Avoid making unnecessary copies

src/CodeStyle/Core/Analyzers/Microsoft.CodeAnalysis.CodeStyle.csproj

@@ -98,6 +98,7 @@
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\ListPool.cs" Link="Formatting\ListPool.cs" />
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\AbstractFormattingRule.cs" Link="Formatting\Rules\AbstractFormattingRule.cs" />
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\BaseIndentationFormattingRule.cs" Link="Formatting\Rules\BaseIndentationFormattingRule.cs" />
+    <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\CompatAbstractFormattingRule.cs" Link="Formatting\Rules\CompatAbstractFormattingRule.cs" />
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\NextAction`1.cs" Link="Formatting\Rules\NextAction`1.cs" />
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\NextOperation`1.cs" Link="Formatting\Rules\NextOperation`1.cs" />
     <Compile Include="..\..\..\Workspaces\Core\Portable\Formatting\Rules\NoOpFormattingRule.cs" Link="Formatting\Rules\NoOpFormattingRule.cs" />

src/EditorFeatures/CSharp/AutomaticCompletion/Sessions/CurlyBraceCompletionSession.cs

@@ -197,7 +197,7 @@ private class BraceCompletionFormattingRule : BaseFormattingRule
 
             public static readonly AbstractFormattingRule Instance = new BraceCompletionFormattingRule();
 
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 // Eg Cases -
                 // new MyObject {
@@ -221,7 +221,7 @@ public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken p
                     }
                 }
 
-                return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
             }
 
             public override void AddAlignTokensOperations(List<AlignTokensOperation> list, SyntaxNode node, OptionSet optionSet, NextAction<AlignTokensOperation> nextOperation)

src/EditorFeatures/CSharp/Formatting/CSharpEditorFormattingService.PasteFormattingRule.cs

@@ -10,7 +10,7 @@ internal partial class CSharpEditorFormattingService : IEditorFormattingService
     {
         internal class PasteFormattingRule : AbstractFormattingRule
         {
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 if (currentToken.Parent != null)
                 {

src/EditorFeatures/CSharp/Formatting/Indentation/SmartTokenFormatter.cs

@@ -118,10 +118,10 @@ private bool CloseBraceOfTryOrDoBlock(SyntaxToken endToken)
 
         private class NoLineChangeFormattingRule : AbstractFormattingRule
         {
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 // no line operation. no line changes what so ever
-                var lineOperation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                var lineOperation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
                 if (lineOperation != null)
                 {
                     // ignore force if same line option
@@ -146,9 +146,9 @@ public override void AddSuppressOperations(List<SuppressOperation> list, SyntaxN
                 // don't suppress anything
             }
 
-            public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+            public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
             {
-                var spaceOperation = base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                var spaceOperation = base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, in nextOperation);
 
                 // if there is force space operation, convert it to ForceSpaceIfSingleLine operation.
                 // (force space basically means remove all line breaks)

src/EditorFeatures/VisualBasic/Formatting/Indentation/SpecialFormattingOperation.vb

@@ -10,7 +10,7 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.Formatting.Indentation
 
     Friend Class SpecialFormattingRule
-        Inherits AbstractFormattingRule
+        Inherits CompatAbstractFormattingRule
 
         Public Sub New()
         End Sub
@@ -19,7 +19,7 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.Formatting.Indentation
             ' don't suppress anything
         End Sub
 
-        Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+        Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
 
             ' unlike regular one. force position of attribute
             Dim attributeNode = TryCast(previousToken.Parent, AttributeListSyntax)
@@ -28,7 +28,7 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.Formatting.Indentation
             End If
 
             ' no line operation. no line changes what so ever
-            Dim lineOperation = MyBase.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, nextOperation)
+            Dim lineOperation = MyBase.GetAdjustNewLinesOperationSlow(previousToken, currentToken, optionSet, nextOperation)
             If lineOperation IsNot Nothing Then
                 ' basically means don't ever put new line if there isn't already one, but do
                 ' indentation.
@@ -38,8 +38,8 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.Formatting.Indentation
             Return Nothing
         End Function
 
-        Public Overrides Function GetAdjustSpacesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
-            Dim spaceOperation = MyBase.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, nextOperation)
+        Public Overrides Function GetAdjustSpacesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
+            Dim spaceOperation = MyBase.GetAdjustSpacesOperationSlow(previousToken, currentToken, optionSet, nextOperation)
 
             ' if there is force space operation, convert it to ForceSpaceIfSingleLine operation.
             ' (force space basically means remove all line breaks)

src/EditorFeatures/VisualBasic/Utilities/LineAdjustmentFormattingRule.vb

@@ -8,14 +8,14 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.Utilities
     Friend NotInheritable Class LineAdjustmentFormattingRule
-        Inherits AbstractFormattingRule
+        Inherits CompatAbstractFormattingRule
 
         Public Shared ReadOnly Instance As New LineAdjustmentFormattingRule()
 
         Private Sub New()
         End Sub
 
-        Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+        Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
             If Not CommonFormattingHelpers.HasAnyWhitespaceElasticTrivia(previousToken, currentToken) Then
                 Return nextOperation.Invoke()
             End If

src/Features/CSharp/Portable/ChangeSignature/ChangeSignatureFormattingRule.cs

@@ -44,14 +44,14 @@ private void AddChangeSignatureIndentOperation(List<IndentBlockOperation> list,
             }
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             if (previousToken.Kind() == SyntaxKind.CommaToken && s_allowableKinds.Contains(previousToken.Parent.Kind()))
             {
                 return FormattingOperations.CreateAdjustNewLinesOperation(0, AdjustNewLinesOption.PreserveLines);
             }
 
-            return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+            return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
         }
     }
 }

src/Features/CSharp/Portable/ExtractMethod/CSharpMethodExtractor.FormattingProvider.cs

@@ -15,10 +15,10 @@ public FormattingRule()
             {
             }
 
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 // for extract method case, for a hybrid case, don't force rule, but preserve user style
-                var operation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                var operation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
                 if (operation == null)
                 {
                     return null;

src/Features/CSharp/Portable/UseAutoProperty/CSharpUseAutoPropertyCodeFixProvider.cs

@@ -96,24 +96,24 @@ private bool ForceSingleSpace(SyntaxToken previousToken, SyntaxToken currentToke
                 return false;
             }
 
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 if (ForceSingleSpace(previousToken, currentToken))
                 {
                     return null;
                 }
 
-                return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
             }
 
-            public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+            public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
             {
                 if (ForceSingleSpace(previousToken, currentToken))
                 {
                     return new AdjustSpacesOperation(1, AdjustSpacesOption.ForceSpaces);
                 }
 
-                return base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+                return base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, in nextOperation);
             }
         }
 

src/Features/CSharp/Portable/UseConditionalExpression/MultiLineConditionalExpressionFormattingRule.cs

@@ -40,7 +40,7 @@ private bool IsQuestionOrColonOfNewConditional(SyntaxToken token)
         }
 
         public override AdjustNewLinesOperation GetAdjustNewLinesOperation(
-            SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             if (IsQuestionOrColonOfNewConditional(currentToken))
             {

src/Features/Core/Portable/CodeRefactorings/AddMissingImports/AbstractAddMissingImportsFeatureService.cs

@@ -243,7 +243,7 @@ public CleanUpNewLinesFormatter(SourceText text)
                 _text = text;
             }
 
-            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+            public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 // Since we know the general shape of these new import statements, we simply look for where
                 // tokens are not on the same line and force them to only be separated by a single newline.

src/Features/Core/Portable/GenerateEqualsAndGetHashCodeFromMembers/FormatLargeBinaryExpressionRule.cs

@@ -27,7 +27,7 @@ public FormatLargeBinaryExpressionRule(ISyntaxFactsService syntaxFacts)
             /// Wrap the large && expression after every && token.
             /// </summary>
             public override AdjustNewLinesOperation GetAdjustNewLinesOperation(
-                SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+                SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 if (_syntaxFacts.IsLogicalAndExpression(previousToken.Parent))
                 {

src/Features/Core/Portable/MetadataAsSource/AbstractMetadataAsSourceService.AbstractMetadataFormattingRule.cs

@@ -16,7 +16,7 @@ protected abstract class AbstractMetadataFormattingRule : AbstractFormattingRule
             protected abstract bool IsNewLine(char c);
 
             public override AdjustNewLinesOperation GetAdjustNewLinesOperation(
-                    SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+                    SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
             {
                 if (previousToken.RawKind == 0 || currentToken.RawKind == 0)
                 {

src/Features/VisualBasic/Portable/ChangeSignature/ChangeSignatureFormattingRule.vb

@@ -32,13 +32,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ChangeSignature
             End If
         End Sub
 
-        Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+        Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
             If previousToken.IsKind(SyntaxKind.CommaToken) AndAlso
                (previousToken.Parent.IsKind(SyntaxKind.ParameterList) OrElse previousToken.Parent.IsKind(SyntaxKind.ArgumentList)) Then
                 Return FormattingOperations.CreateAdjustNewLinesOperation(0, AdjustNewLinesOption.PreserveLines)
             End If
 
-            Return MyBase.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, nextOperation)
+            Return MyBase.GetAdjustNewLinesOperationSlow(previousToken, currentToken, optionSet, nextOperation)
         End Function
     End Class
 End Namespace

src/Features/VisualBasic/Portable/ExtractMethod/VisualBasicMethodExtractor.vb

@@ -113,9 +113,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ExtractMethod
         End Function
 
         Private Class FormattingRule
-            Inherits AbstractFormattingRule
+            Inherits CompatAbstractFormattingRule
 
-            Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+            Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
                 If Not previousToken.IsLastTokenOfStatement() Then
                     Return nextOperation.Invoke()
                 End If

src/Features/VisualBasic/Portable/UseConditionalExpression/MultiLineConditionalExpressionFormattingRule.vb

@@ -20,7 +20,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.UseConditionalExpression
     ''' i.e. both branches will be on a newline, indented once from the parent indentation.
     ''' </summary>
     Friend Class MultiLineConditionalExpressionFormattingRule
-        Inherits AbstractFormattingRule
+        Inherits CompatAbstractFormattingRule
 
         Public Shared ReadOnly Instance As New MultiLineConditionalExpressionFormattingRule()
 
@@ -36,7 +36,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.UseConditionalExpression
             Return False
         End Function
 
-        Public Overrides Function GetAdjustNewLinesOperation(
+        Public Overrides Function GetAdjustNewLinesOperationSlow(
                 previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
             If IsCommaOfNewConditional(previousToken) Then
                 ' We want to force the expressions after the commas to be put on the 

src/VisualStudio/CSharp/Impl/CodeModel/EndRegionFormattingRule.cs

@@ -26,7 +26,7 @@ private bool IsAfterEndRegionBeforeMethodDeclaration(SyntaxToken previousToken,
             return false;
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             if (IsAfterEndRegionBeforeMethodDeclaration(previousToken, currentToken))
             {

src/VisualStudio/CSharp/Impl/Utilities/BlankLineInGeneratedMethodFormattingRule.cs

@@ -15,7 +15,7 @@ private BlankLineInGeneratedMethodFormattingRule()
         {
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             // case: insert blank line in empty method body.
             if (previousToken.Kind() == SyntaxKind.OpenBraceToken &&

src/VisualStudio/Core/Def/Implementation/Venus/ContainedDocumentPreserveFormattingRule.cs

@@ -13,9 +13,9 @@ internal class ContainedDocumentPreserveFormattingRule : AbstractFormattingRule
         private static readonly AdjustSpacesOperation s_preserveSpace = FormattingOperations.CreateAdjustSpacesOperation(0, AdjustSpacesOption.PreserveSpaces);
         private static readonly AdjustNewLinesOperation s_preserveLine = FormattingOperations.CreateAdjustNewLinesOperation(0, AdjustNewLinesOption.PreserveLines);
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
-            var operation = base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+            var operation = base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, in nextOperation);
             if (operation != null)
             {
                 return s_preserveSpace;
@@ -24,9 +24,9 @@ public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previ
             return operation;
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
-            var operation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, ref nextOperation);
+            var operation = base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
             if (operation != null)
             {
                 return s_preserveLine;

src/Workspaces/CSharp/Portable/Formatting/DefaultOperationProvider.cs

@@ -34,13 +34,13 @@ public override void AddAlignTokensOperations(List<AlignTokensOperation> list, S
         {
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             return null;
         }
 
         // return 1 space for every token pairs as a default operation
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             int space = currentToken.Kind() == SyntaxKind.EndOfFileToken ? 0 : 1;
             return FormattingOperations.CreateAdjustSpacesOperation(space, AdjustSpacesOption.DefaultSpacesIfOnSingleLine);

src/Workspaces/CSharp/Portable/Formatting/Rules/ElasticTriviaFormattingRule.cs

@@ -96,7 +96,7 @@ private InitializerExpressionSyntax GetInitializerNode(SyntaxNode node)
             return null;
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             var operation = nextOperation.Invoke();
             if (operation == null)
@@ -218,7 +218,7 @@ private AdjustNewLinesOperation GetAdjustNewLinesOperationBetweenMembers(SyntaxT
             return FormattingOperations.CreateAdjustNewLinesOperation(2 /* +1 for member itself and +1 for a blank line*/, AdjustNewLinesOption.ForceLines);
         }
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             var operation = nextOperation.Invoke();
             if (operation == null)

src/Workspaces/CSharp/Portable/Formatting/Rules/EndOfFileTokenFormattingRule.cs

@@ -9,7 +9,7 @@ internal class EndOfFileTokenFormattingRule : BaseFormattingRule
     {
         internal const string Name = "CSharp End Of File Token Formatting Rule";
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             // * <End Of File> case for C#, make sure we don't insert new line between * and <End of
             // File> tokens.
@@ -21,7 +21,7 @@ public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken p
             return nextOperation.Invoke();
         }
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             // * <End Of File) case
             // for C#, make sure we have nothing between these two tokens

src/Workspaces/CSharp/Portable/Formatting/Rules/NewLineUserSettingFormattingRule.cs

@@ -45,7 +45,7 @@ private bool IsControlBlock(SyntaxNode node)
             }
         }
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             var operation = nextOperation.Invoke();
 
@@ -166,7 +166,7 @@ public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previ
             return operation;
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             var operation = nextOperation.Invoke();
 

src/Workspaces/CSharp/Portable/Formatting/Rules/QueryExpressionFormattingRule.cs

@@ -105,7 +105,7 @@ public override void AddAnchorIndentationOperations(List<AnchorIndentationOperat
             }
         }
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             if (previousToken.IsNestedQueryExpression())
             {

src/Workspaces/CSharp/Portable/Formatting/Rules/SpacingFormattingRule.cs

@@ -11,7 +11,7 @@ namespace Microsoft.CodeAnalysis.CSharp.Formatting
 {
     internal class SpacingFormattingRule : BaseFormattingRule
     {
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             if (optionSet == null)
             {

src/Workspaces/CSharp/Portable/Formatting/Rules/StructuredTriviaFormattingRule.cs

@@ -10,7 +10,7 @@ internal class StructuredTriviaFormattingRule : BaseFormattingRule
     {
         internal const string Name = "CSharp Structured Trivia Formatting Rule";
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             if (previousToken.Parent is StructuredTriviaSyntax || currentToken.Parent is StructuredTriviaSyntax)
             {
@@ -20,7 +20,7 @@ public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken p
             return nextOperation.Invoke();
         }
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             if (previousToken.Parent is StructuredTriviaSyntax || currentToken.Parent is StructuredTriviaSyntax)
             {

src/Workspaces/CSharp/Portable/Formatting/Rules/TokenBasedFormattingRule.cs

@@ -12,7 +12,7 @@ internal class TokenBasedFormattingRule : BaseFormattingRule
     {
         internal const string Name = "CSharp Token Based Formatting Rule";
 
-        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             ////////////////////////////////////////////////////
             // brace related operations
@@ -186,7 +186,7 @@ public override AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken p
             return nextOperation.Invoke();
         }
 
-        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             //////////////////////////////////////////////////////
             // ";" related operations

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

@@ -53,11 +53,11 @@ public ChainedFormattingRules(IEnumerable<AbstractFormattingRule> formattingRule
                 this.AddContinuedOperations);
 
             _newLinesFuncCache = new OperationCache<AdjustNewLinesOperation>(
-                (int index, SyntaxToken token1, SyntaxToken token2, ref NextOperation<AdjustNewLinesOperation> next) => _formattingRules[index].GetAdjustNewLinesOperation(token1, token2, _optionSet, ref next),
+                (int index, SyntaxToken token1, SyntaxToken token2, in NextOperation<AdjustNewLinesOperation> next) => _formattingRules[index].GetAdjustNewLinesOperation(token1, token2, _optionSet, in next),
                 this.GetContinuedOperations);
 
             _spaceFuncCache = new OperationCache<AdjustSpacesOperation>(
-                (int index, SyntaxToken token1, SyntaxToken token2, ref NextOperation<AdjustSpacesOperation> next) => _formattingRules[index].GetAdjustSpacesOperation(token1, token2, _optionSet, ref next),
+                (int index, SyntaxToken token1, SyntaxToken token2, in NextOperation<AdjustSpacesOperation> next) => _formattingRules[index].GetAdjustSpacesOperation(token1, token2, _optionSet, in next),
                 this.GetContinuedOperations);
         }
 
@@ -118,7 +118,7 @@ private TResult GetContinuedOperations<TResult>(int index, SyntaxToken token1, S
             {
                 // Call the handler at the index, passing a continuation that will come back to here with index + 1
                 var continuation = new NextOperation<TResult>(index + 1, token1, token2, funcCache);
-                return funcCache.NextOperation(index, token1, token2, ref continuation);
+                return funcCache.NextOperation(index, token1, token2, in continuation);
             }
         }
     }

src/Workspaces/Core/Portable/Formatting/Engine/OperationCache`1.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 Microsoft.CodeAnalysis.Formatting.Rules;
 
 namespace Microsoft.CodeAnalysis.Formatting
@@ -10,7 +9,7 @@ namespace Microsoft.CodeAnalysis.Formatting
     /// </summary>
     internal readonly struct OperationCache<TResult>
     {
-        public delegate TResult NextOperationFunc(int index, SyntaxToken token1, SyntaxToken token2, ref NextOperation<TResult> next);
+        public delegate TResult NextOperationFunc(int index, SyntaxToken token1, SyntaxToken token2, in NextOperation<TResult> next);
         public delegate TResult ContinuationFunc(int index, SyntaxToken token1, SyntaxToken token2, in OperationCache<TResult> operationCache);
 
         public OperationCache(

src/Workspaces/Core/Portable/Formatting/Rules/AbstractFormattingRule.cs

@@ -47,7 +47,7 @@ public virtual void AddAlignTokensOperations(List<AlignTokensOperation> list, Sy
         /// <summary>
         /// returns AdjustNewLinesOperation between two tokens either by itself or by filtering/replacing a operation returned by NextOperation
         /// </summary>
-        public virtual AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        public virtual AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
         {
             return nextOperation.Invoke();
         }
@@ -55,7 +55,7 @@ public virtual AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken pr
         /// <summary>
         /// returns AdjustSpacesOperation between two tokens either by itself or by filtering/replacing a operation returned by NextOperation
         /// </summary>
-        public virtual AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        public virtual AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
         {
             return nextOperation.Invoke();
         }

src/Workspaces/Core/Portable/Formatting/Rules/CompatAbstractFormattingRule.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.ComponentModel;
+using Microsoft.CodeAnalysis.Options;
+
+namespace Microsoft.CodeAnalysis.Formatting.Rules
+{
+    internal abstract class CompatAbstractFormattingRule : AbstractFormattingRule
+    {
+#pragma warning disable CS0809 // Obsolete member overrides non-obsolete member
+        [Obsolete("Do not call this method directly (it will Stack Overflow).", error: true)]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override sealed AdjustNewLinesOperation GetAdjustNewLinesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustNewLinesOperation> nextOperation)
+        {
+            var nextOperationCopy = nextOperation;
+            return GetAdjustNewLinesOperationSlow(previousToken, currentToken, optionSet, ref nextOperationCopy);
+        }
+
+        [Obsolete("Do not call this method directly (it will Stack Overflow).", error: true)]
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override sealed AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, in NextOperation<AdjustSpacesOperation> nextOperation)
+        {
+            var nextOperationCopy = nextOperation;
+            return GetAdjustSpacesOperationSlow(previousToken, currentToken, optionSet, ref nextOperationCopy);
+        }
+#pragma warning restore CS0809 // Obsolete member overrides non-obsolete member
+
+        /// <summary>
+        /// returns AdjustNewLinesOperation between two tokens either by itself or by filtering/replacing a operation returned by NextOperation
+        /// </summary>
+        public virtual AdjustNewLinesOperation GetAdjustNewLinesOperationSlow(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustNewLinesOperation> nextOperation)
+        {
+            return base.GetAdjustNewLinesOperation(previousToken, currentToken, optionSet, in nextOperation);
+        }
+
+        /// <summary>
+        /// returns AdjustSpacesOperation between two tokens either by itself or by filtering/replacing a operation returned by NextOperation
+        /// </summary>
+        public virtual AdjustSpacesOperation GetAdjustSpacesOperationSlow(SyntaxToken previousToken, SyntaxToken currentToken, OptionSet optionSet, ref NextOperation<AdjustSpacesOperation> nextOperation)
+        {
+            return base.GetAdjustSpacesOperation(previousToken, currentToken, optionSet, in nextOperation);
+        }
+    }
+}

src/Workspaces/VisualBasic/Portable/Formatting/DefaultOperationProvider.vb

@@ -12,7 +12,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
     '
     ' to reduce number of unnecessary heap allocations, most of them just return null.
     Friend NotInheritable Class DefaultOperationProvider
-        Inherits AbstractFormattingRule
+        Inherits CompatAbstractFormattingRule
 
         Public Shared ReadOnly Instance As New DefaultOperationProvider()
 
@@ -31,7 +31,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
         Public Overrides Sub AddAlignTokensOperations(operations As List(Of AlignTokensOperation), node As SyntaxNode, optionSet As OptionSet, nextAction As NextAction(Of AlignTokensOperation))
         End Sub
 
-        Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+        Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
             If previousToken.Parent Is Nothing Then
                 Return Nothing
             End If
@@ -149,7 +149,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
         End Function
 
         ' return 1 space for every token pairs as a default operation
-        Public Overrides Function GetAdjustSpacesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
+        Public Overrides Function GetAdjustSpacesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
             If previousToken.Kind = SyntaxKind.ColonToken AndAlso
                TypeOf previousToken.Parent Is LabelStatementSyntax AndAlso
                currentToken.Kind <> SyntaxKind.EndOfFileToken Then

src/Workspaces/VisualBasic/Portable/Formatting/Rules/AdjustSpaceFormattingRule.vb

@@ -12,7 +12,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
         Public Sub New()
         End Sub
 
-        Public Overrides Function GetAdjustSpacesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextFunc As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
+        Public Overrides Function GetAdjustSpacesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextFunc As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
             ' * <end of file token>
             If currentToken.Kind = SyntaxKind.EndOfFileToken Then
                 Return CreateAdjustSpacesOperation(0, AdjustSpacesOption.ForceSpacesIfOnSingleLine)

src/Workspaces/VisualBasic/Portable/Formatting/Rules/BaseFormattingRule.vb

@@ -5,7 +5,7 @@ Imports Microsoft.CodeAnalysis.Text
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
     Friend Class BaseFormattingRule
-        Inherits AbstractFormattingRule
+        Inherits CompatAbstractFormattingRule
 
         Public Sub New()
         End Sub

src/Workspaces/VisualBasic/Portable/Formatting/Rules/ElasticTriviaFormattingRule.vb

@@ -84,7 +84,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
             End If
         End Sub
 
-        Public Overrides Function GetAdjustSpacesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As Rules.NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
+        Public Overrides Function GetAdjustSpacesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As Rules.NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
             ' if it doesn't have elastic trivia, pass it through
             If Not CommonFormattingHelpers.HasAnyWhitespaceElasticTrivia(previousToken, currentToken) Then
                 Return nextOperation.Invoke()
@@ -120,7 +120,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
             Return operation
         End Function
 
-        Public Overrides Function GetAdjustNewLinesOperation(
+        Public Overrides Function GetAdjustNewLinesOperationSlow(
                 previousToken As SyntaxToken,
                 currentToken As SyntaxToken,
                 optionSet As OptionSet,

src/Workspaces/VisualBasic/Portable/Formatting/Rules/StructuredTriviaFormattingRule.vb

@@ -12,7 +12,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
         Public Sub New()
         End Sub
 
-        Public Overrides Function GetAdjustNewLinesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
+        Public Overrides Function GetAdjustNewLinesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustNewLinesOperation)) As AdjustNewLinesOperation
             If UnderStructuredTrivia(previousToken, currentToken) Then
                 Return Nothing
             End If
@@ -21,7 +21,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Formatting
         End Function
 
 
-        Public Overrides Function GetAdjustSpacesOperation(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
+        Public Overrides Function GetAdjustSpacesOperationSlow(previousToken As SyntaxToken, currentToken As SyntaxToken, optionSet As OptionSet, ByRef nextOperation As NextOperation(Of AdjustSpacesOperation)) As AdjustSpacesOperation
             If UnderStructuredTrivia(previousToken, currentToken) Then
                 If previousToken.Kind = SyntaxKind.HashToken AndAlso SyntaxFacts.IsPreprocessorKeyword(CType(currentToken.Kind, SyntaxKind)) Then
                     Return CreateAdjustSpacesOperation(space:=0, option:=AdjustSpacesOption.ForceSpacesIfOnSingleLine)