Support pure JavaModules

[lefou]

Looks like there is no need for being a ScalaModule at all.
There is some sanity check, but it looks like not really needed.

Fix #154

I also fixed an unrelated issue with ExtraCoursierSupport, which was inheriting ScalaModule. Instead of extending ScalaModule it should use the bindDependency task provided for exactly that use case by CoursierSupport. Without this fix, extending ExtraCoursierSupport can be problematic in downstream modules.

[lolgab]

Can you add a test that checks some java code?

[lolgab]

Suggested change

	case _ =>
	// FIXME: ask Mill, but `mill.main.BuildInfo` isn't available in older versions
	T.task("2.13")
	case _ => T.task("3")

I would set as "3" so it will continue to work for at least two decades. We don't even need to change it to mill.main.BuildInfo

[lolgab]

Actually, it can be null. Let me push a commit on top

[lefou]

We could also remove the whole sanity check or make it optional by using an Option[String] for the Scala version.

[lolgab]

I used String or null since Option can't be used directly with the Java API, and I didn't want to use java's Optional.
I pushed a commit on top

[lolgab]

Very cool that MiMa can be used to test Java projects! It's a very useful tool, maybe this can be another differentiator for Java folks to move to Mill! :)

[lefou]

Yeah, I think we could even drop the need to be a PublishModule, since we already have all targets to configure the jars to compare. Being a PublishModule just brings some nice defaults, but we could match this dynamically, like I did for the scalaBinVersion task. That way, users can use MiMa in arbitrary modules, without messing with mill __.publish targets.

[lolgab]

I think Option has a .orNull method

Suggested change

	scalaBinVersionOrNullTask().getOrElse(null),
	scalaBinVersionOrNullTask().orNull,

[lefou]

Huh, itest for Mill 0.11.0 fails with:

Publishing Artifact(com.github.lolgab,mill-mima_mill0.11_2.13,0.1.0-11-b9e295-DIRTYfe46ad38) to ivy repo /home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/ivyRepo/local
Publishing Artifact(com.github.lolgab,mill-mima-worker-api_2.13,0.1.0-11-b9e295-DIRTYfe46ad38) to ivy repo /home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/ivyRepo/local
Publishing Artifact(com.github.lolgab,mill-mima-worker-impl_2.13,0.1.0-11-b9e295-DIRTYfe46ad38) to ivy repo /home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/ivyRepo/local
Starting integration test [5/5]: java
Invoking integration test [5/5]: java: Targets(targets=List(prepare),expectedExitCode=0,env=Map(),noServer=true)
Failed integration test [5/5]: java

Details for 1 failed tests: 
Output of failed test: java
---------- Output for Invocation: TestInvocationResult(Targets(targets=List(prepare),expectedExitCode=0,env=Map(),noServer=true),Failed,Vector(),Vector(),Some(/home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/java/out-532035302293496723.log))
[info] compiling 2 Scala sources to /home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/java/out/mill-build/compile.dest/classes ...
[error] /home/lefou/work/opensource/lolgab-mill-mima/out/itest/0.11.0/test.dest/java/build.sc:14:8: object creation impossible.
[error] Missing implementation for member of trait ScalaModule:
[error]   def scalaVersion: mill.T[String] = ???
[error] object curr extends Common with Mima {
[error]        ^
[error] one error found
1 targets failed
compile Compilation failed

---------- End of output

But I fail to see where we still require ScalaModule

[lefou]

Oh, there is an issue with the ExtraCoursierSupport for Mill 0.11

[lefou]

This is good for a next review now. Once merged, a new release would be nice.