Scala 3 support

[akitaylor]

It would be great if the library could be used in Scala 3 projects. What are the prerequisites of this upgrade?
As I can see a new version of Shapeless library for Scala 3 exists, however I can't determine whether it is ready to be used in the current project: https://github.com/typelevel/shapeless-3

Is there any oher prerequisite of the migration?

Thanks!

[julienrf]

It is already possible to support Scala 3 by manually re-implementing the “automatic derivation” part with a macro. It might be possible to use Shapeless 3 to ease that work.

Unfortunately, note that Shapeless 3 is only available for Scala 3, which means that a solution that works for both Scala 2 and Scala 3 might be complicated to implement.

[henricook]

Might you be able to help out those of us trying to migrate a little? It sounds like you've posted a solution here @julienrf but I don't know enough to fully understand it

The kind of Scala 3 compile issues I'm seeing currently are:

[error] 10 |  implicit val format: Format[ValidatedEntityDto] = flat.oformat((__ \ "type").format[String])
[error]    |                                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[error]    |missing argument for parameter derivedReads of method oformat in object flat: (implicit 
[error]    |  derivedReads:
[error]    |    shapeless.Lazy[
[error]    |      julienrf.json.derived.DerivedReads[
[error]    |        mydomain.account.dtos.ValidatedEntityDto,
[error]    |        julienrf.json.derived.TypeTag.ShortClassName]
[error]    |    ]
[error]    |  ,
[error]    |derivedOWrites:
[error]    |  shapeless.Lazy[
[error]    |    julienrf.json.derived.DerivedOWrites[
[error]    |      mydomain.account.dtos.ValidatedEntityDto,
[error]    |      julienrf.json.derived.TypeTag.ShortClassName]
[error]    |  ]
[error]    |): play.api.libs.json.OFormat[mydomain.account.dtos.ValidatedEntityDto]

[jvargas-lumu]

Question. If I am using play 3.0.5 with scala 3, there is no way yet to user your library?

[julienrf]

Hello, this is indeed not possible unless someone contributes Scala 3 support in play-json-derived-codecs instead of using Shapeless, or unless Shapeless 2 supports Scala 3.

[javierfvargas]

Hey Julien, same Javier from the previous question here, just from my personal account now. I have a working version in Scala 3. I'd like to share it with you. I modified your project to cross-compile. I can make a PR but it is not something you could merge because it is work in progress, new files are not documented, the SBT file should be reviewed, a some more details. Let me know what do you think would be the best course of action. I don't have any problem if you just copy the code, no credits are required from my side. I just want your library working again for us.

I already have it working great with a code I am migrating that used the Scala 2 version and didn't really need a lot of changes.

[javierfvargas]

Here the branch with my proposal https://github.com/javierfvargas/play-json-derived-codecs/tree/Scala3_draft

[julienrf]

Hey Javier, thank you very much for sharing your work!
I had a cursory look and the changes look good. To move forward, I think it would be great if you could come up with a PR adding support for Scala 3 while still cross-compiling with Scala 2. Ideally, the test suite should also cross-compile and pass with both versions of the language. Is this something you would be interested in contributing?
I am happy to help or guide further, if needed!

[javierfvargas]

Julien. Actually, the project as I uploaded it is ready to be cross-compiled. Indeed, I did it locally using sbt +publishLocal and my project is using it as a dependency now. I followed https://docs.scala-lang.org/scala3/guides/migration/tutorial-macro-cross-building.html

Regarding unittests, What I did was to copy your tests to the scala-3 folder because I realized that some changes may be necessary. Also you can change across scala versions using ++3.3.3 and there you can run the tests, they run smoothly but when it tries to run the JS tests it fails in my environment because I think I do not have the JS artifacts to run them.

I could try to unify the unittests but if you could check the changes and let me know if you have any concerns it would be better.

I can trigger a PR so that you can leave comments and we move the conversation over the code there. I am willing to help but during work-days I will be slower.