Scala example source code file (Imports.scala)

This example Scala source code file (Imports.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

collection, compiler, importhandler, list, memberhandler, nil, nsc, reqandhandler, request, set, string, symbol, t

The Imports.scala Scala example source code

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

package scala.tools.nsc
package interpreter

import scala.collection.{ mutable, immutable }

trait Imports {
  self: IMain =>

  import global._
  import definitions.{ ObjectClass, ScalaPackage, JavaLangPackage, PredefModule }
  import memberHandlers._

  /** Synthetic import handlers for the language defined imports. */
  private def makeWildcardImportHandler(sym: Symbol): ImportHandler = {
    val hd :: tl = sym.fullName.split('.').toList map newTermName
    val tree = Import(
      tl.foldLeft(Ident(hd): Tree)((x, y) => Select(x, y)),
      ImportSelector.wildList
    )
    tree setSymbol sym
    new ImportHandler(tree)
  }

  /** Symbols whose contents are language-defined to be imported. */
  def languageWildcardSyms: List[Symbol] = List(JavaLangPackage, ScalaPackage, PredefModule)
  def languageWildcardHandlers = languageWildcardSyms map makeWildcardImportHandler

  def allImportedNames = importHandlers flatMap (_.importedNames)

  /** Types which have been wildcard imported, such as:
   *    val x = "abc" ; import x._  // type java.lang.String
   *    import java.lang.String._   // object java.lang.String
   *
   *  Used by tab completion.
   *
   *  XXX right now this gets import x._ and import java.lang.String._,
   *  but doesn't figure out import String._.  There's a lot of ad hoc
   *  scope twiddling which should be swept away in favor of digging
   *  into the compiler scopes.
   */
  def sessionWildcards: List[Type] = {
    importHandlers filter (_.importsWildcard) map (_.targetType) distinct
  }

  def languageSymbols        = languageWildcardSyms flatMap membersAtPickler
  def sessionImportedSymbols = importHandlers flatMap (_.importedSymbols)
  def importedSymbols        = languageSymbols ++ sessionImportedSymbols
  def importedTermSymbols    = importedSymbols collect { case x: TermSymbol => x }

  /** Tuples of (source, imported symbols) in the order they were imported.
   */
  def importedSymbolsBySource: List[(Symbol, List[Symbol])] = {
    val lang    = languageWildcardSyms map (sym => (sym, membersAtPickler(sym)))
    val session = importHandlers filter (_.targetType != NoType) map { mh =>
      (mh.targetType.typeSymbol, mh.importedSymbols)
    }

    lang ++ session
  }
  def implicitSymbolsBySource: List[(Symbol, List[Symbol])] = {
    importedSymbolsBySource map {
      case (k, vs) => (k, vs filter (_.isImplicit))
    } filterNot (_._2.isEmpty)
  }

  /** Compute imports that allow definitions from previous
   *  requests to be visible in a new request.  Returns
   *  three pieces of related code:
   *
   *  1. An initial code fragment that should go before
   *  the code of the new request.
   *
   *  2. A code fragment that should go after the code
   *  of the new request.
   *
   *  3. An access path which can be traversed to access
   *  any bindings inside code wrapped by #1 and #2 .
   *
   * The argument is a set of Names that need to be imported.
   *
   * Limitations: This method is not as precise as it could be.
   * (1) It does not process wildcard imports to see what exactly
   * they import.
   * (2) If it imports any names from a request, it imports all
   * of them, which is not really necessary.
   * (3) It imports multiple same-named implicits, but only the
   * last one imported is actually usable.
   */
  case class ComputedImports(prepend: String, append: String, access: String)
  protected def importsCode(wanted: Set[Name], wrapper: Request#Wrapper): ComputedImports = {
    /** Narrow down the list of requests from which imports
     *  should be taken.  Removes requests which cannot contribute
     *  useful imports for the specified set of wanted names.
     */
    case class ReqAndHandler(req: Request, handler: MemberHandler) { }

    def reqsToUse: List[ReqAndHandler] = {
      /** Loop through a list of MemberHandlers and select which ones to keep.
        * 'wanted' is the set of names that need to be imported.
       */
      def select(reqs: List[ReqAndHandler], wanted: Set[Name]): List[ReqAndHandler] = {
        // Single symbol imports might be implicits! See bug #1752.  Rather than
        // try to finesse this, we will mimic all imports for now.
        def keepHandler(handler: MemberHandler) = handler match {
          case _: ImportHandler => true
          case x                => x.definesImplicit || (x.definedNames exists wanted)
        }

        reqs match {
          case Nil                                    => Nil
          case rh :: rest if !keepHandler(rh.handler) => select(rest, wanted)
          case rh :: rest                             =>
            import rh.handler._
            val newWanted = wanted ++ referencedNames -- definedNames -- importedNames
            rh :: select(rest, newWanted)
        }
      }

      /** Flatten the handlers out and pair each with the original request */
      select(allReqAndHandlers reverseMap { case (r, h) => ReqAndHandler(r, h) }, wanted).reverse
    }

    val code, trailingBraces, accessPath = new StringBuilder
    val currentImps = mutable.HashSet[Name]()

    // add code for a new object to hold some imports
    def addWrapper() {
      import nme.{ INTERPRETER_IMPORT_WRAPPER => iw }
      code append (wrapper.prewrap format iw)
      trailingBraces append wrapper.postwrap
      accessPath append s".$iw"
      currentImps.clear()
    }

    def maybeWrap(names: Name*) = if (names exists currentImps) addWrapper()

    def wrapBeforeAndAfter[T](op: => T): T = {
      addWrapper()
      try op finally addWrapper()
    }

    // loop through previous requests, adding imports for each one
    wrapBeforeAndAfter {
      for (ReqAndHandler(req, handler) <- reqsToUse) {
        handler match {
          // If the user entered an import, then just use it; add an import wrapping
          // level if the import might conflict with some other import
          case x: ImportHandler if x.importsWildcard =>
            wrapBeforeAndAfter(code append (x.member + "\n"))
          case x: ImportHandler =>
            maybeWrap(x.importedNames: _*)
            code append (x.member + "\n")
            currentImps ++= x.importedNames

          // For other requests, import each defined name.
          // import them explicitly instead of with _, so that
          // ambiguity errors will not be generated. Also, quote
          // the name of the variable, so that we don't need to
          // handle quoting keywords separately.
          case x =>
            for (sym <- x.definedSymbols) {
              maybeWrap(sym.name)
              code append s"import ${x.path}\n"
              currentImps += sym.name
            }
        }
      }
    }

    ComputedImports(code.toString, trailingBraces.toString, accessPath.toString)
  }

  private def allReqAndHandlers =
    prevRequestList flatMap (req => req.handlers map (req -> _))

  private def membersAtPickler(sym: Symbol): List[Symbol] =
    enteringPickler(sym.info.nonPrivateMembers.toList)
}