Fix(workbench): StackRenderer duplication of tabs on move

Ensure OWNING_ME data is preserved when a CTabItem is recreated during a move operation. This prevents the renderer from creating duplicate tabs for the same part.

Author: vogella

bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRenderer.java

@@ -446,6 +446,7 @@ void subscribeTopicChildrenMoved(@UIEventTopic(UIEvents.ElementContainer.TOPIC_C
 		newItem.setToolTipText(toolTipText);
 		newItem.setFont(font);
 		newItem.setData(data);
+		newItem.setData(OWNING_ME, movedElement);
 		newItem.setControl(control);
 	}
 

tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRendererMoveTest.java

@@ -0,0 +1,97 @@
+package org.eclipse.e4.ui.workbench.renderers.swt;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import jakarta.inject.Inject;
+import java.util.List;
+import org.eclipse.e4.ui.internal.workbench.swt.AbstractPartRenderer;
+import org.eclipse.e4.ui.model.application.MApplication;
+import org.eclipse.e4.ui.model.application.ui.basic.MPart;
+import org.eclipse.e4.ui.model.application.ui.basic.MPartStack;
+import org.eclipse.e4.ui.model.application.ui.basic.MWindow;
+import org.eclipse.e4.ui.tests.rules.WorkbenchContextExtension;
+import org.eclipse.e4.ui.workbench.modeling.EModelService;
+import org.eclipse.swt.custom.CTabFolder;
+import org.eclipse.swt.custom.CTabItem;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+public class StackRendererMoveTest {
+
+	@RegisterExtension
+	public WorkbenchContextExtension contextRule = new WorkbenchContextExtension();
+
+	@Inject
+	private EModelService ems;
+
+	@Inject
+	private MApplication application;
+
+	private MWindow window;
+	private MPartStack partStack;
+
+	@BeforeEach
+	public void setUp() throws Exception {
+		window = ems.createModelElement(MWindow.class);
+		application.getChildren().add(window);
+		application.setSelectedElement(window);
+
+		partStack = ems.createModelElement(MPartStack.class);
+		window.getChildren().add(partStack);
+	}
+
+	@Test
+	public void testPartMoveUpdatesWidget() throws Exception {
+		// Create two parts
+		MPart part1 = ems.createModelElement(MPart.class);
+		part1.setLabel("Part 1");
+		partStack.getChildren().add(part1);
+
+		MPart part2 = ems.createModelElement(MPart.class);
+		part2.setLabel("Part 2");
+		partStack.getChildren().add(part2);
+
+		// Render the window (and thus the stack and parts)
+		contextRule.createAndRunWorkbench(window);
+
+		CTabFolder tabFolder = (CTabFolder) partStack.getWidget();
+		assertEquals(2, tabFolder.getItemCount());
+
+		CTabItem item1 = tabFolder.getItem(0);
+		CTabItem item2 = tabFolder.getItem(1);
+
+		assertEquals(part1, item1.getData(AbstractPartRenderer.OWNING_ME));
+		assertEquals(part2, item2.getData(AbstractPartRenderer.OWNING_ME));
+		assertEquals(item1.getControl(), part1.getWidget());
+		assertEquals(item2.getControl(), part2.getWidget());
+
+		// Move part1 to the end (index 1)
+		// We use model service to move to ensure events are fired
+		ems.move(part1, partStack, 1);
+
+		// Verify model update
+		List<org.eclipse.e4.ui.model.application.ui.basic.MStackElement> children = partStack.getChildren();
+		assertEquals(part2, children.get(0));
+		assertEquals(part1, children.get(1));
+
+		// Verify UI update
+		assertEquals(2, tabFolder.getItemCount());
+		CTabItem newItem1 = tabFolder.getItem(1);
+		CTabItem newItem2 = tabFolder.getItem(0);
+
+		// The old item1 should be disposed
+		assertTrue(item1.isDisposed(), "Old item for part1 should be disposed");
+		
+		// part1 should have a NEW widget item, but the part's widget (content) should be preserved
+		assertNotSame(item1, newItem1);
+		assertEquals(part1, newItem1.getData(AbstractPartRenderer.OWNING_ME), "New item should have OWNING_ME set");
+		assertEquals(part1.getWidget(), newItem1.getControl(), "Part1 widget should be the control of the new item");
+		
+		// part2 should still be valid and same widget
+		assertEquals(item2, newItem2);
+		assertEquals(part2, newItem2.getData(AbstractPartRenderer.OWNING_ME));
+	}
+}