Kinda working for regular parameter/argument lists

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

@@ -356,7 +356,11 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
                     isReducedExtensionMethod = true;
                 }
 
-                var newArguments = PermuteArgumentList(document, declarationSymbol, invocation.ArgumentList.Arguments, signaturePermutation, isReducedExtensionMethod);
+
+                SignatureChange signaturePermutationWithoutAddedParameters = signaturePermutation.WithoutAddedParameters();
+
+                var newArguments = PermuteArgumentList(document, declarationSymbol, invocation.ArgumentList.Arguments, signaturePermutationWithoutAddedParameters, isReducedExtensionMethod);
+                newArguments = AddNewArgumentsToList(document, declarationSymbol, newArguments, signaturePermutation, isReducedExtensionMethod);
                 return invocation.WithArgumentList(invocation.ArgumentList.WithArguments(newArguments).WithAdditionalAnnotations(changeSignatureFormattingAnnotation));
             }
 
@@ -411,6 +415,39 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
             return null;
         }
 
+        private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(Document document, ISymbol declarationSymbol, SeparatedSyntaxList<ArgumentSyntax> newArguments, SignatureChange signaturePermutation, bool isReducedExtensionMethod)
+        {
+            List<ArgumentSyntax> fullList = new List<ArgumentSyntax>();
+
+            var updatedParameters = signaturePermutation.UpdatedConfiguration.ToListOfParameters();
+
+            int indexInExistingList = 0;
+
+            bool seenNameEquals = false;
+
+            for (int i = 0; i < updatedParameters.Count; i++)
+            {
+                if (updatedParameters[i] is AddedParameter addedParameter)
+                {
+                    fullList.Add(SyntaxFactory.Argument(
+                        seenNameEquals ? SyntaxFactory.NameColon(addedParameter.Name) : default,
+                        refKindKeyword: default,
+                        expression: SyntaxFactory.ParseExpression(addedParameter.CallsiteValue)));
+                }
+                else
+                {
+                    if (newArguments[indexInExistingList].NameColon != default)
+                    {
+                        seenNameEquals = true;
+                    }
+
+                    fullList.Add(newArguments[indexInExistingList++]);
+                }
+            }
+
+            return SyntaxFactory.SeparatedList(fullList);
+        }
+
         private SeparatedSyntaxList<T> PermuteDeclaration<T>(SeparatedSyntaxList<T> list, SignatureChange updatedSignature) where T : SyntaxNode
         {
             var originalParameters = updatedSignature.OriginalConfiguration.ToListOfParameters();
@@ -469,7 +506,7 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
             return newArgument;
         }
 
-        private static SeparatedSyntaxList<AttributeArgumentSyntax> PermuteAttributeArgumentList(
+        private SeparatedSyntaxList<AttributeArgumentSyntax> PermuteAttributeArgumentList(
             Document document,
             ISymbol declarationSymbol,
             SeparatedSyntaxList<AttributeArgumentSyntax> arguments,
@@ -485,7 +522,7 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
             return SyntaxFactory.SeparatedList(newArgumentsWithTrivia, GetSeparators(arguments, numSeparatorsToSkip));
         }
 
-        private static SeparatedSyntaxList<ArgumentSyntax> PermuteArgumentList(
+        private SeparatedSyntaxList<ArgumentSyntax> PermuteArgumentList(
             Document document,
             ISymbol declarationSymbol,
             SeparatedSyntaxList<ArgumentSyntax> arguments,
@@ -705,5 +742,10 @@ protected override IEnumerable<AbstractFormattingRule> GetFormattingRules(Docume
         {
             return SpecializedCollections.SingletonEnumerable(new ChangeSignatureFormattingRule()).Concat(Formatter.GetDefaultFormattingRules(document));
         }
+
+        protected override IUnifiedArgumentSyntax CreateRegularArgumentSyntax(string callsiteValue)
+        {
+            return UnifiedArgumentSyntax.Create(SyntaxFactory.Argument(SyntaxFactory.ParseExpression(callsiteValue)));
+        }
     }
 }

src/Features/Core/Portable/ChangeSignature/AbstractChangeSignatureService.cs

@@ -46,6 +46,8 @@ internal abstract class AbstractChangeSignatureService : ILanguageService
             SignatureChange signaturePermutation,
             CancellationToken cancellationToken);
 
+        protected abstract IUnifiedArgumentSyntax CreateRegularArgumentSyntax(string callsiteValue);
+
         protected abstract IEnumerable<AbstractFormattingRule> GetFormattingRules(Document document);
 
         public async Task<ImmutableArray<ChangeSignatureCodeAction>> GetChangeSignatureCodeActionAsync(Document document, TextSpan span, CancellationToken cancellationToken)
@@ -394,7 +396,7 @@ private bool TryGetNodeWithEditableSignatureOrAttributes(Location location, Solu
             return nodeToUpdate != null;
         }
 
-        protected static List<IUnifiedArgumentSyntax> PermuteArguments(
+        protected List<IUnifiedArgumentSyntax> PermuteArguments(
             Document document,
             ISymbol declarationSymbol,
             List<IUnifiedArgumentSyntax> arguments,
@@ -476,13 +478,13 @@ private bool TryGetNodeWithEditableSignatureOrAttributes(Location location, Solu
                 }
             }
 
-            // 6. TODO MOVE AROUND. Add added arguments
+            // 6. TODO MOVE AROUND. Add added arguments (only at end for the moment)
 
             var brandNewParameters = updatedSignature.UpdatedConfiguration.ToListOfParameters().Where(p => p is AddedParameter).Cast<AddedParameter>();
 
             foreach (var brandNewParameter in brandNewParameters)
             {
-                // newArguments.Add(new IUnifiedArgumentSyntax());
+                newArguments.Add(CreateRegularArgumentSyntax(brandNewParameter.CallsiteValue));
             }
 
             return newArguments;

src/Features/Core/Portable/ChangeSignature/ParameterConfiguration.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.Linq;
 
 namespace Microsoft.CodeAnalysis.ChangeSignature
 {
@@ -54,6 +56,11 @@ public static ParameterConfiguration Create(List<CoolParameter> parameters, bool
             return new ParameterConfiguration(thisParameter, parametersWithoutDefaultValues, remainingReorderableParameters, paramsParameter, selectedIndex);
         }
 
+        internal ParameterConfiguration WithoutAddedParameters()
+        {
+            return Create(ToListOfParameters().OfType<ExistingParameter>().ToList<CoolParameter>(), ThisParameter != null, selectedIndex: 0);
+        }
+
         public List<CoolParameter> ToListOfParameters()
         {
             var list = new List<CoolParameter>();

src/Features/Core/Portable/ChangeSignature/SignatureChange.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.Linq;
 using Microsoft.CodeAnalysis.Shared.Extensions;
@@ -39,5 +40,10 @@ public SignatureChange(ParameterConfiguration originalConfiguration, ParameterCo
 
             return _originalIndexToUpdatedIndexMap[parameterIndex];
         }
+
+        internal SignatureChange WithoutAddedParameters()
+        {
+            return new SignatureChange(OriginalConfiguration, UpdatedConfiguration.WithoutAddedParameters());
+        }
     }
 }

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

@@ -607,5 +607,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ChangeSignature
             Return SpecializedCollections.SingletonEnumerable(Of AbstractFormattingRule)(New ChangeSignatureFormattingRule()).
                 Concat(Formatter.GetDefaultFormattingRules(document))
         End Function
+
+        Protected Overrides Function CreateRegularArgumentSyntax(callsiteValue As String) As IUnifiedArgumentSyntax
+            Return UnifiedArgumentSyntax.Create(SyntaxFactory.SimpleArgument(SyntaxFactory.ParseExpression(callsiteValue)))
+        End Function
     End Class
 End Namespace