Add support for Scoverage (#571)

* Add initial work for ScoverageModule

* style: Move package scoverage from lib to contrib

Suggested by @lefou
> I think, it would be better to add under `mill.contrib.scoverage`.

Pull request: #571

* Initial changes to non-hardcoded scoverage version

* Using task context api to specify dataDir

Now measurement data will be written to:
PROJECT_ROOT/out/MODULE/scoverage/data/

and the html report will be written to:
PROJECT_ROOT/out/MODULE/scoverage/data/htmlReport/

* Remove wild card imports in scoverage

Also remove scoverage dependency from build.sc

* Move htmlReport into worker

Based on what I've seen in
scalalib, scalajslib, scalanativelib, playlib, and twirllib modules.

Still need to add tests

* Add basic docs + tests for scoverage

I still am working on testing the actual generation of
reports.

* Use cross-module for scoverage worker

Now we can support multiple versions of scoverage
by adding them to the crossmodule list.

Also now running the local publish script succeeds.

* Add scoverage to ci tests

* Add detailed ScoverageModule documentation

* Test scoverage dataDir

* Remove <pre> tags in scaladoc

* Add scoverage dependency in less hacky way

* Modify scoverage tests to check classpaths

* Put docs in alphabetical order

* Test classpaths for scoverage runtime

* Remove abstract def test: ScoverageTests

* Construct classloader differently

* Revert "Construct classloader differently"

This reverts commit fccf9a94cc38fb9e2be58a9ff90b00b65f339db6.

* Revert "Construct classloader differently"

Also fixes unfound error in html report

This reverts commit fccf9a94cc38fb9e2be58a9ff90b00b65f339db6.

* Fix classpath for scoverage worker

1 files changed, 39 insertions, 0 deletions

diff --git a/contrib/scoverage/src/ScoverageReportWorker.scala b/contrib/scoverage/src/ScoverageReportWorker.scala
new file mode 100644
index 00000000..1aaa31ad
--- /dev/null
+++ b/contrib/scoverage/src/ScoverageReportWorker.scala
@@ -0,0 +1,39 @@
+package mill.contrib.scoverage
+
+import mill.{Agg, T}
+import mill.api.{ClassLoader, Ctx, Result}
+import mill.define.{Discover, ExternalModule, Worker}
+import mill.eval.PathRef
+
+class ScoverageReportWorker {
+  private var scoverageInstanceCache = Option.empty[(Long, api.ScoverageReportWorkerApi)]
+
+  def bridge(classpath: Agg[os.Path])
+                    (implicit ctx: Ctx) = {
+    val classloaderSig =
+      classpath.map(p => p.toString().hashCode + os.mtime(p)).sum
+    scoverageInstanceCache match {
+      case Some((sig, bridge)) if sig == classloaderSig => bridge
+      case _ =>
+        val toolsClassPath = classpath.map(_.toIO.toURI.toURL).toVector
+        ctx.log.debug("Loading classes from\n"+toolsClassPath.mkString("\n"))
+        val cl = ClassLoader.create(
+          toolsClassPath,
+          getClass.getClassLoader
+        )
+        val bridge = cl
+          .loadClass("mill.contrib.scoverage.worker.ScoverageReportWorkerImpl")
+          .getDeclaredConstructor()
+          .newInstance()
+          .asInstanceOf[api.ScoverageReportWorkerApi]
+        scoverageInstanceCache = Some((classloaderSig, bridge))
+        bridge
+    }
+  }
+}
+
+object ScoverageReportWorkerApi extends ExternalModule {
+
+  def scoverageReportWorker = T.worker { new ScoverageReportWorker() }
+  lazy val millDiscover = Discover[this.type]
+}