{"id":2226650,"url":"http://patchwork.ozlabs.org/api/patches/2226650/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhunqjrqt2.gcc.gcc-TEST.redi.37.1.1@forge-stage.sourceware.org/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/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,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"","list_archive_url":null,"date":"2026-04-22T17:58:46","name":"[v1,1/1] libstdc++: Add missing static_assert to std::expected::value()&&","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"6b6278bd4353cf2917d5a2f36582a9db65762e9c","submitter":{"id":93210,"url":"http://patchwork.ozlabs.org/api/people/93210/?format=json","name":"Jonathan Wakely via Sourceware Forge","email":"forge-bot+redi@forge-stage.sourceware.org"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/bmm.hhunqjrqt2.gcc.gcc-TEST.redi.37.1.1@forge-stage.sourceware.org/mbox/","series":[{"id":501058,"url":"http://patchwork.ozlabs.org/api/series/501058/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=501058","date":"2026-04-22T17:58:46","name":"libstdc++: Add missing static_assert to std::expected::value()&&","version":1,"mbox":"http://patchwork.ozlabs.org/series/501058/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2226650/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2226650/checks/","tags":{},"related":[],"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 spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org; dmarc=none (p=none dis=none)\n header.from=forge-stage.sourceware.org","sourceware.org;\n spf=pass smtp.mailfrom=forge-stage.sourceware.org","server2.sourceware.org;\n arc=none smtp.remote-ip=38.145.34.39"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g16Sk2T6Cz1yGs\n\tfor ; Thu, 23 Apr 2026 04:00:05 +1000 (AEST)","from vm01.sourceware.org (localhost [127.0.0.1])\n\tby sourceware.org (Postfix) with ESMTP id E8C3F4BB58F8\n\tfor ; Wed, 22 Apr 2026 18:00:02 +0000 (GMT)","from forge-stage.sourceware.org (vm08.sourceware.org [38.145.34.39])\n by sourceware.org (Postfix) with ESMTPS id DDF754BB58F8\n for ; Wed, 22 Apr 2026 17:59:37 +0000 (GMT)","from forge-stage.sourceware.org (localhost [IPv6:::1])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange x25519 server-signature ECDSA (prime256v1) server-digest SHA256)\n (No client certificate requested)\n by forge-stage.sourceware.org (Postfix) with ESMTPS id B5DB342BFF\n for ; Wed, 22 Apr 2026 17:59:37 +0000 (UTC)"],"DKIM-Filter":["OpenDKIM Filter v2.11.0 sourceware.org E8C3F4BB58F8","OpenDKIM Filter v2.11.0 sourceware.org DDF754BB58F8"],"DMARC-Filter":"OpenDMARC Filter v1.4.2 sourceware.org DDF754BB58F8","ARC-Filter":"OpenARC Filter v1.0.0 sourceware.org DDF754BB58F8","ARC-Seal":"i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1776880777; cv=none;\n b=RRWQDsgyJBTZY2Rj/FEnBuOcZv9fSQ/IGaVLU6wTyJUoPME275zEmlhcBoCvk3P/buBLuyoUXnF/tN5MGomuBDcVt4Kmf4ziMh8JwIFaBpRDyW7nSrPAD3Ibc8h3iBVY5eUp4wnv9Iwaf0NIvrPM0pxp+FU1ly9DP6cFSL5HNOk=","ARC-Message-Signature":"i=1; a=rsa-sha256; d=sourceware.org; s=key;\n t=1776880777; c=relaxed/simple;\n bh=PolDstwKqkVPQ5fIKImSaofrh9ubvEPy0vkmn8kalwc=;\n h=From:Date:Subject:To:Message-ID;\n b=MHy78ydEDRBzUM3bCsrNCJdszoeu7J6NR2/FJtGejoBq010B9Q6H+o8C9fx0fFwEvPmrmZCJddsMvpAUH8ZRaTi3leFw+bkAhxGHkECHSNEP4/m19kopUOYu+xVh8eNo/DI4zqD7JWr0wJhGEvBVuTmYUTsi0gAxqBEASPS2UuQ=","ARC-Authentication-Results":"i=1; server2.sourceware.org","From":"Jonathan Wakely via Sourceware Forge\n ","Date":"Wed, 22 Apr 2026 17:58:46 +0000","Subject":"[PATCH v1 1/1] libstdc++: Add missing static_assert to\n std::expected::value()&&","To":"gcc-patches mailing list ","Message-ID":"\n ","X-Mailer":"batrachomyomachia","X-Pull-Request-Organization":"gcc","X-Pull-Request-Repository":"gcc-TEST","X-Pull-Request":"https://forge.sourceware.org/gcc/gcc-TEST/pulls/37","References":"\n ","In-Reply-To":"\n ","X-Patch-URL":"\n https://forge.sourceware.org/redi/gcc/commit/62b2ee5099bb3aa807112e827ea224427071a2b2","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Reply-To":"gcc-patches mailing list , redi@gcc.gnu.org","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"From: Jonathan Wakely \n\nThe r15-2326-gea435261ad58ea change missed a static_assert for\nis_move_constructible_v in expected::value()&&. When\nexceptions are enabled, the program is ill-formed if the error type is\nnot move constructible, because we can't construct the\nstd::bad_expected_access. But when using -fno-exceptions, we never\nconstruct an exception, so don't need to copy/move the error value. So\nthat the same code compiles with/without exceptions enabled, we should\nenforce the requirement explicitly.\n\nAdd the static_assert, and a test that verifies the Mandates:\nconditions added by LWG 3843 and 3490 are enforced even with\n-fno-exceptions.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/std/expected (expected::value()&&):\n\tAdd missing static_assert for LWG 3940.\n\t* testsuite/20_util/expected/lwg3843.cc: New test.\n---\n libstdc++-v3/include/std/expected | 1 +\n .../testsuite/20_util/expected/lwg3843.cc | 69 +++++++++++++++++++\n 2 files changed, 70 insertions(+)\n create mode 100644 libstdc++-v3/testsuite/20_util/expected/lwg3843.cc","diff":"diff --git a/libstdc++-v3/include/std/expected b/libstdc++-v3/include/std/expected\nindex 7de2aeffc70c..5dc1dfbe5b8a 100644\n--- a/libstdc++-v3/include/std/expected\n+++ b/libstdc++-v3/include/std/expected\n@@ -1541,6 +1541,7 @@ namespace __expected\n value() &&\n {\n \tstatic_assert( is_copy_constructible_v<_Er> );\n+\tstatic_assert( is_move_constructible_v<_Er> );\n \tif (_M_has_value) [[likely]]\n \t return;\n \t_GLIBCXX_THROW_OR_ABORT(bad_expected_access<_Er>(std::move(_M_unex)));\ndiff --git a/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc b/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc\nnew file mode 100644\nindex 000000000000..2afb9cc680bf\n--- /dev/null\n+++ b/libstdc++-v3/testsuite/20_util/expected/lwg3843.cc\n@@ -0,0 +1,69 @@\n+// { dg-do compile { target c++23 } }\n+// { dg-options \"-fno-exceptions\" }\n+\n+#include \n+\n+// 3843. std::expected::value() & assumes E is copy constructible\n+void\n+test_lwg3843()\n+{\n+ struct E1 {\n+ E1(int) { }\n+ E1(E1&) { }\n+ E1(const E1&) = delete;\n+ };\n+ std::expected v1;\n+ v1.value(); // { dg-error \"here\" }\n+ const auto& v1c = v1;\n+ v1c.value(); // { dg-error \"here\" }\n+\n+ struct E2 {\n+ E2(int) { }\n+ E2(const E2&) { }\n+ E2(E2&&) = delete;\n+ };\n+ std::expected v2;\n+ v2.value();\n+ std::move(v2).value(); // { dg-error \"here\" }\n+ const auto& v2c = v2;\n+ v2c.value();\n+ std::move(v2c).value();\n+\n+ struct E3 {\n+ E3(int) { }\n+ E3(const E3&) { }\n+ E3(E3&&) { }\n+ E3(const E3&&) = delete;\n+ };\n+ std::expected v3;\n+ v3.value();\n+ std::move(v3).value();\n+ const auto& v3c = v3;\n+ v3c.value();\n+ std::move(v3c).value(); // { dg-error \"here\" }\n+}\n+\n+// 3940. std::expected::value() also needs E to be copy constructible\n+void\n+test_lwg3940()\n+{\n+ struct E1 {\n+ E1(int) { }\n+ E1(E1&) { }\n+ E1(const E1&) = delete;\n+ };\n+ std::expected v1;\n+ v1.value(); // { dg-error \"here\" }\n+\n+ struct E2 {\n+ E2(int) { }\n+ E2(const E2&) { }\n+ E2(E2&&) = delete;\n+ };\n+ std::expected v2;\n+ std::move(v2).value(); // { dg-error \"here\" }\n+}\n+\n+// { dg-error \"static assertion failed\" \"\" { target *-*-* } 0 }\n+// { dg-prune-output \"use of deleted function\" }\n+// { dg-prune-output \"control reaches end of non-void function\" }\n","prefixes":["v1","1/1"]}