Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__ranges/empty_view.h

@@ -0,0 +1,54 @@
+// -*- 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___RANGES_EMPTY_VIEW_H
+#define _LIBCPP___RANGES_EMPTY_VIEW_H
+
+#include <__config>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/is_object.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace ranges {
+  template<class _Tp>
+    requires is_object_v<_Tp>
+  class empty_view : public view_interface<empty_view<_Tp>> {
+  public:
+    _LIBCPP_HIDE_FROM_ABI static constexpr _Tp* begin() noexcept { return nullptr; }
+    _LIBCPP_HIDE_FROM_ABI static constexpr _Tp* end() noexcept { return nullptr; }
+    _LIBCPP_HIDE_FROM_ABI static constexpr _Tp* data() noexcept { return nullptr; }
+    _LIBCPP_HIDE_FROM_ABI static constexpr size_t size() noexcept { return 0; }
+    _LIBCPP_HIDE_FROM_ABI static constexpr bool empty() noexcept { return true; }
+  };
+
+  template<class _Tp>
+  inline constexpr bool enable_borrowed_range<empty_view<_Tp>> = true;
+
+  namespace views {
+
+  template <class _Tp>
+  inline constexpr empty_view<_Tp> empty{};
+
+  } // namespace views
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_EMPTY_VIEW_H