How do I use Clang's attribute `preferred_name`?

Clang has a non-standard attribute preferred_name that is used e.g. in libc++ to spell std::basic_string<char> as std::string (which is more user-friendly).

I'm trying to use it for my own types, but it doesn't seem to work: https://gcc.godbolt.org/z/re4af1Pej

#include <iostream>#include <string>template <typename T>void foo(){    std::cout << __PRETTY_FUNCTION__ << '\n';}template<typename T> struct my_basic_string;using my_string = my_basic_string<char>;template<typename T> struct __attribute__((__preferred_name__(my_string))) my_basic_string;int main(){    foo<std::string>(); // std::string    foo<my_string>(); // my_basic_string<char>   -- But why not `my_string`?!}

Note that this must be tested on Clang, with -stdlib=libc++ (libstdc++ doesn't have this annotation, and prints std::basic_string<char> instead of std::string).

Am I getting the syntax wrong? I believe I'm doing the same thing as libc++ does: [1], [2].