llvm-project/clang/test/SemaCXX/linkage-spec.cpp

// RUN: clang -fsyntax-only -verify %s
extern "C" {
  extern "C" void f(int);
}

extern "C++" {
  extern "C++" int& g(int);
  float& g();
}
double& g(double);

void test(int x, double d) {
  f(x);
  float &f1 = g();
  int& i1 = g(x);
  double& d1 = g(d);
}