/// <summary>
/// create a new root node from the given root after adding annotations to the tokens
///
/// tokens should belong to the given root
/// </summary>
public static SyntaxNode AddAnnotations(this SyntaxNode root, IEnumerable <Tuple <SyntaxToken, SyntaxAnnotation> > pairs)
{
var tokenMap = pairs.GroupBy(p => p.Item1, p => p.Item2).ToDictionary(g => g.Key, g => g.ToArray());
return(root.ReplaceTokens(tokenMap.Keys, (o, n) => o.WithAdditionalAnnotations(tokenMap[o])));
}