Fix sorting when using a TreePathViewerSorter in AbstractTreeViewer

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

@@ -662,12 +662,13 @@ private int internalCompare(ViewerComparator comparator,
 		return comparator.compare(this, e1, e2);
 	}
 
+	@SuppressWarnings("removal")
 	@Override
 	protected Object[] getSortedChildren(Object parentElementOrTreePath) {
 		Object[] result = null;
 		ViewerComparator comparator = getComparator();
 		if (parentElementOrTreePath != null
-				&& comparator instanceof TreePathViewerComparator tpvs) {
+				&& (comparator instanceof TreePathViewerSorter || comparator instanceof TreePathViewerComparator)) {
 			result = getFilteredChildren(parentElementOrTreePath);
 			// be sure we're not modifying the original array from the model
 			result = result.clone();
@@ -682,7 +683,11 @@ protected Object[] getSortedChildren(Object parentElementOrTreePath) {
 					path = internalGetSorterParentPath(w, comparator);
 				}
 			}
-			tpvs.sort(this, path, result);
+			if (comparator instanceof TreePathViewerSorter tpvs) {
+				tpvs.sort(this, path, result);
+			} else if (comparator instanceof TreePathViewerComparator tpvc) {
+				tpvc.sort(this, path, result);
+			}
 			result = applyItemsLimit(parentElementOrTreePath, result);
 		} else {
 			return super.getSortedChildren(parentElementOrTreePath);

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

@@ -21,6 +21,9 @@
 
 import org.eclipse.jface.viewers.ITreeContentProvider;
 import org.eclipse.jface.viewers.StructuredViewer;
+import org.eclipse.jface.viewers.TreePath;
+import org.eclipse.jface.viewers.TreePathViewerComparator;
+import org.eclipse.jface.viewers.TreePathViewerSorter;
 import org.eclipse.jface.viewers.TreeViewer;
 import org.eclipse.jface.viewers.Viewer;
 import org.eclipse.jface.viewers.ViewerComparator;
@@ -114,6 +117,43 @@ public void testViewerSorterInsertElement() {
 		assertSortedResult(expected);
 	}
 
+	@Test
+	@SuppressWarnings({ "deprecation", "removal" })
+	public void test_GH3900_TreePathViewerSorter() {
+		// A TreePathViewerSorter with reversed order.
+		// In GH 3900, the viewer did not call the overridden method and the results
+		// were sorted lexicographically.
+		var sorter = new TreePathViewerSorter() {
+			@Override
+			public int compare(Viewer viewer, TreePath parentPath, Object e1, Object e2) {
+				return -super.compare(viewer, parentPath, e1, e2);
+			}
+		};
+		fViewer.setSorter(sorter);
+		getTreeViewer().expandAll();
+		TreeItem[] items = getTreeViewer().getTree().getItems();
+		assertEquals(UI, items[0].getText());
+		assertEquals(RUNTIME, items[1].getText());
+		assertEquals(CORE, items[2].getText());
+	}
+
+	@Test
+	public void test_GH3900_TreePathViewerComparator() {
+		// A TreePathViewerComparator with reversed order.
+		var comparator = new TreePathViewerComparator() {
+			@Override
+			public int compare(Viewer viewer, TreePath parentPath, Object e1, Object e2) {
+				return -super.compare(viewer, parentPath, e1, e2);
+			}
+		};
+		fViewer.setComparator(comparator);
+		getTreeViewer().expandAll();
+		TreeItem[] items = getTreeViewer().getTree().getItems();
+		assertEquals(UI, items[0].getText());
+		assertEquals(RUNTIME, items[1].getText());
+		assertEquals(CORE, items[2].getText());
+	}
+
 	@Test
 	public void testViewerComparator() {
 		fViewer.setComparator(new ViewerComparator());