Bug 32254 [Viewers] AbstractTreeViewer uses HashSet to remember expansion state
I20030216 The custom hash table should be used instead. Otherwise expansion state may be lost due to a different equals implementation of the element and the IElementComparer.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CheckboxTreeViewer.java
internalExpand(elements[i], false);
		grayedElements.add(elements[i]);
	}
	Control tree = getControl();
	tree.setRedraw(false);
	internalSetGrayed(grayedElements, tree);
	tree.setRedraw(true);
}
/**
 * Sets the grayed state for the given element and its parents
 * in this viewer.
 *
 * @param element the element
 * @param state <code>true</code> if the item should be grayed,
 *  and <code>false</code> if it should be ungrayed
 * @return <code>true</code> if the element is visible and the gray
 *  state could be set, and <code>false</code> otherwise
 * @see #setGrayed
 */
public boolean setParentsGrayed(Object element, boolean state) {
	Assert.isNotNull(element);
	Widget widget = internalExpand(element, false);
	if (widget instanceof TreeItem) {
		TreeItem item = (TreeItem) widget;
		item.setGrayed(state);
		item = item.getParentItem();
		while (item != null) {
			item.setGrayed(state);
			item = item.getParentItem();