Flatten SourceMethodSymbol hierarchy (#76107)

Once upon a time, there were source method symbols that didn't have attributes, and thus we had `SourceMethodSymbol` and `SourceMethodSymbolWithAttributes`, to simplify/save on symbol size for such methods. Today, there is no such difference, and the only direct implementor of `SourceMethodSymbol` is `SourceMethodSymbolWithAttributes`. Therefore, I've cleaned up the hierarchy by removing the dead intermediate class.

Author: 333fred

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

@@ -12,7 +12,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
-    internal sealed class LambdaSymbol : SourceMethodSymbolWithAttributes
+    internal sealed class LambdaSymbol : SourceMethodSymbol
     {
         private readonly Binder _binder;
         private readonly Symbol _containingSymbol;

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

@@ -7,7 +7,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Symbols
 {
-    internal abstract class LocalFunctionOrSourceMemberMethodSymbol : SourceMethodSymbolWithAttributes
+    internal abstract class LocalFunctionOrSourceMemberMethodSymbol : SourceMethodSymbol
     {
         private TypeWithAnnotations.Boxed? _lazyIteratorElementType;
 

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

@@ -79,7 +79,7 @@ protected SourceComplexParameterSymbolBase(
             _lazyDefaultSyntaxValue = ConstantValue.Unset;
         }
 
-        private Binder WithTypeParametersBinderOpt => (ContainingSymbol as SourceMethodSymbolWithAttributes)?.WithTypeParametersBinder;
+        private Binder WithTypeParametersBinderOpt => (ContainingSymbol as SourceMethodSymbol)?.WithTypeParametersBinder;
 
         internal sealed override SyntaxReference SyntaxReference => _syntaxRef;
 

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

@@ -14,7 +14,7 @@ namespace Microsoft.CodeAnalysis.CSharp.Symbols
     /// things like ordinary methods and constructors, and functions
     /// like lambdas and local functions.
     /// </summary>
-    internal abstract class SourceMethodSymbol : MethodSymbol
+    internal abstract partial class SourceMethodSymbol : MethodSymbol
     {
         /// <summary>
         /// If there are no constraints, returns an empty immutable array. Otherwise, returns an immutable

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

@@ -24,14 +24,14 @@ namespace Microsoft.CodeAnalysis.CSharp.Symbols
     /// <summary>
     /// A source method that can have attributes, including a member method, accessor, or local function.
     /// </summary>
-    internal abstract class SourceMethodSymbolWithAttributes : SourceMethodSymbol, IAttributeTargetSymbol
+    internal abstract partial class SourceMethodSymbol : IAttributeTargetSymbol
     {
         private CustomAttributesBag<CSharpAttributeData> _lazyCustomAttributesBag;
         private CustomAttributesBag<CSharpAttributeData> _lazyReturnTypeCustomAttributesBag;
 
         // some symbols may not have a syntax (e.g. lambdas, synthesized event accessors)
         protected readonly SyntaxReference syntaxReferenceOpt;
-        protected SourceMethodSymbolWithAttributes(SyntaxReference syntaxReferenceOpt)
+        protected SourceMethodSymbol(SyntaxReference syntaxReferenceOpt)
         {
             this.syntaxReferenceOpt = syntaxReferenceOpt;
         }
@@ -1106,7 +1106,7 @@ private void DecodeInterceptsLocationChecksumBased(DecodeWellKnownAttributeArgum
             DeclaringCompilation.AddInterception(matchingTree.FilePath, position, attributeLocation, this);
 
             // Caller must free the returned builder.
-            static ArrayBuilder<string> getNamespaceNames(SourceMethodSymbolWithAttributes @this)
+            static ArrayBuilder<string> getNamespaceNames(SourceMethodSymbol @this)
             {
                 var namespaceNames = ArrayBuilder<string>.GetInstance();
                 for (var containingNamespace = @this.ContainingNamespace; containingNamespace?.IsGlobalNamespace == false; containingNamespace = containingNamespace.ContainingNamespace)
@@ -1424,7 +1424,7 @@ static void checkAndReportManagedTypes(TypeSymbol type, RefKind refKind, SyntaxN
                 }
             }
 
-            static UnmanagedCallersOnlyAttributeData DecodeUnmanagedCallersOnlyAttributeData(SourceMethodSymbolWithAttributes @this, CSharpAttributeData attribute, Location location, BindingDiagnosticBag diagnostics)
+            static UnmanagedCallersOnlyAttributeData DecodeUnmanagedCallersOnlyAttributeData(SourceMethodSymbol @this, CSharpAttributeData attribute, Location location, BindingDiagnosticBag diagnostics)
             {
                 Debug.Assert(attribute.AttributeClass is not null);
                 ImmutableHashSet<CodeAnalysis.Symbols.INamedTypeSymbolInternal>? callingConventionTypes = null;

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

@@ -1255,7 +1255,7 @@ private SynthesizedSealedPropertyAccessor MakeSynthesizedSealedAccessor()
 
         /// <summary>
         /// Symbol to copy bound attributes from, or null if the attributes are not shared among multiple source property symbols.
-        /// Analogous to <see cref="SourceMethodSymbolWithAttributes.BoundAttributesSource"/>.
+        /// Analogous to <see cref="SourceMethodSymbol.BoundAttributesSource"/>.
         /// </summary>
         protected abstract SourcePropertySymbolBase BoundAttributesSource { get; }
 

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

@@ -1890,7 +1890,7 @@ static void checkMethodOverride(
                         {
                             if (implementedMethod.HasUnscopedRefAttributeOnMethodOrProperty())
                             {
-                                if (!implementingMethod.IsExplicitInterfaceImplementation && implementingMethod is SourceMethodSymbolWithAttributes &&
+                                if (!implementingMethod.IsExplicitInterfaceImplementation && implementingMethod is SourceMethodSymbol &&
                                     implementedMethod.ContainingModule != implementingMethod.ContainingModule)
                                 {
                                     checkRefStructInterfacesFeatureAvailabilityOnUnscopedRefAttribute(implementingMethod.HasUnscopedRefAttribute ? implementingMethod : implementingMethod.AssociatedSymbol, diagnostics);

src/Compilers/CSharp/Test/Semantic/Semantics/InterceptorsTests.cs

@@ -6876,7 +6876,7 @@ static void Main()
         Assert.Equal(locationSpecifier.GetHashCode(), model.GetInterceptableLocation(node)!.GetHashCode());
 
         // If Data changes it might be the case that 'SourceText.GetContentHash()' has changed algorithms.
-        // In this case we need to adjust the SourceMethodSymbolWithAttributes.DecodeInterceptsLocationAttribute impl to remain compatible with v1 and consider introducing a v2 which uses the new content hash algorithm.
+        // In this case we need to adjust the SourceMethodSymbol.DecodeInterceptsLocationAttribute impl to remain compatible with v1 and consider introducing a v2 which uses the new content hash algorithm.
         AssertEx.Equal("xRCCFCvTOZMORzSr/fZQFlIAAABQcm9ncmFtLmNz", locationSpecifier.Data);
         AssertEx.Equal("""[global::System.Runtime.CompilerServices.InterceptsLocationAttribute(1, "xRCCFCvTOZMORzSr/fZQFlIAAABQcm9ncmFtLmNz")]""", locationSpecifier.GetInterceptsLocationAttributeSyntax());