Don't create dummy item when removing invalid element from tree #3525

Due to the fix for Bug 210747, a dummy tree-item is added to the viewer
if the same element is removed twice. The problem is that this fix
doesn't distinguish between nodes that haven't been realized yet and
nodes that are not part of the model.

This check has been refined to only call updatePlus(...) if the removed
object is associated with such a dummy node.

To reproduce:

- Create a new project "Project A" and "Project B"
- Create a new text file "test" in "Project A"
- Move "test" to "Project B"

Closes #3525

Author: ptziegler

bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2019 IBM Corporation and others.
+ * Copyright (c) 2000, 2025 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -2095,12 +2095,7 @@ protected void internalRemove(Object[] elementsOrPaths) {
 				Object parent = getParentElement(element);
 				if (parent != null && !equals(parent, getRoot())
 						&& !(parent instanceof TreePath tp && tp.getSegmentCount() == 0)) {
-					Widget[] parentItems = internalFindItems(parent);
-					for (Widget parentItem : parentItems) {
-						if (parentItem instanceof Item it) {
-							updatePlus(it, parent);
-						}
-					}
+					internalRemove(parent, new Object[] { element });
 				}
 			}
 		}

tests/org.eclipse.jface.tests/src/org/eclipse/jface/tests/viewers/TreeViewerTest.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2006 IBM Corporation and others.
+ * Copyright (c) 2000, 2025 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -14,7 +14,11 @@
 package org.eclipse.jface.tests.viewers;
 
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -114,4 +118,64 @@ protected void internalExpandToLevel(Widget widget, int level) {
 		}
 	}
 
+	/**
+	 * Removing the same element twice should not produce a dummy tree-item.
+	 */
+	@Test
+	public void testIssue3525() {
+		TestElement modelRoot = TestElement.createModel(2, 1);
+		TestElement modelParent = modelRoot.getChildAt(0);
+		TestElement modelChild = modelParent.getChildAt(0);
+		fTreeViewer.setInput(modelRoot);
+		fTreeViewer.expandAll();
+
+		TreeItem widgetParent = (TreeItem) fTreeViewer.testFindItem(modelParent);
+		TreeItem widgetChild = (TreeItem) fTreeViewer.testFindItem(modelChild);
+		assertNotNull(widgetParent);
+		assertNotNull(widgetChild);
+		assertArrayEquals(widgetParent.getItems(), new TreeItem[] { widgetChild });
+
+		fTreeViewer.remove(modelChild);
+
+		widgetParent = (TreeItem) fTreeViewer.testFindItem(modelParent);
+		widgetChild = (TreeItem) fTreeViewer.testFindItem(modelChild);
+		assertNotNull(widgetParent);
+		assertNull(widgetChild);
+		assertArrayEquals(widgetParent.getItems(), new TreeItem[0]);
+
+		fTreeViewer.remove(modelChild);
+
+		widgetParent = (TreeItem) fTreeViewer.testFindItem(modelParent);
+		widgetChild = (TreeItem) fTreeViewer.testFindItem(modelChild);
+		assertNotNull(widgetParent);
+		assertNull(widgetChild);
+		assertArrayEquals(widgetParent.getItems(), new TreeItem[0]);
+	}
+
+	/**
+	 * Remove an element that hasn't been realized yet.
+	 */
+	@Test
+	public void testBug210747() {
+		TestElement modelRoot = TestElement.createModel(2, 1);
+		TestElement modelParent = modelRoot.getChildAt(0);
+		TestElement modelChild = modelParent.getChildAt(0);
+		fTreeViewer.setInput(modelRoot);
+		fTreeViewer.setExpandedElements(modelRoot);
+
+		TreeItem widgetParent = (TreeItem) fTreeViewer.testFindItem(modelParent);
+		TreeItem widgetChild = (TreeItem) fTreeViewer.testFindItem(modelChild);
+		assertNotNull(widgetParent);
+		assertNull(widgetChild);
+		assertEquals(widgetParent.getItems().length, 1); // Dummy Item
+		assertNull(widgetParent.getItems()[0].getData());
+
+		fTreeViewer.remove(modelChild);
+
+		widgetParent = (TreeItem) fTreeViewer.testFindItem(modelParent);
+		widgetChild = (TreeItem) fTreeViewer.testFindItem(modelChild);
+		assertNotNull(widgetParent);
+		assertNull(widgetChild);
+		assertArrayEquals(widgetParent.getItems(), new TreeItem[0]);
+	}
 }