Add new rule

Author: Lakshmi Priya Sekar

src/Microsoft.DotNet.CodeFormatting/Rules/HasNewLineBeforeFirstUsingFormattingRule.cs

@@ -0,0 +1,60 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under MIT. See LICENSE in the project root for license information.
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Microsoft.DotNet.CodeFormatting.Rules
+{
+    // [Export(typeof(IFormattingRule))]
+    // This rule negates the changes done by the IsFormatterFormattingRule, when there are #ifdef using 
+    // statements. Thus the formatter will enter an infinite loop. Enable this rule as required.
+    internal sealed class HasNewLineBeforeFirstUsingFormattingRule : IFormattingRule
+    {
+        public async Task<Document> ProcessAsync(Document document, CancellationToken cancellationToken)
+        {
+            var syntaxRoot = await document.GetSyntaxRootAsync(cancellationToken) as CSharpSyntaxNode;
+            if (syntaxRoot == null)
+                return document;
+           
+            var firstUsing = syntaxRoot.DescendantNodesAndSelf().OfType<UsingDirectiveSyntax>().FirstOrDefault();
+            IEnumerable<SyntaxTrivia> newTrivia = Enumerable.Empty<SyntaxTrivia>();
+
+            if (firstUsing == null)
+                return document;
+
+            if (firstUsing.HasLeadingTrivia)
+            {
+                var trivia = firstUsing.GetLeadingTrivia();
+                if (trivia.Last().CSharpKind() == SyntaxKind.EndOfLineTrivia)
+                {
+                    int index = trivia.Count - 2;
+                    while (index >= 0)
+                    {
+                        if (trivia.ElementAt(index).CSharpKind() != SyntaxKind.EndOfLineTrivia)
+                            break;
+                        index--;
+                    }
+
+                    newTrivia = trivia.Take(index + 1);
+                }
+                else
+                {
+                    newTrivia = trivia;
+                }                
+            }
+
+            newTrivia = newTrivia.Concat(new[] { SyntaxFactory.EndOfLine("\n"), SyntaxFactory.EndOfLine("\n") });
+
+            return document.WithSyntaxRoot(syntaxRoot.ReplaceNode(firstUsing, firstUsing.WithLeadingTrivia(newTrivia)));
+        }
+    }
+}