<xstring>: Restrict enabled hash specializations as required by the standard (microsoft#2741)

Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: 2 people

stl/inc/filesystem

@@ -211,21 +211,6 @@ namespace filesystem {
         }
     }
 
-    template <class>
-    inline constexpr bool _Is_EcharT = false;
-    template <>
-    inline constexpr bool _Is_EcharT<char> = true;
-    template <>
-    inline constexpr bool _Is_EcharT<wchar_t> = true;
-#ifdef __cpp_char8_t
-    template <>
-    inline constexpr bool _Is_EcharT<char8_t> = true;
-#endif // __cpp_char8_t
-    template <>
-    inline constexpr bool _Is_EcharT<char16_t> = true;
-    template <>
-    inline constexpr bool _Is_EcharT<char32_t> = true;
-
     template <class _Ty, class = void>
     inline constexpr bool _Is_Source_impl = false;
 

stl/inc/xstring

@@ -917,6 +917,12 @@ constexpr size_t _Traits_rfind_not_ch(_In_reads_(_Hay_size) const _Traits_ptr_t<
     return static_cast<size_t>(-1); // no match
 }
 
+template <class _Ty>
+_INLINE_VAR constexpr bool _Is_EcharT = _Is_any_of_v<_Ty, char, wchar_t,
+#ifdef __cpp_char8_t
+    char8_t,
+#endif // __cpp_char8_t
+    char16_t, char32_t>;
 
 #if _HAS_CXX17
 template <class _Elem, class _Traits = char_traits<_Elem>>
@@ -1824,12 +1830,9 @@ using u32string_view = basic_string_view<char32_t>;
 using wstring_view   = basic_string_view<wchar_t>;
 
 
-template <class _Elem, class _Traits>
-struct hash<basic_string_view<_Elem, _Traits>> {
-    _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef basic_string_view<_Elem, _Traits> _ARGUMENT_TYPE_NAME;
-    _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef size_t _RESULT_TYPE_NAME;
-
-    _NODISCARD size_t operator()(const basic_string_view<_Elem, _Traits> _Keyval) const noexcept {
+template <class _Elem>
+struct hash<basic_string_view<_Elem>> : _Conditionally_enabled_hash<basic_string_view<_Elem>, _Is_EcharT<_Elem>> {
+    _NODISCARD static size_t _Do_hash(const basic_string_view<_Elem> _Keyval) noexcept {
         return _Hash_array_representation(_Keyval.data(), _Keyval.size());
     }
 };
@@ -5191,12 +5194,10 @@ using u8string = basic_string<char8_t, char_traits<char8_t>, allocator<char8_t>>
 using u16string = basic_string<char16_t, char_traits<char16_t>, allocator<char16_t>>;
 using u32string = basic_string<char32_t, char_traits<char32_t>, allocator<char32_t>>;
 
-template <class _Elem, class _Traits, class _Alloc>
-struct hash<basic_string<_Elem, _Traits, _Alloc>> {
-    _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef basic_string<_Elem, _Traits, _Alloc> _ARGUMENT_TYPE_NAME;
-    _CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef size_t _RESULT_TYPE_NAME;
-
-    _NODISCARD size_t operator()(const basic_string<_Elem, _Traits, _Alloc>& _Keyval) const noexcept {
+template <class _Elem, class _Alloc>
+struct hash<basic_string<_Elem, char_traits<_Elem>, _Alloc>>
+    : _Conditionally_enabled_hash<basic_string<_Elem, char_traits<_Elem>, _Alloc>, _Is_EcharT<_Elem>> { // per LWG-3705
+    _NODISCARD static size_t _Do_hash(const basic_string<_Elem, char_traits<_Elem>, _Alloc>& _Keyval) noexcept {
         return _Hash_array_representation(_Keyval.c_str(), _Keyval.size());
     }
 };

tests/libcxx/expected_results.txt

@@ -412,10 +412,6 @@ std/diagnostics/syserr/syserr.errcat/syserr.errcat.nonvirtuals/default_ctor.pass
 # GH-1190 <future>: incorrectly used copy assignment instead of copy construction in set_value
 std/thread/futures/futures.promise/set_value_const.pass.cpp FAIL
 
-# GH-757 <xstring>: Too many enabled hash specializations
-std/strings/basic.string.hash/char_type_hash.fail.cpp FAIL
-std/strings/string.view/string.view.hash/char_type.hash.fail.cpp FAIL
-
 # GH-784 <type_traits>: aligned_storage has incorrect alignment defaults
 std/utilities/meta/meta.trans/meta.trans.other/aligned_storage.pass.cpp FAIL
 

tests/libcxx/skipped_tests.txt

@@ -412,10 +412,6 @@ diagnostics\syserr\syserr.errcat\syserr.errcat.nonvirtuals\default_ctor.pass.cpp
 # GH-1190 <future>: incorrectly used copy assignment instead of copy construction in set_value
 thread\futures\futures.promise\set_value_const.pass.cpp
 
-# GH-757 <xstring>: Too many enabled hash specializations
-strings\basic.string.hash\char_type_hash.fail.cpp
-strings\string.view\string.view.hash\char_type.hash.fail.cpp
-
 # GH-784 <type_traits>: aligned_storage has incorrect alignment defaults
 utilities\meta\meta.trans\meta.trans.other\aligned_storage.pass.cpp