[libc++] Implement views::join_with

* Partially implements P2441R2: `views::join_with` (https://wg21.link/P2441R2): * `views::join_with` cannot be used in constant expression because P2231R1 hasn't been implemented, * Feature test macro `__cpp_lib_ranges_join_with` is not included, * Completes implementation of P2711R1: "Making multi-param constructors of views explicit" (https://wg21.link/P2711R1), * Implements `[range.join.with.*]` parts of P2770R0: "Stashing stashing iterators for proper flattening" (https://wg21.link/P2770R0), * Renames `test/libcxx/ranges/range.adaptors/range.adaptor.tuple` directory to `test/libcxx/ranges/range.adaptors/range.adaptor.helpers` to match the standard: http://eel.is/c++draft/range.adaptor.helpers (this change happened in P2770R0, see point 3 of wording). * Adds `__ranges/helpers.h` file for helper functions.
llvm · Sep 8, 2023 · f113229 · f113229
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diff --git a/libcxx/docs/ReleaseNotes/18.rst b/libcxx/docs/ReleaseNotes/18.rst
@@ -42,6 +42,7 @@ Implemented Papers
 - P2497R0 - Testing for success or failure of ``<charconv>`` functions
 - P2697R1 - Interfacing ``bitset`` with ``string_view``
 - P2443R1 - ``views::chunk_by``
+- P2711R1 - Making multi-param constructors of ``views`` ``explicit``
 
 Improvements and New Features
 -----------------------------

diff --git a/libcxx/docs/Status/Cxx23.rst b/libcxx/docs/Status/Cxx23.rst
@@ -45,7 +45,8 @@ Paper Status
    .. [#note-P1413R3] P1413R3: ``std::aligned_storage_t`` and ``std::aligned_union_t`` are marked deprecated, but
       clang doesn't issue a diagnostic for deprecated using template declarations.
    .. [#note-P2520R0] P2520R0: Libc++ implemented this paper as a DR in C++20 as well.
-   .. [#note-P2711R1] P2711R1: ``join_with_view`` hasn't been done yet since this type isn't implemented yet.
+   .. [#note-P2441R2] P2441R2: ``views::join_with`` cannot be used in constant expressions (depends on P2231R1). Feature test macro is not defined.
+   .. [#note-P2770R0] P2770R0: ``views::join_with`` part only.
    .. [#note-P2693R1] P2693R1: The formatter for ``std::thread::id`` is implemented.
       The formatter for ``stacktrace`` is not implemented, since ``stacktrace`` is
       not implemented yet.
@@ -63,4 +64,4 @@ Library Working Group Issues Status
 .. note::
 
    .. [#note-LWG3750] LWG3750 Only ``__cpp_lib_format_ranges`` is fully implemented.
-   .. [#note-LWG3798] LWG3798: ``join_with_view``, ``zip_transform_view``, and ``adjacent_transform_view`` haven't been done yet since these types aren't implemented yet.
+   .. [#note-LWG3798] LWG3798: ``zip_transform_view`` and ``adjacent_transform_view`` haven't been done yet since these types aren't implemented yet.
diff --git a/libcxx/docs/Status/Cxx23Papers.csv b/libcxx/docs/Status/Cxx23Papers.csv
@@ -47,7 +47,7 @@
 "`P2273R3 <https://wg21.link/P2273R3>`__","LWG","Making ``std::unique_ptr`` constexpr","February 2022","|Complete|","16.0"
 "`P2387R3 <https://wg21.link/P2387R3>`__","LWG","Pipe support for user-defined range adaptors","February 2022","","","|ranges|"
 "`P2440R1 <https://wg21.link/P2440R1>`__","LWG","``ranges::iota``, ``ranges::shift_left`` and ``ranges::shift_right``","February 2022","","","|ranges|"
-"`P2441R2 <https://wg21.link/P2441R2>`__","LWG","``views::join_with``","February 2022","","","|ranges|"
+"`P2441R2 <https://wg21.link/P2441R2>`__","LWG","``views::join_with``","February 2022","|Partial| [#note-P2441R2]_","","|ranges|"
 "`P2442R1 <https://wg21.link/P2442R1>`__","LWG","Windowing range adaptors: ``views::chunk`` and ``views::slide``","February 2022","","","|ranges|"
 "`P2443R1 <https://wg21.link/P2443R1>`__","LWG","``views::chunk_by``","February 2022","|Complete|","18.0","|ranges|"
 "","","","","","",""
@@ -104,9 +104,9 @@
 "`P2708R1 <https://wg21.link/P2708R1>`__","LWG", "No Further Fundamentals TSes", "November 2022","|Nothing to do|","",""
 "","","","","","",""
 "`P0290R4 <https://wg21.link/P0290R4>`__","LWG", "``apply()`` for ``synchronized_value<T>``","February 2023","","","|concurrency TS|"
-"`P2770R0 <https://wg21.link/P2770R0>`__","LWG", "Stashing stashing ``iterators`` for proper flattening","February 2023","","","|ranges|"
+"`P2770R0 <https://wg21.link/P2770R0>`__","LWG", "Stashing stashing ``iterators`` for proper flattening","February 2023","|Partial| [#note-P2770R0]_","","|ranges|"
 "`P2164R9 <https://wg21.link/P2164R9>`__","LWG", "``views::enumerate``","February 2023","","","|ranges|"
-"`P2711R1 <https://wg21.link/P2711R1>`__","LWG", "Making multi-param constructors of ``views`` ``explicit``","February 2023","|Partial| [#note-P2711R1]_","","|ranges|"
+"`P2711R1 <https://wg21.link/P2711R1>`__","LWG", "Making multi-param constructors of ``views`` ``explicit``","February 2023","|Complete|","18.0","|ranges|"
 "`P2609R3 <https://wg21.link/P2609R3>`__","LWG", "Relaxing Ranges Just A Smidge","February 2023","","","|ranges|"
 "`P2713R1 <https://wg21.link/P2713R1>`__","LWG", "Escaping improvements in ``std::format``","February 2023","","","|format|"
 "`P2675R1 <https://wg21.link/P2675R1>`__","LWG", "``format``'s width estimation is too approximate and not forward compatible","February 2023","|Complete|","17.0","|format|"

diff --git a/libcxx/docs/Status/RangesMajorFeatures.csv b/libcxx/docs/Status/RangesMajorFeatures.csv
@@ -2,3 +2,4 @@ Standard,Name,Assignee,CL,Status
 C++23,`ranges::to <https://wg21.link/P1206R7>`_,Konstantin Varlamov,`D142335 <https://reviews.llvm.org/D142335>`_,Complete
 C++23,`Pipe support for user-defined range adaptors <https://wg21.link/P2387R3>`_,Unassigned,No patch yet,Not started
 C++23,`Formatting Ranges <https://wg21.link/P2286R8>`_,Mark de Wever,Various,Complete
+C++23,`Stashing stashing iterators for proper flattening <https://wg21.link/P2770R0>`_,Jakub Mazurkiewicz,`GitHub #65536 <https://github.com/llvm/llvm-project/pull/65536>`_,In progress
diff --git a/libcxx/docs/Status/RangesViews.csv b/libcxx/docs/Status/RangesViews.csv
@@ -28,10 +28,10 @@ C++23,`zip <https://wg21.link/P2321R2>`_,Hui Xie,`D122806 <https://llvm.org/D122
 C++23,`zip_transform <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not started
 C++23,`adjacent <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not started
 C++23,`adjacent_transform <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not started
-C++23,`join_with <https://wg21.link/P2441R2>`_,Unassigned,No patch yet,Not started
+C++23,`join_with <https://wg21.link/P2441R2>`_,Jakub Mazurkiewicz,`GitHub #65536 <https://github.com/llvm/llvm-project/pull/65536>`_,✅
 C++23,`slide <https://wg21.link/P2442R1>`_,Unassigned,No patch yet,Not started
 C++23,`chunk <https://wg21.link/P2442R1>`_,Unassigned,No patch yet,Not started
-C++23,`chunk_by <https://wg21.link/P2443R1>`_,Jakub Mazurkiewicz,`D144767 <https://llvm.org/D144767>`,✅
+C++23,`chunk_by <https://wg21.link/P2443R1>`_,Jakub Mazurkiewicz,`D144767 <https://llvm.org/D144767>`_,✅
 C++23,`as_const <https://wg21.link/P2278R4>`_,Unassigned,No patch yet,Not started
 C++23,`as_rvalue <https://wg21.link/P2446R2>`_,Nikolas Klauser,`D137637 <https://llvm.org/D137637>`_,✅
 C++23,`stride <https://wg21.link/P1899R3>`_,Hristo Hristov and Will Hawkins,`D156924 <https://llvm.org/D156924>`_,In Progress

diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
@@ -620,9 +620,11 @@ set(files
   __ranges/enable_view.h
   __ranges/filter_view.h
   __ranges/from_range.h
+  __ranges/helpers.h
   __ranges/iota_view.h
   __ranges/istream_view.h
   __ranges/join_view.h
+  __ranges/join_with_view.h
   __ranges/lazy_split_view.h
   __ranges/movable_box.h
   __ranges/non_propagating_cache.h

diff --git a/libcxx/include/__ranges/helpers.h b/libcxx/include/__ranges/helpers.h
@@ -0,0 +1,39 @@
+// -*- 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_HELPERS_H
+#define _LIBCPP___RANGES_HELPERS_H
+
+#include <__config>
+
+#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 >= 23
+
+namespace ranges {
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI constexpr _Tp& __as_lvalue(_Tp&& __t) {
+  return static_cast<_Tp&>(__t);
+}
+} // namespace ranges
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_HELPERS_H