This is an issue for discussing and tracking necessary step to prepare for a Dotty/Scala3 cross-build.

Inspired by the awesome "Scala Love" conference, I attempted to cross-build util-core with Dotty 0.23.0-RC1. So far it went smoother than expected. In the end there were about 4 compile-errors that I couldn't directly address.

In any case there's some work that has to be done before a real cross-build can be achieved. So far I've identified the following but I will try and update this list as we learn more.

Preparations:

• Update sbt to recent version (e.g. 1.3.10; needed by sbt-dotty)
• Update Scalatest to 3.1.1 (which is cross-published for Dotty)
• Update twitter/util to Scalatest version available for latest Dotty (Dependency on Twitter codebase) | @mosesn
• Remove deprecated Config code | @mosesn
• Wait for Dotty to fix varargs override issue (see Overriding an @varargs method fails under separate compilation scala/scala3#9463)
• Wait for Scalatest 3.2.0 to be published for Dotty version which includes the varargs fix
• Refactor code which is not supported in Scala 3 (e.g. usage of Manifest/TypeTag reflection)
• Add Scala 3 to the CI matrix to prevent regressions in already supported modules
• Cross-build and cross-publish modules which are needed by Finagle and twitter-server (e.g. util-test and util-tunable)

Resources for Dotty migration/cross-building:

• https://github.com/scalacenter/scala-3-migration-guide
• https://github.com/lampepfl/dotty-example-project#getting-your-project-to-compile-with-dotty

I hope you don't mind this type of issue. This is not meant to push anyone, just as a place to discuss and organize things.

Cheers
~ Felix