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 38Implemented Papers 39------------------ 40 41- P0627R6 (Function to mark unreachable code) 42- P1165R1 (Make stateful allocator propagation more consistent for ``operator+(basic_string)``) 43- P0674R1 (Support arrays in ``make_shared`` and ``allocate_shared``) 44- P0980R1 (Making ``std::string`` constexpr) 45- P2216R3 (std::format improvements) 46- P0174R2 (Deprecating Vestigial Library Parts in C++17) 47- N4190 (Removing auto_ptr, random_shuffle(), And Old <functional> Stuff) 48- P0154R1 (Hardware inference size) 49 50- Marked the following papers as "Complete" (note that some of those might have 51 been implemented in a previous release but not marked as such): 52 53 - P1207R4 (Movability of Single-pass Iterators); 54 - P1474R1 (Helpful pointers for ``ContiguousIterator``); 55 - P1522R1 (Iterator Difference Type and Integer Overflow); 56 - P1523R1 (Views and Size Types); 57 - P1456R1 (Move-only views); 58 - P1870R1 (``forwarding-range`` is too subtle); 59 - P1878R1 (Constraining Readable Types); 60 - P1970R2 (Consistency for ``size()`` functions: Add ``ranges::ssize``); 61 - P1983R0 (Wording for GB301, US296, US292, US291, and US283). 62 63New Features 64------------ 65 66- `pop_heap` now uses an algorithm known as "bottom-up heapsort" or 67 "heapsort with bounce" to reduce the number of comparisons, and rearranges 68 elements using move-assignment instead of `swap`. 69 70- Libc++ now supports a variety of assertions that can be turned on to help catch 71 undefined behavior in user code. This new support is now separate from the old 72 (and incomplete) Debug Mode. Vendors can select whether the library they ship 73 should include assertions or not by default. For details, see 74 :ref:`the documentation <assertions-mode>` about this new feature. 75 76- The implementation of the function ``std::to_chars`` for integral types has 77 moved from the dylib to the header. This means the function no longer has a 78 minimum deployment target. 79 80- The format functions (``std::format``, ``std::format_to``, ``std::format_to_n``, and 81 ``std::formatted_size``) now validate the format string at compile time. 82 When the format string is invalid this will make the code ill-formed instead 83 of throwing an exception at run-time. (This does not affect the ``v`` 84 functions.) 85 86 87API Changes 88----------- 89 90- The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting 91 ``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because 92 they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we 93 still feel that it is worth mentioning in the release notes in case some users 94 had been doing it. 95 96- The header ``<experimental/filesystem>`` has been removed. Instead, use 97 ``<filesystem>`` header. The associated macro 98 ``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed. 99 100- Libc++ is getting ready to remove unnecessary transitive inclusions. This may 101 break your code in the future. To future-proof your code to these removals, 102 please compile your code with ``_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`` defined 103 and fix any compilation error resulting from missing includes. 104 105- The ``<algorithm>``, ``<array>``, ``<optional>``, ``<unordered_map>`` and ``<vector>`` 106 headers no longer transitively include the ``<functional>`` header. If you see compiler 107 errors related to missing declarations in namespace ``std``, make sure you have the 108 necessary includes. 109 110- The integer distributions ``binomial_distribution``, ``discrete_distribution``, 111 ``geometric_distribution``, ``negative_binomial_distribution``, ``poisson_distribution``, 112 and ``uniform_int_distribution`` now conform to the Standard by rejecting 113 template parameter types other than ``short``, ``int``, ``long``, ``long long``, 114 (as an extension) ``__int128_t``, and the unsigned versions thereof. 115 In particular, ``uniform_int_distribution<int8_t>`` is no longer supported. 116 117- The C++14 function ``std::quoted(const char*)`` is no longer supported in 118 C++03 or C++11 modes. 119 120- Setting a custom debug handler with ``std::__libcpp_debug_function`` is not 121 supported anymore. Please migrate to using the new support for 122 :ref:`assertions <assertions-mode>` instead. 123 124- ``vector<bool>::const_reference``, ``vector<bool>::const_iterator::reference`` 125 and ``bitset::const_reference`` are now aliases for `bool` in the unstable ABI. 126 127- The ``_LIBCPP_DEBUG`` macro is not supported anymore. It will be honoured until 128 LLVM 16, and then it will be an error to define that macro. To enable basic 129 assertions (previously ``_LIBCPP_DEBUG=0``), please use ``_LIBCPP_ENABLE_ASSERTIONS=1``. 130 To enable the debug mode (previously ``_LIBCPP_DEBUG=1|2``), please ensure that 131 the library has been built with support for the debug mode, and it will be 132 enabled automatically (no need to define ``_LIBCPP_DEBUG``). 133 134- The ``_LIBCPP_DISABLE_EXTERN_TEMPLATE`` macro is not honored anymore when defined by 135 users of libc++. Instead, users not wishing to take a dependency on libc++ should link 136 against the static version of libc++, which will result in no dependency being 137 taken against the shared library. 138 139- The ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION`` macro has been added to allow 140 re-enabling the ``allocator<void>`` specialization. When used in conjuction with 141 ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS``, this ensures that the members of 142 ``allocator<void>`` removed in C++20 can be accessed. 143 144- The experimental versions of ``boyer_moore_searcher`` and ``boyer_moore_horspool_searcher`` 145 will be removed in LLVM 17. You can disable the deprecation warnings by defining 146 ``_LIBCPP_NO_EXPERIMENTAL_DEPRECATION_WARNING_SEARCHERS``. 147 148- ``std::function`` has been removed in C++03. If you are using it, please remove usages 149 or upgrade to C++11 or later. It is possible to re-enable ``std::function`` in C++03 by defining 150 ``_LIBCPP_ENABLE_CXX03_FUNCTION``. This option will be removed in LLVM 16. 151 152- ``unary_function`` and ``binary_function`` are no longer available in C++17 and C++20. 153 They can be re-enabled by defining ``_LIBCPP_ENABLE_CXX17_REMOVED_UNARY_BINARY_FUNCTION``. 154 They are also marked as ``[[deprecated]]`` in C++11 and later. To disable deprecation warnings 155 you have to define ``_LIBCPP_DISABLE_DEPRECATION_WARNINGS``. Note that this disables 156 all deprecation warnings. 157 158ABI Changes 159----------- 160 161- The ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` macro controlling whether we use an 162 emulation for ``std::nullptr_t`` in C++03 mode has been removed. After this change, 163 ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there 164 will be no way to opt back into the C++03 emulation of ``std::nullptr_t``. 165 166- On FreeBSD, NetBSD, DragonFlyBSD and Solaris, ``std::random_device`` is now implemented on 167 top of ``arc4random()`` instead of reading from ``/dev/urandom``. Any implementation-defined 168 token used when constructing a ``std::random_device`` will now be ignored instead of 169 interpreted as a file to read entropy from. 170 171- ``std::valarray``'s unary operators ``!``, ``+``, ``~`` and ``-`` now return an expression 172 object instead of a ``valarray``. This was done to fix an issue where any expression involving 173 other ``valarray`` operators and one of these unary operators would end up with a dangling 174 reference. This is a potential ABI break for code that exposes ``std::valarray`` on an ABI 175 boundary, specifically if the return type of an ABI-boundary function is ``auto``-deduced 176 from an expression involving unary operators on ``valarray``. If you are concerned by this, 177 you can audit whether your executable or library exports any function that returns a 178 ``valarray``, and if so ensure that any such function uses ``std::valarray`` directly 179 as a return type instead of relying on the type of ``valarray``-expressions, which is 180 not guaranteed by the Standard anyway. 181 182Build System Changes 183-------------------- 184 185- Support for standalone builds have been entirely removed from libc++, libc++abi and 186 libunwind. Please use :ref:`these instructions <build instructions>` for building 187 libc++, libc++abi and/or libunwind. 188 189- The ``{LIBCXX,LIBCXXABI,LIBUNWIND}_TARGET_TRIPLE``, ``{LIBCXX,LIBCXXABI,LIBUNWIND}_SYSROOT`` and 190 ``{LIBCXX,LIBCXXABI,LIBUNWIND}_GCC_TOOLCHAIN`` CMake variables have been removed. Instead, please 191 use the ``CMAKE_CXX_COMPILER_TARGET``, ``CMAKE_SYSROOT`` and ``CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN`` 192 variables provided by CMake. 193 194- When building for Windows, vendors who want to avoid dll-exporting symbols from the static libc++abi 195 library should set ``LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON`` when configuring CMake. The current 196 behavior, which tries to guess the correct dll-export semantics based on whether we're building 197 the libc++ shared library, will be removed in LLVM 16. 198 199- Previously, the C++ ABI library headers would be installed inside ``<prefix>/include/c++/v1`` 200 alongside the libc++ headers as part of building libc++. This is not the case anymore -- the 201 ABI library is expected to install its headers where it wants them as part of its own build. 202 Note that no action is required for most users, who build libc++ against libc++abi, since 203 libc++abi already installs its headers in the right location. However, vendors building 204 libc++ against alternate ABI libraries should make sure that their ABI library installs 205 its own headers. 206 207- The legacy testing configuration is now deprecated and will be removed in the next release. For 208 most users, this should not have any impact. However, if you are testing libc++, libc++abi or 209 libunwind in a configuration or on a platform that used to be supported by the legacy testing 210 configuration and isn't supported by one of the configurations in ``libcxx/test/configs``, 211 ``libcxxabi/test/configs`` or ``libunwind/test/configs``, please move to one of those 212 configurations or define your own. 213 214- The ``LIBCXX_ENABLE_DEBUG_MODE_SUPPORT`` CMake configuration is not supported anymore. If you 215 were disabling support for the debug mode with that flag, please use ``LIBCXX_ENABLE_BACKWARDS_COMPATIBILITY_DEBUG_MODE_SYMBOLS=OFF`` 216 instead. 217 218- MinGW DLL builds of libc++ no longer use dllimport in their headers, which 219 means that the same set of installed headers works for both DLL and static 220 linkage. This means that distributors finally can build both library 221 versions with a single CMake invocation. 222