Explicit handling of scalac plugins and related enablement options

scalalib/src/ScalaModule.scala

@@ -104,6 +104,14 @@ trait ScalaModule extends JavaModule { outer =>
    */
   protected def mandatoryScalacOptions = T { Seq.empty[String] }
 
+  /**
+   * Scalac options to active the compiler plugins.
+   */
+  protected def enablePluginScalacOption: Target[Seq[String]] = T {
+    val resolvedJars = resolveDeps(scalacPluginIvyDeps.map(_.map(_.exclude("*" -> "*"))))()
+    resolvedJars.iterator.toSeq.map(jar => s"-Xplugin:${jar}")
+  }
+
   /**
    * Command-line options to pass to the Scala compiler defined by the user.
    * Consumers should use `allScalacOptions` to read them.
@@ -114,7 +122,8 @@ trait ScalaModule extends JavaModule { outer =>
    * Aggregation of all the options passed to the Scala compiler.
    * In most cases, instead of overriding this Target you want to override `scalacOptions` instead.
    */
-  def allScalacOptions = T { mandatoryScalacOptions() ++ scalacOptions() }
+  def allScalacOptions =
+    T { mandatoryScalacOptions() ++ enablePluginScalacOption() ++ scalacOptions() }
 
   def scalaDocOptions: T[Seq[String]] = T {
     val defaults =

scalalib/worker/src/mill/scalalib/worker/ZincWorkerImpl.scala

@@ -309,19 +309,19 @@ class ZincWorkerImpl(
       reporter: Option[CompileProblemReporter]
   )(implicit ctx: ZincWorkerApi.Ctx): mill.api.Result[(os.Path, os.Path)] = {
     withCompilers(
-      scalaVersion,
-      scalaOrganization,
-      compilerClasspath,
-      scalacPluginClasspath
+      scalaVersion = scalaVersion,
+      scalaOrganization = scalaOrganization,
+      compilerClasspath = compilerClasspath,
+      scalacPluginClasspath = scalacPluginClasspath
     ) { compilers: Compilers =>
       compileInternal(
-        upstreamCompileOutput,
-        sources,
-        compileClasspath,
-        javacOptions,
-        scalacOptions = scalacPluginClasspath.map(jar => s"-Xplugin:$jar").toSeq ++ scalacOptions,
-        compilers,
-        reporter
+        upstreamCompileOutput = upstreamCompileOutput,
+        sources = sources,
+        compileClasspath = compileClasspath,
+        javacOptions = javacOptions,
+        scalacOptions = scalacOptions,
+        compilers = compilers,
+        reporter = reporter
       )
     }
   }