support default values for case class fields

[mberndt123]

It seems like this is all that's required to support defaults for case class fields in Scala 3.

Users need -Yretain-trees in their scalacOptions as per the documentation: https://github.com/softwaremill/magnolia#limitations

I also bumped sbt as it crashes otherwise on recent OpenJDK versions.

[soujiro32167]

This is great! I can't get my test to pass though...

/*
 * Copyright 2019-2023 OVO Energy Limited
 *
 * SPDX-License-Identifier: Apache-2.0
 */

package vulcan.generic

import vulcan.{AvroError, Codec}

final class AvroFieldDefaultSpec extends CodecBase {

  sealed trait Enum extends Product {
    self =>
    def value: String = self.productPrefix
  }

  object Enum {
    case object A extends Enum

    case object B extends Enum

    implicit val codec: Codec[Enum] = deriveEnum(
      symbols = List(A.value, B.value),
      encode = _.value,
      decode = {
        case "A" => Right(A)
        case "B" => Right(B)
        case other => Left(AvroError(s"Invalid S: $other"))
      }
    )
  }

  sealed trait Union

  object Union {
    case class A(a: Int) extends Union

    case class B(b: String) extends Union

    implicit val codec: Codec[Union] = Codec.derive
  }

  describe("AvroFieldDefault") {
    it("should create a schema with a default for a field") {
      case class Foo(
        a: Int = 1,
        b: String = "foo",
      )

      object Foo {
        implicit val codec: Codec[Foo] = Codec.derive
      }

      assert(Foo.codec.schema.exists(_.getField("a").defaultVal() == 1))
      assert(Foo.codec.schema.exists(_.getField("b").defaultVal() == "foo"))
    }
    
    it("should fail when the default value is not of the correct type") {
      case class InvalidDefault(
        a: Int
      )
      object InvalidDefault {
        implicit val codec: Codec[InvalidDefault] = Codec.derive
      }

      assertSchemaError[InvalidDefault]
    }

   it("should fail when annotating an Option") {
     case class InvalidDefault2(
       a: Option[String] = Some("foo")
     )
     object InvalidDefault2 {
       implicit val codec: Codec[InvalidDefault2] = Codec.derive
     }

     assertSchemaError[InvalidDefault2]
   }

   it("should succeed when annotating an enum first element") {
     case class HasSFirst(
                           s: Enum = Enum.A
                         )
     object HasSFirst {
       implicit val codec: Codec[HasSFirst] = Codec.derive
     }

     assert(HasSFirst.codec.schema.exists(_.getField("s").defaultVal() == "A"))
   }

   it("should succeed when annotating an enum second element") {
     case class HasSSecond(
        s: Enum = Enum.B
      )
     object HasSSecond {
       implicit val codec: Codec[HasSSecond] = Codec.derive
     }

     assert(HasSSecond.codec.schema.exists(_.getField("s").defaultVal() == "B"))
   }

   it("should succeed with the first member of a union"){
     case class HasUnion(
       u: Union = Union.A(1)
     )
     object HasUnion {
       implicit val codec: Codec[HasUnion] = Codec.derive
     }

     case class Empty()
     object Empty {
       implicit val codec: Codec[Empty] = Codec.derive
     }

     assertSchemaIs[HasUnion](
       """{"type":"record","name":"HasUnion","namespace":"vulcan.generic.AvroFieldDefaultSpec.<local AvroFieldDefaultSpec>","fields":[{"name":"u","type":[{"type":"record","name":"A","namespace":"vulcan.generic.AvroFieldDefaultSpec.Union","fields":[{"name":"a","type":"int"}]},{"type":"record","name":"B","namespace":"vulcan.generic.AvroFieldDefaultSpec.Union","fields":[{"name":"b","type":"string"}]}],"default":{"a":1}}]}"""
     )

     val result = unsafeDecode[HasUnion](unsafeEncode[Empty](Empty()))

     assert(result == HasUnion(Union.A(1)))

   }

   it("should fail with the second member of a union"){
     case class HasUnionSecond(
       u: Union = Union.B("foo")
     )
     object HasUnionSecond {
       implicit val codec: Codec[HasUnionSecond] = Codec.derive
     }

     assertSchemaError[HasUnionSecond]
   }
  }
}

[mberndt123]

Did you compile with the -Yretain-trees compiler flag?

[mberndt123]

Oh, I had added it to Scala 3 only. I've made the same change for Scala 2 now, for the poor sods stuck on the legacy version 😉

[mberndt123]

I've stolen one of your tests to add it to your PR. Seems to work if you enable the -Yretain-trees compiler flag!

[soujiro32167]

I was sure it was enabled 🤔 Thanks for checking

[mberndt123]

@soujiro32167 So does it work for you now?

[soujiro32167]

I've discovered some fascinating stuff:

   it("should fail when annotating an Option") {
     case class InvalidDefault2(
       a: Option[String] = Some("foo")
     )
     object InvalidDefault2 {
       implicit val codec: Codec[InvalidDefault2] = Codec.derive
     }

     assertSchemaError[InvalidDefault2]
   }

results in a stack overflow error:

An exception or error caused a run to abort. 
java.lang.StackOverflowError
	at vulcan.Codec$OptionCodec.<init>(Codec.scala:1017)
	at vulcan.Codec$.option(Codec.scala:995)
	at vulcan.generic.AvroFieldDefaultSpec$InvalidDefault2$2$.<init>(AvroFieldDefaultSpec.scala:64)
	at vulcan.generic.AvroFieldDefaultSpec.InvalidDefault2$lzycompute$1(AvroFieldDefaultSpec.scala:63)
	at vulcan.generic.AvroFieldDefaultSpec.vulcan$generic$AvroFieldDefaultSpec$$InvalidDefault2$3(AvroFieldDefaultSpec.scala:63)
	at vulcan.generic.AvroFieldDefaultSpec$InvalidDefault2$2$.$anonfun$codec$19(AvroFieldDefaultSpec.scala:64)

while

case class InvalidDefault2(
                            a: Option[String] = Some("foo")
                          )
object InvalidDefault2 {
  implicit val codec: Codec[InvalidDefault2] = Codec.derive
}

final class AvroFieldDefaultSpec extends CodecBase {
  describe("AvroFieldDefault") {
    it("should create a schema with a default for a field") {
      assert(Foo.codec.schema.exists(_.getField("a").defaultVal() == 1))
      assert(Foo.codec.schema.exists(_.getField("b").defaultVal() == "foo"))
    }

   it("should fail when annotating an Option") {

     assertSchemaError[InvalidDefault2]
   }

works just fine 🤯

[soujiro32167]

Added a PR with all the tests https://github.com/mberndt123/vulcan/pull/1

[mberndt123]

@bplommer Any chance this could be merged?

[mberndt123]

Since this project appears to be unmaintained, we've decided to use avro4s instead 🤷🏻‍♂️

[ayoub-benali]

Hi, I just realised that https://github.com/fd4s/vulcan/pull/579 aims at tackling the same problem. @bplommer Is it possible to give this PR a review ?

[soujiro32167]

@mberndt123 could you merge https://github.com/mberndt123/vulcan/pull/1 into your repo? In case this PR gets reviewed

[ayoub-benali]

@soujiro32167 would you be able to make a PR later to add https://github.com/mberndt123/vulcan/pull/1 directly here ?

[soujiro32167]

@ayoub-benali here we go https://github.com/fd4s/vulcan/pull/593