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

[wi101]

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
}

[jdegoes]

/bounty $200

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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

[Anshgrover23]

/attempt #1128

Options

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[987Nabil]

@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?

[omarnagy91]

/attempt #1128

[wi101]

@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

[ifndev]

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 https://github.com/zio/zio-json/blob/6d2abd46385af7002b193d52d19f49dbc42e0d01/zio-json/shared/src/main/scala-2.13/zio/json/JsonCodecVersionSpecific.scala#L5
• 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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[algora-pbc[bot]]

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

[ifndev]

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 :)

[Not-Aru]

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

[algora-pbc[bot]]

🎉🎈 @ifndev has been awarded $200! 🎈🎊

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