1=========================================
2Libc++ 15.0.0 (In-Progress) Release Notes
3=========================================
4
5.. contents::
6   :local:
7   :depth: 2
8
9Written by the `Libc++ Team <https://libcxx.llvm.org>`_
10
11.. warning::
12
13   These are in-progress notes for the upcoming libc++ 15 release.
14   Release notes for previous releases can be found on
15   `the Download Page <https://releases.llvm.org/download.html>`_.
16
17Introduction
18============
19
20This document contains the release notes for the libc++ C++ Standard Library,
21part of the LLVM Compiler Infrastructure, release 15.0.0. Here we describe the
22status of libc++ in some detail, including major improvements from the previous
23release and new feature work. For the general LLVM release notes, see `the LLVM
24documentation <https://llvm.org/docs/ReleaseNotes.html>`_. All LLVM releases may
25be downloaded from the `LLVM releases web site <https://llvm.org/releases/>`_.
26
27For more information about libc++, please see the `Libc++ Web Site
28<https://libcxx.llvm.org>`_ or the `LLVM Web Site <https://llvm.org>`_.
29
30Note that if you are reading this file from a Git checkout or the
31main Libc++ web page, this document applies to the *next* release, not
32the current one. To see the release notes for a specific release, please
33see the `releases page <https://llvm.org/releases/>`_.
34
35What's New in Libc++ 15.0.0?
36============================
37
38New Features
39------------
40
41- Implemented P0627R6 (Function to mark unreachable code)
42
43- Implemented P1165R1 (Make stateful allocator propagation more consistent for ``operator+(basic_string)``)
44
45- `pop_heap` now uses an algorithm known as "bottom-up heapsort" or
46  "heapsort with bounce" to reduce the number of comparisons, and rearranges
47  elements using move-assignment instead of `swap`.
48
49API Changes
50-----------
51
52- The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting
53  ``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because
54  they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we
55  still feel that it is worth mentioning in the release notes in case some users
56  had been doing it.
57
58- The header ``<experimental/filesystem>`` has been removed. Instead, use
59  ``<filesystem>`` header. The associated macro
60  ``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed.
61
62- Some libc++ headers no longer transitively include all of ``<algorithm>``and ``<chrono>``.
63  If, after updating libc++, you see compiler errors related to missing declarations in
64  namespace ``std``, it might be because one of your source files now needs to
65  ``#include <algorithm>`` and/or ``#include <chrono>``.
66
67- The integer distributions ``binomial_distribution``, ``discrete_distribution``,
68  ``geometric_distribution``, ``negative_binomial_distribution``, ``poisson_distribution``,
69  and ``uniform_int_distribution`` now conform to the Standard by rejecting
70  template parameter types other than ``short``, ``int``, ``long``, ``long long``,
71  (as an extension) ``__int128_t``, and the unsigned versions thereof.
72  In particular, ``uniform_int_distribution<int8_t>`` is no longer supported.
73
74- The C++14 function ``std::quoted(const char*)`` is no longer supported in
75  C++03 or C++11 modes.
76
77ABI Changes
78-----------
79
80- The ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` macro controlling whether we use an
81  emulation for ``std::nullptr_t`` in C++03 mode has been removed. After this change,
82  ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there
83  will be no way to opt back into the C++03 emulation of ``std::nullptr_t``.
84
85Build System Changes
86--------------------
87
88- Support for standalone builds have been entirely removed from libc++, libc++abi and
89  libunwind. Please use :ref:`these instructions <build instructions>` for building
90  libc++, libc++abi and/or libunwind.
91
92- The ``{LIBCXX,LIBCXXABI,LIBUNWIND}_TARGET_TRIPLE``, ``{LIBCXX,LIBCXXABI,LIBUNWIND}_SYSROOT`` and
93  ``{LIBCXX,LIBCXXABI,LIBUNWIND}_GCC_TOOLCHAIN`` CMake variables have been removed. Instead, please
94  use the ``CMAKE_CXX_COMPILER_TARGET``, ``CMAKE_SYSROOT`` and ``CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN``
95  variables provided by CMake.
96
97- When building for Windows, vendors who want to avoid dll-exporting symbols from the static libc++abi
98  library should set ``LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON`` when configuring CMake. The current
99  behavior, which tries to guess the correct dll-export semantics based on whether we're building
100  the libc++ shared library, will be removed in LLVM 16.
101
102- Previously, the C++ ABI library headers would be installed inside ``<prefix>/include/c++/v1``
103  alongside the libc++ headers as part of building libc++. This is not the case anymore -- the
104  ABI library is expected to install its headers where it wants them as part of its own build.
105  Note that no action is required for most users, who build libc++ against libc++abi, since
106  libc++abi already installs its headers in the right location. However, vendors building
107  libc++ against alternate ABI libraries should make sure that their ABI library installs
108  its own headers.
109