RSRP-284873: error BC36558: The custom-designed version of 'System.Runtime.CompilerServices.ExtensionAttribute' found by the compiler is not valid. Its attribute usage flags must be set to allow assemblies, classes, and methods.

Option Strict On

Imports System.Runtime.CompilerServices

Namespace System.Runtime.CompilerServices
  <AttributeUsageAttribute(AttributeTargets.Method)>
  Class ExtensionAttribute : Inherits Attribute
  End Class

End Namespace

Module M
  <Extension()> 
  Sub Foo(ByVal x As Object)
  End Sub
End Module