docs/ReleaseNotes.rst

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Libc++ 16.0.0 (In-Progress) Release Notes
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Written by the `Libc++ Team <https://libcxx.llvm.org>`_

.. warning::

   These are in-progress notes for the upcoming libc++ 16 release.
   Release notes for previous releases can be found on
   `the Download Page <https://releases.llvm.org/download.html>`_.

Introduction
============

This document contains the release notes for the libc++ C++ Standard Library,
part of the LLVM Compiler Infrastructure, release 16.0.0. Here we describe the
status of libc++ in some detail, including major improvements from the previous
release and new feature work. For the general LLVM release notes, see `the LLVM
documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.

For more information about libc++, please see the `Libc++ Web Site
<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.

Note that if you are reading this file from a Git checkout or the
main Libc++ web page, this document applies to the *next* release, not
the current one. To see the release notes for a specific release, please
see the `releases page <https://llvm.org/releases/>`_.

What's New in Libc++ 16.0.0?
============================

Implemented Papers
------------------
- P2499R0 - ``string_view`` range constructor should be ``explicit``
- P2417R2 - A more constexpr bitset
- P2445R1 - ``std::forward_like``
- P2273R3 - Making ``std::unique_ptr`` constexpr

Improvements and New Features
-----------------------------
- Declarations of ``std::c8rtomb()`` and ``std::mbrtoc8()`` from P0482R6 are
  now provided when implementations in the global namespace are provided by
  the C library.

Deprecations and Removals
-------------------------
- Several incidental transitive includes have been removed from libc++. Those
  includes are removed based on the language version used. Incidental transitive
  inclusions of the following headers have been removed:

  - C++20: ``chrono``
  - C++2b: ``algorithm``, ``array``, ``atomic``, ``bit``, ``chrono``,
    ``climits``, ``cmath``, ``compare``, ``concepts``, ``cstdarg`, ``cstddef``,
    ``cstdint``, ``cstdlib``, ``cstring``, ``ctime``, ``exception``,
    ``functional``, ``initializer_list``, ``iosfwd``, ``iterator``, ``limits``,
    ``memory``, ``new``, ``numeric``, ``optional``, ``ratio``, ``stdexcept``,
    ``string``, ``tuple``, ``type_traits``, ``typeinfo``, ``unordered_map``,
    ``utility``, ``variant``, ``vector``.

  Users can also remove all incidental transitive includes by defining
  ``_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`` regardless of the language version
  in use. Note that in the future, libc++ reserves the right to remove
  incidental transitive includes more aggressively, in particular regardless
  of the language version in use.


Upcoming Deprecations and Removals
----------------------------------

API Changes
-----------
- The comparison operators on ``thread::id`` are now defined as free-standing
  functions instead of as hidden friends, in conformance with the C++ standard.
  Also see `issue 56187 <https://github.com/llvm/llvm-project/issues/56187>`_.

- ``_LIBCPP_ENABLE_NODISCARD`` and ``_LIBCPP_DISABLE_NODISCARD_AFTER_CXX17`` are no longer respected.
  Any standards-required ``[[nodiscard]]`` applications in C++20 are now always enabled. Any extended applications
  are now enabled by default and can be disabled by defining ``_LIBCPP_DISABLE_NODISCARD_EXT``.

ABI Affecting Changes
---------------------

Build System Changes
--------------------