process mouse wheel event by parent scroll pane if it is not processed by a scroll pane

platform/platform-api/src/com/intellij/ui/components/DefaultScrollBarUI.java

@@ -406,7 +406,7 @@ class DefaultScrollBarUI extends ScrollBarUI {
           Point point = event.getLocationOnScreen();
           SwingUtilities.convertPointFromScreen(point, view);
           Component target = SwingUtilities.getDeepestComponentAt(view, point.x, point.y);
-          if (target != null) target.dispatchEvent(MouseEventAdapter.convert(event, target));
+          MouseEventAdapter.redispatch(event, target);
         }
       }
       return true;

platform/platform-api/src/com/intellij/ui/components/JBScrollBar.java

@@ -243,6 +243,9 @@ public class JBScrollBar extends JScrollBar implements TopComponent, Interpolabl
         setValue(value + valueAdjusted);
       }
     }
+    else if (delta != 0.0) {
+      return true; // do not consume event if it can be processed by parent component
+    }
     event.consume();
     return true;
   }

platform/platform-api/src/com/intellij/ui/components/JBScrollPane.java

@@ -9,6 +9,7 @@ import com.intellij.util.ArrayUtil;
 import com.intellij.util.ReflectionUtil;
 import com.intellij.util.ui.ButtonlessScrollBarUI;
 import com.intellij.util.ui.JBInsets;
+import com.intellij.util.ui.MouseEventAdapter;
 import com.intellij.util.ui.RegionPainter;
 import com.intellij.util.ui.UIUtil;
 import org.jetbrains.annotations.NotNull;
@@ -177,6 +178,10 @@ public class JBScrollPane extends JScrollPane {
                     }
                   }
                 }
+                if (!event.isConsumed()) {
+                  // try to process a mouse wheel event by outer scroll pane
+                  MouseEventAdapter.redispatch(event, UIUtil.getParentOfType(JScrollPane.class, pane.getParent()));
+                }
               }
             }
           };

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

@@ -86,7 +86,7 @@ public abstract class AbstractExpandableItemsHandler<KeyType, ComponentType exte
     MouseEventHandler dispatcher = new MouseEventHandler() {
       @Override
       protected void handle(MouseEvent event) {
-        myComponent.dispatchEvent(MouseEventAdapter.convert(event, myComponent));
+        MouseEventAdapter.redispatch(event, myComponent);
       }
 
       @Override

platform/util/src/com/intellij/util/ui/MouseEventAdapter.java

@@ -128,7 +128,8 @@ public class MouseEventAdapter<T> extends MouseAdapter implements MouseInputList
                                event.isPopupTrigger(),
                                event.getScrollType(),
                                event.getScrollAmount(),
-                               event.getWheelRotation());
+                               event.getWheelRotation(),
+                               event.getPreciseWheelRotation());
   }
 
   @NotNull
@@ -139,4 +140,17 @@ public class MouseEventAdapter<T> extends MouseAdapter implements MouseInputList
                                   event.getPath(),
                                   event.getMenuSelectionManager());
   }
+
+  private static boolean dispatch(Component component, @NotNull MouseEvent event) {
+    component.dispatchEvent(event);
+    return event.isConsumed();
+  }
+
+  public static void redispatch(@NotNull MouseEvent event, Component source) {
+    if (source != null && dispatch(source, convert(event, source))) event.consume();
+  }
+
+  public static void redispatch(@NotNull MouseEvent event, Component source, int x, int y) {
+    if (source != null && dispatch(source, convert(event, source, x, y))) event.consume();
+  }
 }