41a830500a
We marked those macros as deprecated in the last release with the intent of removing them in LLVM 19. This commit performs the removal.
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===========================================
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Libc++ 19.0.0 (In-Progress) Release Notes
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===========================================
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.. contents::
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:local:
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:depth: 2
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Written by the `Libc++ Team <https://libcxx.llvm.org>`_
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.. warning::
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These are in-progress notes for the upcoming libc++ 19.0.0 release.
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Release notes for previous releases can be found on
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`the Download Page <https://releases.llvm.org/download.html>`_.
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Introduction
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============
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This document contains the release notes for the libc++ C++ Standard Library,
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part of the LLVM Compiler Infrastructure, release 19.0.0. Here we describe the
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status of libc++ in some detail, including major improvements from the previous
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release and new feature work. For the general LLVM release notes, see `the LLVM
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documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
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be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
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For more information about libc++, please see the `Libc++ Web Site
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<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.
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Note that if you are reading this file from a Git checkout or the
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main Libc++ web page, this document applies to the *next* release, not
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the current one. To see the release notes for a specific release, please
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see the `releases page <https://llvm.org/releases/>`_.
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What's New in Libc++ 19.0.0?
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==============================
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Implemented Papers
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------------------
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- P2637R3 - Member ``visit``
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- P2652R2 - Disallow User Specialization of ``allocator_traits``
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- P2819R2 - Add ``tuple`` protocol to ``complex``
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- P2495R3 - Interfacing ``stringstream``\s with ``string_view``
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- P2867R2 - Remove Deprecated ``strstream``\s From C++26
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- P2869R4 - Remove Deprecated ``shared_ptr`` Atomic Access APIs from C++26
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- P2872R3 - Remove ``wstring_convert`` From C++26
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- P3142R0 - Printing Blank Lines with ``println`` (as DR against C++23)
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- P2302R4 - ``std::ranges::contains``
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- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
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- P3029R1 - Better ``mdspan``'s CTAD
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Improvements and New Features
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-----------------------------
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- The performance of growing ``std::vector`` has been improved for trivially relocatable types.
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- The performance of ``ranges::fill`` and ``ranges::fill_n`` has been improved for ``vector<bool>::iterator``\s,
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resulting in a performance increase of up to 1400x.
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- The ``std::mismatch`` algorithm has been optimized for integral types, which can lead up to 40x performance
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improvements.
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- The ``std::ranges::minmax`` algorithm has been optimized for integral types, resulting in a performance increase of
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up to 100x.
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- The ``_LIBCPP_ENABLE_CXX26_REMOVED_STRSTREAM`` macro has been added to make the declarations in ``<strstream>`` available.
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- The ``_LIBCPP_ENABLE_CXX26_REMOVED_SHARED_PTR_ATOMICS`` macro has been added to make the declarations in ``<memory>``
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available.
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- The ``_LIBCPP_ENABLE_CXX26_REMOVED_WSTRING_CONVERT`` macro has been added to make the declarations in ``<locale>``
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available.
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- The formatting library is updated to Unicode 15.1.0.
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Deprecations and Removals
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-------------------------
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- The C++20 synchronization library (``<barrier>``, ``<latch>``, ``atomic::wait``, etc.) has been deprecated
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in language modes prior to C++20. If you are using these features prior to C++20, please update to ``-std=c++20``.
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In LLVM 20, the C++20 synchronization library will be removed entirely in language modes prior to C++20.
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- TODO: The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable that was used to enable the safe mode has been deprecated and setting
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it triggers an error; use the ``LIBCXX_HARDENING_MODE`` CMake variable with the value ``extensive`` instead. Similarly,
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the ``_LIBCPP_ENABLE_ASSERTIONS`` macro has been deprecated (setting it to ``1`` still enables the extensive mode in
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the LLVM 19 release while also issuing a deprecation warning). See :ref:`the hardening documentation
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<using-hardening-modes>` for more details.
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- The base template for ``std::char_traits`` has been removed in LLVM 19. If you are using ``std::char_traits`` with
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types other than ``char``, ``wchar_t``, ``char8_t``, ``char16_t``, ``char32_t`` or a custom character type for which you
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specialized ``std::char_traits``, your code will stop working. The Standard does not mandate that a base template is
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provided, and such a base template is bound to be incorrect for some types, which could currently cause unexpected behavior
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while going undetected.
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- The ``_LIBCPP_ENABLE_NARROWING_CONVERSIONS_IN_VARIANT`` macro that changed the behavior for narrowing conversions
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in ``std::variant`` has been removed in LLVM 19.
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- The ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION``
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macros have been removed in LLVM 19.
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- The ``_LIBCPP_ENABLE_CXX17_REMOVED_FEATURES`` and ``_LIBCPP_ENABLE_CXX20_REMOVED_FEATURES`` macros have
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been removed in LLVM 19. C++17 and C++20 removed features can still be re-enabled individually.
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- The ``_LIBCPP_INLINE_VISIBILITY`` and ``_VSTD`` macros have been removed in LLVM 19.
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- The ``_LIBCPP_ATOMIC_ONLY_USE_BUILTINS`` configuration option has been removed in LLVM 19. This should not affect
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many users, except perhaps users using the library with ``-ffreestanding`` with a toolchain where compiler-rt or
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libatomic is not available. If you are one such user, please reach out to the libc++ developers so we can collaborate
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on a path for supporting atomics properly on freestanding platforms.
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- LWG3430 disallow implicit conversion of the source arguments to ``std::filesystem::path`` when
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constructing ``std::basic_*fstream``. This effectively removes the possibility to directly construct
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a ``std::basic_*fstream`` from a ``std::basic_string_view``, a input-iterator or a C-string, instead
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you can construct a temporary ``std::basic_string``. This change has been applied to C++17 and later.
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Upcoming Deprecations and Removals
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----------------------------------
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LLVM 20
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~~~~~~~
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- The ``LIBCXX_ENABLE_ASSERTIONS`` CMake variable and the ``_LIBCPP_ENABLE_ASSERTIONS`` macro that were used to enable
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the safe mode will be removed in LLVM 20.
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LLVM 21
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~~~~~~~
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TODO
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ABI Affecting Changes
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---------------------
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- The optional POSIX macro ``ENODATA`` has been deprecated in C++ and POSIX 2017. The
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``random_device`` could throw a ``system_error`` with this value. It now
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throws ``ENOMSG``.
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Build System Changes
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--------------------
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- The ``LIBCXX_EXECUTOR`` and ``LIBCXXABI_EXECUTOR`` CMake variables have been removed. Please
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set ``LIBCXX_TEST_PARAMS`` to ``executor=<...>`` instead.
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- The Cmake variable ``LIBCXX_ENABLE_CLANG_TIDY`` has been removed. The build system has been changed
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to automatically detect the presence of ``clang-tidy`` and the required ``Clang`` libraries.
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