[libc++][ranges] LWG3736: `move_iterator` missing `disable_sized_sentinel_for` specialization #85611

xiaoyang-sde · 2024-03-18T07:54:29Z

Abstract

This pull request implements LWG3736: move_iterator missing disable_sized_sentinel_for specialization. Here is an example similar to those described in the report, where unsized_it doesn't model sized_sentinel_for<unsized_it>:

#include <iterator>

struct unsized_it {
  using value_type      = int;
  using difference_type = std::ptrdiff_t;

  value_type& operator*() const;
  bool operator==(const unsized_it&) const;
  difference_type operator-(const unsized_it&) const { return 0; }
};

template <>
inline constexpr bool std::disable_sized_sentinel_for<unsized_it, unsized_it> = true;

static_assert(!std::sized_sentinel_for<unsized_it, unsized_it>);
static_assert(!std::sized_sentinel_for<std::move_iterator<unsized_it>, std::move_iterator<unsized_it>>);

Reference

…tinel_for' specialization

github-actions · 2024-03-18T07:54:47Z

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llvmbot · 2024-03-18T07:55:18Z

@llvm/pr-subscribers-libcxx

Author: Xiaoyang Liu (xiaoyang-sde)

Changes

Abstract

This pull request implements LWG3736: move_iterator missing disable_sized_sentinel_for specialization. Here is an example similar to those described in the report, where unsized_it doesn't model sized_sentinel_for<unsized_it>:

#include &lt;iterator&gt;

struct unsized_it {
  using value_type      = int;
  using difference_type = std::ptrdiff_t;

  value_type&amp; operator*() const;
  bool operator==(const unsized_it&amp;) const;
  difference_type operator-(const unsized_it&amp;) const { return 0; }
};

template &lt;&gt;
inline constexpr bool std::disable_sized_sentinel_for&lt;unsized_it, unsized_it&gt; = true;

static_assert(!std::sized_sentinel_for&lt;unsized_it, unsized_it&gt;);
static_assert(!std::sized_sentinel_for&lt;std::move_iterator&lt;unsized_it&gt;, std::move_iterator&lt;unsized_it&gt;&gt;);

Reference

Full diff: https://github.com/llvm/llvm-project/pull/85611.diff

4 Files Affected:

(modified) libcxx/docs/Status/Cxx23Issues.csv (+1-1)
(modified) libcxx/include/__iterator/move_iterator.h (+6)
(modified) libcxx/include/iterator (+5)
(added) libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp (+26)

diff --git a/libcxx/docs/Status/Cxx23Issues.csv b/libcxx/docs/Status/Cxx23Issues.csv
index 43282f357150cf..0625dfe3a1d853 100644
--- a/libcxx/docs/Status/Cxx23Issues.csv
+++ b/libcxx/docs/Status/Cxx23Issues.csv
@@ -201,7 +201,7 @@
 "`3677 <https://wg21.link/LWG3677>`__","Is a cv-qualified ``pair`` specially handled in uses-allocator construction?", "November 2022","|Complete|","18.0",""
 "`3717 <https://wg21.link/LWG3717>`__","``common_view::end`` should improve ``random_access_range`` case", "November 2022","","","|ranges|"
 "`3732 <https://wg21.link/LWG3732>`__","``prepend_range`` and ``append_range`` can't be amortized constant time", "November 2022","|Nothing to do|","","|ranges|"
-"`3736 <https://wg21.link/LWG3736>`__","``move_iterator`` missing ``disable_sized_sentinel_for`` specialization", "November 2022","","","|ranges|"
+"`3736 <https://wg21.link/LWG3736>`__","``move_iterator`` missing ``disable_sized_sentinel_for`` specialization", "November 2022","|Complete|","19.0","|ranges|"
 "`3737 <https://wg21.link/LWG3737>`__","``take_view::sentinel`` should provide ``operator-``", "November 2022","","","|ranges|"
 "`3738 <https://wg21.link/LWG3738>`__","Missing preconditions for ``take_view`` constructor", "November 2022","|Complete|","16.0","|ranges|"
 "`3743 <https://wg21.link/LWG3743>`__","``ranges::to``'s reserve may be ill-formed", "November 2022","","","|ranges|"
diff --git a/libcxx/include/__iterator/move_iterator.h b/libcxx/include/__iterator/move_iterator.h
index eefd5b37484548..6382c947060bfe 100644
--- a/libcxx/include/__iterator/move_iterator.h
+++ b/libcxx/include/__iterator/move_iterator.h
@@ -330,6 +330,12 @@ operator+(typename move_iterator<_Iter>::difference_type __n, const move_iterato
 }
 #endif // _LIBCPP_STD_VER >= 20
 
+#if _LIBCPP_STD_VER >= 20
+template <class _Iter1, class _Iter2>
+  requires(!sized_sentinel_for<_Iter1, _Iter2>)
+inline constexpr bool disable_sized_sentinel_for<move_iterator<_Iter1>, move_iterator<_Iter2>> = true;
+#endif // _LIBCPP_STD_VER >= 20
+
 template <class _Iter>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 move_iterator<_Iter> make_move_iterator(_Iter __i) {
   return move_iterator<_Iter>(std::move(__i));
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
index 5779bf828711b8..40ac6d18bc1d37 100644
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -475,6 +475,11 @@ constexpr move_iterator<Iterator> operator+(   // constexpr in C++17
 template <class Iterator>   // constexpr in C++17
 constexpr  move_iterator<Iterator> make_move_iterator(const Iterator& i);
 
+template<class Iterator1, class Iterator2>
+    requires (!sized_sentinel_for<Iterator1, Iterator2>)
+  inline constexpr bool disable_sized_sentinel_for<move_iterator<Iterator1>,
+                                                    move_iterator<Iterator2>> = true;
+
 template<semiregular S>
 class move_sentinel {
 public:
diff --git a/libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp b/libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp
new file mode 100644
index 00000000000000..b2593d395d0fad
--- /dev/null
+++ b/libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+
+#include <iterator>
+
+struct unsized_it {
+  using value_type      = int;
+  using difference_type = std::ptrdiff_t;
+
+  value_type& operator*() const;
+  bool operator==(const unsized_it&) const;
+  difference_type operator-(const unsized_it&) const { return 0; }
+};
+
+template <>
+inline constexpr bool std::disable_sized_sentinel_for<unsized_it, unsized_it> = true;
+
+static_assert(!std::sized_sentinel_for<unsized_it, unsized_it>);
+static_assert(!std::sized_sentinel_for<std::move_iterator<unsized_it>, std::move_iterator<unsized_it>>);

ldionne

This basically LGTM with a minor comment to improve testing. Thanks a lot for the patch!

libcxx/include/iterator

libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp

…inel_for' specialization Co-authored-by: Louis Dionne <[email protected]>

…inel_for' specialization

var-const

Thanks!

xiaoyang-sde · 2024-04-02T13:53:30Z

Thanks!

Thanks for approving this pull request! Would you mind merging it? (I don't have the permission to do so.)

libcxx/include/iterator

var-const · 2024-04-03T21:22:11Z

@xiaoyang-sde Sorry, I have a last-minute comment. Other than that, LGTM, happy to merge as soon as the comment is resolved (one way or another).

…inel_for' specialization

ldionne · 2024-04-11T21:18:34Z

LGTM once the CI is green. Whoever sees this first can merge once green. Thanks!

github-actions · 2024-04-12T14:09:22Z

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Xiaoyang Liu added 3 commits March 18, 2024 00:08

[libc++] [ranges] LWG3736: 'move_iterator' missing 'disable_sized_sen…

b2617a4

…tinel_for' specialization

[libc++] [ranges] implement 'sized_sentinel.compile.pass.cpp'

af6c27a

[libc++] [ranges] update 'iterator' synopsis

90da6ab

xiaoyang-sde requested a review from a team as a code owner March 18, 2024 07:54

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Mar 18, 2024

xiaoyang-sde changed the title ~~[libc++] [ranges] LWG3736: move_iterator missing disable_sized_sentinel_for specialization~~ [libc++][ranges] LWG3736: move_iterator missing disable_sized_sentinel_for specialization Mar 19, 2024

ldionne self-assigned this Mar 20, 2024

ldionne added the ranges Issues related to `<ranges>` label Mar 20, 2024

ldionne reviewed Mar 20, 2024

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libcxx/include/iterator Outdated Show resolved Hide resolved

libcxx/test/std/iterators/predef.iterators/move.iterators/sized_sentinel.compile.pass.cpp Show resolved Hide resolved

Xiaoyang Liu and others added 2 commits March 19, 2024 23:58

[libc++][ranges] LWG3736: 'move_iterator' missing 'disable_sized_sent…

42ea56c

…inel_for' specialization Co-authored-by: Louis Dionne <[email protected]>

[libc++][ranges] LWG3736: 'move_iterator' missing 'disable_sized_sent…

62f348e

…inel_for' specialization

var-const approved these changes Apr 2, 2024

View reviewed changes

var-const requested changes Apr 3, 2024

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libcxx/include/iterator Show resolved Hide resolved

[libc++][ranges] LWG3736: 'move_iterator' missing 'disable_sized_sent…

aad349c

…inel_for' specialization

xiaoyang-sde requested a review from var-const April 6, 2024 01:39

Xiaoyang Liu and others added 2 commits April 5, 2024 18:41

[libc++][ranges] LWG3736: 'move_iterator' missing 'disable_sized_sent…

665a0cb

…inel_for' specialization

Apply the issue as a DR

63fe54e

ldionne approved these changes Apr 11, 2024

View reviewed changes

ldionne merged commit f4e3226 into llvm:main Apr 12, 2024

xiaoyang-sde deleted the move_iterator branch April 12, 2024 14:18

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[libc++][ranges] LWG3736: `move_iterator` missing `disable_sized_sentinel_for` specialization #85611

[libc++][ranges] LWG3736: `move_iterator` missing `disable_sized_sentinel_for` specialization #85611