Scala example source code file (SymbolLoaders.scala)

This example Scala source code file (SymbolLoaders.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

abstractfile, classfileloader, classsymbol, compiler, flagassigningcompleter, io, nosymbol, nsc, reflection, some, string, symbol, symbolloader, unit, utilities

The SymbolLoaders.scala Scala example source code

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

package scala.tools.nsc
package symtab

import java.io.IOException
import scala.compat.Platform.currentTime
import scala.tools.nsc.util.{ ClassPath }
import classfile.ClassfileParser
import scala.reflect.internal.MissingRequirementError
import scala.reflect.internal.util.Statistics
import scala.reflect.io.{ AbstractFile, NoAbstractFile }

/** This class ...
 *
 *  @author  Martin Odersky
 *  @version 1.0
 */
abstract class SymbolLoaders {
  val symbolTable: symtab.SymbolTable {
    def settings: Settings
  }
  val platform: backend.Platform {
    val symbolTable: SymbolLoaders.this.symbolTable.type
  }
  import symbolTable._
  /**
   * Required by ClassfileParser. Check documentation in that class for details.
   */
  def lookupMemberAtTyperPhaseIfPossible(sym: Symbol, name: Name): Symbol
  /**
   * Should forward to `Run.compileLate`. The more principled fix would be to
   * determine why this functionality is needed and extract it into a separate
   * interface.
   */
  protected def compileLate(srcfile: AbstractFile): Unit
  import SymbolLoadersStats._

  protected def enterIfNew(owner: Symbol, member: Symbol, completer: SymbolLoader): Symbol = {
    assert(owner.info.decls.lookup(member.name) == NoSymbol, owner.fullName + "." + member.name)
    owner.info.decls enter member
    member
  }

  protected def signalError(root: Symbol, ex: Throwable) {
    if (settings.debug) ex.printStackTrace()
    globalError(ex.getMessage() match {
      case null => "i/o error while loading " + root.name
      case msg  => "error while loading " + root.name + ", " + msg
    })
  }

  /** Enter class with given `name` into scope of `root`
   *  and give them `completer` as type.
   */
  def enterClass(owner: Symbol, name: String, completer: SymbolLoader): Symbol = {
    val clazz = owner.newClass(newTypeName(name))
    clazz setInfo completer
    enterIfNew(owner, clazz, completer)
  }

  /** Enter module with given `name` into scope of `root`
   *  and give them `completer` as type.
   */
  def enterModule(owner: Symbol, name: String, completer: SymbolLoader): Symbol = {
    val module = owner.newModule(newTermName(name))
    module setInfo completer
    module.moduleClass setInfo moduleClassLoader
    enterIfNew(owner, module, completer)
  }

  /** Enter package with given `name` into scope of `root`
   *  and give them `completer` as type.
   */
  def enterPackage(root: Symbol, name: String, completer: SymbolLoader): Symbol = {
    val pname = newTermName(name)
    val preExisting = root.info.decls lookup pname
    if (preExisting != NoSymbol) {
      // Some jars (often, obfuscated ones) include a package and
      // object with the same name. Rather than render them unusable,
      // offer a setting to resolve the conflict one way or the other.
      // This was motivated by the desire to use YourKit probes, which
      // require yjp.jar at runtime. See SI-2089.
      if (settings.termConflict.isDefault)
        throw new TypeError(
          root+" contains object and package with same name: "+
          name+"\none of them needs to be removed from classpath"
        )
      else if (settings.termConflict.value == "package") {
        warning(
          "Resolving package/object name conflict in favor of package " +
          preExisting.fullName + ".  The object will be inaccessible."
        )
        root.info.decls.unlink(preExisting)
      }
      else {
        warning(
          "Resolving package/object name conflict in favor of object " +
          preExisting.fullName + ".  The package will be inaccessible."
        )
        return NoSymbol
      }
    }
    // todo: find out initialization sequence for pkg/pkg.moduleClass is different from enterModule
    val pkg = root.newPackage(pname)
    pkg.moduleClass setInfo completer
    pkg setInfo pkg.moduleClass.tpe
    root.info.decls enter pkg
    pkg
  }

  /** Enter class and module with given `name` into scope of `root`
   *  and give them `completer` as type.
   */
  def enterClassAndModule(root: Symbol, name: String, completer: SymbolLoader) {
    val clazz = enterClass(root, name, completer)
    val module = enterModule(root, name, completer)
    if (!clazz.isAnonymousClass) {
      // Diagnostic for SI-7147
      def msg: String = {
        def symLocation(sym: Symbol) = if (sym == null) "null" else s"${clazz.fullLocationString} (from ${clazz.associatedFile})"
        sm"""Inconsistent class/module symbol pair for `$name` loaded from ${symLocation(root)}.
            |clazz = ${symLocation(clazz)}; clazz.companionModule = ${clazz.companionModule}
            |module = ${symLocation(module)}; module.companionClass = ${module.companionClass}"""
      }
      assert(clazz.companionModule == module, msg)
      assert(module.companionClass == clazz, msg)
    }
  }

  /** In batch mode: Enter class and module with given `name` into scope of `root`
   *  and give them a source completer for given `src` as type.
   *  In IDE mode: Find all toplevel definitions in `src` and enter then into scope of `root`
   *  with source completer for given `src` as type.
   *  (overridden in interactive.Global).
   */
  def enterToplevelsFromSource(root: Symbol, name: String, src: AbstractFile) {
    enterClassAndModule(root, name, new SourcefileLoader(src))
  }

  /** The package objects of scala and scala.reflect should always
   *  be loaded in binary if classfiles are available, even if sourcefiles
   *  are newer. Late-compiling these objects from source leads to compilation
   *  order issues.
   *  Note: We do a name-base comparison here because the method is called before we even
   *  have ReflectPackage defined.
   */
  def binaryOnly(owner: Symbol, name: String): Boolean =
    name == "package" &&
    (owner.fullName == "scala" || owner.fullName == "scala.reflect")

  /** Initialize toplevel class and module symbols in `owner` from class path representation `classRep`
   */
  def initializeFromClassPath(owner: Symbol, classRep: ClassPath[AbstractFile]#ClassRep) {
    ((classRep.binary, classRep.source) : @unchecked) match {
      case (Some(bin), Some(src))
      if platform.needCompile(bin, src) && !binaryOnly(owner, classRep.name) =>
        if (settings.verbose) inform("[symloader] picked up newer source file for " + src.path)
        enterToplevelsFromSource(owner, classRep.name, src)
      case (None, Some(src)) =>
        if (settings.verbose) inform("[symloader] no class, picked up source file for " + src.path)
        enterToplevelsFromSource(owner, classRep.name, src)
      case (Some(bin), _) =>
        enterClassAndModule(owner, classRep.name, newClassLoader(bin))
    }
  }

  /** Create a new loader from a binary classfile.
   *  This is intented as a hook allowing to support loading symbols from
   *  files other than .class files.
   */
  protected def newClassLoader(bin: AbstractFile): SymbolLoader =
    new ClassfileLoader(bin)

  /**
   * A lazy type that completes itself by calling parameter doComplete.
   * Any linked modules/classes or module classes are also initialized.
   * Todo: consider factoring out behavior from TopClassCompleter/SymbolLoader into
   * supertrait SymLoader
   */
  abstract class SymbolLoader extends SymLoader {

    /** Load source or class file for `root`, return */
    protected def doComplete(root: Symbol): Unit

    def sourcefile: Option[AbstractFile] = None

    /**
     * Description of the resource (ClassPath, AbstractFile)
     * being processed by this loader
     */
    protected def description: String

    private var ok = false

    private def setSource(sym: Symbol) {
      sourcefile foreach (sf => sym match {
        case cls: ClassSymbol => cls.associatedFile = sf
        case mod: ModuleSymbol => mod.moduleClass.associatedFile = sf
        case _ => ()
      })
    }

    override def complete(root: Symbol) {
      try {
        val start = currentTime
        val currentphase = phase
        doComplete(root)
        phase = currentphase
        informTime("loaded " + description, start)
        ok = true
        setSource(root)
        setSource(root.companionSymbol) // module -> class, class -> module
      }
      catch {
        case ex @ (_: IOException | _: MissingRequirementError) =>
          ok = false
          signalError(root, ex)
      }
      initRoot(root)
      if (!root.isPackageClass) initRoot(root.companionSymbol)
    }

    override def load(root: Symbol) { complete(root) }

    private def markAbsent(sym: Symbol): Unit = {
      val tpe: Type = if (ok) NoType else ErrorType

      if (sym != NoSymbol)
        sym setInfo tpe
    }
    private def initRoot(root: Symbol) {
      if (root.rawInfo == this)
        List(root, root.moduleClass) foreach markAbsent
      else if (root.isClass && !root.isModuleClass)
        root.rawInfo.load(root)
    }
  }

  /**
   * Load contents of a package
   */
  class PackageLoader(classpath: ClassPath[AbstractFile]) extends SymbolLoader with FlagAgnosticCompleter {
    protected def description = "package loader "+ classpath.name

    protected def doComplete(root: Symbol) {
      assert(root.isPackageClass, root)
      root.setInfo(new PackageClassInfoType(newScope, root))

      if (!root.isRoot) {
        for (classRep <- classpath.classes) {
          initializeFromClassPath(root, classRep)
        }
      }
      if (!root.isEmptyPackageClass) {
        for (pkg <- classpath.packages) {
          enterPackage(root, pkg.name, new PackageLoader(pkg))
        }

        openPackageModule(root)
      }
    }
  }

  class ClassfileLoader(val classfile: AbstractFile) extends SymbolLoader with FlagAssigningCompleter {
    private object classfileParser extends {
      val symbolTable: SymbolLoaders.this.symbolTable.type = SymbolLoaders.this.symbolTable
    } with ClassfileParser {
      override protected type ThisConstantPool = ConstantPool
      override protected def newConstantPool: ThisConstantPool = new ConstantPool
      override protected def lookupMemberAtTyperPhaseIfPossible(sym: Symbol, name: Name): Symbol =
        SymbolLoaders.this.lookupMemberAtTyperPhaseIfPossible(sym, name)
      /*
       * The type alias and the cast (where the alias is used) is needed due to problem described
       * in SI-7585. In this particular case, the problem is that we need to make sure that symbol
       * table used by symbol loaders is exactly the same as they one used by classfileParser.
       * If you look at the path-dependent types we have here everything should work out ok but
       * due to issue described in SI-7585 type-checker cannot tie the knot here.
       *
       */
      private type SymbolLoadersRefined = SymbolLoaders { val symbolTable: classfileParser.symbolTable.type }
      val loaders = SymbolLoaders.this.asInstanceOf[SymbolLoadersRefined]
      val classPath = platform.classPath
    }

    protected def description = "class file "+ classfile.toString

    protected def doComplete(root: Symbol) {
      val start = if (Statistics.canEnable) Statistics.startTimer(classReadNanos) else null
      classfileParser.parse(classfile, root)
      if (root.associatedFile eq NoAbstractFile) {
        root match {
          // In fact, the ModuleSymbol forwards its setter to the module class
          case _: ClassSymbol | _: ModuleSymbol =>
            debuglog("ClassfileLoader setting %s.associatedFile = %s".format(root.name, classfile))
            root.associatedFile = classfile
          case _ =>
            debuglog("Not setting associatedFile to %s because %s is a %s".format(classfile, root.name, root.shortSymbolClass))
        }
      }
      if (Statistics.canEnable) Statistics.stopTimer(classReadNanos, start)
    }
    override def sourcefile: Option[AbstractFile] = classfileParser.srcfile
  }

  class SourcefileLoader(val srcfile: AbstractFile) extends SymbolLoader with FlagAssigningCompleter {
    protected def description = "source file "+ srcfile.toString
    override def fromSource = true
    override def sourcefile = Some(srcfile)
    protected def doComplete(root: Symbol): Unit = compileLate(srcfile)
  }

  object moduleClassLoader extends SymbolLoader with FlagAssigningCompleter {
    protected def description = "module class loader"
    protected def doComplete(root: Symbol) { root.sourceModule.initialize }
  }

  /** used from classfile parser to avoid cyclies */
  var parentsLevel = 0
  var pendingLoadActions: List[() => Unit] = Nil
}

object SymbolLoadersStats {
  import scala.reflect.internal.TypesStats.typerNanos
  val classReadNanos = Statistics.newSubTimer  ("time classfilereading", typerNanos)
}