[Clang] Bug with lookup

[elizabethandrews]

The following code compiles with GCC and MSVC but fails with clang

namespace a {
template <typename> class b {
  public:
  typedef int string_type;
  operator string_type();
};
} // namespace a
template <class> void c() {
    &a::b<char>::operator string_type; 
}

Godbolt - https://godbolt.org/z/sWs8rvq98

Clang accepts the code if string_type is qualified - https://godbolt.org/z/efPd9d8Gz . Based on examples in http://eel.is/c++draft/basic.lookup#unqual-5, I think the lookup should succeed without qualification as well.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (elizabethandrews)

The following code compiles with GCC and MSVC but fails with clang

namespace a {
template <typename> class b {
  public:
  typedef int string_type;
  operator string_type();
};
} // namespace a
template <class> void c() {
    &a::b<char>::operator string_type; 
}

Godbolt - https://godbolt.org/z/sWs8rvq98

Clang accepts the code if string_type is qualified - https://godbolt.org/z/efPd9d8Gz . Based on examples in http://eel.is/c++draft/basic.lookup#unqual-5, I think the lookup should succeed without qualification as well.

[cor3ntin]

@sdkrystian @Endilll