read json throws NullPointerException with Scala3

[otto-ringhofer]

Reading json generated by write throws NullPointerException with Scala3, the same code with Scala2.13 runs without problems.

build.sbt

scalaVersion := "3.1.0" // 2.13.7 works correct, 3.1.0 crashes
libraryDependencies ++= Seq("com.lihaoyi" %% "upickle" % "1.4.2")

Code reproducing the problem

import upickle.default._

object ShowCrash {
  case class Node(name: String, kids: Vector[Node])

  implicit val nodeRW: ReadWriter[Node] = macroRW[Node]

  val ndb = Node("b", Vector.empty)
  val nda = Node("a", Vector(ndb))

  def main(args: Array[String]): Unit = {
    println(s"nda: $nda")
    val json = write(nda)
    println(s"json: $json")
    val node = read[Node](json)
    println(s"node: $node")
  }
}

Fails with:

nda: Node(a,Vector(Node(b,Vector())))
json: {"name":"a","kids":[{"name":"b","kids":[]}]}
[error] (run-main-1) java.lang.NullPointerException
[error] java.lang.NullPointerException
[error]         at ujson.CharParser.parseNested(CharParser.scala:401)

[edwardcwang]

Another example with Scala 3.1.1 and upickle 2.0.0; not sure if it's the same etiology or not.

Stacktrace:

java.lang.NullPointerException
  ujson.CharParser.visitString(CharParser.scala:617)
  ujson.CharParser.parseStringValue(CharParser.scala:586)
  ujson.CharParser.parseNested(CharParser.scala:379)
  ujson.CharParser.parseTopLevel0(CharParser.scala:324)
  ujson.CharParser.parseTopLevel(CharParser.scala:308)
  ujson.CharParser.parse(CharParser.scala:59)
  ujson.StringParser$.transform(StringParser.scala:28)
  ujson.StringParser$.transform(StringParser.scala:28)
  ujson.Readable$fromTransformer.transform(Readable.scala:13)
  upickle.Api.read$$anonfun$1(Api.scala:37)
  upickle.core.TraceVisitor$.withTrace(TraceVisitor.scala:18)
  upickle.Api.read(Api.scala:37)
  upickle.Api.read$(Api.scala:17)
  upickle.default$.read(Api.scala:157)

Code:

import upickle.default._

case class TestClass(val map: Map[String, Boolean | Int])
object TestClass {
  implicit val rw: upickle.default.ReadWriter[TestClass] =
    upickle.default.macroRW
  implicit val unionRw: upickle.default.ReadWriter[Boolean | Int] =
    upickle.default
      .readwriter[String]
      .bimap[Boolean | Int](
        x => {
          println(s"DEBUG: x = ${x.toString}")
          x.toString
        },
        a => {
          println(s"DEBUG: a = ${a}")
          a match {
            case "true"  => true
            case "false" => false
            case x       => x.toInt
          }
        }
      )
}

def main(): Unit = {
  val myStr = """
{"map":{
  "x":"1","y":"-2","z":"true"
}}
"""

  // Bad
  upickle.default.read[TestClass](myStr)

  // OK
  upickle.default.read[Map[String, Map[String, String]]](myStr)

  val myObj = TestClass(Map("x" -> 1, "y" -> -2, "z" -> true))

  // Bad
  upickle.default.read[TestClass](
    upickle.default.write(myObj)
  )

  // OK
  upickle.default.read[Map[String, Map[String, String]]](
    upickle.default.write(myObj)
  )
}

[Cutkh]

I've experienced the same issue and found a (even more Scala3 idiomatic) workaround: replace the implicit val with a given.
This works at least for the first example above, as well as the code below.

I'm not sure if this is a compiler or a macro issue.

In the code below it actually is sufficient to replace only one implicit val with a given and leave the other be.

final case class Status(statusDetail: Detail)
enum Detail:
  case NoDetail, SomeDetail

// given rwStatus : ReadWriter[Status] = macroRW

// given rwDetail: ReadWriter[Detail] =
//   readwriter[Int].bimap[Detail](_.ordinal, Detail.fromOrdinal)

implicit val rwStatus : ReadWriter[Status] = macroRW

implicit val rwDetail: ReadWriter[Detail] = readwriter[Int].bimap[Detail](_.ordinal, Detail.fromOrdinal)

object TestUpickle:

  def main(args : Array[String]) =
      val someValue = Status(Detail.NoDetail)
      println(write(someValue))
      //Throws NPE when using implicits but works for given
      println(read[Status](write(someValue)))
end TestUpickle

Versions:

JVM version: 18.0.2
Scala version:  3.1.3
Upickle: 2.0.0

Thrown Exception:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "upickle.core.Visitor.visitFloat64StringParts(java.lang.CharSequence, int, int, int)" because "facade" is null
	at ujson.CharParser.visitFloat64StringPartsWithWrapper(CharParser.scala:161)
CharParser.scala:161
	at ujson.CharParser.parseNum(CharParser.scala:148)
CharParser.scala:148
	at ujson.CharParser.parseNested(CharParser.scala:409)
CharParser.scala:409
	at ujson.CharParser.parseTopLevel0(CharParser.scala:324)
CharParser.scala:324
	at ujson.CharParser.parseTopLevel(CharParser.scala:308)
CharParser.scala:308
	at ujson.CharParser.parse(CharParser.scala:59)
CharParser.scala:59
2
	at ujson.StringParser$.transform(StringParser.scala:28)
StringParser.scala:28
	at ujson.Readable$fromTransformer.transform(Readable.scala:13)
Readable.scala:13
	at upickle.Api.read$$anonfun$1(Api.scala:37)
Api.scala:37
	at upickle.core.TraceVisitor$.withTrace(TraceVisitor.scala:18)
TraceVisitor.scala:18
	at upickle.Api.read(Api.scala:37)
Api.scala:37
	at upickle.Api.read$(Api.scala:17)
Api.scala:17
	at upickle.default$.read(Api.scala:157)
Api.scala:157
	at programs.TestUpickle$.main(TestUpickle.scala:26)
TestUpickle.scala:26
	at programs.TestUpickle.main(TestUpickle.scala)