{"id":2225763,"url":"http://patchwork.ozlabs.org/api/patches/2225763/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/aeeOi00Sv-Bt873g@redhat.com/","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":"2026-04-21T14:49:47","name":"[v2] c++/reflection: bogus -Wmissing-field-initializers with [PR124950]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"7e31f9bbd726291ef75b11c95784e4a4226b13a4","submitter":{"id":14370,"url":"http://patchwork.ozlabs.org/api/people/14370/?format=json","name":"Marek Polacek","email":"polacek@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/aeeOi00Sv-Bt873g@redhat.com/mbox/","series":[{"id":500830,"url":"http://patchwork.ozlabs.org/api/series/500830/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500830","date":"2026-04-21T14:49:47","name":"[v2] c++/reflection: bogus -Wmissing-field-initializers with [PR124950]","version":2,"mbox":"http://patchwork.ozlabs.org/series/500830/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225763/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225763/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\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=Y5diyvRN;\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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charset=us-ascii","Content-Disposition":"inline","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 ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"On Tue, Apr 21, 2026 at 07:19:13AM +0100, Jonathan Wakely wrote:\n> On Tue, 21 Apr 2026, 02:43 Tim Song, wrote:\n> \n> > Might be better to leave out the initializer for name since not specifying\n> > it is pretty unusual? That matches what Barry proposed in some version of\n> > P3795 before it was removed in an LWG telecon (for lack of normative\n> > effect).\n> >\n> \n> Yes, I think that was what LWG agreed with, but couldn't say so in the\n> standard wording.\n\nThat means that we'll emit a warning with\n\n data_member_spec (^^int, { .bit_width = 8 })\n\nwhich I don't like, but if that's what's been decided, here's an\nupdated patch.\n \n> And would it be simpler to initialize alignment and bit_width with {}\n> instead of nullopt? There's only one constructor that's viable for {} so no\n> need to do resolution to find the best match for =nullopt.\n\nDone.\n\nTested reflect/*, ok for trunk?\n\n-- >8 --\nWe emit -Wmissing-field-initializers warnings for code like\n\n data_member_spec (^^int, { .name = \"dms\" })\n\nwhich seems undesirable. We can initialize the members of\nstd::meta::data_member_options to suppress that warning (clang's \nhas these initializers too).\n\n\tPR c++/124950\n\nlibstdc++-v3/ChangeLog:\n\n\t* include/std/meta (std::meta::data_member_options): Initialize\n\talignment, bit_width, and annotations members.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/data_member_spec7.C: New test.\n---\n gcc/testsuite/g++.dg/reflect/data_member_spec7.C | 9 +++++++++\n libstdc++-v3/include/std/meta | 6 +++---\n 2 files changed, 12 insertions(+), 3 deletions(-)\n create mode 100644 gcc/testsuite/g++.dg/reflect/data_member_spec7.C\n\n\nbase-commit: 6adc49fc08cb87b0e7c8ead3176b45dae2ff4e2a","diff":"diff --git a/gcc/testsuite/g++.dg/reflect/data_member_spec7.C b/gcc/testsuite/g++.dg/reflect/data_member_spec7.C\nnew file mode 100644\nindex 00000000000..057db043bf8\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/data_member_spec7.C\n@@ -0,0 +1,9 @@\n+// PR c++/124950\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection -Wmissing-field-initializers\" }\n+// Test that we don't emit bogus -Wmissing-field-initializers warnings.\n+\n+#include \n+using namespace std::meta;\n+constexpr auto dms = data_member_spec (^^int, { .name = \"dms\" });\n+constexpr auto dms2 = data_member_spec (^^int, { .bit_width = 8 }); // { dg-warning \"missing initializer\" }\ndiff --git a/libstdc++-v3/include/std/meta b/libstdc++-v3/include/std/meta\nindex 22b4da44cdd..b12f49a2096 100644\n--- a/libstdc++-v3/include/std/meta\n+++ b/libstdc++-v3/include/std/meta\n@@ -424,10 +424,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION\n };\n \n optional<_Name> name;\n- optional alignment;\n- optional bit_width;\n+ optional alignment = {};\n+ optional bit_width = {};\n bool no_unique_address = false;\n- vector annotations;\n+ vector annotations = {};\n };\n consteval info data_member_spec(info, data_member_options);\n consteval bool is_data_member_spec(info);\n","prefixes":["v2"]}