llvm-project/clang/test/SemaCXX/libstdcxx_is_pod_hack.cpp

// RUN: %clang_cc1 -fsyntax-only %s

// This is a test for an egregious hack in Clang that works around
// issues with GCC's evolution. libstdc++ 4.2.x uses __is_pod as an
// identifier (to declare a struct template like the one below), while
// GCC 4.3 and newer make __is_pod a keyword. Clang treats __is_pod as
// a keyword *unless* it is introduced following the struct keyword.

template<typename T>
struct __is_pod {
  __is_pod() {}
};

__is_pod<int> ipi;

// Ditto for __is_same.
template<typename T>
struct __is_same {
};

__is_same<int> isi;

// Another, similar egregious hack for __is_signed, which is a type
// trait in Embarcadero's compiler but is used as an identifier in
// libstdc++.
struct test_is_signed {
  static const bool __is_signed = true;
};

bool check_signed = test_is_signed::__is_signed;

template<bool B> struct must_be_true {};
template<> struct must_be_true<false>;

void foo() {
  bool b = __is_pod(int);
  must_be_true<__is_pod(int)> mbt;
}
#if !__has_feature(is_pod)
#  error __is_pod should still be available.
#endif