Add pre-C++11 is_constructible wrappers for 3 arguments

[dim]

Summary

After rL319736 for D28253 (which fixes PR28929), gcc cannot compile <memory> anymore in pre-C+11 modes, complaining:

In file included from /usr/include/c++/v1/memory:648:0,
                 from test.cpp:1:
/usr/include/c++/v1/memory: In static member function 'static std::__1::shared_ptr<_Tp> std::__1::shared_ptr<_Tp>::make_shared(_A0&, _A1&, _A2&)':
/usr/include/c++/v1/memory:4365:5: error: wrong number of template arguments (4, should be at least 1)
     static_assert((is_constructible<_Tp, _A0, _A1, _A2>::value), "Can't construct object in make_shared" );
     ^
In file included from /usr/include/c++/v1/memory:649:0,
                 from test.cpp:1:
/usr/include/c++/v1/type_traits:3198:29: note: provided for 'template<class _Tp, class _A0, class _A1> struct std::__1::is_constructible'
 struct _LIBCPP_TEMPLATE_VIS is_constructible
                             ^~~~~~~~~~~~~~~~
In file included from /usr/include/c++/v1/memory:648:0,
                 from test.cpp:1:
/usr/include/c++/v1/memory:4365:5: error: template argument 1 is invalid
     static_assert((is_constructible<_Tp, _A0, _A1, _A2>::value), "Can't construct object in make_shared" );
     ^
/usr/include/c++/v1/memory: In static member function 'static std::__1::shared_ptr<_Tp> std::__1::shared_ptr<_Tp>::allocate_shared(const _Alloc&, _A0&, _A1&, _A2&)':
/usr/include/c++/v1/memory:4444:5: error: wrong number of template arguments (4, should be at least 1)
     static_assert((is_constructible<_Tp, _A0, _A1, _A2>::value), "Can't construct object in allocate_shared" );
     ^
In file included from /usr/include/c++/v1/memory:649:0,
                 from test.cpp:1:
/usr/include/c++/v1/type_traits:3198:29: note: provided for 'template<class _Tp, class _A0, class _A1> struct std::__1::is_constructible'
 struct _LIBCPP_TEMPLATE_VIS is_constructible
                             ^~~~~~~~~~~~~~~~
In file included from /usr/include/c++/v1/memory:648:0,
                 from test.cpp:1:
/usr/include/c++/v1/memory:4444:5: error: template argument 1 is invalid
     static_assert((is_constructible<_Tp, _A0, _A1, _A2>::value), "Can't construct object in allocate_shared" );
     ^

This is also reported in https://bugs.freebsd.org/224946 (FreeBSD is apparently one of the very few projects that regularly builds programs against libc++ with gcc).

The reason is that the static assertions are invoking is_constructible with three arguments, while gcc does not have the built-in is_constructible feature, and the pre-C++11 is_constructible wrappers in <type_traits> only provide up to two arguments.

I have added additional wrappers for three arguments, modified the is_constructible entry point to take three arguments instead, and added a simple test to is_constructible.pass.cpp.

[EricWF]

LGTM.

include/type_traits

 template <class _Tp, class _A0, class _A1>
 decltype((_Tp(_VSTD::declval<_A0>(), _VSTD::declval<_A1>()), true_type()))
 __is_constructible2_test(_Tp&, _A0&, _A1&);
 
 template <class _A0, class _A1>
 false_type
 __is_constructible2_test(__any, _A0&, _A1&);
 
+template <class _Tp, class _A0, class _A1, class _A2>
+decltype((_Tp(_VSTD::declval<_A0>(), _VSTD::declval<_A1>(), _VSTD::declval<_A2>()), true_type()))
+__is_constructible3_test(_Tp&, _A0&, _A1&, _A2&);
+
+template <class _A0, class _A1, class _A2>
+false_type
+__is_constructible3_test(__any, _A0&, _A1&, _A2&);
+
 template <bool, class _Tp>
 struct __is_constructible0_imp // false, _Tp is not a scalar
     : public common_type
              <
                  decltype(__is_constructible0_test(declval<_Tp&>()))
              >::type
     {};
 
 template <bool, class _Tp, class _A0>
 struct __is_constructible1_imp // false, _Tp is not a scalar
     : public common_type
              <
                  decltype(__is_constructible1_test(declval<_Tp&>(), declval<_A0&>()))
              >::type
     {};
 
 template <bool, class _Tp, class _A0, class _A1>
 struct __is_constructible2_imp // false, _Tp is not a scalar
     : public common_type
              <
                  decltype(__is_constructible2_test(declval<_Tp&>(), declval<_A0>(), declval<_A1>()))
              >::type
     {};
 
+template <bool, class _Tp, class _A0, class _A1, class _A2>
+struct __is_constructible3_imp // false, _Tp is not a scalar
+    : public common_type
+             <
+                 decltype(__is_constructible3_test(declval<_Tp&>(), declval<_A0>(), declval<_A1>(), declval<_A2>()))
+             >::type
+    {};
+
 //      handle scalars and reference types
 
 //      Scalars are default constructible, references are not
 
 template <class _Tp>
 struct __is_constructible0_imp<true, _Tp>
     : public is_scalar<_Tp>
     {};
 
 template <class _Tp, class _A0>
 struct __is_constructible1_imp<true, _Tp, _A0>
     : public is_convertible<_A0, _Tp>
     {};
 
 template <class _Tp, class _A0, class _A1>
 struct __is_constructible2_imp<true, _Tp, _A0, _A1>
     : public false_type
     {};
 
+template <class _Tp, class _A0, class _A1, class _A2>
+struct __is_constructible3_imp<true, _Tp, _A0, _A1, _A2>
+    : public false_type
+    {};
+
 //      Treat scalars and reference types separately
 
 template <bool, class _Tp>
 struct __is_constructible0_void_check
     : public __is_constructible0_imp<is_scalar<_Tp>::value || is_reference<_Tp>::value,
                                 _Tp>
     {};
 
 template <bool, class _Tp, class _A0>
 struct __is_constructible1_void_check
     : public __is_constructible1_imp<is_scalar<_Tp>::value || is_reference<_Tp>::value,
                                 _Tp, _A0>
     {};
 
 template <bool, class _Tp, class _A0, class _A1>
 struct __is_constructible2_void_check
     : public __is_constructible2_imp<is_scalar<_Tp>::value || is_reference<_Tp>::value,
                                 _Tp, _A0, _A1>
     {};
 
+template <bool, class _Tp, class _A0, class _A1, class _A2>
+struct __is_constructible3_void_check
+    : public __is_constructible3_imp<is_scalar<_Tp>::value || is_reference<_Tp>::value,
+                                _Tp, _A0, _A1, _A2>
+    {};
+
 //      If any of T or Args is void, is_constructible should be false
 
 template <class _Tp>
 struct __is_constructible0_void_check<true, _Tp>
     : public false_type
     {};
 
 template <class _Tp, class _A0>
 struct __is_constructible1_void_check<true, _Tp, _A0>
     : public false_type
     {};
 
 template <class _Tp, class _A0, class _A1>
 struct __is_constructible2_void_check<true, _Tp, _A0, _A1>
     : public false_type
     {};
 
+template <class _Tp, class _A0, class _A1, class _A2>
+struct __is_constructible3_void_check<true, _Tp, _A0, _A1, _A2>
+    : public false_type
+    {};
+
 //      is_constructible entry point
 
 template <class _Tp, class _A0 = __is_construct::__nat,
-                     class _A1 = __is_construct::__nat>
+                     class _A1 = __is_construct::__nat,
+                     class _A2 = __is_construct::__nat>
 struct _LIBCPP_TEMPLATE_VIS is_constructible
-    : public __is_constructible2_void_check<is_void<_Tp>::value
+    : public __is_constructible3_void_check<is_void<_Tp>::value
                                         || is_abstract<_Tp>::value
                                         || is_function<_Tp>::value
                                         || is_void<_A0>::value
-                                        || is_void<_A1>::value,
-                                           _Tp, _A0, _A1>
+                                        || is_void<_A1>::value
+                                        || is_void<_A2>::value,
+                                           _Tp, _A0, _A1, _A2>
     {};
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_constructible<_Tp, __is_construct::__nat, __is_construct::__nat>
     : public __is_constructible0_void_check<is_void<_Tp>::value
                                         || is_abstract<_Tp>::value
                                         || is_function<_Tp>::value,
                                            _Tp>
     {};
 
 template <class _Tp, class _A0>
 struct _LIBCPP_TEMPLATE_VIS is_constructible<_Tp, _A0, __is_construct::__nat>
     : public __is_constructible1_void_check<is_void<_Tp>::value
                                         || is_abstract<_Tp>::value
                                         || is_function<_Tp>::value
                                         || is_void<_A0>::value,
                                            _Tp, _A0>
     {};
 
+template <class _Tp, class _A0, class _A1>
+struct _LIBCPP_TEMPLATE_VIS is_constructible<_Tp, _A0, _A1, __is_construct::__nat>
+    : public __is_constructible2_void_check<is_void<_Tp>::value
+                                        || is_abstract<_Tp>::value
+                                        || is_function<_Tp>::value
+                                        || is_void<_A0>::value
+                                        || is_void<_A1>::value,
+                                           _Tp, _A0, _A1>
+    {};
+
 //      Array types are default constructible if their element type
 //      is default constructible
 
 template <class _Ap, size_t _Np>
 struct __is_constructible0_imp<false, _Ap[_Np]>
     : public is_constructible<typename remove_all_extents<_Ap>::type>
     {};
 
 template <class _Ap, size_t _Np, class _A0>
 struct __is_constructible1_imp<false, _Ap[_Np], _A0>
     : public false_type
     {};
 
 template <class _Ap, size_t _Np, class _A0, class _A1>
 struct __is_constructible2_imp<false, _Ap[_Np], _A0, _A1>
     : public false_type
     {};
 
+template <class _Ap, size_t _Np, class _A0, class _A1, class _A2>
+struct __is_constructible3_imp<false, _Ap[_Np], _A0, _A1, _A2>
+    : public false_type
+    {};
+
 //      Incomplete array types are not constructible
 
 template <class _Ap>
 struct __is_constructible0_imp<false, _Ap[]>
     : public false_type
     {};
 
 template <class _Ap, class _A0>
 struct __is_constructible1_imp<false, _Ap[], _A0>
     : public false_type
     {};
 
 template <class _Ap, class _A0, class _A1>
 struct __is_constructible2_imp<false, _Ap[], _A0, _A1>
     : public false_type
     {};
 
+template <class _Ap, class _A0, class _A1, class _A2>
+struct __is_constructible3_imp<false, _Ap[], _A0, _A1, _A2>
+    : public false_type
+    {};
+
 #endif // __has_feature(is_constructible)
 
 
 #if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES) && !defined(_LIBCPP_HAS_NO_VARIADICS)
 template <class _Tp, class ..._Args>
 _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_constructible_v
     = is_constructible<_Tp, _Args...>::value;
 #endif

test/std/utilities/meta/meta.unary/meta.unary.prop/is_constructible.pass.cpp

 #define LIBCPP11_STATIC_ASSERT(...) ((void)0)
 #endif
 
 
 struct A
 {
     explicit A(int);
     A(int, double);
+    A(int, long, double);
 #if TEST_STD_VER >= 11
 private:
 #endif
     A(char);
 };
 
 struct Base {};
 struct Derived : public Base {};

 {
     static_assert(( std::is_constructible<T, A0, A1>::value), "");
     LIBCPP11_STATIC_ASSERT((std::__libcpp_is_constructible<T, A0, A1>::type::value), "");
 #if TEST_STD_VER > 14
     static_assert(( std::is_constructible_v<T, A0, A1>), "");
 #endif
 }
 
+template <class T, class A0, class A1, class A2>
+void test_is_constructible()
+{
+    static_assert(( std::is_constructible<T, A0, A1, A2>::value), "");
+    LIBCPP11_STATIC_ASSERT((std::__libcpp_is_constructible<T, A0, A1, A2>::type::value), "");
+#if TEST_STD_VER > 14
+    static_assert(( std::is_constructible_v<T, A0, A1, A2>), "");
+#endif
+}
+
 template <class T>
 void test_is_not_constructible()
 {
     static_assert((!std::is_constructible<T>::value), "");
     LIBCPP11_STATIC_ASSERT((!std::__libcpp_is_constructible<T>::type::value), "");
 #if TEST_STD_VER > 14
     static_assert((!std::is_constructible_v<T>), "");
 #endif

 {
     typedef Base B;
     typedef Derived D;
 
     test_is_constructible<int> ();
     test_is_constructible<int, const int> ();
     test_is_constructible<A, int> ();
     test_is_constructible<A, int, double> ();
+    test_is_constructible<A, int, long, double> ();
     test_is_constructible<int&, int&> ();
 
     test_is_not_constructible<A> ();
 #if TEST_STD_VER >= 11
     test_is_not_constructible<A, char> ();
 #else
     test_is_constructible<A, char> ();
 #endif