Merge pull request #16516 from CyrusNajmabadi/generateMethodRefReturns

Add support for generating methods that return-by-ref.
Fixes #16398

src/EditorFeatures/CSharp/EventHookup/EventHookupCommandHandler_TabKeyCommand.cs

@@ -277,6 +277,7 @@ private void GenerateAndAddEventHandler(ITextView textView, ITextBuffer subjectB
                 accessibility: Accessibility.Private,
                 modifiers: new DeclarationModifiers(isStatic: eventHookupExpression.IsInStaticContext()),
                 returnType: delegateType.DelegateInvokeMethod.ReturnType,
+                returnsByRef: delegateType.DelegateInvokeMethod.ReturnsByRef,
                 explicitInterfaceSymbol: null,
                 name: eventHandlerMethodName,
                 typeParameters: null,

src/EditorFeatures/CSharpTest/Diagnostics/GenerateMethod/GenerateMethodTests.cs

@@ -7358,6 +7358,37 @@ private object Issue(int i)
     {
         throw new NotImplementedException();
     }
+}");
+        }
+
+        [WorkItem(16398, "https://github.com/dotnet/roslyn/issues/16398")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsGenerateMethod)]
+        public async Task TestReturnsByRef()
+        {
+            await TestAsync(
+@"
+using System;
+
+class C 
+{
+    public void Foo()
+    {
+        ref int i = ref [|Bar|]();
+    }
+}",
+@"using System;
+
+class C 
+{
+    public void Foo()
+    {
+        ref int i = ref Bar();
+    }
+
+    private ref int Bar()
+    {
+        throw new NotImplementedException();
+    }
 }");
         }
     }

src/EditorFeatures/CSharpTest/ImplementInterface/ImplementInterfaceTests.cs

@@ -6815,6 +6815,44 @@ class Class : IComInterface
     public void X() { throw new NotImplementedException(); }
     public void MOverload(int i) { throw new NotImplementedException(); }
     public int Prop => throw new NotImplementedException();
+}");
+        }
+
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsImplementInterface)]
+        public async Task TestRefReturns()
+        {
+            await TestAsync(
+@"
+using System;
+
+interface I {
+    ref int IFoo();
+    ref int Foo { get; }
+    ref int this[int i] { get; }
+}
+
+class C : [|I|]
+{
+}",
+@"
+using System;
+
+interface I {
+    ref int IFoo();
+    ref int Foo { get; }
+    ref int this[int i] { get; }
+}
+
+class C : I
+{
+    public ref int this[int i] => throw new NotImplementedException();
+
+    public ref int Foo => throw new NotImplementedException();
+
+    public ref int IFoo()
+    {
+        throw new NotImplementedException();
+    }
 }");
         }
     }

src/EditorFeatures/Test/CodeGeneration/CodeGenerationTests.cs

@@ -138,6 +138,7 @@ public partial class CodeGenerationTests
                     accessibility,
                     modifiers,
                     GetTypeSymbol(returnType)(context.SemanticModel),
+                    false,
                     explicitInterfaceSymbol,
                     name,
                     typeParameters,
@@ -317,6 +318,7 @@ public partial class CodeGenerationTests
                     accessibility,
                     modifiers,
                     GetTypeSymbol(returnType)(context.SemanticModel),
+                    false,
                     name,
                     typeParameters,
                     parameterSymbols);
@@ -406,6 +408,7 @@ public partial class CodeGenerationTests
                     defaultAccessibility,
                     new DeclarationModifiers(isAbstract: getStatements == null),
                     typeSymbol,
+                    false,
                     null,
                     "get_" + name,
                     null,
@@ -416,6 +419,7 @@ public partial class CodeGenerationTests
                     setterAccessibility,
                     new DeclarationModifiers(isAbstract: setStatements == null),
                     GetTypeSymbol(typeof(void))(context.SemanticModel),
+                    false,
                     null,
                     "set_" + name,
                     null,
@@ -439,6 +443,7 @@ public partial class CodeGenerationTests
                     defaultAccessibility,
                     modifiers,
                     typeSymbol,
+                    false,
                     explicitInterfaceSymbol,
                     name,
                     getParameterSymbols,

src/EditorFeatures/VisualBasic/NavigationBar/GenerateEventHandlerItem.vb

@@ -55,6 +55,7 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.NavigationBar
                 accessibility:=Accessibility.Private,
                 modifiers:=New DeclarationModifiers(),
                 returnType:=delegateInvokeMethod.ReturnType,
+                returnsByRef:=delegateInvokeMethod.ReturnsByRef,
                 explicitInterfaceSymbol:=Nothing,
                 name:=methodName,
                 typeParameters:=Nothing,

src/EditorFeatures/VisualBasic/NavigationBar/GenerateFinalizerItem.vb

@@ -44,6 +44,7 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.NavigationBar
                 accessibility:=Accessibility.Protected,
                 modifiers:=New DeclarationModifiers(isOverride:=True),
                 returnType:=compilation.GetSpecialType(SpecialType.System_Void),
+                returnsByRef:=False,
                 explicitInterfaceSymbol:=Nothing,
                 name:=WellKnownMemberNames.DestructorName,
                 typeParameters:=Nothing,

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

@@ -93,6 +93,7 @@ protected override OperationStatus<IMethodSymbol> GenerateMethodDefinition(Cance
                     accessibility: Accessibility.Private,
                     modifiers: CreateMethodModifiers(),
                     returnType: this.AnalyzerResult.ReturnType,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: _methodName.ToString(),
                     typeParameters: CreateMethodTypeParameters(cancellationToken),

src/Features/CSharp/Portable/GenerateMember/GenerateConstructor/CSharpGenerateConstructorService.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.Generic;
+using System.Collections.Immutable;
 using System.Composition;
 using System.Linq;
 using System.Threading;
@@ -36,14 +37,14 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
 
         protected override bool TryInitializeConstructorInitializerGeneration(
             SemanticDocument document, SyntaxNode node, CancellationToken cancellationToken,
-            out SyntaxToken token, out IList<ArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn)
+            out SyntaxToken token, out ImmutableArray<ArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn)
         {
             var constructorInitializer = (ConstructorInitializerSyntax)node;
 
             if (!constructorInitializer.ArgumentList.CloseParenToken.IsMissing)
             {
                 token = constructorInitializer.ThisOrBaseKeyword;
-                arguments = constructorInitializer.ArgumentList.Arguments.ToList();
+                arguments = constructorInitializer.ArgumentList.Arguments.ToImmutableArray();
 
                 var semanticModel = document.SemanticModel;
                 var currentType = semanticModel.GetEnclosingNamedType(constructorInitializer.SpanStart, cancellationToken);
@@ -54,7 +55,7 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
             }
 
             token = default(SyntaxToken);
-            arguments = null;
+            arguments = default(ImmutableArray<ArgumentSyntax>);
             typeToGenerateIn = null;
             return false;
         }
@@ -93,7 +94,7 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
             SyntaxNode node,
             CancellationToken cancellationToken,
             out SyntaxToken token,
-            out IList<ArgumentSyntax> arguments,
+            out ImmutableArray<ArgumentSyntax> arguments,
             out INamedTypeSymbol typeToGenerateIn)
         {
             var simpleName = (SimpleNameSyntax)node;
@@ -109,14 +110,14 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
                 {
                     var symbolInfo = document.SemanticModel.GetSymbolInfo(objectCreationExpression.Type, cancellationToken);
                     token = simpleName.Identifier;
-                    arguments = objectCreationExpression.ArgumentList.Arguments.ToList();
+                    arguments = objectCreationExpression.ArgumentList.Arguments.ToImmutableArray();
                     typeToGenerateIn = symbolInfo.GetAnySymbol() as INamedTypeSymbol;
                     return typeToGenerateIn != null;
                 }
             }
 
             token = default(SyntaxToken);
-            arguments = null;
+            arguments = default(ImmutableArray<ArgumentSyntax>);
             typeToGenerateIn = null;
             return false;
         }
@@ -126,8 +127,8 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
             SyntaxNode node,
             CancellationToken cancellationToken,
             out SyntaxToken token,
-            out IList<ArgumentSyntax> arguments,
-            out IList<AttributeArgumentSyntax> attributeArguments,
+            out ImmutableArray<ArgumentSyntax> arguments,
+            out ImmutableArray<AttributeArgumentSyntax> attributeArguments,
             out INamedTypeSymbol typeToGenerateIn)
         {
             var simpleName = (SimpleNameSyntax)node;
@@ -145,8 +146,11 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
                     if (symbolInfo.CandidateReason == CandidateReason.OverloadResolutionFailure && !symbolInfo.CandidateSymbols.IsEmpty)
                     {
                         token = simpleName.Identifier;
-                        attributeArguments = attribute.ArgumentList.Arguments.ToList();
-                        arguments = attributeArguments.Select(x => SyntaxFactory.Argument(x.NameColon ?? ((x.NameEquals != null) ? SyntaxFactory.NameColon(x.NameEquals.Name) : null), default(SyntaxToken), x.Expression)).ToList();
+                        attributeArguments = attribute.ArgumentList.Arguments.ToImmutableArray();
+                        arguments = attributeArguments.Select(
+                            x => SyntaxFactory.Argument(
+                                x.NameColon ?? (x.NameEquals != null ? SyntaxFactory.NameColon(x.NameEquals.Name) : null),
+                                default(SyntaxToken), x.Expression)).ToImmutableArray();
 
                         typeToGenerateIn = symbolInfo.CandidateSymbols.FirstOrDefault().ContainingSymbol as INamedTypeSymbol;
                         return typeToGenerateIn != null;
@@ -155,23 +159,19 @@ protected override bool IsClassDeclarationGeneration(SemanticDocument document,
             }
 
             token = default(SyntaxToken);
-            arguments = null;
-            attributeArguments = null;
+            arguments = default(ImmutableArray<ArgumentSyntax>);
+            attributeArguments = default(ImmutableArray<AttributeArgumentSyntax>);
             typeToGenerateIn = null;
             return false;
         }
 
-        protected override IList<ParameterName> GenerateParameterNames(
+        protected override ImmutableArray<ParameterName> GenerateParameterNames(
             SemanticModel semanticModel, IEnumerable<ArgumentSyntax> arguments, IList<string> reservedNames)
-        {
-            return semanticModel.GenerateParameterNames(arguments, reservedNames);
-        }
+            => semanticModel.GenerateParameterNames(arguments, reservedNames);
 
-        protected override IList<ParameterName> GenerateParameterNames(
+        protected override ImmutableArray<ParameterName> GenerateParameterNames(
             SemanticModel semanticModel, IEnumerable<AttributeArgumentSyntax> arguments, IList<string> reservedNames)
-        {
-            return semanticModel.GenerateParameterNames(arguments, reservedNames);
-        }
+            => semanticModel.GenerateParameterNames(arguments, reservedNames).ToImmutableArray();
 
         protected override string GenerateNameForArgument(
             SemanticModel semanticModel, ArgumentSyntax argument)

src/Features/CSharp/Portable/GenerateMember/GenerateParameterizedMember/CSharpGenerateConversionService.cs

@@ -38,7 +38,8 @@ protected override bool ContainingTypesOrSelfHasUnsafeKeyword(INamedTypeSymbol c
             return containingType.ContainingTypesOrSelfHasUnsafeKeyword();
         }
 
-        protected override AbstractInvocationInfo CreateInvocationMethodInfo(SemanticDocument document, AbstractGenerateParameterizedMemberService<CSharpGenerateConversionService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax>.State state)
+        protected override AbstractInvocationInfo CreateInvocationMethodInfo(
+            SemanticDocument document, AbstractGenerateParameterizedMemberService<CSharpGenerateConversionService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax>.State state)
         {
             return new CSharpGenerateParameterizedMemberService<CSharpGenerateConversionService>.InvocationExpressionInfo(document, state);
         }
@@ -196,7 +197,8 @@ protected override bool IsValidSymbol(ISymbol symbol, SemanticModel semanticMode
             return true;
         }
 
-        private static IMethodSymbol GenerateMethodSymbol(INamedTypeSymbol typeToGenerateIn, INamedTypeSymbol parameterSymbol)
+        private static IMethodSymbol GenerateMethodSymbol(
+            INamedTypeSymbol typeToGenerateIn, INamedTypeSymbol parameterSymbol)
         {
             // Remove any generic parameters
             if (typeToGenerateIn.IsGenericType)
@@ -205,15 +207,16 @@ private static IMethodSymbol GenerateMethodSymbol(INamedTypeSymbol typeToGenerat
             }
 
             return CodeGenerationSymbolFactory.CreateMethodSymbol(
-                            attributes: SpecializedCollections.EmptyList<AttributeData>(),
-                            accessibility: default(Accessibility),
-                            modifiers: default(DeclarationModifiers),
-                            returnType: typeToGenerateIn,
-                            explicitInterfaceSymbol: null,
-                            name: null,
-                            typeParameters: SpecializedCollections.EmptyList<ITypeParameterSymbol>(),
-                            parameters: new[] { CodeGenerationSymbolFactory.CreateParameterSymbol(parameterSymbol, "v") },
-                            methodKind: MethodKind.Conversion);
+                attributes: SpecializedCollections.EmptyList<AttributeData>(),
+                accessibility: default(Accessibility),
+                modifiers: default(DeclarationModifiers),
+                returnType: typeToGenerateIn,
+                returnsByRef: false,
+                explicitInterfaceSymbol: null,
+                name: null,
+                typeParameters: SpecializedCollections.EmptyList<ITypeParameterSymbol>(),
+                parameters: new[] { CodeGenerationSymbolFactory.CreateParameterSymbol(parameterSymbol, "v") },
+                methodKind: MethodKind.Conversion);
         }
 
         protected override string GetImplicitConversionDisplayText(AbstractGenerateParameterizedMemberService<CSharpGenerateConversionService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax>.State state)

src/Features/CSharp/Portable/GenerateMember/GenerateParameterizedMember/CSharpGenerateMethodService.cs

@@ -21,19 +21,13 @@ internal partial class CSharpGenerateMethodService :
         AbstractGenerateMethodService<CSharpGenerateMethodService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax>
     {
         protected override bool IsExplicitInterfaceGeneration(SyntaxNode node)
-        {
-            return node is MethodDeclarationSyntax;
-        }
+            => node is MethodDeclarationSyntax;
 
         protected override bool IsSimpleNameGeneration(SyntaxNode node)
-        {
-            return node is SimpleNameSyntax;
-        }
+            => node is SimpleNameSyntax;
 
         protected override bool ContainingTypesOrSelfHasUnsafeKeyword(INamedTypeSymbol containingType)
-        {
-            return containingType.ContainingTypesOrSelfHasUnsafeKeyword();
-        }
+            => containingType.ContainingTypesOrSelfHasUnsafeKeyword();
 
         protected override AbstractInvocationInfo CreateInvocationMethodInfo(SemanticDocument document, AbstractGenerateParameterizedMemberService<CSharpGenerateMethodService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax>.State state)
         {
@@ -41,14 +35,10 @@ protected override AbstractInvocationInfo CreateInvocationMethodInfo(SemanticDoc
         }
 
         protected override bool AreSpecialOptionsActive(SemanticModel semanticModel)
-        {
-            return CSharpCommonGenerationServiceMethods.AreSpecialOptionsActive(semanticModel);
-        }
+            => CSharpCommonGenerationServiceMethods.AreSpecialOptionsActive(semanticModel);
 
         protected override bool IsValidSymbol(ISymbol symbol, SemanticModel semanticModel)
-        {
-            return CSharpCommonGenerationServiceMethods.IsValidSymbol(symbol, semanticModel);
-        }
+            => CSharpCommonGenerationServiceMethods.IsValidSymbol(symbol, semanticModel);
 
         protected override bool TryInitializeExplicitInterfaceState(
             SemanticDocument document,
@@ -154,7 +144,7 @@ protected override bool IsValidSymbol(ISymbol symbol, SemanticModel semanticMode
             return false;
         }
 
-        protected override ITypeSymbol CanGenerateMethodForSimpleNameOrMemberAccessExpression(
+        protected override ITypeSymbol DetermineReturnTypeForSimpleNameOrMemberAccessExpression(
             ITypeInferenceService typeInferenceService,
             SemanticModel semanticModel,
             ExpressionSyntax expression,

src/Features/CSharp/Portable/GenerateMember/GenerateParameterizedMember/CSharpGenerateParameterizedMemberService.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis;
@@ -30,24 +31,27 @@ public InvocationExpressionInfo(SemanticDocument document, State state)
                 _invocationExpression = state.InvocationExpressionOpt;
             }
 
-            protected override IList<ParameterName> DetermineParameterNames(CancellationToken cancellationToken)
+            protected override ImmutableArray<ParameterName> DetermineParameterNames(CancellationToken cancellationToken)
             {
                 return this.Document.SemanticModel.GenerateParameterNames(
                     _invocationExpression.ArgumentList);
             }
 
+            protected override bool DetermineReturnsByRef(CancellationToken cancellationToken)
+                => _invocationExpression.IsParentKind(SyntaxKind.RefExpression);
+
             protected override ITypeSymbol DetermineReturnTypeWorker(CancellationToken cancellationToken)
             {
                 // Defer to the type inferrer to figure out what the return type of this new method
                 // should be.
-                var typeInference = this.Document.Project.LanguageServices.GetService<ITypeInferenceService>();
+                var typeInference = this.Document.Document.GetLanguageService<ITypeInferenceService>();
                 var inferredType = typeInference.InferType(
-                    this.Document.SemanticModel, _invocationExpression, objectAsDefault: true, 
+                    this.Document.SemanticModel, _invocationExpression, objectAsDefault: true,
                     nameOpt: this.State.IdentifierToken.ValueText, cancellationToken: cancellationToken);
                 return inferredType;
             }
 
-            protected override IList<ITypeParameterSymbol> GetCapturedTypeParameters(CancellationToken cancellationToken)
+            protected override ImmutableArray<ITypeParameterSymbol> GetCapturedTypeParameters(CancellationToken cancellationToken)
             {
                 var result = new List<ITypeParameterSymbol>();
                 var semanticModel = this.Document.SemanticModel;
@@ -57,10 +61,10 @@ protected override IList<ITypeParameterSymbol> GetCapturedTypeParameters(Cancell
                     type.GetReferencedTypeParameters(result);
                 }
 
-                return result;
+                return result.ToImmutableArray();
             }
 
-            protected override IList<ITypeParameterSymbol> GenerateTypeParameters(CancellationToken cancellationToken)
+            protected override ImmutableArray<ITypeParameterSymbol> GenerateTypeParameters(CancellationToken cancellationToken)
             {
                 // Generate dummy type parameter names for a generic method.  If the user is inside a
                 // generic method, and calls a generic method with type arguments from the outer
@@ -78,11 +82,11 @@ protected override IList<ITypeParameterSymbol> GenerateTypeParameters(Cancellati
                         s => !State.TypeToGenerateIn.GetAllTypeParameters().Any(t => t.Name == s),
                         cancellationToken);
 
-                    return new List<ITypeParameterSymbol> { typeParameter };
+                    return ImmutableArray.Create(typeParameter);
                 }
                 else
                 {
-                    var list = new List<ITypeParameterSymbol>();
+                    var list = ArrayBuilder<ITypeParameterSymbol>.GetInstance();
 
                     var usedIdentifiers = new HashSet<string> { "T" };
                     foreach (var type in genericName.TypeArgumentList.Arguments)
@@ -97,7 +101,7 @@ protected override IList<ITypeParameterSymbol> GenerateTypeParameters(Cancellati
                         list.Add(typeParameter);
                     }
 
-                    return list;
+                    return list.ToImmutableAndFree();
                 }
             }
 
@@ -127,18 +131,16 @@ private ITypeParameterSymbol GetMethodTypeParameter(TypeSyntax type, Cancellatio
                 return null;
             }
 
-            protected override IList<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken)
+            protected override ImmutableArray<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken)
             {
                 return
                     _invocationExpression.ArgumentList.Arguments.Select(
                         a => a.RefOrOutKeyword.Kind() == SyntaxKind.RefKeyword ? RefKind.Ref :
-                             a.RefOrOutKeyword.Kind() == SyntaxKind.OutKeyword ? RefKind.Out : RefKind.None).ToList();
+                             a.RefOrOutKeyword.Kind() == SyntaxKind.OutKeyword ? RefKind.Out : RefKind.None).ToImmutableArray();
             }
 
-            protected override IList<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken)
-            {
-                return _invocationExpression.ArgumentList.Arguments.Select(a => DetermineParameterType(a, cancellationToken)).ToList();
-            }
+            protected override ImmutableArray<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken)
+                => _invocationExpression.ArgumentList.Arguments.Select(a => DetermineParameterType(a, cancellationToken)).ToImmutableArray();
 
             private ITypeSymbol DetermineParameterType(
                 ArgumentSyntax argument,
@@ -147,10 +149,8 @@ protected override IList<ITypeSymbol> DetermineParameterTypes(CancellationToken
                 return argument.DetermineParameterType(this.Document.SemanticModel, cancellationToken);
             }
 
-            protected override IList<bool> DetermineParameterOptionality(CancellationToken cancellationToken)
-            {
-                return _invocationExpression.ArgumentList.Arguments.Select(a => false).ToList();
-            }
+            protected override ImmutableArray<bool> DetermineParameterOptionality(CancellationToken cancellationToken)
+                => _invocationExpression.ArgumentList.Arguments.Select(a => false).ToImmutableArray();
 
             protected override bool IsIdentifierName()
             {
@@ -163,9 +163,9 @@ protected override bool IsImplicitReferenceConversion(Compilation compilation, I
                 return conversion.IsImplicit && conversion.IsReference;
             }
 
-            protected override IList<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken)
+            protected override ImmutableArray<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken)
             {
-                var result = new List<ITypeSymbol>();
+                var result = ArrayBuilder<ITypeSymbol>.GetInstance();
 
                 if (State.SimpleNameOpt is GenericNameSyntax)
                 {
@@ -176,8 +176,8 @@ protected override IList<ITypeSymbol> DetermineTypeArguments(CancellationToken c
                     }
                 }
 
-                return result;
+                return result.ToImmutableAndFree();
             }
         }
     }
-}
+}
\ No newline at end of file

src/Features/CSharp/Portable/GenerateType/CSharpGenerateTypeService.cs

@@ -893,6 +893,7 @@ internal override async Task<Solution> TryAddUsingsOrImportToDocumentAsync(Solut
                 explicitInterfaceSymbol: null,
                 name: propertyName.Identifier.ValueText,
                 type: propertyType,
+                returnsByRef: false,
                 parameters: null,
                 getMethod: s_accessor,
                 setMethod: s_accessor,

src/Features/Core/Portable/Completion/Providers/AbstractPartialMethodCompletionProvider.cs

@@ -61,14 +61,16 @@ protected override async Task<ISymbol> GenerateMemberAsync(ISymbol member, IName
             var syntaxFactory = document.GetLanguageService<SyntaxGenerator>();
             var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
+            var method = (IMethodSymbol)member;
             return CodeGenerationSymbolFactory.CreateMethodSymbol(attributes: new List<AttributeData>(),
                 accessibility: Accessibility.NotApplicable,
                 modifiers: MemberInsertionCompletionItem.GetModifiers(item),
                 returnType: semanticModel.Compilation.GetSpecialType(SpecialType.System_Void),
+                returnsByRef: method.ReturnsByRef,
                 explicitInterfaceSymbol: null,
                 name: member.Name,
-                typeParameters: ((IMethodSymbol)member).TypeParameters,
-                parameters: member.GetParameters().Select(p => CodeGenerationSymbolFactory.CreateParameterSymbol(p.GetAttributes(), p.RefKind, p.IsParams, p.Type, p.Name)).ToList(),
+                typeParameters: method.TypeParameters,
+                parameters: method.Parameters.Select(p => CodeGenerationSymbolFactory.CreateParameterSymbol(p.GetAttributes(), p.RefKind, p.IsParams, p.Type, p.Name)).ToList(),
                 statements: syntaxFactory.CreateThrowNotImplementedStatementBlock(semanticModel.Compilation));
         }
 

src/Features/Core/Portable/EncapsulateField/AbstractEncapsulateFieldService.cs

@@ -306,6 +306,7 @@ protected async Task<Solution> AddPropertyAsync(Document document, Solution dest
                 accessibility: ComputeAccessibility(accessibility, field.Type),
                 modifiers: new DeclarationModifiers(isStatic: field.IsStatic, isReadOnly: field.IsReadOnly, isUnsafe: field.IsUnsafe()),
                 type: field.Type,
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: propertyName,
                 parameters: SpecializedCollections.EmptyList<IParameterSymbol>(),

src/Features/Core/Portable/ExtractInterface/AbstractExtractInterfaceService.cs

@@ -347,6 +347,7 @@ private IList<ISymbol> CreateInterfaceMembers(IEnumerable<ISymbol> includedMembe
                             accessibility: Accessibility.Public,
                             modifiers: new DeclarationModifiers(isAbstract: true, isUnsafe: method.IsUnsafe()),
                             returnType: method.ReturnType,
+                            returnsByRef: method.ReturnsByRef,
                             explicitInterfaceSymbol: null,
                             name: method.Name,
                             typeParameters: method.TypeParameters,
@@ -359,6 +360,7 @@ private IList<ISymbol> CreateInterfaceMembers(IEnumerable<ISymbol> includedMembe
                             accessibility: Accessibility.Public,
                             modifiers: new DeclarationModifiers(isAbstract: true, isUnsafe: property.IsUnsafe()),
                             type: property.Type,
+                            returnsByRef: property.ReturnsByRef,
                             explicitInterfaceSymbol: null,
                             name: property.Name,
                             parameters: property.Parameters,

src/Features/Core/Portable/GenerateMember/GenerateConstructor/AbstractGenerateConstructorService.Editor.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -71,7 +72,7 @@ private async Task<Document> GenerateThisOrBaseDelegatingConstructorAsync()
             {
                 // We don't have to deal with the zero length case, since there's nothing to
                 // delegate.  It will fall out of the GenerateFieldDelegatingConstructor above.
-                for (int i = _state.Arguments.Count; i >= 1; i--)
+                for (int i = _state.Arguments.Length; i >= 1; i--)
                 {
                     var edit = await GenerateThisOrBaseDelegatingConstructorAsync(i).ConfigureAwait(false);
                     if (edit != null)
@@ -156,9 +157,11 @@ private async Task<Document> GenerateDelegatedConstructorAsync()
                 }
 
                 var arguments = _state.Arguments.Take(argumentCount).ToList();
-                var remainingArguments = _state.Arguments.Skip(argumentCount).ToList();
-                var remainingAttributeArguments = _state.AttributeArguments != null ? _state.AttributeArguments.Skip(argumentCount).ToList() : null;
-                var remainingParameterTypes = _state.ParameterTypes.Skip(argumentCount).ToList();
+                var remainingArguments = _state.Arguments.Skip(argumentCount).ToImmutableArray();
+                var remainingAttributeArguments = _state.AttributeArguments != null 
+                    ? _state.AttributeArguments.Skip(argumentCount).ToImmutableArray() 
+                    : (ImmutableArray<TAttributeArgumentSyntax>?)null;
+                var remainingParameterTypes = _state.ParameterTypes.Skip(argumentCount).ToImmutableArray();
 
                 var instanceConstructors = namedType.InstanceConstructors.Where(IsSymbolAccessible).ToSet();
                 if (instanceConstructors.IsEmpty())
@@ -233,10 +236,10 @@ private async Task<Document> GenerateDelegatedConstructorAsync()
 
             private async Task<Document> GenerateFieldDelegatingConstructorAsync()
             {
-                var arguments = _state.Arguments.ToList();
+                var arguments = _state.Arguments;
                 var parameterTypes = _state.ParameterTypes;
 
-                var typeParametersNames = _state.TypeToGenerateIn.GetAllTypeParameters().Select(t => t.Name).ToList();
+                var typeParametersNames = _state.TypeToGenerateIn.GetAllTypeParameters().Select(t => t.Name).ToImmutableArray();
                 var parameterNames = GetParameterNames(arguments, typeParametersNames);
                 GetParameters(arguments, _state.AttributeArguments, parameterTypes, parameterNames,
                     out var parameterToExistingFieldMap, out var parameterToNewFieldMap, out var parameters);
@@ -261,8 +264,8 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
                 return result;
             }
 
-            private IList<ParameterName> GetParameterNames(
-                List<TArgumentSyntax> arguments, List<string> typeParametersNames)
+            private ImmutableArray<ParameterName> GetParameterNames(
+                ImmutableArray<TArgumentSyntax> arguments, ImmutableArray<string> typeParametersNames)
             {
                 return _state.AttributeArguments != null
                     ? _service.GenerateParameterNames(_document.SemanticModel, _state.AttributeArguments, typeParametersNames)
@@ -270,10 +273,10 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
             }
 
             private void GetParameters(
-                IList<TArgumentSyntax> arguments,
-                IList<TAttributeArgumentSyntax> attributeArguments,
-                IList<ITypeSymbol> parameterTypes,
-                IList<ParameterName> parameterNames,
+                ImmutableArray<TArgumentSyntax> arguments,
+                ImmutableArray<TAttributeArgumentSyntax>? attributeArguments,
+                ImmutableArray<ITypeSymbol> parameterTypes,
+                ImmutableArray<ParameterName> parameterNames,
                 out Dictionary<string, ISymbol> parameterToExistingFieldMap,
                 out Dictionary<string, string> parameterToNewFieldMap,
                 out List<IParameterSymbol> parameters)
@@ -282,13 +285,16 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
                 parameterToNewFieldMap = new Dictionary<string, string>();
                 parameters = new List<IParameterSymbol>();
 
-                for (var i = 0; i < parameterNames.Count; i++)
+                for (var i = 0; i < parameterNames.Length; i++)
                 {
                     // See if there's a matching field we can use.  First test in a case sensitive
                     // manner, then case insensitively.
-                    if (!TryFindMatchingField(arguments, attributeArguments, parameterNames, parameterTypes, i, parameterToExistingFieldMap, parameterToNewFieldMap, caseSensitive: true))
+                    if (!TryFindMatchingField(
+                            arguments, attributeArguments, parameterNames, parameterTypes, i, parameterToExistingFieldMap, 
+                            parameterToNewFieldMap, caseSensitive: true, newParameterNames: out parameterNames))
                     {
-                        if (!TryFindMatchingField(arguments, attributeArguments, parameterNames, parameterTypes, i, parameterToExistingFieldMap, parameterToNewFieldMap, caseSensitive: false))
+                        if (!TryFindMatchingField(arguments, attributeArguments, parameterNames, parameterTypes, i, parameterToExistingFieldMap, 
+                                parameterToNewFieldMap, caseSensitive: false, newParameterNames: out parameterNames))
                         {
                             parameterToNewFieldMap[parameterNames[i].BestNameForParameter] = 
                                 parameterNames[i].NameBasedOnArgument;
@@ -305,18 +311,20 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
             }
 
             private bool TryFindMatchingField(
-                IList<TArgumentSyntax> arguments,
-                IList<TAttributeArgumentSyntax> attributeArguments,
-                IList<ParameterName> parameterNames,
-                IList<ITypeSymbol> parameterTypes,
+                ImmutableArray<TArgumentSyntax> arguments,
+                ImmutableArray<TAttributeArgumentSyntax>? attributeArguments,
+                ImmutableArray<ParameterName> parameterNames,
+                ImmutableArray<ITypeSymbol> parameterTypes,
                 int index,
                 Dictionary<string, ISymbol> parameterToExistingFieldMap,
                 Dictionary<string, string> parameterToNewFieldMap,
-                bool caseSensitive)
+                bool caseSensitive,
+                out ImmutableArray<ParameterName> newParameterNames)
             {
                 var parameterName = parameterNames[index];
                 var parameterType = parameterTypes[index];
                 var isFixed = _service.IsNamedArgument(arguments[index]);
+                var newParameterNamesList = parameterNames.ToList();
 
                 // For non-out parameters, see if there's already a field there with the same name.
                 // If so, and it has a compatible type, then we can just assign to that field.
@@ -346,9 +354,9 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
                                 // this field.  So we need to create a new field.  Find a name not in
                                 // use so we can assign to that.  
                                 var newFieldName = NameGenerator.EnsureUniqueness(
-                                    attributeArguments != null ?
-                                    _service.GenerateNameForArgument(_document.SemanticModel, attributeArguments[index]) :
-                                    _service.GenerateNameForArgument(_document.SemanticModel, arguments[index]),
+                                    attributeArguments != null
+                                        ? _service.GenerateNameForArgument(_document.SemanticModel, attributeArguments.Value[index])
+                                        : _service.GenerateNameForArgument(_document.SemanticModel, arguments[index]),
                                     GetUnavailableMemberNames().Concat(parameterToNewFieldMap.Values));
 
                                 if (isFixed)
@@ -361,16 +369,18 @@ private async Task<Document> GenerateFieldDelegatingConstructorAsync()
                                 {
                                     // Can change the parameter name, so do so.
                                     var newParameterName = new ParameterName(newFieldName, isFixed: false);
-                                    parameterNames[index] = newParameterName;
+                                    newParameterNamesList[index] = newParameterName;
                                     parameterToNewFieldMap[newParameterName.BestNameForParameter] = newFieldName;
                                 }
                             }
 
+                            newParameterNames = newParameterNamesList.ToImmutableArray();
                             return true;
                         }
                     }
                 }
 
+                newParameterNames = newParameterNamesList.ToImmutableArray();
                 return false;
             }
 

src/Features/Core/Portable/GenerateMember/GenerateConstructor/AbstractGenerateConstructorService.State.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -18,15 +19,15 @@ internal abstract partial class AbstractGenerateConstructorService<TService, TAr
     {
         protected internal class State
         {
-            public IList<TArgumentSyntax> Arguments { get; private set; }
+            public ImmutableArray<TArgumentSyntax> Arguments { get; private set; }
 
-            public IList<TAttributeArgumentSyntax> AttributeArguments { get; private set; }
+            public ImmutableArray<TAttributeArgumentSyntax> AttributeArguments { get; private set; }
 
             // The type we're creating a constructor for.  Will be a class or struct type.
             public INamedTypeSymbol TypeToGenerateIn { get; private set; }
 
             public IList<RefKind> ParameterRefKinds { get; private set; }
-            public IList<ITypeSymbol> ParameterTypes { get; private set; }
+            public ImmutableArray<ITypeSymbol> ParameterTypes { get; private set; }
 
             public IMethodSymbol DelegatedConstructorOpt { get; private set; }
 
@@ -90,7 +91,9 @@ private State()
                     return false;
                 }
 
-                this.ParameterTypes = this.ParameterTypes ?? GetParameterTypes(service, document, cancellationToken);
+                this.ParameterTypes = this.ParameterTypes.IsDefault
+                    ? GetParameterTypes(service, document, cancellationToken)
+                    : this.ParameterTypes;
                 this.ParameterRefKinds = this.ParameterRefKinds ?? this.Arguments.Select(service.GetRefKind).ToList();
 
                 return !ClashesWithExistingConstructor(document, cancellationToken);
@@ -105,12 +108,12 @@ private bool ClashesWithExistingConstructor(SemanticDocument document, Cancellat
 
             private bool Matches(IMethodSymbol ctor, ISyntaxFactsService service)
             {
-                if (ctor.Parameters.Length != this.ParameterTypes.Count)
+                if (ctor.Parameters.Length != this.ParameterTypes.Length)
                 {
                     return false;
                 }
 
-                for (int i = 0; i < this.ParameterTypes.Count; i++)
+                for (int i = 0; i < this.ParameterTypes.Length; i++)
                 {
                     var ctorParameter = ctor.Parameters[i];
                     var result = SymbolEquivalenceComparer.Instance.Equals(ctorParameter.Type, this.ParameterTypes[i]) &&
@@ -135,15 +138,15 @@ private bool Matches(IMethodSymbol ctor, ISyntaxFactsService service)
 
             private string GetParameterName(ISyntaxFactsService service, int index)
             {
-                if (index >= this.Arguments?.Count)
+                if (this.Arguments.IsDefault || index >= this.Arguments.Length)
                 {
                     return string.Empty;
                 }
 
-                return service.GetNameForArgument(this.Arguments?[index]);
+                return service.GetNameForArgument(this.Arguments[index]);
             }
 
-            internal List<ITypeSymbol> GetParameterTypes(
+            internal ImmutableArray<ITypeSymbol> GetParameterTypes(
                 TService service,
                 SemanticDocument document,
                 CancellationToken cancellationToken)
@@ -154,7 +157,7 @@ private string GetParameterName(ISyntaxFactsService service, int index)
                     ? this.AttributeArguments.Select(a => service.GetAttributeArgumentType(semanticModel, a, cancellationToken))
                     : this.Arguments.Select(a => service.GetArgumentType(semanticModel, a, cancellationToken));
 
-                return allTypes.Select(t => FixType(t, semanticModel, allTypeParameters)).ToList();
+                return allTypes.Select(t => FixType(t, semanticModel, allTypeParameters)).ToImmutableArray();
             }
 
             private ITypeSymbol FixType(ITypeSymbol typeSymbol, SemanticModel semanticModel, IEnumerable<ITypeParameterSymbol> allTypeParameters)
@@ -204,7 +207,7 @@ private ITypeSymbol FixType(ITypeSymbol typeSymbol, SemanticModel semanticModel,
                 {
                     this.Token = token;
                     this.DelegatedConstructorOpt = constructor;
-                    this.ParameterTypes = constructor.Parameters.Select(p => p.Type).ToList();
+                    this.ParameterTypes = constructor.Parameters.Select(p => p.Type).ToImmutableArray();
                     this.ParameterRefKinds = constructor.Parameters.Select(p => p.RefKind).ToList();
                 }
                 cancellationToken.ThrowIfCancellationRequested();

src/Features/Core/Portable/GenerateMember/GenerateConstructor/AbstractGenerateConstructorService.cs

@@ -26,12 +26,14 @@ protected AbstractGenerateConstructorService()
         protected abstract bool IsClassDeclarationGeneration(SemanticDocument document, SyntaxNode node, CancellationToken cancellationToken);
         protected abstract bool IsConstructorInitializerGeneration(SemanticDocument document, SyntaxNode node, CancellationToken cancellationToken);
 
-        protected abstract bool TryInitializeSimpleNameGenerationState(SemanticDocument document, SyntaxNode simpleName, CancellationToken cancellationToken, out SyntaxToken token, out IList<TArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn);
+        protected abstract bool TryInitializeSimpleNameGenerationState(SemanticDocument document, SyntaxNode simpleName, CancellationToken cancellationToken, out SyntaxToken token, out ImmutableArray<TArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn);
         protected abstract bool TryInitializeClassDeclarationGenerationState(SemanticDocument document, SyntaxNode classDeclaration, CancellationToken cancellationToken, out SyntaxToken token, out IMethodSymbol constructor, out INamedTypeSymbol typeToGenerateIn);
-        protected abstract bool TryInitializeConstructorInitializerGeneration(SemanticDocument document, SyntaxNode constructorInitializer, CancellationToken cancellationToken, out SyntaxToken token, out IList<TArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn);
-        protected abstract bool TryInitializeSimpleAttributeNameGenerationState(SemanticDocument document, SyntaxNode simpleName, CancellationToken cancellationToken, out SyntaxToken token, out IList<TArgumentSyntax> arguments, out IList<TAttributeArgumentSyntax> attributeArguments, out INamedTypeSymbol typeToGenerateIn);
-        protected abstract IList<ParameterName> GenerateParameterNames(SemanticModel semanticModel, IEnumerable<TArgumentSyntax> arguments, IList<string> reservedNames = null);
-        protected virtual IList<ParameterName> GenerateParameterNames(SemanticModel semanticModel, IEnumerable<TAttributeArgumentSyntax> arguments, IList<string> reservedNames = null) { return null; }
+        protected abstract bool TryInitializeConstructorInitializerGeneration(SemanticDocument document, SyntaxNode constructorInitializer, CancellationToken cancellationToken, out SyntaxToken token, out ImmutableArray<TArgumentSyntax> arguments, out INamedTypeSymbol typeToGenerateIn);
+        protected abstract bool TryInitializeSimpleAttributeNameGenerationState(SemanticDocument document, SyntaxNode simpleName, CancellationToken cancellationToken, out SyntaxToken token, out ImmutableArray<TArgumentSyntax> arguments, out ImmutableArray<TAttributeArgumentSyntax> attributeArguments, out INamedTypeSymbol typeToGenerateIn);
+        protected abstract ImmutableArray<ParameterName> GenerateParameterNames(SemanticModel semanticModel, IEnumerable<TArgumentSyntax> arguments, IList<string> reservedNames = null);
+        protected virtual ImmutableArray<ParameterName> GenerateParameterNames(SemanticModel semanticModel, IEnumerable<TAttributeArgumentSyntax> arguments, IList<string> reservedNames = null)
+            => default(ImmutableArray<ParameterName>);
+
         protected abstract string GenerateNameForArgument(SemanticModel semanticModel, TArgumentSyntax argument);
         protected virtual string GenerateNameForArgument(SemanticModel semanticModel, TAttributeArgumentSyntax argument) { return null; }
         protected abstract RefKind GetRefKind(TArgumentSyntax argument);

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateMethodService.State.cs

@@ -150,7 +150,7 @@ internal new class State : AbstractGenerateParameterizedMemberService<TService,
                 }
                 else
                 {
-                    var typeInference = document.Project.LanguageServices.GetService<ITypeInferenceService>();
+                    var typeInference = document.Document.GetLanguageService<ITypeInferenceService>();
                     var delegateType = typeInference.InferDelegateType(semanticModel, this.SimpleNameOrMemberAccessExpression, cancellationToken);
                     if (delegateType != null && delegateType.DelegateInvokeMethod != null)
                     {
@@ -160,7 +160,7 @@ internal new class State : AbstractGenerateParameterizedMemberService<TService,
                     {
                         // We don't have and invocation expression or a delegate, but we may have a special expression without parenthesis.  Lets see
                         // if the type inference service can directly infer the type for our expression.
-                        var expressionType = service.CanGenerateMethodForSimpleNameOrMemberAccessExpression(typeInference, semanticModel, this.SimpleNameOrMemberAccessExpression, cancellationToken);
+                        var expressionType = service.DetermineReturnTypeForSimpleNameOrMemberAccessExpression(typeInference, semanticModel, this.SimpleNameOrMemberAccessExpression, cancellationToken);
                         if (expressionType == null)
                         {
                             return false;
@@ -212,13 +212,15 @@ internal new class State : AbstractGenerateParameterizedMemberService<TService,
                 return true;
             }
 
-            private static IMethodSymbol CreateMethodSymbolWithReturnType(ITypeSymbol expressionType)
+            private static IMethodSymbol CreateMethodSymbolWithReturnType(
+                ITypeSymbol expressionType)
             {
                 return CodeGenerationSymbolFactory.CreateMethodSymbol(
                     attributes: SpecializedCollections.EmptyList<AttributeData>(),
                     accessibility: default(Accessibility),
                     modifiers: default(DeclarationModifiers),
                     returnType: expressionType,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: null,
                     typeParameters: SpecializedCollections.EmptyList<ITypeParameterSymbol>(),

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateMethodService.cs

@@ -22,7 +22,7 @@ internal abstract partial class AbstractGenerateMethodService<TService, TSimpleN
         protected abstract bool IsExplicitInterfaceGeneration(SyntaxNode node);
         protected abstract bool TryInitializeExplicitInterfaceState(SemanticDocument document, SyntaxNode node, CancellationToken cancellationToken, out SyntaxToken identifierToken, out IMethodSymbol methodSymbol, out INamedTypeSymbol typeToGenerateIn);
         protected abstract bool TryInitializeSimpleNameState(SemanticDocument document, TSimpleNameSyntax simpleName, CancellationToken cancellationToken, out SyntaxToken identifierToken, out TExpressionSyntax simpleNameOrMemberAccessExpression, out TInvocationExpressionSyntax invocationExpressionOpt, out bool isInConditionalExpression);
-        protected abstract ITypeSymbol CanGenerateMethodForSimpleNameOrMemberAccessExpression(ITypeInferenceService typeInferenceService, SemanticModel semanticModel, TExpressionSyntax expression, CancellationToken cancellationToken);
+        protected abstract ITypeSymbol DetermineReturnTypeForSimpleNameOrMemberAccessExpression(ITypeInferenceService typeInferenceService, SemanticModel semanticModel, TExpressionSyntax expression, CancellationToken cancellationToken);
 
         public async Task<ImmutableArray<CodeAction>> GenerateMethodAsync(
             Document document,

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateParameterizedMemberService.AbstractInvocationInfo.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.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis;
@@ -16,22 +17,22 @@ internal abstract class AbstractInvocationInfo : SignatureInfo
         {
             protected abstract bool IsIdentifierName();
 
-            protected abstract IList<ITypeParameterSymbol> GetCapturedTypeParameters(CancellationToken cancellationToken);
-            protected abstract IList<ITypeParameterSymbol> GenerateTypeParameters(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ITypeParameterSymbol> GetCapturedTypeParameters(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ITypeParameterSymbol> GenerateTypeParameters(CancellationToken cancellationToken);
 
             protected AbstractInvocationInfo(SemanticDocument document, State state)
                 : base(document, state)
             {
             }
 
-            protected override IList<ITypeParameterSymbol> DetermineTypeParametersWorker(
+            protected override ImmutableArray<ITypeParameterSymbol> DetermineTypeParametersWorker(
                 CancellationToken cancellationToken)
             {
                 var typeParameters = ComputeTypeParameters(cancellationToken);
-                return typeParameters.Select(tp => MassageTypeParameter(tp, cancellationToken)).ToList();
+                return typeParameters.SelectAsArray(tp => MassageTypeParameter(tp, cancellationToken));
             }
 
-            private IList<ITypeParameterSymbol> ComputeTypeParameters(
+            private ImmutableArray<ITypeParameterSymbol> ComputeTypeParameters(
                 CancellationToken cancellationToken)
             {
                 if (IsIdentifierName())
@@ -40,7 +41,7 @@ protected AbstractInvocationInfo(SemanticDocument document, State state)
                     // a generic method if the expression 'x' captured any method type variables.
                     var capturedTypeParameters = GetCapturedTypeParameters(cancellationToken);
                     var availableTypeParameters = this.State.TypeToGenerateIn.GetAllTypeParameters();
-                    var result = capturedTypeParameters.Except(availableTypeParameters).ToList();
+                    var result = capturedTypeParameters.Except(availableTypeParameters).ToImmutableArray();
                     return result;
                 }
                 else

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateParameterizedMemberService.MethodSignatureInfo.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.Generic;
-using System.Linq;
+using System.Collections.Immutable;
 using System.Threading;
-using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Utilities;
 using Roslyn.Utilities;
 
@@ -27,36 +26,26 @@ protected class MethodSignatureInfo : SignatureInfo
             protected override ITypeSymbol DetermineReturnTypeWorker(CancellationToken cancellationToken)
                 => _methodSymbol.ReturnType;
 
-            protected override IList<ITypeParameterSymbol> DetermineTypeParametersWorker(CancellationToken cancellationToken)
-            {
-                return _methodSymbol.TypeParameters;
-            }
+            protected override bool DetermineReturnsByRef(CancellationToken cancellationToken)
+                => _methodSymbol.ReturnsByRef;
 
-            protected override IList<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken)
-            {
-                return _methodSymbol.Parameters.Select(p => p.RefKind).ToList();
-            }
+            protected override ImmutableArray<ITypeParameterSymbol> DetermineTypeParametersWorker(CancellationToken cancellationToken)
+                => _methodSymbol.TypeParameters;
 
-            protected override IList<bool> DetermineParameterOptionality(CancellationToken cancellationToken)
-            {
-                return _methodSymbol.Parameters.Select(p => p.IsOptional).ToList();
-            }
+            protected override ImmutableArray<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken)
+                => _methodSymbol.Parameters.SelectAsArray(p => p.RefKind);
 
-            protected override IList<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken)
-            {
-                return _methodSymbol.Parameters.Select(p => p.Type).ToList();
-            }
+            protected override ImmutableArray<bool> DetermineParameterOptionality(CancellationToken cancellationToken)
+                => _methodSymbol.Parameters.SelectAsArray(p => p.IsOptional);
 
-            protected override IList<ParameterName> DetermineParameterNames(CancellationToken cancellationToken)
-            {
-                return _methodSymbol.Parameters.Select(p => new ParameterName(p.Name, isFixed: true))
-                                               .ToList();
-            }
+            protected override ImmutableArray<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken)
+                => _methodSymbol.Parameters.SelectAsArray(p => p.Type);
 
-            protected override IList<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken)
-            {
-                return SpecializedCollections.EmptyList<ITypeSymbol>();
-            }
+            protected override ImmutableArray<ParameterName> DetermineParameterNames(CancellationToken cancellationToken)
+                => _methodSymbol.Parameters.SelectAsArray(p => new ParameterName(p.Name, isFixed: true));
+
+            protected override ImmutableArray<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken)
+                => ImmutableArray<ITypeSymbol>.Empty;
         }
     }
-}
+}
\ No newline at end of file

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateParameterizedMemberService.SignatureInfo.cs

@@ -22,7 +22,7 @@ internal abstract class SignatureInfo
         {
             protected readonly SemanticDocument Document;
             protected readonly State State;
-            private IList<ITypeParameterSymbol> _typeParameters;
+            private ImmutableArray<ITypeParameterSymbol> _typeParameters;
             private IDictionary<ITypeSymbol, ITypeParameterSymbol> _typeArgumentToTypeParameterMap;
 
             public SignatureInfo(
@@ -33,12 +33,15 @@ internal abstract class SignatureInfo
                 this.State = state;
             }
 
-            public IList<ITypeParameterSymbol> DetermineTypeParameters(CancellationToken cancellationToken)
+            public ImmutableArray<ITypeParameterSymbol> DetermineTypeParameters(CancellationToken cancellationToken)
             {
-                return _typeParameters ?? (_typeParameters = DetermineTypeParametersWorker(cancellationToken));
+                return _typeParameters.IsDefault
+                    ? (_typeParameters = DetermineTypeParametersWorker(cancellationToken))
+                    : _typeParameters;
             }
 
-            protected abstract IList<ITypeParameterSymbol> DetermineTypeParametersWorker(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ITypeParameterSymbol> DetermineTypeParametersWorker(CancellationToken cancellationToken);
+            protected abstract bool DetermineReturnsByRef(CancellationToken cancellationToken);
 
             public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
             {
@@ -51,12 +54,12 @@ public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
                 return FixType(type, cancellationToken);
             }
 
-            protected abstract IList<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ITypeSymbol> DetermineTypeArguments(CancellationToken cancellationToken);
             protected abstract ITypeSymbol DetermineReturnTypeWorker(CancellationToken cancellationToken);
-            protected abstract IList<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken);
-            protected abstract IList<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken);
-            protected abstract IList<bool> DetermineParameterOptionality(CancellationToken cancellationToken);
-            protected abstract IList<ParameterName> DetermineParameterNames(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<RefKind> DetermineParameterModifiers(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ITypeSymbol> DetermineParameterTypes(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<bool> DetermineParameterOptionality(CancellationToken cancellationToken);
+            protected abstract ImmutableArray<ParameterName> DetermineParameterNames(CancellationToken cancellationToken);
 
             internal IPropertySymbol GenerateProperty(
                 SyntaxGenerator factory,
@@ -76,6 +79,7 @@ public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
                     accessibility: accessibility,
                     modifiers: new DeclarationModifiers(isStatic: State.IsStatic, isAbstract: isAbstract),
                     type: DetermineReturnType(cancellationToken),
+                    returnsByRef: DetermineReturnsByRef(cancellationToken),
                     explicitInterfaceSymbol: null,
                     name: this.State.IdentifierToken.ValueText,
                     parameters: DetermineParameters(cancellationToken),
@@ -90,14 +94,20 @@ public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
             {
                 var parameters = DetermineParameters(cancellationToken);
                 var returnType = DetermineReturnType(cancellationToken);
-                var isUnsafe = (parameters
-                    .Any(p => p.Type.IsUnsafe()) || returnType.IsUnsafe()) &&
-                    !State.IsContainedInUnsafeType;
+                var isUnsafe = false;
+                if (!State.IsContainedInUnsafeType)
+                {
+                    isUnsafe = returnType.IsUnsafe() || parameters.Any(p => p.Type.IsUnsafe());
+                }
+
+                var returnsByRef = DetermineReturnsByRef(cancellationToken);
+
                 var method = CodeGenerationSymbolFactory.CreateMethodSymbol(
                     attributes: null,
                     accessibility: DetermineAccessibility(isAbstract),
                     modifiers: new DeclarationModifiers(isStatic: State.IsStatic, isAbstract: isAbstract, isUnsafe: isUnsafe),
                     returnType: returnType,
+                    returnsByRef: returnsByRef,
                     explicitInterfaceSymbol: null,
                     name: this.State.IdentifierToken.ValueText,
                     typeParameters: DetermineTypeParameters(cancellationToken),
@@ -156,7 +166,7 @@ public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
 
                 var result = new Dictionary<ITypeSymbol, ITypeParameterSymbol>();
 
-                for(var i = 0; i < typeArguments.Count; i++)
+                for(var i = 0; i < typeArguments.Length; i++)
                 {
                     if (typeArguments[i] != null)
                     {
@@ -179,15 +189,15 @@ public ITypeSymbol DetermineReturnType(CancellationToken cancellationToken)
                     : new[] { throwStatement };
             }
 
-            private IList<IParameterSymbol> DetermineParameters(CancellationToken cancellationToken)
+            private ImmutableArray<IParameterSymbol> DetermineParameters(CancellationToken cancellationToken)
             {
                 var modifiers = DetermineParameterModifiers(cancellationToken);
                 var types = DetermineParameterTypes(cancellationToken).Select(t => FixType(t, cancellationToken)).ToList();
                 var optionality = DetermineParameterOptionality(cancellationToken);
                 var names = DetermineParameterNames(cancellationToken);
 
-                var result = new List<IParameterSymbol>();
-                for (var i = 0; i < modifiers.Count; i++)
+                var result = ArrayBuilder<IParameterSymbol>.GetInstance();
+                for (var i = 0; i < modifiers.Length; i++)
                 {
                     result.Add(CodeGenerationSymbolFactory.CreateParameterSymbol(
                         attributes: null,
@@ -198,7 +208,7 @@ private IList<IParameterSymbol> DetermineParameters(CancellationToken cancellati
                         name: names[i].BestNameForParameter));
                 }
 
-                return result;
+                return result.ToImmutableAndFree();
             }
 
             private Accessibility DetermineAccessibility(bool isAbstract)

src/Features/Core/Portable/GenerateMember/GenerateParameterizedMember/AbstractGenerateParameterizedMemberService.cs

@@ -64,7 +64,7 @@ protected ImmutableArray<CodeAction> GetActions(Document document, State state,
                 var typeParameters = state.SignatureInfo.DetermineTypeParameters(cancellationToken);
                 var returnType = state.SignatureInfo.DetermineReturnType(cancellationToken);
 
-                if (typeParameters.Count == 0 && returnType.SpecialType != SpecialType.System_Void)
+                if (typeParameters.Length == 0 && returnType.SpecialType != SpecialType.System_Void)
                 {
                     result.Add(new GenerateParameterizedMemberCodeAction((TService)this, document, state, isAbstract: false, generateProperty: true));
 

src/Features/Core/Portable/GenerateMember/GenerateVariable/AbstractGenerateVariableService.CodeAction.cs

@@ -66,6 +66,7 @@ protected override async Task<Document> GetChangedDocumentAsync(CancellationToke
                             accessibility: DetermineMaximalAccessibility(_state),
                             modifiers: new DeclarationModifiers(isStatic: _state.IsStatic, isUnsafe: generateUnsafe),
                             type: _state.TypeMemberType,
+                            returnsByRef: false,
                             explicitInterfaceSymbol: null,
                             name: _state.IdentifierToken.ValueText,
                             isIndexer: _state.IsIndexer,

src/Features/Core/Portable/GenerateType/AbstractGenerateTypeService.GenerateNamedType.cs

@@ -46,9 +46,10 @@ private INamedTypeSymbol GenerateNamedType(GenerateTypeOptionsResult options)
                         options.Accessibility,
                         DetermineModifiers(),
                         DetermineReturnType(options),
-                        options.TypeName,
-                        DetermineTypeParameters(options),
-                        DetermineParameters(options));
+                        returnsByRef: false,
+                        name: options.TypeName,
+                        typeParameters: DetermineTypeParameters(options),
+                        parameters: DetermineParameters(options));
                 }
 
                 return CodeGenerationSymbolFactory.CreateNamedTypeSymbol(

src/Features/VisualBasic/Portable/CodeFixes/GenerateEvent/GenerateEventCodeFixProvider.vb

@@ -120,7 +120,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeFixes.GenerateEvent
             Dim delegateType = CodeGenerationSymbolFactory.CreateDelegateTypeSymbol(
                 attributes:=Nothing, accessibility:=Accessibility.Public, modifiers:=Nothing,
                 returnType:=semanticModel.Compilation.GetSpecialType(SpecialType.System_Void),
-                name:=eventHandlerName, parameters:=delegateSymbol.GetParameters())
+                returnsByRef:=False, name:=eventHandlerName,
+                parameters:=delegateSymbol.GetParameters())
 
             Dim generatedEvent = CodeGenerationSymbolFactory.CreateEventSymbol(
                 attributes:=SpecializedCollections.EmptyList(Of AttributeData)(),
@@ -270,7 +271,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeFixes.GenerateEvent
 
                 Dim eventHandlerType = CodeGenerationSymbolFactory.CreateDelegateTypeSymbol(
                     eventType.GetAttributes(), eventType.DeclaredAccessibility,
-                    modifiers:=Nothing, returnType:=returnType,
+                    modifiers:=Nothing, returnType:=returnType, returnsByRef:=false,
                     name:=actualEventName + "EventHandler",
                     typeParameters:=eventType.TypeParameters, parameters:=parameters)
 
@@ -374,7 +375,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.CodeFixes.GenerateEvent
             Dim delegateType = CodeGenerationSymbolFactory.CreateDelegateTypeSymbol(
                 attributes:=Nothing, accessibility:=Accessibility.Public, modifiers:=Nothing,
                 returnType:=semanticModel.Compilation.GetSpecialType(SpecialType.System_Void),
-                name:=actualEventName + "Handler", parameters:=boundMethod.GetParameters())
+                returnsByRef:=False, name:=actualEventName + "Handler",
+                parameters:=boundMethod.GetParameters())
 
             Dim generatedEvent = CodeGenerationSymbolFactory.CreateEventSymbol(
                 attributes:=Nothing, accessibility:=Accessibility.Public, modifiers:=Nothing,

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

@@ -66,6 +66,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.ExtractMethod
                     accessibility:=Accessibility.Private,
                     modifiers:=CreateMethodModifiers(),
                     returnType:=Me.AnalyzerResult.ReturnType,
+                    returnsByRef:=False,
                     explicitInterfaceSymbol:=Nothing,
                     name:=_methodName.ToString(),
                     typeParameters:=CreateMethodTypeParameters(cancellationToken),

src/Features/VisualBasic/Portable/GenerateMember/GenerateConstructor/VisualBasicGenerateConstructorService.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+Imports System.Collections.Immutable
 Imports System.Composition
 Imports System.Threading
 Imports Microsoft.CodeAnalysis.GenerateMember.GenerateConstructor
@@ -20,7 +21,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
         Protected Overrides Function GenerateParameterNames(
                 semanticModel As SemanticModel,
                 arguments As IEnumerable(Of ArgumentSyntax),
-                Optional reservedNames As IList(Of String) = Nothing) As IList(Of ParameterName)
+                Optional reservedNames As IList(Of String) = Nothing) As ImmutableArray(Of ParameterName)
             Return semanticModel.GenerateParameterNames(arguments?.ToList(), reservedNames)
         End Function
 
@@ -48,7 +49,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
 
         Protected Overrides Function TryInitializeConstructorInitializerGeneration(
                 document As SemanticDocument, node As SyntaxNode, cancellationToken As CancellationToken,
-                ByRef token As SyntaxToken, ByRef arguments As IList(Of ArgumentSyntax), ByRef typeToGenerateIn As INamedTypeSymbol) As Boolean
+                ByRef token As SyntaxToken, ByRef arguments As ImmutableArray(Of ArgumentSyntax), ByRef typeToGenerateIn As INamedTypeSymbol) As Boolean
             Dim simpleName = DirectCast(node, SimpleNameSyntax)
             Dim memberAccess = DirectCast(simpleName.Parent, MemberAccessExpressionSyntax)
             Dim invocation = DirectCast(memberAccess.Parent, InvocationExpressionSyntax)
@@ -58,7 +59,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
 
                 If containingType IsNot Nothing Then
                     token = simpleName.Identifier
-                    arguments = invocation.ArgumentList.Arguments.ToList()
+                    arguments = invocation.ArgumentList.Arguments.ToImmutableArray()
                     typeToGenerateIn = If(memberAccess.Expression.IsKind(SyntaxKind.MyBaseExpression),
                                           containingType.BaseType,
                                           containingType)
@@ -82,7 +83,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
                 node As SyntaxNode,
                 cancellationToken As CancellationToken,
                 ByRef token As SyntaxToken,
-                ByRef arguments As IList(Of ArgumentSyntax),
+                ByRef arguments As ImmutableArray(Of ArgumentSyntax),
                 ByRef typeToGenerateIn As INamedTypeSymbol) As Boolean
 
             Dim simpleName = DirectCast(node, SimpleNameSyntax)
@@ -97,7 +98,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
                     Dim semanticModel = document.SemanticModel
 
                     token = simpleName.Identifier
-                    arguments = objectCreationExpression.ArgumentList.Arguments.ToList()
+                    arguments = objectCreationExpression.ArgumentList.Arguments.ToImmutableArray()
 
                     Dim symbolInfo = semanticModel.GetSymbolInfo(objectCreationExpression.Type, cancellationToken)
                     typeToGenerateIn = TryCast(symbolInfo.GetAnySymbol(), INamedTypeSymbol)
@@ -117,8 +118,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
                 node As SyntaxNode,
                 cancellationToken As CancellationToken,
                 ByRef token As SyntaxToken,
-                ByRef arguments As IList(Of ArgumentSyntax),
-                ByRef attributeArguments As IList(Of AttributeSyntax),
+                ByRef arguments As ImmutableArray(Of ArgumentSyntax),
+                ByRef attributeArguments As ImmutableArray(Of AttributeSyntax),
                 ByRef typeToGenerateIn As INamedTypeSymbol) As Boolean
 
             Dim simpleName = DirectCast(node, SimpleNameSyntax)
@@ -133,7 +134,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateConstructor
                     Dim symbolInfo = document.SemanticModel.GetSymbolInfo(attribute, cancellationToken)
                     If symbolInfo.CandidateReason = CandidateReason.OverloadResolutionFailure AndAlso Not symbolInfo.CandidateSymbols.IsEmpty Then
                         token = simpleName.Identifier
-                        arguments = attribute.ArgumentList.Arguments.ToList()
+                        arguments = attribute.ArgumentList.Arguments.ToImmutableArray()
                         attributeArguments = Nothing
                         typeToGenerateIn = TryCast(symbolInfo.CandidateSymbols.FirstOrDefault().ContainingSymbol, INamedTypeSymbol)
 

src/Features/VisualBasic/Portable/GenerateMember/GenerateParameterizedMember/VisualBasicGenerateConversionService.vb

@@ -8,7 +8,6 @@ Imports Microsoft.CodeAnalysis.GenerateMember.GenerateParameterizedMember
 Imports Microsoft.CodeAnalysis.Host.Mef
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
-
 Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
     <ExportLanguageService(GetType(IGenerateConversionService), LanguageNames.VisualBasic), [Shared]>
     Partial Friend Class VisualBasicGenerateConversionService
@@ -138,18 +137,19 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                 typeToGenerateIn = typeToGenerateIn.ConstructUnboundGenericType.ConstructedFrom
             End If
             Return CodeGenerationSymbolFactory.CreateMethodSymbol(
-                            attributes:=SpecializedCollections.EmptyList(Of AttributeData),
-                            accessibility:=Nothing,
-                            modifiers:=Nothing,
-                            returnType:=typeToGenerateIn,
-                            explicitInterfaceSymbol:=Nothing,
-                            name:=Nothing,
-                            typeParameters:=SpecializedCollections.EmptyList(Of ITypeParameterSymbol),
-                            parameters:={CodeGenerationSymbolFactory.CreateParameterSymbol(parameterSymbol, "v")},
-                            statements:=Nothing,
-                            handlesExpressions:=Nothing,
-                            returnTypeAttributes:=Nothing,
-                            methodKind:=MethodKind.Conversion)
+                attributes:=SpecializedCollections.EmptyList(Of AttributeData),
+                accessibility:=Nothing,
+                modifiers:=Nothing,
+                returnType:=typeToGenerateIn,
+                returnsByRef:=False,
+                explicitInterfaceSymbol:=Nothing,
+                name:=Nothing,
+                typeParameters:=SpecializedCollections.EmptyList(Of ITypeParameterSymbol),
+                parameters:={CodeGenerationSymbolFactory.CreateParameterSymbol(parameterSymbol, "v")},
+                statements:=Nothing,
+                handlesExpressions:=Nothing,
+                returnTypeAttributes:=Nothing,
+                methodKind:=MethodKind.Conversion)
         End Function
 
         Protected Overrides Function GetExplicitConversionDisplayText(state As AbstractGenerateParameterizedMemberService(Of VisualBasicGenerateConversionService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax).State) As String
@@ -160,7 +160,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
             Return String.Format(VBFeaturesResources.Generate_widening_conversion_in_0, state.TypeToGenerateIn.Name)
         End Function
     End Class
-End Namespace
-
-
-
+End Namespace
\ No newline at end of file

src/Features/VisualBasic/Portable/GenerateMember/GenerateParameterizedMember/VisualBasicGenerateMethodService.vb

@@ -152,7 +152,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
             Return New VisualBasicGenerateParameterizedMemberService(Of VisualBasicGenerateMethodService).InvocationExpressionInfo(document, state)
         End Function
 
-        Protected Overrides Function CanGenerateMethodForSimpleNameOrMemberAccessExpression(typeInferenceService As ITypeInferenceService, semanticModel As SemanticModel, expression As ExpressionSyntax, cancellationToken As CancellationToken) As ITypeSymbol
+        Protected Overrides Function DetermineReturnTypeForSimpleNameOrMemberAccessExpression(typeInferenceService As ITypeInferenceService, semanticModel As SemanticModel, expression As ExpressionSyntax, cancellationToken As CancellationToken) As ITypeSymbol
             Return typeInferenceService.InferType(semanticModel, expression, True, cancellationToken)
         End Function
     End Class

src/Features/VisualBasic/Portable/GenerateMember/GenerateParameterizedMember/VisualBasicGenerateParameterizedMemberService.vb

@@ -8,6 +8,7 @@ Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 Imports Microsoft.CodeAnalysis.GenerateMember.GenerateParameterizedMember
 Imports Microsoft.CodeAnalysis.Utilities
+Imports System.Collections.Immutable
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
     Partial Friend MustInherit Class VisualBasicGenerateParameterizedMemberService(Of TService As AbstractGenerateParameterizedMemberService(Of TService, SimpleNameSyntax, ExpressionSyntax, InvocationExpressionSyntax))
@@ -24,14 +25,18 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                 Me.InvocationExpression = state.InvocationExpressionOpt
             End Sub
 
-            Protected Overrides Function DetermineParameterNames(cancellationToken As CancellationToken) As IList(Of ParameterName)
-                Dim typeParametersNames = Me.DetermineTypeParameters(cancellationToken).Select(Function(t) t.Name).ToList()
+            Protected Overrides Function DetermineParameterNames(cancellationToken As CancellationToken) As ImmutableArray(Of ParameterName)
+                Dim typeParametersNames = Me.DetermineTypeParameters(cancellationToken).SelectAsArray(Function(t) t.Name)
                 Return Me.Document.SemanticModel.GenerateParameterNames(
                     Me.InvocationExpression.ArgumentList, reservedNames:=typeParametersNames)
             End Function
 
+            Protected Overrides Function DetermineReturnsByRef(cancellationToken As CancellationToken) As Boolean
+                Return False
+            End Function
+
             Protected Overrides Function DetermineReturnTypeWorker(cancellationToken As CancellationToken) As ITypeSymbol
-                Select Case CType(Me.State.IdentifierToken, SyntaxToken).GetTypeCharacter()
+                Select Case Me.State.IdentifierToken.GetTypeCharacter()
                     Case TypeCharacter.Integer
                         Return Me.Document.SemanticModel.Compilation.GetSpecialType(SpecialType.System_Int32)
                     Case TypeCharacter.Long
@@ -53,7 +58,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                 Return inferredType
             End Function
 
-            Protected Overrides Function GetCapturedTypeParameters(cancellationToken As CancellationToken) As IList(Of ITypeParameterSymbol)
+            Protected Overrides Function GetCapturedTypeParameters(cancellationToken As CancellationToken) As ImmutableArray(Of ITypeParameterSymbol)
                 Dim result = New List(Of ITypeParameterSymbol)()
                 If Not Me.InvocationExpression.ArgumentList Is Nothing Then
                     For Each argument In Me.InvocationExpression.ArgumentList.Arguments
@@ -62,10 +67,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                     Next
                 End If
 
-                Return result
+                Return result.ToImmutableArray()
             End Function
 
-            Protected Overrides Function GenerateTypeParameters(cancellationToken As CancellationToken) As IList(Of ITypeParameterSymbol)
+            Protected Overrides Function GenerateTypeParameters(cancellationToken As CancellationToken) As ImmutableArray(Of ITypeParameterSymbol)
                 ' Generate dummy type parameter names for a generic method.  If the user is inside a
                 ' generic method, and calls a generic method with type arguments from the outer
                 ' method, then use those same names for the generated type parameters.
@@ -79,12 +84,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                         Function(s) Not State.TypeToGenerateIn.GetAllTypeParameters().Any(Function(t) t.Name = s),
                         cancellationToken)
 
-                    Return New List(Of ITypeParameterSymbol) From {typeParameter}
+                    Return ImmutableArray.Create(typeParameter)
                 End If
 
                 Dim usedIdentifiers = New HashSet(Of String) From {"T"}
 
-                Dim list = New List(Of ITypeParameterSymbol)()
+                Dim list = ArrayBuilder(Of ITypeParameterSymbol).GetInstance()
                 For Each typeArgument In genericName.TypeArgumentList.Arguments
                     Dim typeParameter = GetUniqueTypeParameter(typeArgument,
                         Function(s) Not usedIdentifiers.Contains(s) AndAlso Not State.TypeToGenerateIn.GetAllTypeParameters().Any(Function(t) t.Name = s),
@@ -95,7 +100,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                     list.Add(typeParameter)
                 Next
 
-                Return list
+                Return list.ToImmutableAndFree()
             End Function
 
             Private Function GetUniqueTypeParameter(type As TypeSyntax,
@@ -120,22 +125,22 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                 Return Nothing
             End Function
 
-            Protected Overrides Function DetermineParameterModifiers(cancellationToken As CancellationToken) As IList(Of RefKind)
+            Protected Overrides Function DetermineParameterModifiers(cancellationToken As CancellationToken) As ImmutableArray(Of RefKind)
                 Return If(Me.InvocationExpression.ArgumentList IsNot Nothing AndAlso Me.InvocationExpression.ArgumentList.GetArgumentCount() > 0,
-                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) RefKind.None).ToList(),
-                          SpecializedCollections.EmptyList(Of RefKind))
+                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) RefKind.None).ToImmutableArray(),
+                          ImmutableArray(Of RefKind).Empty)
             End Function
 
-            Protected Overrides Function DetermineParameterTypes(cancellationToken As CancellationToken) As IList(Of ITypeSymbol)
+            Protected Overrides Function DetermineParameterTypes(cancellationToken As CancellationToken) As ImmutableArray(Of ITypeSymbol)
                 Return If(Me.InvocationExpression.ArgumentList IsNot Nothing AndAlso Me.InvocationExpression.ArgumentList.GetArgumentCount() > 0,
-                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) DetermineParameterType(a, cancellationToken)).ToList(),
-                          SpecializedCollections.EmptyList(Of ITypeSymbol))
+                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) DetermineParameterType(a, cancellationToken)).ToImmutableArray(),
+                          ImmutableArray(Of ITypeSymbol).Empty)
             End Function
 
-            Protected Overrides Function DetermineParameterOptionality(cancellationToken As CancellationToken) As IList(Of Boolean)
+            Protected Overrides Function DetermineParameterOptionality(cancellationToken As CancellationToken) As ImmutableArray(Of Boolean)
                 Return If(Me.InvocationExpression.ArgumentList IsNot Nothing AndAlso Me.InvocationExpression.ArgumentList.GetArgumentCount() > 0,
-                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) DetermineParameterOptionality(a, cancellationToken)).ToList(),
-                          SpecializedCollections.EmptyList(Of Boolean))
+                          Me.InvocationExpression.ArgumentList.Arguments.Select(Function(a) DetermineParameterOptionality(a, cancellationToken)).ToImmutableArray(),
+                          ImmutableArray(Of Boolean).Empty)
             End Function
 
             Private Overloads Function DetermineParameterOptionality(argument As ArgumentSyntax,
@@ -157,8 +162,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                 Return conversion.IsWidening AndAlso conversion.IsReference
             End Function
 
-            Protected Overrides Function DetermineTypeArguments(cancellationToken As CancellationToken) As IList(Of ITypeSymbol)
-                Dim Result = New List(Of ITypeSymbol)()
+            Protected Overrides Function DetermineTypeArguments(cancellationToken As CancellationToken) As ImmutableArray(Of ITypeSymbol)
+                Dim Result = ArrayBuilder(Of ITypeSymbol).GetInstance()
 
                 If TypeOf State.SimpleNameOpt Is GenericNameSyntax Then
                     For Each typeArgument In DirectCast(State.SimpleNameOpt, GenericNameSyntax).TypeArgumentList.Arguments
@@ -167,7 +172,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateMember.GenerateMethod
                     Next
                 End If
 
-                Return Result
+                Return Result.ToImmutableAndFree()
             End Function
         End Class
     End Class

src/Features/VisualBasic/Portable/GenerateType/VisualBasicGenerateTypeService.vb

@@ -697,6 +697,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.GenerateType
                             explicitInterfaceSymbol:=Nothing,
                             name:=propertyName.ToString,
                             type:=typeSymbol,
+                            returnsByRef:=False,
                             parameters:=Nothing,
                             getMethod:=Nothing,
                             setMethod:=Nothing,

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

@@ -187,6 +187,7 @@ public static string GetEventHandlerMemberId(Document document, string className
                 accessibility: Accessibility.Protected,
                 modifiers: new DeclarationModifiers(),
                 returnType: targetDocument.Project.GetCompilationAsync(cancellationToken).WaitAndGetResult_Venus(cancellationToken).GetSpecialType(SpecialType.System_Void),
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: eventHandlerName,
                 typeParameters: null,

src/VisualStudio/Core/Impl/CodeModel/AbstractCodeModelObject_CodeGen.cs

@@ -59,6 +59,7 @@ protected SyntaxNode CreateDelegateTypeDeclaration(SyntaxNode containerNode, str
                 accessibility: CodeModelService.GetAccessibility(access, SymbolKind.NamedType, destination),
                 modifiers: new DeclarationModifiers(),
                 returnType: returnType,
+                returnsByRef: false,
                 name: name);
 
             return CodeGenerationService.CreateNamedTypeDeclaration(
@@ -80,6 +81,7 @@ protected SyntaxNode CreateEventDeclaration(SyntaxNode containerNode, string nam
                     accessibility: Accessibility.NotApplicable,
                     modifiers: new DeclarationModifiers(),
                     returnType: null,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: "add_" + name,
                     typeParameters: null,
@@ -90,6 +92,7 @@ protected SyntaxNode CreateEventDeclaration(SyntaxNode containerNode, string nam
                     accessibility: Accessibility.NotApplicable,
                     modifiers: new DeclarationModifiers(),
                     returnType: null,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: "remove_" + name,
                     typeParameters: null,
@@ -136,6 +139,7 @@ protected SyntaxNode CreateMethodDeclaration(SyntaxNode containerNode, string na
                 accessibility: CodeModelService.GetAccessibility(access, SymbolKind.Method, destination),
                 modifiers: new DeclarationModifiers(),
                 returnType: returnType,
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: name,
                 typeParameters: null,
@@ -158,6 +162,7 @@ protected SyntaxNode CreatePropertyDeclaration(SyntaxNode containerNode, string
                     accessibility: Accessibility.NotApplicable,
                     modifiers: new DeclarationModifiers(),
                     returnType: null,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: "get_" + name,
                     typeParameters: null,
@@ -173,6 +178,7 @@ protected SyntaxNode CreatePropertyDeclaration(SyntaxNode containerNode, string
                     accessibility: Accessibility.NotApplicable,
                     modifiers: new DeclarationModifiers(),
                     returnType: null,
+                    returnsByRef: false,
                     explicitInterfaceSymbol: null,
                     name: "set_" + name,
                     typeParameters: null,
@@ -184,6 +190,7 @@ protected SyntaxNode CreatePropertyDeclaration(SyntaxNode containerNode, string
                 accessibility: CodeModelService.GetAccessibility(access, SymbolKind.Field, destination),
                 modifiers: new DeclarationModifiers(),
                 type: type,
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: name,
                 parameters: null,

src/Workspaces/CSharp/Portable/CodeGeneration/PropertyGenerator.cs

@@ -96,7 +96,7 @@ public static bool CanBeGenerated(IPropertySymbol property)
             var declaration = SyntaxFactory.IndexerDeclaration(
                     attributeLists: AttributeGenerator.GenerateAttributeLists(property.GetAttributes(), options),
                     modifiers: GenerateModifiers(property, destination, options),
-                    type: property.Type.GenerateTypeSyntax(),
+                    type: GeneratePropertyType(property),
                     explicitInterfaceSpecifier: explicitInterfaceSpecifier,
                     parameterList: ParameterGenerator.GenerateBracketedParameterList(property.Parameters, explicitInterfaceSpecifier != null, options),
                     accessorList: GenerateAccessorList(property, destination, workspace, options, parseOptions));
@@ -106,6 +106,13 @@ public static bool CanBeGenerated(IPropertySymbol property)
                 AddAnnotationsTo(property, declaration));
         }
 
+        private static TypeSyntax GeneratePropertyType(IPropertySymbol property)
+        {
+            return property.ReturnsByRef
+                            ? property.Type.GenerateRefTypeSyntax()
+                            : property.Type.GenerateTypeSyntax();
+        }
+
         private static MemberDeclarationSyntax GeneratePropertyDeclaration(
            IPropertySymbol property, CodeGenerationDestination destination,
            Workspace workspace, CodeGenerationOptions options, ParseOptions parseOptions)
@@ -123,7 +130,7 @@ public static bool CanBeGenerated(IPropertySymbol property)
             var propertyDeclaration = SyntaxFactory.PropertyDeclaration(
                 attributeLists: AttributeGenerator.GenerateAttributeLists(property.GetAttributes(), options),
                 modifiers: GenerateModifiers(property, destination, options),
-                type: property.Type.GenerateTypeSyntax(),
+                type: GeneratePropertyType(property),
                 explicitInterfaceSpecifier: explicitInterfaceSpecifier,
                 identifier: property.Name.ToIdentifierToken(),
                 accessorList: accessorList,

src/Workspaces/CSharp/Portable/Extensions/SemanticModelExtensions.cs

@@ -254,9 +254,8 @@ private static bool CanBindToken(SyntaxToken token)
             return type.CreateParameterName(capitalize);
         }
 
-        public static IList<ParameterName> GenerateParameterNames(
-            this SemanticModel semanticModel,
-            ArgumentListSyntax argumentList)
+        public static ImmutableArray<ParameterName> GenerateParameterNames(
+            this SemanticModel semanticModel, ArgumentListSyntax argumentList)
         {
             return semanticModel.GenerateParameterNames(argumentList.Arguments);
         }
@@ -268,7 +267,7 @@ private static bool CanBindToken(SyntaxToken token)
             return semanticModel.GenerateParameterNames(argumentList.Arguments);
         }
 
-        public static IList<ParameterName> GenerateParameterNames(
+        public static ImmutableArray<ParameterName> GenerateParameterNames(
             this SemanticModel semanticModel,
             IEnumerable<ArgumentSyntax> arguments,
             IList<string> reservedNames = null)
@@ -285,11 +284,11 @@ private static bool CanBindToken(SyntaxToken token)
             return GenerateNames(reservedNames, isFixed, parameterNames);
         }
 
-        private static IList<ParameterName> GenerateNames(IList<string> reservedNames, List<bool> isFixed, List<string> parameterNames)
+        private static ImmutableArray<ParameterName> GenerateNames(IList<string> reservedNames, List<bool> isFixed, List<string> parameterNames)
         {
             return NameGenerator.EnsureUniqueness(parameterNames, isFixed)
                                 .Select((name, index) => new ParameterName(name, isFixed[index]))
-                                .Skip(reservedNames.Count).ToList();
+                                .Skip(reservedNames.Count).ToImmutableArray();
         }
 
         public static IList<ParameterName> GenerateParameterNames(

src/Workspaces/CSharp/Portable/LanguageServices/CSharpTypeInferenceService.TypeInferrer.cs

@@ -87,7 +87,11 @@ private IEnumerable<TypeInferenceInfo> GetTypesComplex(ExpressionSyntax expressi
 
             private IEnumerable<TypeInferenceInfo> GetTypesSimple(ExpressionSyntax expression)
             {
-                if (expression != null)
+                if (expression is RefTypeSyntax refType)
+                {
+                    return GetTypes(refType.Type);
+                }
+                else if (expression != null)
                 {
                     var typeInfo = SemanticModel.GetTypeInfo(expression, CancellationToken);
                     var symbolInfo = SemanticModel.GetSymbolInfo(expression, CancellationToken);
@@ -154,6 +158,7 @@ private IEnumerable<TypeInferenceInfo> GetTypesSimple(ExpressionSyntax expressio
                     case ParenthesizedLambdaExpressionSyntax parenthesizedLambdaExpression: return InferTypeInParenthesizedLambdaExpression(parenthesizedLambdaExpression);
                     case PostfixUnaryExpressionSyntax postfixUnary: return InferTypeInPostfixUnaryExpression(postfixUnary);
                     case PrefixUnaryExpressionSyntax prefixUnary: return InferTypeInPrefixUnaryExpression(prefixUnary);
+                    case RefExpressionSyntax refExpression: return InferTypeInRefExpression(refExpression);
                     case ReturnStatementSyntax returnStatement: return InferTypeForReturnStatement(returnStatement);
                     case SimpleLambdaExpressionSyntax simpleLambdaExpression: return InferTypeInSimpleLambdaExpression(simpleLambdaExpression);
                     case SwitchLabelSyntax switchLabel: return InferTypeInSwitchLabel(switchLabel);
@@ -1802,6 +1807,9 @@ private static ITypeSymbol GetMemberType(ISymbol memberSymbol)
                 return null;
             }
 
+            private IEnumerable<TypeInferenceInfo> InferTypeInRefExpression(RefExpressionSyntax refExpression)
+                => InferTypes(refExpression);
+
             private IEnumerable<TypeInferenceInfo> InferTypeForReturnStatement(ReturnStatementSyntax returnStatement, SyntaxToken? previousToken = null)
             {
                 InferTypeForReturnStatement(returnStatement, previousToken,

src/Workspaces/Core/Portable/CodeGeneration/CodeGenerationSymbolFactory.cs

@@ -43,6 +43,7 @@ public static bool IsCodeGenerationSymbol(this ISymbol symbol)
             Accessibility accessibility,
             DeclarationModifiers modifiers,
             ITypeSymbol type,
+            bool returnsByRef,
             IPropertySymbol explicitInterfaceSymbol,
             string name,
             IList<IParameterSymbol> parameters,
@@ -57,6 +58,7 @@ public static bool IsCodeGenerationSymbol(this ISymbol symbol)
                 accessibility,
                 modifiers,
                 type,
+                returnsByRef,
                 explicitInterfaceSymbol,
                 name,
                 isIndexer,
@@ -70,7 +72,11 @@ public static bool IsCodeGenerationSymbol(this ISymbol symbol)
         /// <summary>
         /// Creates a property symbol that can be used to describe a property declaration.
         /// </summary>
-        public static IPropertySymbol CreatePropertySymbol(IList<AttributeData> attributes, Accessibility accessibility, DeclarationModifiers modifiers, ITypeSymbol type, IPropertySymbol explicitInterfaceSymbol, string name, IList<IParameterSymbol> parameters, IMethodSymbol getMethod, IMethodSymbol setMethod, bool isIndexer = false)
+        public static IPropertySymbol CreatePropertySymbol(
+            IList<AttributeData> attributes, Accessibility accessibility, DeclarationModifiers modifiers,
+            ITypeSymbol type, bool returnsByRef, IPropertySymbol explicitInterfaceSymbol, string name, 
+            IList<IParameterSymbol> parameters, IMethodSymbol getMethod, IMethodSymbol setMethod,
+            bool isIndexer = false)
         {
             return CreatePropertySymbol(
                 containingType: null,
@@ -78,6 +84,7 @@ public static IPropertySymbol CreatePropertySymbol(IList<AttributeData> attribut
                 accessibility: accessibility,
                 modifiers: modifiers,
                 type: type,
+                returnsByRef: returnsByRef,
                 explicitInterfaceSymbol: explicitInterfaceSymbol,
                 name: name,
                 parameters: parameters,
@@ -116,7 +123,15 @@ public static IMethodSymbol CreateDestructorSymbol(IList<AttributeData> attribut
             return result;
         }
 
-        internal static IMethodSymbol CreateMethodSymbol(INamedTypeSymbol containingType, IList<AttributeData> attributes, Accessibility accessibility, DeclarationModifiers modifiers, ITypeSymbol returnType, IMethodSymbol explicitInterfaceSymbol, string name, IList<ITypeParameterSymbol> typeParameters, IList<IParameterSymbol> parameters, IList<SyntaxNode> statements = null, IList<SyntaxNode> handlesExpressions = null, IList<AttributeData> returnTypeAttributes = null, MethodKind methodKind = MethodKind.Ordinary, bool returnsByRef = false)
+        internal static IMethodSymbol CreateMethodSymbol(
+            INamedTypeSymbol containingType, IList<AttributeData> attributes,
+            Accessibility accessibility, DeclarationModifiers modifiers,
+            ITypeSymbol returnType, bool returnsByRef,
+            IMethodSymbol explicitInterfaceSymbol, string name,
+            IList<ITypeParameterSymbol> typeParameters, IList<IParameterSymbol> parameters,
+            IList<SyntaxNode> statements = null, IList<SyntaxNode> handlesExpressions = null,
+            IList<AttributeData> returnTypeAttributes = null,
+            MethodKind methodKind = MethodKind.Ordinary)
         {
             var result = new CodeGenerationMethodSymbol(containingType, attributes, accessibility, modifiers, returnType, returnsByRef, explicitInterfaceSymbol, name, typeParameters, parameters, returnTypeAttributes, methodKind);
             CodeGenerationMethodInfo.Attach(result, modifiers.IsNew, modifiers.IsUnsafe, modifiers.IsPartial, modifiers.IsAsync, statements, handlesExpressions);
@@ -126,9 +141,14 @@ internal static IMethodSymbol CreateMethodSymbol(INamedTypeSymbol containingType
         /// <summary>
         /// Creates a method symbol that can be used to describe a method declaration.
         /// </summary>
-        public static IMethodSymbol CreateMethodSymbol(IList<AttributeData> attributes, Accessibility accessibility, DeclarationModifiers modifiers, ITypeSymbol returnType, IMethodSymbol explicitInterfaceSymbol, string name, IList<ITypeParameterSymbol> typeParameters, IList<IParameterSymbol> parameters, IList<SyntaxNode> statements = null, IList<SyntaxNode> handlesExpressions = null, IList<AttributeData> returnTypeAttributes = null, MethodKind methodKind = MethodKind.Ordinary)
+        public static IMethodSymbol CreateMethodSymbol(
+            IList<AttributeData> attributes, Accessibility accessibility, DeclarationModifiers modifiers,
+            ITypeSymbol returnType, bool returnsByRef, IMethodSymbol explicitInterfaceSymbol, string name,
+            IList<ITypeParameterSymbol> typeParameters, IList<IParameterSymbol> parameters, 
+            IList<SyntaxNode> statements = null, IList<SyntaxNode> handlesExpressions = null, 
+            IList<AttributeData> returnTypeAttributes = null, MethodKind methodKind = MethodKind.Ordinary)
         {
-            return CreateMethodSymbol(null, attributes, accessibility, modifiers, returnType, explicitInterfaceSymbol, name, typeParameters, parameters, statements, handlesExpressions, returnTypeAttributes, methodKind);
+            return CreateMethodSymbol(null, attributes, accessibility, modifiers, returnType, returnsByRef, explicitInterfaceSymbol, name, typeParameters, parameters, statements, handlesExpressions, returnTypeAttributes, methodKind);
         }
 
         /// <summary>
@@ -223,6 +243,7 @@ public static IArrayTypeSymbol CreateArrayTypeSymbol(ITypeSymbol elementType, in
                 accessibility ?? accessor.DeclaredAccessibility,
                 accessor.GetSymbolModifiers().WithIsAbstract(statements == null),
                 accessor.ReturnType,
+                accessor.ReturnsByRef,
                 explicitInterfaceSymbol ?? accessor.ExplicitInterfaceImplementations.FirstOrDefault(),
                 accessor.Name,
                 accessor.TypeParameters,
@@ -243,9 +264,12 @@ public static IArrayTypeSymbol CreateArrayTypeSymbol(ITypeSymbol elementType, in
                 attributes,
                 accessibility,
                 new DeclarationModifiers(isAbstract: statements == null),
-                null, null,
-                string.Empty,
-                null, null,
+                returnType: null, 
+                returnsByRef: false, 
+                explicitInterfaceSymbol: null,
+                name: string.Empty,
+                typeParameters: null, 
+                parameters: null,
                 statements: statements);
         }
 
@@ -283,6 +307,7 @@ public static INamedTypeSymbol CreateNamedTypeSymbol(IList<AttributeData> attrib
             Accessibility accessibility, 
             DeclarationModifiers modifiers, 
             ITypeSymbol returnType, 
+            bool returnsByRef,
             string name, 
             IList<ITypeParameterSymbol> typeParameters = null, 
             IList<IParameterSymbol> parameters = null)
@@ -292,6 +317,7 @@ public static INamedTypeSymbol CreateNamedTypeSymbol(IList<AttributeData> attrib
                 accessibility: Accessibility.Public,
                 modifiers: new DeclarationModifiers(),
                 returnType: returnType,
+                returnsByRef: returnsByRef,
                 explicitInterfaceSymbol: null,
                 name: "Invoke",
                 typeParameters: null,
@@ -337,6 +363,7 @@ public static INamespaceSymbol CreateNamespaceSymbol(string name, IList<ISymbol>
                 accessibility ?? method.DeclaredAccessibility,
                 modifiers ?? method.GetSymbolModifiers(),
                 method.ReturnType,
+                method.ReturnsByRef,
                 explicitInterfaceSymbol,
                 name ?? method.Name,
                 method.TypeParameters,
@@ -361,6 +388,7 @@ public static INamespaceSymbol CreateNamespaceSymbol(string name, IList<ISymbol>
                 accessibility ?? property.DeclaredAccessibility,
                 modifiers ?? property.GetSymbolModifiers(),
                 property.Type,
+                property.ReturnsByRef,
                 explicitInterfaceSymbol,
                 name ?? property.Name,
                 property.Parameters,

src/Workspaces/Core/Portable/CodeGeneration/Symbols/CodeGenerationMethodSymbol.cs

@@ -10,12 +10,12 @@ namespace Microsoft.CodeAnalysis.CodeGeneration
 {
     internal partial class CodeGenerationMethodSymbol : CodeGenerationAbstractMethodSymbol
     {
-        private readonly ITypeSymbol _returnType;
-        private readonly bool _returnsByRef;
-        private readonly ImmutableArray<ITypeParameterSymbol> _typeParameters;
-        private readonly ImmutableArray<IParameterSymbol> _parameters;
-        private readonly ImmutableArray<IMethodSymbol> _explicitInterfaceImplementations;
-        private readonly MethodKind _methodKind;
+        public override ITypeSymbol ReturnType { get; }
+        public override ImmutableArray<ITypeParameterSymbol> TypeParameters { get; }
+        public override ImmutableArray<IParameterSymbol> Parameters { get; }
+        public override ImmutableArray<IMethodSymbol> ExplicitInterfaceImplementations { get; }
+        public override bool ReturnsByRef { get; }
+        public override MethodKind MethodKind { get; }
 
         public CodeGenerationMethodSymbol(
             INamedTypeSymbol containingType,
@@ -32,48 +32,17 @@ internal partial class CodeGenerationMethodSymbol : CodeGenerationAbstractMethod
             MethodKind methodKind = MethodKind.Ordinary)
             : base(containingType, attributes, declaredAccessibility, modifiers, name, returnTypeAttributes)
         {
-            _returnType = returnType;
-            _returnsByRef = returnsByRef;
-            _typeParameters = typeParameters.AsImmutableOrEmpty();
-            _parameters = parameters.AsImmutableOrEmpty();
-            _explicitInterfaceImplementations = explicitInterfaceSymbolOpt == null
+            this.ReturnType = returnType;
+            this.ReturnsByRef = returnsByRef;
+            this.TypeParameters = typeParameters.AsImmutableOrEmpty();
+            this.Parameters = parameters.AsImmutableOrEmpty();
+            this.MethodKind = methodKind;
+
+            this.ExplicitInterfaceImplementations = explicitInterfaceSymbolOpt == null
                 ? ImmutableArray.Create<IMethodSymbol>()
                 : ImmutableArray.Create(explicitInterfaceSymbolOpt);
 
             this.OriginalDefinition = this;
-            _methodKind = methodKind;
-        }
-
-        public override ITypeSymbol ReturnType
-        {
-            get
-            {
-                return _returnType;
-            }
-        }
-
-        public override ImmutableArray<ITypeParameterSymbol> TypeParameters
-        {
-            get
-            {
-                return _typeParameters;
-            }
-        }
-
-        public override ImmutableArray<IParameterSymbol> Parameters
-        {
-            get
-            {
-                return _parameters;
-            }
-        }
-
-        public override ImmutableArray<IMethodSymbol> ExplicitInterfaceImplementations
-        {
-            get
-            {
-                return _explicitInterfaceImplementations;
-            }
         }
 
         protected override CodeGenerationSymbol Clone()
@@ -94,13 +63,7 @@ protected override CodeGenerationSymbol Clone()
             return result;
         }
 
-        public override int Arity
-        {
-            get
-            {
-                return this.TypeParameters.Length;
-            }
-        }
+        public override int Arity => this.TypeParameters.Length;
 
         public override bool ReturnsVoid
         {
@@ -110,53 +73,14 @@ public override bool ReturnsVoid
             }
         }
 
-        public override bool ReturnsByRef
-        {
-            get
-            {
-                return _returnsByRef;
-            }
-        }
-
         public override ImmutableArray<ITypeSymbol> TypeArguments
-        {
-            get
-            {
-                return this.TypeParameters.As<ITypeSymbol>();
-            }
-        }
-
-        public override IMethodSymbol ConstructedFrom
-        {
-            get
-            {
-                return this;
-            }
-        }
+            => this.TypeParameters.As<ITypeSymbol>();
 
-        public override IMethodSymbol OverriddenMethod
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public override IMethodSymbol ConstructedFrom => this;
 
-        public override IMethodSymbol ReducedFrom
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public override IMethodSymbol OverriddenMethod => null;
 
-        public override MethodKind MethodKind
-        {
-            get
-            {
-                return _methodKind;
-            }
-        }
+        public override IMethodSymbol ReducedFrom => null;
 
         public override ITypeSymbol GetTypeInferredDuringReduction(ITypeParameterSymbol reducedFromTypeParameter)
         {
@@ -168,20 +92,8 @@ public override IMethodSymbol ReduceExtensionMethod(ITypeSymbol receiverType)
             return null;
         }
 
-        public override IMethodSymbol PartialImplementationPart
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public override IMethodSymbol PartialImplementationPart => null;
 
-        public override IMethodSymbol PartialDefinitionPart
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public override IMethodSymbol PartialDefinitionPart => null;
     }
-}
+}
\ No newline at end of file

src/Workspaces/Core/Portable/CodeGeneration/Symbols/CodeGenerationPropertySymbol.cs

@@ -10,6 +10,7 @@ namespace Microsoft.CodeAnalysis.CodeGeneration
     internal class CodeGenerationPropertySymbol : CodeGenerationSymbol, IPropertySymbol
     {
         public ITypeSymbol Type { get; }
+        public bool ReturnsByRef { get; }
         public bool IsIndexer { get; }
 
         public ImmutableArray<IParameterSymbol> Parameters { get; }
@@ -24,6 +25,7 @@ internal class CodeGenerationPropertySymbol : CodeGenerationSymbol, IPropertySym
             Accessibility declaredAccessibility,
             DeclarationModifiers modifiers,
             ITypeSymbol type,
+            bool returnsByRef,
             IPropertySymbol explicitInterfaceSymbolOpt,
             string name,
             bool isIndexer,
@@ -33,6 +35,7 @@ internal class CodeGenerationPropertySymbol : CodeGenerationSymbol, IPropertySym
             : base(containingType, attributes, declaredAccessibility, modifiers, name)
         {
             this.Type = type;
+            this.ReturnsByRef = returnsByRef;
             this.IsIndexer = isIndexer;
             this.Parameters = parametersOpt.AsImmutableOrEmpty();
             this.ExplicitInterfaceImplementations = explicitInterfaceSymbolOpt == null
@@ -46,7 +49,7 @@ protected override CodeGenerationSymbol Clone()
         {
             var result = new CodeGenerationPropertySymbol(
                 this.ContainingType, this.GetAttributes(), this.DeclaredAccessibility,
-                this.Modifiers, this.Type, this.ExplicitInterfaceImplementations.FirstOrDefault(),
+                this.Modifiers, this.Type, this.ReturnsByRef, this.ExplicitInterfaceImplementations.FirstOrDefault(),
                 this.Name, this.IsIndexer, this.Parameters.IsDefault ? null : (IList<IParameterSymbol>)this.Parameters,
                 this.GetMethod, this.SetMethod);
             CodeGenerationPropertyInfo.Attach(result,
@@ -57,23 +60,13 @@ protected override CodeGenerationSymbol Clone()
             return result;
         }
 
-        public override SymbolKind Kind
-        {
-            get
-            {
-                return SymbolKind.Property;
-            }
-        }
+        public override SymbolKind Kind => SymbolKind.Property;
 
         public override void Accept(SymbolVisitor visitor)
-        {
-            visitor.VisitProperty(this);
-        }
+            => visitor.VisitProperty(this);
 
         public override TResult Accept<TResult>(SymbolVisitor<TResult> visitor)
-        {
-            return visitor.VisitProperty(this);
-        }
+            => visitor.VisitProperty(this);
 
         public bool IsReadOnly
         {
@@ -91,52 +84,14 @@ public bool IsWriteOnly
             }
         }
 
-        public bool ReturnsByRef
-        {
-            get
-            {
-                return this.GetMethod != null && this.GetMethod.ReturnsByRef;
-            }
-        }
-
-        public new IPropertySymbol OriginalDefinition
-        {
-            get
-            {
-                return this;
-            }
-        }
+        public new IPropertySymbol OriginalDefinition => this;
 
-        public IPropertySymbol OverriddenProperty
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public IPropertySymbol OverriddenProperty => null;
 
-        public bool IsWithEvents
-        {
-            get
-            {
-                return false;
-            }
-        }
+        public bool IsWithEvents => false;
 
-        public ImmutableArray<CustomModifier> RefCustomModifiers
-        {
-            get
-            {
-                return ImmutableArray.Create<CustomModifier>();
-            }
-        }
+        public ImmutableArray<CustomModifier> RefCustomModifiers => ImmutableArray<CustomModifier>.Empty;
 
-        public ImmutableArray<CustomModifier> TypeCustomModifiers
-        {
-            get
-            {
-                return ImmutableArray.Create<CustomModifier>();
-            }
-        }
+        public ImmutableArray<CustomModifier> TypeCustomModifiers => ImmutableArray<CustomModifier>.Empty;
     }
-}
+}
\ No newline at end of file

src/Workspaces/Core/Portable/Shared/Extensions/ICodeDefinitionFactoryExtensions_CreateEqualsMethod.cs

@@ -31,6 +31,7 @@ internal static partial class ICodeDefinitionFactoryExtensions
                 accessibility: Accessibility.Public,
                 modifiers: new DeclarationModifiers(isOverride: true),
                 returnType: compilation.GetSpecialType(SpecialType.System_Boolean),
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: EqualsName,
                 typeParameters: null,

src/Workspaces/Core/Portable/Shared/Extensions/ICodeDefinitionFactoryExtensions_CreateGetHashCodeMethod.cs

@@ -25,6 +25,7 @@ internal static partial class ICodeDefinitionFactoryExtensions
                 accessibility: Accessibility.Public,
                 modifiers: new DeclarationModifiers(isOverride: true),
                 returnType: compilation.GetSpecialType(SpecialType.System_Int32),
+                returnsByRef: false,
                 explicitInterfaceSymbol: null,
                 name: GetHashCodeName,
                 typeParameters: null,

src/Workspaces/Core/Portable/Shared/Extensions/IMethodSymbolExtensions.cs

@@ -76,6 +76,7 @@ public static IMethodSymbol RenameTypeParameters(this IMethodSymbol method, ILis
                 method.DeclaredAccessibility,
                 method.GetSymbolModifiers(),
                 method.ReturnType.SubstituteTypes(mapping, typeGenerator),
+                method.ReturnsByRef,
                 method.ExplicitInterfaceImplementations.FirstOrDefault(),
                 method.Name,
                 updatedTypeParameters,
@@ -84,7 +85,8 @@ public static IMethodSymbol RenameTypeParameters(this IMethodSymbol method, ILis
                         p.HasExplicitDefaultValue, p.HasExplicitDefaultValue ? p.ExplicitDefaultValue : null)).ToList());
         }
 
-        public static IMethodSymbol RenameParameters(this IMethodSymbol method, IList<string> parameterNames)
+        public static IMethodSymbol RenameParameters(
+            this IMethodSymbol method, IList<string> parameterNames)
         {
             var parameterList = method.Parameters;
             if (parameterList.Select(p => p.Name).SequenceEqual(parameterNames))
@@ -100,6 +102,7 @@ public static IMethodSymbol RenameParameters(this IMethodSymbol method, IList<st
                 method.DeclaredAccessibility,
                 method.GetSymbolModifiers(),
                 method.ReturnType,
+                method.ReturnsByRef,
                 method.ExplicitInterfaceImplementations.FirstOrDefault(),
                 method.Name,
                 method.TypeParameters,
@@ -199,6 +202,7 @@ public static IMethodSymbol RenameParameters(this IMethodSymbol method, IList<st
                 method.DeclaredAccessibility,
                 method.GetSymbolModifiers(),
                 method.ReturnType,
+                method.ReturnsByRef,
                 method.ExplicitInterfaceImplementations.FirstOrDefault(),
                 method.Name,
                 method.TypeParameters,

src/Workspaces/Core/Portable/Shared/Extensions/IPropertySymbolExtensions.cs

@@ -26,6 +26,7 @@ public static IPropertySymbol RenameParameters(this IPropertySymbol property, IL
                 property.DeclaredAccessibility,
                 property.GetSymbolModifiers(),
                 property.Type,
+                property.ReturnsByRef,
                 property.ExplicitInterfaceImplementations.FirstOrDefault(),
                 property.Name,
                 parameters,
@@ -58,6 +59,7 @@ public static IPropertySymbol RenameParameters(this IPropertySymbol property, IL
                 property.DeclaredAccessibility,
                 property.GetSymbolModifiers(),
                 property.Type,
+                property.ReturnsByRef,
                 property.ExplicitInterfaceImplementations.FirstOrDefault(),
                 property.Name,
                 property.Parameters.Select(p =>

src/Workspaces/VisualBasic/Portable/Extensions/SemanticModelExtensions.vb

@@ -134,9 +134,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
         <Extension()>
         Public Function GenerateParameterNames(semanticModel As SemanticModel,
                                                arguments As ArgumentListSyntax,
-                                               Optional reservedNames As IEnumerable(Of String) = Nothing) As IList(Of ParameterName)
+                                               Optional reservedNames As IEnumerable(Of String) = Nothing) As ImmutableArray(Of ParameterName)
             If arguments Is Nothing Then
-                Return SpecializedCollections.EmptyList(Of ParameterName)()
+                Return ImmutableArray(Of ParameterName).Empty
             End If
 
             Return GenerateParameterNames(semanticModel, arguments.Arguments.ToList(), reservedNames)
@@ -145,7 +145,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
         <Extension()>
         Public Function GenerateParameterNames(semanticModel As SemanticModel,
                                                arguments As IList(Of ArgumentSyntax),
-                                               Optional reservedNames As IEnumerable(Of String) = Nothing) As IList(Of ParameterName)
+                                               Optional reservedNames As IEnumerable(Of String) = Nothing) As ImmutableArray(Of ParameterName)
             reservedNames = If(reservedNames, SpecializedCollections.EmptyEnumerable(Of String))
             Return semanticModel.GenerateParameterNames(
                 arguments,
@@ -155,9 +155,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
         <Extension()>
         Public Function GenerateParameterNames(semanticModel As SemanticModel,
                                                arguments As IList(Of ArgumentSyntax),
-                                               canUse As Func(Of String, Boolean)) As IList(Of ParameterName)
+                                               canUse As Func(Of String, Boolean)) As ImmutableArray(Of ParameterName)
             If arguments.Count = 0 Then
-                Return SpecializedCollections.EmptyList(Of ParameterName)()
+                Return ImmutableArray(Of ParameterName).Empty
             End If
 
             ' We can't change the names of named parameters.  Any other names we're flexible on.
@@ -169,7 +169,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Extensions
             Dim parameterNames = arguments.Select(Function(a) semanticModel.GenerateNameForArgument(a)).ToList()
             Return NameGenerator.EnsureUniqueness(parameterNames, isFixed, canUse).
                                  Select(Function(name, index) New ParameterName(name, isFixed(index))).
-                                 ToList()
+                                 ToImmutableArray()
         End Function
 
         Private Function SetEquals(array1 As ImmutableArray(Of ISymbol), array2 As ImmutableArray(Of ISymbol)) As Boolean