Extensions: adjust SpecialName on implementation methods

src/Compilers/CSharp/Portable/Symbols/ErrorMethodSymbol.cs

@@ -83,6 +83,8 @@ internal sealed override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         public override Accessibility DeclaredAccessibility
         {
             get { return Accessibility.Public; }

src/Compilers/CSharp/Portable/Symbols/Extensions/RewrittenMethodSymbol.cs

@@ -76,6 +76,8 @@ internal sealed override int CalculateLocalSyntaxOffset(int localPosition, Synta
         internal sealed override UnmanagedCallersOnlyAttributeData? GetUnmanagedCallersOnlyAttributeData(bool forceComplete)
             => _originalMethod.GetUnmanagedCallersOnlyAttributeData(forceComplete);
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         public sealed override ImmutableArray<CustomModifier> RefCustomModifiers
         {
             get { return _typeMap.SubstituteCustomModifiers(_originalMethod.RefCustomModifiers); }

src/Compilers/CSharp/Portable/Symbols/Extensions/SourceExtensionImplementationMethodSymbol.cs

@@ -36,7 +36,7 @@ public SourceExtensionImplementationMethodSymbol(MethodSymbol sourceMethod)
         public override MethodKind MethodKind => MethodKind.Ordinary;
         public override bool IsImplicitlyDeclared => true;
 
-        internal override bool HasSpecialName => false;
+        internal override bool HasSpecialName => _originalMethod.HasSpecialNameAttribute;
 
         internal override int ParameterCount
         {

src/Compilers/CSharp/Portable/Symbols/FunctionPointers/FunctionPointerMethodSymbol.cs

@@ -848,6 +848,7 @@ public override bool IsVararg
         internal override bool IsMetadataNewSlot(bool ignoreInterfaceImplementationChanges = false) => false;
         internal override bool IsMetadataVirtual(IsMetadataVirtualOption option = IsMetadataVirtualOption.None) => false;
         internal sealed override UnmanagedCallersOnlyAttributeData? GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
 
         internal override bool GenerateDebugInfo => throw ExceptionUtilities.Unreachable();
         internal override ObsoleteAttributeData? ObsoleteAttributeData => throw ExceptionUtilities.Unreachable();

src/Compilers/CSharp/Portable/Symbols/Metadata/PE/PEMethodSymbol.cs

@@ -1682,6 +1682,8 @@ internal override ObsoleteAttributeData ObsoleteAttributeData
 
             return _uncommonFields?._lazyUnmanagedCallersOnlyAttributeData;
         }
+
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
 #nullable disable
 
         internal override bool GenerateDebugInfo => false;

src/Compilers/CSharp/Portable/Symbols/MethodSymbol.cs

@@ -96,6 +96,8 @@ public virtual bool IsGenericMethod
         /// </summary>
         internal virtual bool IsDirectlyExcludedFromCodeCoverage { get => false; }
 
+        internal abstract bool HasSpecialNameAttribute { get; }
+
         /// <summary>
         /// If a method is annotated with `[MemberNotNull(...)]` attributes, returns the list of members
         /// listed in those attributes.

src/Compilers/CSharp/Portable/Symbols/NativeIntegerTypeSymbol.cs

@@ -374,6 +374,8 @@ public override ImmutableArray<ParameterSymbol> Parameters
 
         internal override UnmanagedCallersOnlyAttributeData? GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => UnderlyingMethod.GetUnmanagedCallersOnlyAttributeData(forceComplete);
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         public override Symbol? AssociatedSymbol => _associatedSymbol;
 
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree)

src/Compilers/CSharp/Portable/Symbols/ReducedExtensionMethodSymbol.cs

@@ -444,6 +444,8 @@ internal sealed override ObsoleteAttributeData ObsoleteAttributeData
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete)
             => _reducedFrom.GetUnmanagedCallersOnlyAttributeData(forceComplete);
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         public override Accessibility DeclaredAccessibility
         {
             get { return _reducedFrom.DeclaredAccessibility; }

src/Compilers/CSharp/Portable/Symbols/Retargeting/RetargetingMethodSymbol.cs

@@ -256,6 +256,8 @@ public override ImmutableArray<CSharpAttributeData> GetReturnTypeAttributes()
             return _lazyUnmanagedAttributeData;
         }
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override bool TryGetThisParameter(out ParameterSymbol? thisParameter)
         {
             if (!_underlyingMethod.TryGetThisParameter(out var underlyingParameter))

src/Compilers/CSharp/Portable/Symbols/SignatureOnlyMethodSymbol.cs

@@ -124,6 +124,8 @@ internal sealed override bool HasAsyncMethodBuilderAttribute(out TypeSymbol buil
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => throw ExceptionUtilities.Unreachable();
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override ImmutableArray<string> GetAppliedConditionalSymbols() { throw ExceptionUtilities.Unreachable(); }
 
         public override ImmutableArray<TypeWithAnnotations> TypeArgumentsWithAnnotations { get { throw ExceptionUtilities.Unreachable(); } }

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

@@ -5,7 +5,6 @@
 #nullable disable
 
 using System;
-using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
@@ -1677,11 +1676,13 @@ internal override bool HasSpecialName
                     return true;
                 }
 
-                var data = GetDecodedWellKnownAttributeData();
-                return data != null && data.HasSpecialNameAttribute;
+                return HasSpecialNameAttribute;
             }
         }
 
+        internal sealed override bool HasSpecialNameAttribute =>
+            GetDecodedWellKnownAttributeData()?.HasSpecialNameAttribute == true;
+
         internal sealed override bool IsDirectlyExcludedFromCodeCoverage =>
             GetDecodedWellKnownAttributeData()?.HasExcludeFromCodeCoverageAttribute == true;
 

src/Compilers/CSharp/Portable/Symbols/SubstitutedMethodSymbol.cs

@@ -216,6 +216,8 @@ public override ImmutableArray<CSharpAttributeData> GetReturnTypeAttributes()
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete)
             => this.OriginalDefinition.GetUnmanagedCallersOnlyAttributeData(forceComplete);
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         public sealed override Symbol AssociatedSymbol
         {
             get

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedEntryPointSymbol.cs

@@ -205,6 +205,8 @@ internal sealed override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override Cci.CallingConvention CallingConvention
         {
             get { return 0; }

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedGlobalMethodSymbol.cs

@@ -145,6 +145,8 @@ internal sealed override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal sealed override ImmutableArray<string> GetAppliedConditionalSymbols()
         {
             return ImmutableArray<string>.Empty;

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedIntrinsicOperatorSymbol.cs

@@ -408,6 +408,8 @@ internal override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree)
         {
             throw ExceptionUtilities.Unreachable();

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedMethodSymbol.cs

@@ -72,6 +72,8 @@ internal sealed override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree localTree)
         {
             throw ExceptionUtilities.Unreachable();

src/Compilers/CSharp/Portable/Symbols/Synthesized/SynthesizedStaticConstructor.cs

@@ -367,6 +367,8 @@ internal sealed override ObsoleteAttributeData? ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData? GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => null;
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override ImmutableArray<string> GetAppliedConditionalSymbols()
         {
             return ImmutableArray<string>.Empty;

src/Compilers/CSharp/Test/Emit3/Semantics/ExtensionTests.cs

@@ -2122,7 +2122,7 @@ public static class Extensions
 
         VerifyTypeIL(verifier, "Extensions", """
 .class public auto ansi abstract sealed beforefieldinit Extensions
-extends [netstandard]System.Object
+    extends [netstandard]System.Object
 {
     .custom instance void [netstandard]System.Runtime.CompilerServices.ExtensionAttribute::.ctor() = (
         01 00 00 00
@@ -2132,10 +2132,10 @@ .class nested public auto ansi sealed specialname beforefieldinit '<>E__0'
         extends [netstandard]System.Object
     {
         // Methods
-        .method private hidebysig specialname static
+        .method private hidebysig specialname static 
             void '<Extension>$' (
                 object ''
-            ) cil managed
+            ) cil managed 
         {
             .custom instance void [netstandard]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
                 01 00 00 00
@@ -2145,19 +2145,19 @@ 01 00 00 00
             .maxstack 8
             IL_0000: ret
         } // end of method '<>E__0'::'<Extension>$'
-        .method private hidebysig specialname static
-            int32 get_Property () cil managed
+        .method private hidebysig specialname static 
+            int32 get_Property () cil managed 
         {
             // Method begins at RVA 0x206d
             // Code size 2 (0x2)
             .maxstack 8
             IL_0000: ldnull
             IL_0001: throw
         } // end of method '<>E__0'::get_Property
-        .method private hidebysig specialname static
+        .method private hidebysig specialname static 
             void set_Property (
                 int32 'value'
-            ) cil managed
+            ) cil managed 
         {
             // Method begins at RVA 0x206d
             // Code size 2 (0x2)
@@ -2174,7 +2174,7 @@ .property int32 Property()
     } // end of class <>E__0
     // Methods
     .method private hidebysig static
-        int32 get_Property () cil managed
+        int32 get_Property () cil managed 
     {
         // Method begins at RVA 0x2067
         // Code size 3 (0x3)
@@ -2185,7 +2185,7 @@ .maxstack 8
     .method private hidebysig static
         void set_Property (
             int32 'value'
-        ) cil managed
+        ) cil managed 
     {
         // Method begins at RVA 0x206b
         // Code size 1 (0x1)
@@ -9953,10 +9953,10 @@ .class nested public auto ansi sealed specialname beforefieldinit '<>E__0'
         extends [mscorlib]System.Object
     {
         // Methods
-        .method private hidebysig specialname static
+        .method private hidebysig specialname static 
             void '<Extension>$' (
                 object o
-            ) cil managed
+            ) cil managed 
         {
             .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
                 01 00 00 00
@@ -9966,8 +9966,8 @@ 01 00 00 00
             .maxstack 8
             IL_0000: ret
         } // end of method '<>E__0'::'<Extension>$'
-        .method public hidebysig specialname
-            instance string get_P () cil managed
+        .method public hidebysig specialname 
+            instance string get_P () cil managed 
         {
             // Method begins at RVA 0x2071
             // Code size 2 (0x2)
@@ -9985,7 +9985,7 @@ .property instance string P()
     .method public hidebysig static
         string get_P (
             object o
-        ) cil managed
+        ) cil managed 
     {
         // Method begins at RVA 0x2067
         // Code size 7 (0x7)
@@ -41115,6 +41115,81 @@ .method public hidebysig static void M () cil managed
         Assert.False(comp.GlobalNamespace.GetTypeMember("E").GetTypeMembers().Single().IsExtension);
     }
 
+    [Fact]
+    public void SpecialName_04()
+    {
+        var src = """
+static class E
+{
+    extension(int i)
+    {
+        [System.Runtime.CompilerServices.SpecialName]
+        public void M() => throw null!;
+
+        public void M2() => throw null!;
+
+        [System.Runtime.CompilerServices.SpecialName]
+        public int P => throw null!;
+
+        public int P2 => throw null!;
+    }
+
+    [System.Runtime.CompilerServices.SpecialName]
+    public static void M3() => throw null!;
+}
+""";
+        var comp = CreateCompilation(src);
+        comp.VerifyEmitDiagnostics();
+
+        var extension = comp.GlobalNamespace.GetTypeMember("E").GetTypeMembers().Single();
+        Assert.True(extension.GetMember<MethodSymbol>("M").HasSpecialName);
+        Assert.False(extension.GetMember<MethodSymbol>("M2").HasSpecialName);
+
+        Assert.True(extension.GetMember<PropertySymbol>("P").HasSpecialName);
+        Assert.True(extension.GetMember<MethodSymbol>("get_P").HasSpecialName);
+
+        Assert.False(extension.GetMember<PropertySymbol>("P2").HasSpecialName);
+        Assert.True(extension.GetMember<MethodSymbol>("get_P2").HasSpecialName);
+
+        Assert.True(comp.GetMember<MethodSymbol>("E.M").HasSpecialName);
+        Assert.False(comp.GetMember<MethodSymbol>("E.M2").HasSpecialName);
+        Assert.True(comp.GetMember<MethodSymbol>("E.M3").HasSpecialName);
+
+        Assert.False(comp.GetMember<MethodSymbol>("E.get_P").HasSpecialName);
+
+        Assert.False(comp.GetMember<MethodSymbol>("E.get_P2").HasSpecialName);
+    }
+
+    [Fact]
+    public void SpecialName_05()
+    {
+        var src = """
+static class E
+{
+    extension(int i)
+    {
+        public int P
+        {
+            [System.Runtime.CompilerServices.SpecialName]
+            get => 0;
+            [System.Runtime.CompilerServices.SpecialName]
+            set { }
+        }
+    }
+}
+""";
+        var comp = CreateCompilation(src);
+        comp.VerifyEmitDiagnostics();
+
+        var extension = comp.GlobalNamespace.GetTypeMember("E").GetTypeMembers().Single();
+        Assert.False(extension.GetMember<PropertySymbol>("P").HasSpecialName);
+        Assert.True(extension.GetMember<MethodSymbol>("get_P").HasSpecialName);
+        Assert.True(extension.GetMember<MethodSymbol>("set_P").HasSpecialName);
+
+        Assert.True(comp.GetMember<MethodSymbol>("E.get_P").HasSpecialName);
+        Assert.True(comp.GetMember<MethodSymbol>("E.set_P").HasSpecialName);
+    }
+
     [Fact]
     public void WellKnownAttribute_SkipLocalsInit_01()
     {

src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/Symbols/EECompilationContextMethod.cs

@@ -78,6 +78,8 @@ internal override int CalculateLocalSyntaxOffset(int localPosition, SyntaxTree l
             return _underlyingMethod.GetUnmanagedCallersOnlyAttributeData(forceComplete);
         }
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override bool IsNullableAnalysisEnabled()
         {
             return _underlyingMethod.IsNullableAnalysisEnabled();

src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/Symbols/EEMethodSymbol.cs

@@ -458,6 +458,8 @@ internal override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => throw ExceptionUtilities.Unreachable();
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override bool HasUnscopedRefAttribute => false;
 
         internal override bool UseUpdatedEscapeRules => false;

src/ExpressionEvaluator/CSharp/Source/ExpressionCompiler/Symbols/PlaceholderMethodSymbol.cs

@@ -218,6 +218,8 @@ internal override ObsoleteAttributeData ObsoleteAttributeData
 
         internal sealed override UnmanagedCallersOnlyAttributeData GetUnmanagedCallersOnlyAttributeData(bool forceComplete) => throw ExceptionUtilities.Unreachable();
 
+        internal sealed override bool HasSpecialNameAttribute => throw ExceptionUtilities.Unreachable();
+
         internal override bool HasUnscopedRefAttribute => false;
 
         internal override bool UseUpdatedEscapeRules => false;