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GET /api/patches/2227946/?format=api
{ "id": 2227946, "url": "http://patchwork.ozlabs.org/api/patches/2227946/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/20260424143332.2133358-1-tkaminsk@redhat.com/", "project": { "id": 17, "url": "http://patchwork.ozlabs.org/api/projects/17/?format=api", "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": "<20260424143332.2133358-1-tkaminsk@redhat.com>", "list_archive_url": null, "date": "2026-04-24T14:31:38", "name": "[v2] libsdc++: Restore check for validity of std::get for elements_view.", "commit_ref": null, "pull_url": null, "state": "new", "archived": false, "hash": "9e7f1707367415fb74827db3b91cee1f87f50bde", "submitter": { "id": 90409, "url": "http://patchwork.ozlabs.org/api/people/90409/?format=api", "name": "Tomasz Kamiński", "email": "tkaminsk@redhat.com" }, "delegate": null, "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/20260424143332.2133358-1-tkaminsk@redhat.com/mbox/", "series": [ { "id": 501377, "url": "http://patchwork.ozlabs.org/api/series/501377/?format=api", "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=501377", "date": "2026-04-24T14:31:38", "name": "[v2] libsdc++: Restore check for validity of std::get for elements_view.", "version": 2, "mbox": "http://patchwork.ozlabs.org/series/501377/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/patches/2227946/comments/", "check": "pending", "checks": "http://patchwork.ozlabs.org/api/patches/2227946/checks/", "tags": {}, "related": [], "headers": { "Return-Path": "<gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org>", "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 (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=ZvcpxHk/;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; 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server2.sourceware.org", "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1777041217;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references;\n bh=kl7B7CrD5nx7elEnYsCNQg6Z+QQ2s2kEXRvXKHhMkP0=;\n b=ZvcpxHk/Tuf61hDeerWG35Q+xIMrdqDjg0EDTOrpfK4OJnvcYBftPeGkR2YUEabhtt0Fty\n WUggwqY8Bs52p3Z8f5TBEFYxu8ctSzyFcnyPJXDEjihnlCOtxIf78wXDbop6Cb+b109y0V\n BKJ0/ufAHxtB90nNrtzsFJSFI3ZOZS4=", "X-MC-Unique": "khS2OsGfNIm32K2hYCkTlQ-1", "X-Mimecast-MFC-AGG-ID": "khS2OsGfNIm32K2hYCkTlQ_1777041215", "From": "=?utf-8?q?Tomasz_Kami=C5=84ski?= <tkaminsk@redhat.com>", "To": "libstdc++@gcc.gnu.org,\n\tgcc-patches@gcc.gnu.org", "Cc": "Patrick Palka <ppalka@redhat.com>", "Subject": "[PATCH v2] libsdc++: Restore check for validity of std::get for\n elements_view.", "Date": "Fri, 24 Apr 2026 16:31:38 +0200", "Message-ID": "<20260424143332.2133358-1-tkaminsk@redhat.com>", "In-Reply-To": "<80063e98-c765-7b32-d582-92b20c013f5d@idea>", "References": "<80063e98-c765-7b32-d582-92b20c013f5d@idea>", "MIME-Version": "1.0", "X-Scanned-By": "MIMEDefang 3.4.1 on 10.30.177.4", "X-Mimecast-Spam-Score": "0", "X-Mimecast-MFC-PROC-ID": "M5TlYEP-mtnrOuvFmHnZ9ALF8kZDlQOYPXEW_U5VmLo_1777041215", "X-Mimecast-Originator": "redhat.com", "Content-Type": "text/plain; charset=UTF-8", "Content-Transfer-Encoding": "8bit", "X-BeenThere": "gcc-patches@gcc.gnu.org", "X-Mailman-Version": "2.1.30", "Precedence": "list", "List-Id": "Gcc-patches mailing list <gcc-patches.gcc.gnu.org>", "List-Unsubscribe": "<https://gcc.gnu.org/mailman/options/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=unsubscribe>", "List-Archive": "<https://gcc.gnu.org/pipermail/gcc-patches/>", "List-Post": "<mailto:gcc-patches@gcc.gnu.org>", "List-Help": "<mailto:gcc-patches-request@gcc.gnu.org?subject=help>", "List-Subscribe": "<https://gcc.gnu.org/mailman/listinfo/gcc-patches>,\n <mailto:gcc-patches-request@gcc.gnu.org?subject=subscribe>", "Errors-To": "gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org" }, "content": "Resolves LWG3797, \"elements_view insufficiently constrained\".\n\nWhen P2165R4 updated __has_tuple_element in C++23 to reuse __tuple_like\nconcept, it dropped the requirement of validity of get, assuming that for\ntuple_like type with size of N, get<I> on lvalue is well-formed for any I < N.\nThis however does not hold for ranges::subrange (tuple-like of size 2) with\nmove-only iterator, for which get can only be applied on rvalue. In consequence\nconstrains allowed instantiating elements_view for range of such subrange,\nbut instantiating it's iterator lead to hard error from iterator_category\ncomputation.\n\nThis patch applies the requirements on validity of get also in C++23 and\nlater standard modes.\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/std/ranges (__detail::__has_tuple_element): Check\n\tif std::get<_Nm>(__t) returns referenceable type also for C++23\n\tand later.\n\t* testsuite/std/ranges/adaptors/elements.cc: Add test covering\n\tvector of ranges::subrange with move-only iterator.\n\nReviewed-by: Patrick Palka <ppalka@redhat.com>\nSigned-off-by: Tomasz Kamiński <tkaminsk@redhat.com>\n---\nv2 applies suggestion from Patrick:\n - keep seprate defintion of __has_tuple_element for pre/post C++23\n - add mention of LWG3797 in comment\n\nTested on x86_654-linux. OK for trunk?\n\n libstdc++-v3/include/std/ranges | 9 ++++++++-\n .../testsuite/std/ranges/adaptors/elements.cc | 16 ++++++++++++++++\n 2 files changed, 24 insertions(+), 1 deletion(-)", "diff": "diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges\nindex 55d3c520ba4..7d8b37f8c5c 100644\n--- a/libstdc++-v3/include/std/ranges\n+++ b/libstdc++-v3/include/std/ranges\n@@ -4355,8 +4355,15 @@ namespace views::__adaptor\n namespace __detail\n {\n #if __cpp_lib_tuple_like // >= C++23\n+ // _GLIBCXX_RESOLVE_LIB_DEFECTS\n+ // 3797. elements_view insufficiently constrained\n template<typename _Tp, size_t _Nm>\n- concept __has_tuple_element = __tuple_like<_Tp> && _Nm < tuple_size_v<_Tp>;\n+ concept __has_tuple_element = __tuple_like<_Tp> && _Nm < tuple_size_v<_Tp>\n+ && requires(_Tp __t)\n+\t {\n+\t { std::get<_Nm>(__t) }\n+\t -> convertible_to<const tuple_element_t<_Nm, _Tp>&>;\n+\t };\n #else\n template<typename _Tp, size_t _Nm>\n concept __has_tuple_element = requires(_Tp __t)\ndiff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc\nindex 5237d787e7b..d384cfd5adf 100644\n--- a/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc\n+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/elements.cc\n@@ -27,6 +27,22 @@\n namespace ranges = std::ranges;\n namespace views = ranges::views;\n \n+template<size_t N, typename Rg>\n+concept can_elements = requires (Rg&& rg)\n+{ views::elements<0>(rg); };\n+\n+static_assert( !can_elements<0, std::vector<int>> );\n+static_assert( can_elements<0, std::tuple<int>[4]> );\n+static_assert( can_elements<1, std::vector<std::pair<int, int>>> );\n+\n+// Test LWG 3797. elements_view insufficiently constrained\n+using move_only_iter_range = __gnu_test::test_input_range_nocopy<int>;\n+using move_only_iter_subrange = ranges::subrange<\n+ ranges::iterator_t<move_only_iter_range>,\n+ ranges::sentinel_t<move_only_iter_range>>;\n+static_assert( can_elements<0, std::vector<ranges::subrange<int*>>> );\n+static_assert( !can_elements<0, std::vector<move_only_iter_subrange>> );\n+\n void\n test01()\n {\n", "prefixes": [ "v2" ] }