Unable to locate the JsonDecoder for a type constructor containing a nested type.

Hello,

This issue appeared when updating to zio-json: 0.7.0.
Here is an example:

final case class Id[A](value: A)
object Id {
  implicit def decoder[A: JsonDecoder]: JsonDecoder[Id[A]] = DeriveJsonDecoder.gen[Id[A]]
}

final case class Person(name: String) extends AnyVal
object Person {
  implicit val decoder: JsonDecoder[Person] = DeriveJsonDecoder.gen
}


final case class People(ids: Id[Person])
object People {
  implicit val decoder: JsonDecoder[People] = DeriveJsonDecoder.gen
}

Error:

magnolia: could not find JsonDecoder.Typeclass for type Id[Person]
[error]     in parameter 'ids' of product type People
[error]   implicit val decoder: JsonDecoder[People] = DeriveJsonDecoder.gen

People.decoder cannot find the decoder for Id[Person].
There is an issue on finding the Id.decoder ..

when we manually add the decoder to Id companion object:

object Id {
    implicit val decoderIds: JsonDecoder[Id[Person]] = DeriveJsonDecoder.gen
}

The same error appears. But it works only when we add that decoder to People companion.

object People {
  implicit val decoderIds: JsonDecoder[Id[Person]] = Id.decoder
  implicit val decoder: JsonDecoder[People] = DeriveJsonDecoder.gen
}

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Attempt	Started (GMT+0)	Solution
🔴 @Anshgrover23	Jun 28, 2024, 4:11:00 PM	WIP
🔴 @omarnagy91	Jul 9, 2024, 4:58:42 AM	WIP
🟢 @ifndev	Jul 29, 2024, 1:45:06 PM	#1139

/attempt #1128

Options

Cancel my attempt

@wi101 I am unable to reproduce What Scala version are you using? Are the definitions all in the same file? Are you sure you have no conflicting versions in your project?

/attempt #1128

@987Nabil

This is the full example (the same file)

import zio.json.{DeriveJsonDecoder, JsonDecoder}

final case class Id[A](value: A)
object Id {
  implicit def decoder[A: JsonDecoder]: JsonDecoder[Id[A]] = DeriveJsonDecoder.gen[Id[A]]
}

final case class Person(name: String) extends AnyVal
object Person {
  implicit val decoder: JsonDecoder[Person] = DeriveJsonDecoder.gen
}


final case class People(ids: Id[Person])
object People {
  implicit val decoder: JsonDecoder[People] = DeriveJsonDecoder.gen
}

scalaVersion: 2.13.14
zioJsonVersion: 0.7.0

Hi, this issue seems stale so I gave it a shot.

What I found out:

PR #1115 introduced "codec derivation for types that already have encoder and decoder"
Faced with an error in one of the tests (same test case as this issue) with scala 2.12, it was decided to remove the feature for this specific version.
Turns out it doesn't work on 2.13 either

What I did:

I reverted the VersionSpecific code as it did not fix the issue
I identified the problematic line

zio-json/zio-json/shared/src/main/scala-2.13/zio/json/JsonCodecVersionSpecific.scala

Line 5 in 6d2abd4

implicit def fromEncoderDecoder[A](implicit encoder: JsonEncoder[A], decoder: JsonDecoder[A]): JsonCodec[A] =
As I couldn't find a reason for the 'encoder' parameter being implicit, and found no test cases justifying it, i made it explicit again
Tests now passes on all Scala versions
Code provided by @wi101 compiles successfully
PR yet to be submitted...

/attempt #1128

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@ifndev	1 bounty from 1 project	Python, C++, TypeScript & more		Cancel attempt

💡 @ifndev submitted a pull request that claims the bounty. You can visit your bounty board to reward.

Just submitted PR #1139

It's based on the assumption that making the 'encoder' parameter implicit was a mistake, so it may be wrong.
Ideally, adding a test for a specific case covered by PR #1115 would be a good idea.

Let me know if I missed something :)

Hey, when can we expect the PR to be merged? I am working on an implementation that depends on this fix.

🎉🎈 @ifndev has been awarded $200! 🎈🎊