[PATCH] Deprecate nested types in std::hash

[PATCH] Deprecate nested types in std::hash

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 1425 bytes --]

C++17 deprecates the argument_type and result_type members of
std::hash specializations. This adds the deprecated attribute to them.

C++17 also deprecates those nested typedefs (and weak result types) in
owner_less, plus, minus, function, reference_wrapper, bind,
{multi,}map::value_compare etc. but we can do that later. I wanted to
make this change now for the new hash<variant<T...>> and
hash<optional<T>> specializations that are new in C++17.

I'm also adding partial specializations for __is_fast_hash for those
new hash specializations, so that unordered containers of
optional<string> or variant<..., string, ...> will cache the hash
code.

	* include/bits/c++config (_GLIBCXX17_DEPRECATED): Define.
	* include/bits/functional_hash.h (__hash_base::result_type)
	(__hash_base::argument_type): Add _GLIBCXX17_DEPRECATED.
	* include/std/optional (hash<optional<T>>::result_type)
	(hash<optional<T>>::argument_type): Add deprecated attribute.
	(__is_fast_hash<hash<optional<T>>>): Add partial specialization.
	* include/std/variant (hash<variant<Types...>>::result_type)
	(hash<variant<Types...>>::argument_type): Add deprecated attribute.
	(__is_fast_hash<hash<variant<Types...>>>): Add partial specialization.

Tested powerpc64le, committed to trunk.

I don't think this is suitable for backporting to gcc-7-branch. The
__is_fast_hash parts would cause incompatibilities between 7.2 and 7.3
for unordered containers.


[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 4148 bytes --]

commit 5ecfc92eb86d8e6a90e1168fe6b4b2ab8cd0f8e4
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Sep 20 14:33:42 2017 +0100

    Deprecate nested types in std::hash
    
            * include/bits/c++config (_GLIBCXX17_DEPRECATED): Define.
            * include/bits/functional_hash.h (__hash_base::result_type)
            (__hash_base::argument_type): Add _GLIBCXX17_DEPRECATED.
            * include/std/optional (hash<optional<T>>::result_type)
            (hash<optional<T>>::argument_type): Add deprecated attribute.
            (__is_fast_hash<hash<optional<T>>>): Add partial specialization.
            * include/std/variant (hash<variant<Types...>>::result_type)
            (hash<variant<Types...>>::argument_type): Add deprecated attribute.
            (__is_fast_hash<hash<variant<Types...>>>): Add partial specialization.

diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index d5d1d24ee1a..21e3fbb2741 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -77,6 +77,7 @@
 // Macros for deprecated attributes.
 //   _GLIBCXX_USE_DEPRECATED
 //   _GLIBCXX_DEPRECATED
+//   _GLIBCXX17_DEPRECATED
 #ifndef _GLIBCXX_USE_DEPRECATED
 # define _GLIBCXX_USE_DEPRECATED 1
 #endif
@@ -87,6 +88,12 @@
 # define _GLIBCXX_DEPRECATED
 #endif
 
+#if defined(__DEPRECATED) && (__cplusplus >= 201703L)
+# define _GLIBCXX17_DEPRECATED [[__deprecated__]]
+#else
+# define _GLIBCXX17_DEPRECATED
+#endif
+
 // Macros for ABI tag attributes.
 #ifndef _GLIBCXX_ABI_TAG_CXX11
 # define _GLIBCXX_ABI_TAG_CXX11 __attribute ((__abi_tag__ ("cxx11")))
diff --git a/libstdc++-v3/include/bits/functional_hash.h b/libstdc++-v3/include/bits/functional_hash.h
index 38be1724d3f..c0936843ac0 100644
--- a/libstdc++-v3/include/bits/functional_hash.h
+++ b/libstdc++-v3/include/bits/functional_hash.h
@@ -49,8 +49,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Result, typename _Arg>
     struct __hash_base
     {
-      typedef _Result     result_type;
-      typedef _Arg      argument_type;
+      typedef _Result     result_type _GLIBCXX17_DEPRECATED;
+      typedef _Arg      argument_type _GLIBCXX17_DEPRECATED;
     };
 
   /// Primary class template hash.
diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index 2df9b5443ef..e017eedbde7 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1028,10 +1028,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     : private __poison_hash<remove_const_t<_Tp>>,
       public __optional_hash_call_base<_Tp>
     {
-      using result_type = size_t;
-      using argument_type = optional<_Tp>;
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = optional<_Tp>;
     };
 
+  template<typename _Tp>
+    struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
+    { };
+
   /// @}
 
   template <typename _Tp> optional(_Tp) -> optional<_Tp>;
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index ee2571b7857..8f574f63924 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1420,15 +1420,15 @@ namespace __variant
 	variant<_Types...>, std::index_sequence_for<_Types...>>,
       public __variant_hash_call_base<_Types...>
     {
-      using result_type = size_t;
-      using argument_type = variant<_Types...>;
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = variant<_Types...>;
     };
 
   template<>
     struct hash<monostate>
     {
-      using result_type = size_t;
-      using argument_type = monostate;
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = monostate;
 
       size_t
       operator()(const monostate& __t) const noexcept
@@ -1438,6 +1438,11 @@ namespace __variant
       }
     };
 
+  template<typename... _Types>
+    struct __is_fast_hash<hash<variant<_Types...>>>
+    : bool_constant<(__is_fast_hash<_Types>::value && ...)>
+    { };
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std