existing change signature service tests fixed

src/EditorFeatures/VisualBasicTest/ChangeSignature/ReorderParameters.InvocationErrors.vb

@@ -30,14 +30,14 @@ End Class]]></Text>.NormalizedValue()
         End Function
 
         <WpfFact, Trait(Traits.Feature, Traits.Features.ChangeSignature)>
-        Public Async Function TestReorderMethodParameters_InsufficientParameters_None() As Task
+        Public Async Function TestReorderMethodParameters_NoExistingParameters() As Task
             Dim markup = <Text><![CDATA[
 Class C
     Sub $$M()
     End Sub
 End Class]]></Text>.NormalizedValue()
 
-            Await TestChangeSignatureViaCommandAsync(LanguageNames.VisualBasic, markup, expectedSuccess:=False, expectedErrorText:=FeaturesResources.This_signature_does_not_contain_parameters_that_can_be_changed)
+            Await TestChangeSignatureViaCommandAsync(LanguageNames.VisualBasic, markup, expectedSuccess:=True)
         End Function
 
         <WpfFact, Trait(Traits.Feature, Traits.Features.ChangeSignature)>

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

@@ -448,9 +448,12 @@ private SyntaxNode GetNodeContainingTargetNode(SyntaxNode matchingNode)
             return null;
         }
 
-        private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(SeparatedSyntaxList<ArgumentSyntax> newArguments, SignatureChange signaturePermutation)
+        private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(
+            SeparatedSyntaxList<ArgumentSyntax> newArguments,
+            SignatureChange signaturePermutation)
         {
             List<ArgumentSyntax> fullList = new List<ArgumentSyntax>();
+            List<SyntaxToken> separators = new List<SyntaxToken>();
 
             var updatedParameters = signaturePermutation.UpdatedConfiguration.ToListOfParameters();
 
@@ -468,6 +471,7 @@ private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(SeparatedSynta
                             seenNameEquals ? SyntaxFactory.NameColon(addedParameter.Name) : default,
                             refKindKeyword: default,
                             expression: SyntaxFactory.ParseExpression(addedParameter.CallsiteValue)));
+                        separators.Add(SyntaxFactory.Token(SyntaxKind.CommaToken));
                     }
                 }
                 else
@@ -479,12 +483,28 @@ private SeparatedSyntaxList<ArgumentSyntax> AddNewArgumentsToList(SeparatedSynta
                             seenNameEquals = true;
                         }
 
+                        if (indexInExistingList < newArguments.SeparatorCount)
+                        {
+                            separators.Add(newArguments.GetSeparator(indexInExistingList));
+                        }
+
                         fullList.Add(newArguments[indexInExistingList++]);
                     }
                 }
             }
 
-            return SyntaxFactory.SeparatedList(fullList);
+            // Add the rest of existing parameters, e.g. from the params argument.
+            while (indexInExistingList < newArguments.Count)
+            {
+                if (indexInExistingList < newArguments.SeparatorCount)
+                {
+                    separators.Add(newArguments.GetSeparator(indexInExistingList));
+                }
+
+                fullList.Add(newArguments[indexInExistingList++]);
+            }
+
+            return SyntaxFactory.SeparatedList(fullList, separators);
         }
 
         private SeparatedSyntaxList<T> PermuteDeclaration<T>(SeparatedSyntaxList<T> list, SignatureChange updatedSignature) where T : SyntaxNode

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

@@ -10,6 +10,7 @@ Imports Microsoft.CodeAnalysis.Formatting
 Imports Microsoft.CodeAnalysis.Host.Mef
 Imports Microsoft.CodeAnalysis.PooledObjects
 Imports System.Composition
+Imports Microsoft.CodeAnalysis.Utilities
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.ChangeSignature
     <ExportLanguageService(GetType(AbstractChangeSignatureService), LanguageNames.VisualBasic), [Shared]>
@@ -425,17 +426,20 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ChangeSignature
         End Function
 
         Private Function PermuteDeclaration(Of T As SyntaxNode)(list As SeparatedSyntaxList(Of T), updatedSignature As SignatureChange) As SeparatedSyntaxList(Of T)
-            Dim originalParameters = updatedSignature.OriginalConfiguration.ToListOfParameters()
+            Dim originalParameterSymbols = updatedSignature.OriginalConfiguration.ToListOfParameters().Select(Function(p) p.Symbol).ToArray()
             Dim reorderedParameters = updatedSignature.UpdatedConfiguration.ToListOfParameters()
 
             Dim newParameters = New List(Of T)
             For Each newParam In reorderedParameters
-                Dim pos = originalParameters.IndexOf(newParam)
-                Dim param = list(pos)
-                newParameters.Add(param)
+                Dim existingParam = TryCast(newParam, ExistingParameter)
+                If existingParam IsNot Nothing Then
+                    Dim pos = originalParameterSymbols.IndexOf(existingParam.Symbol)
+                    Dim param = list(pos)
+                    newParameters.Add(param)
+                End If
             Next
 
-            Dim numSeparatorsToSkip = originalParameters.Count - reorderedParameters.Count
+            Dim numSeparatorsToSkip = originalParameterSymbols.Length - reorderedParameters.Count
             Return SyntaxFactory.SeparatedList(newParameters, GetSeparators(list, numSeparatorsToSkip))
         End Function