Provide method to avoid expanding widgets in AbstractTreeViewer

Co-authored-by: Heiko Klare <[email protected]>

Author: fedejeanne

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

@@ -29,6 +29,7 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.function.Function;
+import java.util.function.Predicate;
 
 import org.eclipse.core.runtime.Assert;
 import org.eclipse.core.runtime.IStatus;
@@ -1850,12 +1851,40 @@ protected Widget internalGetWidgetToSelect(Object elementOrTreePath) {
 	 */
 	private void internalConditionalExpandToLevel(Widget widget, int level,
 			Function<Widget, Boolean> shouldChildrenExpand) {
+		internalConditionalExpandToLevel(widget, level, getShouldWidgetExpand(), shouldChildrenExpand);
+	}
+
+	/**
+	 * @return the predicate that determines if a widget should be expanded when
+	 *         expanding the tree.
+	 * @since 3.36
+	 */
+	protected Predicate<Widget> getShouldWidgetExpand() {
+		return w -> true;
+	}
+
+	/**
+	 * Same as
+	 * {@link #internalConditionalExpandToLevel(Widget, int, Function, Function)}
+	 * but with an extra parameter to determine if the widget itself should be
+	 * expanded.
+	 *
+	 * @param shouldWidgetExpand evaluates if the widget itself needs to be
+	 *                           expanded.
+	 */
+	private void internalConditionalExpandToLevel(Widget widget, int level, Predicate<Widget> shouldWidgetExpand,
+			Function<Widget, Boolean> shouldChildrenExpand) {
 		if (level == ALL_LEVELS || level > 0) {
 			Object data = widget.getData();
 			if (widget instanceof Item it && data != null && !isExpandable(it, null, data)) {
 				return;
 			}
 			createChildren(widget, false);
+
+			if (!shouldWidgetExpand.test(widget)) {
+				return;
+			}
+
 			// XXX for performance widget should be expanded after expanding children:
 			if (widget instanceof Item it) {
 				setExpanded(it, true);
@@ -1866,7 +1895,7 @@ private void internalConditionalExpandToLevel(Widget widget, int level,
 					int newLevel = (level == ALL_LEVELS ? ALL_LEVELS
 							: level - 1);
 					for (Item element : children) {
-						internalConditionalExpandToLevel(element, newLevel, shouldChildrenExpand);
+						internalConditionalExpandToLevel(element, newLevel, shouldWidgetExpand, shouldChildrenExpand);
 					}
 				}
 			}