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Scala 2 builds

Jelly-JVM is written in Scala 3, but we also provide packages that mostly work with Scala 2.13. They include only Scala 2 dependencies and are published to Maven Central.

How to use this?

  • In your project enable the Scala 2.13 TASTy reader – read more in Scala docs.
  • Add Jelly-JVM dependencies with the _2.13 suffilx, e.g., eu.ostrzyciel.jelly %% jelly-core % 0.14.0 in sbt (assuming you are building a Scala 2.13 project).
  • If you get conflicting Scala version suffix errors from sbt, you may need to add exclusion rules like this: 
    libraryDependencies ++= List(
  "eu.ostrzyciel.jelly" %% "jelly-stream" % jellyVersion,
  "eu.ostrzyciel.jelly" %% "jelly-grpc" % jellyVersion,
  "eu.ostrzyciel.jelly" %% "jelly-rdf4j" % jellyVersion,
).map(_ excludeAll (
  // These are two leftover Scala 3 dependencies that are improperly handled in the pseudo-Scala 2
  // version of Jelly due to a quirk with how the scalapb plugin works. We must exclude them here.
  ExclusionRule(organization = "org.apache.pekko", name = "pekko-grpc-runtime_3"),
  ExclusionRule(organization = "com.thesamet.scalapb", name = "scalapb-runtime_3"),
))

That's it!

Is this supported?

Kind of. It does work (we tested it), but it's not a perfect solution, as Jelly-JVM was from the start designed only for Scala 3. Support for Scala 2 will be dropped in Jelly-JVM 1.2.0 – the support will remain as-is in versions 1.0.x and 1.1.x.

Technical notes – maintainer guide

The thing is a rather ugly hack in sbt. On the one hand, we need sbt to think we need Scala 2 dependencies for one build, and that we want to publish these artifacts with the _2.13 suffix in Maven. On the other, this is still Scala 3 code and it must be compiled with the Scala 3 compiler.

The solution looks like this – we trick sbt, by having two Scala 3 builds (one with a slightly different version), and then treating one of them differently using conditionals. Don't judge me.