Bug 162655 [Undo] [IDE] - Undoing a delete should check for existence of resources to be restored
N20061027. - I deleted two projects (along with their content). I read the warning that undo delete cannot restore the content and said "OK." - Then I checked out those same projects from HEAD. - Then I selected "Undo Delete Resources." This overwrote my code with empty projects. I think that "Undo Delete Resources" should become invalid if the resources exist again, because you'll end up replacing content without keeping a backup.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/undo/AbstractResourcesOperation.java
* @throws CoreException
	 *             propagates any CoreExceptions thrown from the resources API
	 */
	protected void delete(IProgressMonitor monitor, IAdaptable uiInfo,
			boolean deleteContent) throws CoreException {
		setResourceDescriptions(WorkspaceUndoUtil.delete(resources, monitor,
				uiInfo, deleteContent));
		setTargetResources(new IResource[0]);
	}
	/**
	 * Recreate any resources known by this operation. Store enough information
	 * to undo and redo the operation.
	 * 
	 * @param monitor
	 *            the progress monitor to use for the operation
	 * @param uiInfo
	 *            the IAdaptable (or <code>null</code>) provided by the
	 *            caller in order to supply UI information for prompting the
	 *            user if necessary. When this parameter is not
	 *            <code>null</code>, it contains an adapter for the
	 *            org.eclipse.swt.widgets.Shell.class
	 * @throws CoreException
	 *             propagates any CoreExceptions thrown from the resources API
	 */
	protected void recreate(IProgressMonitor monitor, IAdaptable uiInfo)
			throws CoreException {
		setTargetResources(WorkspaceUndoUtil.recreate(resourceDescriptions,
				monitor, uiInfo));
		setResourceDescriptions(new ResourceDescription[0]);
	}