Initial module-specific extension support to GenIdea (#684)

* Initial module-specific extension support to GenIdea

* Contribute Facets to JavaModule
* Generate additional files under .idea directory

* Introduced more generel Element result type and unit tests

* Moved intellijModulePath into GenIdeaModule

* Added unit test for GenIdea extension

(Missed that previously)

12 files changed, 365 insertions, 40 deletions

diff --git a/scalalib/src/GenIdeaImpl.scala b/scalalib/src/GenIdeaImpl.scala
index f737d473..f91eadaf 100755
--- a/scalalib/src/GenIdeaImpl.scala
+++ b/scalalib/src/GenIdeaImpl.scala
@@ -10,9 +10,11 @@ import mill.api.{Loose, Result, Strict}
 import mill.define._
 import mill.eval.{Evaluator, PathRef}
 import mill.{T, scalalib}
-import os.Path
-
+import os.{Path, RelPath}
 import scala.util.Try
+import scala.xml.{Elem, MetaData, NodeSeq, Null, UnprefixedAttribute}
+
+import mill.scalalib.GenIdeaModule.{IdeaConfigFile, JavaFacet}
 
 
 object GenIdea extends ExternalModule {
@@ -34,10 +36,13 @@ case class GenIdeaImpl(evaluator: Evaluator,
                        ctx: Log with Home,
                        rootModule: BaseModule,
                        discover: Discover[_]) {
+  import GenIdeaImpl._
+
   val cwd: Path = rootModule.millSourcePath
 
-  def run(): Unit = {
+  val ideaConfigVersion = 4
 
+  def run(): Unit = {
 
     val pp = new scala.xml.PrettyPrinter(999, 4)
     val jdkInfo = extractCurrentJdk(cwd / ".idea" / "misc.xml").getOrElse(("JDK_1_8", "1.8 (1)"))
@@ -68,7 +73,7 @@ case class GenIdeaImpl(evaluator: Evaluator,
                     ctx: Option[Log],
                     fetchMillModules: Boolean = true): Seq[(os.RelPath, scala.xml.Node)] = {
 
-    val modules = rootModule.millInternal.segmentsToModules.values
+    val modules: Seq[(Segments, JavaModule)] = rootModule.millInternal.segmentsToModules.values
       .collect{ case x: scalalib.JavaModule => x }
       .flatMap(_.transitiveModuleDeps)
       .map(x => (x.millModuleSegments, x))
@@ -112,7 +117,9 @@ case class GenIdeaImpl(evaluator: Evaluator,
                              pluginClasspath: Loose.Agg[Path],
                              scalaOptions: Seq[String],
                              compilerClasspath: Loose.Agg[Path],
-                             libraryClasspath: Loose.Agg[Path]
+                             libraryClasspath: Loose.Agg[Path],
+                             facets: Seq[JavaFacet],
+                             configFileContributions: Seq[IdeaConfigFile]
                              )
 
     val resolved = evalOrElse(evaluator, Task.sequence(for((path, mod) <- modules) yield {
@@ -149,6 +156,14 @@ case class GenIdeaImpl(evaluator: Evaluator,
         mod.resolveDeps(scalacPluginsIvyDeps)()
       }
 
+      val facets = T.task{
+        mod.ideaJavaModuleFacets(ideaConfigVersion)()
+      }
+
+      val configFileContributions = T.task{
+        mod.ideaConfigFiles(ideaConfigVersion)()
+      }
+
       T.task {
         val resolvedCp: Loose.Agg[PathRef] = externalDependencies()
         val resolvedSrcs: Loose.Agg[PathRef] = externalSources()
@@ -156,6 +171,8 @@ case class GenIdeaImpl(evaluator: Evaluator,
         val resolvedCompilerCp: Loose.Agg[PathRef] = scalaCompilerClasspath()
         val resolvedLibraryCp: Loose.Agg[PathRef] = externalLibraryDependencies()
         val scalacOpts: Seq[String] = scalacOptions()
+        val resolvedFacets: Seq[JavaFacet] = facets()
+        val resolvedConfigFileContributions: Seq[IdeaConfigFile] = configFileContributions()
 
         ResolvedModule(
           path,
@@ -164,7 +181,9 @@ case class GenIdeaImpl(evaluator: Evaluator,
           resolvedSp.map(_.path).filter(_.ext == "jar"),
           scalacOpts,
           resolvedCompilerCp.map(_.path),
-          resolvedLibraryCp.map(_.path)
+          resolvedLibraryCp.map(_.path),
+          resolvedFacets,
+          resolvedConfigFileContributions
         )
       }
     }), Seq())
@@ -175,6 +194,38 @@ case class GenIdeaImpl(evaluator: Evaluator,
 
     val librariesProperties = resolved.flatMap(x => x.libraryClasspath.map(_ -> x.compilerClasspath)).toMap
 
+    val configFileContributions = resolved.flatMap(_.configFileContributions)
+
+    type FileComponent = (String, String)
+    def collisionFree(confs: Seq[IdeaConfigFile]): Map[String, Seq[IdeaConfigFile]] = {
+      var seen: Map[FileComponent, Seq[GenIdeaModule.Element]] = Map()
+      var result: Map[String, Seq[IdeaConfigFile]] = Map()
+      confs.foreach { conf =>
+        val key = conf.name -> conf.component
+        seen.get(key) match {
+          case None =>
+            seen += key -> conf.config
+            result += conf.name -> (result.get(conf.name).getOrElse(Seq()) ++ Seq(conf))
+          case Some(existing) if conf.config == existing =>
+          // identical, ignore
+          case Some(existing) =>
+            def details(elements: Seq[GenIdeaModule.Element]) = {
+              elements.map(ideaConfigElementTemplate(_).toString().replaceAll("\\n", ""))
+            }
+            val msg = s"Config collision in file `${conf.name}` and component `${conf.component}`: ${details(conf.config)} vs. ${details(existing)}"
+            ctx.map(_.log.error(msg))
+        }
+      }
+      result
+    }
+
+    //TODO: also check against fixed files
+    val fileContributions: Seq[(RelPath, Elem)] = collisionFree(configFileContributions).toSeq.map {
+      case (file, configs) =>
+        val map: Map[String, Seq[GenIdeaModule.Element]] = configs.groupBy(_.component).mapValues(_.flatMap(_.config))
+        (os.rel / ".idea" / file) -> ideaConfigFileTemplate(map)
+    }
+
     val pathShortLibNameDuplicate = allResolved
       .distinct
       .groupBy(_.last)
@@ -245,7 +296,7 @@ case class GenIdeaImpl(evaluator: Evaluator,
     val allBuildLibraries : Set[ResolvedLibrary] =
       resolvedLibraries(buildLibraryPaths ++ buildDepsPaths).toSet
 
-    val fixedFiles = Seq(
+    val fixedFiles: Seq[(RelPath, Elem)] = Seq(
       Tuple2(os.rel/".idea"/"misc.xml", miscXmlTemplate(jdkInfo)),
       Tuple2(os.rel/".idea"/"scala_settings.xml", scalaSettingsTemplate()),
       Tuple2(
@@ -277,7 +328,7 @@ case class GenIdeaImpl(evaluator: Evaluator,
       for(name <- names) yield Tuple2(os.rel/".idea"/'libraries/s"$name.xml", libraryXmlTemplate(name, path, sources, librariesProperties.getOrElse(path, Loose.Agg.empty)))
     }
 
-    val moduleFiles = resolved.map{ case ResolvedModule(path, resolvedDeps, mod, _, _, _, _) =>
+    val moduleFiles = resolved.map{ case ResolvedModule(path, resolvedDeps, mod, _, _, _, _, facets, _) =>
       val Seq(
         resourcesPathRefs: Seq[PathRef],
         sourcesPathRef: Seq[PathRef],
@@ -313,19 +364,13 @@ case class GenIdeaImpl(evaluator: Evaluator,
         generatedSourceOutPath.dest,
         Strict.Agg.from(resolvedDeps.map(pathToLibName)),
         Strict.Agg.from(mod.moduleDeps.map{ m => moduleName(moduleLabels(m))}.distinct),
-        isTest
+        isTest,
+        facets
       )
       Tuple2(os.rel/".idea_modules"/s"${moduleName(path)}.iml", elem)
     }
 
-    fixedFiles ++ libraries ++ moduleFiles
-  }
-
-  def evalOrElse[T](evaluator: Evaluator, e: Task[T], default: => T): T = {
-    evaluator.evaluate(Agg(e)).values match {
-      case Seq() => default
-      case Seq(e: T) => e
-    }
+    fixedFiles ++ fileContributions ++ libraries ++ moduleFiles
   }
 
   def relify(p: os.Path) = {
@@ -333,23 +378,47 @@ case class GenIdeaImpl(evaluator: Evaluator,
     (Seq.fill(r.ups)("..") ++ r.segments).mkString("/")
   }
 
-  def moduleName(p: Segments) = p.value.foldLeft(StringBuilder.newBuilder) {
-    case (sb, Segment.Label(s)) if sb.isEmpty => sb.append(s)
-    case (sb, Segment.Cross(s)) if sb.isEmpty => sb.append(s.mkString("-"))
-    case (sb, Segment.Label(s)) => sb.append(".").append(s)
-    case (sb, Segment.Cross(s)) => sb.append("-").append(s.mkString("-"))
-  }.mkString.toLowerCase()
+  def ideaConfigElementTemplate(element: GenIdeaModule.Element): Elem = {
 
-  def scalaSettingsTemplate() = {
+    val example = <config/>
+
+    val attribute1: MetaData =
+      if (element.attributes.isEmpty) Null
+      else element.attributes.toSeq.reverse.foldLeft(Null.asInstanceOf[MetaData]) {
+        case (prevAttr, (k, v)) =>
+          new UnprefixedAttribute(k, v, prevAttr)
+      }
+
+    new Elem(
+      prefix = null,
+      label = element.name,
+      attributes1 = attribute1,
+      example.scope,
+      minimizeEmpty = true,
+      child = element.childs.map(ideaConfigElementTemplate): _*
+    )
+  }
+
+  def ideaConfigFileTemplate(components: Map[String, Seq[GenIdeaModule.Element]]): Elem = {
+    <project version={ "" + ideaConfigVersion }>
+      {
+        components.toSeq.map { case (name, config) =>
+          <component name={ name }>{config.map(ideaConfigElementTemplate)}</component>
+        }
+      }
+    </project>
+  }
 
-    <project version="4">
+  def scalaSettingsTemplate() = {
+//    simpleIdeaConfigFileTemplate(Map("ScalaProjectSettings" -> Map("scFileMode" -> "Ammonite")))
+    <project version={"" + ideaConfigVersion}>
       <component name="ScalaProjectSettings">
         <option name="scFileMode" value="Ammonite" />
       </component>
     </project>
   }
   def miscXmlTemplate(jdkInfo: (String,String)) = {
-    <project version="4">
+    <project version={"" + ideaConfigVersion}>
       <component name="ProjectRootManager" version="2" languageLevel={jdkInfo._1} project-jdk-name={jdkInfo._2} project-jdk-type="JavaSDK">
         <output url="file://$PROJECT_DIR$/target/idea_output"/>
       </component>
@@ -357,7 +426,7 @@ case class GenIdeaImpl(evaluator: Evaluator,
   }
 
   def allModulesXmlTemplate(selectors: Seq[String]) = {
-    <project version="4">
+    <project version={"" + ideaConfigVersion}>
       <component name="ProjectModuleManager">
         <modules>
           <module
@@ -377,7 +446,7 @@ case class GenIdeaImpl(evaluator: Evaluator,
     </project>
   }
   def rootXmlTemplate(libNames: Strict.Agg[String]) = {
-    <module type="JAVA_MODULE" version="4">
+    <module type="JAVA_MODULE" version={"" + ideaConfigVersion}>
       <component name="NewModuleRootManager">
         <output url="file://$MODULE_DIR$/../out"/>
         <content url="file://$MODULE_DIR$/..">
@@ -430,9 +499,10 @@ case class GenIdeaImpl(evaluator: Evaluator,
                         generatedSourceOutputPath: os.Path,
                         libNames: Strict.Agg[String],
                         depNames: Strict.Agg[String],
-                        isTest: Boolean
-                       ) = {
-    <module type="JAVA_MODULE" version="4">
+                        isTest: Boolean,
+                        facets: Seq[GenIdeaModule.JavaFacet]
+                       ): Elem = {
+    <module type="JAVA_MODULE" version={"" + ideaConfigVersion}>
       <component name="NewModuleRootManager">
         {
           val outputUrl = "file://$MODULE_DIR$/" + relify(compileOutputPath) + "/dest/classes"
@@ -479,11 +549,16 @@ case class GenIdeaImpl(evaluator: Evaluator,
         yield <orderEntry type="module" module-name={depName} exported="" />
         }
       </component>
+      { if (facets.isEmpty) NodeSeq.Empty else { <component name="FacetManager">
+            { for (facet <- facets) yield { <facet type={ facet.`type` } name={ facet.name }>
+                  { ideaConfigElementTemplate(facet.config) }
+                </facet> } }
+          </component> } }
     </module>
   }
   def scalaCompilerTemplate(settings: Map[(Loose.Agg[os.Path], Seq[String]), Seq[JavaModule]]) = {
 
-    <project version="4">
+    <project version={"" + ideaConfigVersion}>
       <component name="ScalaCompilerConfiguration">
         {
         for((((plugins, params), mods), i) <- settings.toSeq.zip(1 to settings.size))
@@ -507,3 +582,28 @@ case class GenIdeaImpl(evaluator: Evaluator,
     </project>
   }
 }
+
+object GenIdeaImpl {
+
+  /**
+    * Create the module name (to be used by Idea) for the module based on it segments.
+    * @see [[Module.millModuleSegments]]
+    */
+  def moduleName(p: Segments): String = p.value.foldLeft(StringBuilder.newBuilder) {
+    case (sb, Segment.Label(s)) if sb.isEmpty => sb.append(s)
+    case (sb, Segment.Cross(s)) if sb.isEmpty => sb.append(s.mkString("-"))
+    case (sb, Segment.Label(s)) => sb.append(".").append(s)
+    case (sb, Segment.Cross(s)) => sb.append("-").append(s.mkString("-"))
+  }.mkString.toLowerCase()
+
+  /**
+    * Evaluate the given task `e`. In case, the task has no successful result(s), return the `default` value instead.
+    */
+  def evalOrElse[T](evaluator: Evaluator, e: Task[T], default: => T): T = {
+    evaluator.evaluate(Agg(e)).values match {
+      case Seq() => default
+      case Seq(e: T) => e
+    }
+  }
+
+}
diff --git a/scalalib/src/GenIdeaModule.scala b/scalalib/src/GenIdeaModule.scala
new file mode 100644
index 00000000..e874da8b
--- /dev/null
+++ b/scalalib/src/GenIdeaModule.scala
@@ -0,0 +1,51 @@
+package mill.scalalib
+
+import mill.define.Command
+import mill.{Module, T}
+
+/**
+ * Module specific configuration of the Idea project file generator.
+ */
+trait GenIdeaModule extends Module {
+  import GenIdeaModule._
+
+  def intellijModulePath: os.Path = millSourcePath
+
+  /**
+    * Skip Idea project file generation.
+    */
+  def skipIdea: Boolean = false
+
+  /**
+    * Contribute facets to the Java module configuration.
+    * @param ideaConfigVersion The IDEA configuration version in use. Probably `4`.
+    * @return
+    */
+  def ideaJavaModuleFacets(ideaConfigVersion: Int): Command[Seq[JavaFacet]] = T.command { Seq[JavaFacet]() }
+
+  /**
+    * Contribute components to idea config files.
+    */
+  def ideaConfigFiles(ideaConfigVersion: Int): Command[Seq[IdeaConfigFile]] = T.command { Seq[IdeaConfigFile]() }
+
+  }
+
+object GenIdeaModule {
+  import upickle.default._
+
+  case class Element(name: String, attributes: Map[String, String] = Map(), childs: Seq[Element] = Seq())
+  object Element {
+    implicit def rw: ReadWriter[Element] = macroRW
+  }
+
+  final case class JavaFacet(`type`: String, name: String, config: Element)
+  object JavaFacet {
+    implicit def rw: ReadWriter[JavaFacet] = macroRW
+  }
+
+  final case class IdeaConfigFile(name: String, component: String, config: Seq[Element])
+  object IdeaConfigFile {
+    implicit def rw: ReadWriter[IdeaConfigFile] = macroRW
+  }
+
+}
diff --git a/scalalib/src/JavaModule.scala b/scalalib/src/JavaModule.scala
index c7066d15..b9987ca1 100644
--- a/scalalib/src/JavaModule.scala
+++ b/scalalib/src/JavaModule.scala
@@ -17,7 +17,7 @@ import mill.api.Loose.Agg
 /**
   * Core configuration required to compile a single Scala compilation target
   */
-trait JavaModule extends mill.Module with TaskModule { outer =>
+trait JavaModule extends mill.Module with TaskModule with GenIdeaModule { outer =>
   def zincWorker: ZincWorkerModule = mill.scalalib.ZincWorkerModule
 
   trait Tests extends TestModule{
@@ -554,14 +554,7 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     */
   def artifactId: T[String] = artifactName()
 
-  def intellijModulePath: os.Path = millSourcePath
-
   def forkWorkingDir = T{ ammonite.ops.pwd }
-
-  /**
-   * Skip Idea project file generation.
-   */
-  def skipIdea: Boolean = false
 }
 
 trait TestModule extends JavaModule with TaskModule {
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/build.sc b/scalalib/test/resources/gen-idea-extended-hello-world/build.sc
new file mode 100644
index 00000000..4d1affbb
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/build.sc
@@ -0,0 +1,44 @@
+import mill.scalalib
+import mill.define.Command
+import mill.scalalib.GenIdeaModule._
+
+trait HelloWorldModule extends scalalib.ScalaModule {
+  def scalaVersion = "2.12.4"
+  object test extends super.Tests {
+    def testFrameworks = Seq("utest.runner.Framework")
+  }
+
+  def ideaJavaModuleFacets(ideaConfigVersion: Int): Command[Seq[JavaFacet]] = T.command {
+    ideaConfigVersion match {
+      case 4 =>
+        Seq(
+          JavaFacet("AspectJ", "AspectJ",
+            Element("configuration", childs = Seq(
+              Element("projectLibrary", childs = Seq(
+                Element("option", Map("name" -> "name", "value" -> "/tmp"))
+              ))
+            ))
+          )
+        )
+    }
+  }
+
+  override def ideaConfigFiles(ideaConfigVersion: Int): Command[Seq[IdeaConfigFile]] = T.command {
+    ideaConfigVersion match {
+      case 4 =>
+        Seq(
+          IdeaConfigFile(
+            name = "compiler.xml",
+            component = "AjcSettings",
+            config = Seq(Element("option", Map("name" -> "ajcPath", "value" -> "/tmp/aspectjtools.jar")))),
+          IdeaConfigFile(
+            name = "compiler.xml",
+            component = "CompilerConfiguration",
+            config = Seq(Element("option", Map("name" -> "DEFAULT_COMPILER", "value" -> "ajc")))
+          )
+        )
+    }
+  }
+}
+
+object HelloWorld extends HelloWorldModule
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea/compiler.xml b/scalalib/test/resources/gen-idea-extended-hello-world/idea/compiler.xml
new file mode 100644
index 00000000..3622ff42
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea/compiler.xml
@@ -0,0 +1,8 @@
+<project version="4">
+    <component name="CompilerConfiguration">
+        <option name="DEFAULT_COMPILER" value="ajc"/>
+    </component>
+    <component name="AjcSettings">
+        <option name="ajcPath" value="/tmp/aspectjtools.jar"/>
+    </component>
+</project>
\ No newline at end of file
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea/libraries/scala-library-2.12.4.jar.xml b/scalalib/test/resources/gen-idea-extended-hello-world/idea/libraries/scala-library-2.12.4.jar.xml
new file mode 100644
index 00000000..5f7c5056
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea/libraries/scala-library-2.12.4.jar.xml
@@ -0,0 +1,18 @@
+<component name="libraryTable">
+    <library name="scala-library-2.12.4.jar" type="Scala">
+        <properties>
+            <compiler-classpath>
+                <root url="file://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/modules/scala-xml_2.12/1.0.6/scala-xml_2.12-1.0.6.jar"/>
+                <root url="file://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/scala-compiler/2.12.4/scala-compiler-2.12.4.jar"/>
+                <root url="file://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.4/scala-library-2.12.4.jar"/>
+                <root url="file://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/scala-reflect/2.12.4/scala-reflect-2.12.4.jar"/>
+            </compiler-classpath>
+        </properties>
+        <CLASSES>
+            <root url="jar://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.4/scala-library-2.12.4.jar!/"/>
+        </CLASSES>
+        <SOURCES>
+            <root url="jar://COURSIER_HOME/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.4/scala-library-2.12.4-sources.jar!/"/>
+        </SOURCES>
+    </library>
+</component>
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea/misc.xml b/scalalib/test/resources/gen-idea-extended-hello-world/idea/misc.xml
new file mode 100644
index 00000000..f4f144ce
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea/misc.xml
@@ -0,0 +1,5 @@
+<project version="4">
+    <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" project-jdk-name="1.8 (1)" project-jdk-type="JavaSDK">
+        <output url="file://$PROJECT_DIR$/target/idea_output"/>
+    </component>
+</project>
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea/modules.xml b/scalalib/test/resources/gen-idea-extended-hello-world/idea/modules.xml
new file mode 100644
index 00000000..193fa62d
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea/modules.xml
@@ -0,0 +1,9 @@
+<project version="4">
+    <component name="ProjectModuleManager">
+        <modules>
+            <module fileurl="file://$PROJECT_DIR$/.idea_modules/mill-build.iml" filepath="$PROJECT_DIR$/.idea_modules/mill-build.iml"/>
+            <module fileurl="file://$PROJECT_DIR$/.idea_modules/helloworld.iml" filepath="$PROJECT_DIR$/.idea_modules/helloworld.iml"/>
+            <module fileurl="file://$PROJECT_DIR$/.idea_modules/helloworld.test.iml" filepath="$PROJECT_DIR$/.idea_modules/helloworld.test.iml"/>
+        </modules>
+    </component>
+</project>
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.iml b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.iml
new file mode 100644
index 00000000..94810f20
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.iml
@@ -0,0 +1,26 @@
+<module type="JAVA_MODULE" version="4">
+    <component name="NewModuleRootManager">
+        <output url="file://$MODULE_DIR$/../out/HelloWorld/compile/dest/classes"/>
+        <exclude-output/>
+        <content url="file://$MODULE_DIR$/../out/HelloWorld/generatedSources/dest"/>
+        <content url="file://$MODULE_DIR$/../HelloWorld">
+            <sourceFolder url="file://$MODULE_DIR$/../HelloWorld/src" isTestSource="false"/>
+            <sourceFolder url="file://$MODULE_DIR$/../HelloWorld/resources" type="java-resource"/>
+            <excludeFolder url="file://$MODULE_DIR$/../HelloWorld/target"/>
+        </content>
+        <orderEntry type="inheritedJdk"/>
+        <orderEntry type="sourceFolder" forTests="false"/>
+        <orderEntry type="library" name="scala-sdk-2.12.4" level="application"/>
+        <orderEntry type="library" name="scala-library-2.12.4-sources.jar" level="project"/>
+        <orderEntry type="library" name="scala-library-2.12.4.jar" level="project"/>
+    </component>
+    <component name="FacetManager">
+        <facet type="AspectJ" name="AspectJ">
+            <configuration>
+                <projectLibrary>
+                    <option name="name" value="/tmp"/>
+                </projectLibrary>
+            </configuration>
+        </facet>
+    </component>
+</module>
\ No newline at end of file
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.test.iml b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.test.iml
new file mode 100644
index 00000000..26fac21d
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/helloworld.test.iml
@@ -0,0 +1,18 @@
+<module type="JAVA_MODULE" version="4">
+    <component name="NewModuleRootManager">
+        <output-test url="file://$MODULE_DIR$/../out/HelloWorld/test/compile/dest/classes"/>
+        <exclude-output/>
+        <content url="file://$MODULE_DIR$/../out/HelloWorld/test/generatedSources/dest"/>
+        <content url="file://$MODULE_DIR$/../HelloWorld/test">
+            <sourceFolder url="file://$MODULE_DIR$/../HelloWorld/test/src" isTestSource="true"/>
+            <sourceFolder url="file://$MODULE_DIR$/../HelloWorld/test/resources" type="java-test-resource"/>
+            <excludeFolder url="file://$MODULE_DIR$/../HelloWorld/test/target"/>
+        </content>
+        <orderEntry type="inheritedJdk"/>
+        <orderEntry type="sourceFolder" forTests="false"/>
+        <orderEntry type="library" name="scala-sdk-2.12.4" level="application"/>
+        <orderEntry type="library" name="scala-library-2.12.4-sources.jar" level="project"/>
+        <orderEntry type="library" name="scala-library-2.12.4.jar" level="project"/>
+        <orderEntry type="module" module-name="helloworld" exported=""/>
+    </component>
+</module>
diff --git a/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/mill-build.iml b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/mill-build.iml
new file mode 100644
index 00000000..46fd8c3b
--- /dev/null
+++ b/scalalib/test/resources/gen-idea-extended-hello-world/idea_modules/mill-build.iml
@@ -0,0 +1,12 @@
+<module type="JAVA_MODULE" version="4">
+    <component name="NewModuleRootManager">
+        <output url="file://$MODULE_DIR$/../out"/>
+        <content url="file://$MODULE_DIR$/..">
+            <excludeFolder url="file://$MODULE_DIR$/../project"/>
+            <excludeFolder url="file://$MODULE_DIR$/../target"/>
+        </content>
+        <exclude-output/>
+        <orderEntry type="inheritedJdk"/>
+        <orderEntry type="sourceFolder" forTests="false"/>
+    </component>
+</module>
\ No newline at end of file
diff --git a/scalalib/test/src/GenIdeaExtendedTests.scala b/scalalib/test/src/GenIdeaExtendedTests.scala
new file mode 100644
index 00000000..0a4de2e7
--- /dev/null
+++ b/scalalib/test/src/GenIdeaExtendedTests.scala
@@ -0,0 +1,41 @@
+package mill.scalalib
+
+import mill.util.ScriptTestSuite
+import os.Path
+import utest._
+
+object GenIdeaExtendedTests extends ScriptTestSuite(false) {
+
+  override def workspaceSlug: String = "gen-idea-extended-hello-world"
+
+  override def scriptSourcePath: Path = os.pwd / 'scalalib / 'test / 'resources / workspaceSlug
+
+  def tests: Tests = Tests {
+    'genIdeaTests - {
+      initWorkspace()
+      eval("mill.scalalib.GenIdea/idea")
+
+      Seq(
+        s"$workspaceSlug/idea_modules/helloworld.iml" -> workspacePath / ".idea_modules" /"helloworld.iml",
+        s"$workspaceSlug/idea_modules/helloworld.test.iml" -> workspacePath / ".idea_modules" /"helloworld.test.iml",
+        s"$workspaceSlug/idea/libraries/scala-library-2.12.4.jar.xml" ->
+          workspacePath / ".idea" / "libraries" / "scala-library-2.12.4.jar.xml",
+
+        s"$workspaceSlug/idea/modules.xml" -> workspacePath / ".idea" / "modules.xml",
+        s"$workspaceSlug/idea/misc.xml" -> workspacePath / ".idea" / "misc.xml",
+        s"$workspaceSlug/idea/compiler.xml" -> workspacePath / ".idea" / "compiler.xml"
+
+      ).foreach { case (resource, generated) =>
+          val resourceString = scala.io.Source.fromResource(resource).getLines().mkString("\n")
+          val generatedString = normaliseLibraryPaths(os.read(generated))
+
+          assert(resourceString == generatedString)
+        }
+    }
+  }
+
+  private def normaliseLibraryPaths(in: String): String = {
+    in.replaceAll(coursier.paths.CoursierPaths.cacheDirectory().toString, "COURSIER_HOME")
+  }
+
+}