clang/test/PCH/cxx-friends.h

// Header for PCH test cxx-friends.cpp

class A {
  int x;
  friend class F;
};

namespace PR12585 {
  struct future_base {
    template<typename> class setter;
  };
  template<typename> class promise {
    // We used to inject this into future_base with no access specifier,
    // then crash during AST writing.
    template<typename> friend class future_base::setter;
    int k;
  };
}