/// <summary>
/// Adds documentation header async.
/// </summary>
/// <param name="document">The document.</param>
/// <param name="root">The root.</param>
/// <param name="declarationSyntax">The declaration syntax.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>A Document.</returns>
private async Task <Document> AddDocumentationHeaderAsync(Document document, SyntaxNode root, FieldDeclarationSyntax declarationSyntax, CancellationToken cancellationToken)
{
SyntaxTriviaList leadingTrivia = declarationSyntax.GetLeadingTrivia();
VariableDeclaratorSyntax field = declarationSyntax.DescendantNodes().OfType <VariableDeclaratorSyntax>().First();
string comment = CommentHelper.CreateFieldComment(field.Identifier.ValueText);
DocumentationCommentTriviaSyntax commentTrivia = await Task.Run(() => DocumentationHeaderHelper.CreateOnlySummaryDocumentationCommentTrivia(comment), cancellationToken);
SyntaxTriviaList newLeadingTrivia = leadingTrivia.Insert(leadingTrivia.Count - 1, SyntaxFactory.Trivia(commentTrivia));
FieldDeclarationSyntax newDeclaration = declarationSyntax.WithLeadingTrivia(newLeadingTrivia);
SyntaxNode newRoot = root.ReplaceNode(declarationSyntax, newDeclaration);
return(document.WithSyntaxRoot(newRoot));
}