[libc++] Remove functions deprecated in C++17 and removed in C++20

Works towards P0619R4. - `std::uncaught_exception` was not previously deprecated. This patch deprecates it since C++17 as per N4259. `std::uncaught_exceptions` is used instead as libc++ unconditionally provides this function. - `std::get_temporary_buffer` is replaced with the internal version `__get_temporary_buffer`. - `std::return_temporary_buffer` is replaced with direct `__libcpp_deallocate_unsized` call. Escape hatches: - `_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION` restores `std::uncaught_exception`. - `_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER` restores `std::get_temporary_buffer` and `std::return_temporary_buffer`.
llvm · Jul 28, 2024 · bf4e6d5 · bf4e6d5
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diff --git a/libcxx/docs/Status/Cxx17.rst b/libcxx/docs/Status/Cxx17.rst
@@ -40,6 +40,7 @@ Paper Status
 
 .. note::
 
+   .. [#note-N4259] N4259: ``std::uncaught_exception`` is deprecated since version 20.0.
    .. [#note-P0067] P0067: ``std::(to|from)_chars`` for integrals has been available since version 7.0. ``std::to_chars`` for ``float`` and ``double`` since version 14.0 ``std::to_chars`` for ``long double`` uses the implementation for ``double``.
    .. [#note-P0226] P0226: Progress is tracked `here <https://https://libcxx.llvm.org/Status/SpecialMath.html>`_.
    .. [#note-P0607] P0607: The parts of P0607 that are not done are the ``<regex>`` bits.

diff --git a/libcxx/docs/Status/Cxx17Papers.csv b/libcxx/docs/Status/Cxx17Papers.csv
@@ -4,7 +4,7 @@
 "`N4169 <https://wg21.link/n4169>`__","LWG","A proposal to add invoke function template","Urbana","|Complete|","3.7"
 "`N4190 <https://wg21.link/n4190>`__","LWG","Removing auto_ptr, random_shuffle(), And Old <functional> Stuff.","Urbana","|Complete|","15.0"
 "`N4258 <https://wg21.link/n4258>`__","LWG","Cleaning-up noexcept in the Library.","Urbana","|In Progress|","3.7"
-"`N4259 <https://wg21.link/n4259>`__","CWG","Wording for std::uncaught_exceptions","Urbana","|Complete|","3.7"
+"`N4259 <https://wg21.link/n4259>`__","CWG","Wording for std::uncaught_exceptions","Urbana","|Complete| [#note-N4259]_","3.7"
 "`N4277 <https://wg21.link/n4277>`__","LWG","TriviallyCopyable ``reference_wrapper``\ .","Urbana","|Complete|","3.2"
 "`N4279 <https://wg21.link/n4279>`__","LWG","Improved insertion interface for unique-key maps.","Urbana","|Complete|","3.7"
 "`N4280 <https://wg21.link/n4280>`__","LWG","Non-member size() and more","Urbana","|Complete|","3.6"

diff --git a/libcxx/docs/Status/Cxx20.rst b/libcxx/docs/Status/Cxx20.rst
@@ -44,7 +44,7 @@ Paper Status
    .. [#note-P0645] P0645: The paper is implemented but still marked as an incomplete feature
       (the feature-test macro is not set).
    .. [#note-P0966] P0966: It was previously erroneously marked as complete in version 8.0. See `bug 45368 <https://llvm.org/PR45368>`__.
-   .. [#note-P0619] P0619: Only sections D.8, D.9, D.10 and D.13 are implemented. Sections D.4, D.7, D.11, and D.12 remain undone.
+   .. [#note-P0619] P0619: Section D.4 remains undone.
    .. [#note-P0883.1] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.
    .. [#note-P0883.2] P0883: ``ATOMIC_FLAG_INIT`` was marked deprecated in version 14.0, but was undeprecated with the implementation of LWG3659 in version 15.0.
    .. [#note-P0660] P0660: The paper is implemented but the features are experimental and can be enabled via ``-fexperimental-library``.

diff --git a/libcxx/docs/UsingLibcxx.rst b/libcxx/docs/UsingLibcxx.rst
@@ -215,6 +215,9 @@ C++17 Specific Configuration Macros
 
 C++20 Specific Configuration Macros
 -----------------------------------
+**_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION**:
+  This macro is used to re-enable `uncaught_exception`.
+
 **_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE**:
   This macro is used to re-enable the function
   ``std::shared_ptr<...>::unique()``.
@@ -231,6 +234,9 @@ C++20 Specific Configuration Macros
 **_LIBCPP_ENABLE_CXX20_REMOVED_RAW_STORAGE_ITERATOR**:
   This macro is used to re-enable `raw_storage_iterator`.
 
+**_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER**:
+  This macro is used to re-enable `get_temporary_buffer` and `return_temporary_buffer`.
+
 **_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS**:
   This macro is used to re-enable `is_literal_type`, `is_literal_type_v`,
   `result_of` and `result_of_t`.

diff --git a/libcxx/include/__algorithm/inplace_merge.h b/libcxx/include/__algorithm/inplace_merge.h
@@ -211,10 +211,7 @@ _LIBCPP_HIDE_FROM_ABI void __inplace_merge(
   difference_type __len1     = _IterOps<_AlgPolicy>::distance(__first, __middle);
   difference_type __len2     = _IterOps<_AlgPolicy>::distance(__middle, __last);
   difference_type __buf_size = std::min(__len1, __len2);
-  // TODO: Remove the use of std::get_temporary_buffer
-  _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-  pair<value_type*, ptrdiff_t> __buf = std::get_temporary_buffer<value_type>(__buf_size);
-  _LIBCPP_SUPPRESS_DEPRECATED_POP
+  pair<value_type*, ptrdiff_t> __buf = std::__get_temporary_buffer<value_type>(__buf_size);
   unique_ptr<value_type, __return_temporary_buffer> __h(__buf.first);
   return std::__inplace_merge<_AlgPolicy>(
       std::move(__first), std::move(__middle), std::move(__last), __comp, __len1, __len2, __buf.first, __buf.second);

diff --git a/libcxx/include/__algorithm/stable_partition.h b/libcxx/include/__algorithm/stable_partition.h
@@ -135,10 +135,7 @@ __stable_partition_impl(_ForwardIterator __first, _ForwardIterator __last, _Pred
   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 = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
+    __p = std::__get_temporary_buffer<value_type>(__len);
     __h.reset(__p.first);
   }
   return std::__stable_partition_impl<_AlgPolicy, _Predicate&>(
@@ -275,10 +272,7 @@ _LIBCPP_HIDE_FROM_ABI _BidirectionalIterator __stable_partition_impl(
   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 = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
+    __p = std::__get_temporary_buffer<value_type>(__len);
     __h.reset(__p.first);
   }
   return std::__stable_partition_impl<_AlgPolicy, _Predicate&>(

diff --git a/libcxx/include/__algorithm/stable_sort.h b/libcxx/include/__algorithm/stable_sort.h
@@ -244,10 +244,7 @@ __stable_sort_impl(_RandomAccessIterator __first, _RandomAccessIterator __last,
   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 = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
+    __buf = std::__get_temporary_buffer<value_type>(__len);
     __h.reset(__buf.first);
   }
 

diff --git a/libcxx/include/__exception/operations.h b/libcxx/include/__exception/operations.h
@@ -29,7 +29,9 @@ using terminate_handler = void (*)();
 _LIBCPP_EXPORTED_FROM_ABI terminate_handler set_terminate(terminate_handler) _NOEXCEPT;
 _LIBCPP_EXPORTED_FROM_ABI terminate_handler get_terminate() _NOEXCEPT;
 
-_LIBCPP_EXPORTED_FROM_ABI bool uncaught_exception() _NOEXCEPT;
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
+_LIBCPP_EXPORTED_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 bool uncaught_exception() _NOEXCEPT;
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION)
 _LIBCPP_EXPORTED_FROM_ABI int uncaught_exceptions() _NOEXCEPT;
 
 class _LIBCPP_EXPORTED_FROM_ABI exception_ptr;

diff --git a/libcxx/include/__memory/temporary_buffer.h b/libcxx/include/__memory/temporary_buffer.h
@@ -22,8 +22,8 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
-_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
-get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
+_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI 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);
@@ -56,20 +56,28 @@ get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
   return __r;
 }
 
-template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 void return_temporary_buffer(_Tp* __p) _NOEXCEPT {
-  std::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
-}
-
 struct __return_temporary_buffer {
-  _LIBCPP_SUPPRESS_DEPRECATED_PUSH
   template <class _Tp>
   _LIBCPP_HIDE_FROM_ABI void operator()(_Tp* __p) const {
-    std::return_temporary_buffer(__p);
+    std::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
   }
-  _LIBCPP_SUPPRESS_DEPRECATED_POP
 };
 
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
+template <class _Tp>
+_LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
+get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
+  return std::__get_temporary_buffer<_Tp>(__n);
+}
+
+template <class _Tp>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 void return_temporary_buffer(_Tp* __p) _NOEXCEPT {
+  std::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
+}
+
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___MEMORY_TEMPORARY_BUFFER_H
diff --git a/libcxx/include/__ostream/basic_ostream.h b/libcxx/include/__ostream/basic_ostream.h
@@ -152,7 +152,7 @@ basic_ostream<_CharT, _Traits>::sentry::sentry(basic_ostream<_CharT, _Traits>& _
 
 template <class _CharT, class _Traits>
 basic_ostream<_CharT, _Traits>::sentry::~sentry() {
-  if (__os_.rdbuf() && __os_.good() && (__os_.flags() & ios_base::unitbuf) && !uncaught_exception()) {
+  if (__os_.rdbuf() && __os_.good() && (__os_.flags() & ios_base::unitbuf) && uncaught_exceptions() == 0) {
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_NO_EXCEPTIONS

diff --git a/libcxx/include/exception b/libcxx/include/exception
@@ -47,7 +47,7 @@ terminate_handler set_terminate(terminate_handler  f ) noexcept;
 terminate_handler get_terminate() noexcept;
 [[noreturn]] void terminate() noexcept;
 
-bool uncaught_exception()  noexcept;
+bool uncaught_exception()  noexcept;  // deprecated in C++17, removed in C++20
 int  uncaught_exceptions() noexcept;  // C++17
 
 typedef unspecified exception_ptr;

diff --git a/libcxx/include/memory b/libcxx/include/memory
@@ -182,8 +182,8 @@ public:
     raw_storage_iterator  operator++(int);
 };
 
-template <class T> pair<T*,ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
-template <class T> void               return_temporary_buffer(T* p) noexcept;
+template <class T> pair<T*,ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept; // deprecated in C++17, removed in C++20
+template <class T> void               return_temporary_buffer(T* p) noexcept;     // deprecated in C++17, removed in C++20
 
 template <class T> T* addressof(T& r) noexcept;
 template <class T> T* addressof(const T&& r) noexcept = delete;

diff --git a/libcxx/include/syncstream b/libcxx/include/syncstream
@@ -358,7 +358,7 @@ private:
   // TODO Use a more generic buffer.
   // That buffer should be light with almost no additional headers. Then
   // it can be use here, the __retarget_buffer, and place that use
-  // the now deprecated get_temporary_buffer
+  // the now removed get_temporary_buffer
 
   basic_string<_CharT, _Traits, _Allocator> __str_;
   bool __emit_on_sync_{false};

diff --git a/libcxx/modules/std/exception.inc b/libcxx/modules/std/exception.inc
@@ -21,6 +21,5 @@ export namespace std {
   using std::terminate;
   using std::terminate_handler;
   using std::throw_with_nested;
-  using std::uncaught_exception;
   using std::uncaught_exceptions;
 } // namespace std
diff --git a/libcxx/src/exception.cpp b/libcxx/src/exception.cpp
@@ -6,6 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define _LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION
+#define _LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 #include <exception>
 #include <new>
 #include <typeinfo>

diff --git a/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp
@@ -10,6 +10,7 @@
 
 // check that <memory> functions are marked [[nodiscard]]
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
 // clang-format off

diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.partitions/stable_partition.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.partitions/stable_partition.pass.cpp
@@ -282,9 +282,6 @@ test()
     assert(array[9] == P(0, 2));
   }
 #if TEST_STD_VER >= 11 && !defined(TEST_HAS_NO_EXCEPTIONS)
-  // TODO: Re-enable this test once we're no longer using get_temporary_buffer().
-  // For now it trips up GCC due to the use of always_inline.
-#if 0
   { // check that the algorithm still works when no memory is available
     std::vector<int> vec(150, 3);
     vec[5]                             = 6;
@@ -300,7 +297,6 @@ test()
     assert(std::is_partitioned(vec.begin(), vec.end(), [](int i) { return i < 5; }));
     getGlobalMemCounter()->reset();
   }
-#endif
 #endif // TEST_STD_VER >= 11 && !defined(TEST_HAS_NO_EXCEPTIONS)
 }
 

diff --git a/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp b/libcxx/test/std/language.support/support.exception/uncaught/uncaught_exception.pass.cpp
@@ -7,6 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: no-exceptions
+
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_UNCAUGHT_EXCEPTION
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
+
 // test uncaught_exception
 
 #include <exception>

diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
@@ -8,6 +8,7 @@
 
 // UNSUPPORTED: c++03
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
 // <memory>

diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
@@ -8,6 +8,7 @@
 
 // <memory>
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
 // template <class T>

diff --git a/libcxx/utils/libcxx/test/modules.py b/libcxx/utils/libcxx/test/modules.py
@@ -52,13 +52,6 @@
     "std::operator==",
 ]
 
-# TODO MODULES remove zombie names
-# https://libcxx.llvm.org/Status/Cxx20.html#note-p0619
-SkipDeclarations["memory"] = [
-    "std::return_temporary_buffer",
-    "std::get_temporary_buffer",
-]
-
 # include/__type_traits/is_swappable.h
 SkipDeclarations["type_traits"] = [
     "std::swap",