{"id":2224109,"url":"http://patchwork.ozlabs.org/api/patches/2224109/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/aeFFooo_IfeHlQCw@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":"2026-04-16T20:25:06","name":"[v2] c++/reflection: splicing null reflection","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"812676607cca705301a042f592fb3518a70321a4","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/aeFFooo_IfeHlQCw@redhat.com/mbox/","series":[{"id":500202,"url":"http://patchwork.ozlabs.org/api/series/500202/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=500202","date":"2026-04-16T20:25:06","name":"[v2] c++/reflection: splicing null reflection","version":2,"mbox":"http://patchwork.ozlabs.org/series/500202/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2224109/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2224109/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=hBSGX7jw;\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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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 01:29:29PM -0400, Jason Merrill wrote:\n> On 4/16/26 11:38 AM, Marek Polacek wrote:\n> > 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> > \n> > Sounds good, thanks.\n> > \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> > detect splicing a null reflection.\n> > \n> > gcc/cp/ChangeLog:\n> > \n> > \t* reflect.cc (check_splice_expr): Detect a null reflection.\n> > \n> > gcc/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> > diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc\n> > index 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\n> > diff --git a/gcc/testsuite/g++.dg/reflect/null6.C b/gcc/testsuite/g++.dg/reflect/null6.C\n> > new file mode 100644\n> > index 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> \n> Please also test null in a splice-type-specifier, with and without template\n> arguments.\n\nDone. And actually let's check for a null reflection in splice. This\nis on top of Jakub's PR123783 patch.\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 (splice): Detect a null reflection.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/null6.C: New test.\n---\n gcc/cp/reflect.cc | 6 ++++++\n gcc/testsuite/g++.dg/reflect/null6.C | 8 ++++++++\n 2 files changed, 14 insertions(+)\n create mode 100644 gcc/testsuite/g++.dg/reflect/null6.C\n\n\nbase-commit: 7c84b2a62827b3509b25727694c9f0eac9e96b80\nprerequisite-patch-id: f332a4def1290bc364844d365a541cc651e461e1","diff":"diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc\nindex bcd43cf2ab6..59f8354a3cf 100644\n--- a/gcc/cp/reflect.cc\n+++ b/gcc/cp/reflect.cc\n@@ -8525,6 +8525,12 @@ splice (tree refl)\n return error_mark_node;\n }\n \n+ if (compare_reflections (refl, get_null_reflection ()))\n+ {\n+ error_at (loc, \"cannot splice a null reflection\");\n+ return error_mark_node;\n+ }\n+\n /* This isn't checked in check_splice_expr, because reflect_kind isn't\n available there and variable_of (parameters_of (...)[...]) can be\n spliced. */\ndiff --git a/gcc/testsuite/g++.dg/reflect/null6.C b/gcc/testsuite/g++.dg/reflect/null6.C\nnew file mode 100644\nindex 00000000000..8b91ef756eb\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/null6.C\n@@ -0,0 +1,8 @@\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+[:null:] t1;\t\t // { dg-error \"cannot splice a null reflection|expected\" }\n+[:null:] t2;\t // { dg-error \"cannot splice a null reflection|expected\" }\n","prefixes":["v2"]}