How to use PureConfig in Scala 3?

[beneyal]

Hi 🙂

I couldn't find an answer, so I hope it's okay I'm asking here.

I'm migrating a project to Scala 3.1.2, and have this line in my Dependencies.scala:

lazy val pureConfig: Seq[ModuleID] = Seq(
  "com.github.pureconfig" %% "pureconfig" % "0.17.1"
)

When I try to compile using SBT, I get an error Error downloading com.github.pureconfig:pureconfig_3:0.17.1 because it's not found.

My resolvers look like this:

resolvers ++= Seq(
  // a bunch of local resolvers
  Opts.resolver.mavenLocalFile,
  Resolver.defaultLocal,
  Resolver.mavenLocal,
  Resolver.sonatypeRepo("releases"),
  Resolver.sonatypeRepo("snapshots"),
  DefaultMavenRepository
)

What am I missing?

Thank you very much!

[bwbecker]

I'm attempting the same thing. I note that on Maven, pureconfig-core has an artifact for Scala3 (https://mvnrepository.com/artifact/com.github.pureconfig/pureconfig-core) but that just pureconfig does not (https://mvnrepository.com/artifact/com.github.pureconfig/pureconfig). pureconfig-generic also does not have a Scala3 artifact.

So my conclusion is that maintainers are in the process of converting the library but aren't done yet and we'll either need to get involved or be patient.

[leifwickland]

@ruippeixotog Does #1082 accurately describe what's holding up a Scala 3 version of pureconfig-generic?

[ruippeixotog]

Hey everyone! #1082 describes the shortcomings of our project structure, which isn't very user-friendly when it comes to Scala 3.

However, while #1082 makes things somewhat harder, I don't think it's the main reason why we don't have pureconfig-generic for Scala 3. Shapeless itself isn't published for Scala 3 and Scala 3's philosophy is a bit different when it comes to derived instances. There's https://github.com/typelevel/shapeless-3, but it's not a drop-in replacement for Scala 2 in any sense.

Scala 3 has built-in support for type class derivation, PureConfig has some early support for it, and I think that's the recommended way from now on - meaning that we'll probably never have some pureconfig-generic for Scala 3 and definitely never a drop-in replacement. We may have some optional pureconfig-shapeless3 or pureconfig-magnolia modules in the future that improve the capabilities of generic derivation or provide faster/better alternatives.

tl;dr: you'll have to start using pureconfig-core and migrate your code to use native Scala 3 derivation as described here.

[erikerlandson]

I am starting to port coulomb-pureconfig into the Scala 3 world, and I'm trying to figure out what approaches are currently available to me.

My main interest is coming up with ConfigReader and ConfigWriter for the following sealed hierarchy RuntimeUnit:
https://github.com/erikerlandson/coulomb/blob/475db4ef4bb4ef2e19c8a9961f302f836cd9b455/runtime/src/main/scala/coulomb/runtime/runtime.scala#L24

IIUC, one can do derives ConfigReader, however I'd philosophically prefer to not bake pureconfig directly into coulomb-runtime. That leaves the following options:
https://pureconfig.github.io/docs/complex-types.html#complex-types

However Method-1 (again, IIUC) is not yet supported in scala-3 because it makes use of a CoproductHint.

So I wanted to ask, can I make use of Method 2 in scala 3 via pureconfig-core ?

(Method-3 makes use of shapeless, which I want to avoid since its relation to scala-3 is not yet very well defined)

[erikerlandson]

Followup on my comment above, the answer is "yes, Method 2 works!"
https://github.com/erikerlandson/coulomb/blob/b6c819d9ae443d4e39130905a9e2d2b66342ade4/pureconfig/src/main/scala/coulomb/pureconfig.scala#L32

[mdedetrich]

Scala 3 has built-in support for type class derivation, PureConfig has some early support for it, and I think that's the recommended way from now on - meaning that we'll probably never have some pureconfig-generic for Scala 3 and definitely never a drop-in replacement. We may have some optional pureconfig-shapeless3 or pureconfig-magnolia modules in the future that improve the capabilities of generic derivation or provide faster/better alternatives.

tl;dr: you'll have to start using pureconfig-core and migrate your code to use native Scala 3 derivation as described here.

Is not having a pureconfig-generic a hard line in the sand? The reason why I am asking this is because it create a quite burden for libraries that depend on pureconfig to cross compile against Scala 2 vs Scala 3 due to differing source requirements.

This difference is also not trivial, it means that not only do you have to have separate variations ConfigReader (which byitelf would be annoying but at least more tolerable) but also the case class data structures that you are mapping your pureconfig readers to (Scala 2 doesn't have any support for generic derivation and hence code like sealed trait AnimalConf derives ConfigReader doesn't even compile for Scala 2).

If someone was to solve #1082 and also provide a pureconfig-generic for Scala 3 would it be considered for upstream?

[bambuchaAdm]

Do you think putting note about this in getting started would be helpful? I can create PR but need just acknowledge.

[ChidiRnweke]

tl;dr: you'll have to start using pureconfig-core and migrate your code to use native Scala 3 derivation as described here.

Can this be added to the quick start of the documentation in the meantime? I think it would be helpful for Scala 3 users to figure this out without having to dig through issues to get it to work :)

If you give me the go I'm willing to draft a small PR to add ~5-10 lines to the docs (quickstart and readme.md) saying the users need to add "com.github.pureconfig" %% "pureconfig-core" % "0.17.6" in Scala 3 and refer them to the scala-3 derivation page.

[ruippeixotog]

I'm happy to review PRs to improve documentation, @ChidiRnweke. Thanks for helping!

[ChidiRnweke]

I'm happy to review PRs to improve documentation, @ChidiRnweke. Thanks for helping!

The (short documentation) PRs have been here for a while, can you merge it if you have the time? Thanks in advance :)

[ruippeixotog]

Finally done!