private static void AddInvocation(
                HelpBuilder builder,
                IReadOnlyCollection <ISymbol> symbols,
                Func <ISymbol, HelpItem> formatter)
            {
                if (symbols?.Any() != true)
                {
                    return;
                }

                var helpItems = symbols
                                .Select(formatter).ToList();

                var maxWidth = helpItems
                               .Select(line => line.Invocation.Length)
                               .OrderByDescending(textLength => textLength)
                               .First();

                foreach (var helpItem in helpItems)
                {
                    builder.AppendHelpItem(helpItem, maxWidth);
                }
            }