include/__availability

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___AVAILABILITY
#define _LIBCPP___AVAILABILITY

#include <__config>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#   pragma GCC system_header
#endif

// Libc++ is shipped by various vendors. In particular, it is used as a system
// library on macOS, iOS and other Apple platforms. In order for users to be
// able to compile a binary that is intended to be deployed to an older version
// of a platform, Clang provides availability attributes [1]. These attributes
// can be placed on declarations and are used to describe the life cycle of a
// symbol in the library.
//
// The main goal is to ensure a compile-time error if a symbol that hasn't been
// introduced in a previously released library is used in a program that targets
// that previously released library. Normally, this would be a load-time error
// when one tries to launch the program against the older library.
//
// For example, the filesystem library was introduced in the dylib in macOS 10.15.
// If a user compiles on a macOS 10.15 host but targets macOS 10.13 with their
// program, the compiler would normally not complain (because the required
// declarations are in the headers), but the dynamic loader would fail to find
// the symbols when actually trying to launch the program on macOS 10.13. To
// turn this into a compile-time issue instead, declarations are annotated with
// when they were introduced, and the compiler can produce a diagnostic if the
// program references something that isn't available on the deployment target.
//
// This mechanism is general in nature, and any vendor can add their markup to
// the library (see below). Whenever a new feature is added that requires support
// in the shared library, a macro should be added below to mark this feature
// as unavailable. When vendors decide to ship the feature as part of their
// shared library, they can update the markup appropriately.
//
// Note that this mechanism is disabled by default in the "upstream" libc++.
// Availability annotations are only meaningful when shipping libc++ inside
// a platform (i.e. as a system library), and so vendors that want them should
// turn those annotations on at CMake configuration time.
//
// [1]: https://clang.llvm.org/docs/AttributeReference.html#availability


// For backwards compatibility, allow users to define _LIBCPP_DISABLE_AVAILABILITY
// for a while.
#if defined(_LIBCPP_DISABLE_AVAILABILITY)
#   if !defined(_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
#       define _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS
#   endif
#endif

// Availability markup is disabled when building the library, or when the compiler
// doesn't support the proper attributes.
#if defined(_LIBCPP_BUILDING_LIBRARY) ||                                        \
    defined(_LIBCXXABI_BUILDING_LIBRARY) ||                                     \
    !__has_feature(attribute_availability_with_strict) ||                       \
    !__has_feature(attribute_availability_in_templates) ||                      \
    !__has_extension(pragma_clang_attribute_external_declaration)
#   if !defined(_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)
#       define _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS
#   endif
#endif

#if defined(_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS)

    // This controls the availability of std::shared_mutex and std::shared_timed_mutex,
    // which were added to the dylib later.
#   define _LIBCPP_AVAILABILITY_SHARED_MUTEX

    // These macros control the availability of std::bad_optional_access and
    // other exception types. These were put in the shared library to prevent
    // code bloat from every user program defining the vtable for these exception
    // types.
#   define _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS
#   define _LIBCPP_AVAILABILITY_BAD_VARIANT_ACCESS
#   define _LIBCPP_AVAILABILITY_BAD_ANY_CAST

    // This controls the availability of std::uncaught_exceptions().
#   define _LIBCPP_AVAILABILITY_UNCAUGHT_EXCEPTIONS

    // This controls the availability of the sized version of ::operator delete,
    // which was added to the dylib later.
#   define _LIBCPP_AVAILABILITY_SIZED_NEW_DELETE

    // This controls the availability of the std::future_error exception.
#   define _LIBCPP_AVAILABILITY_FUTURE_ERROR

    // This controls the availability of std::type_info's vtable.
    // I can't imagine how using std::type_info can work at all if
    // this isn't supported.
#   define _LIBCPP_AVAILABILITY_TYPEINFO_VTABLE

    // This controls the availability of std::locale::category members
    // (e.g. std::locale::collate), which are defined in the dylib.
#   define _LIBCPP_AVAILABILITY_LOCALE_CATEGORY

    // This controls the availability of atomic operations on std::shared_ptr
    // (e.g. `std::atomic_store(std::shared_ptr)`), which require a shared
    // lock table located in the dylib.
#   define _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR

    // These macros control the availability of all parts of <filesystem> that
    // depend on something in the dylib.
#   define _LIBCPP_AVAILABILITY_FILESYSTEM
#   define _LIBCPP_AVAILABILITY_FILESYSTEM_PUSH
#   define _LIBCPP_AVAILABILITY_FILESYSTEM_POP

    // This controls the availability of std::to_chars.
#   define _LIBCPP_AVAILABILITY_TO_CHARS

    // This controls the availability of the C++20 synchronization library,
    // which requires shared library support for various operations
    // (see libcxx/src/atomic.cpp).
#   define _LIBCPP_AVAILABILITY_SYNC

#elif defined(__APPLE__)

#   define _LIBCPP_AVAILABILITY_SHARED_MUTEX                                    \
        __attribute__((availability(macosx,strict,introduced=10.12)))           \
        __attribute__((availability(ios,strict,introduced=10.0)))               \
        __attribute__((availability(tvos,strict,introduced=10.0)))              \
        __attribute__((availability(watchos,strict,introduced=3.0)))
#   define _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS                             \
        __attribute__((availability(macosx,strict,introduced=10.13)))           \
        __attribute__((availability(ios,strict,introduced=11.0)))               \
        __attribute__((availability(tvos,strict,introduced=11.0)))              \
        __attribute__((availability(watchos,strict,introduced=4.0)))
#   define _LIBCPP_AVAILABILITY_BAD_VARIANT_ACCESS                              \
        _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS
#   define _LIBCPP_AVAILABILITY_BAD_ANY_CAST                                    \
        _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS
#   define _LIBCPP_AVAILABILITY_UNCAUGHT_EXCEPTIONS                             \
        __attribute__((availability(macosx,strict,introduced=10.12)))           \
        __attribute__((availability(ios,strict,introduced=10.0)))               \
        __attribute__((availability(tvos,strict,introduced=10.0)))              \
        __attribute__((availability(watchos,strict,introduced=3.0)))
#   define _LIBCPP_AVAILABILITY_SIZED_NEW_DELETE                                \
        __attribute__((availability(macosx,strict,introduced=10.12)))           \
        __attribute__((availability(ios,strict,introduced=10.0)))               \
        __attribute__((availability(tvos,strict,introduced=10.0)))              \
        __attribute__((availability(watchos,strict,introduced=3.0)))
#   define _LIBCPP_AVAILABILITY_FUTURE_ERROR                                    \
        __attribute__((availability(ios,strict,introduced=6.0)))
#   define _LIBCPP_AVAILABILITY_TYPEINFO_VTABLE                                 \
        __attribute__((availability(macosx,strict,introduced=10.9)))            \
        __attribute__((availability(ios,strict,introduced=7.0)))
#   define _LIBCPP_AVAILABILITY_LOCALE_CATEGORY                                 \
        __attribute__((availability(macosx,strict,introduced=10.9)))            \
        __attribute__((availability(ios,strict,introduced=7.0)))
#   define _LIBCPP_AVAILABILITY_ATOMIC_SHARED_PTR                               \
        __attribute__((availability(macosx,strict,introduced=10.9)))            \
        __attribute__((availability(ios,strict,introduced=7.0)))
#   define _LIBCPP_AVAILABILITY_FILESYSTEM                                      \
        __attribute__((availability(macosx,strict,introduced=10.15)))           \
        __attribute__((availability(ios,strict,introduced=13.0)))               \
        __attribute__((availability(tvos,strict,introduced=13.0)))              \
        __attribute__((availability(watchos,strict,introduced=6.0)))
#   define _LIBCPP_AVAILABILITY_FILESYSTEM_PUSH                                 \
        _Pragma("clang attribute push(__attribute__((availability(macosx,strict,introduced=10.15))), apply_to=any(function,record))") \
        _Pragma("clang attribute push(__attribute__((availability(ios,strict,introduced=13.0))), apply_to=any(function,record))")     \
        _Pragma("clang attribute push(__attribute__((availability(tvos,strict,introduced=13.0))), apply_to=any(function,record))")    \
        _Pragma("clang attribute push(__attribute__((availability(watchos,strict,introduced=6.0))), apply_to=any(function,record))")
#   define _LIBCPP_AVAILABILITY_FILESYSTEM_POP                                  \
        _Pragma("clang attribute pop")                                          \
        _Pragma("clang attribute pop")                                          \
        _Pragma("clang attribute pop")                                          \
        _Pragma("clang attribute pop")
#   define _LIBCPP_AVAILABILITY_TO_CHARS                                        \
        _LIBCPP_AVAILABILITY_FILESYSTEM
#   define _LIBCPP_AVAILABILITY_SYNC                                            \
        __attribute__((unavailable))

#else

// ...New vendors can add availability markup here...

#   error "It looks like you're trying to enable vendor availability markup, but you haven't defined the corresponding macros yet!"

#endif

// Define availability attributes that depend on _LIBCPP_NO_EXCEPTIONS.
// Those are defined in terms of the availability attributes above, and
// should not be vendor-specific.
#if defined(_LIBCPP_NO_EXCEPTIONS)
#   define _LIBCPP_AVAILABILITY_FUTURE
#   define _LIBCPP_AVAILABILITY_THROW_BAD_ANY_CAST
#   define _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
#   define _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS
#else
#   define _LIBCPP_AVAILABILITY_FUTURE                    _LIBCPP_AVAILABILITY_FUTURE_ERROR
#   define _LIBCPP_AVAILABILITY_THROW_BAD_ANY_CAST        _LIBCPP_AVAILABILITY_BAD_ANY_CAST
#   define _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS
#   define _LIBCPP_AVAILABILITY_THROW_BAD_VARIANT_ACCESS  _LIBCPP_AVAILABILITY_BAD_VARIANT_ACCESS
#endif

#endif  // _LIBCPP___AVAILABILITY