[libcxx][ranges] Add `ranges::common_view`.

Differential Revision: https://reviews.llvm.org/D105753

libcxx/docs/Status/RangesPaper.csv

@@ -145,5 +145,5 @@ Section,Description,Dependencies,Assignee,Complete
 `[range.single] <http://wg21.link/range.single>`_,single_view,[view.interface],Zoe Carver,In Progress
 `[range.split] <http://wg21.link/range.split>`_,split_view,[range.all],Unassigned,Not started
 `[range.counted] <http://wg21.link/range.counted>`_,view::counted,[range.subrange],Zoe Carver,Not started
-`[range.common] <http://wg21.link/range.common>`_,common_view,[range.all],Zoe Carver,In Progress
+`[range.common] <http://wg21.link/range.common>`_,common_view,[range.all],Zoe Carver,✅
 `[range.reverse] <http://wg21.link/range.reverse>`_,reverse_view,[range.all],Unassigned,Not started

libcxx/include/CMakeLists.txt

@@ -184,6 +184,7 @@ set(files
   __random/uniform_int_distribution.h
   __ranges/access.h
   __ranges/all.h
+  __ranges/common_view.h
   __ranges/concepts.h
   __ranges/copyable_box.h
   __ranges/dangling.h

libcxx/include/__ranges/common_view.h

@@ -0,0 +1,113 @@
+// -*- 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_COMMON_VIEW_H
+#define _LIBCPP___RANGES_COMMON_VIEW_H
+
+#include <__config>
+#include <__iterator/common_iterator.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <concepts>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if !defined(_LIBCPP_HAS_NO_RANGES)
+
+namespace ranges {
+
+template<view _View>
+  requires (!common_range<_View> && copyable<iterator_t<_View>>)
+class common_view : public view_interface<common_view<_View>> {
+  _View __base_ = _View();
+
+public:
+  _LIBCPP_HIDE_FROM_ABI
+  common_view() requires default_initializable<_View> = default;
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr explicit common_view(_View __v) : __base_(_VSTD::move(__v)) { }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr _View base() const& requires copy_constructible<_View> { return __base_; }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr _View base() && { return _VSTD::move(__base_); }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto begin() {
+    if constexpr (random_access_range<_View> && sized_range<_View>)
+      return ranges::begin(__base_);
+    else
+      return common_iterator<iterator_t<_View>, sentinel_t<_View>>(ranges::begin(__base_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto begin() const requires range<const _View> {
+    if constexpr (random_access_range<const _View> && sized_range<const _View>)
+      return ranges::begin(__base_);
+    else
+      return common_iterator<iterator_t<const _View>, sentinel_t<const _View>>(ranges::begin(__base_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto end() {
+    if constexpr (random_access_range<_View> && sized_range<_View>)
+      return ranges::begin(__base_) + ranges::size(__base_);
+    else
+      return common_iterator<iterator_t<_View>, sentinel_t<_View>>(ranges::end(__base_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto end() const requires range<const _View> {
+    if constexpr (random_access_range<const _View> && sized_range<const _View>)
+      return ranges::begin(__base_) + ranges::size(__base_);
+    else
+      return common_iterator<iterator_t<const _View>, sentinel_t<const _View>>(ranges::end(__base_));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto size() requires sized_range<_View> {
+    return ranges::size(__base_);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto size() const requires sized_range<const _View> {
+    return ranges::size(__base_);
+  }
+};
+
+template<class _Range>
+common_view(_Range&&)
+  -> common_view<views::all_t<_Range>>;
+
+template<class _View>
+inline constexpr bool enable_borrowed_range<common_view<_View>> = enable_borrowed_range<_View>;
+
+} // namespace ranges
+
+#endif // !defined(_LIBCPP_HAS_NO_RANGES)
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_COMMON_VIEW_H

libcxx/include/module.modulemap

@@ -613,6 +613,7 @@ module std [system] {
     module __ranges {
       module access                 { private header "__ranges/access.h"                }
       module all                    { private header "__ranges/all.h"                   }
+      module common_view            { private header "__ranges/common_view.h"           }
       module concepts               { private header "__ranges/concepts.h"              }
       module copyable_box           { private header "__ranges/copyable_box.h"          }
       module dangling               { private header "__ranges/dangling.h"              }

libcxx/include/ranges

@@ -146,6 +146,13 @@ namespace std::ranges {
              can-reference<invoke_result_t<F&, range_reference_t<V>>>
   class transform_view;
 
+  // [range.common], common view
+  template<view V>
+    requires (!common_range<V> && copyable<iterator_t<V>>)
+  class common_view;
+
+  template<class T>
+  inline constexpr bool enable_borrowed_range<common_view<T>> = enable_borrowed_range<T>;
 }
 
 */
@@ -153,6 +160,7 @@ namespace std::ranges {
 #include <__config>
 #include <__ranges/access.h>
 #include <__ranges/all.h>
+#include <__ranges/common_view.h>
 #include <__ranges/concepts.h>
 #include <__ranges/dangling.h>
 #include <__ranges/data.h>

libcxx/test/libcxx/diagnostics/detail.headers/ranges/common_view.module.verify.cpp

@@ -0,0 +1,16 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__ranges/common_view.h'}}
+#include <__ranges/common_view.h>

libcxx/test/std/ranges/range.adaptors/range.common.view/base.pass.cpp

@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// constexpr V base() const& requires copy_constructible<V>;
+// constexpr V base() &&;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+#include "test_range.h"
+
+struct ContiguousView : std::ranges::view_base {
+  int *ptr_;
+  constexpr ContiguousView(int* ptr) : ptr_(ptr) {}
+  constexpr ContiguousView(ContiguousView&&) = default;
+  constexpr ContiguousView& operator=(ContiguousView&&) = default;
+  constexpr friend int* begin(ContiguousView& view) { return view.ptr_; }
+  constexpr friend int* begin(ContiguousView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr) : ptr_(ptr) {}
+  constexpr friend int* begin(CopyableView& view) { return view.ptr_; }
+  constexpr friend int* begin(CopyableView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+constexpr bool hasLValueQualifiedBase(auto&& view) {
+    return requires { view.base(); };
+}
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    std::ranges::common_view<CopyableView> common(CopyableView{buffer});
+    assert(common.base().ptr_ == buffer);
+    assert(std::move(common).base().ptr_ == buffer);
+
+    ASSERT_SAME_TYPE(decltype(common.base()), CopyableView);
+    ASSERT_SAME_TYPE(decltype(std::move(common).base()), CopyableView);
+    static_assert(hasLValueQualifiedBase(common));
+  }
+
+  {
+    std::ranges::common_view<ContiguousView> common(ContiguousView{buffer});
+    assert(std::move(common).base().ptr_ == buffer);
+
+    ASSERT_SAME_TYPE(decltype(std::move(common).base()), ContiguousView);
+    static_assert(!hasLValueQualifiedBase(common));
+  }
+
+  {
+    const std::ranges::common_view<CopyableView> common(CopyableView{buffer});
+    assert(common.base().ptr_ == buffer);
+    assert(std::move(common).base().ptr_ == buffer);
+
+    ASSERT_SAME_TYPE(decltype(common.base()), CopyableView);
+    ASSERT_SAME_TYPE(decltype(std::move(common).base()), CopyableView);
+    static_assert(hasLValueQualifiedBase(common));
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/begin.pass.cpp

@@ -0,0 +1,160 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// constexpr auto begin();
+// constexpr auto begin() const requires range<const V>;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+#include "test_range.h"
+
+struct ContiguousView : std::ranges::view_base {
+  int *ptr_;
+  constexpr ContiguousView(int* ptr) : ptr_(ptr) {}
+  constexpr ContiguousView(ContiguousView&&) = default;
+  constexpr ContiguousView& operator=(ContiguousView&&) = default;
+  constexpr friend int* begin(ContiguousView& view) { return view.ptr_; }
+  constexpr friend int* begin(ContiguousView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr) : ptr_(ptr) {}
+  constexpr friend int* begin(CopyableView& view) { return view.ptr_; }
+  constexpr friend int* begin(CopyableView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+struct MutableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr MutableView(int* ptr) : ptr_(ptr) {}
+  constexpr int* begin() { return ptr_; }
+  constexpr sentinel_wrapper<int*> end() { return sentinel_wrapper<int*>{ptr_ + 8}; }
+};
+
+using ForwardIter = forward_iterator<int*>;
+struct SizedForwardView : std::ranges::view_base {
+  int *ptr_;
+  constexpr SizedForwardView(int* ptr) : ptr_(ptr) {}
+  constexpr friend ForwardIter begin(SizedForwardView& view) { return ForwardIter(view.ptr_); }
+  constexpr friend ForwardIter begin(SizedForwardView const& view) { return ForwardIter(view.ptr_); }
+  constexpr friend sentinel_wrapper<ForwardIter> end(SizedForwardView& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+  constexpr friend sentinel_wrapper<ForwardIter> end(SizedForwardView const& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+};
+// Required to make SizedForwardView a sized view.
+constexpr auto operator-(sentinel_wrapper<ForwardIter> sent, ForwardIter iter) {
+  return sent.base().base() - iter.base();
+}
+constexpr auto operator-(ForwardIter iter, sentinel_wrapper<ForwardIter> sent) {
+  return iter.base() - sent.base().base();
+}
+
+using RandomAccessIter = random_access_iterator<int*>;
+struct SizedRandomAccessView : std::ranges::view_base {
+  int *ptr_;
+  constexpr SizedRandomAccessView(int* ptr) : ptr_(ptr) {}
+  constexpr friend RandomAccessIter begin(SizedRandomAccessView& view) { return RandomAccessIter(view.ptr_); }
+  constexpr friend RandomAccessIter begin(SizedRandomAccessView const& view) { return RandomAccessIter(view.ptr_); }
+  constexpr friend sentinel_wrapper<RandomAccessIter> end(SizedRandomAccessView& view) {
+    return sentinel_wrapper<RandomAccessIter>{RandomAccessIter(view.ptr_ + 8)};
+  }
+  constexpr friend sentinel_wrapper<RandomAccessIter> end(SizedRandomAccessView const& view) {
+    return sentinel_wrapper<RandomAccessIter>{RandomAccessIter(view.ptr_ + 8)};
+  }
+};
+// Required to make SizedRandomAccessView a sized view.
+constexpr auto operator-(sentinel_wrapper<RandomAccessIter> sent, RandomAccessIter iter) {
+  return sent.base().base() - iter.base();
+}
+constexpr auto operator-(RandomAccessIter iter, sentinel_wrapper<RandomAccessIter> sent) {
+  return iter.base() - sent.base().base();
+}
+
+template<class T>
+concept BeginEnabled = requires(const std::ranges::common_view<T>& comm) {
+  comm.begin();
+};
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    static_assert( BeginEnabled<CopyableView>);
+    static_assert(!BeginEnabled<MutableView>);
+  }
+
+  {
+    std::ranges::common_view<SizedRandomAccessView> comm(SizedRandomAccessView{buffer});
+    assert(comm.begin() == begin(SizedRandomAccessView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), RandomAccessIter);
+  }
+
+  {
+    const std::ranges::common_view<SizedRandomAccessView> comm(SizedRandomAccessView{buffer});
+    assert(comm.begin() == begin(SizedRandomAccessView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), RandomAccessIter);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  // The non-constexpr tests:
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    std::ranges::common_view<SizedForwardView> comm(SizedForwardView{buffer});
+    assert(comm.begin() == begin(SizedForwardView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), std::common_iterator<ForwardIter, sentinel_wrapper<ForwardIter>>);
+  }
+
+  {
+    std::ranges::common_view<ContiguousView> comm(ContiguousView{buffer});
+    assert(comm.begin() == begin(ContiguousView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), std::common_iterator<int*, sentinel_wrapper<int*>>);
+  }
+
+  {
+    const std::ranges::common_view<SizedForwardView> comm(SizedForwardView{buffer});
+    assert(comm.begin() == begin(SizedForwardView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), std::common_iterator<ForwardIter, sentinel_wrapper<ForwardIter>>);
+  }
+
+  {
+    const std::ranges::common_view<CopyableView> comm(CopyableView{buffer});
+    assert(comm.begin() == begin(CopyableView(buffer)));
+    ASSERT_SAME_TYPE(decltype(comm.begin()), std::common_iterator<int*, sentinel_wrapper<int*>>);
+  }
+
+  return 0;
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/borrowing.compile.pass.cpp

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class T>
+//   inline constexpr bool enable_borrowed_range<common_view<T>> = enable_borrowed_range<T>;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_iterators.h"
+
+struct View : std::ranges::view_base {
+  friend int* begin(View&);
+  friend int* begin(View const&);
+  friend sentinel_wrapper<int*> end(View&);
+  friend sentinel_wrapper<int*> end(View const&);
+};
+
+struct BorrowableView : std::ranges::view_base {
+  friend int* begin(BorrowableView&);
+  friend int* begin(BorrowableView const&);
+  friend sentinel_wrapper<int*> end(BorrowableView&);
+  friend sentinel_wrapper<int*> end(BorrowableView const&);
+};
+
+template<>
+inline constexpr bool std::ranges::enable_borrowed_range<BorrowableView> = true;
+
+static_assert(!std::ranges::enable_borrowed_range<std::ranges::common_view<View>>);
+static_assert( std::ranges::enable_borrowed_range<std::ranges::common_view<BorrowableView>>);

libcxx/test/std/ranges/range.adaptors/range.common.view/ctad.compile.pass.cpp

@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// template<class R>
+//   common_view(R&&) -> common_view<views::all_t<R>>;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_iterators.h"
+
+struct View : std::ranges::view_base {
+  friend int* begin(View&);
+  friend int* begin(View const&);
+  friend sentinel_wrapper<int*> end(View&);
+  friend sentinel_wrapper<int*> end(View const&);
+};
+
+struct Range {
+  friend int* begin(Range&);
+  friend int* begin(Range const&);
+  friend sentinel_wrapper<int*> end(Range&);
+  friend sentinel_wrapper<int*> end(Range const&);
+};
+
+struct BorrowedRange {
+  friend int* begin(BorrowedRange&);
+  friend int* begin(BorrowedRange const&);
+  friend sentinel_wrapper<int*> end(BorrowedRange&);
+  friend sentinel_wrapper<int*> end(BorrowedRange const&);
+};
+
+template<>
+inline constexpr bool std::ranges::enable_borrowed_range<BorrowedRange> = true;
+
+void testCTAD() {
+    View v;
+    Range r;
+    BorrowedRange br;
+    static_assert(std::same_as<
+        decltype(std::ranges::common_view(v)),
+        std::ranges::common_view<View>
+    >);
+    static_assert(std::same_as<
+        decltype(std::ranges::common_view(r)),
+        std::ranges::common_view<std::ranges::ref_view<Range>>
+    >);
+    // std::ranges::common_view(std::move(r)) invalid. RValue range must be borrowed.
+    static_assert(std::same_as<
+        decltype(std::ranges::common_view(br)),
+        std::ranges::common_view<std::ranges::ref_view<BorrowedRange>>
+    >);
+    static_assert(std::same_as<
+        decltype(std::ranges::common_view(std::move(br))),
+        std::ranges::common_view<std::ranges::subrange<
+          int *, sentinel_wrapper<int *>, std::ranges::subrange_kind::unsized>>
+    >);
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/ctor.default.pass.cpp

@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// common_view() requires default_initializable<V> = default;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_iterators.h"
+#include "test_range.h"
+
+int globalBuffer[4] = {1,2,3,4};
+
+struct ContiguousView : std::ranges::view_base {
+  int *ptr_;
+  constexpr ContiguousView(int* ptr) : ptr_(ptr) {}
+  constexpr ContiguousView(ContiguousView&&) = default;
+  constexpr ContiguousView& operator=(ContiguousView&&) = default;
+  constexpr friend int* begin(ContiguousView& view) { return view.ptr_; }
+  constexpr friend int* begin(ContiguousView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(ContiguousView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr = globalBuffer) : ptr_(ptr) {}
+  constexpr friend int* begin(CopyableView& view) { return view.ptr_; }
+  constexpr friend int* begin(CopyableView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 4};
+  }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 4};
+  }
+};
+
+struct DefaultConstructibleView : std::ranges::view_base {
+  DefaultConstructibleView();
+  friend int* begin(DefaultConstructibleView& view);
+  friend int* begin(DefaultConstructibleView const& view);
+  friend sentinel_wrapper<int*> end(DefaultConstructibleView& view);
+  friend sentinel_wrapper<int*> end(DefaultConstructibleView const& view);
+};
+
+int main(int, char**) {
+  static_assert(!std::default_initializable<std::ranges::common_view<ContiguousView>>);
+  static_assert( std::default_initializable<std::ranges::common_view<DefaultConstructibleView>>);
+
+  std::ranges::common_view<CopyableView> common;
+  assert(*common.begin() == 1);
+
+  return 0;
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/ctor.view.pass.cpp

@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// constexpr explicit common_view(V r);
+
+#include <ranges>
+#include <cassert>
+
+#include "test_iterators.h"
+#include "test_range.h"
+
+struct ContiguousView : std::ranges::view_base {
+  int *ptr_;
+  constexpr ContiguousView(int* ptr) : ptr_(ptr) {}
+  constexpr ContiguousView(ContiguousView&&) = default;
+  constexpr ContiguousView& operator=(ContiguousView&&) = default;
+  friend constexpr int* begin(ContiguousView& view) { return view.ptr_; }
+  friend constexpr int* begin(ContiguousView const& view) { return view.ptr_; }
+  friend constexpr sentinel_wrapper<int*> end(ContiguousView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  friend constexpr sentinel_wrapper<int*> end(ContiguousView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr) : ptr_(ptr) {}
+  friend constexpr int* begin(CopyableView& view) { return view.ptr_; }
+  friend constexpr int* begin(CopyableView const& view) { return view.ptr_; }
+  friend constexpr sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  friend constexpr sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    std::ranges::common_view<ContiguousView> common(ContiguousView{buffer});
+    assert(std::move(common).base().ptr_ == buffer);
+  }
+
+  {
+    ContiguousView v{buffer};
+    std::ranges::common_view<ContiguousView> common(std::move(v));
+    assert(std::move(common).base().ptr_ == buffer);
+  }
+
+  {
+    const CopyableView v{buffer};
+    const std::ranges::common_view<CopyableView> common(v);
+    assert(common.base().ptr_ == buffer);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+  const std::ranges::common_view<ContiguousView> common(ContiguousView{buffer});
+  assert(common.begin() == buffer);
+
+  return 0;
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/end.pass.cpp

@@ -0,0 +1,132 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// constexpr auto end();
+// constexpr auto end() const requires range<const V>;
+
+#include <ranges>
+#include <cassert>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+#include "test_range.h"
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr) : ptr_(ptr) {}
+  friend constexpr int* begin(CopyableView& view) { return view.ptr_; }
+  friend constexpr int* begin(CopyableView const& view) { return view.ptr_; }
+  friend constexpr sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  friend constexpr sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+using ForwardIter = forward_iterator<int*>;
+struct SizedForwardView : std::ranges::view_base {
+  int *ptr_;
+  constexpr SizedForwardView(int* ptr) : ptr_(ptr) {}
+  friend constexpr ForwardIter begin(SizedForwardView& view) { return ForwardIter(view.ptr_); }
+  friend constexpr ForwardIter begin(SizedForwardView const& view) { return ForwardIter(view.ptr_); }
+  friend constexpr sentinel_wrapper<ForwardIter> end(SizedForwardView& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+  friend constexpr sentinel_wrapper<ForwardIter> end(SizedForwardView const& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+};
+
+constexpr auto operator-(sentinel_wrapper<ForwardIter> sent, ForwardIter iter) {
+  return sent.base().base() - iter.base();
+}
+constexpr auto operator-(ForwardIter iter, sentinel_wrapper<ForwardIter> sent) {
+  return iter.base() - sent.base().base();
+}
+
+using RandomAccessIter = random_access_iterator<int*>;
+struct SizedRandomcAccessView : std::ranges::view_base {
+  int *ptr_;
+  constexpr SizedRandomcAccessView(int* ptr) : ptr_(ptr) {}
+  friend constexpr RandomAccessIter begin(SizedRandomcAccessView& view) { return RandomAccessIter(view.ptr_); }
+  friend constexpr RandomAccessIter begin(SizedRandomcAccessView const& view) { return RandomAccessIter(view.ptr_); }
+  friend constexpr sentinel_wrapper<RandomAccessIter> end(SizedRandomcAccessView& view) {
+    return sentinel_wrapper<RandomAccessIter>{RandomAccessIter(view.ptr_ + 8)};
+  }
+  friend constexpr sentinel_wrapper<RandomAccessIter> end(SizedRandomcAccessView const& view) {
+    return sentinel_wrapper<RandomAccessIter>{RandomAccessIter(view.ptr_ + 8)};
+  }
+};
+
+constexpr auto operator-(sentinel_wrapper<RandomAccessIter> sent, RandomAccessIter iter) {
+  return sent.base().base() - iter.base();
+}
+constexpr auto operator-(RandomAccessIter iter, sentinel_wrapper<RandomAccessIter> sent) {
+  return iter.base() - sent.base().base();
+}
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    std::ranges::common_view<SizedRandomcAccessView> comm(SizedRandomcAccessView{buffer});
+    assert(comm.end().base() == buffer + 8);
+    // Note this should NOT be the sentinel type.
+    ASSERT_SAME_TYPE(decltype(comm.end()), RandomAccessIter);
+  }
+
+  {
+    const std::ranges::common_view<SizedRandomcAccessView> comm(SizedRandomcAccessView{buffer});
+    assert(comm.end().base() == buffer + 8);
+    // Note this should NOT be the sentinel type.
+    ASSERT_SAME_TYPE(decltype(comm.end()), RandomAccessIter);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  using CommonForwardIter = std::common_iterator<ForwardIter, sentinel_wrapper<ForwardIter>>;
+  using CommonIntIter = std::common_iterator<int*, sentinel_wrapper<int*>>;
+
+  {
+    std::ranges::common_view<SizedForwardView> comm(SizedForwardView{buffer});
+    assert(comm.end() == CommonForwardIter(sentinel_wrapper<ForwardIter>(ForwardIter(buffer + 8))));
+    ASSERT_SAME_TYPE(decltype(comm.end()), CommonForwardIter);
+  }
+
+  {
+    std::ranges::common_view<CopyableView> comm(CopyableView{buffer});
+    assert(comm.end() == CommonIntIter(sentinel_wrapper<int*>(buffer + 8)));
+    ASSERT_SAME_TYPE(decltype(comm.end()), CommonIntIter);
+  }
+
+  {
+    const std::ranges::common_view<SizedForwardView> comm(SizedForwardView{buffer});
+    assert(comm.end() == CommonForwardIter(sentinel_wrapper<ForwardIter>(ForwardIter(buffer + 8))));
+    ASSERT_SAME_TYPE(decltype(comm.end()), CommonForwardIter);
+  }
+
+  {
+    const std::ranges::common_view<CopyableView> comm(CopyableView{buffer});
+    assert(comm.end() == CommonIntIter(sentinel_wrapper<int*>(buffer + 8)));
+    ASSERT_SAME_TYPE(decltype(comm.end()), CommonIntIter);
+  }
+
+  return 0;
+}

libcxx/test/std/ranges/range.adaptors/range.common.view/size.pass.cpp

@@ -0,0 +1,87 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// constexpr auto size() requires sized_range<V>
+// constexpr auto size() const requires sized_range<const V>
+
+#include <ranges>
+#include <cassert>
+
+#include "test_iterators.h"
+#include "test_range.h"
+
+struct CopyableView : std::ranges::view_base {
+  int *ptr_;
+  constexpr CopyableView(int* ptr) : ptr_(ptr) {}
+  constexpr friend int* begin(CopyableView& view) { return view.ptr_; }
+  constexpr friend int* begin(CopyableView const& view) { return view.ptr_; }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+  constexpr friend sentinel_wrapper<int*> end(CopyableView const& view) {
+    return sentinel_wrapper<int*>{view.ptr_ + 8};
+  }
+};
+
+using ForwardIter = forward_iterator<int*>;
+struct SizedForwardView : std::ranges::view_base {
+  int *ptr_;
+  constexpr SizedForwardView(int* ptr) : ptr_(ptr) {}
+  constexpr friend ForwardIter begin(SizedForwardView& view) { return ForwardIter(view.ptr_); }
+  constexpr friend ForwardIter begin(SizedForwardView const& view) { return ForwardIter(view.ptr_); }
+  constexpr friend sentinel_wrapper<ForwardIter> end(SizedForwardView& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+  constexpr friend sentinel_wrapper<ForwardIter> end(SizedForwardView const& view) {
+    return sentinel_wrapper<ForwardIter>{ForwardIter(view.ptr_ + 8)};
+  }
+};
+
+constexpr auto operator-(sentinel_wrapper<ForwardIter> sent, ForwardIter iter) {
+  return sent.base().base() - iter.base();
+}
+constexpr auto operator-(ForwardIter iter, sentinel_wrapper<ForwardIter> sent) {
+  return iter.base() - sent.base().base();
+}
+
+template<class T>
+concept SizeEnabled = requires(const std::ranges::common_view<T>& comm) {
+  comm.size();
+};
+
+constexpr bool test() {
+  int buffer[8] = {1, 2, 3, 4, 5, 6, 7, 8};
+
+  {
+    static_assert( SizeEnabled<SizedForwardView>);
+    static_assert(!SizeEnabled<CopyableView>);
+  }
+
+  {
+    std::ranges::common_view<SizedForwardView> common(SizedForwardView{buffer});
+    assert(common.size() == 8);
+  }
+
+  {
+    const std::ranges::common_view<SizedForwardView> common(SizedForwardView{buffer});
+    assert(common.size() == 8);
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}

libcxx/test/support/test_iterators.h

@@ -924,6 +924,9 @@ public:
     return base_ == other;
   }
 
+  constexpr const I& base() const& { return base_; }
+  constexpr I base() && { return std::move(base_); }
+
 private:
   I base_ = I();
 };