[libcxx-commits] [libcxx] [libc++] Implement P1789R3: Library Support for Expansion Statements (PR #167184)
Matthias Wippich via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Dec 23 08:04:10 PST 2025
https://github.com/Tsche updated https://github.com/llvm/llvm-project/pull/167184
>From 6026f6ad21a090aafe751489befbdab8b98d6886 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sat, 8 Nov 2025 23:10:28 +0100
Subject: [PATCH 01/19] [libc++] P1789R3: Library Support for Expansion
Statements
---
libcxx/docs/FeatureTestMacroTable.rst | 2 +
libcxx/docs/ReleaseNotes/22.rst | 1 +
libcxx/docs/Status/Cxx2cPapers.csv | 2 +-
libcxx/include/__utility/integer_sequence.h | 29 +++++++++++
libcxx/include/version | 4 +-
.../utility.version.compile.pass.cpp | 4 +-
.../version.version.compile.pass.cpp | 4 +-
.../intseq.binding/integer_seq.pass.cpp | 49 +++++++++++++++++++
.../intseq.binding/integer_seq.verify.cpp | 24 +++++++++
.../generate_feature_test_macro_components.py | 5 +-
10 files changed, 117 insertions(+), 7 deletions(-)
create mode 100644 libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
create mode 100644 libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index 4a82461b80534..32911d0f64449 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -474,6 +474,8 @@ Status
---------------------------------------------------------- -----------------
``__cpp_lib_inplace_vector`` *unimplemented*
---------------------------------------------------------- -----------------
+ ``__cpp_lib_integer_sequence`` ``202511L``
+ ---------------------------------------------------------- -----------------
``__cpp_lib_is_sufficiently_aligned`` ``202411L``
---------------------------------------------------------- -----------------
``__cpp_lib_is_virtual_base_of`` ``202406L``
diff --git a/libcxx/docs/ReleaseNotes/22.rst b/libcxx/docs/ReleaseNotes/22.rst
index 82271be7a22ab..ef1eb69faee72 100644
--- a/libcxx/docs/ReleaseNotes/22.rst
+++ b/libcxx/docs/ReleaseNotes/22.rst
@@ -52,6 +52,7 @@ Implemented Papers
- P2944R3: Comparisons for ``reference_wrapper`` (`Github <https://llvm.org/PR105424>`__)
- P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)
- P3567R2: ``flat_meow`` Fixes (`Github <https://llvm.org/PR162022>`__)
+- P1789R3: Library Support for Expansion Statements (`Github <https://llvm.org/PR167184>`__)
Improvements and New Features
-----------------------------
diff --git a/libcxx/docs/Status/Cxx2cPapers.csv b/libcxx/docs/Status/Cxx2cPapers.csv
index 3687e3dac2a8f..22be2e2fb40a6 100644
--- a/libcxx/docs/Status/Cxx2cPapers.csv
+++ b/libcxx/docs/Status/Cxx2cPapers.csv
@@ -169,7 +169,7 @@
"`P3819R0 <https://wg21.link/P3819R0>`__","Remove ``evaluation_exception()`` from contract-violation handling for C++26","2025-11 (Kona)","","","`#171280 <https://github.com/llvm/llvm-project/issues/171280>`__",""
"`P3612R1 <https://wg21.link/P3612R1>`__","Harmonize proxy-reference operations (LWG 3638 and 4187)","2025-11 (Kona)","","","`#171281 <https://github.com/llvm/llvm-project/issues/171281>`__",""
"`P3778R0 <https://wg21.link/P3778R0>`__","Fix for ``type_order`` template definition","2025-11 (Kona)","","","`#171284 <https://github.com/llvm/llvm-project/issues/171284>`__",""
-"`P1789R3 <https://wg21.link/P1789R3>`__","Library Support for Expansion Statements","2025-11 (Kona)","","","`#167268 <https://github.com/llvm/llvm-project/issues/167268>`__",""
+"`P1789R3 <https://wg21.link/P1789R3>`__","Library Support for Expansion Statements","2025-11 (Kona)","|Complete|","22","`#167268 <https://github.com/llvm/llvm-project/issues/167268>`__",""
"`P3922R1 <https://wg21.link/P3922R1>`__","Missing deduction guide from ``simd::mask`` to ``simd::vec``","2025-11 (Kona)","","","`#171285 <https://github.com/llvm/llvm-project/issues/171285>`__",""
"`P3878R1 <https://wg21.link/P3878R1>`__","Standard library hardening should not use the 'observe' semantic","2025-11 (Kona)","","","`#171286 <https://github.com/llvm/llvm-project/issues/171286>`__",""
"`P3887R1 <https://wg21.link/P3887R1>`__","Make ``when_all`` a Ronseal Algorithm","2025-11 (Kona)","","","`#171289 <https://github.com/llvm/llvm-project/issues/171289>`__",""
diff --git a/libcxx/include/__utility/integer_sequence.h b/libcxx/include/__utility/integer_sequence.h
index 9450d526ed32c..6c688ef018af6 100644
--- a/libcxx/include/__utility/integer_sequence.h
+++ b/libcxx/include/__utility/integer_sequence.h
@@ -13,6 +13,11 @@
#include <__cstddef/size_t.h>
#include <__type_traits/is_integral.h>
+#if _LIBCPP_STD_VER >= 26
+# include <__tuple/tuple_element.h>
+# include <__tuple/tuple_size.h>
+#endif
+
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
@@ -70,6 +75,30 @@ _LIBCPP_HIDE_FROM_ABI constexpr void __for_each_index_sequence(index_sequence<_I
}
# endif // _LIBCPP_STD_VER >= 20
+# if _LIBCPP_STD_VER >= 26
+// structured binding support for integer_sequence
+template <typename _Tp, _Tp... _Indices>
+struct tuple_size<integer_sequence<_Tp, _Indices...>> : public integral_constant<size_t, sizeof...(_Indices)> {};
+
+template <size_t _Ip, typename _Tp, _Tp... _Indices>
+struct tuple_element<_Ip, integer_sequence<_Tp, _Indices...>> {
+ static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::tuple_element<> (std::integer_sequence)");
+ using type _LIBCPP_NODEBUG = _Tp;
+};
+
+template <size_t _Ip, typename _Tp, _Tp... _Indices>
+struct tuple_element<_Ip, const integer_sequence<_Tp, _Indices...>> {
+ static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::tuple_element<> (const std::integer_sequence)");
+ using type _LIBCPP_NODEBUG = _Tp;
+};
+
+template <size_t _Ip, typename _Tp, _Tp... _Indices>
+_LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) _NOEXCEPT {
+ static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::get<> (std::integer_sequence)");
+ return _Indices...[_Ip];
+}
+# endif // _LIBCPP_STD_VER >= 20
+
# endif // _LIBCPP_STD_VER >= 14
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/version b/libcxx/include/version
index f959c0ab227ac..12cd691fae2d5 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -141,7 +141,7 @@ __cpp_lib_incomplete_container_elements 201505L <forward_list> <
__cpp_lib_inplace_vector 202406L <inplace_vector>
__cpp_lib_int_pow2 202002L <bit>
__cpp_lib_integer_comparison_functions 202002L <utility>
-__cpp_lib_integer_sequence 201304L <utility>
+__cpp_lib_integer_sequence 202511L <utility>
__cpp_lib_integral_constant_callable 201304L <type_traits>
__cpp_lib_interpolate 201902L <cmath> <numeric>
__cpp_lib_invoke 201411L <functional>
@@ -583,6 +583,8 @@ __cpp_lib_void_t 201411L <type_traits>
// # define __cpp_lib_generate_random 202403L
// # define __cpp_lib_hazard_pointer 202306L
// # define __cpp_lib_inplace_vector 202406L
+# undef __cpp_lib_integer_sequence
+# define __cpp_lib_integer_sequence 202511L
# define __cpp_lib_is_sufficiently_aligned 202411L
# if __has_builtin(__builtin_is_virtual_base_of)
# define __cpp_lib_is_virtual_base_of 202406L
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/utility.version.compile.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/utility.version.compile.pass.cpp
index b882a5df04ae3..1d82ef9ec0e86 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/utility.version.compile.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/utility.version.compile.pass.cpp
@@ -432,8 +432,8 @@
# ifndef __cpp_lib_integer_sequence
# error "__cpp_lib_integer_sequence should be defined in c++26"
# endif
-# if __cpp_lib_integer_sequence != 201304L
-# error "__cpp_lib_integer_sequence should have the value 201304L in c++26"
+# if __cpp_lib_integer_sequence != 202511L
+# error "__cpp_lib_integer_sequence should have the value 202511L in c++26"
# endif
# if !defined(_LIBCPP_VERSION)
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
index 28fae95c1c1f7..b3b424a1d77ce 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
@@ -7156,8 +7156,8 @@
# ifndef __cpp_lib_integer_sequence
# error "__cpp_lib_integer_sequence should be defined in c++26"
# endif
-# if __cpp_lib_integer_sequence != 201304L
-# error "__cpp_lib_integer_sequence should have the value 201304L in c++26"
+# if __cpp_lib_integer_sequence != 202511L
+# error "__cpp_lib_integer_sequence should have the value 202511L in c++26"
# endif
# ifndef __cpp_lib_integral_constant_callable
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
new file mode 100644
index 0000000000000..8deda77419e66
--- /dev/null
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+// <utility>
+
+// structured binding support for integer_sequence
+
+#include <tuple>
+#include <utility>
+#include <type_traits>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main(int, char**)
+{
+ using empty = std::integer_sequence<int>;
+ using size4 = std::integer_sequence<int, 9, 8, 7, 2>;
+
+ static_assert ( std::tuple_size_v<empty> == 0, "empty size wrong" );
+ static_assert ( std::tuple_size_v<const empty> == 0, "empty size wrong" );
+
+ static_assert ( std::tuple_size_v<size4> == 4, "size4 size wrong" );
+ static_assert ( std::tuple_size_v<const size4> == 4, "size4 size wrong" );
+
+ static_assert ( std::is_same_v<std::tuple_element_t<0, size4>, int>, "size4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<1, size4>, int>, "size4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<2, size4>, int>, "size4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<3, size4>, int>, "size4 type wrong" );
+
+ static_assert ( std::is_same_v<std::tuple_element_t<0, const size4>, int>, "const4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<1, const size4>, int>, "const4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<2, const size4>, int>, "const4 type wrong" );
+ static_assert ( std::is_same_v<std::tuple_element_t<3, const size4>, int>, "const4 type wrong" );
+
+ constexpr static size4 seq4{};
+ static_assert ( get<0> (seq4) == 9, "size4 element 0 wrong" );
+ static_assert ( get<1> (seq4) == 8, "size4 element 1 wrong" );
+ static_assert ( get<2> (seq4) == 7, "size4 element 2 wrong" );
+ static_assert ( get<3> (seq4) == 2, "size4 element 3 wrong" );
+
+ return 0;
+}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
new file mode 100644
index 0000000000000..9c93d11b28ceb
--- /dev/null
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+// <utility>
+
+// Expect failures for tuple_element and get with empty integer_sequence
+
+#include <utility>
+
+void f() {
+ using test1 = typename std::tuple_element<0, std::integer_sequence<int>>::type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
+ using test2 = typename std::tuple_element<0, const std::integer_sequence<int>>::type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
+
+ auto empty = std::integer_sequence<int>();
+ // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
+ // expected-error-re@*:* {{invalid index 0 for pack '{{.*}}' of size 0}}
+ (void)std::get<0>(empty);
+}
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index ff965aaa4ff89..753cfb7547e7e 100644
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -764,7 +764,10 @@ def add_version_header(tc):
},
{
"name": "__cpp_lib_integer_sequence",
- "values": {"c++14": 201304},
+ "values": {
+ "c++14": 201304,
+ "c++26": 202511, # P1789R3 Library Support for Expansion Statements
+ },
"headers": ["utility"],
},
{
>From 7f346b255e521bbd835e491a3ea14dd72d8b0c0f Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sat, 8 Nov 2025 23:31:03 +0100
Subject: [PATCH 02/19] fix formatting issues
---
.../intseq.binding/integer_seq.pass.cpp | 51 +++++++++----------
.../intseq.binding/integer_seq.verify.cpp | 14 ++---
.../generate_feature_test_macro_components.py | 2 +-
3 files changed, 34 insertions(+), 33 deletions(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
index 8deda77419e66..7220bccb601a8 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
@@ -18,32 +18,31 @@
#include "test_macros.h"
-int main(int, char**)
-{
- using empty = std::integer_sequence<int>;
- using size4 = std::integer_sequence<int, 9, 8, 7, 2>;
-
- static_assert ( std::tuple_size_v<empty> == 0, "empty size wrong" );
- static_assert ( std::tuple_size_v<const empty> == 0, "empty size wrong" );
-
- static_assert ( std::tuple_size_v<size4> == 4, "size4 size wrong" );
- static_assert ( std::tuple_size_v<const size4> == 4, "size4 size wrong" );
-
- static_assert ( std::is_same_v<std::tuple_element_t<0, size4>, int>, "size4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<1, size4>, int>, "size4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<2, size4>, int>, "size4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<3, size4>, int>, "size4 type wrong" );
-
- static_assert ( std::is_same_v<std::tuple_element_t<0, const size4>, int>, "const4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<1, const size4>, int>, "const4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<2, const size4>, int>, "const4 type wrong" );
- static_assert ( std::is_same_v<std::tuple_element_t<3, const size4>, int>, "const4 type wrong" );
-
- constexpr static size4 seq4{};
- static_assert ( get<0> (seq4) == 9, "size4 element 0 wrong" );
- static_assert ( get<1> (seq4) == 8, "size4 element 1 wrong" );
- static_assert ( get<2> (seq4) == 7, "size4 element 2 wrong" );
- static_assert ( get<3> (seq4) == 2, "size4 element 3 wrong" );
+int main(int, char**) {
+ using empty = std::integer_sequence<int>;
+ using size4 = std::integer_sequence<int, 9, 8, 7, 2>;
+
+ static_assert(std::tuple_size_v<empty> == 0, "empty size wrong");
+ static_assert(std::tuple_size_v<const empty> == 0, "empty size wrong");
+
+ static_assert(std::tuple_size_v<size4> == 4, "size4 size wrong");
+ static_assert(std::tuple_size_v<const size4> == 4, "size4 size wrong");
+
+ static_assert(std::is_same_v<std::tuple_element_t<0, size4>, int>, "size4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<1, size4>, int>, "size4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<2, size4>, int>, "size4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<3, size4>, int>, "size4 type wrong");
+
+ static_assert(std::is_same_v<std::tuple_element_t<0, const size4>, int>, "const4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<1, const size4>, int>, "const4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<2, const size4>, int>, "const4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<3, const size4>, int>, "const4 type wrong");
+
+ constexpr static size4 seq4{};
+ static_assert(get<0>(seq4) == 9, "size4 element 0 wrong");
+ static_assert(get<1>(seq4) == 8, "size4 element 1 wrong");
+ static_assert(get<2>(seq4) == 7, "size4 element 2 wrong");
+ static_assert(get<3>(seq4) == 2, "size4 element 3 wrong");
return 0;
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
index 9c93d11b28ceb..5863a692ad5a3 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
@@ -14,11 +14,13 @@
#include <utility>
void f() {
- using test1 = typename std::tuple_element<0, std::integer_sequence<int>>::type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
- using test2 = typename std::tuple_element<0, const std::integer_sequence<int>>::type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
+ using test1 = typename std::tuple_element<0, std::integer_sequence<int>>::
+ type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
+ using test2 = typename std::tuple_element<0, const std::integer_sequence<int>>::
+ type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
- auto empty = std::integer_sequence<int>();
- // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
- // expected-error-re@*:* {{invalid index 0 for pack '{{.*}}' of size 0}}
- (void)std::get<0>(empty);
+ auto empty = std::integer_sequence<int>();
+ // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
+ // expected-error-re@*:* {{invalid index 0 for pack '{{.*}}' of size 0}}
+ (void)std::get<0>(empty);
}
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index 753cfb7547e7e..f61d6f991cb15 100644
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -766,7 +766,7 @@ def add_version_header(tc):
"name": "__cpp_lib_integer_sequence",
"values": {
"c++14": 201304,
- "c++26": 202511, # P1789R3 Library Support for Expansion Statements
+ "c++26": 202511, # P1789R3 Library Support for Expansion Statements
},
"headers": ["utility"],
},
>From 9a1e54229708b1953955a913c003aad9bc256aa7 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sat, 8 Nov 2025 23:37:19 +0100
Subject: [PATCH 03/19] regenerate <version>
---
libcxx/include/version | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/libcxx/include/version b/libcxx/include/version
index 12cd691fae2d5..ab781466f5ed5 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -142,6 +142,7 @@ __cpp_lib_inplace_vector 202406L <inplace_vector>
__cpp_lib_int_pow2 202002L <bit>
__cpp_lib_integer_comparison_functions 202002L <utility>
__cpp_lib_integer_sequence 202511L <utility>
+ 201304L // C++14
__cpp_lib_integral_constant_callable 201304L <type_traits>
__cpp_lib_interpolate 201902L <cmath> <numeric>
__cpp_lib_invoke 201411L <functional>
@@ -583,7 +584,7 @@ __cpp_lib_void_t 201411L <type_traits>
// # define __cpp_lib_generate_random 202403L
// # define __cpp_lib_hazard_pointer 202306L
// # define __cpp_lib_inplace_vector 202406L
-# undef __cpp_lib_integer_sequence
+# undef __cpp_lib_integer_sequence
# define __cpp_lib_integer_sequence 202511L
# define __cpp_lib_is_sufficiently_aligned 202411L
# if __has_builtin(__builtin_is_virtual_base_of)
>From 4ee911f69076533596faf8515fa6083f6be1078c Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sat, 8 Nov 2025 23:58:48 +0100
Subject: [PATCH 04/19] fix failing test
---
.../std/utilities/intseq/intseq.binding/integer_seq.verify.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
index 5863a692ad5a3..e25d95fbda32e 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
@@ -21,6 +21,6 @@ void f() {
auto empty = std::integer_sequence<int>();
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
- // expected-error-re@*:* {{invalid index 0 for pack '{{.*}}' of size 0}}
+ // expected-error-re@*:* {{invalid index 0 for pack {{.*}} of size 0}}
(void)std::get<0>(empty);
}
>From 41222218ca42e2b22262e19470301aba1120fc2b Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sun, 9 Nov 2025 06:45:16 +0100
Subject: [PATCH 05/19] apply review comments
---
libcxx/include/__utility/integer_sequence.h | 4 +--
.../intseq.binding/integer_seq.pass.cpp | 35 +++++++++----------
2 files changed, 19 insertions(+), 20 deletions(-)
diff --git a/libcxx/include/__utility/integer_sequence.h b/libcxx/include/__utility/integer_sequence.h
index 6c688ef018af6..336f55adf401b 100644
--- a/libcxx/include/__utility/integer_sequence.h
+++ b/libcxx/include/__utility/integer_sequence.h
@@ -78,7 +78,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr void __for_each_index_sequence(index_sequence<_I
# if _LIBCPP_STD_VER >= 26
// structured binding support for integer_sequence
template <typename _Tp, _Tp... _Indices>
-struct tuple_size<integer_sequence<_Tp, _Indices...>> : public integral_constant<size_t, sizeof...(_Indices)> {};
+struct tuple_size<integer_sequence<_Tp, _Indices...>> : integral_constant<size_t, sizeof...(_Indices)> {};
template <size_t _Ip, typename _Tp, _Tp... _Indices>
struct tuple_element<_Ip, integer_sequence<_Tp, _Indices...>> {
@@ -97,7 +97,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) _NOE
static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::get<> (std::integer_sequence)");
return _Indices...[_Ip];
}
-# endif // _LIBCPP_STD_VER >= 20
+# endif // _LIBCPP_STD_VER >= 26
# endif // _LIBCPP_STD_VER >= 14
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
index 7220bccb601a8..fc3f039c1d265 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
@@ -20,29 +20,28 @@
int main(int, char**) {
using empty = std::integer_sequence<int>;
+ static_assert(std::tuple_size_v<empty> == 0);
+ static_assert(std::tuple_size_v<const empty> == 0);
+
using size4 = std::integer_sequence<int, 9, 8, 7, 2>;
+ static_assert(std::tuple_size_v<size4> == 4);
+ static_assert(std::tuple_size_v<const size4> == 4);
- static_assert(std::tuple_size_v<empty> == 0, "empty size wrong");
- static_assert(std::tuple_size_v<const empty> == 0, "empty size wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<0, size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<1, size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<2, size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<3, size4>, int>);
- static_assert(std::tuple_size_v<size4> == 4, "size4 size wrong");
- static_assert(std::tuple_size_v<const size4> == 4, "size4 size wrong");
-
- static_assert(std::is_same_v<std::tuple_element_t<0, size4>, int>, "size4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<1, size4>, int>, "size4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<2, size4>, int>, "size4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<3, size4>, int>, "size4 type wrong");
-
- static_assert(std::is_same_v<std::tuple_element_t<0, const size4>, int>, "const4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<1, const size4>, int>, "const4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<2, const size4>, int>, "const4 type wrong");
- static_assert(std::is_same_v<std::tuple_element_t<3, const size4>, int>, "const4 type wrong");
+ static_assert(std::is_same_v<std::tuple_element_t<0, const size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<1, const size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<2, const size4>, int>);
+ static_assert(std::is_same_v<std::tuple_element_t<3, const size4>, int>);
constexpr static size4 seq4{};
- static_assert(get<0>(seq4) == 9, "size4 element 0 wrong");
- static_assert(get<1>(seq4) == 8, "size4 element 1 wrong");
- static_assert(get<2>(seq4) == 7, "size4 element 2 wrong");
- static_assert(get<3>(seq4) == 2, "size4 element 3 wrong");
+ static_assert(get<0>(seq4) == 9);
+ static_assert(get<1>(seq4) == 8);
+ static_assert(get<2>(seq4) == 7);
+ static_assert(get<3>(seq4) == 2);
return 0;
}
>From b34fb3c47faa92f73e66d1a98b97b7e0b172e959 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sun, 9 Nov 2025 06:48:46 +0100
Subject: [PATCH 06/19] remove extraneous space
---
.../std/utilities/intseq/intseq.binding/integer_seq.pass.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
index fc3f039c1d265..c5baba7a101d9 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
@@ -22,7 +22,7 @@ int main(int, char**) {
using empty = std::integer_sequence<int>;
static_assert(std::tuple_size_v<empty> == 0);
static_assert(std::tuple_size_v<const empty> == 0);
-
+
using size4 = std::integer_sequence<int, 9, 8, 7, 2>;
static_assert(std::tuple_size_v<size4> == 4);
static_assert(std::tuple_size_v<const size4> == 4);
>From 22750c8fd305a5146e0f6a47181d7d1522583b0d Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sun, 9 Nov 2025 07:36:32 +0100
Subject: [PATCH 07/19] address more review comments
---
libcxx/include/utility | 12 ++++++++++++
...seq.pass.cpp => integer_seq.compile.pass.cpp} | 16 ++++++++++------
.../intseq/intseq.binding/integer_seq.verify.cpp | 16 ++++++++++++----
3 files changed, 34 insertions(+), 10 deletions(-)
rename libcxx/test/std/utilities/intseq/intseq.binding/{integer_seq.pass.cpp => integer_seq.compile.pass.cpp} (78%)
diff --git a/libcxx/include/utility b/libcxx/include/utility
index bc4eaf6a0cd02..1b19243afca1b 100644
--- a/libcxx/include/utility
+++ b/libcxx/include/utility
@@ -216,6 +216,18 @@ template<size_t N>
template<class... T>
using index_sequence_for = make_index_sequence<sizeof...(T)>;
+template<class T, T... Values> // C++26
+ struct tuple_size<integer_sequence<T, Values...>>;
+
+template<size_t I, class T, T... Values> // C++26
+ struct tuple_element<I, integer_sequence<T, Values...>>;
+
+template<size_t I, class T, T... Values> // C++26
+ struct tuple_element<I, const integer_sequence<T, Values...>>;
+
+template<size_t I, class T, T... Values> // C++26
+ constexpr T get(integer_sequence<T, Values...>) noexcept;
+
template<class T, class U=T>
constexpr T exchange(T& obj, U&& new_value) // constexpr in C++17, noexcept in C++23
noexcept(is_nothrow_move_constructible<T>::value && is_nothrow_assignable<T&, U>::value);
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
similarity index 78%
rename from libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
rename to libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
index c5baba7a101d9..4d23f2c03e77b 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
@@ -7,18 +7,24 @@
//===----------------------------------------------------------------------===//
// REQUIRES: std-at-least-c++26
+
// <utility>
-// structured binding support for integer_sequence
+// template<class T, T... Values>
+// struct tuple_size<integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, const integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// constexpr T get(integer_sequence<T, Values...>) noexcept;
#include <tuple>
#include <utility>
#include <type_traits>
#include <cassert>
-#include "test_macros.h"
-
-int main(int, char**) {
+constexpr void test() {
using empty = std::integer_sequence<int>;
static_assert(std::tuple_size_v<empty> == 0);
static_assert(std::tuple_size_v<const empty> == 0);
@@ -42,6 +48,4 @@ int main(int, char**) {
static_assert(get<1>(seq4) == 8);
static_assert(get<2>(seq4) == 7);
static_assert(get<3>(seq4) == 2);
-
- return 0;
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
index e25d95fbda32e..3e9d8d7d18dfc 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
@@ -7,17 +7,25 @@
//===----------------------------------------------------------------------===//
// REQUIRES: std-at-least-c++26
+
// <utility>
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, const integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// constexpr T get(integer_sequence<T, Values...>) noexcept;
+
// Expect failures for tuple_element and get with empty integer_sequence
#include <utility>
void f() {
- using test1 = typename std::tuple_element<0, std::integer_sequence<int>>::
- type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
- using test2 = typename std::tuple_element<0, const std::integer_sequence<int>>::
- type; // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
+ // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
+ using test1 = std::tuple_element_t<0, std::integer_sequence<int>>;
+ // expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
+ using test2 = std::tuple_element_t<0, const std::integer_sequence<int>>;
auto empty = std::integer_sequence<int>();
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
>From 00ae58d734c93a97e277faaa1fbb189f1fb1b196 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 08:23:02 +0100
Subject: [PATCH 08/19] add github issue to documentation, sort includes, minor
style changes
---
libcxx/include/__utility/integer_sequence.h | 17 +++++++----------
.../intseq.binding/integer_seq.compile.pass.cpp | 7 +++++--
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/libcxx/include/__utility/integer_sequence.h b/libcxx/include/__utility/integer_sequence.h
index 336f55adf401b..af38e311b98ef 100644
--- a/libcxx/include/__utility/integer_sequence.h
+++ b/libcxx/include/__utility/integer_sequence.h
@@ -11,13 +11,10 @@
#include <__config>
#include <__cstddef/size_t.h>
+#include <__tuple/tuple_element.h>
+#include <__tuple/tuple_size.h>
#include <__type_traits/is_integral.h>
-#if _LIBCPP_STD_VER >= 26
-# include <__tuple/tuple_element.h>
-# include <__tuple/tuple_size.h>
-#endif
-
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
@@ -77,23 +74,23 @@ _LIBCPP_HIDE_FROM_ABI constexpr void __for_each_index_sequence(index_sequence<_I
# if _LIBCPP_STD_VER >= 26
// structured binding support for integer_sequence
-template <typename _Tp, _Tp... _Indices>
+template <class _Tp, _Tp... _Indices>
struct tuple_size<integer_sequence<_Tp, _Indices...>> : integral_constant<size_t, sizeof...(_Indices)> {};
-template <size_t _Ip, typename _Tp, _Tp... _Indices>
+template <size_t _Ip, class _Tp, _Tp... _Indices>
struct tuple_element<_Ip, integer_sequence<_Tp, _Indices...>> {
static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::tuple_element<> (std::integer_sequence)");
using type _LIBCPP_NODEBUG = _Tp;
};
-template <size_t _Ip, typename _Tp, _Tp... _Indices>
+template <size_t _Ip, class _Tp, _Tp... _Indices>
struct tuple_element<_Ip, const integer_sequence<_Tp, _Indices...>> {
static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::tuple_element<> (const std::integer_sequence)");
using type _LIBCPP_NODEBUG = _Tp;
};
-template <size_t _Ip, typename _Tp, _Tp... _Indices>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) _NOEXCEPT {
+template <size_t _Ip, class _Tp, _Tp... _Indices>
+_LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) noexcept {
static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::get<> (std::integer_sequence)");
return _Indices...[_Ip];
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
index 4d23f2c03e77b..27597ea9b6044 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
@@ -19,12 +19,13 @@
// template<size_t I, class T, T... Values>
// constexpr T get(integer_sequence<T, Values...>) noexcept;
+#include <cassert>
#include <tuple>
-#include <utility>
#include <type_traits>
-#include <cassert>
+#include <utility>
constexpr void test() {
+ // std::tuple_size_v
using empty = std::integer_sequence<int>;
static_assert(std::tuple_size_v<empty> == 0);
static_assert(std::tuple_size_v<const empty> == 0);
@@ -33,6 +34,7 @@ constexpr void test() {
static_assert(std::tuple_size_v<size4> == 4);
static_assert(std::tuple_size_v<const size4> == 4);
+ // std::tuple_element_t
static_assert(std::is_same_v<std::tuple_element_t<0, size4>, int>);
static_assert(std::is_same_v<std::tuple_element_t<1, size4>, int>);
static_assert(std::is_same_v<std::tuple_element_t<2, size4>, int>);
@@ -43,6 +45,7 @@ constexpr void test() {
static_assert(std::is_same_v<std::tuple_element_t<2, const size4>, int>);
static_assert(std::is_same_v<std::tuple_element_t<3, const size4>, int>);
+ // std::get
constexpr static size4 seq4{};
static_assert(get<0>(seq4) == 9);
static_assert(get<1>(seq4) == 8);
>From af09adaef6737d2aa0ffda6dce57790523d4aa63 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 08:24:02 +0100
Subject: [PATCH 09/19] rename tests
---
.../{integer_seq.compile.pass.cpp => binding.compile.pass.cpp} | 0
.../intseq.binding/{integer_seq.verify.cpp => binding.verify.cpp} | 0
2 files changed, 0 insertions(+), 0 deletions(-)
rename libcxx/test/std/utilities/intseq/intseq.binding/{integer_seq.compile.pass.cpp => binding.compile.pass.cpp} (100%)
rename libcxx/test/std/utilities/intseq/intseq.binding/{integer_seq.verify.cpp => binding.verify.cpp} (100%)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/binding.compile.pass.cpp
similarity index 100%
rename from libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.compile.pass.cpp
rename to libcxx/test/std/utilities/intseq/intseq.binding/binding.compile.pass.cpp
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/binding.verify.cpp
similarity index 100%
rename from libcxx/test/std/utilities/intseq/intseq.binding/integer_seq.verify.cpp
rename to libcxx/test/std/utilities/intseq/intseq.binding/binding.verify.cpp
>From a5871cc2ede6d034c7cdb396c7b8a660ddc92435 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 15:03:41 +0100
Subject: [PATCH 10/19] rename tests, add noexceptness and return type checks,
add structured binding test
---
.../structured_binding.pass.cpp | 41 +++++++++++++++++++
...s.cpp => tuple_interface.compile.pass.cpp} | 6 +++
....verify.cpp => tuple_interface.verify.cpp} | 0
3 files changed, 47 insertions(+)
create mode 100644 libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
rename libcxx/test/std/utilities/intseq/intseq.binding/{binding.compile.pass.cpp => tuple_interface.compile.pass.cpp} (93%)
rename libcxx/test/std/utilities/intseq/intseq.binding/{binding.verify.cpp => tuple_interface.verify.cpp} (100%)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
new file mode 100644
index 0000000000000..d993f38c91f0e
--- /dev/null
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+
+// <utility>
+
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// struct tuple_element<I, const integer_sequence<T, Values...>>;
+// template<size_t I, class T, T... Values>
+// constexpr T get(integer_sequence<T, Values...>) noexcept;
+
+#include <cassert>
+#include <utility>
+
+template <typename...>
+void test_structured_bindings() {
+ constexpr static auto [...empty] = std::make_index_sequence<0>();
+ static_assert(sizeof...(empty) == 0);
+
+ constexpr static auto [...size4] = std::make_index_sequence<4>();
+ static_assert(sizeof...(size4) == 4);
+
+ // these cannot yet be static_asserts
+ assert(size4...[0] == 0);
+ assert(size4...[1] == 1);
+ assert(size4...[2] == 2);
+ assert(size4...[3] == 3);
+}
+
+int main(int, char**) {
+ test_structured_bindings();
+ return 0;
+}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/binding.compile.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
similarity index 93%
rename from libcxx/test/std/utilities/intseq/intseq.binding/binding.compile.pass.cpp
rename to libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
index 27597ea9b6044..84282d987919f 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/binding.compile.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
@@ -20,6 +20,7 @@
// constexpr T get(integer_sequence<T, Values...>) noexcept;
#include <cassert>
+#include <concepts>
#include <tuple>
#include <type_traits>
#include <utility>
@@ -51,4 +52,9 @@ constexpr void test() {
static_assert(get<1>(seq4) == 8);
static_assert(get<2>(seq4) == 7);
static_assert(get<3>(seq4) == 2);
+
+ static_assert(noexcept(get<0>(seq4)));
+
+ constexpr std::same_as<int> decltype(auto) r = get<0>(seq4);
+ static_assert(r == 9);
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/binding.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
similarity index 100%
rename from libcxx/test/std/utilities/intseq/intseq.binding/binding.verify.cpp
rename to libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
>From 4bb0481a88c5e6d7b818bc11a00672b18ceb67ff Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 15:09:00 +0100
Subject: [PATCH 11/19] fix formatting issues
---
.../intseq/intseq.binding/structured_binding.pass.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index d993f38c91f0e..8c951f2619dcd 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -22,10 +22,10 @@
template <typename...>
void test_structured_bindings() {
- constexpr static auto [...empty] = std::make_index_sequence<0>();
+ constexpr static auto [... empty] = std::make_index_sequence<0>();
static_assert(sizeof...(empty) == 0);
- constexpr static auto [...size4] = std::make_index_sequence<4>();
+ constexpr static auto [... size4] = std::make_index_sequence<4>();
static_assert(sizeof...(size4) == 4);
// these cannot yet be static_asserts
>From b2ccb843d20dcb5be22cf3e6a6d31ddb27dbe35a Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 18:01:49 +0100
Subject: [PATCH 12/19] drop constexpr
---
.../intseq/intseq.binding/structured_binding.pass.cpp | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index 8c951f2619dcd..f0af9af89bc1a 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -22,13 +22,12 @@
template <typename...>
void test_structured_bindings() {
- constexpr static auto [... empty] = std::make_index_sequence<0>();
+ auto [... empty] = std::make_index_sequence<0>();
static_assert(sizeof...(empty) == 0);
- constexpr static auto [... size4] = std::make_index_sequence<4>();
+ auto [... size4] = std::make_index_sequence<4>();
static_assert(sizeof...(size4) == 4);
- // these cannot yet be static_asserts
assert(size4...[0] == 0);
assert(size4...[1] == 1);
assert(size4...[2] == 2);
>From 79bf2e23a838df283f5a1018b4b774959fff909b Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 10 Nov 2025 23:33:42 +0100
Subject: [PATCH 13/19] guard p1061 structured bindings behind FTM, add
structured binding test case
---
.../intseq.binding/structured_binding.pass.cpp | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index f0af9af89bc1a..4702fbe989cd0 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -20,8 +20,18 @@
#include <cassert>
#include <utility>
-template <typename...>
void test_structured_bindings() {
+ auto [elt0, elt1, elt2, elt3] = std::make_index_sequence<4>();
+
+ assert(elt0 == 0);
+ assert(elt1 == 1);
+ assert(elt2 == 2);
+ assert(elt3 == 3);
+}
+
+#if __cpp_structured_bindings >= 202411L
+template <typename...>
+void test_p1061_structured_bindings() {
auto [... empty] = std::make_index_sequence<0>();
static_assert(sizeof...(empty) == 0);
@@ -33,8 +43,12 @@ void test_structured_bindings() {
assert(size4...[2] == 2);
assert(size4...[3] == 3);
}
+#endif
int main(int, char**) {
test_structured_bindings();
+#if __cpp_structured_bindings >= 202411L
+ test_p1061_structured_bindings();
+#endif
return 0;
}
>From f50a1ac94f229e4ad4065a96db8eb3a16fff4e51 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Fri, 14 Nov 2025 01:44:17 +0100
Subject: [PATCH 14/19] make get nodiscard, add nodiscard test, clean up tests
---
libcxx/include/__utility/integer_sequence.h | 4 +-
.../intseq.binding/nodiscard.verify.cpp | 23 ++++++++++++
.../structured_binding.pass.cpp | 37 +++++++++----------
.../tuple_interface.compile.pass.cpp | 10 ++---
.../intseq.binding/tuple_interface.verify.cpp | 2 +-
5 files changed, 48 insertions(+), 28 deletions(-)
create mode 100644 libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp
diff --git a/libcxx/include/__utility/integer_sequence.h b/libcxx/include/__utility/integer_sequence.h
index af38e311b98ef..a84f572c3339c 100644
--- a/libcxx/include/__utility/integer_sequence.h
+++ b/libcxx/include/__utility/integer_sequence.h
@@ -73,7 +73,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr void __for_each_index_sequence(index_sequence<_I
# endif // _LIBCPP_STD_VER >= 20
# if _LIBCPP_STD_VER >= 26
-// structured binding support for integer_sequence
+// [intseq.binding], structured binding support
template <class _Tp, _Tp... _Indices>
struct tuple_size<integer_sequence<_Tp, _Indices...>> : integral_constant<size_t, sizeof...(_Indices)> {};
@@ -90,7 +90,7 @@ struct tuple_element<_Ip, const integer_sequence<_Tp, _Indices...>> {
};
template <size_t _Ip, class _Tp, _Tp... _Indices>
-_LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) noexcept {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp get(integer_sequence<_Tp, _Indices...>) noexcept {
static_assert(_Ip < sizeof...(_Indices), "Index out of bounds in std::get<> (std::integer_sequence)");
return _Indices...[_Ip];
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp
new file mode 100644
index 0000000000000..82c0ed1aee175
--- /dev/null
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+
+// <utility>
+
+// template<size_t I, class T, T... Values>
+// [[nodiscard]] constexpr T get(integer_sequence<T, Values...>) noexcept;
+
+// check that get is marked [[nodiscard]]
+
+#include <utility>
+
+void f() {
+ std::index_sequence<1> seq;
+ get<0>(seq); // expected-warning {{ignoring return value of function}}
+}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index 4702fbe989cd0..3d6745bf17a73 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -20,35 +20,34 @@
#include <cassert>
#include <utility>
-void test_structured_bindings() {
+constexpr bool test_structured_bindings() {
auto [elt0, elt1, elt2, elt3] = std::make_index_sequence<4>();
-
+
assert(elt0 == 0);
assert(elt1 == 1);
assert(elt2 == 2);
assert(elt3 == 3);
-}
#if __cpp_structured_bindings >= 202411L
-template <typename...>
-void test_p1061_structured_bindings() {
- auto [... empty] = std::make_index_sequence<0>();
- static_assert(sizeof...(empty) == 0);
-
- auto [... size4] = std::make_index_sequence<4>();
- static_assert(sizeof...(size4) == 4);
-
- assert(size4...[0] == 0);
- assert(size4...[1] == 1);
- assert(size4...[2] == 2);
- assert(size4...[3] == 3);
-}
+ []<typename...> {
+ auto [... empty] = std::make_index_sequence<0>();
+ static_assert(sizeof...(empty) == 0);
+
+ auto [... size4] = std::make_index_sequence<4>();
+ static_assert(sizeof...(size4) == 4);
+
+ assert(size4...[0] == 0);
+ assert(size4...[1] == 1);
+ assert(size4...[2] == 2);
+ assert(size4...[3] == 3);
+ }();
#endif
+ return true;
+}
+
int main(int, char**) {
test_structured_bindings();
-#if __cpp_structured_bindings >= 202411L
- test_p1061_structured_bindings();
-#endif
+ static_assert(test_structured_bindings());
return 0;
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
index 84282d987919f..026f20eb8c09f 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.compile.pass.cpp
@@ -25,7 +25,7 @@
#include <type_traits>
#include <utility>
-constexpr void test() {
+void test() {
// std::tuple_size_v
using empty = std::integer_sequence<int>;
static_assert(std::tuple_size_v<empty> == 0);
@@ -47,14 +47,12 @@ constexpr void test() {
static_assert(std::is_same_v<std::tuple_element_t<3, const size4>, int>);
// std::get
- constexpr static size4 seq4{};
- static_assert(get<0>(seq4) == 9);
+ constexpr static size4 seq4;
+ constexpr std::same_as<int> decltype(auto) elt0 = get<0>(seq4);
+ static_assert(elt0 == 9);
static_assert(get<1>(seq4) == 8);
static_assert(get<2>(seq4) == 7);
static_assert(get<3>(seq4) == 2);
static_assert(noexcept(get<0>(seq4)));
-
- constexpr std::same_as<int> decltype(auto) r = get<0>(seq4);
- static_assert(r == 9);
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
index 3e9d8d7d18dfc..d5be826f52c12 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
@@ -27,7 +27,7 @@ void f() {
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
using test2 = std::tuple_element_t<0, const std::integer_sequence<int>>;
- auto empty = std::integer_sequence<int>();
+ std::integer_sequence<int> empty;
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::get<> (std::integer_sequence)}}
// expected-error-re@*:* {{invalid index 0 for pack {{.*}} of size 0}}
(void)std::get<0>(empty);
>From 3a169cef95820380d3fb2f88d424a7cfd8e17e0e Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sun, 14 Dec 2025 22:21:54 +0100
Subject: [PATCH 15/19] move nodiscard test to test/libcxx, fixup tests names
---
.../utilities/intseq/intseq.binding/nodiscard.verify.cpp | 2 +-
.../intseq/intseq.binding/structured_binding.pass.cpp | 6 +++---
.../intseq/intseq.binding/tuple_interface.verify.cpp | 2 +-
3 files changed, 5 insertions(+), 5 deletions(-)
rename libcxx/test/{std => libcxx}/utilities/intseq/intseq.binding/nodiscard.verify.cpp (98%)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp b/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
similarity index 98%
rename from libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp
rename to libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
index 82c0ed1aee175..f930a400ea635 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
@@ -17,7 +17,7 @@
#include <utility>
-void f() {
+void test() {
std::index_sequence<1> seq;
get<0>(seq); // expected-warning {{ignoring return value of function}}
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index 3d6745bf17a73..3f52f18282543 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -20,7 +20,7 @@
#include <cassert>
#include <utility>
-constexpr bool test_structured_bindings() {
+constexpr bool test() {
auto [elt0, elt1, elt2, elt3] = std::make_index_sequence<4>();
assert(elt0 == 0);
@@ -47,7 +47,7 @@ constexpr bool test_structured_bindings() {
}
int main(int, char**) {
- test_structured_bindings();
- static_assert(test_structured_bindings());
+ test();
+ static_assert(test());
return 0;
}
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
index d5be826f52c12..a1c894e985729 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/tuple_interface.verify.cpp
@@ -21,7 +21,7 @@
#include <utility>
-void f() {
+void test() {
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (std::integer_sequence)}}
using test1 = std::tuple_element_t<0, std::integer_sequence<int>>;
// expected-error-re@*:* {{static assertion failed{{.*}}Index out of bounds in std::tuple_element<> (const std::integer_sequence)}}
>From 444e1d44f9b20a4e68151b1ca9c64c3accaad551 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Sun, 14 Dec 2025 22:30:32 +0100
Subject: [PATCH 16/19] rerun formatter
---
.../libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp b/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
index f930a400ea635..0e88871020906 100644
--- a/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
@@ -19,5 +19,5 @@
void test() {
std::index_sequence<1> seq;
- get<0>(seq); // expected-warning {{ignoring return value of function}}
+ get<0>(seq); // expected-warning {{ignoring return value of function}}
}
>From 4c500a267bd123bc932c165f23f709d3f75be294 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Mon, 15 Dec 2025 07:16:45 +0100
Subject: [PATCH 17/19] add todo
---
.../utilities/intseq/intseq.binding/structured_binding.pass.cpp | 1 +
1 file changed, 1 insertion(+)
diff --git a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
index 3f52f18282543..650e0d651ea7d 100644
--- a/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
+++ b/libcxx/test/std/utilities/intseq/intseq.binding/structured_binding.pass.cpp
@@ -28,6 +28,7 @@ constexpr bool test() {
assert(elt2 == 2);
assert(elt3 == 3);
+// TODO: remove this macro guard once GCC16 is available
#if __cpp_structured_bindings >= 202411L
[]<typename...> {
auto [... empty] = std::make_index_sequence<0>();
>From 3b945133552ebb4f2ba96e75437f3d6bfef7b249 Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Tue, 16 Dec 2025 05:50:03 +0100
Subject: [PATCH 18/19] fold intseq.binding/nodiscard.verify.cpp into
nodiscard.verify.cpp
---
.../intseq.binding/nodiscard.verify.cpp | 23 -------------------
.../utilities/intseq/nodiscard.verify.cpp | 3 +++
2 files changed, 3 insertions(+), 23 deletions(-)
delete mode 100644 libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
diff --git a/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp b/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
deleted file mode 100644
index 0e88871020906..0000000000000
--- a/libcxx/test/libcxx/utilities/intseq/intseq.binding/nodiscard.verify.cpp
+++ /dev/null
@@ -1,23 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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++26
-
-// <utility>
-
-// template<size_t I, class T, T... Values>
-// [[nodiscard]] constexpr T get(integer_sequence<T, Values...>) noexcept;
-
-// check that get is marked [[nodiscard]]
-
-#include <utility>
-
-void test() {
- std::index_sequence<1> seq;
- get<0>(seq); // expected-warning {{ignoring return value of function}}
-}
diff --git a/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp b/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
index 4ca52ace08dd3..8d2f35cadc553 100644
--- a/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
@@ -18,4 +18,7 @@ void test() {
std::integer_sequence<int, 49, 82, 94> seq;
seq.size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if TEST_STD_VER >= 26
+ get<0>(seq); // expected-warning {{ignoring return value of function}}
+#endif
}
>From 50eae4abdd1fc6e6166e64083f288fc9e9e736ca Mon Sep 17 00:00:00 2001
From: Tsche <che at pydong.org>
Date: Tue, 16 Dec 2025 19:22:45 +0100
Subject: [PATCH 19/19] add test_macro.h include
---
libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp | 2 ++
1 file changed, 2 insertions(+)
diff --git a/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp b/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
index 8d2f35cadc553..811759f37823c 100644
--- a/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/utilities/intseq/nodiscard.verify.cpp
@@ -14,6 +14,8 @@
#include <utility>
+#include "test_macros.h"
+
void test() {
std::integer_sequence<int, 49, 82, 94> seq;
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