test/SemaCXX/attr-lifetimebound.cpp

// RUN: %clang_cc1 -std=c++2a -verify %s

namespace usage_invalid {
  // FIXME: Should we diagnose a void return type?
  void voidreturn(int &param [[clang::lifetimebound]]);

  int *not_class_member() [[clang::lifetimebound]]; // expected-error {{non-member function has no implicit object parameter}}
  struct A {
    A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a constructor}}
    ~A() [[clang::lifetimebound]]; // expected-error {{cannot be applied to a destructor}}
    static int *static_class_member() [[clang::lifetimebound]]; // expected-error {{static member function has no implicit object parameter}}
    int not_function [[clang::lifetimebound]]; // expected-error {{only applies to parameters and implicit object parameters}}
    int [[clang::lifetimebound]] also_not_function; // expected-error {{cannot be applied to types}}
  };
  int *attr_with_param(int &param [[clang::lifetimebound(42)]]); // expected-error {{takes no arguments}}
}

namespace usage_ok {
  struct IntRef { int *target; };

  int &refparam(int &param [[clang::lifetimebound]]);
  int &classparam(IntRef param [[clang::lifetimebound]]);

  // Do not diagnose non-void return types; they can still be lifetime-bound.
  long long ptrintcast(int &param [[clang::lifetimebound]]) {
    return (long long)&param;
  }
  // Likewise.
  int &intptrcast(long long param [[clang::lifetimebound]]) {
    return *(int*)param;
  }

  struct A {
    A();
    A(int);
    int *class_member() [[clang::lifetimebound]];
    operator int*() [[clang::lifetimebound]];
  };

  int *p = A().class_member(); // expected-warning {{temporary whose address is used as value of local variable 'p' will be destroyed at the end of the full-expression}}
  int *q = A(); // expected-warning {{temporary whose address is used as value of local variable 'q' will be destroyed at the end of the full-expression}}
  int *r = A(1); // expected-warning {{temporary whose address is used as value of local variable 'r' will be destroyed at the end of the full-expression}}
}

# 1 "<std>" 1 3
namespace std {
  using size_t = __SIZE_TYPE__;
  struct string {
    string();
    string(const char*);

    char &operator[](size_t) const [[clang::lifetimebound]];
  };
  string operator""s(const char *, size_t);

  struct string_view {
    string_view();
    string_view(const char *p [[clang::lifetimebound]]);
    string_view(const string &s [[clang::lifetimebound]]);
  };
  string_view operator""sv(const char *, size_t);

  struct vector {
    int *data();
    size_t size();
  };

  template<typename K, typename V> struct map {};
}
# 68 "attr-lifetimebound.cpp" 2

using std::operator""s;
using std::operator""sv;

namespace p0936r0_examples {
  std::string_view s = "foo"s; // expected-warning {{temporary}}

  std::string operator+(std::string_view s1, std::string_view s2);
  void f() {
    std::string_view sv = "hi";
    std::string_view sv2 = sv + sv; // expected-warning {{temporary}}
    sv2 = sv + sv; // FIXME: can we infer that we should warn here too?
  }

  struct X { int a, b; };
  const int &f(const X &x [[clang::lifetimebound]]) { return x.a; }
  const int &r = f(X()); // expected-warning {{temporary}}

  char &c = std::string("hello my pretty long strong")[0]; // expected-warning {{temporary}}

  struct reversed_range {
    int *begin();
    int *end();
    int *p;
    std::size_t n;
  };
  template <typename R> reversed_range reversed(R &&r [[clang::lifetimebound]]) {
    return reversed_range{r.data(), r.size()};
  }

  std::vector make_vector();
  void use_reversed_range() {
    // FIXME: Don't expose the name of the internal range variable.
    for (auto x : reversed(make_vector())) {} // expected-warning {{temporary implicitly bound to local reference will be destroyed at the end of the full-expression}}
  }

  template <typename K, typename V>
  const V &findOrDefault(const std::map<K, V> &m [[clang::lifetimebound]],
                         const K &key,
                         const V &defvalue [[clang::lifetimebound]]);

  // FIXME: Maybe weaken the wording here: "local reference 'v' could bind to temporary that will be destroyed at end of full-expression"?
  std::map<std::string, std::string> m;
  const std::string &v = findOrDefault(m, "foo"s, "bar"s); // expected-warning {{temporary bound to local reference 'v'}}
}

// definitions for std::move, std::forward et al.
namespace std {
inline namespace foo {

template <class T> struct remove_reference {
    typedef T type;
};
template <class T> struct remove_reference<T &> {
    typedef T type;
};
template <class T> struct remove_reference<T &&> {
    typedef T type;
};

template <class T> constexpr typename remove_reference<T>::type &&move(T &&t) {
    return static_cast<typename remove_reference<T>::type>(t);
}

template <class T>
constexpr T &&forward(typename remove_reference<T>::type &t) {
    return static_cast<T &&>(t);
}

template <class T>
constexpr T &&forward(typename remove_reference<T>::type &&t) {
    return static_cast<T &&>(t);
}

template <class T> constexpr const T &as_const(T &x) { return x; }

template <class T, bool RValueRef> struct PickRef {
    using type = typename remove_reference<T>::type &;
};
template <class T> struct PickRef<T, true> {
    using type = typename remove_reference<T>::type &&;
};

template <class T> struct is_lvalue_reference {
    static constexpr bool value = false;
};

template <class T> struct is_lvalue_reference<T &> {
    static constexpr bool value = true;
};

template <class T> struct is_const {
    static constexpr bool value = false;
};

template <class T> struct is_const<const T> {
    static constexpr bool value = true;
};

template <bool B, class T, class F> struct conditional {
    using type = T;
};

template <class T, class F> struct conditional<false, T, F> {
    using type = F;
};

template <class U, class T>
using CopyConst = typename conditional<is_const<remove_reference<U>>::value,
                                       const T, T>::type;

template <class U, class T>
using OverrideRef =
    typename conditional<is_lvalue_reference<U &&>::value,
                         typename remove_reference<T>::type &,
                         typename remove_reference<T>::type &&>::type;

template <class U, class T>
using ForwardLikeRetType = OverrideRef<U &&, CopyConst<U, T>>;

template <class U>
constexpr auto forward_like(auto &&t) -> ForwardLikeRetType<U, decltype(t)> {
    return static_cast<ForwardLikeRetType<U, decltype(t)>>(t);
}

template <class T>
auto move_if_noexcept(T &t) ->
    typename PickRef<T, noexcept(T(static_cast<T &&>(t)))>::type {
    return static_cast<
        typename PickRef<T, noexcept(T(static_cast<T &&>(t)))>::type>(t);
}

template <class T> T *addressof(T &arg) {
    return reinterpret_cast<T *>(
        &const_cast<char &>(reinterpret_cast<const volatile char &>(arg)));
}

} // namespace foo
} // namespace std

namespace move_forward_et_al_examples {
  struct S {
    S &self() [[clang::lifetimebound]] { return *this; }
  };

  S &&Move = std::move(S{}); // expected-warning {{temporary bound to local reference 'Move' will be destroyed at the end of the full-expression}}
  S MoveOk = std::move(S{});

  S &&Forward = std::forward<S &&>(S{}); // expected-warning {{temporary bound to local reference 'Forward' will be destroyed at the end of the full-expression}}
  S ForwardOk = std::forward<S &&>(S{});

  S &&ForwardLike = std::forward_like<int&&>(S{}); // expected-warning {{temporary bound to local reference 'ForwardLike' will be destroyed at the end of the full-expression}}
  S ForwardLikeOk = std::forward_like<int&&>(S{});

  const S &Const = std::as_const(S{}.self()); // expected-warning {{temporary bound to local reference 'Const' will be destroyed at the end of the full-expression}}
  const S ConstOk = std::as_const(S{}.self());

  S &&MoveIfNoExcept = std::move_if_noexcept(S{}.self()); // expected-warning {{temporary bound to local reference 'MoveIfNoExcept' will be destroyed at the end of the full-expression}}
  S MoveIfNoExceptOk = std::move_if_noexcept(S{}.self());

  S *AddressOf = std::addressof(S{}.self()); // expected-warning {{temporary whose address is used as value of local variable 'AddressOf' will be destroyed at the end of the full-expression}}
  S X;
  S *AddressOfOk = std::addressof(X);
} // namespace move_forward_et_al_examples