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This change implements the C library dependent portions of P0482R6 (char8_t: A type for UTF-8 characters and strings (Revision 6)) by declaring std::c8rtomb() and std::mbrtoc8() in the <cuchar> header when implementations are provided by the C library as specified by WG14 N2653 (char8_t: A type for UTF-8 characters and strings (Revision 1)) as adopted for C23. A _LIBCPP_HAS_NO_C8RTOMB_MBRTOC8 macro is defined by the libc++ __config header unless it is known that the C library provides these functions in the current compilation mode. This macro is used for testing purposes and may be of use to libc++ users. At present, the only C library known to implement these functions is GNU libc as of its 2.36 release. Reviewed By: ldionne Differential Revision: https://reviews.llvm.org/D130946
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=========================================
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Libc++ 16.0.0 (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++ 16 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 16.0.0. 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++ 16.0.0?
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============================
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Implemented Papers
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------------------
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- P2499R0 - ``string_view`` range constructor should be ``explicit``
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- P2417R2 - A more constexpr bitset
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- P2445R1 - ``std::forward_like``
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- P2273R3 - Making ``std::unique_ptr`` constexpr
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Improvements and New Features
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-----------------------------
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- Declarations of ``std::c8rtomb()`` and ``std::mbrtoc8()`` from P0482R6 are
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now provided when implementations in the global namespace are provided by
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the C library.
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Deprecations and Removals
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-------------------------
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- Several incidental transitive includes have been removed from libc++. Those
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includes are removed based on the language version used. Incidental transitive
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inclusions of the following headers have been removed:
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- C++20: ``chrono``
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- C++2b: ``algorithm``, ``array``, ``atomic``, ``bit``, ``chrono``,
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``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdarg``, ``cstdlib``,
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``cstring``, ``ctime``, ``exception``, ``functional``,
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``initializer_list``, ``iosfwd``, ``iterator``, ``memory``, ``new``,
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``optional``, ``ratio``, ``stdexcept``, ``tuple``, ``typeinfo``,
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``unordered_map``, ``utility``, ``variant``, ``vector``.
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Users can also remove all incidental transitive includes by defining
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``_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`` regardless of the language version
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in use. Note that in the future, libc++ reserves the right to remove
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incidental transitive includes more aggressively, in particular regardless
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of the language version in use.
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Upcoming Deprecations and Removals
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----------------------------------
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API Changes
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-----------
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- The comparison operators on ``thread::id`` are now defined as free-standing
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functions instead of as hidden friends, in conformance with the C++ standard.
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Also see `issue 56187 <https://github.com/llvm/llvm-project/issues/56187>`_.
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- ``_LIBCPP_ENABLE_NODISCARD`` and ``_LIBCPP_DISABLE_NODISCARD_AFTER_CXX17`` are no longer respected.
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Any standards-required ``[[nodiscard]]`` applications in C++20 are now always enabled. Any extended applications
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are now enabled by default and can be disabled by defining ``_LIBCPP_DISABLE_NODISCARD_EXT``.
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ABI Affecting Changes
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---------------------
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Build System Changes
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--------------------
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