module grouper: support grouping for ModuleDescription

This is needed to show unloaded modules in a tree.

platform/projectModel-api/src/com/intellij/openapi/module/ModuleDescription.kt

@@ -37,4 +37,10 @@ interface ModuleDescription {
 @ApiStatus.Experimental
 interface UnloadedModuleDescription : ModuleDescription {
   val contentRoots: List<VirtualFilePointer>
+  val groupPath: List<String>
+}
+
+@ApiStatus.Experimental
+interface LoadedModuleDescription : ModuleDescription {
+  val module: Module
 }

platform/projectModel-api/src/com/intellij/openapi/module/ModuleGrouper.kt

@@ -34,6 +34,11 @@ abstract class ModuleGrouper {
    */
   abstract fun getGroupPath(module: Module): List<String>
 
+  /**
+   * Returns names of parent groups for a module
+   */
+  abstract fun getGroupPath(description: ModuleDescription): List<String>
+
   /**
    * Returns name which should be used for a module when it's shown under its group
    */
@@ -48,6 +53,11 @@ abstract class ModuleGrouper {
    */
   abstract fun getModuleAsGroupPath(module: Module): List<String>?
 
+  /**
+   * If [description] itself can be considered as a group, returns its groups. Otherwise returns null.
+   */
+  abstract fun getModuleAsGroupPath(description: ModuleDescription): List<String>?
+
   abstract fun getAllModules(): Array<Module>
 
   companion object {
@@ -78,11 +88,15 @@ private class QualifiedNameGrouper(project: Project, model: ModifiableModuleMode
     return getGroupPathByModuleName(getModuleName(module))
   }
 
+  override fun getGroupPath(description: ModuleDescription) = getGroupPathByModuleName(description.name)
+
   override fun getShortenedNameByFullModuleName(name: String) = StringUtil.getShortName(name)
 
   override fun getGroupPathByModuleName(name: String) = name.split('.').dropLast(1)
 
   override fun getModuleAsGroupPath(module: Module) = getModuleName(module).split('.')
+
+  override fun getModuleAsGroupPath(description: ModuleDescription) = description.name.split('.')
 }
 
 private class ExplicitModuleGrouper(project: Project, model: ModifiableModuleModel?): ModuleGrouperBase(project, model) {
@@ -91,9 +105,17 @@ private class ExplicitModuleGrouper(project: Project, model: ModifiableModuleMod
     return if (path != null) Arrays.asList(*path) else emptyList()
   }
 
+  override fun getGroupPath(description: ModuleDescription) = when (description) {
+    is LoadedModuleDescription -> getGroupPath(description.module)
+    is UnloadedModuleDescription -> description.groupPath
+    else -> throw IllegalArgumentException(description.javaClass.name)
+  }
+
   override fun getShortenedNameByFullModuleName(name: String) = name
 
   override fun getGroupPathByModuleName(name: String): List<String> = emptyList()
 
   override fun getModuleAsGroupPath(module: Module) = null
+  
+  override fun getModuleAsGroupPath(description: ModuleDescription) = null
 }

platform/projectModel-impl/src/com/intellij/openapi/module/impl/LoadedModuleDescriptionImpl.kt

@@ -15,14 +15,14 @@
  */
 package com.intellij.openapi.module.impl
 
+import com.intellij.openapi.module.LoadedModuleDescription
 import com.intellij.openapi.module.Module
-import com.intellij.openapi.module.ModuleDescription
 import com.intellij.openapi.roots.ModuleRootManager
 
 /**
  * @author nik
  */
-class LoadedModuleDescription(private val module: Module): ModuleDescription {
+class LoadedModuleDescriptionImpl(override val module: Module): LoadedModuleDescription {
   override val name: String
     get() = module.name
 

platform/projectModel-impl/src/com/intellij/openapi/module/impl/ModuleManagerImpl.java

@@ -81,7 +81,7 @@ public abstract class ModuleManagerImpl extends ModuleManager implements Disposa
 
   private static final Logger LOG = Logger.getInstance("#com.intellij.openapi.module.impl.ModuleManagerImpl");
   private static final Key<String> DISPOSED_MODULE_NAME = Key.create("DisposedNeverAddedModuleName");
-  private static final String MODULE_GROUP_SEPARATOR = "/";
+  public static final String MODULE_GROUP_SEPARATOR = "/";
 
   protected final Project myProject;
   protected final MessageBus myMessageBus;
@@ -985,7 +985,7 @@ public abstract class ModuleManagerImpl extends ModuleManager implements Disposa
     Module[] modules = getModules();
     List<ModuleDescription> descriptions = new ArrayList<>(modules.length + myUnloadedModules.size());
     for (Module module : modules) {
-      descriptions.add(new LoadedModuleDescription(module));
+      descriptions.add(new LoadedModuleDescriptionImpl(module));
     }
     descriptions.addAll(myUnloadedModules.values());
     return descriptions;
@@ -1014,7 +1014,7 @@ public abstract class ModuleManagerImpl extends ModuleManager implements Disposa
       else {
         Module module = findModuleByName(name);
         if (module != null) {
-          LoadedModuleDescription description = new LoadedModuleDescription(module);
+          LoadedModuleDescriptionImpl description = new LoadedModuleDescriptionImpl(module);
           ModuleSaveItem saveItem = new ModuleSaveItem(module);
           ModulePath modulePath = new ModulePath(saveItem.getModuleFilePath(), saveItem.getGroupPathString());
           VirtualFilePointerManager pointerManager = VirtualFilePointerManager.getInstance();

platform/projectModel-impl/src/com/intellij/openapi/module/impl/UnloadedModuleDescriptionImpl.kt

@@ -32,6 +32,9 @@ import java.nio.file.Paths
 class UnloadedModuleDescriptionImpl(val modulePath: ModulePath,
                                     override val dependencyModuleNames: List<String>,
                                     override val contentRoots: List<VirtualFilePointer>) : UnloadedModuleDescription {
+  override val groupPath: List<String>
+    get() = modulePath.group?.split(ModuleManagerImpl.MODULE_GROUP_SEPARATOR) ?: emptyList()
+
   override val name: String
     get() = modulePath.moduleName