WIP: Add Dotty build for kernel only

[Alistair-Johnson]

resolves #2356

[kailuowang]

We probably need to change sbt release steps to accommodate this change (different crossScalaVersions for different modules). Basically, we need to do this

    releaseCrossBuild := false,
    releaseProcess := Seq[ReleaseStep](
      checkSnapshotDependencies,
      inquireVersions,
      releaseStepCommandAndRemaining("+clean"),
      releaseStepCommandAndRemaining("+test"),
      setReleaseVersion,
      commitReleaseVersion,
      tagRelease,
      releaseStepCommandAndRemaining("+publishSigned"),
      setNextVersion,
      commitNextVersion,
      releaseStepCommand("sonatypeReleaseAll"),
      pushChanges)
    

also set crossScalaVersions at root to Nil

[Alistair-Johnson]

re the release, it's currently worse than that.

In sbt shell, ++0.10.0-RC1 and then compile will start compiling all the projects under cats, even though 0.10.0-RC1 is only set in kernelJVM. So naturally, +compile won't work either.

Additionally, there are no tests in kernelJVM.

The publish_cmd in travis-publish.sh will go wrong for the same reasons.

So...I think next step is to fix the build in interactive sbt so it works cleanly, otherwise I'm not sure we will have much fun moving forward.

[Alistair-Johnson]

@smarter

The build issues I can/will look at, but I was expecting the compat files of TraversableOnce and WrappedMutableMapBase to be the same as for the 2.13 build. In fact, it looks like the dotty version is a mix of 2.12 and 2.13

It's not a big deal for cats, but I would just to point these out to you in case there is indeed an issue with dotty here.

[smarter]

In fact, it looks like the dotty version is a mix of 2.12 and 2.13

No. Dotty right now only uses the Scala 2.12 standard library (so that you can depend on Scala 2.12 projects in your Dotty build). We'll switch to 2.13 once it's released.

[Alistair-Johnson]

Thanks...I'll change that back to 2,12 👍

[smarter]

If you add .withDottyCompat(scalaVersion.value) you should be able to keep this dependency when compiling with Dotty too (https://github.com/lampepfl/dotty-example-project#getting-your-project-to-compile-with-dotty)

[Alistair-Johnson]

Oh...I missed that!! Cool

[smarter]

That setting doesn't exist in Dotty currently

[smarter]

There's no -Xlint in Dotty currently (and I hope scalafix can completely replace -Xlint)

[smarter]

Latest is 0.2.6 (looks like we forgot to update the example projects)

[Alistair-Johnson]

Indeed... my proof that I did Read The Fantastic Manual, but missed the important bit.

[diesalbla]

Since @travisbrown is already working on a Scala 3 / Dotty migration branch, perhaps this one is no longer needed. #3269

[larsrh]

Thanks for the notice, @diesalbla. Closing this one in favour of #3269.