Bug 138608 [Viewers] JFace AbstractTreeViewer: itemExists doesn't handle equal tree entries
I use a TreeViewer with - setUseHashLookup(true) - without any sorter or filter - with a comparer When I try to add an object that is equal to an existing entry in the tree, it will not be added. This is because the method private boolean itemExists(Item[] items, Object element) { if(usingElementMap()) { return findItem(element) != null; } for (int i = 0; i < items.length; i++) { if(items[i].getData().equals(element)) { return true; } } return false; } takes a shortcut if there is an element map, but the shortcut doesn't handle the 'multiple equal elements' case. There is a workaround, however: Setting a dummy sorter will avoid the call to itemExists and multiple equal elements can be added to the tree.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
Widget w = findItem(element);
				if (w instanceof Item) {
					Item item = (Item) w;
					path = getTreePathFromItem(item);
				}
				if (path == null) {
					path = new TreePath(new Object[] { element });
				}
			}
			return tpcp.hasChildren(path);
		}
        if (cp instanceof ITreeContentProvider) {
			ITreeContentProvider tcp = (ITreeContentProvider) cp;
			return tcp.hasChildren(element);	
		}
		return false;
    }
    
    /**
     * Return whether the given element is expandable.
     * @param item the tree item for the element
     * @param parentPath the parent path if it is knwon or <code>null</code> if it needs to be determines
     * @param element the element
     * @return whether the given element is expandable
     */
    private boolean isExpandable(Item item, TreePath parentPath, Object element) {
    	if (isTreePathContentProvider()) {
    		TreePath path;
    		if (parentPath != null) {
    			path = parentPath.createChildPath(element);