update SA1518 to ignore empty (0 bytes) files

Author: DWIAltonaAnalytics

StyleCop.Analyzers/StyleCop.Analyzers.Test/LayoutRules/SA1518UnitTests.cs

@@ -49,6 +49,22 @@ internal async Task TestWithBlankLinesAtEndOfFileAsync(OptionSetting? newlineAtE
             await VerifyCSharpFixAsync(newlineAtEndOfFile, testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
         }
 
+        /// <summary>
+        /// Verifies that empty files will not produce a warning.
+        /// </summary>
+        /// <param name="newlineAtEndOfFile">The effective <see cref="OptionSetting"/> setting.</param>
+        /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
+        [Theory]
+        [InlineData(null)]
+        [InlineData(OptionSetting.Allow)]
+        [InlineData(OptionSetting.Require)]
+        [InlineData(OptionSetting.Omit)]
+        internal async Task TestWithEmptyFileAsync(OptionSetting? newlineAtEndOfFile)
+        {
+            var testCode = string.Empty;
+            await VerifyCSharpDiagnosticAsync(newlineAtEndOfFile, testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
         /// <summary>
         /// Verifies that linefeed only blank lines at the end of the file will produce a warning.
         /// </summary>

StyleCop.Analyzers/StyleCop.Analyzers/Helpers/SyntaxTreeHelpers.cs

@@ -72,6 +72,14 @@ public static bool IsWhitespaceOnly(this SyntaxTree tree, CancellationToken canc
                 && TriviaHelper.IndexOfFirstNonWhitespaceTrivia(firstToken.LeadingTrivia) == -1;
         }
 
+        public static bool IsEmpty(this SyntaxTree tree, CancellationToken cancellationToken)
+        {
+            var root = tree.GetRoot(cancellationToken);
+            var firstToken = root.GetFirstToken(includeZeroWidth: true);
+
+            return firstToken.IsKind(SyntaxKind.EndOfFileToken) && firstToken.FullSpan.Length == 0;
+        }
+
         internal static bool ContainsUsingAlias(this SyntaxTree tree, ConcurrentDictionary<SyntaxTree, bool> cache)
         {
             if (tree == null)

StyleCop.Analyzers/StyleCop.Analyzers/LayoutRules/SA1518UseLineEndingsCorrectlyAtEndOfFile.cs

@@ -72,6 +72,12 @@ public override void Initialize(AnalysisContext context)
 
         private static void HandleSyntaxTree(SyntaxTreeAnalysisContext context, StyleCopSettings settings)
         {
+            if (context.Tree.IsEmpty(context.CancellationToken))
+            {
+                // Empty file never contain line endings.
+                return;
+            }
+
             var endOfFileToken = context.Tree.GetRoot().GetLastToken(includeZeroWidth: true);
             TextSpan reportedSpan = new TextSpan(endOfFileToken.SpanStart, 0);