[libc++] Implement P0174R2 (Deprecating Vestigial Library Parts in C++17)

[ldionne]

LGTM without the allocator<void> part (and with passing CI).

libcxx/include/__memory/allocator.h

34

There's a bit of history behind this, but TLDR, I don't think we want to do this part: https://reviews.llvm.org/D104323.

In particular, I think reading https://github.com/llvm/llvm-project/issues/49643 by @jwakely is relevant.

[Mordante]

libcxx/include/__memory/allocator.h

34

Can you add some comment why this is intended not to be deprecated.
That way we can avoid a third deprecation round.

[philnik]

• [libc++] Try to fix CI

[philnik]

• next try

[Mordante]

LGTM modulo one nit and when the CI is happy.

libcxx/test/std/utilities/memory/temporary.buffer/depr.verify.cpp

11

[philnik]

• Try to fix CI

libcxx/docs/ReleaseNotes.rst

 - Implemented P0627R6 (Function to mark unreachable code)
 
 - Implemented P1165R1 (Make stateful allocator propagation more consistent for ``operator+(basic_string)``)
 
 - Implemented P0674R1 (Support arrays in ``make_shared`` and ``allocate_shared``)
 
 - Implemented P0980R1 (Making ``std::string`` constexpr)
 
+- Implemented P0174R2 (Deprecating Vestigial Library Parts in C++17)
+
 - Marked the following papers as "Complete" (note that some of those might have
   been implemented in a previous release but not marked as such):
 
     - P1207R4 (Movability of Single-pass Iterators);
     - P1474R1 (Helpful pointers for ``ContiguousIterator``);
     - P1522R1 (Iterator Difference Type and Integer Overflow);
     - P1523R1 (Views and Size Types);
     - P1456R1 (Move-only views);

libcxx/docs/Status/Cxx17Papers.csv

 "`p0040r3 <https://wg21.link/p0040r3>`__","LWG","Extending memory management tools","Oulu","|Complete|","4.0"
 "`p0063r3 <https://wg21.link/p0063r3>`__","LWG","C++17 should refer to C11 instead of C99","Oulu","|Complete|","7.0"
 "`p0067r3 <https://wg21.link/p0067r3>`__","LWG","Elementary string conversions","Oulu","Now `P0067R5 <https://wg21.link/P0067R5>`__","n/a"
 "`p0083r3 <https://wg21.link/p0083r3>`__","LWG","Splicing Maps and Sets","Oulu","|Complete|","8.0"
 "`p0084r2 <https://wg21.link/p0084r2>`__","LWG","Emplace Return Type","Oulu","|Complete|","4.0"
 "`p0088r3 <https://wg21.link/p0088r3>`__","LWG","Variant: a type-safe union for C++17","Oulu","|Complete|","4.0"
 "`p0137r1 <https://wg21.link/p0137r1>`__","CWG","Core Issue 1776: Replacement of class objects containing reference members","Oulu","|Complete|","6.0"
 "`p0163r0 <https://wg21.link/p0163r0>`__","LWG","shared_ptr::weak_type","Oulu","|Complete|","3.9"
-"`p0174r2 <https://wg21.link/p0174r2>`__","LWG","Deprecating Vestigial Library Parts in C++17","Oulu","|Partial|",""
+"`p0174r2 <https://wg21.link/p0174r2>`__","LWG","Deprecating Vestigial Library Parts in C++17","Oulu","|Complete|","15.0"
 "`p0175r1 <https://wg21.link/p0175r1>`__","LWG","Synopses for the C library","Oulu","",""
 "`p0180r2 <https://wg21.link/p0180r2>`__","LWG","Reserve a New Library Namespace for Future Standardization","Oulu","|Nothing To Do|","n/a"
 "`p0181r1 <https://wg21.link/p0181r1>`__","LWG","Ordered by Default","Oulu","*Removed in Kona*","n/a"
 "`p0209r2 <https://wg21.link/p0209r2>`__","LWG","make_from_tuple: apply for construction","Oulu","|Complete|","3.9"
 "`p0219r1 <https://wg21.link/p0219r1>`__","LWG","Relative Paths for Filesystem","Oulu","|Complete|","7.0"
 "`p0254r2 <https://wg21.link/p0254r2>`__","LWG","Integrating std::string_view and std::string","Oulu","|Complete|","4.0"
 "`p0258r2 <https://wg21.link/p0258r2>`__","LWG","has_unique_object_representations","Oulu","|Complete|","6.0"
 "`p0295r0 <https://wg21.link/p0295r0>`__","LWG","Adopt Selected Library Fundamentals V2 Components for C++17","Oulu","|Complete|","4.0"

libcxx/include/__algorithm/inplace_merge.h

 inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last,
               _Compare __comp)
 {
     typedef typename iterator_traits<_BidirectionalIterator>::value_type value_type;
     typedef typename iterator_traits<_BidirectionalIterator>::difference_type difference_type;
     difference_type __len1 = _VSTD::distance(__first, __middle);
     difference_type __len2 = _VSTD::distance(__middle, __last);
     difference_type __buf_size = _VSTD::min(__len1, __len2);
+// TODO: Remove the use of std::get_temporary_buffer
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
     pair<value_type*, ptrdiff_t> __buf = _VSTD::get_temporary_buffer<value_type>(__buf_size);
+_LIBCPP_SUPPRESS_DEPRECATED_POP
     unique_ptr<value_type, __return_temporary_buffer> __h(__buf.first);
     typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
     return _VSTD::__inplace_merge<_Comp_ref>(__first, __middle, __last, __comp, __len1, __len2,
                                             __buf.first, __buf.second);
 }
 
 template <class _BidirectionalIterator>
 inline _LIBCPP_INLINE_VISIBILITY

libcxx/include/__algorithm/stable_partition.h

__stable_partition(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred,
     // *__first is known to be false
     typedef typename iterator_traits<_ForwardIterator>::difference_type difference_type;
     typedef typename iterator_traits<_ForwardIterator>::value_type value_type;
     difference_type __len = _VSTD::distance(__first, __last);
     pair<value_type*, ptrdiff_t> __p(0, 0);
     unique_ptr<value_type, __return_temporary_buffer> __h;
     if (__len >= __alloc_limit)
     {
+// TODO: Remove the use of std::get_temporary_buffer
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
         __p = _VSTD::get_temporary_buffer<value_type>(__len);
+_LIBCPP_SUPPRESS_DEPRECATED_POP
         __h.reset(__p.first);
     }
     return _VSTD::__stable_partition<_Predicate&>(__first, __last, __pred, __len, __p, forward_iterator_tag());
 }
 
 template <class _Predicate, class _BidirectionalIterator, class _Distance, class _Pair>
 _BidirectionalIterator
 __stable_partition(_BidirectionalIterator __first, _BidirectionalIterator __last, _Predicate __pred,
__stable_partition(_BidirectionalIterator __first, _BidirectionalIterator __last, _Predicate __pred,
     // *__first is known to be false
     // *__last is known to be true
     // __len >= 2
     difference_type __len = _VSTD::distance(__first, __last) + 1;
     pair<value_type*, ptrdiff_t> __p(0, 0);
     unique_ptr<value_type, __return_temporary_buffer> __h;
     if (__len >= __alloc_limit)
     {
+// TODO: Remove the use of std::get_temporary_buffer
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
         __p = _VSTD::get_temporary_buffer<value_type>(__len);
+_LIBCPP_SUPPRESS_DEPRECATED_POP
         __h.reset(__p.first);
     }
     return _VSTD::__stable_partition<_Predicate&>(__first, __last, __pred, __len, __p, bidirectional_iterator_tag());
 }
 
 template <class _ForwardIterator, class _Predicate>
 inline _LIBCPP_INLINE_VISIBILITY
 _ForwardIterator
 stable_partition(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred)
 {
     return _VSTD::__stable_partition<_Predicate&>(__first, __last, __pred, typename iterator_traits<_ForwardIterator>::iterator_category());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___ALGORITHM_STABLE_PARTITION_H

libcxx/include/__algorithm/stable_sort.h

 {
     typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
     typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
     difference_type __len = __last - __first;
     pair<value_type*, ptrdiff_t> __buf(0, 0);
     unique_ptr<value_type, __return_temporary_buffer> __h;
     if (__len > static_cast<difference_type>(__stable_sort_switch<value_type>::value))
     {
+// TODO: Remove the use of std::get_temporary_buffer
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
         __buf = _VSTD::get_temporary_buffer<value_type>(__len);
+_LIBCPP_SUPPRESS_DEPRECATED_POP
         __h.reset(__buf.first);
     }
     typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
     _VSTD::__stable_sort<_Comp_ref>(__first, __last, __comp, __len, __buf.first, __buf.second);
 }
 
 template <class _RandomAccessIterator>
 inline _LIBCPP_INLINE_VISIBILITY

libcxx/include/__memory/allocator.h

 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp> class allocator;
 
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION)
+// These specializations shouldn't be marked _LIBCPP_DEPRECATED_IN_CXX17.
+// Specializing allocator<void> is deprecated, but not using it.
 template <>
 class _LIBCPP_TEMPLATE_VIS allocator<void>
 {
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS)
 public:
     _LIBCPP_DEPRECATED_IN_CXX17 typedef void*             pointer;
     _LIBCPP_DEPRECATED_IN_CXX17 typedef const void*       const_pointer;
     _LIBCPP_DEPRECATED_IN_CXX17 typedef void              value_type;
 
     template <class _Up> struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {typedef allocator<_Up> other;};

libcxx/include/__memory/temporary_buffer.h

 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
-_LIBCPP_NODISCARD_EXT _LIBCPP_NO_CFI
+_LIBCPP_NODISCARD_EXT _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17
 pair<_Tp*, ptrdiff_t>
 get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT
 {
     pair<_Tp*, ptrdiff_t> __r(0, 0);
     const ptrdiff_t __m = (~ptrdiff_t(0) ^
                            ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1)))
                            / sizeof(_Tp);
     if (__n > __m)
#endif
             break;
         }
         __n /= 2;
     }
     return __r;
 }
 
 template <class _Tp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_DEPRECATED_IN_CXX17
 void return_temporary_buffer(_Tp* __p) _NOEXCEPT
 {
   _VSTD::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
 }
 
 struct __return_temporary_buffer
 {
+_LIBCPP_SUPPRESS_DEPRECATED_PUSH
     template <class _Tp>
     _LIBCPP_INLINE_VISIBILITY void operator()(_Tp* __p) const {_VSTD::return_temporary_buffer(__p);}
+_LIBCPP_SUPPRESS_DEPRECATED_POP
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___MEMORY_TEMPORARY_BUFFER_H

libcxx/test/libcxx/diagnostics/nodiscard_extensions.pass.cpp

 // All entities to which libc++ applies [[nodiscard]] as an extension should
 // be tested here and in nodiscard_extensions.fail.cpp. They should also
 // be listed in `UsingLibcxx.rst` in the documentation for the extension.
 
 // Disable any builtin recognition of std::* in the compiler, that might also
 // trigger -Wunused-value warnings.
 // ADDITIONAL_COMPILE_FLAGS: -fno-builtin
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 #include <algorithm>
 #include <bit> // bit_cast
 #include <cstddef> // to_integer
 #include <functional> // identity
 #include <iterator>
 #include <memory>
 #include <utility> // to_underlying
 

libcxx/test/libcxx/diagnostics/nodiscard_extensions.verify.cpp

 // Test that entities declared [[nodiscard]] as an extension by libc++, are
 // only actually declared such when _LIBCPP_ENABLE_NODISCARD is specified.
 
 // All entities to which libc++ applies [[nodiscard]] as an extension should
 // be tested here and in nodiscard_extensions.pass.cpp. They should also
 // be listed in `UsingLibcxx.rst` in the documentation for the extension.
 
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_NODISCARD
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
 #include <algorithm>
 #include <bit> // bit_cast
 #include <cstddef> // to_integer
 #include <functional> // identity
 #include <iterator>
 #include <memory>
 #include <utility> // to_underlying

libcxx/test/std/utilities/memory/temporary.buffer/depr.verify.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: c++17
+
+// Ensure allocator<void> is deprecated
+
+#include <memory>
+
+void test() {
+  auto a = std::get_temporary_buffer<int>(1); // expected-warning {{'get_temporary_buffer<int>' is deprecated}}
+  std::return_temporary_buffer(a.first); // expected-warning {{'return_temporary_buffer<int>' is deprecated}}
+}