Add support for Scala 3

[lukaseder]

Our Scala extension library does not yet formally support Scala 3, nor does our ScalaGenerator. This task is to collect changes in both cases:

• scala_3 extension library
• ScalaGenerator
• We'll have to run code generation tests both on Scala 2.13 and 3 to be sure everything works
• Native enum type support: https://dotty.epfl.ch/docs/reference/enums/enums.html see also: Add <enumsAsScalaSealedTraits/> to let ScalaGenerator generate Java enums #10998
• Opt-in null support: https://dotty.epfl.ch/3.0.0/docs/reference/other-new-features/explicit-nulls.html

Known issues:

• scalac 3 can't compile code that worked with scalac 2 and Java, when extending Java class with lots of covariant overrides scala/scala3#18764
• Compile errors of generated classes using scala 3 #15760
• Compilation error in ScalaGenerator generated code of UpdatableRecord subclasses when using scalac 3 #16072
• Compilation error in ScalaGenerator generated code of generated DAOs when using scalac 3 #16074

Once implemented, the jOOQ Open Source Edition will require at least Scala 3 to work.

[eltherion]

@lukaseder Any chance to have support for Scala 3.x by the end of this year? It is a highly anticipated feature as Scala 3.0 has been released over 2 years ago. 🙏

[lukaseder]

@eltherion I cannot make any promises as this probably amounts to quite a big project, especially the code generation parts.

What are you looking for, specifically? As far as I understand, jOOQ just works out of the box with Scala 3 as well, so you probably have any specific ideas?

[eltherion]

@lukaseder I meant jooq-scala artifact. It's available only for Scala 2.13.

[lukaseder]

Yes, that'll be part of this task. I don't see offering an upgrade to this scala extensions library as an independent task (e.g. supporting Scala 3 only in the extensions library but not in the code generator doesn't make sense).

Is there anything missing from that library to make it work for Scala 3? Anything specific that doesn't work (anymore), currently? Keeping in mind that this extensions library is just a bunch of implicit class and implicit def utilities, so it's completely optional.

[eltherion]

Hmm, in this case I think no, thank you for the answer! 🙏

[lukaseder]

Thanks for the feedback. Just in case, if something in vanilla jOOQ (without extensions) doesn't work well in Scala 3, you can always create separate bug reports. We can fix bugs before officially supporting Scala 3 in the extensions and code generator.

[lukaseder]

As discussed in the comments here:

• Compilation error in ScalaGenerator generated code of UpdatableRecord subclasses when using scalac 3 #16072

Scala 3 is really such a moving target with tons of compiler regressions and incompatible changes that I can't really commit to any Scala 3 strategy right now. There's always the JavaGenerator for the pragmatic folks...