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
}
		return null;
	}
	/**
     * Adds the given child elements to this viewer as children of the given
     * parent element.
     * <p>
     * EXPERIMENTAL.  Not to be used except by JDT.
     * This method was added to support JDT's explorations
     * into grouping by working sets, which requires viewers to support multiple 
     * equal elements.  See bug 76482 for more details.  This support will
     * likely be removed in Eclipse 3.2 in favour of proper support for
     * multiple equal elements. 
     * </p>
     *
     * @param widget 
     *           the widget for the parent element
     * @param parentElementOrTreePath
     *           the parent element
     * @param childElements
     *           the child elements to add
     * @since 3.1
     */
    protected void internalAdd(Widget widget, Object parentElementOrTreePath, Object[] childElements) {
    	Object parent;
    	TreePath path;
    	if (parentElementOrTreePath instanceof TreePath) {
			path = (TreePath) parentElementOrTreePath;
			parent = path.getLastSegment();
		} else {