[dtech]

> The crucial point here is if Scala 3 maintains backwards compatibility with Scala 2.x.

The Scala team is keenly aware. Scala 3 can use Scala 2.13 libraries - in fact the 3.0 stdlib is the exact same .jar as the 2.13 stdlib - and a future version of 2.13 will be able to use scala 3 artifacts as long as it doesn't use 3+ only language features.

More details at https://scalacenter.github.io/scala-3-migration-guide/docs/c...

[merb]

Except Macros. So a lot of stuff.

[dtech]

Yes, but they're mostly constrained in libraries and there's a way to publish them so both 2.13 and 3 can consume them. You can expect "core" ecosystem libraries to be cross-published and most others don't depend on macros.

Note that most things you'd need macros for in 2.13 have language support in 3, so for user code - if that even uses macros at all - the upgrade path is fairly straightforward.