[libc++][ranges] Ensure range access CPOs are provided in <iterator>

[frederick-vs-ja]

Per [range.access.general]/1, these CPOs are also provided in <iterator>. Currently only some of them are provided via transitive inclusion when only <iterator> is included.

Fixes #151698.

Drive-by: Add an entry for ranges::reserve_hint in the general test file for CPOs.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: A. Jiang (frederick-vs-ja)

Changes

Per [range.access.general]/1, these CPOs are also provided in <iterator>. Currently only some of them are provided via transitive inclusion when only <iterator> is included.

Fixes #151698.

Drive-by: Add an entry for ranges::reserve_hint in the general test file for CPOs.

---

Full diff: https://github.com/llvm/llvm-project/pull/151745.diff

4 Files Affected:

• (modified) libcxx/include/iterator (+10)
• (modified) libcxx/include/ranges (+1-7)
• (modified) libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp (+4)
• (added) libcxx/test/std/ranges/range.access/include.iterator.compile.pass.cpp (+60)

diff --git a/libcxx/include/iterator b/libcxx/include/iterator
index d25fdfd2a8b33..fc8bdc5e6bcf6 100644
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -737,6 +737,16 @@ template <class E> constexpr const E* data(initializer_list<E> il) noexcept;
 #  include <compare>
 #  include <concepts>
 
+// [range.access.general]
+#  if _LIBCPP_STD_VER >= 20
+#    include <__ranges/access.h>
+#    include <__ranges/data.h>
+#    include <__ranges/empty.h>
+#    include <__ranges/rbegin.h>
+#    include <__ranges/rend.h>
+#    include <__ranges/size.h>
+#  endif
+
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header
 #  endif
diff --git a/libcxx/include/ranges b/libcxx/include/ranges
index 96d7a6b897188..b86dd78ecb255 100644
--- a/libcxx/include/ranges
+++ b/libcxx/include/ranges
@@ -405,17 +405,14 @@ namespace std {
 #  include <__config>
 
 #  if _LIBCPP_STD_VER >= 20
-#    include <__ranges/access.h>
 #    include <__ranges/all.h>
 #    include <__ranges/common_view.h>
 #    include <__ranges/concepts.h>
 #    include <__ranges/counted.h>
 #    include <__ranges/dangling.h>
-#    include <__ranges/data.h>
 #    include <__ranges/drop_view.h>
 #    include <__ranges/drop_while_view.h>
 #    include <__ranges/elements_view.h>
-#    include <__ranges/empty.h>
 #    include <__ranges/empty_view.h>
 #    include <__ranges/enable_borrowed_range.h>
 #    include <__ranges/enable_view.h>
@@ -423,12 +420,9 @@ namespace std {
 #    include <__ranges/iota_view.h>
 #    include <__ranges/join_view.h>
 #    include <__ranges/lazy_split_view.h>
-#    include <__ranges/rbegin.h>
 #    include <__ranges/ref_view.h>
-#    include <__ranges/rend.h>
 #    include <__ranges/reverse_view.h>
 #    include <__ranges/single_view.h>
-#    include <__ranges/size.h>
 #    include <__ranges/split_view.h>
 #    include <__ranges/subrange.h>
 #    include <__ranges/take_view.h>
@@ -460,7 +454,7 @@ namespace std {
 // [ranges.syn]
 #  include <compare>
 #  include <initializer_list>
-#  include <iterator>
+#  include <iterator> // some CPOs are provided in <iterator> per [range.access.general]
 
 // [tuple.helper]
 #  include <__tuple/tuple_element.h>
diff --git a/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp b/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp
index 678483b9b2f2f..49497875dcf95 100644
--- a/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp
+++ b/libcxx/test/std/library/description/conventions/customization.point.object/cpo.compile.pass.cpp
@@ -81,6 +81,10 @@ static_assert(test(std::ranges::rend, a));
 static_assert(test(std::ranges::size, a));
 static_assert(test(std::ranges::ssize, a));
 
+#if TEST_STD_VER >= 26
+// static_assert(test(std::views::reserve_hint, a));
+#endif
+
 // [range.factories]
 // views::empty<T> is not a CPO
 static_assert(test(std::views::iota, 1));
diff --git a/libcxx/test/std/ranges/range.access/include.iterator.compile.pass.cpp b/libcxx/test/std/ranges/range.access/include.iterator.compile.pass.cpp
new file mode 100644
index 0000000000000..a3c59166eeab0
--- /dev/null
+++ b/libcxx/test/std/ranges/range.access/include.iterator.compile.pass.cpp
@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// 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: std-at-least-c++20
+
+// [range.access.general]/1:
+// In addition to being available via inclusion of the <ranges> header, the customization point objects in
+// [range.access] are available when the header <iterator> is included.
+
+#include <iterator>
+#include <type_traits>
+
+#include "test_macros.h"
+
+template <class CPO, class... Args>
+constexpr bool test(CPO& o, Args&&...) {
+  static_assert(std::is_const_v<CPO>);
+  static_assert(std::is_class_v<CPO>);
+  static_assert(std::is_trivially_copyable_v<CPO>);
+  static_assert(std::is_trivially_default_constructible_v<CPO>);
+
+  auto p  = o;
+  using T = decltype(p);
+
+  // The type of a customization point object, ignoring cv-qualifiers, shall model semiregular.
+  static_assert(std::semiregular<T>);
+
+  // The type T of a customization point object, ignoring cv-qualifiers, shall model...
+  static_assert(std::invocable<T&, Args...>);
+  static_assert(std::invocable<const T&, Args...>);
+  static_assert(std::invocable<T, Args...>);
+  static_assert(std::invocable<const T, Args...>);
+
+  return true;
+}
+
+int a[10];
+
+static_assert(test(std::ranges::begin, a));
+static_assert(test(std::ranges::end, a));
+static_assert(test(std::ranges::cbegin, a));
+static_assert(test(std::ranges::cdata, a));
+static_assert(test(std::ranges::cend, a));
+static_assert(test(std::ranges::crbegin, a));
+static_assert(test(std::ranges::crend, a));
+static_assert(test(std::ranges::data, a));
+static_assert(test(std::ranges::empty, a));
+static_assert(test(std::ranges::rbegin, a));
+static_assert(test(std::ranges::rend, a));
+static_assert(test(std::ranges::size, a));
+static_assert(test(std::ranges::ssize, a));
+
+#if TEST_STD_VER >= 26
+// static_assert(test(std::views::reserve_hint, a));
+#endif

[ldionne]

LGTM with a small comment about ensuring that the CPOs can actually be called.

[ldionne]

Suggested change

	auto p = o;
	auto p = o;
	(void)o(args...); // to make sure the CPO can actually be used

[frederick-vs-ja]

Ah, given we actually call CPOs, it perhaps makes more sense to test both compile time and runtime invocability. I'm now changing the test file to .pass.cpp.