3.1 release blogpost

[Kordyjan]

The first draft of the 3.1 release blogpost.

[Kordyjan]

@prolativ: can you take a look and suggest changes?

@pikinier20: can you suggest a few sentences about Scastie in Scaladoc and provide a gif showing the new functionality.

[SethTisue]

I apologize for not suggesting this sooner, but I think it's really important that the blog post be super explicit and up-front about the following:

https://twitter.com/SethTisue/status/1450260785762947076

PSA: Scala 3.0 cannot consume 3.1-compiled libraries. Scala 3 minor versions are backwards compatible only, not forwards. This is a big change from Scala 2.

here's what happens if you try:
% echo 'class C' > C.scala
% scalac --scala-version 3.1.0 C.scala
% echo 'class D { new C }' > D.scala
% scalac --scala-version 3.0.0 D.scala
http://dotty.tools.tasty.UnpickleException
TASTy signature has wrong version

So unlike Scala 2, you cannot upgrade your libraries at will. If the library maintainers have moved to a newer Scala 3 minor version, you must move as well in order to use the latest library version.

(Keep in mind that Scala 2 version numbers are epoch.major.minor; Scala 3 version numbers are major.minor.patch.)

(Note that Scala.js has long worked this way; it's normal to have to upgrade Scala.js before upgrading a library. sbt is the same; it's normal to need to upgrade sbt itself before upgrading a plugin. It's fine; I believe we'll all adjust to Scala 3 now being this way too.)

[smarter]

We could have a blurb similar to the one used in the Scala.js blog posts: https://www.scala-js.org/news/2021/08/04/announcing-scalajs-1.7.0/ (starting from "This is a minor release").

[Kordyjan]

I've added a paragraph about compatibility.
@SethTisue @smarter Can you take a look?

[SethTisue]

We are actively working on technical solutions to support forward-compatibility in 3.2.0.

Is this a promise? It isn't, right? We aren't sure if this will actually happen in 3.2.0? If so, consider weakening the wording a little, perhaps to "We are exploring possible technical solutions to..."

[Kordyjan]

It is intended to be a promise - a promise that we will not release another minor version until we have a solution for the compatibility problem.

[dwijnand]

I don't think we should commit - and therefore sound like we're committing - to that. That's not to say I'm not all for finding something better and shipping it in 3.2.0. But if it takes 6 months we might ship everything else as a minor release before the solution. So let's mention intent and desire, but no commitment.

[dwijnand]

This is missing the bit about suggesting to update in a minor version, if updating.

[Kordyjan]

This is missing the bit about suggesting to update in a minor version, if updating.

After #1284 (comment) I and @romanowski decided that if we are recommending not publishing builds for 3.1 at all, it will only add to the confusion if later we suggest in which version the bump should be performed.