50 Add cross compilation ability

[Zejnilovic]

Uses @wajda 's cross-compilation plugin adds 2.11 and 2.12 compilations

Fixes #50

[dk1844]

Will it play nice with the release plugin?
We probably want to release both 2.11 & 2.12 versions with the same version number, so at-once somehow. I wonder if we can.

[dk1844]

The comment scares me a bit.

I have a hunch that we don't know if this will work with Spark 3, yet.

[Zejnilovic]

Yeah, I am trying to take it one problem at a time. Also, I think this was a problem from 2.2 to 2.4. Version 3 could be fine.

[wajda]

Spline agent is being tested with Spark 3.0. AFAIK our commons Json4s wrapper works fine in all versions

[Zejnilovic]

Will it play nice with the release plugin?
We probably want to release both 2.11 & 2.12 versions with the same version number, so at-once somehow. I wonder if we can.

This is a setup used by our commons so it should

[wajda]

Will it play nice with the release plugin?
We probably want to release both 2.11 & 2.12 versions with the same version number, so at-once somehow. I wonder if we can.

If we're talking about release:prepare then yes, it will play nicely with it. The trick here is to use release plugin to only take care about versioning (i.e. increment version, create tag in VCS etc). For that you don't care about scala version simply because you don't compile/deploy/publish anything, you only work with the codebase itself, which is the same both all scala binary versions. Even though technically release plugin needs to compile the project, it's enough for the build to pass for any (default) scala ver. The assumption is that the actual testing per every Scala ver is done from the same commit in the CI pipeline before conducting the release stage.

The actual deployment is than done from the tag by running several builds, one per Scala version.
For instance, this is a respective TeamCity build conf for Commons project - https://teamcity.jetbrains.com/admin/editBuildRunners.html?id=buildType:OpenSourceProjects_AbsaOSS_Commons_AutoDeployToOssrh

[Zejnilovic]

A side effect of the cross compilation plugin