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- P0618R0 (Deprecating <codecvt>) 50- P2418R2 (Add support for ``std::generator``-like types to ``std::format``) 51- LWG3659 (Consider ``ATOMIC_FLAG_INIT`` undeprecation) 52 53- Marked the following papers as "Complete" (note that some of those might have 54 been implemented in a previous release but not marked as such): 55 56 - P1207R4 (Movability of Single-pass Iterators); 57 - P1474R1 (Helpful pointers for ``ContiguousIterator``); 58 - P1522R1 (Iterator Difference Type and Integer Overflow); 59 - P1523R1 (Views and Size Types); 60 - P1456R1 (Move-only views); 61 - P1870R1 (``forwarding-range`` is too subtle); 62 - P1878R1 (Constraining Readable Types); 63 - P1970R2 (Consistency for ``size()`` functions: Add ``ranges::ssize``); 64 - P1983R0 (Wording for GB301, US296, US292, US291, and US283). 65 66New Features 67------------ 68 69- `pop_heap` now uses an algorithm known as "bottom-up heapsort" or 70 "heapsort with bounce" to reduce the number of comparisons, and rearranges 71 elements using move-assignment instead of `swap`. 72 73- Libc++ now supports a variety of assertions that can be turned on to help catch 74 undefined behavior in user code. This new support is now separate from the old 75 (and incomplete) Debug Mode. Vendors can select whether the library they ship 76 should include assertions or not by default. For details, see 77 :ref:`the documentation <assertions-mode>` about this new feature. 78 79- The implementation of the function ``std::to_chars`` for integral types has 80 moved from the dylib to the header. This means the function no longer has a 81 minimum deployment target. 82 83- The format functions (``std::format``, ``std::format_to``, ``std::format_to_n``, and 84 ``std::formatted_size``) now validate the format string at compile time. 85 When the format string is invalid this will make the code ill-formed instead 86 of throwing an exception at run-time. (This does not affect the ``v`` 87 functions.) 88 89- All format functions in ``<format>`` allow the usage of non-copyable types as 90 argument for the formatting functions. This change causes bit fields to become 91 invalid arguments for the formatting functions. 92 93API Changes 94----------- 95 96- The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting 97 ``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because 98 they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we 99 still feel that it is worth mentioning in the release notes in case some users 100 had been doing it. 101 102- The header ``<experimental/filesystem>`` has been removed. Instead, use 103 ``<filesystem>`` header. The associated macro 104 ``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed. 105 106- Libc++ is getting ready to remove unnecessary transitive inclusions. This may 107 break your code in the future. To future-proof your code to these removals, 108 please compile your code with ``_LIBCPP_REMOVE_TRANSITIVE_INCLUDES`` defined 109 and fix any compilation error resulting from missing includes. 110 111- The ``<algorithm>``, ``<array>``, ``<optional>``, ``<unordered_map>`` and ``<vector>`` 112 headers no longer transitively include the ``<functional>`` header. If you see compiler 113 errors related to missing declarations in namespace ``std``, make sure you have the 114 necessary includes. 115 116- The integer distributions ``binomial_distribution``, ``discrete_distribution``, 117 ``geometric_distribution``, ``negative_binomial_distribution``, ``poisson_distribution``, 118 and ``uniform_int_distribution`` now conform to the Standard by rejecting 119 template parameter types other than ``short``, ``int``, ``long``, ``long long``, 120 (as an extension) ``__int128_t``, and the unsigned versions thereof. 121 In particular, ``uniform_int_distribution<int8_t>`` is no longer supported. 122 123- The C++14 function ``std::quoted(const char*)`` is no longer supported in 124 C++03 or C++11 modes. 125 126- Setting a custom debug handler with ``std::__libcpp_debug_function`` is not 127 supported anymore. Please migrate to using the new support for 128 :ref:`assertions <assertions-mode>` instead. 129 130- ``vector<bool>::const_reference``, ``vector<bool>::const_iterator::reference`` 131 and ``bitset::const_reference`` are now aliases for `bool` in the unstable ABI. 132 133- The ``_LIBCPP_DEBUG`` macro is not supported anymore. It will be honoured until 134 LLVM 16, and then it will be an error to define that macro. To enable basic 135 assertions (previously ``_LIBCPP_DEBUG=0``), please use ``_LIBCPP_ENABLE_ASSERTIONS=1``. 136 To enable the debug mode (previously ``_LIBCPP_DEBUG=1|2``), please ensure that 137 the library has been built with support for the debug mode, and it will be 138 enabled automatically (no need to define ``_LIBCPP_DEBUG``). 139 140- The ``_LIBCPP_DISABLE_EXTERN_TEMPLATE`` macro is not honored anymore when defined by 141 users of libc++. Instead, users not wishing to take a dependency on libc++ should link 142 against the static version of libc++, which will result in no dependency being 143 taken against the shared library. 144 145- The ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_VOID_SPECIALIZATION`` macro has been added to allow 146 re-enabling the ``allocator<void>`` specialization. When used in conjuction with 147 ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS``, this ensures that the members of 148 ``allocator<void>`` removed in C++20 can be accessed. 149 150- The experimental versions of ``boyer_moore_searcher`` and ``boyer_moore_horspool_searcher`` 151 will be removed in LLVM 17. You can disable the deprecation warnings by defining 152 ``_LIBCPP_NO_EXPERIMENTAL_DEPRECATION_WARNING_SEARCHERS``. 153 154- ``std::function`` has been removed in C++03. If you are using it, please remove usages 155 or upgrade to C++11 or later. It is possible to re-enable ``std::function`` in C++03 by defining 156 ``_LIBCPP_ENABLE_CXX03_FUNCTION``. This option will be removed in LLVM 16. 157 158- ``unary_function`` and ``binary_function`` are no longer available in C++17 and C++20. 159 They can be re-enabled by defining ``_LIBCPP_ENABLE_CXX17_REMOVED_UNARY_BINARY_FUNCTION``. 160 They are also marked as ``[[deprecated]]`` in C++11 and later. To disable deprecation warnings 161 you have to define ``_LIBCPP_DISABLE_DEPRECATION_WARNINGS``. Note that this disables 162 all deprecation warnings. 163 164- The contents of ``<codecvt>``, ``wstring_convert`` and ``wbuffer_convert`` have been marked as deprecated. 165 To disable deprecation warnings you have to define ``_LIBCPP_DISABLE_DEPRECATION_WARNINGS``. Note that this 166 disables all deprecation warnings. 167 168ABI Changes 169----------- 170 171- The ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` macro controlling whether we use an 172 emulation for ``std::nullptr_t`` in C++03 mode has been removed. After this change, 173 ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there 174 will be no way to opt back into the C++03 emulation of ``std::nullptr_t``. 175 176- On FreeBSD, NetBSD, DragonFlyBSD and Solaris, ``std::random_device`` is now implemented on 177 top of ``arc4random()`` instead of reading from ``/dev/urandom``. Any implementation-defined 178 token used when constructing a ``std::random_device`` will now be ignored instead of 179 interpreted as a file to read entropy from. 180 181- ``std::valarray``'s unary operators ``!``, ``+``, ``~`` and ``-`` now return an expression 182 object instead of a ``valarray``. This was done to fix an issue where any expression involving 183 other ``valarray`` operators and one of these unary operators would end up with a dangling 184 reference. This is a potential ABI break for code that exposes ``std::valarray`` on an ABI 185 boundary, specifically if the return type of an ABI-boundary function is ``auto``-deduced 186 from an expression involving unary operators on ``valarray``. If you are concerned by this, 187 you can audit whether your executable or library exports any function that returns a 188 ``valarray``, and if so ensure that any such function uses ``std::valarray`` directly 189 as a return type instead of relying on the type of ``valarray``-expressions, which is 190 not guaranteed by the Standard anyway. 191 192Build System Changes 193-------------------- 194 195- Support for standalone builds have been entirely removed from libc++, libc++abi and 196 libunwind. Please use :ref:`these instructions <build instructions>` for building 197 libc++, libc++abi and/or libunwind. 198 199- The ``{LIBCXX,LIBCXXABI,LIBUNWIND}_TARGET_TRIPLE``, ``{LIBCXX,LIBCXXABI,LIBUNWIND}_SYSROOT`` and 200 ``{LIBCXX,LIBCXXABI,LIBUNWIND}_GCC_TOOLCHAIN`` CMake variables have been removed. Instead, please 201 use the ``CMAKE_CXX_COMPILER_TARGET``, ``CMAKE_SYSROOT`` and ``CMAKE_CXX_COMPILER_EXTERNAL_TOOLCHAIN`` 202 variables provided by CMake. 203 204- When building for Windows, vendors who want to avoid dll-exporting symbols from the static libc++abi 205 library should set ``LIBCXXABI_HERMETIC_STATIC_LIBRARY=ON`` when configuring CMake. The current 206 behavior, which tries to guess the correct dll-export semantics based on whether we're building 207 the libc++ shared library, will be removed in LLVM 16. 208 209- Previously, the C++ ABI library headers would be installed inside ``<prefix>/include/c++/v1`` 210 alongside the libc++ headers as part of building libc++. This is not the case anymore -- the 211 ABI library is expected to install its headers where it wants them as part of its own build. 212 Note that no action is required for most users, who build libc++ against libc++abi, since 213 libc++abi already installs its headers in the right location. However, vendors building 214 libc++ against alternate ABI libraries should make sure that their ABI library installs 215 its own headers. 216 217- The legacy testing configuration is now deprecated and will be removed in the next release. For 218 most users, this should not have any impact. However, if you are testing libc++, libc++abi or 219 libunwind in a configuration or on a platform that used to be supported by the legacy testing 220 configuration and isn't supported by one of the configurations in ``libcxx/test/configs``, 221 ``libcxxabi/test/configs`` or ``libunwind/test/configs``, please move to one of those 222 configurations or define your own. 223 224- The ``LIBCXX_ENABLE_DEBUG_MODE_SUPPORT`` CMake configuration is not supported anymore. If you 225 were disabling support for the debug mode with that flag, please use ``LIBCXX_ENABLE_BACKWARDS_COMPATIBILITY_DEBUG_MODE_SYMBOLS=OFF`` 226 instead. 227 228- MinGW DLL builds of libc++ no longer use dllimport in their headers, which 229 means that the same set of installed headers works for both DLL and static 230 linkage. This means that distributors finally can build both library 231 versions with a single CMake invocation. 232 233- The ``LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT`` configuration option has been removed. Indeed, 234 the risk of ODR violations from mixing different versions of libc++ in the same program has 235 been mitigated with a different technique that is simpler and does not have the drawbacks of 236 using internal linkage. 237