Eventually Migrate to Scala 3

[fm3]

We should have a look at how complicated a migration to scala 3 would be

• Can we continue to use the current library dependencies?
• How much of our logic requires on features that are removed in scala 3? (implicit execution context, database access context?)

We should also have a look at what benefits such a migration would bring, is it worth the effort?

• What cool new language features woud it bring?
• Can we expect performance boosts? During development / In production?

Play 2.9 is reportedly compatible with scala 3. #7366 upgrades to play 2.9

[frcroth]

Findings:

• netlift web framework does not support scala 3. There is a fork, which builds to scala 3 (https://github.com/talenteca/olon-web-framework) but there are no artefacts for scala 3. To support dependencies on scala 2.13, use cross(CrossVersion.for3Use2_13)
• Scapegoat does not work for scala 3: Please compile support for Scala 3.0.0 scapegoat-scala/scapegoat#521
• A lot of depencies of dependencies are not immediately supported with crossVersion. Need to exclude these subdependencies.
• List of dependencies needing some adjustment (cross version and exclusion):
  • lift-common
  • reactivemongo-bson-api
  • webknossos-wrap
  • spire
  • redisclient
  • swagger-scala-module
  • routes-compiler
  • scalatestplus-play
  • play-silhouette
  • play-silhouette-crypto-jca
  • jwt-play-json
  • slick
  • slick-hikaricp
  • slick-codegen
  • scala-xml
• This was not used, but may be of help: https://docs.scala-lang.org/scala3/guides/migration/scala3-migrate.html
  Did these dependency things on https://github.com/scalableminds/webknossos/tree/scala3-spike

[mkurz]

fyi, routes-compiler was renamed is now called play-routes-compiler

[mkurz]

And play-silhouette now lives in https://github.com/playframework/play-silhouette and we are working towards a new release

[mkurz]

slick does not currently provide scala 3 artifacts

[fm3]

Thanks for the updates @mkurz ! We decided to postpone the webknossos Scala 3 upgrade for now. However, we are very much looking forward to the silhouette release 😁 Thanks for all your work!