Implement a formatting analyzer

src/EditorFeatures/CSharpTest/Formatting/FormattingAnalyzerTests.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Diagnostics;
+using Microsoft.CodeAnalysis.Formatting;
+using Microsoft.CodeAnalysis.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Formatting
+{
+    public class FormattingAnalyzerTests : AbstractCSharpDiagnosticProviderBasedUserDiagnosticTest
+    {
+        internal override (DiagnosticAnalyzer, CodeFixProvider) CreateDiagnosticProviderAndFixer(Workspace workspace)
+            => (new FormattingDiagnosticAnalyzer(), new FormattingCodeFixProvider());
+
+        [Fact, Trait(Traits.Feature, Traits.Features.Formatting)]
+        public async Task TrailingWhitespace()
+        {
+            var testCode =
+                "class X[| |]" + Environment.NewLine +
+                "{" + Environment.NewLine +
+                "}" + Environment.NewLine;
+            var expected =
+                "class X" + Environment.NewLine +
+                "{" + Environment.NewLine +
+                "}" + Environment.NewLine;
+            await TestInRegularAndScriptAsync(testCode, expected);
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.Formatting)]
+        public async Task TestMissingSpace()
+        {
+            var testCode = @"
+class TypeName
+{
+    void Method()
+    {
+        if$$(true)return;
+    }
+}
+";
+            var expected = @"
+class TypeName
+{
+    void Method()
+    {
+        if (true)return;
+    }
+}
+";
+
+            await TestInRegularAndScriptAsync(testCode, expected);
+        }
+    }
+}

src/Features/Core/Portable/CodeFixes/PredefinedCodeFixProviderNames.cs

@@ -21,6 +21,7 @@ internal static class PredefinedCodeFixProviderNames
         public const string AddMissingReference = nameof(AddMissingReference);
         public const string AddImport = nameof(AddImport);
         public const string FullyQualify = nameof(FullyQualify);
+        public const string FixFormatting = nameof(FixFormatting);
         public const string FixIncorrectFunctionReturnType = nameof(FixIncorrectFunctionReturnType);
         public const string FixIncorrectExitContinue = nameof(FixIncorrectExitContinue);
         public const string GenerateConstructor = nameof(GenerateConstructor);

src/Features/Core/Portable/Diagnostics/Analyzers/IDEDiagnosticIds.cs

@@ -84,6 +84,8 @@ internal static class IDEDiagnosticIds
 
         public const string UseExpressionBodyForLambdaExpressionsDiagnosticId = "IDE0053";
 
+        public const string FormattingDiagnosticId = "IDE0054";
+
         // Analyzer error Ids
         public const string AnalyzerChangedId = "IDE1001";
         public const string AnalyzerDependencyConflictId = "IDE1002";

src/Features/Core/Portable/FeaturesResources.Designer.cs

@@ -1369,6 +1369,33 @@ internal class FeaturesResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Fix formatting.
+        /// </summary>
+        internal static string Formatting_analyzer_code_fix {
+            get {
+                return ResourceManager.GetString("Formatting_analyzer_code_fix", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Fix formatting.
+        /// </summary>
+        internal static string Formatting_analyzer_message {
+            get {
+                return ResourceManager.GetString("Formatting_analyzer_message", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Fix formatting.
+        /// </summary>
+        internal static string Formatting_analyzer_title {
+            get {
+                return ResourceManager.GetString("Formatting_analyzer_title", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Formatting document.
         /// </summary>

src/Features/Core/Portable/FeaturesResources.resx

@@ -1430,4 +1430,13 @@ This version used in: {2}</value>
   <data name="Type_0_has_a_private_member_1_that_can_be_removed_as_the_value_assigned_to_it_is_never_read" xml:space="preserve">
     <value>Type '{0}' has a private member '{1}' that can be removed as the value assigned to it is never read.</value>
   </data>
+  <data name="Formatting_analyzer_code_fix" xml:space="preserve">
+    <value>Fix formatting</value>
+  </data>
+  <data name="Formatting_analyzer_message" xml:space="preserve">
+    <value>Fix formatting</value>
+  </data>
+  <data name="Formatting_analyzer_title" xml:space="preserve">
+    <value>Fix formatting</value>
+  </data>
 </root>
\ No newline at end of file

src/Features/Core/Portable/Formatting/FormattingCodeFixProvider.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Composition;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Editing;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Formatting
+{
+    [ExportCodeFixProvider(LanguageNames.CSharp, LanguageNames.VisualBasic, Name = PredefinedCodeFixProviderNames.FixFormatting)]
+    [Shared]
+    internal class FormattingCodeFixProvider : SyntaxEditorBasedCodeFixProvider
+    {
+        public override ImmutableArray<string> FixableDiagnosticIds
+            => ImmutableArray.Create(IDEDiagnosticIds.FormattingDiagnosticId);
+
+        public override Task RegisterCodeFixesAsync(CodeFixContext context)
+        {
+            context.RegisterCodeFix(
+                new MyCodeAction(c => FixOneAsync(context.Document, context.Diagnostics, c)),
+                context.Diagnostics);
+
+            return Task.CompletedTask;
+        }
+
+        protected async Task<Document> FixOneAsync(Document document, ImmutableArray<Diagnostic> diagnostics, CancellationToken cancellationToken)
+        {
+            var tree = await document.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
+            var text = await document.GetTextAsync(cancellationToken).ConfigureAwait(false);
+            var changes = new List<TextChange>();
+            foreach (var diagnostic in diagnostics)
+            {
+                if (!tree.Equals(diagnostic.Location.SourceTree)
+                    || !diagnostic.Properties.TryGetValue(FormattingDiagnosticAnalyzer.ReplaceTextKey, out var replacement))
+                {
+                    continue;
+                }
+
+                changes.Add(new TextChange(diagnostic.Location.SourceSpan, replacement));
+            }
+
+            changes.Sort((left, right) => left.Span.Start.CompareTo(right.Span.Start));
+
+            return document.WithText(text.WithChanges(changes));
+        }
+
+        protected override async Task FixAllAsync(Document document, ImmutableArray<Diagnostic> diagnostics, SyntaxEditor editor, CancellationToken cancellationToken)
+        {
+            var options = await document.GetOptionsAsync(cancellationToken).ConfigureAwait(false);
+            var updatedDocument = await Formatter.FormatAsync(document, options, cancellationToken).ConfigureAwait(false);
+            editor.ReplaceNode(editor.OriginalRoot, await updatedDocument.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false));
+        }
+
+        private sealed class MyCodeAction : CodeAction.DocumentChangeAction
+        {
+            public MyCodeAction(Func<CancellationToken, Task<Document>> createChangedDocument)
+                : base(FeaturesResources.Formatting_analyzer_code_fix, createChangedDocument, FeaturesResources.Formatting_analyzer_code_fix)
+            {
+            }
+        }
+    }
+}

src/Features/Core/Portable/Formatting/FormattingDiagnosticAnalyzer.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis.CodeStyle;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.Formatting
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
+    internal class FormattingDiagnosticAnalyzer
+        : AbstractCodeStyleDiagnosticAnalyzer
+    {
+        public static readonly string ReplaceTextKey = nameof(ReplaceTextKey);
+
+        public static readonly ImmutableDictionary<string, string> RemoveTextProperties =
+            ImmutableDictionary.Create<string, string>().Add(ReplaceTextKey, "");
+
+        public FormattingDiagnosticAnalyzer()
+            : base(
+                IDEDiagnosticIds.FormattingDiagnosticId,
+                new LocalizableResourceString(nameof(FeaturesResources.Formatting_analyzer_title), FeaturesResources.ResourceManager, typeof(FeaturesResources)),
+                new LocalizableResourceString(nameof(FeaturesResources.Formatting_analyzer_message), FeaturesResources.ResourceManager, typeof(FeaturesResources)))
+        {
+        }
+
+        public override DiagnosticAnalyzerCategory GetAnalyzerCategory()
+            => DiagnosticAnalyzerCategory.SyntaxAnalysis;
+
+        public override bool OpenFileOnly(Workspace workspace)
+            => false;
+
+        protected override void InitializeWorker(AnalysisContext context)
+            => context.RegisterSyntaxTreeAction(AnalyzeSyntaxTree);
+
+        private void AnalyzeSyntaxTree(SyntaxTreeAnalysisContext context)
+        {
+            if (!(context.Options is WorkspaceAnalyzerOptions workspaceAnalyzerOptions))
+            {
+                return;
+            }
+
+            var options = context.Options.GetDocumentOptionSetAsync(context.Tree, context.CancellationToken).GetAwaiter().GetResult();
+            if (options == null)
+            {
+                return;
+            }
+
+            var workspace = workspaceAnalyzerOptions.Services.Workspace;
+            var formattingChanges = Formatter.GetFormattedTextChanges(context.Tree.GetRoot(context.CancellationToken), workspace, options, context.CancellationToken);
+            foreach (var formattingChange in formattingChanges)
+            {
+                var change = formattingChange;
+                if (change.NewText.Length > 0 && !change.Span.IsEmpty)
+                {
+                    var oldText = context.Tree.GetText(context.CancellationToken);
+
+                    // Handle cases where the change is a substring removal from the beginning
+                    var offset = change.Span.Length - change.NewText.Length;
+                    if (offset >= 0 && oldText.GetSubText(new TextSpan(change.Span.Start + offset, change.NewText.Length)).ContentEquals(SourceText.From(change.NewText)))
+                    {
+                        change = new TextChange(new TextSpan(change.Span.Start, offset), "");
+                    }
+                    else
+                    {
+                        // Handle cases where the change is a substring removal from the end
+                        if (change.NewText.Length < change.Span.Length
+                            && oldText.GetSubText(new TextSpan(change.Span.Start, change.NewText.Length)).ContentEquals(SourceText.From(change.NewText)))
+                        {
+                            change = new TextChange(new TextSpan(change.Span.Start + change.NewText.Length, change.Span.Length - change.NewText.Length), "");
+                        }
+                    }
+                }
+
+                if (change.NewText.Length == 0 && change.Span.IsEmpty)
+                {
+                    // No actual change
+                    continue;
+                }
+
+                ImmutableDictionary<string, string> properties;
+                if (change.NewText.Length == 0)
+                {
+                    properties = RemoveTextProperties;
+                }
+                else
+                {
+                    properties = ImmutableDictionary.Create<string, string>().Add(ReplaceTextKey, change.NewText);
+                }
+
+                var location = Location.Create(context.Tree, change.Span);
+                context.ReportDiagnostic(DiagnosticHelper.Create(
+                    Descriptor,
+                    location,
+                    ReportDiagnostic.Default,
+                    additionalLocations: null,
+                    properties));
+            }
+        }
+    }
+}

src/Features/Core/Portable/xlf/FeaturesResources.cs.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Opravit překlep {0}</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Formátuje se dokument.</target>

src/Features/Core/Portable/xlf/FeaturesResources.de.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Tippfehler "{0}" korrigieren</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Dokument wird formatiert</target>

src/Features/Core/Portable/xlf/FeaturesResources.es.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Corregir error de escritura "{0}"</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Aplicando formato al documento</target>

src/Features/Core/Portable/xlf/FeaturesResources.fr.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Corriger la faute de frappe '{0}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Mise en forme du document</target>

src/Features/Core/Portable/xlf/FeaturesResources.it.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Correggere l'errore di ortografia '{0}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Formattazione del documento</target>

src/Features/Core/Portable/xlf/FeaturesResources.ja.xlf

@@ -62,6 +62,21 @@
         <target state="translated">'{0}' の入力ミスを修正します</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">ドキュメントの書式設定</target>

src/Features/Core/Portable/xlf/FeaturesResources.ko.xlf

@@ -62,6 +62,21 @@
         <target state="translated">오타 '{0}' 수정</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">문서 서식 지정</target>

src/Features/Core/Portable/xlf/FeaturesResources.pl.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Popraw błąd pisowni „{0}”</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Formatowanie dokumentu</target>

src/Features/Core/Portable/xlf/FeaturesResources.pt-BR.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Corrigir erro de digitação '{0}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Formatando documento</target>

src/Features/Core/Portable/xlf/FeaturesResources.ru.xlf

@@ -62,6 +62,21 @@
         <target state="translated">Исправьте опечатку "{0}"</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Форматирование документа</target>

src/Features/Core/Portable/xlf/FeaturesResources.tr.xlf

@@ -62,6 +62,21 @@
         <target state="translated">'{0}' yazım hatasını düzeltin</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">Belge biçimlendiriliyor</target>

src/Features/Core/Portable/xlf/FeaturesResources.zh-Hans.xlf

@@ -62,6 +62,21 @@
         <target state="translated">修正笔误“{0}”</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">设置文档格式</target>

src/Features/Core/Portable/xlf/FeaturesResources.zh-Hant.xlf

@@ -62,6 +62,21 @@
         <target state="translated">修正錯字 '{0}'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Formatting_analyzer_code_fix">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_message">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="Formatting_analyzer_title">
+        <source>Fix formatting</source>
+        <target state="new">Fix formatting</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Formatting_document">
         <source>Formatting document</source>
         <target state="translated">正在將文件格式化</target>

src/Workspaces/Core/Portable/Formatting/Engine/AbstractFormatEngine.cs

@@ -92,9 +92,13 @@ internal abstract partial class AbstractFormatEngine
                 _language = token1.Language;
             }
 
-            // set synchronous task executor if it is debug mode or if there is not many things to format
-            this.TaskExecutor = optionSet.GetOption(FormattingOptions.DebugMode, _language) ? TaskExecutor.Synchronous :
-                                    (SpanToFormat.Length < ConcurrentThreshold) ? TaskExecutor.Synchronous : executor;
+            // set synchronous task executor if it is enabled (explicitly or as part of debug mode) or if there is not
+            // many things to format
+            var synchronousExecutorAllowed =
+                !optionSet.GetOption(FormattingOptions.AllowConcurrent)
+                || optionSet.GetOption(FormattingOptions.DebugMode, _language);
+            var useSynchronousExecutor = synchronousExecutorAllowed || SpanToFormat.Length < ConcurrentThreshold;
+            TaskExecutor = useSynchronousExecutor ? TaskExecutor.Synchronous : executor;
         }
 
         protected abstract AbstractTriviaDataFactory CreateTriviaFactory();

src/Workspaces/Core/Portable/Formatting/Formatter.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -281,7 +282,13 @@ internal static Task<IFormattingResult> GetFormattingResult(SyntaxNode node, IEn
         /// <param name="cancellationToken">An optional cancellation token.</param>
         /// <returns>The changes necessary to format the tree.</returns>
         public static IList<TextChange> GetFormattedTextChanges(SyntaxNode node, Workspace workspace, OptionSet options = null, CancellationToken cancellationToken = default)
-            => GetFormattedTextChangesAsync(node, workspace, options, cancellationToken).WaitAndGetResult_CanCallOnBackground(cancellationToken);
+        {
+            options = options ?? workspace.Options;
+            options = options.WithChangedOption(FormattingOptions.AllowConcurrent, false);
+            var resultTask = GetFormattedTextChangesAsync(node, workspace, options, cancellationToken);
+            Debug.Assert(resultTask.IsCompleted);
+            return resultTask.WaitAndGetResult_CanCallOnBackground(cancellationToken);
+        }
 
         internal static Task<IList<TextChange>> GetFormattedTextChangesAsync(SyntaxNode node, Workspace workspace, OptionSet options = null, CancellationToken cancellationToken = default)
             => GetFormattedTextChangesAsync(node, SpecializedCollections.SingletonEnumerable(node.FullSpan), workspace, options, rules: null, cancellationToken: cancellationToken);

src/Workspaces/Core/Portable/Formatting/FormattingOptions.cs

@@ -45,6 +45,7 @@ private static Optional<string> ParseEditorConfigEndOfLine(string endOfLineValue
         }
 
         internal static PerLanguageOption<bool> DebugMode { get; } = new PerLanguageOption<bool>(nameof(FormattingOptions), nameof(DebugMode), defaultValue: false);
+        internal static Option<bool> AllowConcurrent { get; } = new Option<bool>(nameof(FormattingOptions), nameof(AllowConcurrent), defaultValue: true);
 
         internal static Option<bool> AllowDisjointSpanMerging { get; } = new Option<bool>(nameof(FormattingOptions), nameof(AllowDisjointSpanMerging), defaultValue: false);