ConstructingParser throws NoSuchMethodError in Scala 3

[cayhorstmann]

Save https://horstmann.com/unblog/2020-11-27/index.html to a local file and run

import java.io.File
import scala.xml.parsing.ConstructingParser
val filename="..."
val file = new File(filename)
val parser = ConstructingParser.fromFile(file, preserveWS = true)
val doc = parser.document().docElem

In Scala 2, this works perfectly. In Scala 3.0.0, an exception is thrown:

java.lang.NoSuchMethodError: 'scala.xml.parsing.MarkupParser scala.xml.parsing.MarkupParser$WithLookAhead.scala$xml$parsing$MarkupParser$WithLookAhead$$$outer()'
  at scala.xml.parsing.MarkupParser.lookahead(MarkupParser.scala:77)
  at scala.xml.parsing.MarkupParser.lookahead$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.lookahead(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParserCommon.peek(MarkupParserCommon.scala:267)
  at scala.xml.parsing.MarkupParserCommon.xTakeUntil(MarkupParserCommon.scala:249)
  at scala.xml.parsing.MarkupParserCommon.xTakeUntil$(MarkupParserCommon.scala:25)
  at scala.xml.parsing.ConstructingParser.xTakeUntil(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.xCharData(MarkupParser.scala:382)
  at scala.xml.parsing.MarkupParser.xCharData$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.xCharData(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content1(MarkupParser.scala:427)
  at scala.xml.parsing.MarkupParser.content1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content(MarkupParser.scala:462)
  at scala.xml.parsing.MarkupParser.content$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.element1(MarkupParser.scala:591)
  at scala.xml.parsing.MarkupParser.element1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.element1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content1(MarkupParser.scala:436)
  at scala.xml.parsing.MarkupParser.content1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content(MarkupParser.scala:462)
  at scala.xml.parsing.MarkupParser.content$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.element1(MarkupParser.scala:591)
  at scala.xml.parsing.MarkupParser.element1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.element1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content1(MarkupParser.scala:436)
  at scala.xml.parsing.MarkupParser.content1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content(MarkupParser.scala:462)
  at scala.xml.parsing.MarkupParser.content$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.element1(MarkupParser.scala:591)
  at scala.xml.parsing.MarkupParser.element1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.element1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content1(MarkupParser.scala:436)
  at scala.xml.parsing.MarkupParser.content1$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content1(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.content(MarkupParser.scala:462)
  at scala.xml.parsing.MarkupParser.content$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.content(ConstructingParser.scala:52)
  at scala.xml.parsing.MarkupParser.document(MarkupParser.scala:251)
  at scala.xml.parsing.MarkupParser.document$(MarkupParser.scala:33)
  at scala.xml.parsing.ConstructingParser.document(ConstructingParser.scala:52)

The offending code is

def lookahead(): BufferedIterator[Char] = curInput match {
    case curInputWLA: WithLookAhead =>
      curInputWLA.lookahead()

The library dependency in build.sbt:

libraryDependencies ++= Seq(
  "org.scala-lang.modules" %% "scala-xml" % "2.0.0",
)

[SethTisue]

I'm able to reproduce the problem locally in the Scala 3 REPL.

Once we dig into this it seems like it has to ultimately be a Scala 3 bug rather than something we did wrong in this repo. Regardless, we need this scala-xml ticket anyway because we'll need to publish a new version of the library once there's a compiler fix.

[joroKr21]

Next step would be to getDeclaredMethods of the WithLookAhead class and see what is the name of the outer accessor (if it exists)

[SethTisue]

minimized (not sure the string is absolutely minimal, but it doesn't matter, we just want something short that triggers it)

  @Test
  def issue541: Unit = {
    val xml =
      """|<script>// <![CDATA[
         |[]; // ]]>
         |</script>""".stripMargin
    val parser = ConstructingParser.fromSource(Source.fromString(xml), preserveWS = true)
    parser.document().docElem  // shouldn't crash
  }

[SethTisue]

I've reported the Scala 3 compiler bug responsible over at scala/scala3#13096

Here in this repo, I will submit a pull request with a workaround.

[SethTisue]

PR: #542

[SethTisue]

fixed in 2.0.1 which is now published