1 files changed, 183 insertions, 0 deletions
diff --git a/libcxx/include/__ranges/take_while_view.h b/libcxx/include/__ranges/take_while_view.h
new file mode 100644
index 000000000000..59c0a4f82889
--- /dev/null
+++ b/libcxx/include/__ranges/take_while_view.h
@@ -0,0 +1,183 @@
+// -*- 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_TAKE_WHILE_VIEW_H
+#define _LIBCPP___RANGES_TAKE_WHILE_VIEW_H
+
+#include <__concepts/constructible.h>
+#include <__concepts/convertible_to.h>
+#include <__config>
+#include <__functional/bind_back.h>
+#include <__functional/invoke.h>
+#include <__iterator/concepts.h>
+#include <__memory/addressof.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/copyable_box.h>
+#include <__ranges/range_adaptor.h>
+#include <__ranges/view_interface.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/is_object.h>
+#include <__type_traits/maybe_const.h>
+#include <__utility/forward.h>
+#include <__utility/in_place.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace ranges {
+
+// The spec uses the unnamed requirement inside the `begin` and `end` member functions:
+//     constexpr auto begin() const
+//       requires range<const V> && indirect_unary_predicate<const Pred, iterator_t<const V>>
+// However, due to a clang-14 and clang-15 bug, the above produces a hard error when `const V` is not a range.
+// The workaround is to create a named concept and use the concept instead.
+// As of take_while_view is implemented, the clang-trunk has already fixed the bug.
+// It is OK to remove the workaround once our CI no longer uses clang-14, clang-15 based compilers,
+// because we don't actually expect a lot of vendors to ship a new libc++ with an old clang.
+template <class _View, class _Pred>
+concept __take_while_const_is_range =
+    range<const _View> && indirect_unary_predicate<const _Pred, iterator_t<const _View>>;
+
+template <class, class, bool>
+class __take_while_view_sentinel;
+
+template <view _View, class _Pred>
+  requires input_range<_View> && is_object_v<_Pred> && indirect_unary_predicate<const _Pred, iterator_t<_View>>
+class take_while_view : public view_interface<take_while_view<_View, _Pred>> {
+  template <class, class, bool>
+  friend class __take_while_view_sentinel;
+
+  template <bool _Const>
+  using __sentinel = __take_while_view_sentinel<_View, _Pred, _Const>;
+
+  _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
+  _LIBCPP_NO_UNIQUE_ADDRESS __copyable_box<_Pred> __pred_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI take_while_view()
+    requires default_initializable<_View> && default_initializable<_Pred>
+  = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr take_while_view(_View __base, _Pred __pred)
+      : __base_(std::move(__base)), __pred_(std::in_place, std::move(__pred)) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() const&
+    requires copy_constructible<_View>
+  {
+    return __base_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return std::move(__base_); }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr const _Pred& pred() const { return *__pred_; }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin()
+    requires(!__simple_view<_View>)
+  {
+    return ranges::begin(__base_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const
+    requires __take_while_const_is_range<_View, _Pred>
+  {
+    return ranges::begin(__base_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end()
+    requires(!__simple_view<_View>)
+  {
+    return __sentinel</*_Const=*/false>(ranges::end(__base_), std::addressof(*__pred_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr auto end() const
+    requires __take_while_const_is_range<_View, _Pred>
+  {
+    return __sentinel</*_Const=*/true>(ranges::end(__base_), std::addressof(*__pred_));
+  }
+};
+
+template <class _Range, class _Pred>
+take_while_view(_Range&&, _Pred) -> take_while_view<views::all_t<_Range>, _Pred>;
+
+template <class _View, class _Pred, bool _Const>
+class __take_while_view_sentinel {
+  using _Base = __maybe_const<_Const, _View>;
+
+  sentinel_t<_Base> __end_ = sentinel_t<_Base>();
+  const _Pred* __pred_     = nullptr;
+
+  template <class, class, bool>
+  friend class __take_while_view_sentinel;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI __take_while_view_sentinel() = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr explicit __take_while_view_sentinel(sentinel_t<_Base> __end, const _Pred* __pred)
+      : __end_(std::move(__end)), __pred_(__pred) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr __take_while_view_sentinel(__take_while_view_sentinel<_View, _Pred, !_Const> __s)
+    requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
+      : __end_(std::move(__s.__end_)), __pred_(__s.__pred_) {}
+
+  _LIBCPP_HIDE_FROM_ABI constexpr sentinel_t<_Base> base() const { return __end_; }
+
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool
+  operator==(const iterator_t<_Base>& __x, const __take_while_view_sentinel& __y) {
+    return __x == __y.__end_ || !std::invoke(*__y.__pred_, *__x);
+  }
+
+  template <bool _OtherConst = !_Const>
+    requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
+  _LIBCPP_HIDE_FROM_ABI friend constexpr bool
+  operator==(const iterator_t<__maybe_const<_OtherConst, _View>>& __x, const __take_while_view_sentinel& __y) {
+    return __x == __y.__end_ || !std::invoke(*__y.__pred_, *__x);
+  }
+};
+
+namespace views {
+namespace __take_while {
+
+struct __fn {
+  template <class _Range, class _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Range&& __range, _Pred&& __pred) const
+      noexcept(noexcept(/**/ take_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred))))
+          -> decltype(/*--*/ take_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred))) {
+    return /*-------------*/ take_while_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred));
+  }
+
+  template <class _Pred>
+    requires constructible_from<decay_t<_Pred>, _Pred>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Pred&& __pred) const
+      noexcept(is_nothrow_constructible_v<decay_t<_Pred>, _Pred>) {
+    return __range_adaptor_closure_t(std::__bind_back(*this, std::forward<_Pred>(__pred)));
+  }
+};
+
+} // namespace __take_while
+
+inline namespace __cpo {
+inline constexpr auto take_while = __take_while::__fn{};
+} // namespace __cpo
+} // namespace views
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___RANGES_TAKE_WHILE_VIEW_H