error: cannot find class or module with type name 'scala.collection.immutable.ListMap.Node'

[richard-jepps]

This might help somebody else as it seems like "game over" if you hit this as a library user, but it's fairly easy to work around.

This example code:

import scala.collection.immutable.HashMap

object ListMapNode {
  def main(args: Array[String]): Unit = {
    import scala.pickling.Defaults._
    import scala.pickling.json._

    val broken = HashMap(new BadHashCode(0) -> 0, new BadHashCode(1) -> 1)

    broken.pickle
  }
}

class BadHashCode(unique: Int) {
  override def hashCode(): Int = 666
}

... produces this exception:

Exception in thread "main" java.lang.RuntimeException: error: cannot find class or module with type name 'scala.collection.immutable.ListMap.Node' full type string: 'scala.collection.immutable.ListMap.Node' at scala.sys.package$.error(package.scala:27) at scala.pickling.internal.package$.liftedTree1$1(package.scala:71) at scala.pickling.internal.package$.typeFromString(package.scala:66) at scala.pickling.FastTypeTag$$anon$2.tpe$lzycompute(FastTags.scala:141) at scala.pickling.FastTypeTag$$anon$2.tpe(FastTags.scala:141) at scala.pickling.runtime.RuntimePickler.pickleInto(RuntimePickler.scala:163) at scala.pickling.runtime.RuntimePickler$DefaultLogic.pickleLogic(RuntimePickler.scala:101) at scala.pickling.runtime.RuntimePickler$Logic$$anonfun$run$1.apply(RuntimePickler.scala:85) at scala.pickling.runtime.RuntimePickler$Logic$$anonfun$run$1.apply(RuntimePickler.scala:84) at scala.pickling.json.JSONPickleBuilder$$anonfun$putField$1.apply(JSONPickleFormat.scala:151) at scala.pickling.json.JSONPickleBuilder$$anonfun$putField$1.apply(JSONPickleFormat.scala:147) at scala.pickling.json.JSONPickleBuilder.ignoringSharedRef(JSONPickleFormat.scala:146) at scala.pickling.json.JSONPickleBuilder.putField(JSONPickleFormat.scala:147) at scala.pickling.runtime.RuntimePickler$Logic.run(RuntimePickler.scala:84) at scala.pickling.runtime.RuntimePickler$$anon$2$$anonfun$putFields$1.apply(RuntimePickler.scala:200) at scala.pickling.runtime.RuntimePickler$$anon$2$$anonfun$putFields$1.apply(RuntimePickler.scala:200) at scala.collection.immutable.List.foreach(List.scala:381) at scala.pickling.runtime.RuntimePickler$$anon$2.putFields(RuntimePickler.scala:200) at scala.pickling.runtime.RuntimePickler$$anon$2.pickle(RuntimePickler.scala:210) at org.reductio.scratch.ListMapNode$ScalaCollectionImmutableHashMap$u005BorgReductioScratchBadHashCode$u002CscalaInt$u005DPickler$macro$1$2$.pickle(ListMapNode.scala:15) at org.reductio.scratch.ListMapNode$ScalaCollectionImmutableHashMap$u005BorgReductioScratchBadHashCode$u002CscalaInt$u005DPickler$macro$1$2$.pickle(ListMapNode.scala:15) at scala.pickling.functions$.pickleInto(functions.scala:26) at scala.pickling.functions$.pickle(functions.scala:14) at scala.pickling.PickleOps.pickle(Ops.scala:9) at org.reductio.scratch.ListMapNode$.main(ListMapNode.scala:15) at org.reductio.scratch.ListMapNode.main(ListMapNode.scala) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:497) at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)

I'm using 0.11.x commit b3a2ad1

Unfortunately the stack trace is truncated within the pickling code, but the line that causes the error is line 68 in the scala.pickling package object:

mirror.staticClass(typename)

... which fails at runtime when looking up a protected class nested inside a public class.

This specific issue is straightforward to workaround, either:

• Use Map instead of HashMap, or ...
• Make sure that your key class produces unique hash codes.