PR feedback and followup on merge from main

Author: AlekseyTs

src/Compilers/CSharp/Portable/Binder/BinderFactory.BinderFactoryVisitor.cs

@@ -198,6 +198,9 @@ private static Binder WithExtensionReceiverParameterBinderIfNecessary(Binder res
             {
                 if (method is { IsStatic: false, ContainingType: SourceNamedTypeSymbol { IsExtension: true, ExtensionParameter: { } parameter } })
                 {
+                    // PROTOTYPE: Depending on whether we consider method parameters and receiver parameter in the same scope and
+                    //            what are the name conflict/shadowing rules, we might consider to adjust behavior of InMethodBinder instead.
+                    //            If we decide to keep usage of WithParametersBinder, we might want to update XML doc comment for it.
                     return new WithParametersBinder([parameter], resultBinder);
                 }
 

src/Compilers/CSharp/Portable/Lowering/ExtensionMethodBodyRewriter.cs

@@ -39,6 +39,7 @@ public ExtensionMethodBodyRewriter(MethodSymbol sourceMethod, SourceExtensionImp
             bool haveExtraParameter = sourceMethod.ParameterCount != implementationMethod.ParameterCount;
             if (haveExtraParameter)
             {
+                Debug.Assert(implementationMethod.ParameterCount - 1 == sourceMethod.ParameterCount);
                 var receiverParameter = (WrappedParameterSymbol)implementationMethod.Parameters[0];
                 _symbolMap = _symbolMap.Add(receiverParameter.UnderlyingParameter, receiverParameter);
             }

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

@@ -3614,7 +3614,7 @@ private void AddSynthesizedExtensionImplementationsIfNecessary(MembersAndInitial
                     {
                         if (member is MethodSymbol { IsImplicitlyDeclared: false } method)
                         {
-                            builder.AddNonTypeMember(new SourceExtensionImplementationMethodSymbol(method), declaredMembersAndInitializers);
+                            builder.AddNonTypeMember(this, new SourceExtensionImplementationMethodSymbol(method), declaredMembersAndInitializers);
                         }
                     }
                 }