Release 3.0.0-RC2

[anatoliykmetyuk]

• Finalize release
  • Look at the milestone of the version being released. Move all the open issues from it to the next milestone.
  • Merge branch of the previous release into master to guarantee that all of the commits are propagated to master
• Publish artifacts to Maven via CI
  • Create branch 3.0.0-RC2 from master
  • On that branch, set baseVersion and tag it as 3.0.0-RC2
  • On master, set baseVersion to the next version to be released
• Update scalaVersion (and, if applicable, the sbt-dotty version) in the Dotty ecosystem projects
  • https://github.com/scala/scala3-example-project
  • https://github.com/scala/scala3-example-project/tree/mill
  • https://github.com/scala/scala3.g8
  • https://github.com/scala/scala3-cross.g8
  • https://github.com/lampepfl/scala3-staging.g8
  • https://github.com/scala/scala3-tasty-inspector.g8
  • https://github.com/lampepfl/homebrew-brew
  • https://github.com/lampepfl/packtest
  • https://github.com/lampepfl/xml-interpolator
  • https://github.com/scalacenter/scastie
    • PR submitted
    • PR merged
    • https://scastie.scala-lang.org/ -> Build Settings -> Dotty mentions <rc-version>
  • Dotty reference compiler
    • PR submitted
    • PR merged
  • Scalac
    • PR submitted
    • PR merged
  • Update the dotty-repl Coursier app definition
    • PR submitted: Upgrade Dotty to 3.0.0-RC2 coursier/apps#90
• Announce the release
  • Publish releases for the RC and stable versions on GitHub Releases
  • Publish Blog Post on dotty.epfl.ch
  • Make an announcement thread on https://contributors.scala-lang.org
  • Tweet the announcement blog post on https://twitter.com/scala_lang

Instructions on how to release

[smarter]

When upgrading the scalaVersion in the example projects, I suggest also upgrading to sbt 1.5.0-RC2 and removing sbt-dotty: this way we'll get more people to test that sbt 1.5 works well with scala 3 by default.

[japgolly]

Experimental feature experimental.erasedDefinitions may only be used with nightly or snapshot version of compiler

Oh wow... Wow so we can't use any "experimental" features any more... ok... Can't help but feel like this decision treat users like children who don't understand what "experimental" means. Ultimately it's going to prevent the Dotty team from getting a bunch of early, useful feedback from users trying this stuff out in RCs. Feels like a real shoot-yourself-in-the-foot move.

How are features going to become non-experimental? Take erased classes for example, I would've tested the hell out of them but now will it just be the Dotty team testing it internally, to later remove the experimental status? If so when? What version? 3.0.0? or 3.0.1? Seeing as the announcement isn't out yet, it'd be really useful to clarify how this is going to work out.

[smarter]

Can't help but feel like this decision treat users like children who don't understand what "experimental" means.

And if we allow experimental features in release builds, people complain that experimental is meaningless and we're just recklessly adding features to the language, there's no way to make everyone happy here: https://www.reddit.com/r/scala/comments/m50trg/martin_odersky_explains_the_motivations_behind/gqxj2zv/

How are features going to become non-experimental?

By following the SIP process hopefully.

will it just be the Dotty team testing it internally

No, we very much want people to test these features themselves, we just require that they use a nightly build to do so, given that we provide nightly builds on Maven Central, I don't think this is a tall order, it's also very much inspired by the way Rust does thing which seems to have worked well for them so far.

If so when? What version?

Depends on when/if the feature is accepted by the SIP committee and the community.

[SethTisue]

I strongly support this change. But I would like to add:

Historically, it has been rather difficult to use Scala 2 nightlies on some codebases, namely if there are dependencies, perhaps transitive ones, that are fully cross-versioned (as opposed to only by major version): so e.g. kind-projector, Scalameta. I've struggled with this myself, even though I'm pretty well versed in sbt. In simple cases I'm sometimes able to resolve it adding an override or by publishing a dependency locally, but sometimes it gets tricky. (In other cases I use dbuild, but I'm almost the only person for whom that's a reasonable solution.)

I assume users might run into comparable difficulties in testing Scala 3 nightlies with their codebases. If so, it remains a build tool issue and not a language issue, but: I believe this change will put some pressure on build tool maintainers to make nightlies convenient to use on more projects. Whether it's through documentation, or actual changes to the tool, or both. (Typically sbt leads on these sorts of issues and then the other tools try to catch up.)

/cc @eed3si9n

[smarter]

I'm not sure what build tool issue you have in mind, if you're using a project whose cross-version is the full compiler version, that means it relies on APIs which might change between every version, so you can't expect it to work with a nightly. If you're feeling brave you can always try replacing "foo" %%% "bla" by "foo_specificversion" % "bla" in your build, but a build tool shouldn't do that for you automatically since there's no guarantee it will work. (I'd say the real solution here is: don't use compiler plugins, implement your changes in the actual compiler instead!).

[SethTisue]

so you can't expect it to work with a nightly

It might not, but often it does; and if it does, it's a win because now I can test something I couldn't have otherwise tested.

If you're feeling brave you can always try replacing "foo" %%% "bla" by "foo_specificversion" % "bla" in your build

in my experience it's often not that simple, because of transitive dependencies

[anatoliykmetyuk]

When upgrading the scalaVersion in the example projects, I suggest also upgrading to sbt 1.5.0-RC2 and removing sbt-dotty: this way we'll get more people to test that sbt 1.5 works well with scala 3 by default.

Getting errors like:

    useScala3doc := true,
    ^
sbt.compiler.EvalException: Type error in expression

And

lazy val crossVersions = Seq(Option(rcVersion), dottyLatestNightlyBuild()).flatten
                                                ^
sbt.compiler.EvalException: Type error in expression

I set sbt.version=1.5.0-RC2 in project/build.properties and removed the SBT Dotty plugin on scala3-example-project. Any ideas on how to migrate those settings?

[eed3si9n]

scala3-example-project/build.sbt:2: error: not found: value dottyLatestNightlyBuild
lazy val crossVersions = Seq(Option(rcVersion), dottyLatestNightlyBuild()).flatten
                                                ^
scala3-example-project/build.sbt:11: error: not found: value useScala3doc
    useScala3doc := true,
    ^
sbt.compiler.EvalException: Type error in expression
[error] sbt.compiler.EvalException: Type error in expression
[error] Use 'last' for the full log.
[warn] Project loading failed: (r)etry, (q)uit, (l)ast, or (i)gnore? (default: r)

It says the values are not found, so maybe the feature was dropped? Could you open an issue under sbt/sbt? We can continue the discussion there.

[smarter]

@anatoliykmetyuk you should just remove the useScala3doc setting, it's no longer needed.

[smarter]

Oh and dottyLatestNightlyBuild doesn't exist in sbt either and should be removed from the example project (I don't think it should have ever been added, this is supposed to be a simple example you can copy-paste, it shouldn't include more advanced things like cross-compilation)

[anatoliykmetyuk]

Is the removal of these settings issue-worthy at sbt/sbt?

[smarter]

No, not adding these settings was intentional

[japgolly]

No, we very much want people to test these features themselves, we just require that they use a nightly build to do

Well in that case I'd be happy to help test the new features. I was already looking forward to anyway. The problem is it seems near impossible for me to do so because I'm not working on a dependency-free project, I'm working on a chain of libraries that depend on each other and I'm depending on other libraries that've been published for RC1 (and soon RC2) proper. I spent a limited amount of time trying to make that work and failed. If using nighties is going to become a more common practice then can we get some documentation on how to configure sbt? Ideally it would be alongside the RC2 release notes because this is the first release to force people on to nightlies, and I imagine many others are going to struggle with how to setup sbt to mix-and-match all different versions.