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=========================================
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Libc++ 15.0.0 (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++ 15 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 15.0.0. 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++ 15.0.0?
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============================
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New Features
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------------
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- Implemented P0627R6 (Function to mark unreachable code)
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- Implemented P1165R1 (Make stateful allocator propagation more consistent for ``operator+(basic_string)``)
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- `pop_heap` now uses an algorithm known as "bottom-up heapsort" or
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"heapsort with bounce" to reduce the number of comparisons, and rearranges
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elements using move-assignment instead of `swap`.
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- Libc++ now supports a variety of assertions that can be turned on to help catch
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undefined behavior in user code. This new support is now separate from the old
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(and incomplete) Debug Mode. Vendors can select whether the library they ship
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should include assertions or not by default. For details, see
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:ref:`the documentation <assertions-mode>` about this new feature.
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API Changes
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-----------
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- The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting
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``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because
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they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we
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still feel that it is worth mentioning in the release notes in case some users
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had been doing it.
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- The header ``<experimental/filesystem>`` has been removed. Instead, use
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``<filesystem>`` header. The associated macro
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``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed.
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- Some libc++ headers no longer transitively include all of ``<algorithm>``, ``<chrono>`` and ``<utility>``.
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If, after updating libc++, you see compiler errors related to missing declarations in
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namespace ``std``, it might be because one of your source files now needs to
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``#include <algorithm>``, ``#include <chrono>`` and/or ``#include <utility>``.
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- The integer distributions ``binomial_distribution``, ``discrete_distribution``,
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``geometric_distribution``, ``negative_binomial_distribution``, ``poisson_distribution``,
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and ``uniform_int_distribution`` now conform to the Standard by rejecting
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template parameter types other than ``short``, ``int``, ``long``, ``long long``,
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(as an extension) ``__int128_t``, and the unsigned versions thereof.
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In particular, ``uniform_int_distribution<int8_t>`` is no longer supported.
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- The C++14 function ``std::quoted(const char*)`` is no longer supported in
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C++03 or C++11 modes.
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- Setting a custom debug handler with ``std::__libcpp_debug_function`` is not
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supported anymore. Please migrate to using the new support for
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:ref:`assertions <assertions-mode>` instead.
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ABI Changes
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-----------
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- The ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` macro controlling whether we use an
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emulation for ``std::nullptr_t`` in C++03 mode has been removed. After this change,
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``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there
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will be no way to opt back into the C++03 emulation of ``std::nullptr_t``.
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Build System Changes
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--------------------
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- Support for standalone builds have been entirely removed from libc++, libc++abi and
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libunwind. Please use :ref:`these instructions <build instructions>` for building
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libc++, libc++abi and/or libunwind.
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- The ``{LIBCXX,LIBCXXABI,LIBUNWIND}_TARGET_TRIPLE``, ``{LIBCXX,LIBCXXABI,LIBUNWIND}_SYSROOT`` and
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``{LIBCXX,LIBCXXABI,LIBUNWIND}_GCC_TOOLCHAIN`` CMake variables have been removed. Instead, please
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use the ``CMAKE_CXX_COMPILER_TARGET``, ``CMAKE_SYSROOT`` and ``CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN``
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variables provided by CMake.
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- When building for Windows, vendors who want to avoid dll-exporting symbols from the static libc++abi
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library should set ``LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON`` when configuring CMake. The current
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behavior, which tries to guess the correct dll-export semantics based on whether we're building
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the libc++ shared library, will be removed in LLVM 16.
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- Previously, the C++ ABI library headers would be installed inside ``<prefix>/include/c++/v1``
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alongside the libc++ headers as part of building libc++. This is not the case anymore -- the
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ABI library is expected to install its headers where it wants them as part of its own build.
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Note that no action is required for most users, who build libc++ against libc++abi, since
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libc++abi already installs its headers in the right location. However, vendors building
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libc++ against alternate ABI libraries should make sure that their ABI library installs
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its own headers.
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- The legacy testing configuration is now deprecated and will be removed in the next release. For
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most users, this should not have any impact. However, if you are testing libc++ in a configuration
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or on a platform that used to be supported by the legacy testing configuration and isn't supported
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by one of the configurations in ``libcxx/test/configs``, please reach out to the libc++ developers
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to get your configuration supported officially.
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