Workaround for "Find Usages broken" bug in Scala Plugin

Bug tracker: https://youtrack.jetbrains.com/issue/SCL-16768

Correct initialization of `ScalaCompilerReferenceService` is required for "Find usages" feature to work correcly. Unfortunately, it's broken in that way, it does nothing when there are no modules in the project right after the moment, when the project is opened. This happens when a project is imported, the module creation starts after opening then.

Author: Tomasz Pasternak

src/com/twitter/intellij/pants/service/scala/PantsScalaDataService.scala

@@ -7,16 +7,23 @@ import java.io.File
 import java.util
 import java.util.Collections
 
+import com.intellij.ProjectTopics
 import com.intellij.openapi.diagnostic.Logger
 import com.intellij.openapi.externalSystem.model.project.ProjectData
 import com.intellij.openapi.externalSystem.model.{DataNode, ExternalSystemException, Key, ProjectKeys}
 import com.intellij.openapi.externalSystem.service.project.IdeModifiableModelsProvider
 import com.intellij.openapi.externalSystem.service.project.manage.ProjectDataService
-import com.intellij.openapi.project.Project
+import com.intellij.openapi.externalSystem.util.ExternalSystemApiUtil
+import com.intellij.openapi.module.Module
+import com.intellij.openapi.project.{ModuleListener, Project}
 import com.intellij.openapi.roots.impl.libraries.LibraryEx.ModifiableModelEx
 import com.intellij.openapi.roots.libraries.Library
 import com.intellij.openapi.util.Computable
+import com.twitter.intellij.pants.util.PantsUtil
+import org.jetbrains.plugins.scala.findUsages.compilerReferences.ScalaCompilerReferenceService
 import org.jetbrains.plugins.scala.project.{LibraryExt, ScalaLibraryProperties, ScalaLibraryType, Version}
+import com.twitter.intellij.pants.settings.PantsSettings
+import com.twitter.intellij.pants.util.PantsConstants
 
 import scala.collection.JavaConverters.{asScalaSetConverter, iterableAsScalaIterableConverter}
 
@@ -37,6 +44,34 @@ class PantsScalaDataService extends ProjectDataService[ScalaModelData, Library]
     modelsProvider: IdeModifiableModelsProvider
   ): Unit = {
     toImport.asScala.toSet.foreach[Unit](doImport(_, modelsProvider))
+
+    // Workaround for bug in Scala Plugin https://youtrack.jetbrains.com/issue/SCL-16768
+    //
+    // Correct initialization of `ScalaCompilerReferenceService` is required for "Find usages"
+    // feature to work correctly. Unfortunately, it's broken in that way, it does nothing when
+    // there are no modules in the project right after the moment, when the project is opened.
+    // This happens when a project is imported, the module creation starts after opening project.
+    val pantsSettings = ExternalSystemApiUtil.getSettings(project, PantsConstants.SYSTEM_ID).asInstanceOf[PantsSettings]
+    if (pantsSettings.isUseIntellijCompiler) {
+      doOnceOnPantsModuleAdded(project) {
+        ScalaCompilerReferenceService(project).initializeReferenceService()
+      }
+    }
+  }
+
+  private def doOnceOnPantsModuleAdded(project: Project)(action: => Unit): Unit = {
+    project.getMessageBus.connect().subscribe(ProjectTopics.MODULES, new ModuleListener {
+      var done = false
+
+      override def moduleAdded(project: Project, module: Module): Unit = {
+        if (!done) {
+          if (PantsUtil.isPantsModule(module)) {
+            action
+            done = true;
+          }
+        }
+      }
+    })
   }
 
   private def doImport(scalaNode: DataNode[ScalaModelData], modelsProvider: IdeModifiableModelsProvider) {
@@ -74,9 +109,7 @@ class PantsScalaDataService extends ProjectDataService[ScalaModelData, Library]
                                  project: Project,
                                  modelsProvider: IdeModifiableModelsProvider
   ): Computable[util.Collection[Library]] =
-    new Computable[util.Collection[Library]] {
-      override def compute(): util.Collection[Library] = Collections.emptyList()
-    }
+    () => Collections.emptyList()
 
   override def removeData(toRemove: Computable[util.Collection[Library]],
                           toIgnore: util.Collection[DataNode[ScalaModelData]],