faster lookup element painting

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupCellRenderer.java

@@ -28,6 +28,7 @@ import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.codeStyle.MinusculeMatcher;
 import com.intellij.psi.codeStyle.NameUtil;
 import com.intellij.ui.*;
+import com.intellij.ui.components.JBList;
 import com.intellij.ui.speedSearch.SpeedSearchUtil;
 import com.intellij.util.containers.ContainerUtil;
 import com.intellij.util.containers.FList;
@@ -172,17 +173,20 @@ public class LookupCellRenderer implements ListCellRenderer {
                      myTailComponent.getPreferredSize().getWidth() +
                      myTypeLabel.getPreferredSize().getWidth();
 
-    myPanel.removeAll();
-    if (isSelected && w > list.getWidth()) {
-      myPanel.setLayout(new BoxLayout(myPanel, BoxLayout.X_AXIS));
-      myPanel.add(myNameComponent);
-      myPanel.add(myTailComponent);
-      myPanel.add(myTypeLabel);
-    } else {
-      myPanel.setLayout(new BorderLayout());
-      myPanel.add(myNameComponent, BorderLayout.WEST);
-      myPanel.add(myTailComponent, BorderLayout.CENTER);
-      myPanel.add(myTypeLabel, BorderLayout.EAST);
+    boolean useBoxLayout = isSelected && w > list.getWidth() && ((JBList)list).getExpandableItemsHandler().isEnabled();
+    if (useBoxLayout != myPanel.getLayout() instanceof BoxLayout) {
+      myPanel.removeAll();
+      if (useBoxLayout) {
+        myPanel.setLayout(new BoxLayout(myPanel, BoxLayout.X_AXIS));
+        myPanel.add(myNameComponent);
+        myPanel.add(myTailComponent);
+        myPanel.add(myTypeLabel);
+      } else {
+        myPanel.setLayout(new BorderLayout());
+        myPanel.add(myNameComponent, BorderLayout.WEST);
+        myPanel.add(myTailComponent, BorderLayout.CENTER);
+        myPanel.add(myTypeLabel, BorderLayout.EAST);
+      }
     }
 
     return myPanel;

platform/platform-api/src/com/intellij/ui/ExpandableItemsHandler.java

@@ -21,6 +21,8 @@ import java.util.Collection;
 
 public interface ExpandableItemsHandler<T> {
   void setEnabled(boolean enabled);
+  
+  boolean isEnabled();
 
   @NotNull
   Collection<T> getExpandedItems();

platform/platform-api/src/com/intellij/ui/ExpandableItemsHandlerFactory.java

@@ -58,6 +58,11 @@ public abstract class ExpandableItemsHandlerFactory {
     public void setEnabled(boolean enabled) {
     }
 
+    @Override
+    public boolean isEnabled() {
+      return false;
+    }
+
     @NotNull
     @Override
     public Collection<Object> getExpandedItems() {

platform/platform-impl/src/com/intellij/ui/AbstractExpandableItemsHandler.java

@@ -159,6 +159,11 @@ public abstract class AbstractExpandableItemsHandler<KeyType, ComponentType exte
     if (!myEnabled) hideHint();
   }
 
+  @Override
+  public boolean isEnabled() {
+    return myEnabled;
+  }
+
   @NotNull
   @Override
   public Collection<KeyType> getExpandedItems() {