Local function GetAttributes

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
 using System.Diagnostics;
 using Roslyn.Utilities;
@@ -200,7 +202,7 @@ public override string ToString()
             return ToString(null, null);
         }
 
-        public string ToString(string format, IFormatProvider formatProvider)
+        public string ToString(string? format, IFormatProvider? formatProvider)
         {
             return ErrorFacts.GetMessage(_id, formatProvider as System.Globalization.CultureInfo);
         }
@@ -221,7 +223,7 @@ public static LocalizableErrorArgument Localize(this MessageID id)
         //   If this method returns non-null, use that.
         // Features should be mutually exclusive between RequiredFeature and RequiredVersion.
         //   (hence the above rule - RequiredVersion throws when RequiredFeature returns non-null)
-        internal static string RequiredFeature(this MessageID feature)
+        internal static string? RequiredFeature(this MessageID feature)
         {
             // Check for current experimental features, if any, in the current branch.
             switch (feature)
@@ -235,7 +237,7 @@ internal static bool CheckFeatureAvailability(
             this MessageID feature,
             DiagnosticBag diagnostics,
             SyntaxNode syntax,
-            Location location = null)
+            Location? location = null)
         {
             var diag = GetFeatureAvailabilityDiagnosticInfoOpt(feature, (CSharpParseOptions)syntax.SyntaxTree.Options);
             if (diag is object)
@@ -260,15 +262,15 @@ internal static bool CheckFeatureAvailability(
             return true;
         }
 
-        internal static CSDiagnosticInfo GetFeatureAvailabilityDiagnosticInfoOpt(this MessageID feature, CSharpParseOptions options)
+        internal static CSDiagnosticInfo? GetFeatureAvailabilityDiagnosticInfoOpt(this MessageID feature, CSharpParseOptions options)
             => options.IsFeatureEnabled(feature) ? null : GetDisabledFeatureDiagnosticInfo(feature, options.LanguageVersion);
 
-        internal static CSDiagnosticInfo GetFeatureAvailabilityDiagnosticInfoOpt(this MessageID feature, CSharpCompilation compilation)
+        internal static CSDiagnosticInfo? GetFeatureAvailabilityDiagnosticInfoOpt(this MessageID feature, CSharpCompilation compilation)
             => compilation.IsFeatureEnabled(feature) ? null : GetDisabledFeatureDiagnosticInfo(feature, compilation.LanguageVersion);
 
         private static CSDiagnosticInfo GetDisabledFeatureDiagnosticInfo(MessageID feature, LanguageVersion availableVersion)
         {
-            string requiredFeature = feature.RequiredFeature();
+            string? requiredFeature = feature.RequiredFeature();
             if (requiredFeature != null)
             {
                 return new CSDiagnosticInfo(ErrorCode.ERR_FeatureIsExperimental, feature.Localize(), requiredFeature);

src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs

@@ -1,5 +1,7 @@
 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
@@ -12,7 +14,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
-    internal sealed class LocalFunctionSymbol : SourceMethodSymbol
+    internal sealed class LocalFunctionSymbol : SourceMethodSymbol, IAttributeTargetSymbol
     {
         private readonly Binder _binder;
         private readonly LocalFunctionStatementSyntax _syntax;
@@ -25,8 +27,11 @@ internal sealed class LocalFunctionSymbol : SourceMethodSymbol
         private bool _lazyIsVarArg;
         // Initialized in two steps. Hold a copy if accessing during initialization.
         private ImmutableArray<TypeParameterConstraintClause> _lazyTypeParameterConstraints;
-        private TypeWithAnnotations.Boxed _lazyReturnType;
-        private TypeWithAnnotations.Boxed _lazyIteratorElementType;
+        private TypeWithAnnotations.Boxed? _lazyReturnType;
+        private TypeWithAnnotations.Boxed? _lazyIteratorElementType;
+
+        private CustomAttributesBag<CSharpAttributeData>? _lazyCustomAttributesBag;
+        private CustomAttributesBag<CSharpAttributeData>? _lazyReturnTypeCustomAttributesBag;
 
         // Lock for initializing lazy fields and registering their diagnostics
         // Acquire this lock when initializing lazy objects to guarantee their declaration
@@ -121,6 +126,9 @@ internal void GetDeclarationDiagnostics(DiagnosticBag addTo)
 
             ComputeReturnType();
 
+            GetAttributes();
+            GetReturnTypeAttributes();
+
             addTo.AddRange(_declarationDiagnostics);
         }
 
@@ -202,7 +210,7 @@ public override TypeWithAnnotations ReturnTypeWithAnnotations
             get
             {
                 ComputeReturnType();
-                return _lazyReturnType.Value;
+                return _lazyReturnType!.Value;
             }
         }
 
@@ -341,17 +349,17 @@ internal override TypeWithAnnotations IteratorElementTypeWithAnnotations
 
         internal override MethodImplAttributes ImplementationAttributes => default(MethodImplAttributes);
 
-        internal override ObsoleteAttributeData ObsoleteAttributeData => null;
+        internal override ObsoleteAttributeData? ObsoleteAttributeData => null;
 
-        internal override MarshalPseudoCustomAttributeData ReturnValueMarshallingInformation => null;
+        internal override MarshalPseudoCustomAttributeData? ReturnValueMarshallingInformation => null;
 
         internal override CallingConvention CallingConvention => CallingConvention.Default;
 
         internal override bool HasDeclarativeSecurity => false;
 
         internal override bool RequiresSecurityObject => false;
 
-        public override Symbol AssociatedSymbol => null;
+        public override Symbol? AssociatedSymbol => null;
 
         public override Accessibility DeclaredAccessibility => ModifierUtils.EffectiveAccessibility(_declarationModifiers);
 
@@ -375,7 +383,13 @@ internal override TypeWithAnnotations IteratorElementTypeWithAnnotations
 
         internal override bool IsDeclaredReadOnly => false;
 
-        public override DllImportData GetDllImportData() => null;
+        IAttributeTargetSymbol IAttributeTargetSymbol.AttributesOwner => this;
+
+        AttributeLocation IAttributeTargetSymbol.AllowedAttributeLocations => AttributeLocation.Method | AttributeLocation.Return;
+
+        AttributeLocation IAttributeTargetSymbol.DefaultAttributeLocation => AttributeLocation.Method;
+
+        public override DllImportData? GetDllImportData() => null;
 
         internal override ImmutableArray<string> GetAppliedConditionalSymbols() => ImmutableArray<string>.Empty;
 
@@ -393,25 +407,29 @@ internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree l
             throw ExceptionUtilities.Unreachable;
         }
 
-        internal override bool TryGetThisParameter(out ParameterSymbol thisParameter)
+        internal override bool TryGetThisParameter(out ParameterSymbol? thisParameter)
         {
             // Local function symbols have no "this" parameter
             thisParameter = null;
             return true;
         }
 
-        private static void ReportAttributesDisallowed(SyntaxList<AttributeListSyntax> attributes, DiagnosticBag diagnostics)
+        private void ReportAttributesDisallowed(SyntaxList<AttributeListSyntax> attributes, DiagnosticBag diagnostics)
         {
-            foreach (var attrList in attributes)
+            var diagnosticInfo = MessageID.IDS_FeatureLocalFunctionAttributes.GetFeatureAvailabilityDiagnosticInfoOpt((CSharpParseOptions)_syntax.SyntaxTree.Options);
+            if (diagnosticInfo is object)
             {
-                diagnostics.Add(ErrorCode.ERR_AttributesInLocalFuncDecl, attrList.Location);
+                foreach (var attrList in attributes)
+                {
+                    diagnostics.Add(diagnosticInfo, attrList.Location);
+                }
             }
         }
 
         private ImmutableArray<SourceMethodTypeParameterSymbol> MakeTypeParameters(DiagnosticBag diagnostics)
         {
             var result = ArrayBuilder<SourceMethodTypeParameterSymbol>.GetInstance();
-            var typeParameters = _syntax.TypeParameterList.Parameters;
+            var typeParameters = _syntax.TypeParameterList?.Parameters ?? default;
             for (int ordinal = 0; ordinal < typeParameters.Count; ordinal++)
             {
                 var parameter = typeParameters[ordinal];
@@ -420,7 +438,6 @@ private ImmutableArray<SourceMethodTypeParameterSymbol> MakeTypeParameters(Diagn
                     diagnostics.Add(ErrorCode.ERR_IllegalVarianceSyntax, parameter.VarianceKeyword.GetLocation());
                 }
 
-                // Attributes are currently disallowed on local function type parameters
                 ReportAttributesDisallowed(parameter.AttributeLists, diagnostics);
 
                 var identifier = parameter.Identifier;
@@ -493,6 +510,33 @@ public override ImmutableArray<TypeParameterConstraintClause> GetTypeParameterCo
             return _lazyTypeParameterConstraints;
         }
 
+        public override ImmutableArray<CSharpAttributeData> GetAttributes()
+        {
+            var lazyCustomAttributesBag = _lazyCustomAttributesBag;
+            if (lazyCustomAttributesBag == null)
+            {
+                LoadAndValidateAttributes(OneOrMany.Create(_syntax.AttributeLists), ref _lazyCustomAttributesBag);
+                lazyCustomAttributesBag = _lazyCustomAttributesBag;
+            }
+
+            return lazyCustomAttributesBag.Attributes;
+        }
+
+        public override ImmutableArray<CSharpAttributeData> GetReturnTypeAttributes()
+        {
+            var lazyReturnTypeCustomAttributesBag = _lazyReturnTypeCustomAttributesBag;
+            if (lazyReturnTypeCustomAttributesBag == null)
+            {
+                LoadAndValidateAttributes(
+                    OneOrMany.Create(_syntax.AttributeLists),
+                    ref _lazyReturnTypeCustomAttributesBag,
+                    symbolPart: AttributeLocation.Return);
+                lazyReturnTypeCustomAttributesBag = _lazyReturnTypeCustomAttributesBag;
+            }
+
+            return lazyReturnTypeCustomAttributesBag.Attributes;
+        }
+
         public override int GetHashCode()
         {
             // this is what lambdas do (do not use hashes of other fields)
@@ -504,8 +548,7 @@ public sealed override bool Equals(Symbol symbol, TypeCompareKind compareKind)
             if ((object)this == symbol) return true;
 
             var localFunction = symbol as LocalFunctionSymbol;
-            return (object)localFunction != null
-                && localFunction._syntax == _syntax;
+            return localFunction?._syntax == _syntax;
         }
     }
 }

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncIteratorTests.cs

@@ -6571,12 +6571,8 @@ async System.Collections.Generic.IAsyncEnumerable<int> local([EnumeratorCancella
     }
 }
 ";
-            var comp = CreateCompilationWithAsyncIterator(new[] { source, EnumeratorCancellationAttributeType });
-            comp.VerifyDiagnostics(
-                // (13,70): error CS8205: Attributes are not allowed on local function parameters or type parameters
-                //         async System.Collections.Generic.IAsyncEnumerable<int> local([EnumeratorCancellation] CancellationToken token)
-                Diagnostic(ErrorCode.ERR_AttributesInLocalFuncDecl, "[EnumeratorCancellation]").WithLocation(13, 70)
-                );
+            var comp = CreateCompilationWithTasksExtensions(new[] { source, EnumeratorCancellationAttributeType, AsyncStreamsTypes }, parseOptions: TestOptions.RegularPreview);
+            comp.VerifyDiagnostics();
         }
 
         [Fact, WorkItem(35166, "https://github.com/dotnet/roslyn/issues/35166")]