Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__fwd/array.h

@@ -0,0 +1,26 @@
+//===---------------------------------------------------------------------===//
+//
+// 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___FWD_ARRAY_H
+#define _LIBCPP___FWD_ARRAY_H
+
+#include <__config>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp, size_t _Size>
+struct _LIBCPP_TEMPLATE_VIS array;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_ARRAY_H

third_party/libcxx/__fwd/fstream.h

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_FSTREAM_H
+#define _LIBCPP___FWD_FSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_filebuf;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_ifstream;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_ofstream;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_fstream;
+
+using filebuf  = basic_filebuf<char>;
+using ifstream = basic_ifstream<char>;
+using ofstream = basic_ofstream<char>;
+using fstream  = basic_fstream<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wfilebuf  = basic_filebuf<wchar_t>;
+using wifstream = basic_ifstream<wchar_t>;
+using wofstream = basic_ofstream<wchar_t>;
+using wfstream  = basic_fstream<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(filebuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfilebuf)) basic_filebuf;
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(ifstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wifstream)) basic_ifstream;
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(ofstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wofstream)) basic_ofstream;
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(fstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfstream)) basic_fstream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_FSTREAM_H

third_party/libcxx/__fwd/get.h

@@ -0,0 +1,115 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_GET_H
+#define _LIBCPP___FWD_GET_H
+
+#include <__concepts/copyable.h>
+#include <__config>
+#include <__fwd/array.h>
+#include <__fwd/pair.h>
+#include <__fwd/subrange.h>
+#include <__fwd/tuple.h>
+#include <__tuple/tuple_element.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_CXX03_LANG
+
+template <size_t _Ip, class ..._Tp>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+typename tuple_element<_Ip, tuple<_Tp...> >::type&
+get(tuple<_Tp...>&) _NOEXCEPT;
+
+template <size_t _Ip, class ..._Tp>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const typename tuple_element<_Ip, tuple<_Tp...> >::type&
+get(const tuple<_Tp...>&) _NOEXCEPT;
+
+template <size_t _Ip, class ..._Tp>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+typename tuple_element<_Ip, tuple<_Tp...> >::type&&
+get(tuple<_Tp...>&&) _NOEXCEPT;
+
+template <size_t _Ip, class ..._Tp>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const typename tuple_element<_Ip, tuple<_Tp...> >::type&&
+get(const tuple<_Tp...>&&) _NOEXCEPT;
+
+#endif //_LIBCPP_CXX03_LANG
+
+template <size_t _Ip, class _T1, class _T2>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+typename tuple_element<_Ip, pair<_T1, _T2> >::type&
+get(pair<_T1, _T2>&) _NOEXCEPT;
+
+template <size_t _Ip, class _T1, class _T2>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
+get(const pair<_T1, _T2>&) _NOEXCEPT;
+
+#ifndef _LIBCPP_CXX03_LANG
+template <size_t _Ip, class _T1, class _T2>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
+get(pair<_T1, _T2>&&) _NOEXCEPT;
+
+template <size_t _Ip, class _T1, class _T2>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
+get(const pair<_T1, _T2>&&) _NOEXCEPT;
+#endif
+
+template <size_t _Ip, class _Tp, size_t _Size>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+_Tp&
+get(array<_Tp, _Size>&) _NOEXCEPT;
+
+template <size_t _Ip, class _Tp, size_t _Size>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const _Tp&
+get(const array<_Tp, _Size>&) _NOEXCEPT;
+
+#ifndef _LIBCPP_CXX03_LANG
+template <size_t _Ip, class _Tp, size_t _Size>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+_Tp&&
+get(array<_Tp, _Size>&&) _NOEXCEPT;
+
+template <size_t _Ip, class _Tp, size_t _Size>
+_LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+const _Tp&&
+get(const array<_Tp, _Size>&&) _NOEXCEPT;
+#endif
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace ranges {
+
+template <size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
+  requires((_Index == 0 && copyable<_Iter>) || _Index == 1)
+_LIBCPP_HIDE_FROM_ABI constexpr auto get(const subrange<_Iter, _Sent, _Kind>& __subrange);
+
+template <size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
+  requires(_Index < 2)
+_LIBCPP_HIDE_FROM_ABI constexpr auto get(subrange<_Iter, _Sent, _Kind>&& __subrange);
+
+} // namespace ranges
+
+using ranges::get;
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_GET_H

third_party/libcxx/__fwd/hash.h

@@ -0,0 +1,25 @@
+//===---------------------------------------------------------------------===//
+//
+// 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___FWD_HASH_H
+#define _LIBCPP___FWD_HASH_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+struct _LIBCPP_TEMPLATE_VIS hash;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_HASH_H

third_party/libcxx/__fwd/ios.h

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_IOS_H
+#define _LIBCPP___FWD_IOS_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_ios;
+
+using ios = basic_ios<char>;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wios = basic_ios<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(ios) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wios)) basic_ios;
+
+#if defined(_NEWLIB_VERSION)
+// On newlib, off_t is 'long int'
+using streamoff = long int; // for char_traits in <string>
+#else
+using streamoff = long long; // for char_traits in <string>
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_IOS_H

third_party/libcxx/__fwd/istream.h

@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_ISTREAM_H
+#define _LIBCPP___FWD_ISTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_istream;
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_iostream;
+
+using istream  = basic_istream<char>;
+using iostream = basic_iostream<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wistream  = basic_istream<wchar_t>;
+using wiostream = basic_iostream<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(istream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistream)) basic_istream;
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(iostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wiostream)) basic_iostream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_ISTREAM_H

third_party/libcxx/__fwd/memory_resource.h

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_MEMORY_RESOURCE_H
+#define _LIBCPP___FWD_MEMORY_RESOURCE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace pmr {
+template <class _ValueType>
+class _LIBCPP_TEMPLATE_VIS polymorphic_allocator;
+} // namespace pmr
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_MEMORY_RESOURCE_H

third_party/libcxx/__fwd/ostream.h

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_OSTREAM_H
+#define _LIBCPP___FWD_OSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_ostream;
+
+using ostream = basic_ostream<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wostream = basic_ostream<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(ostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostream)) basic_ostream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_OSTREAM_H

third_party/libcxx/__fwd/pair.h

@@ -0,0 +1,25 @@
+//===---------------------------------------------------------------------===//
+//
+// 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___FWD_PAIR_H
+#define _LIBCPP___FWD_PAIR_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class, class>
+struct _LIBCPP_TEMPLATE_VIS pair;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_PAIR_H

third_party/libcxx/__fwd/span.h

@@ -0,0 +1,37 @@
+// -*- 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___FWD_SPAN_H
+#define _LIBCPP___FWD_SPAN_H
+
+#include <__config>
+#include <cstddef>
+#include <limits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+inline constexpr size_t dynamic_extent = numeric_limits<size_t>::max();
+template <typename _Tp, size_t _Extent = dynamic_extent> class span;
+
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___FWD_SPAN_H

third_party/libcxx/__fwd/sstream.h

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_SSTREAM_H
+#define _LIBCPP___FWD_SSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_stringbuf;
+
+template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_istringstream;
+template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_ostringstream;
+template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_stringstream;
+
+using stringbuf     = basic_stringbuf<char>;
+using istringstream = basic_istringstream<char>;
+using ostringstream = basic_ostringstream<char>;
+using stringstream  = basic_stringstream<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wstringbuf     = basic_stringbuf<wchar_t>;
+using wistringstream = basic_istringstream<wchar_t>;
+using wostringstream = basic_ostringstream<wchar_t>;
+using wstringstream  = basic_stringstream<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits, class _Allocator>
+class _LIBCPP_PREFERRED_NAME(stringbuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringbuf)) basic_stringbuf;
+template <class _CharT, class _Traits, class _Allocator>
+class _LIBCPP_PREFERRED_NAME(istringstream)
+    _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistringstream)) basic_istringstream;
+template <class _CharT, class _Traits, class _Allocator>
+class _LIBCPP_PREFERRED_NAME(ostringstream)
+    _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostringstream)) basic_ostringstream;
+template <class _CharT, class _Traits, class _Allocator>
+class _LIBCPP_PREFERRED_NAME(stringstream)
+    _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringstream)) basic_stringstream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_SSTREAM_H

third_party/libcxx/__fwd/streambuf.h

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_STREAMBUF_H
+#define _LIBCPP___FWD_STREAMBUF_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_streambuf;
+
+using streambuf = basic_streambuf<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wstreambuf = basic_streambuf<wchar_t>;
+#endif
+
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(streambuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstreambuf)) basic_streambuf;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_STREAMBUF_H

third_party/libcxx/__fwd/string.h

@@ -0,0 +1,110 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_STRING_H
+#define _LIBCPP___FWD_STRING_H
+
+#include <__config>
+#include <__fwd/memory_resource.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT>
+struct _LIBCPP_TEMPLATE_VIS char_traits;
+template <>
+struct char_traits<char>;
+
+#ifndef _LIBCPP_HAS_NO_CHAR8_T
+template <>
+struct char_traits<char8_t>;
+#endif
+
+template <>
+struct char_traits<char16_t>;
+template <>
+struct char_traits<char32_t>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <>
+struct char_traits<wchar_t>;
+#endif
+
+template <class _Tp>
+class _LIBCPP_TEMPLATE_VIS allocator;
+
+template <class _CharT, class _Traits = char_traits<_CharT>, class _Allocator = allocator<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_string;
+
+using string = basic_string<char>;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wstring = basic_string<wchar_t>;
+#endif
+
+#ifndef _LIBCPP_HAS_NO_CHAR8_T
+using u8string = basic_string<char8_t>;
+#endif
+
+using u16string = basic_string<char16_t>;
+using u32string = basic_string<char32_t>;
+
+#if _LIBCPP_STD_VER >= 17
+
+namespace pmr {
+template <class _CharT, class _Traits = char_traits<_CharT>>
+using basic_string = std::basic_string<_CharT, _Traits, polymorphic_allocator<_CharT>>;
+
+using string = basic_string<char>;
+
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+using wstring = basic_string<wchar_t>;
+#  endif
+
+#  ifndef _LIBCPP_HAS_NO_CHAR8_T
+using u8string = basic_string<char8_t>;
+#  endif
+
+using u16string = basic_string<char16_t>;
+using u32string = basic_string<char32_t>;
+
+} // namespace pmr
+
+#endif // _LIBCPP_STD_VER >= 17
+
+// clang-format off
+template <class _CharT, class _Traits, class _Allocator>
+class _LIBCPP_PREFERRED_NAME(string)
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+      _LIBCPP_PREFERRED_NAME(wstring)
+#endif
+#ifndef _LIBCPP_HAS_NO_CHAR8_T
+      _LIBCPP_PREFERRED_NAME(u8string)
+#endif
+      _LIBCPP_PREFERRED_NAME(u16string)
+      _LIBCPP_PREFERRED_NAME(u32string)
+#if _LIBCPP_STD_VER >= 17
+      _LIBCPP_PREFERRED_NAME(pmr::string)
+#  ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+      _LIBCPP_PREFERRED_NAME(pmr::wstring)
+#  endif
+#  ifndef _LIBCPP_HAS_NO_CHAR8_T
+      _LIBCPP_PREFERRED_NAME(pmr::u8string)
+#  endif
+      _LIBCPP_PREFERRED_NAME(pmr::u16string)
+      _LIBCPP_PREFERRED_NAME(pmr::u32string)
+#endif
+      basic_string;
+// clang-format on
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_STRING_H

third_party/libcxx/__fwd/string_view.h

@@ -0,0 +1,50 @@
+// -*- 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___FWD_STRING_VIEW_H
+#define _LIBCPP___FWD_STRING_VIEW_H
+
+#include <__config>
+#include <iosfwd> // char_traits
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template<class _CharT, class _Traits = char_traits<_CharT> >
+class _LIBCPP_TEMPLATE_VIS basic_string_view;
+
+typedef basic_string_view<char>     string_view;
+#ifndef _LIBCPP_HAS_NO_CHAR8_T
+typedef basic_string_view<char8_t>  u8string_view;
+#endif
+typedef basic_string_view<char16_t> u16string_view;
+typedef basic_string_view<char32_t> u32string_view;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_string_view<wchar_t>  wstring_view;
+#endif
+
+// clang-format off
+template <class _CharT, class _Traits>
+class _LIBCPP_PREFERRED_NAME(string_view)
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+      _LIBCPP_PREFERRED_NAME(wstring_view)
+#endif
+#ifndef _LIBCPP_HAS_NO_CHAR8_T
+      _LIBCPP_PREFERRED_NAME(u8string_view)
+#endif
+      _LIBCPP_PREFERRED_NAME(u16string_view)
+      _LIBCPP_PREFERRED_NAME(u32string_view)
+      basic_string_view;
+// clang-format on
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_STRING_VIEW_H

third_party/libcxx/__fwd/subrange.h

@@ -0,0 +1,38 @@
+//===---------------------------------------------------------------------===//
+//
+// 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___FWD_SUBRANGE_H
+#define _LIBCPP___FWD_SUBRANGE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 20
+
+#include <__iterator/concepts.h>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+enum class _LIBCPP_ENUM_VIS subrange_kind : bool { unsized, sized };
+
+template <input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent, subrange_kind _Kind>
+  requires(_Kind == subrange_kind::sized || !sized_sentinel_for<_Sent, _Iter>)
+class _LIBCPP_TEMPLATE_VIS subrange;
+
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 20
+
+#endif // _LIBCPP___FWD_SUBRANGE_H

third_party/libcxx/__fwd/tuple.h

@@ -0,0 +1,29 @@
+//===---------------------------------------------------------------------===//
+//
+// 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___FWD_TUPLE_H
+#define _LIBCPP___FWD_TUPLE_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_CXX03_LANG
+
+template <class...>
+class _LIBCPP_TEMPLATE_VIS tuple;
+
+#endif // _LIBCPP_CXX03_LANG
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_TUPLE_H