[libcxx] Fix detection of __is_final.

[EricWF]

Summary

Currently we only enable the use of is_final(...) with Clang. GCC also provides is_final(...) since 4.7 in all standard modes. This patch creates the macro _LIBCPP_HAS_IS_FINAL to note the availability of __is_final.

[EricWF]

Ping. Libc++ can't be used with GCC until this lands.

[EricWF]

Change all occurrences of __is_final(Tp) to use is_final<Tp>::value.

Perhaps we should use _LIBCPP_HAS_NO_IS_FINAL instead of _LIBCPP_HAS_IS_FINAL?

[EricWF]

Only expose is_tuple in C++14 and beyond. Create and internally use __libcpp_is_final in all other standard modes.

[mclow.lists]

What do you think of making __libcpp_is_final be false when we don't have __is_final.

Then the #if in unordered_map, memory, map, etc. can be removed.

[EricWF]

Address @mclow.list's review comments. Default __libcpp_is_final to false when we don't have the intrinsics and remove the preprocessor blocks around its usage.

[EricWF]

Any more comments on this patch?

[mclow.lists]

LGTM.

include/__config

 #ifdef _WIN32
 #  define _LIBCPP_LITTLE_ENDIAN 1
 #  define _LIBCPP_BIG_ENDIAN    0
-// Compiler intrinsics (GCC or MSVC)
-#  if defined(__clang__) \
-   || (defined(_MSC_VER) && _MSC_VER >= 1400) \
-   || (defined(__GNUC__) && _GNUC_VER > 403)
+// Compiler intrinsics (MSVC)
+#if defined(_MSC_VER) && _MSC_VER >= 1400
 #    define _LIBCPP_HAS_IS_BASE_OF
 #  endif
 #  if defined(_MSC_VER) && !defined(__clang__)

 #  endif
 #endif  // _WIN32
 
-#ifdef __linux__
-#  if defined(__GNUC__) && _GNUC_VER >= 403
-#    define _LIBCPP_HAS_IS_BASE_OF
-#  endif
-#endif
-
 #ifdef __sun__
 # include <sys/isa_defs.h>
 # ifdef _LITTLE_ENDIAN

 #  define _LIBCPP_HAS_IS_BASE_OF
 #endif
 
+#if __has_feature(is_final)
+#  define _LIBCPP_HAS_IS_FINAL
+#endif
+
 // Objective-C++ features (opt-in)
 #if __has_feature(objc_arc)
 #define _LIBCPP_HAS_OBJC_ARC

 #if _GNUC_VER >= 407
 #define _LIBCPP_UNDERLYING_TYPE(T) __underlying_type(T)
 #define _LIBCPP_IS_LITERAL(T) __is_literal_type(T)
+#define _LIBCPP_HAS_IS_FINAL
+#endif
+
+#if defined(__GNUC__) && _GNUC_VER >= 403
+#  define _LIBCPP_HAS_IS_BASE_OF
 #endif
 
 #if !__EXCEPTIONS

 #define _LIBCPP_HAS_NO_NULLPTR
 #define _LIBCPP_HAS_NO_UNICODE_CHARS
 #define _LIBCPP_HAS_IS_BASE_OF
+#define _LIBCPP_HAS_IS_FINAL
 #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
 
 #if defined(_AIX)

include/exception

 throw_with_nested(_Tp&& __t, typename enable_if<
                   is_class<typename remove_reference<_Tp>::type>::value &&
                   !is_base_of<nested_exception, typename remove_reference<_Tp>::type>::value
-#if _LIBCPP_STD_VER > 11 && __has_feature(is_final)
-                  && !is_final<typename remove_reference<_Tp>::type>::value
-#endif
+                  && !__libcpp_is_final<typename remove_reference<_Tp>::type>::value
                                     >::type* = 0)
 #else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 throw_with_nested (_Tp& __t, typename enable_if<

 throw_with_nested(_Tp&& __t, typename enable_if<
                   !is_class<typename remove_reference<_Tp>::type>::value ||
                   is_base_of<nested_exception, typename remove_reference<_Tp>::type>::value
-#if _LIBCPP_STD_VER > 11 && __has_feature(is_final)
-                  || is_final<typename remove_reference<_Tp>::type>::value
-#endif
+                  || __libcpp_is_final<typename remove_reference<_Tp>::type>::value
                                     >::type* = 0)
 #else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 throw_with_nested (_Tp& __t, typename enable_if<

include/ext/hash_map

 #include <__hash_table>
 #include <functional>
 #include <stdexcept>
+#include <type_traits>
 #include <ext/__hash>
 
 #if __DEPRECATED

 #endif
 #endif
 
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
+#endif
 
 namespace __gnu_cxx {
 
 using namespace std;
 
-template <class _Tp, class _Hash, bool = is_empty<_Hash>::value
-#if __has_feature(is_final)
-                                         && !__is_final(_Hash)
-#endif
+template <class _Tp, class _Hash,
+          bool = is_empty<_Hash>::value && !__libcpp_is_final<_Hash>::value
         >
 class __hash_map_hasher
     : private _Hash

         {return __hash_(__x);}
 };
 
-template <class _Tp, class _Pred, bool = is_empty<_Pred>::value
-#if __has_feature(is_final)
-                                         && !__is_final(_Pred)
-#endif
+template <class _Tp, class _Pred,
+          bool = is_empty<_Pred>::value && !__libcpp_is_final<_Pred>::value
          >
 class __hash_map_equal
     : private _Pred

include/map

 #include <utility>
 #include <functional>
 #include <initializer_list>
+#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header

 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Key, class _CP, class _Compare, bool = is_empty<_Compare>::value
-#if __has_feature(is_final)
-                                                        && !__is_final(_Compare)
-#endif
+template <class _Key, class _CP, class _Compare,
+          bool = is_empty<_Compare>::value && !__libcpp_is_final<_Compare>::value
          >
 class __map_value_compare
     : private _Compare

include/memory

 template <class _T1, class _T2, bool = is_same<typename remove_cv<_T1>::type,
                                                      typename remove_cv<_T2>::type>::value,
                                 bool = is_empty<_T1>::value
-#if __has_feature(is_final)
-                                       && !__is_final(_T1)
-#endif
-                                ,
+                                       && !__libcpp_is_final<_T1>::value,
                                 bool = is_empty<_T2>::value
-#if __has_feature(is_final)
-                                       && !__is_final(_T2)
-#endif
+                                       && !__libcpp_is_final<_T2>::value
          >
 struct __libcpp_compressed_pair_switch;
 

include/tuple

 
 // __tuple_leaf
 
-template <size_t _Ip, class _Hp, bool=is_empty<_Hp>::value
-#if __has_feature(is_final)
-                                 && !__is_final(_Hp)
-#endif
+template <size_t _Ip, class _Hp,
+          bool=is_empty<_Hp>::value && !__libcpp_is_final<_Hp>::value
          >
 class __tuple_leaf;
 

include/type_traits

 
 // is_final
 
-#if _LIBCPP_STD_VER > 11 && __has_feature(is_final)
-template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY 
+#if defined(_LIBCPP_HAS_IS_FINAL)
+template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
+__libcpp_is_final : public integral_constant<bool, __is_final(_Tp)> {};
+#else
+template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
+__libcpp_is_final : public false_type {};
+#endif
+
+#if defined(_LIBCPP_HAS_IS_FINAL) && _LIBCPP_STD_VER > 11
+template <class _Tp> struct _LIBCPP_TYPE_VIS_ONLY
 is_final : public integral_constant<bool, __is_final(_Tp)> {};
 #endif
 

include/unordered_map

 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Key, class _Cp, class _Hash, bool = is_empty<_Hash>::value
-#if __has_feature(is_final)
-                                         && !__is_final(_Hash)
-#endif
+template <class _Key, class _Cp, class _Hash,
+          bool = is_empty<_Hash>::value && !__libcpp_is_final<_Hash>::value
          >
 class __unordered_map_hasher
     : private _Hash

         {return __hash_(__x);}
 };
 
-template <class _Key, class _Cp, class _Pred, bool = is_empty<_Pred>::value
-#if __has_feature(is_final)
-                                         && !__is_final(_Pred)
-#endif
+template <class _Key, class _Cp, class _Pred,
+          bool = is_empty<_Pred>::value && !__libcpp_is_final<_Pred>::value
          >
 class __unordered_map_equal
     : private _Pred