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BD Automatic derivation for recursive types is broken in Scala 3 · Issue #1980 · circe/circe · GitHub
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Automatic derivation for recursive types is broken in Scala 3 #1980

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luksow opened this issue Jun 28, 2022 · 8 comments
Open

Automatic derivation for recursive types is broken in Scala 3 #1980

luksow opened this issue Jun 28, 2022 · 8 comments

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@luksow
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luksow commented Jun 28, 2022

Hi,

#!/usr/bin/env scala-cli
using scala "3.1.2"

using lib "io.circe:circe-core_3:0.14.1"
using lib "io.circe:circe-parser_3:0.14.1"
using lib "io.circe:circe-generic_3:0.14.1"

import io.circe._
import io.circe.generic.auto._

case class R1(int: Int, r: Seq[R1])
case class R2(int: Int, r: Option[R2])

summon[Encoder[R1]]
summon[Encoder[R2]]

Both summons fail but with slightly different messages:

[error] ./circe.sc:14:20: cannot reduce summonFrom with
[error]  patterns :  case given encodeA @ _:io.circe.Encoder[Seq[circe.R1]]
[error]              case given evidence$1 @ _:deriving.Mirror.Of[Seq[circe.R1]]
[error] summon[Encoder[R1]]
[error]

and

[error] ./circe.sc:15:20: method derived is declared as `inline`, but was not inlined
[error] 
[error] Try increasing `-Xmax-inlines` above 32
[error] summon[Encoder[R2]]
[error]                    ^

Probably related to scala/scala3#8183
@armanbilge
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Thanks for the report. Note that the following works.

//> using scala "3.1.3"

//> using lib "io.circe::circe-core::0.14.2"
//> using lib "io.circe::circe-parser::0.14.2"

import io.circe._

case class R1(int: Int, r: Seq[R1]) derives Encoder.AsObject
case class R2(int: Int, r: Option[R2]) derives Encoder.AsObject

@main def main =
  summon[Encoder[R1]]
  summon[Encoder[R2]]

@luksow
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luksow commented Jun 28, 2022

@armanbilge Yes, thanks for mentoning this workaround and sorry I forgot to 😃

I'm also looking for a different workaround as I'm not a big fan of mixing my precious data classes with 3rd party libraries - for the sake of domain purity.

@armanbilge
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What is the "3rd party library" in this situation?

@armanbilge
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Is this what you want?

//> using scala "3.1.3"

//> using lib "io.circe::circe-core::0.14.2"
//> using lib "io.circe::circe-parser::0.14.2"

import io.circe._

case class R1(int: Int, r: Seq[R1])
case class R2(int: Int, r: Option[R2])

given Encoder.AsObject[R1] = Encoder.AsObject.derived
given Encoder.AsObject[R2] = Encoder.AsObject.derived

@main def main =
  summon[Encoder[R1]]
  summon[Encoder[R2]]

@luksow
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luksow commented Jun 28, 2022

Oh yes, this looks much better, thanks!!!

3rd party library in that case is circe. if I have a module that consists of only data classes, I prefer to have no dependencies and keep serialization/deserialization where it belongs (ex. router).

@djx314
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djx314 commented Jul 8, 2022 •
edited
Loading

And it seems that when a lib can use derives AObject, it can also use

given Encoder.AsObject[R1] = AObject.derived

It is not the privilege of circe.

@amumurst amumurst mentioned this issue Jul 31, 2022
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12 tasks
@luksow
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luksow commented Dec 7, 2022

New findings, it's probably some "by-name" calls missing, because this doesn't work:

using scala "3.2.1"

import scala.deriving.*
import scala.compiletime.{erasedValue, summonInline}

trait Show[A]:
  def show(a: A): String

given Show[Int] with {
  def show(a: Int): String = a.toString
}

inline def summonAll[T <: Tuple]: List[Show[_]] =
  inline erasedValue[T] match
    case _: EmptyTuple => Nil
    case _: (t *: ts) => summonInline[Show[t]] :: summonAll[ts]

inline given Option[A](using inline s: Show[A]): Show[Option[A]] = new Show[Option[A]] {
  override def show(a: Option[A]): String = a.map(s.show).getOrElse("")
}



inline given[A] (using m: Mirror.Of[A]): Show[A] = new Show[A] {
  override def show(a: A): String = {
    val elemInstances = summonAll[m.MirroredElemTypes]
    elemInstances.mkString(", ")
  }
}

case class Rec(int: Int, rs: Option[Rec])

object Main extends App {
  summon[Show[Rec]]
}

but this is ok:

using scala "3.2.1"

import scala.deriving.*
import scala.compiletime.{erasedValue, summonInline}

trait Show[A]:
  def show(a: A): String

given Show[Int] with {
  def show(a: Int): String = a.toString
}

inline def summonAll[T <: Tuple]: List[Show[_]] =
  inline erasedValue[T] match
    case _: EmptyTuple => Nil
    case _: (t *: ts) => summonInline[Show[t]] :: summonAll[ts]

inline given Option[A](using inline s: => Show[A]): Show[Option[A]] = new Show[Option[A]] {
  override def show(a: Option[A]): String = a.map(s.show).getOrElse("")
}



inline given[A] (using m: Mirror.Of[A]): Show[A] = new Show[A] {
  override def show(a: A): String = {
    val elemInstances = summonAll[m.MirroredElemTypes]
    elemInstances.mkString(", ")
  }
}

case class Rec(int: Int, rs: Option[Rec])

object Main extends App {
  summon[Show[Rec]]
}

@hodga hodga mentioned this issue Nov 28, 2023
Closed
@hamnis hamnis closed this as completed Aug 9, 2024
@luksow
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luksow commented Aug 16, 2024

@hamnis I believe this is still an issue with 0.14.9 and Scala 3.4.2:

//> using dep io.circe::circe-core:0.14.9
//> using dep io.circe::circe-generic:0.14.9
//> using dep io.circe::circe-parser:0.14.9

import io.circe._
import io.circe.generic.auto._

case class R1(int: Int, r: Seq[R1])
case class R2(int: Int, r: Option[R2])

summon[Encoder[R1]]
summon[Encoder[R2]]

output:

[error] ./Main.sc:11:20
[error] cannot reduce summonFrom with
[error]  patterns :  case given encodeA @ _:io.circe.Encoder[Seq[Main$_.this.R1]]
[error]              case given m @ _:scala.deriving.Mirror.Of[Seq[Main$_.this.R1]]
[error] summon[Encoder[R1]]
[error]                    ^
[error] ./Main.sc:12:20
[error] Failed to find an instance of Encoder[scala.Option[Main$_.this.R2]]
[error] summon[Encoder[R2]]
[error]

@hamnis hamnis reopened this Aug 16, 2024
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@hamnis @luksow @armanbilge @djx314








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