[{"id":3678178,"web_url":"http://patchwork.ozlabs.org/comment/3678178/","msgid":"<05317d8e-be32-4c67-8d50-becc3864e65e@redhat.com>","list_archive_url":null,"date":"2026-04-16T13:40:47","subject":"Re: [PATCH] c++/reflection: null reflection in inform_tree_category","submitter":{"id":4337,"url":"http://patchwork.ozlabs.org/api/people/4337/","name":"Jason Merrill","email":"jason@redhat.com"},"content":"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\nCan we diagnose sooner trying to splice a null reflection? That should \nbe ill-formed regardless of whether we expect it to be a type or \nexpression or whatever.\n\n> gcc/cp/ChangeLog:\n> \n> \t* error.cc (inform_tree_category): Don't print unknown_type_node.\n> \n> gcc/testsuite/ChangeLog:\n> \n> \t* g++.dg/reflect/null6.C: New test.\n> ---\n> gcc/cp/error.cc | 2 +-\n> gcc/testsuite/g++.dg/reflect/null6.C | 8 ++++++++\n> 2 files changed, 9 insertions(+), 1 deletion(-)\n> create mode 100644 gcc/testsuite/g++.dg/reflect/null6.C\n> \n> diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc\n> index b3e66924e31..f0097bf6808 100644\n> --- a/gcc/cp/error.cc\n> +++ b/gcc/cp/error.cc\n> @@ -3988,7 +3988,7 @@ inform_tree_category (tree t)\n> if (TREE_CODE (t) == TYPE_DECL)\n> t = TREE_TYPE (t);\n> \n> - if (TYPE_P (t))\n> + if (TYPE_P (t) && t != unknown_type_node)\n> inform (loc, \"but %qE is a type\", t);\n> else if (EXPR_P (t))\n> inform (loc, \"but %qE is an expression\", t);\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..55bf15ef959\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 \"expected a reflection of an expression\" }\n> +// { dg-message \"add .typename.\" \"\" { target *-*-* } .-1 }\n> +// { dg-bogus \"is a type\" \"\" { target *-*-* } .-2 }\n> \n> base-commit: 77d4080e1e5f9d467816e2e2e878edbfbb7ee1c1","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=GMxDp8ih;\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=GMxDp8ih","sourceware.org; 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