Generic case class error in Scala 3

[amnaredo]

Case classes with type parameters should be supported according to the documentation.

Currently this does not seem to work and causes the case class reader object traversal to crash.

Environment

• uPickle: 1.4.0
• Scala: 3.0.0
• JRE: 17

Reproduce

import upickle.default._

object Main extends App:

  case class Container[T](
    value: T
  )

  given ReadWriter[Container[String]] = macroRW

  val container = Container("test")
  val json = """{ "value": "test" }"""

  println("\nWrite:")
  println(write(container))

  println("\nRead:")
  println(read[Container[String]](json))

Result

Write:
{}

Read:
java.lang.ArrayIndexOutOfBoundsException: 0
    at Main$$anon$2.productElement(main.scala:9)
    at Main$Container$.fromProduct(main.scala:5)
    at Main$Container$.fromProduct(main.scala:5)
    at Main$$anon$1.make(main.scala:9)
    at Main$$anon$1.make(main.scala:9)
    at upickle.implicits.CaseClassReaderPiece$$anon$1.visitEnd(CaseClassReader.scala:30)
    at ujson.CharParser.liftedTree1$1(CharParser.scala:496)
    at ujson.CharParser.tryCloseCollection(CharParser.scala:496)
    at ujson.CharParser.parseNested(CharParser.scala:462)
    at ujson.CharParser.parseTopLevel0(CharParser.scala:323)
    at ujson.CharParser.parseTopLevel(CharParser.scala:307)
    at ujson.CharParser.parse(CharParser.scala:59)
    at ujson.StringParser$.transform(StringParser.scala:28)
    at ujson.StringParser$.transform(StringParser.scala:28)
    at ujson.Readable$fromTransformer.transform(Readable.scala:13)
    at upickle.Api.read$$anonfun$1(Api.scala:37)
    at upickle.core.TraceVisitor$.withTrace(TraceVisitor.scala:18)
    at upickle.Api.read(Api.scala:37)
    at upickle.Api.read$(Api.scala:17)
    at upickle.default$.read(Api.scala:133)
    at Main$.<clinit>(main.scala:18)

Expected

Write:
{ "value" : "test" }

Read:
Container("test")

ID: 353 Original Author: martin-ockajak