Save with original Encoding

The Encoding of a file in Roslyn can change as it is rewritten.  Make
sure to save with the original file encoding.

Author: jaredpar

src/Microsoft.DotNet.CodeFormatting/FormattingEngineImplementation.cs

@@ -105,18 +105,12 @@ private async Task SaveChanges(Solution solution, Solution originalSolution, Can
                     var sourceText = await document.GetTextAsync(cancellationToken);
                     using (var file = File.Open(document.FilePath, FileMode.Truncate, FileAccess.Write))
                     {
-                        var encoding = sourceText.Encoding;
+                        // The encoding of the file can change during the rewrite.  Make sure to save with the
+                        // original encoding
+                        var originalDocument = originalSolution.GetDocument(documentId);
+                        var originalSourceText = await originalDocument.GetTextAsync(cancellationToken);
 
-                        // TODO: It seems like a bug that Encoding could change but it is definitely
-                        // happening.  Ex: ArrayBuilder.Enumerator.cs
-                        if (encoding == null)
-                        {
-                            var originalDocument = originalSolution.GetDocument(documentId);
-                            var originalSourceText = await originalDocument.GetTextAsync(cancellationToken);
-                            encoding = originalSourceText.Encoding;
-                        }
-
-                        using (var writer = new StreamWriter(file, encoding))
+                        using (var writer = new StreamWriter(file, originalSourceText.Encoding))
                         {
                             sourceText.Write(writer, cancellationToken);
                         }

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

@@ -24,7 +24,7 @@ internal sealed class HasNoIllegalHeadersFormattingRule : ILocalSemanticFormatti
         // We are going to remove any multiline comments that *only* contain these characters
         private const string CommentFormattingCharacters = "*/=-";
 
-        public async Task<SyntaxNode> ProcessAsync(Document document, SyntaxNode syntaxNode, CancellationToken cancellationToken)
+        public Task<SyntaxNode> ProcessAsync(Document document, SyntaxNode syntaxNode, CancellationToken cancellationToken)
         {
             var leadingTrivia = syntaxNode.GetLeadingTrivia();
             SyntaxTriviaList newTrivia = leadingTrivia;
@@ -71,9 +71,9 @@ public async Task<SyntaxNode> ProcessAsync(Document document, SyntaxNode syntaxN
             }
 
             if (leadingTrivia.Equals(newTrivia))
-                return syntaxNode;
+                return Task.FromResult(syntaxNode);
 
-            return syntaxNode.WithLeadingTrivia(newTrivia);
+            return Task.FromResult(syntaxNode.WithLeadingTrivia(newTrivia));
         }
 
         private string[] GetIllegalHeaders(Document document)