[{"id":3678290,"web_url":"http://patchwork.ozlabs.org/comment/3678290/","msgid":"","list_archive_url":null,"date":"2026-04-16T17:29:29","subject":"Re: [PATCH] c++/reflection: splicing null reflection","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"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\nPlease also test null in a splice-type-specifier, with and without \ntemplate arguments.\n\nJason","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=d9JoTqNt;\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; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.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=d9JoTqNt","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; 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