{"id":2224037,"url":"http://patchwork.ozlabs.org/api/patches/2224037/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/aeECjy5O6sXf2YA5@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":"2026-04-16T15:38:55","name":"c++/reflection: splicing null reflection","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"262c04fa1d60281820ccb3887e9c9a54425dcff4","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/aeECjy5O6sXf2YA5@redhat.com/mbox/","series":[{"id":500180,"url":"http://patchwork.ozlabs.org/api/series/500180/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500180","date":"2026-04-16T15:38:55","name":"c++/reflection: splicing null reflection","version":1,"mbox":"http://patchwork.ozlabs.org/series/500180/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2224037/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2224037/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=hIBYxAgi;\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 Thu, Apr 16, 2026 at 09:40:47AM -0400, Jason Merrill wrote:\n> On 4/15/26 7:52 PM, Marek Polacek wrote:\n> > Tested reflect/* on x86_64-pc-linux-gnu, ok for trunk?\n> > \n> > -- >8 --\n> > Here we are printing:\n> > \n> > note: but ''lang_type' not supported by dump_expr' is a type\n> > \n> > because we represent a null reflection with unknown_type_node. Let's\n> > not print anything in that case; unknown_type_node can also be\n> > .\n> \n> Can we diagnose sooner trying to splice a null reflection? That should be\n> ill-formed regardless of whether we expect it to be a type or expression or\n> whatever.\n\nSounds good, thanks.\n\nTested reflect/* on x86_64-pc-linux-gnu, ok for trunk?\n\n-- >8 --\nHere we are printing:\n\n note: but ''lang_type' not supported by dump_expr' is a type\n\nbecause we represent a null reflection with unknown_type_node. Let's\ndetect splicing a null reflection.\n\ngcc/cp/ChangeLog:\n\n\t* reflect.cc (check_splice_expr): Detect a null reflection.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/null6.C: New test.\n---\n gcc/cp/reflect.cc | 7 +++++++\n gcc/testsuite/g++.dg/reflect/null6.C | 6 ++++++\n 2 files changed, 13 insertions(+)\n create mode 100644 gcc/testsuite/g++.dg/reflect/null6.C\n\n\nbase-commit: 257daea0bf0ff41ca3278bc27db65a6aa475cc62","diff":"diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc\nindex 2b7e7033953..ea7616a62bc 100644\n--- a/gcc/cp/reflect.cc\n+++ b/gcc/cp/reflect.cc\n@@ -8929,6 +8929,13 @@ check_splice_expr (location_t loc, location_t start_loc, tree t,\n \t\t bool address_p, bool member_access_p, bool template_p,\n \t\t bool targs_p, bool complain_p)\n {\n+ if (t == unknown_type_node)\n+ {\n+ if (complain_p)\n+\terror_at (loc, \"cannot splice a null reflection\");\n+ return false;\n+ }\n+\n /* We may not have gotten an expression. */\n if (TREE_CODE (t) == TYPE_DECL\n || TREE_CODE (t) == NAMESPACE_DECL\ndiff --git a/gcc/testsuite/g++.dg/reflect/null6.C b/gcc/testsuite/g++.dg/reflect/null6.C\nnew file mode 100644\nindex 00000000000..bfa2b6ba241\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/null6.C\n@@ -0,0 +1,6 @@\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection\" }\n+\n+using info = decltype(^^::);\n+constexpr auto null = info{};\n+constexpr auto q = [:null:]; // { dg-error \"cannot splice a null reflection\" }\n","prefixes":[]}