Extend TreeUI and ProjectView/ProjectViewPane APIs

platform/lang-impl/src/com/intellij/ide/projectView/impl/AbstractProjectViewPSIPane.java

@@ -115,9 +115,11 @@ public abstract class AbstractProjectViewPSIPane extends AbstractProjectViewPane
       });
     }
     myTreeStructure = createStructure();
-    setTreeBuilder(createBuilder(treeModel));
 
-    installComparator();
+    BaseProjectTreeBuilder treeBuilder = createBuilder(treeModel);
+    installComparator(treeBuilder);
+    setTreeBuilder(treeBuilder);
+
     initTree();
 
     Disposer.register(getTreeBuilder(), new UiNotifyConnector(myTree, new Activatable() {

platform/lang-impl/src/com/intellij/ide/projectView/impl/AbstractProjectViewPane.java

@@ -468,8 +468,12 @@ public abstract class AbstractProjectViewPane implements DataProvider, Disposabl
   }
 
   public void installComparator() {
+    installComparator(getTreeBuilder());
+  }
+
+  public void installComparator(AbstractTreeBuilder treeBuilder) {
     final ProjectView projectView = ProjectView.getInstance(myProject);
-    getTreeBuilder().setNodeDescriptorComparator(new GroupByTypeComparator(projectView, getId()));
+    treeBuilder.setNodeDescriptorComparator(new GroupByTypeComparator(projectView, getId()));
   }
 
   public JTree getTree() {
@@ -633,6 +637,14 @@ public abstract class AbstractProjectViewPane implements DataProvider, Disposabl
     myTreeBuilder = treeBuilder;
   }
 
+  public boolean supportsFoldersAlwaysOnTop() {
+    return true;
+  }
+
+  public boolean supportsSortByType() {
+    return true;
+  }
+
   private class MyDragSource implements DnDSource {
     @Override
     public boolean canStartDragging(DnDAction action, Point dragOrigin) {

platform/lang-impl/src/com/intellij/ide/projectView/impl/ProjectViewImpl.java

@@ -1878,7 +1878,8 @@ public class ProjectViewImpl extends ProjectView implements PersistentStateCompo
     public void update(final AnActionEvent e) {
       super.update(e);
       final Presentation presentation = e.getPresentation();
-      presentation.setVisible(getCurrentProjectViewPane() != null);
+      AbstractProjectViewPane pane = getCurrentProjectViewPane();
+      presentation.setVisible(pane != null && pane.supportsSortByType());
     }
   }
 
@@ -1901,7 +1902,8 @@ public class ProjectViewImpl extends ProjectView implements PersistentStateCompo
     public void update(final AnActionEvent e) {
       super.update(e);
       final Presentation presentation = e.getPresentation();
-      presentation.setEnabledAndVisible(getCurrentProjectViewPane() != null);
+      AbstractProjectViewPane pane = getCurrentProjectViewPane();
+      presentation.setEnabledAndVisible(pane != null && pane.supportsFoldersAlwaysOnTop());
     }
   }
 

platform/platform-api/src/com/intellij/util/ui/tree/TreeUtil.java

@@ -794,14 +794,27 @@ public final class TreeUtil {
     expand(tree, new TreePath(tree.getModel().getRoot()), levels);
   }
 
-  private static void expand(@NotNull JTree tree, @NotNull TreePath path, int levels) {
-    if (levels == 0) return;
+  /**
+   * Expands n levels of the tree counting from the root and return true if there is no nodes to expand
+   * @param tree to expand nodes of
+   * @param levels depths of the expantion
+   */
+  public static boolean expandWithResult(@NotNull JTree tree, int levels) {
+    return expand(tree, new TreePath(tree.getModel().getRoot()), levels);
+  }
+
+  private static boolean expand(@NotNull JTree tree, @NotNull TreePath path, int levels) {
+    if (levels == 0) return false;
     tree.expandPath(path);
     TreeNode node = (TreeNode)path.getLastPathComponent();
     Enumeration children = node.children();
+
+    boolean isReady = true;
     while (children.hasMoreElements()) {
-      expand(tree, path.pathByAddingChild(children.nextElement()) , levels - 1);
+      if (!expand(tree, path.pathByAddingChild(children.nextElement()) , levels - 1))
+        isReady = false;
     }
+    return isReady;
   }
 
   @NotNull