Scala example source code file (Parsers.scala)

This example Scala source code file (Parsers.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

block, boolean, collection, compiler, eof, ident, int, list, mutable, nil, nsc, parser, quasiquoteparser, reflection, tree, utilities

The Parsers.scala Scala example source code

package scala.tools.reflect
package quasiquotes

import scala.tools.nsc.ast.parser.{Parsers => ScalaParser}
import scala.tools.nsc.ast.parser.Tokens._
import scala.compat.Platform.EOL
import scala.reflect.internal.util.{BatchSourceFile, SourceFile, FreshNameCreator}
import scala.collection.mutable.ListBuffer
import scala.util.Try

/** Builds upon the vanilla Scala parser and teams up together with Placeholders.scala to emulate holes.
 *  A principled solution to splicing into Scala syntax would be a parser that natively supports holes.
 *  Unfortunately, that's outside of our reach in Scala 2.11, so we have to emulate.
 */
trait Parsers { self: Quasiquotes =>
  import global.{Try => _, _}
  import build.implodePatDefs

  abstract class Parser extends {
    val global: self.global.type = self.global
  } with ScalaParser {
    def parse(code: String): Tree = {
      try {
        val file = new BatchSourceFile(nme.QUASIQUOTE_FILE, code)
        val parser = new QuasiquoteParser(file)
        parser.checkNoEscapingPlaceholders { parser.parseRule(entryPoint) }
      } catch {
        case mi: MalformedInput => c.abort(correspondingPosition(mi.offset), mi.msg)
      }
    }

    def correspondingPosition(offset: Int): Position = {
      val posMapList = posMap.toList
      def containsOffset(start: Int, end: Int) = start <= offset && offset < end
      def fallbackPosition = posMapList match {
        case (pos1, (start1, end1)) :: _   if start1 > offset => pos1
        case _ :+ ((pos2, (start2, end2))) if end2 <= offset  => pos2.withPoint(pos2.point + (end2 - start2))
      }
      posMapList.sliding(2).collect {
        case (pos1, (start1, end1)) :: _                        if containsOffset(start1, end1) => (pos1, offset - start1)
        case (pos1, (start1, end1)) :: (pos2, (start2, _)) :: _ if containsOffset(end1, start2) => (pos1, end1 - start1)
        case _ :: (pos2, (start2, end2)) :: _                   if containsOffset(start2, end2) => (pos2, offset - start2)
      }.map { case (pos, offset) =>
        pos.withPoint(pos.point + offset)
      }.toList.headOption.getOrElse(fallbackPosition)
    }

    override def token2string(token: Int): String = token match {
      case EOF => "end of quote"
      case _ => super.token2string(token)
    }

    def entryPoint: QuasiquoteParser => Tree

    class QuasiquoteParser(source0: SourceFile) extends SourceFileParser(source0) { parser =>
      def isHole: Boolean = isIdent && isHole(in.name)

      def isHole(name: Name): Boolean = holeMap.contains(name)

      override implicit lazy val fresh: FreshNameCreator = new FreshNameCreator(nme.QUASIQUOTE_PREFIX)

      override val treeBuilder = new ParserTreeBuilder {
        override implicit def fresh: FreshNameCreator = parser.fresh

        // q"(..$xs)"
        override def makeTupleTerm(trees: List[Tree]): Tree = TuplePlaceholder(trees)

        // tq"(..$xs)"
        override def makeTupleType(trees: List[Tree]): Tree = TupleTypePlaceholder(trees)

        // q"{ $x }"
        override def makeBlock(stats: List[Tree]): Tree = stats match {
          case (head @ Ident(name)) :: Nil if isHole(name) => Block(Nil, head)
          case _ => super.makeBlock(stats)
        }

        // tq"$a => $b"
        override def makeFunctionTypeTree(argtpes: List[Tree], restpe: Tree): Tree = FunctionTypePlaceholder(argtpes, restpe)

        // make q"val (x: T) = rhs" be equivalent to q"val x: T = rhs" for sake of bug compatibility (SI-8211)
        override def makePatDef(mods: Modifiers, pat: Tree, rhs: Tree) = pat match {
          case TuplePlaceholder(inParensPat :: Nil) => super.makePatDef(mods, inParensPat, rhs)
          case _ => super.makePatDef(mods, pat, rhs)
        }
      }
      import treeBuilder.{global => _, unit => _, _}

      // q"def foo($x)"
      override def param(owner: Name, implicitmod: Int, caseParam: Boolean): ValDef =
        if (isHole && lookingAhead { in.token == COMMA || in.token == RPAREN }) {
          ParamPlaceholder(implicitmod, ident())
        } else super.param(owner, implicitmod, caseParam)

      // q"($x) => ..." && q"class X { selfie => }
      override def convertToParam(tree: Tree): ValDef = tree match {
        case Ident(name) if isHole(name) => ParamPlaceholder(NoFlags, name)
        case _ => super.convertToParam(tree)
      }

      // q"foo match { case $x }"
      override def caseClause(): CaseDef =
        if (isHole && lookingAhead { in.token == CASE || in.token == RBRACE || in.token == SEMI }) {
          val c = CasePlaceholder(ident())
          while (in.token == SEMI) in.nextToken()
          c
        } else
          super.caseClause()

      override def caseBlock(): Tree = super.caseBlock() match {
        case Block(Nil, expr) => expr
        case other => other
      }

      override def isAnnotation: Boolean = super.isAnnotation || (isHole && lookingAhead { isAnnotation })

      override def isModifier: Boolean = super.isModifier || (isHole && lookingAhead { isModifier })

      override def isLocalModifier: Boolean = super.isLocalModifier || (isHole && lookingAhead { isLocalModifier })

      override def isTemplateIntro: Boolean = super.isTemplateIntro || (isHole && lookingAhead { isTemplateIntro })

      override def isDefIntro: Boolean = super.isDefIntro || (isHole && lookingAhead { isDefIntro })

      override def isDclIntro: Boolean = super.isDclIntro || (isHole && lookingAhead { isDclIntro })

      override def isStatSep(token: Int) = token == EOF || super.isStatSep(token)

      override def expectedMsg(token: Int): String =
        if (isHole) expectedMsgTemplate(token2string(token), "unquotee")
        else super.expectedMsg(token)

      // $mods def foo
      // $mods T
      override def readAnnots(annot: => Tree): List[Tree] = in.token match {
        case AT =>
          in.nextToken()
          annot :: readAnnots(annot)
        case _ if isHole && lookingAhead { isAnnotation || isModifier || isDefIntro || isIdent || isStatSep || in.token == LPAREN } =>
          val ann = ModsPlaceholder(in.name)
          in.nextToken()
          ann :: readAnnots(annot)
        case _ =>
          Nil
      }

      override def refineStat(): List[Tree] =
        if (isHole && !isDclIntro) {
          val result = RefineStatPlaceholder(in.name) :: Nil
          in.nextToken()
          result
        } else super.refineStat()

      override def ensureEarlyDef(tree: Tree) = tree match {
        case Ident(name: TermName) if isHole(name) => EarlyDefPlaceholder(name)
        case _ => super.ensureEarlyDef(tree)
      }

      override def isTypedParam(tree: Tree) = super.isTypedParam(tree) || (tree match {
        case Ident(name) if isHole(name) => true
        case _ => false
      })

      override def topStat = super.topStat.orElse {
        case _ if isHole =>
          val stats = PackageStatPlaceholder(in.name) :: Nil
          in.nextToken()
          stats
      }

      override def enumerator(isFirst: Boolean, allowNestedIf: Boolean = true) =
        if (isHole && lookingAhead { in.token == EOF || in.token == RPAREN || isStatSep }) {
          val res = ForEnumPlaceholder(in.name) :: Nil
          in.nextToken()
          res
        } else super.enumerator(isFirst, allowNestedIf)
    }
  }

  /** Wrapper around tree parsed in q"..." quote. Needed to support ..$ splicing on top-level. */
  object Q {
    def apply(tree: Tree): Block = Block(Nil, tree).updateAttachment(Q)
    def unapply(tree: Tree): Option[Tree] = tree match {
      case Block(Nil, contents) if tree.hasAttachment[Q.type] => Some(contents)
      case _ => None
    }
  }

  object TermParser extends Parser {
    def entryPoint = parser => Q(implodePatDefs(gen.mkTreeOrBlock(parser.templateOrTopStatSeq())))
  }

  object TypeParser extends Parser {
    def entryPoint = { parser =>
      if (parser.in.token == EOF)
        TypeTree()
      else
        parser.typ()
    }
  }

  object CaseParser extends Parser {
    def entryPoint = parser => implodePatDefs(parser.caseClause())
  }

  object PatternParser extends Parser {
    def entryPoint = { parser =>
      val pat = parser.noSeq.pattern()
      gen.patvarTransformer.transform(pat)
    }
  }

  object ForEnumeratorParser extends Parser {
    def entryPoint = { parser =>
      val enums = parser.enumerator(isFirst = false, allowNestedIf = false)
      assert(enums.length == 1)
      implodePatDefs(enums.head)
    }
  }

  object FreshName extends FreshNameExtractor(nme.QUASIQUOTE_PREFIX)
}