sourceModule)
          EmptyTree
        case _ =>
          super.transform(tree)
      }
    }

    private def postTransform(tree: Tree): Tree = {
      val sym = tree.symbol
      val tree1 = tree match {
        case Select(qual, name) if sym.isStaticModule && !sym.isTopLevel =>
          exitingFlatten {
            atPos(tree.pos) {
              val ref = gen.mkAttributedRef(sym)
              if (isQualifierSafeToElide(qual)) ref
              else Block(List(qual), ref).setType(tree.tpe) // need to execute the qualifier but refer directly to the lifted module.
            }
          }
        case _ =>
          tree
      }
      tree1 setType flattened(tree1.tpe)
    }

    /** Transform statements and add lifted definitions to them. */
    override def transformStats(stats: List[Tree], exprOwner: Symbol): List[Tree] = {
      val stats1 = super.transformStats(stats, exprOwner)
      if (currentOwner.isPackageClass) {
        val lifted = liftedDefs(currentOwner).toList
        stats1 ::: lifted
      }
      else stats1
    }
  }
}