Bring the scala3-v2 branch up-to-date, review, publish

[adamw]

We've started work on Magnolia v2 for Scala 3 some time ago, which included support for AnyVals some time ago, but the effort has stalled. Since then, the scala3 and scala3-v2 branches have diverged. This is a an umbrella task to fix this situation and push the v2 release:

• merge any changes from scala3 to scala3-v2
• review & merge Add isSingletonCasesEnum flag #457 (comment)
• verify that [question] Derivation differences between Scala 2 and 3 #550 (comment) is fixed with the new release, update magnolia usages in tapir
• make sure all scala 3 & scala 2 types are supported in the new release
• review the code to make sure the API & macro usage is consistent

[baldram]

Hey! Is there any known workaround for auto derivation that would allow to deal with value classes and opaque types that would not require me to teach Magnolia how to handle each specific type?

This is an issue with libraries like Difflicious. Say, I want to compare two case classes. For the recursive derivation process, I need to define manually Differ for each specific type (opaque/AnyVal), e.g. given Differ[Foo] = Differ.useEquals(v => String.valueOf(Foo.unwrap(v))).

PS: Below is a workaround I developed for AnyVal and opaque type. This workaround extends Difflicious to support value objects. Ideally, however, would be to implement this support at the Magnolia level.

A feedback on potential issues, gaps, or areas for improvement is welcome.

• https://gist.github.com/baldram/c794d81ce3940133f90b41db0be1e710
• https://gist.github.com/baldram/00f2195c07f5b9d95f99ca28906d795d

[adamw]

I don't know of any workarounds, other than implementing this in Magnolia, which I'm well aware is well overdue - but, we lack the manpower to tackle this at this moment unfortunately