Scala example source code file (MarkupParsers.scala)

This example Scala source code file (MarkupParsers.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

arraybuffer, boolean, collection, compiler, confusedaboutbracescontrol, nsc, position, string, su, tree, truncatedxmlcontrol, unit, utilities, xml

The MarkupParsers.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author Burak Emir
 */

package scala.tools.nsc
package ast.parser

import scala.collection.mutable
import mutable.{ Buffer, ArrayBuffer, ListBuffer }
import scala.util.control.ControlThrowable
import scala.tools.nsc.util.CharArrayReader
import scala.tools.nsc.ast.parser.xml.{MarkupParserCommon, Utility}
import scala.reflect.internal.Chars.{ SU, LF }

// XXX/Note: many/most of the functions in here are almost direct cut and pastes
// from another file - scala.xml.parsing.MarkupParser, it looks like.
// (It was like that when I got here.) They used to be commented "[Duplicate]" but
// since approximately all of them were, I snipped it as noise.  As far as I can
// tell this wasn't for any particularly good reason, but slightly different
// compiler and library parser interfaces meant it would take some setup.
//
// I rewrote most of these, but not as yet the library versions: so if you are
// tempted to touch any of these, please be aware of that situation and try not
// to let it get any worse.  -- paulp
trait MarkupParsers {
  self: Parsers =>

  case object MissingEndTagControl extends ControlThrowable {
    override def getMessage = "start tag was here: "
  }

  case object ConfusedAboutBracesControl extends ControlThrowable {
    override def getMessage = " I encountered a '}' where I didn't expect one, maybe this tag isn't closed <"
  }

  case object TruncatedXMLControl extends ControlThrowable {
    override def getMessage = "input ended while parsing XML"
  }

  import global._

  class MarkupParser(parser: SourceFileParser, final val preserveWS: Boolean) extends MarkupParserCommon {
    import Utility.{ isNameStart, isSpace }
    import Tokens.{ LBRACE, RBRACE }

    type PositionType = Position
    type InputType    = CharArrayReader
    type ElementType  = Tree
    type AttributesType = mutable.Map[String, Tree]
    type NamespaceType = Any  // namespaces ignored

    def mkAttributes(name: String, other: NamespaceType): AttributesType = xAttributes

    val eof = false

    def truncatedError(msg: String): Nothing = throw TruncatedXMLControl
    def xHandleError(that: Char, msg: String) =
      if (ch == SU) throw TruncatedXMLControl
      else reportSyntaxError(msg)

    var input : CharArrayReader = _
    def lookahead(): BufferedIterator[Char] =
      (input.buf drop input.charOffset).iterator.buffered

    import parser.{ symbXMLBuilder => handle, o2p, r2p }

    def curOffset : Int = input.charOffset - 1
    var tmppos : Position = NoPosition
    def ch = input.ch
    /** this method assign the next character to ch and advances in input */
    def nextch() { input.nextChar() }

    protected def ch_returning_nextch: Char = {
      val result = ch; input.nextChar(); result
    }

    def mkProcInstr(position: Position, name: String, text: String): ElementType =
      parser.symbXMLBuilder.procInstr(position, name, text)

    var xEmbeddedBlock = false

    private val debugLastStartElement = new mutable.Stack[(Int, String)]
    private def debugLastPos = debugLastStartElement.top._1
    private def debugLastElem = debugLastStartElement.top._2

    private def errorBraces() = {
      reportSyntaxError("in XML content, please use '}}' to express '}'")
      throw ConfusedAboutBracesControl
    }
    def errorNoEnd(tag: String) = {
      reportSyntaxError("expected closing tag of " + tag)
      throw MissingEndTagControl
    }

    /** checks whether next character starts a Scala block, if yes, skip it.
     * @return true if next character starts a scala block
     */
    def xCheckEmbeddedBlock: Boolean = {
      // attentions, side-effect, used in xText
      xEmbeddedBlock = (ch == '{') && { nextch(); (ch != '{') }
      xEmbeddedBlock
    }

    /** parse attribute and add it to listmap
     *  [41] Attributes   ::= { S Name Eq AttValue }
     *       AttValue     ::= `'` { _  } `'`
     *                      | `"` { _ } `"`
     *                      | `{` scalablock `}`
     */
    def xAttributes = {
      val aMap = mutable.LinkedHashMap[String, Tree]()

      while (isNameStart(ch)) {
        val start = curOffset
        val key = xName
        xEQ()
        val mid = curOffset
        val value: Tree = ch match {
          case '"' | '\'' =>
            val tmp = xAttributeValue(ch_returning_nextch)

            try handle.parseAttribute(r2p(start, mid, curOffset), tmp)
            catch {
              case e: RuntimeException =>
                errorAndResult("error parsing attribute value", parser.errorTermTree)
            }

          case '{'  =>
            nextch()
            xEmbeddedExpr
          case SU =>
            throw TruncatedXMLControl
          case _ =>
            errorAndResult("' or \" delimited attribute value or '{' scala-expr '}' expected", Literal(Constant("<syntax-error>")))
        }
        // well-formedness constraint: unique attribute names
        if (aMap contains key)
          reportSyntaxError("attribute %s may only be defined once" format key)

        aMap(key) = value
        if (ch != '/' && ch != '>')
          xSpace()
      }
      aMap
    }

    /** '<! CharData ::= [CDATA[ ( {char} - {char}"]]>"{char} ) ']]>'
     *
     * see [15]
     */
    def xCharData: Tree = {
      val start = curOffset
      xToken("[CDATA[")
      val mid = curOffset
      xTakeUntil(handle.charData, () => r2p(start, mid, curOffset), "]]>")
    }

    def xUnparsed: Tree = {
      val start = curOffset
      xTakeUntil(handle.unparsed, () => r2p(start, start, curOffset), "</xml:unparsed>")
    }

    /** Comment ::= '<!--' ((Char - '-') | ('-' (Char - '-')))* '-->'
     *
     * see [15]
     */
    def xComment: Tree = {
      val start = curOffset - 2   // Rewinding to include "<!"
      xToken("--")
      xTakeUntil(handle.comment, () => r2p(start, start, curOffset), "-->")
    }

    def appendText(pos: Position, ts: Buffer[Tree], txt: String): Unit = {
      def append(t: String) = ts append handle.text(pos, t)

      if (preserveWS) append(txt)
      else {
        val sb = new StringBuilder()

        txt foreach { c =>
          if (!isSpace(c)) sb append c
          else if (sb.isEmpty || !isSpace(sb.last)) sb append ' '
        }

        val trimmed = sb.toString.trim
        if (!trimmed.isEmpty) append(trimmed)
      }
    }

    /** adds entity/character to ts as side-effect
     *  @precond ch == '&'
     */
    def content_AMP(ts: ArrayBuffer[Tree]) {
      nextch()
      val toAppend = ch match {
        case '#' => // CharacterRef
          nextch()
          val theChar = handle.text(tmppos, xCharRef)
          xToken(';')
          theChar
        case _ =>   // EntityRef
          val n = xName
          xToken(';')
          handle.entityRef(tmppos, n)
      }

      ts append toAppend
    }

    /**
     *  @precond ch == '{'
     *  @postcond: xEmbeddedBlock == false!
     */
    def content_BRACE(p: Position, ts: ArrayBuffer[Tree]): Unit =
      if (xCheckEmbeddedBlock) ts append xEmbeddedExpr
      else appendText(p, ts, xText)

    /** Returns true if it encounters an end tag (without consuming it),
     *  appends trees to ts as side-effect.
     */
    private def content_LT(ts: ArrayBuffer[Tree]): Boolean = {
      if (ch == '/')
        return true   // end tag

      val toAppend = ch match {
        case '!'    => nextch() ; if (ch =='[') xCharData else xComment // CDATA or Comment
        case '?'    => nextch() ; xProcInstr                            // PI
        case _      => element                                        // child node
      }

      ts append toAppend
      false
    }

    def content: Buffer[Tree] = {
      val ts = new ArrayBuffer[Tree]
      while (true) {
        if (xEmbeddedBlock)
          ts append xEmbeddedExpr
        else {
          tmppos = o2p(curOffset)
          ch match {
            // end tag, cdata, comment, pi or child node
            case '<'  => nextch() ; if (content_LT(ts)) return ts
            // either the character '{' or an embedded scala block }
            case '{'  => content_BRACE(tmppos, ts)  // }
            // EntityRef or CharRef
            case '&'  => content_AMP(ts)
            case SU   => return ts
            // text content - here xEmbeddedBlock might be true
            case _    => appendText(tmppos, ts, xText)
          }
        }
      }
      unreachable
    }

    /** '<' element ::= xmlTag1 '>'  { xmlExpr | '{' simpleExpr '}' } ETag
     *                | xmlTag1 '/' '>'
     */
    def element: Tree = {
      val start = curOffset
      val (qname, attrMap) = xTag(())
      if (ch == '/') { // empty element
        xToken("/>")
        handle.element(r2p(start, start, curOffset), qname, attrMap, empty = true, new ListBuffer[Tree])
      }
      else { // handle content
        xToken('>')
        if (qname == "xml:unparsed")
          return xUnparsed

        debugLastStartElement.push((start, qname))
        val ts = content
        xEndTag(qname)
        debugLastStartElement.pop()
        val pos = r2p(start, start, curOffset)
        qname match {
          case "xml:group" => handle.group(pos, ts)
          case _ => handle.element(pos, qname, attrMap, empty = false, ts)
        }
      }
    }

    /** parse character data.
     *  precondition: xEmbeddedBlock == false (we are not in a scala block)
     */
    private def xText: String = {
      assert(!xEmbeddedBlock, "internal error: encountered embedded block")
      val buf = new StringBuilder
      def done = buf.toString

      while (ch != SU) {
        if (ch == '}') {
          if (charComingAfter(nextch()) == '}') nextch()
          else errorBraces()
        }

        buf append ch
        nextch()
        if (xCheckEmbeddedBlock || ch == '<' ||  ch == '&')
          return done
      }
      done
    }

    /** Some try/catch/finally logic used by xLiteral and xLiteralPattern.  */
    private def xLiteralCommon(f: () => Tree, ifTruncated: String => Unit): Tree = {
      try return f()
      catch {
        case c @ TruncatedXMLControl  =>
          ifTruncated(c.getMessage)
        case c @ (MissingEndTagControl | ConfusedAboutBracesControl) =>
          parser.syntaxError(debugLastPos, c.getMessage + debugLastElem + ">")
        case _: ArrayIndexOutOfBoundsException =>
          parser.syntaxError(debugLastPos, "missing end tag in XML literal for <%s>" format debugLastElem)
      }
      finally parser.in resume Tokens.XMLSTART

      parser.errorTermTree
    }

    /** Use a lookahead parser to run speculative body, and return the first char afterward. */
    private def charComingAfter(body: => Unit): Char = {
      try {
        input = input.lookaheadReader
        body
        ch
      }
      finally input = parser.in
    }

    /** xLiteral = element { element }
     *  @return Scala representation of this xml literal
     */
    def xLiteral: Tree = xLiteralCommon(
      () => {
        input = parser.in
        handle.isPattern = false

        val ts = new ArrayBuffer[Tree]
        val start = curOffset
        tmppos = o2p(curOffset)    // Iuli: added this line, as it seems content_LT uses tmppos when creating trees
        content_LT(ts)

        // parse more XML ?
        if (charComingAfter(xSpaceOpt()) == '<') {
          xSpaceOpt()
          while (ch == '<') {
            nextch()
            ts append element
            xSpaceOpt()
          }
          handle.makeXMLseq(r2p(start, start, curOffset), ts)
        }
        else {
          assert(ts.length == 1)
          ts(0)
        }
      },
      msg => parser.incompleteInputError(msg)
    )

    /** @see xmlPattern. resynchronizes after successful parse
     *  @return this xml pattern
     */
    def xLiteralPattern: Tree = xLiteralCommon(
      () => {
        input = parser.in
        saving[Boolean, Tree](handle.isPattern, handle.isPattern = _) {
          handle.isPattern = true
          val tree = xPattern
          xSpaceOpt()
          tree
        }
      },
      msg => parser.syntaxError(curOffset, msg)
    )

    def escapeToScala[A](op: => A, kind: String) = {
      xEmbeddedBlock = false
      val res = saving[List[Int], A](parser.in.sepRegions, parser.in.sepRegions = _) {
        parser.in resume LBRACE
        op
      }
      if (parser.in.token != RBRACE)
        reportSyntaxError(" expected end of Scala "+kind)

      res
    }

    def xEmbeddedExpr: Tree = escapeToScala(parser.block(), "block")

    /** xScalaPatterns  ::= patterns
     */
    def xScalaPatterns: List[Tree] = escapeToScala(parser.xmlSeqPatterns(), "pattern")

    def reportSyntaxError(pos: Int, str: String) = parser.syntaxError(pos, str)
    def reportSyntaxError(str: String) {
      reportSyntaxError(curOffset, "in XML literal: " + str)
      nextch()
    }

    /** '<' xPattern  ::= Name [S] { xmlPattern | '{' pattern3 '}' } ETag
     *                  | Name [S] '/' '>'
     */
    def xPattern: Tree = {
      val start = curOffset
      val qname = xName
      debugLastStartElement.push((start, qname))
      xSpaceOpt()

      val ts = new ArrayBuffer[Tree]
      val isEmptyTag = (ch == '/') && { nextch() ; true }
      xToken('>')

      if (!isEmptyTag) {
        // recurses until it hits a termination condition, then returns
        def doPattern: Boolean = {
          val start1 = curOffset
          if (xEmbeddedBlock) ts ++= xScalaPatterns
          else ch match {
            case '<'  => // tag
              nextch()
              if (ch != '/') ts append xPattern   // child
              else return false                   // terminate

            case '{'  => // embedded Scala patterns
              while (ch == '{') {
                nextch()
                ts ++= xScalaPatterns
              }
              assert(!xEmbeddedBlock, "problem with embedded block")

            case SU   =>
              throw TruncatedXMLControl

            case _    => // text
              appendText(r2p(start1, start1, curOffset), ts, xText)
              // here xEmbeddedBlock might be true:
              // if (xEmbeddedBlock) throw new ApplicationError("after:"+text); // assert
          }
          true
        }

        while (doPattern) { }  // call until false
        xEndTag(qname)
        debugLastStartElement.pop()
      }

      handle.makeXMLpat(r2p(start, start, curOffset), qname, ts)
    }
  } /* class MarkupParser */
}