Consider scoping the scala version only in ThisBuild or in Global

problem

scalaVersion is scoped for every build. This often causes problems when people want to set their scala versions globally, because they are overriden by the sbt defaults.

expectation

When people override the scala version in Global or in ThisBuild, sbt should pick up the scala versions from there since sbt does not scope sbt version to every project.

notes

I am not sure this is technically possible. But I think it’s an interesting effort that will make sbt more intuitive. @olafurpg has complained several times that this is the current behaviour.

sbt version: 0.13.x and 1.x.

[dwijnand]

Due to the mechanics of derive and what we do with it in Defaults (namely define scalaVersion, scalaBinaryVersion and, specifically, crossScalaVersions) this is a regression in sbt 0.13.16-M1.

steps

Given this build:

val t = project in file(".")
aggregateProjects(foo, bar)

      scalaVersion in ThisBuild := "2.11.11"
crossScalaVersions in ThisBuild := Seq("2.10.6", "2.11.11", "2.12.2")

val foo = project
val bar = project

problem

In sbt 0.13.16-M1 or sbt 0.13.16-RC1:

> show crossScalaVersions
[info] foo/*:crossScalaVersions
[info] 	List(2.11.11)
[info] bar/*:crossScalaVersions
[info] 	List(2.11.11)
[info] t/*:crossScalaVersions
[info] 	List(2.11.11)

expectation

How it used to work, such as in sbt 0.13.15:

> show crossScalaVersions
[info] foo/*:crossScalaVersions
[info] 	List(2.10.6, 2.11.11, 2.12.2)
[info] bar/*:crossScalaVersions
[info] 	List(2.10.6, 2.11.11, 2.12.2)
[info] t/*:crossScalaVersions
[info] 	List(2.10.6, 2.11.11, 2.12.2)

notes

The commit that folded sbt-cross-building into sbt introduced the project-scoped scalaVersion setting: https://github.com/sbt/sbt/commit/ff017eb475fbf18b8066125596bcd1a8cd8fb3ff#diff-6373e7f7122325e753b75fe1cc76ff5fR247

[eed3si9n]

This is a feature interaction between sbt version cross building and Scala version cross building.

Normally I try not to mess with existing globally-scoped keys, and I was aware that people often define scalaVersion in ThisBuild, so I did define a forwarder:

+    scalaVersion := {
+      val scalaV = scalaVersion.value
+      val sv = (sbtBinaryVersion in pluginCrossBuild).value
+      if (sbtPlugin.value) scalaVersionFromSbtBinaryVersion(sv)
+      else scalaV
+    },

I think I just need to do something similar with crossScalaVersions.

Note that recently merged https://github.com/sbt/sbt/pull/3356 re-injects scalaVersion at project-level on ^^. This might allow us to remove project-level scalaVersion initialization in Defaults, but I considering ^ compile etc crossScalaVersions forwarding still might be needed.