[libc++] P1789R3: Library Support for Expansion Statements #167184
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@llvm/pr-subscribers-libcxx Author: None (Tsche) ChangesP1789R3 was accepted for C++26 through LWG motion 14 at the 2025 Kona meeting. This patch implements it, along with tests and documentation changes. Full diff: https://github.com/llvm/llvm-project/pull/167184.diff 10 Files Affected:
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index d5ed9188b1b23..349164a96de87 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 a6a0ac8670fb5..685e7a22be28a 100644
--- a/libcxx/docs/ReleaseNotes/22.rst
+++ b/libcxx/docs/ReleaseNotes/22.rst
@@ -48,6 +48,7 @@ Implemented Papers
- P2835R7: Expose ``std::atomic_ref``'s object address (`Github <https://llvm.org/PR118377>`__)
- P2944R3: Comparisons for ``reference_wrapper`` (`Github <https://llvm.org/PR105424>`__)
- P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)
+- P1789R3: Library Support for Expansion Statements
Improvements and New Features
-----------------------------
diff --git a/libcxx/docs/Status/Cxx2cPapers.csv b/libcxx/docs/Status/Cxx2cPapers.csv
index e0e47b864d38f..7347408fbb3c1 100644
--- a/libcxx/docs/Status/Cxx2cPapers.csv
+++ b/libcxx/docs/Status/Cxx2cPapers.csv
@@ -157,3 +157,5 @@
"`P3552R3 <https://wg21.link/P3552R3>`__","Add a Coroutine Task Type","2025-06 (Sofia)","","","`#148182 <https://github.com/llvm/llvm-project/issues/148182>`__",""
"`P1317R2 <https://wg21.link/P1317R2>`__","Remove return type deduction in ``std::apply``","2025-06 (Sofia)","","","`#148183 <https://github.com/llvm/llvm-project/issues/148183>`__",""
"","","","","","",""
+"`P1789R3 <https://wg21.link/P1789R3>`__","Library Support for Expansion Statements`","2025-11 (Kona)","|Complete|","22","",""
+"","","","","","",""
diff --git a/libcxx/include/__utility/integer_sequence.h b/libcxx/include/__utility/integer_sequence.h
index 329826ae5eda2..8889c1196a450 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
@@ -67,6 +72,30 @@ _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 b0030602f854a..c9a4c58a9a289 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>
@@ -582,6 +582,8 @@ __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 8189c5c4e5985..355ca57bac64c 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 22209f53d50d7..914172410e332 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"],
},
{
|
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✅ With the latest revision this PR passed the Python code formatter. |
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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P1789R3 was accepted for C++26 through LWG motion 14 at the 2025 Kona meeting. This patch implements it, along with tests and documentation changes.