Adds a using directive if one doesn't already exist at the top of file after existing using directives via Roslyn. - CSharp Microsoft.CodeAnalysis

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Description

Adds a using directive if one doesn't already exist at the top of file after existing using directives via Roslyn.

Demo Code

// Copyright (c) .NET Foundation. All rights reserved.
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp;
using Microsoft.CodeAnalysis;
using System.Linq;
using System.Diagnostics.Contracts;
using System.Diagnostics;
using System;/* w  w  w  .  j a  v a 2s .  c o m*/

public class Main{
        /// <summary>
        /// Adds a using directive if one doesn't already exist at the top of file
        /// after existing using directives.
        /// 
        /// Does not handle the scenarios where usings are defined within an inner node of
        /// given root node, ex, if the root node is CompilationUnit and usings are defined
        /// within a Namespace Declaration instead of top of the file, the new using is
        /// just added at the top of the file.
        /// </summary>
        /// <param name="namespaceName">The namespace to be added.</param>
        /// <param name="rootNode">Parent syntax node for which the childs are examined
        /// to see if a using with the given namespace already exists</param>
        /// <returns>A new syntax node containing the new using statement as an immediate
        /// child of given rootNode. If the using statement is already present, the rootNode
        /// is returned. Otherwise, a new statement is added at the end of existing
        /// usings and the new node is returned.</returns>
        public static CompilationUnitSyntax AddUsingDirectiveIfNeeded(string namespaceName, CompilationUnitSyntax rootNode)
        {
            Contract.Assert(rootNode != null);

            if (String.IsNullOrEmpty(namespaceName))
            {
                return rootNode;
            }

            if (rootNode.Usings.Any(usingNode => usingNode.Name.ToString() == namespaceName))
            {
                // Using already present, return this node
                return rootNode;
            }

            var insertTree = CSharpSyntaxTree.ParseText("using " + namespaceName + ";" + Environment.NewLine);
            var usingStatement = insertTree.GetRoot().ChildNodes().First() as UsingDirectiveSyntax;
            Debug.Assert(usingStatement != null);

            return rootNode.AddUsings(usingStatement);
        }
}

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