Support the sbt/zinc build

[dwijnand]

I had to switch back to regular sbt-extras because the coursier-based one (https://github.com/coursier/sbt-extras) that uses this launcher doesn't completely work inside sbt/zinc's build.

It fails to correctly feed the compiler-interface dependency (xsbti) when compiling the compiler-bridge (xsbt) for anything other than Scala 2.12 (the default version):

> compilerBridge210/compile
[info] Compiling 24 Scala sources to /d/zinc/internal/compiler-bridge/target-2.10/scala-2.10/classes ...
[info] Non-compiled module 'compiler-bridge_2.10' for Scala 2.10.7. Compiling...
/var/folders/8r/km1jjvy15md88bvtrzvmn0rw0000gn/T/sbt_25bfa7c6/xsbt/API.scala:12: error: object api is not a member of package xsbti
import xsbti.api._
             ^
...

cc @jvican

[alexarchambault]

That seems to originate from some issues with the DependencyResolution that sbt-lm-coursier provides via the dependencyResolution key. (sbt-lm-coursier being the coursier plugin injected by default by the coursier-based sbt launcher.)

As a workaround, one can manually add sbt-coursier (addSbtPlugin("io.get-coursier" % "sbt-coursier" % "1.1.0-M13-4") in project/project/plugins.sbt, then addSbtCoursier in project/plugins.sbt). That way, the sbt launcher doesn't try to inject sbt-lm-coursier.

[alexarchambault]

In more details, the issue with the DependencyResolution from sbt-lm-coursier has to see with inter-project dependencies. Namely, there's a org.scala-sbt:compiler-interface project in the zinc build. It takes over any org.scala-sbt:compiler-interface dependency in the build. Which is an issue with org.scala-sbt:compiler-bridge_2.10:1.2.5, that should have directly pulled org.scala-sbt:compiler-interface:1.2.5