StackRenderer updates correctly when part is moved

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

@@ -395,6 +395,66 @@ void subscribeTopicChildrenChanged(@UIEventTopic(UIEvents.ElementContainer.TOPIC
 		shouldTopRightAdjusted(event);
 	}
 
+	@Inject
+	@Optional
+	void subscribeTopicChildrenMoved(@UIEventTopic(UIEvents.ElementContainer.TOPIC_CHILDREN) Event event) {
+		if (!UIEvents.isMOVE(event)) {
+			return;
+		}
+		// Ensure that this event is for a MPartStack
+		Object element = event.getProperty(UIEvents.EventTags.ELEMENT);
+		if (!(element instanceof MPartStack)) {
+			return;
+		}
+
+		MPartStack stack = (MPartStack) element;
+		if (stack.getRenderer() != this) {
+			return;
+		}
+
+		MUIElement movedElement = (MUIElement) event.getProperty(UIEvents.EventTags.NEW_VALUE);
+
+		CTabFolder tabFolder = (CTabFolder) stack.getWidget();
+		if (tabFolder == null || tabFolder.isDisposed()) {
+			return;
+		}
+
+		CTabItem item = findItemForPart(movedElement, stack);
+		if (item == null || item.isDisposed()) {
+			return;
+		}
+
+		int newIndex = calcIndexFor(stack, movedElement);
+
+		// Remember the control, it will be disposed with the CTabItem otherwise
+		Control control = item.getControl();
+		item.setControl(null);
+
+		// As CTabItem cannot be reordered, we need to dispose and recreate it
+		String text = item.getText();
+		Image image = item.getImage();
+		boolean showClose = item.getShowClose();
+		String toolTipText = item.getToolTipText();
+		Font font = item.getFont();
+		Object data = item.getData();
+
+		boolean wasSelected = tabFolder.getSelection() == item;
+
+		item.dispose();
+
+		CTabItem newItem = new CTabItem(tabFolder, (showClose ? SWT.CLOSE : SWT.NONE), newIndex);
+		newItem.setText(text);
+		newItem.setImage(image);
+		newItem.setToolTipText(toolTipText);
+		newItem.setFont(font);
+		newItem.setData(data);
+		newItem.setData(OWNING_ME, movedElement);
+		newItem.setControl(control);
+		if (wasSelected) {
+			tabFolder.setSelection(newItem);
+		}
+	}
+
 	@Inject
 	@Optional
 	void subscribeTopicUILabelChanged(@UIEventTopic(UIEvents.UILabel.TOPIC_ALL) Event event) {
@@ -623,6 +683,14 @@ void subscribeTopicSelectedelementChanged(
 		tabStateHandler.handleEvent(event);
 	}
 
+	@Override
+	public void removeGui(MUIElement element, Object widget) {
+		if (widget instanceof CTabFolder tabFolder && !tabFolder.isDisposed()) {
+			tabFolder.dispose();
+		}
+		element.setWidget(null);
+	}
+
 	@Override
 	protected boolean requiresFocus(MPart element) {
 		MUIElement inStack = element.getCurSharedRef() != null ? element.getCurSharedRef() : element;
@@ -1010,7 +1078,7 @@ protected void createTab(MElementContainer<MUIElement> stack, MUIElement element
 		}
 	}
 
-	private int calcIndexFor(MElementContainer<MUIElement> stack, final MUIElement part) {
+	private int calcIndexFor(MElementContainer<? extends MUIElement> stack, final MUIElement part) {
 		int index = 0;
 
 		// Find the -visible- part before this element
@@ -1036,7 +1104,7 @@ public void childRendered(final MElementContainer<MUIElement> parentElement, MUI
 		createTab(parentElement, element);
 	}
 
-	private CTabItem findItemForPart(MUIElement element, MElementContainer<MUIElement> stack) {
+	private CTabItem findItemForPart(MUIElement element, MElementContainer<? extends MUIElement> stack) {
 		if (stack == null) {
 			stack = element.getParent();
 		}

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

@@ -0,0 +1,99 @@
+package org.eclipse.e4.ui.workbench.renderers.swt;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+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");
+		assertFalse(item2.isDisposed(), "Item2 should not 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));
+	}
+}

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

@@ -573,6 +573,32 @@ public void testToolbarIsReparentedToNewCompositeForTopRightOfTabFolder() {
 		assertSame(tabFolder.getTopRight(), toolbarControl.getParent());
 	}
 
+	@Test
+	public void testPartReordering() {
+		MPart part1 = ems.createModelElement(MPart.class);
+		part1.setLabel("Part 1");
+		MPart part2 = ems.createModelElement(MPart.class);
+		part2.setLabel("Part 2");
+
+		partStack.getChildren().add(part1);
+		partStack.getChildren().add(part2);
+
+		contextRule.createAndRunWorkbench(window);
+
+		CTabFolder tabFolder = (CTabFolder) partStack.getWidget();
+		assertEquals(2, tabFolder.getItemCount());
+		assertEquals("Part 1", tabFolder.getItem(0).getText());
+		assertEquals("Part 2", tabFolder.getItem(1).getText());
+
+		// Move part2 to index 0
+		partStack.getChildren().remove(part2);
+		partStack.getChildren().add(0, part2);
+
+		// Verify order in Widget
+		assertEquals("Part 2", tabFolder.getItem(0).getText());
+		assertEquals("Part 1", tabFolder.getItem(1).getText());
+	}
+
 	// helper functions
 
 	/*