Project with multiple scala versions

[arjantop]

It it currently possible to have a single project with multiple scala versions? Spark (for example) is one of the projects that lags behind in supported scala versions. So that one team could be using scala 2.12 and the other 2.11 with spark.

[johnynek]

There is no support for this now, and it would be non-trivial.

What we do at Stripe is have separate repositories for scala 2.11 and 2.12 code. There is a 2.12 branch of these rules:
https://github.com/bazelbuild/rules_scala/tree/scala2_12

[arjantop]

Thanks, just researching and evaluating bazel. We had such multiple scala versions mess in the past.

[pauldraper]

FYI, brief description of how https://github.com/andyscott/rules_scala_annex decided to implement multiple Scala versions in a single workspace:

A ScalaConfiguration provider.

ScalaConfiguration = provider(
    fields = {
        "compiler_classpath": "the compiler classpath",
        "runtime_classpath": "the minimal runtime classpath",
    },
)

And an easy way for users to define Scala versions.

# define @scala
scala_repository("scala", ("org.scala-lang", "2.12.4"), "@compiler_bridge_2_12//:src")

And all scala_* rules have a scala attribute that requires a ScalaConfiguration. The attribute defaults to @scala, but you could specify @scala_2_11, @scala_2_12, @scala_dotty, @scala_lightbend, etc. explicitly for each target. Nothing real fancy....there's no checks for matching Scala versions, or any cross-compilation help.

Actually, an example of use is rules_scala_annex's own runners (scalac, scalafmt, proto). They have deps and certain Scala version requirements, and so they use a Scala version (@scala_annex_scala_2_12) isolated from the user's choice of Scala version.

[arjantop]

@pauldraper Are there plans to eventually merge the two efforts?

[pauldraper]

No clear plan as of this time; I just wanted to share a possible approach for this project.

[ittaiz]

I think the best approach (if you can wait) is to hold on for Bazel’s support for activating multiple toolchains on the same run from the command line.

…

On Wed, 3 Oct 2018 at 17:45 Paul Draper ***@***.***> wrote: No clear plan as of this time; I just wanted to share a possible approach for this project. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#393 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABUIF2lgwB7e4DsIKU_LZrwzk6aJtRh3ks5uhM1ugaJpZM4Rf-7w> .