{"id":2232021,"url":"http://patchwork.ozlabs.org/api/1.1/patches/2232021/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/oro6iyfbxp.fsf_-_@lxoliva.fsfla.org/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/1.1/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null},"msgid":"","date":"2026-05-02T08:33:22","name":"[v3] libstdc++: check value in std::{con,dis}junction","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"ca396ca552484f91b317b572f10f8fd1314eb54e","submitter":{"id":74937,"url":"http://patchwork.ozlabs.org/api/1.1/people/74937/?format=json","name":"Alexandre Oliva","email":"oliva@adacore.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/oro6iyfbxp.fsf_-_@lxoliva.fsfla.org/mbox/","series":[{"id":502518,"url":"http://patchwork.ozlabs.org/api/1.1/series/502518/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=502518","date":"2026-05-02T08:33:22","name":"[v3] libstdc++: check value in std::{con,dis}junction","version":3,"mbox":"http://patchwork.ozlabs.org/series/502518/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2232021/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2232021/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n secure) header.d=adacore.com header.i=@adacore.com header.a=rsa-sha256\n header.s=google header.b=JrciEa2d;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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it just seems good practice to check\nthat the requirements are met instead of silently swallowing what is\nlikely an error, that I'm told other compilers report. That said, it's\nprobably just a pedantic overcompliance matter, since any use of\n::value, which is to be expected, would report the error anyway.\n\nSo this is probably my last attempt at this. Instead of using\ntype::value, I introduce __type as a typedef to the base type to\nsimplify the static_assert.\n\nI'd appreciate an explicit decline in case we don't want this, so that I\ndon't keep on pinging and waiting for a resolution. (ditto for\nhttps://gcc.gnu.org/pipermail/gcc-patches/2026-April/713470.html BTW :-)\nTIA,\n\nRegstrapping on x86_64-linux-gnu. Ok to install?\n\n\nWhen std::{con,dis}junction is passed a type that doesn't have a\n\"value\" static data member, or whose value doesn't convert to bool, is\nambiguous or inaccessible, we stop iterating over the types and use\nthat type for the {con,dis}junction, without any diagnostic.\n\nWe'd get a diagnostic when attempting to use its value data member as\na bool, but if the member isn't used, compilation is successful,\ndespite the failure to meet the requirements for \"value\" in\n[meta.logical]/4. A diagnostic is not required, but it may be useful.\n\nCheck that the selected type parameter has a value member, and that\nits value member is convertible to bool at the user-visible class; an\nassert in the _impl class would fuse errors whose malformed type\nstarts a shared tail, so introduce __type in the user-visible class to\nshorten the assert.\n\n\nfor libstdc++-v3/ChangeLog\n\n\t* include/std/type_traits (disjunction, conjunction): Check\n\tthat value converts to bool. Move implementation down.\n---\n libstdc++-v3/include/std/type_traits | 142 ++++++++++----------\n .../logical_traits/requirements/junction_neg.cc | 31 ++++\n 2 files changed, 105 insertions(+), 68 deletions(-)\n create mode 100644 libstdc++-v3/testsuite/20_util/logical_traits/requirements/junction_neg.cc","diff":"diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits\nindex 1c03c22e8eed4..d8de3f013a73c 100644\n--- a/libstdc++-v3/include/std/type_traits\n+++ b/libstdc++-v3/include/std/type_traits\n@@ -213,74 +213,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n { };\n /// @endcond\n \n-#ifdef __cpp_lib_logical_traits // C++ >= 17\n-\n- /// @cond undocumented\n- template\n- inline constexpr bool __or_v = __or_<_Bn...>::value;\n- template\n- inline constexpr bool __and_v = __and_<_Bn...>::value;\n-\n- namespace __detail\n- {\n- template\n- struct __disjunction_impl\n- { using type = _B1; };\n-\n- template\n- struct __disjunction_impl<__enable_if_t, _B1, _B2, _Bn...>\n- { using type = typename __disjunction_impl::type; };\n-\n- template\n- struct __conjunction_impl\n- { using type = _B1; };\n-\n- template\n- struct __conjunction_impl<__enable_if_t, _B1, _B2, _Bn...>\n- { using type = typename __conjunction_impl::type; };\n- } // namespace __detail\n- /// @endcond\n-\n- template\n- struct conjunction\n- : __detail::__conjunction_impl::type\n- { };\n-\n- template<>\n- struct conjunction<>\n- : true_type\n- { };\n-\n- template\n- struct disjunction\n- : __detail::__disjunction_impl::type\n- { };\n-\n- template<>\n- struct disjunction<>\n- : false_type\n- { };\n-\n- template\n- struct negation\n- : __not_<_Pp>::type\n- { };\n-\n- /** @ingroup variable_templates\n- * @{\n- */\n- template\n- inline constexpr bool conjunction_v = conjunction<_Bn...>::value;\n-\n- template\n- inline constexpr bool disjunction_v = disjunction<_Bn...>::value;\n-\n- template\n- inline constexpr bool negation_v = negation<_Pp>::value;\n- /// @}\n-\n-#endif // __cpp_lib_logical_traits\n-\n // Forward declarations\n template\n struct is_object;\n@@ -3871,6 +3803,80 @@ template\n /// @}\n #endif // __cpp_lib_type_trait_variable_templates\n \n+#ifdef __cpp_lib_logical_traits // C++ >= 17\n+\n+ /// @cond undocumented\n+ template\n+ inline constexpr bool __or_v = __or_<_Bn...>::value;\n+ template\n+ inline constexpr bool __and_v = __and_<_Bn...>::value;\n+\n+ namespace __detail\n+ {\n+ template\n+ struct __disjunction_impl\n+ { using type = _B1; };\n+\n+ template\n+ struct __disjunction_impl<__enable_if_t, _B1, _B2, _Bn...>\n+ { using type = typename __disjunction_impl::type; };\n+\n+ template\n+ struct __conjunction_impl\n+ { using type = _B1; };\n+\n+ template\n+ struct __conjunction_impl<__enable_if_t, _B1, _B2, _Bn...>\n+ { using type = typename __conjunction_impl::type; };\n+ } // namespace __detail\n+ /// @endcond\n+\n+ template\n+ struct conjunction\n+ : __detail::__conjunction_impl::type\n+ {\n+ typedef typename __detail::__conjunction_impl::type __type;\n+ static_assert(is_convertible_v);\n+ };\n+\n+ template<>\n+ struct conjunction<>\n+ : true_type\n+ { };\n+\n+ template\n+ struct disjunction\n+ : __detail::__disjunction_impl::type\n+ {\n+ typedef typename __detail::__disjunction_impl::type __type;\n+ static_assert(is_convertible_v);\n+ };\n+\n+ template<>\n+ struct disjunction<>\n+ : false_type\n+ { };\n+\n+ template\n+ struct negation\n+ : __not_<_Pp>::type\n+ { };\n+\n+ /** @ingroup variable_templates\n+ * @{\n+ */\n+ template\n+ inline constexpr bool conjunction_v = conjunction<_Bn...>::value;\n+\n+ template\n+ inline constexpr bool disjunction_v = disjunction<_Bn...>::value;\n+\n+ template\n+ inline constexpr bool negation_v = negation<_Pp>::value;\n+ /// @}\n+\n+#endif // __cpp_lib_logical_traits\n+\n #ifdef __cpp_lib_has_unique_object_representations // C++ >= 17 && HAS_UNIQ_OBJ_REP\n /// has_unique_object_representations\n /// @since C++17\ndiff --git a/libstdc++-v3/testsuite/20_util/logical_traits/requirements/junction_neg.cc b/libstdc++-v3/testsuite/20_util/logical_traits/requirements/junction_neg.cc\nnew file mode 100644\nindex 0000000000000..bfa502fe03116\n--- /dev/null\n+++ b/libstdc++-v3/testsuite/20_util/logical_traits/requirements/junction_neg.cc\n@@ -0,0 +1,31 @@\n+// { dg-do compile { target c++17 } }\n+\n+#include \n+\n+class S {}; // not convertible to bool\n+\n+struct T {\n+ static constexpr S value{};\n+};\n+\n+// 4 Every template type argument for which Bi::value is instantiated shall be\n+// usable as a base class and shall have a member value which is convertible to\n+// bool, is not hidden, and is unambiguously available in the type.\n+\n+// ctT and dfT test that we don't fuse error messages when the type that\n+// doesn't satisfy the requirements start a shared tail of types in the _impl\n+// instantiations.\n+\n+std::conjunction cT; // { dg-error \"here\" }\n+std::conjunction cTt; // { dg-error \"here\" }\n+std::conjunction cTf; // { dg-error \"here\" }\n+std::conjunction ctT; // { dg-error \"here\" }\n+std::conjunction cfT;\n+\n+std::disjunction dT; // { dg-error \"here\" }\n+std::disjunction dTf; // { dg-error \"here\" }\n+std::disjunction dTt; // { dg-error \"here\" }\n+std::disjunction dfT; // { dg-error \"here\" }\n+std::disjunction dtT;\n+\n+// { dg-prune-output {(static assertion failed|could not convert|evaluates to false)} }\n","prefixes":["v3"]}