[{"id":3678368,"web_url":"http://patchwork.ozlabs.org/comment/3678368/","msgid":"","list_archive_url":null,"date":"2026-04-16T20:28:39","subject":"Re: [PATCH v2] 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 4:25 PM, Marek Polacek wrote:\n> 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> \n> Done. And actually let's check for a null reflection in splice. This\n> is on top of Jakub's PR123783 patch.\n> \n> Tested reflect/* on x86_64-pc-linux-gnu, ok for trunk?\n\nOK.\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 (splice): 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 | 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> diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc\n> index 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. */\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..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> \n> base-commit: 7c84b2a62827b3509b25727694c9f0eac9e96b80\n> prerequisite-patch-id: f332a4def1290bc364844d365a541cc651e461e1","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=YXsWu7Vy;\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; 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=YXsWu7Vy","sourceware.org; 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