on drag out of inactive tab, restore selection to tab which was selected before drag out started (IDEA-61536)

platform/platform-api/src/com/intellij/ui/tabs/TabInfo.java

@@ -86,6 +86,12 @@ public final class TabInfo implements Queryable, PlaceProvider<String> {
   private Queryable myQueryable;
   private DragOutDelegate myDragOutDelegate;
 
+  /**
+   * The tab which was selected before the mouse was pressed on this tab. Focus will be transferred to that tab if this tab is dragged
+   * out of its container. (IDEA-61536)
+   */
+  private WeakReference<TabInfo> myPreviousSelection = new WeakReference<TabInfo>(null);
+
   public TabInfo(final JComponent component) {
     myComponent = component;
     myPreferredFocusableComponent = component;
@@ -371,6 +377,15 @@ public final class TabInfo implements Queryable, PlaceProvider<String> {
     return myDragOutDelegate;
   }
 
+  public void setPreviousSelection(@Nullable TabInfo previousSelection) {
+    myPreviousSelection = new WeakReference<TabInfo>(previousSelection);
+  }
+
+  @Nullable
+  public TabInfo getPreviousSelection() {
+    return myPreviousSelection.get();
+  }
+
   public interface DragOutDelegate {
 
     void dragOutStarted(MouseEvent mouseEvent, TabInfo info);

platform/platform-api/src/com/intellij/ui/tabs/impl/TabLabel.java

@@ -88,6 +88,10 @@ public class TabLabel extends JPanel {
     addMouseListener(new MouseAdapter() {
       public void mousePressed(final MouseEvent e) {
         if (myTabs.isSelectionClick(e, false) && myInfo.isEnabled()) {
+          final TabInfo selectedInfo = myTabs.getSelectedInfo();
+          if (selectedInfo != myInfo) {
+            myInfo.setPreviousSelection(selectedInfo);
+          }
           Component c = SwingUtilities.getDeepestComponentAt(e.getComponent(), e.getX(), e.getY());
           if (c instanceof InplaceButton) return;
           myTabs.select(info, true);
@@ -102,6 +106,7 @@ public class TabLabel extends JPanel {
       }
 
       public void mouseReleased(final MouseEvent e) {
+        myInfo.setPreviousSelection(null);
         handlePopup(e);
       }
     });

platform/platform-impl/src/com/intellij/openapi/fileEditor/impl/EditorTabbedContainer.java

@@ -212,7 +212,12 @@ final class EditorTabbedContainer implements Disposable, CloseAction.CloseTarget
 
   public ActionCallback removeTabAt(final int componentIndex, int indexToSelect, boolean transferFocus) {
     TabInfo toSelect = indexToSelect >= 0 && indexToSelect < myTabs.getTabCount() ? myTabs.getTabAt(indexToSelect) : null;
-    final ActionCallback callback = myTabs.removeTab(myTabs.getTabAt(componentIndex), toSelect, transferFocus);
+    final TabInfo info = myTabs.getTabAt(componentIndex);
+    // removing hidden tab happens on end of drag-out, we've already selected the correct tab for this case in dragOutStarted
+    if (info.isHidden()) {
+      toSelect = null;
+    }
+    final ActionCallback callback = myTabs.removeTab(info, toSelect, transferFocus);
     return myProject.isOpen() ? callback : new ActionCallback.Done();
   }
 
@@ -554,8 +559,12 @@ final class EditorTabbedContainer implements Disposable, CloseAction.CloseTarget
 
     @Override
     public void dragOutStarted(MouseEvent mouseEvent, TabInfo info) {
+      final TabInfo previousSelection = info.getPreviousSelection();
       final Image img = myTabs.getComponentImage(info);
       info.setHidden(true);
+      if (previousSelection != null) {
+        myTabs.select(previousSelection, true);
+      }
 
       myFile = (VirtualFile)info.getObject();
       Presentation presentation = new Presentation(info.getText());