[libcxx] [llvm] [clang-tools-extra] [clang] [libc++][span] P2821R5: span.at() (PR #74994)

Hristo Hristov via cfe-commits cfe-commits at lists.llvm.org
Sun Dec 10 09:13:49 PST 2023


https://github.com/H-G-Hristov updated https://github.com/llvm/llvm-project/pull/74994

>From 6e26ca239c49e1b7d9ab72217db7339e92df163f Mon Sep 17 00:00:00 2001
From: Zingam <zingam at outlook.com>
Date: Sun, 10 Dec 2023 14:16:02 +0200
Subject: [PATCH 1/5] [libc++][span] P2821R5: span.at()

---
 libcxx/include/span                           |  30 +++
 .../views/views.span/span.elem/at.pass.cpp    | 246 ++++++++++++++++++
 .../views.span/span.elem/op_idx.pass.cpp      |   1 -
 3 files changed, 276 insertions(+), 1 deletion(-)
 create mode 100644 libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp

diff --git a/libcxx/include/span b/libcxx/include/span
index 69b0a2875e26c..b015d7cf1c15b 100644
--- a/libcxx/include/span
+++ b/libcxx/include/span
@@ -92,6 +92,7 @@ public:
 
     // [span.elem], span element access
     constexpr reference operator[](size_type idx) const;
+    constexpr reference at(size_type idx) const; // since C++26
     constexpr reference front() const;
     constexpr reference back() const;
     constexpr pointer data() const noexcept;
@@ -146,6 +147,9 @@ template<class R>
 #include <__utility/forward.h>
 #include <array>        // for array
 #include <cstddef>      // for byte
+#if _LIBCPP_STD_VER >= 26
+#  include <stdexcept>
+#endif
 #include <version>
 
 // standard-mandated includes
@@ -343,6 +347,15 @@ public:
         return __data_[__idx];
     }
 
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __idx) const {
+      if (__idx >= size()) {
+        __throw_out_of_range();
+      }
+      return *(data() + __idx);
+    }
+#  endif
+
     _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept
     {
         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T, N>::front() on empty span");
@@ -383,6 +396,10 @@ public:
 
 private:
     pointer    __data_;
+
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_NORETURN _LIBCPP_HIDE_FROM_ABI void __throw_out_of_range() const { std::__throw_out_of_range("span"); }
+#  endif
 };
 
 
@@ -510,6 +527,15 @@ public:
         return __data_[__idx];
     }
 
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_HIDE_FROM_ABI constexpr reference at(size_type __idx) const {
+      if (__idx >= size()) {
+        __throw_out_of_range();
+      }
+      return *(data() + __idx);
+    }
+#  endif
+
     _LIBCPP_INLINE_VISIBILITY constexpr reference front() const noexcept
     {
         _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(!empty(), "span<T>::front() on empty span");
@@ -552,6 +578,10 @@ public:
 private:
     pointer   __data_;
     size_type __size_;
+
+#  if _LIBCPP_STD_VER >= 26
+    _LIBCPP_NORETURN _LIBCPP_HIDE_FROM_ABI void __throw_out_of_range() const { std::__throw_out_of_range("span"); }
+#  endif
 };
 
 template <class _Tp, size_t _Extent>
diff --git a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
new file mode 100644
index 0000000000000..2a9ce2baeec1a
--- /dev/null
+++ b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
@@ -0,0 +1,246 @@
+//===----------------------------------------------------------------------===//
+//
+// 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, c++20, c++23
+
+// <span>
+
+// constexpr reference at(size_type idx) const; // since C++26
+
+#include <array>
+#include <cassert>
+#include <concepts>
+#include <span>
+#include <stdexcept>
+#include <vector>
+
+#include "test_macros.h"
+
+// template <typename Span>
+// constexpr bool testConstexprSpan(Span sp, std::size_t idx)
+// {
+//     LIBCPP_ASSERT(noexcept(sp[idx]));
+
+//     typename Span::reference r1 = sp[idx];
+//     typename Span::reference r2 = *(sp.data() + idx);
+
+//     return r1 == r2;
+// }
+
+// template <typename Span>
+// void testRuntimeSpan(Span sp, std::size_t idx)
+// {
+//     LIBCPP_ASSERT(noexcept(sp[idx]));
+
+//     typename Span::reference r1 = sp[idx];
+//     typename Span::reference r2 = *(sp.data() + idx);
+
+//     assert(r1 == r2);
+// }
+
+// struct A{};
+// constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
+//           int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
+
+// int main(int, char**)
+// {
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 1), 0), "");
+
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 2), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 2), 1), "");
+
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 1), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 2), "");
+
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 1), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 2), "");
+//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 3), "");
+
+//     static_assert(testConstexprSpan(std::span<const int, 1>(iArr1, 1), 0), "");
+
+//     static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2), 1), "");
+
+//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 1), "");
+//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 2), "");
+
+//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 0), "");
+//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 1), "");
+//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 2), "");
+//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 3), "");
+
+//     testRuntimeSpan(std::span<int>(iArr2, 1), 0);
+
+//     testRuntimeSpan(std::span<int>(iArr2, 2), 0);
+//     testRuntimeSpan(std::span<int>(iArr2, 2), 1);
+
+//     testRuntimeSpan(std::span<int>(iArr2, 3), 0);
+//     testRuntimeSpan(std::span<int>(iArr2, 3), 1);
+//     testRuntimeSpan(std::span<int>(iArr2, 3), 2);
+
+//     testRuntimeSpan(std::span<int>(iArr2, 4), 0);
+//     testRuntimeSpan(std::span<int>(iArr2, 4), 1);
+//     testRuntimeSpan(std::span<int>(iArr2, 4), 2);
+//     testRuntimeSpan(std::span<int>(iArr2, 4), 3);
+
+//     testRuntimeSpan(std::span<int, 1>(iArr2, 1), 0);
+
+//     testRuntimeSpan(std::span<int, 2>(iArr2, 2), 0);
+//     testRuntimeSpan(std::span<int, 2>(iArr2, 2), 1);
+
+//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 0);
+//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 1);
+//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 2);
+
+//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 0);
+//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 1);
+//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 2);
+//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 3);
+
+//     std::string s;
+//     testRuntimeSpan(std::span<std::string>   (&s, 1), 0);
+//     testRuntimeSpan(std::span<std::string, 1>(&s, 1), 0);
+
+//   return 0;
+// }
+
+constexpr bool test() {
+  //   {
+  //     typedef double T;
+  //     typedef std::array<T, 3> C;
+  //     C const c                      = {1, 2, 3.5};
+  //     typename C::const_reference r1 = c.at(0);
+  //     assert(r1 == 1);
+
+  //     typename C::const_reference r2 = c.at(2);
+  //     assert(r2 == 3.5);
+  //   }
+
+  const auto testSpan =
+      [](auto span, int idx, int expectedValue) {
+        {
+          std::same_as<decltype(span)::reference> elem = span.at(idx);
+          assert(elem == expectedValue);
+        }
+
+        {
+          std::same_as<decltype(span)::const_reference> elem = std::as_const(span).at(idx);
+          assert(elem == expectedValue);
+        }
+      }
+
+  // With static extent
+
+  std::array arr{0, 1, 2, 3, 4, 5, 9084};
+  std::span arrSpan{ar};
+
+  assert(std::dynamic_extent != arrSpan.extent);
+
+  testSpan(arrSpan, 0, 0);
+  testSpan(arrSpan, 1, 1);
+  testSpan(arrSpan, 5, 9084);
+
+  {
+    std::same_as<decltype(arrSpan)::reference> arrElem = arrSpan.at(1);
+    assert(arrElem == 1);
+  }
+
+  {
+    std::same_as<decltype(arrSpan)::const_reference> arrElem = std::as_const(arrSpan).at(1);
+    assert(arrElem == 1);
+  }
+
+  // With dynamic extent
+
+  std::vector vec{0, 1, 2, 3, 4, 5};
+  std::span vecSpan{vec};
+  
+  assert(std::dynamic_extent == vecSpan.extent)
+
+  {
+    std::same_as<decltype(vecSpan)::reference> vecElem = vecSpan.at(1);
+    assert(vec_elem == 1);
+  }
+
+  {
+    std::same_as<decltype(vecSpan)::reference> vecElem = std::as_const(vecSpan).at(1);
+    assert(vec_elem == 1);
+  }
+
+  return true;
+}
+
+void test_exceptions() {
+#ifndef TEST_HAS_NO_EXCEPTIONS
+  // With static extent
+  {
+    const std::array arr{1, 2, 3, 4};
+
+    try {
+      TEST_IGNORE_NODISCARD arr.at(4);
+      assert(false);
+    } catch (std::out_of_range const&) {
+      // pass
+    } catch (...) {
+      assert(false);
+    }
+  }
+
+  {
+    const std::array<int, 0> arr{};
+
+    try {
+      TEST_IGNORE_NODISCARD arr.at(0);
+      assert(false);
+    } catch (std::out_of_range const&) {
+      // pass
+    } catch (...) {
+      assert(false);
+    }
+  }
+
+  // With dynamic extent
+
+  {
+    const std::vector vec{1, 2, 3, 4};
+
+    try {
+      TEST_IGNORE_NODISCARD vec.at(4);
+      assert(false);
+    } catch (std::out_of_range const&) {
+      // pass
+    } catch (...) {
+      assert(false);
+    }
+  }
+
+  {
+    const std::vector<int> vec{};
+
+    try {
+      TEST_IGNORE_NODISCARD vec.at(0);
+      assert(false);
+    } catch (std::out_of_range const&) {
+      // pass
+    } catch (...) {
+      assert(false);
+    }
+  }
+#endif
+}
+
+int main(int, char**) {
+  test();
+  test_exceptions();
+  static_assert(test());
+
+  return 0;
+}
\ No newline at end of file
diff --git a/libcxx/test/std/containers/views/views.span/span.elem/op_idx.pass.cpp b/libcxx/test/std/containers/views/views.span/span.elem/op_idx.pass.cpp
index e46fd267ef5cc..b7f36c5758588 100644
--- a/libcxx/test/std/containers/views/views.span/span.elem/op_idx.pass.cpp
+++ b/libcxx/test/std/containers/views/views.span/span.elem/op_idx.pass.cpp
@@ -41,7 +41,6 @@ void testRuntimeSpan(Span sp, std::size_t idx)
     assert(r1 == r2);
 }
 
-struct A{};
 constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
           int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
 

>From ed7ee83fa9b10a37295d050e1edc538b05a22504 Mon Sep 17 00:00:00 2001
From: Zingam <zingam at outlook.com>
Date: Sun, 10 Dec 2023 16:03:08 +0200
Subject: [PATCH 2/5] Cleanup tests

---
 libcxx/docs/ReleaseNotes/18.rst               |   1 +
 libcxx/docs/Status/Cxx2cPapers.csv            |   2 +-
 .../views/views.span/span.elem/at.pass.cpp    | 139 ++----------------
 z_libcxx-dev-tools                            |   1 +
 4 files changed, 18 insertions(+), 125 deletions(-)
 create mode 160000 z_libcxx-dev-tools

diff --git a/libcxx/docs/ReleaseNotes/18.rst b/libcxx/docs/ReleaseNotes/18.rst
index abefe4c28ca95..05542f034e63b 100644
--- a/libcxx/docs/ReleaseNotes/18.rst
+++ b/libcxx/docs/ReleaseNotes/18.rst
@@ -54,6 +54,7 @@ Implemented Papers
 - P2871R3 - Remove Deprecated Unicode Conversion Facets from C++26
 - P2870R3 - Remove basic_string::reserve()
 - P2909R4 - Fix formatting of code units as integers (Dude, where’s my ``char``?)
+- P2821R5 - span.at()
 
 
 Improvements and New Features
diff --git a/libcxx/docs/Status/Cxx2cPapers.csv b/libcxx/docs/Status/Cxx2cPapers.csv
index 1d071b7ebcb4a..b97dc44795ac8 100644
--- a/libcxx/docs/Status/Cxx2cPapers.csv
+++ b/libcxx/docs/Status/Cxx2cPapers.csv
@@ -35,7 +35,7 @@
 "`P2909R4 <https://wg21.link/P2909R4>`__","LWG","Fix formatting of code units as integers (Dude, where’s my ``char``?)","Kona November 2023","|Complete|","18.0","|format| |DR|"
 "`P0952R2 <https://wg21.link/P0952R2>`__","LWG","A new specification for ``std::generate_canonical``","Kona November 2023","","",""
 "`P2447R6 <https://wg21.link/P2447R6>`__","LWG","``std::span`` over an initializer list","Kona November 2023","","",""
-"`P2821R5 <https://wg21.link/P2821R5>`__","LWG","``span.at()``","Kona November 2023","","",""
+"`P2821R5 <https://wg21.link/P2821R5>`__","LWG","``span.at()``","Kona November 2023","|Complete|","18.0",""
 "`P2868R3 <https://wg21.link/P2868R3>`__","LWG","Remove Deprecated ``std::allocator`` Typedef From C++26","Kona November 2023","","",""
 "`P2870R3 <https://wg21.link/P2870R3>`__","LWG","Remove ``basic_string::reserve()`` From C++26","Kona November 2023","|Complete|","18.0",""
 "`P2871R3 <https://wg21.link/P2871R3>`__","LWG","Remove Deprecated Unicode Conversion Facets from C++26","Kona November 2023","|Complete|","18.0",""
diff --git a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
index 2a9ce2baeec1a..8daaa6bb6fa12 100644
--- a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
+++ b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
@@ -17,144 +17,35 @@
 #include <concepts>
 #include <span>
 #include <stdexcept>
+#include <utility>
 #include <vector>
 
 #include "test_macros.h"
 
-// template <typename Span>
-// constexpr bool testConstexprSpan(Span sp, std::size_t idx)
-// {
-//     LIBCPP_ASSERT(noexcept(sp[idx]));
-
-//     typename Span::reference r1 = sp[idx];
-//     typename Span::reference r2 = *(sp.data() + idx);
-
-//     return r1 == r2;
-// }
-
-// template <typename Span>
-// void testRuntimeSpan(Span sp, std::size_t idx)
-// {
-//     LIBCPP_ASSERT(noexcept(sp[idx]));
-
-//     typename Span::reference r1 = sp[idx];
-//     typename Span::reference r2 = *(sp.data() + idx);
-
-//     assert(r1 == r2);
-// }
-
-// struct A{};
-// constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
-//           int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
-
-// int main(int, char**)
-// {
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 1), 0), "");
-
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 2), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 2), 1), "");
-
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 1), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 3), 2), "");
-
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 1), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 2), "");
-//     static_assert(testConstexprSpan(std::span<const int>(iArr1, 4), 3), "");
-
-//     static_assert(testConstexprSpan(std::span<const int, 1>(iArr1, 1), 0), "");
-
-//     static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int, 2>(iArr1, 2), 1), "");
-
-//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 1), "");
-//     static_assert(testConstexprSpan(std::span<const int, 3>(iArr1, 3), 2), "");
-
-//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 0), "");
-//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 1), "");
-//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 2), "");
-//     static_assert(testConstexprSpan(std::span<const int, 4>(iArr1, 4), 3), "");
-
-//     testRuntimeSpan(std::span<int>(iArr2, 1), 0);
-
-//     testRuntimeSpan(std::span<int>(iArr2, 2), 0);
-//     testRuntimeSpan(std::span<int>(iArr2, 2), 1);
-
-//     testRuntimeSpan(std::span<int>(iArr2, 3), 0);
-//     testRuntimeSpan(std::span<int>(iArr2, 3), 1);
-//     testRuntimeSpan(std::span<int>(iArr2, 3), 2);
-
-//     testRuntimeSpan(std::span<int>(iArr2, 4), 0);
-//     testRuntimeSpan(std::span<int>(iArr2, 4), 1);
-//     testRuntimeSpan(std::span<int>(iArr2, 4), 2);
-//     testRuntimeSpan(std::span<int>(iArr2, 4), 3);
-
-//     testRuntimeSpan(std::span<int, 1>(iArr2, 1), 0);
-
-//     testRuntimeSpan(std::span<int, 2>(iArr2, 2), 0);
-//     testRuntimeSpan(std::span<int, 2>(iArr2, 2), 1);
-
-//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 0);
-//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 1);
-//     testRuntimeSpan(std::span<int, 3>(iArr2, 3), 2);
-
-//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 0);
-//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 1);
-//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 2);
-//     testRuntimeSpan(std::span<int, 4>(iArr2, 4), 3);
-
-//     std::string s;
-//     testRuntimeSpan(std::span<std::string>   (&s, 1), 0);
-//     testRuntimeSpan(std::span<std::string, 1>(&s, 1), 0);
-
-//   return 0;
-// }
+constexpr void testSpan(auto span, int idx, int expectedValue) {
+  std::same_as<typename decltype(span)::reference> decltype(auto) elem = span.at(idx);
+  assert(elem == expectedValue);
+}
 
 constexpr bool test() {
-  //   {
-  //     typedef double T;
-  //     typedef std::array<T, 3> C;
-  //     C const c                      = {1, 2, 3.5};
-  //     typename C::const_reference r1 = c.at(0);
-  //     assert(r1 == 1);
-
-  //     typename C::const_reference r2 = c.at(2);
-  //     assert(r2 == 3.5);
-  //   }
-
-  const auto testSpan =
-      [](auto span, int idx, int expectedValue) {
-        {
-          std::same_as<decltype(span)::reference> elem = span.at(idx);
-          assert(elem == expectedValue);
-        }
-
-        {
-          std::same_as<decltype(span)::const_reference> elem = std::as_const(span).at(idx);
-          assert(elem == expectedValue);
-        }
-      }
-
   // With static extent
 
   std::array arr{0, 1, 2, 3, 4, 5, 9084};
-  std::span arrSpan{ar};
+  std::span arrSpan{arr};
 
   assert(std::dynamic_extent != arrSpan.extent);
 
   testSpan(arrSpan, 0, 0);
   testSpan(arrSpan, 1, 1);
-  testSpan(arrSpan, 5, 9084);
+  testSpan(arrSpan, 6, 9084);
 
   {
-    std::same_as<decltype(arrSpan)::reference> arrElem = arrSpan.at(1);
+    std::same_as<typename decltype(arrSpan)::reference> decltype(auto) arrElem = arrSpan.at(1);
     assert(arrElem == 1);
   }
 
   {
-    std::same_as<decltype(arrSpan)::const_reference> arrElem = std::as_const(arrSpan).at(1);
+    std::same_as<typename decltype(arrSpan)::reference> decltype(auto) arrElem = std::as_const(arrSpan).at(1);
     assert(arrElem == 1);
   }
 
@@ -162,17 +53,17 @@ constexpr bool test() {
 
   std::vector vec{0, 1, 2, 3, 4, 5};
   std::span vecSpan{vec};
-  
-  assert(std::dynamic_extent == vecSpan.extent)
+
+  assert(std::dynamic_extent == vecSpan.extent);
 
   {
-    std::same_as<decltype(vecSpan)::reference> vecElem = vecSpan.at(1);
-    assert(vec_elem == 1);
+    std::same_as<typename decltype(vecSpan)::reference> decltype(auto) vecElem = vecSpan.at(1);
+    assert(vecElem == 1);
   }
 
   {
-    std::same_as<decltype(vecSpan)::reference> vecElem = std::as_const(vecSpan).at(1);
-    assert(vec_elem == 1);
+    std::same_as<typename decltype(vecSpan)::reference> decltype(auto) vecElem = std::as_const(vecSpan).at(1);
+    assert(vecElem == 1);
   }
 
   return true;
diff --git a/z_libcxx-dev-tools b/z_libcxx-dev-tools
new file mode 160000
index 0000000000000..229818e01844e
--- /dev/null
+++ b/z_libcxx-dev-tools
@@ -0,0 +1 @@
+Subproject commit 229818e01844e2cad56818bf06703600071848c0

>From f02f8a0e8667fec1e5b5e16a13a9b5e52c52e58d Mon Sep 17 00:00:00 2001
From: Zingam <zingam at outlook.com>
Date: Sun, 10 Dec 2023 18:25:42 +0200
Subject: [PATCH 3/5] Removed bad file

---
 z_libcxx-dev-tools | 1 -
 1 file changed, 1 deletion(-)
 delete mode 160000 z_libcxx-dev-tools

diff --git a/z_libcxx-dev-tools b/z_libcxx-dev-tools
deleted file mode 160000
index 229818e01844e..0000000000000
--- a/z_libcxx-dev-tools
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 229818e01844e2cad56818bf06703600071848c0

>From e8e8457304f87e4780144fe3bc3bf918c335b726 Mon Sep 17 00:00:00 2001
From: Zingam <zingam at outlook.com>
Date: Sun, 10 Dec 2023 18:31:46 +0200
Subject: [PATCH 4/5] Fixed test_exceptions

---
 .../views/views.span/span.elem/at.pass.cpp     | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
index 8daaa6bb6fa12..68c2fca62a67c 100644
--- a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
+++ b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
@@ -73,10 +73,11 @@ void test_exceptions() {
 #ifndef TEST_HAS_NO_EXCEPTIONS
   // With static extent
   {
-    const std::array arr{1, 2, 3, 4};
+    std::array arr{1, 2, 3, 4};
+    const std::span arrSpan{arr};
 
     try {
-      TEST_IGNORE_NODISCARD arr.at(4);
+      TEST_IGNORE_NODISCARD arrSpan.at(4);
       assert(false);
     } catch (std::out_of_range const&) {
       // pass
@@ -86,10 +87,11 @@ void test_exceptions() {
   }
 
   {
-    const std::array<int, 0> arr{};
+    std::array<int, 0> arr{};
+    const std::span arrSpan{arr};
 
     try {
-      TEST_IGNORE_NODISCARD arr.at(0);
+      TEST_IGNORE_NODISCARD arrSpan.at(0);
       assert(false);
     } catch (std::out_of_range const&) {
       // pass
@@ -101,7 +103,8 @@ void test_exceptions() {
   // With dynamic extent
 
   {
-    const std::vector vec{1, 2, 3, 4};
+    std::vector vec{1, 2, 3, 4};
+    const std::span vecSpan{vec};
 
     try {
       TEST_IGNORE_NODISCARD vec.at(4);
@@ -114,7 +117,8 @@ void test_exceptions() {
   }
 
   {
-    const std::vector<int> vec{};
+    std::vector<int> vec{};
+    const std::span vecSpan{vec};
 
     try {
       TEST_IGNORE_NODISCARD vec.at(0);
@@ -134,4 +138,4 @@ int main(int, char**) {
   static_assert(test());
 
   return 0;
-}
\ No newline at end of file
+}

>From 9340bc0c3be951e6431926ebb8c7f3a5f71a7d1c Mon Sep 17 00:00:00 2001
From: Zingam <zingam at outlook.com>
Date: Sun, 10 Dec 2023 19:12:42 +0200
Subject: [PATCH 5/5] Fixed tests

---
 .../views/views.span/span.elem/at.pass.cpp    | 43 ++++++++-----------
 1 file changed, 18 insertions(+), 25 deletions(-)

diff --git a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
index 68c2fca62a67c..f3d6fbd9fb28a 100644
--- a/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
+++ b/libcxx/test/std/containers/views/views.span/span.elem/at.pass.cpp
@@ -23,8 +23,17 @@
 #include "test_macros.h"
 
 constexpr void testSpan(auto span, int idx, int expectedValue) {
-  std::same_as<typename decltype(span)::reference> decltype(auto) elem = span.at(idx);
-  assert(elem == expectedValue);
+  // non-const
+  {
+    std::same_as<typename decltype(span)::reference> decltype(auto) elem = span.at(idx);
+    assert(elem == expectedValue);
+  }
+
+  // const
+  {
+    std::same_as<typename decltype(span)::reference> decltype(auto) elem = std::as_const(span).at(idx);
+    assert(elem == expectedValue);
+  }
 }
 
 constexpr bool test() {
@@ -39,32 +48,16 @@ constexpr bool test() {
   testSpan(arrSpan, 1, 1);
   testSpan(arrSpan, 6, 9084);
 
-  {
-    std::same_as<typename decltype(arrSpan)::reference> decltype(auto) arrElem = arrSpan.at(1);
-    assert(arrElem == 1);
-  }
-
-  {
-    std::same_as<typename decltype(arrSpan)::reference> decltype(auto) arrElem = std::as_const(arrSpan).at(1);
-    assert(arrElem == 1);
-  }
-
   // With dynamic extent
 
-  std::vector vec{0, 1, 2, 3, 4, 5};
+  std::vector vec{0, 1, 2, 3, 4, 5, 9084};
   std::span vecSpan{vec};
 
   assert(std::dynamic_extent == vecSpan.extent);
 
-  {
-    std::same_as<typename decltype(vecSpan)::reference> decltype(auto) vecElem = vecSpan.at(1);
-    assert(vecElem == 1);
-  }
-
-  {
-    std::same_as<typename decltype(vecSpan)::reference> decltype(auto) vecElem = std::as_const(vecSpan).at(1);
-    assert(vecElem == 1);
-  }
+  testSpan(vecSpan, 0, 0);
+  testSpan(vecSpan, 1, 1);
+  testSpan(vecSpan, 6, 9084);
 
   return true;
 }
@@ -77,7 +70,7 @@ void test_exceptions() {
     const std::span arrSpan{arr};
 
     try {
-      TEST_IGNORE_NODISCARD arrSpan.at(4);
+      TEST_IGNORE_NODISCARD arrSpan.at(arr.size() + 1);
       assert(false);
     } catch (std::out_of_range const&) {
       // pass
@@ -107,7 +100,7 @@ void test_exceptions() {
     const std::span vecSpan{vec};
 
     try {
-      TEST_IGNORE_NODISCARD vec.at(4);
+      TEST_IGNORE_NODISCARD vecSpan.at(vec.size() + 1);
       assert(false);
     } catch (std::out_of_range const&) {
       // pass
@@ -121,7 +114,7 @@ void test_exceptions() {
     const std::span vecSpan{vec};
 
     try {
-      TEST_IGNORE_NODISCARD vec.at(0);
+      TEST_IGNORE_NODISCARD vecSpan.at(0);
       assert(false);
     } catch (std::out_of_range const&) {
       // pass



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