{"id":2228026,"url":"http://patchwork.ozlabs.org/api/patches/2228026/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260424220245.853318-1-polacek@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":"<20260424220245.853318-1-polacek@redhat.com>","list_archive_url":null,"date":"2026-04-24T22:02:45","name":"c++/reflection: disallow reflecting block-scope externs (CWG 3065) [PR124756]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"ccd86bbe775c56af804604d926e90eb22003eb65","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/20260424220245.853318-1-polacek@redhat.com/mbox/","series":[{"id":501406,"url":"http://patchwork.ozlabs.org/api/series/501406/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=501406","date":"2026-04-24T22:02:45","name":"c++/reflection: disallow reflecting block-scope externs (CWG 3065) [PR124756]","version":1,"mbox":"http://patchwork.ozlabs.org/series/501406/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2228026/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2228026/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=WbTrsRJd;\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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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1777068179;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding;\n bh=7BT+3Cvt9NhPgfuyx0AgZ0fJCCUwGK+zcc2KdvGeW4g=;\n b=WbTrsRJdcnJKl1ZPbX8cxNujskwN9tqITVN1pWM3cECmBmIoRB8fczBqQHxM90jztLbSeW\n bwv8GHh91dXgWkyKlmxQuXRFH24mLOjWvcdoLJc4Rg+3w9RsYy4i3qL0XnT1bIGVZ3m4xF\n sSE+tP6X7zqLNK4O6teYXPAJJ65XCus=","X-MC-Unique":"H-5EA3BTN5KVC42bXbM9YA-1","X-Mimecast-MFC-AGG-ID":"H-5EA3BTN5KVC42bXbM9YA_1777068170","From":"Marek Polacek ","To":"GCC Patches ,\n\tJason Merrill ","Subject":"[PATCH] c++/reflection: disallow reflecting block-scope externs (CWG\n 3065) [PR124756]","Date":"Fri, 24 Apr 2026 18:02:45 -0400","Message-ID":"<20260424220245.853318-1-polacek@redhat.com>","MIME-Version":"1.0","X-Scanned-By":"MIMEDefang 3.4.1 on 10.30.177.93","X-Mimecast-Spam-Score":"0","X-Mimecast-MFC-PROC-ID":"Bc1EMZ05kQSEG7DcIrkHsdi4L8QFtJKILtiDzhVvHk0_1777068170","X-Mimecast-Originator":"redhat.com","Content-Transfer-Encoding":"8bit","content-type":"text/plain; charset=\"US-ASCII\"; x-default=true","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":"Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?\n\n-- >8 --\nThe discussion in CWG 3065 concluded that reflection on a block-scope\nextern declaration is ill-formed. This patch makes it so, and it also\nhappens to fix a crash.\n\n\tPR c++/124756\n\ngcc/cp/ChangeLog:\n\n\t* reflect.cc (get_reflection): Give an error when taking the\n\treflection of a block-scope extern.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/identifier_of3.C: Add dg-error.\n\t* g++.dg/reflect/pr123612.C: Likewise.\n\t* g++.dg/reflect/error13.C: New test.\n---\n gcc/cp/reflect.cc | 8 +++--\n gcc/testsuite/g++.dg/reflect/error13.C | 30 +++++++++++++++++++\n gcc/testsuite/g++.dg/reflect/identifier_of3.C | 17 ++++++-----\n gcc/testsuite/g++.dg/reflect/pr123612.C | 13 ++++----\n 4 files changed, 52 insertions(+), 16 deletions(-)\n create mode 100644 gcc/testsuite/g++.dg/reflect/error13.C\n\n\nbase-commit: 86964edc9964067c107a63efb957c50efa58b3a9","diff":"diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc\nindex 27e1efee106..b85315de4e3 100644\n--- a/gcc/cp/reflect.cc\n+++ b/gcc/cp/reflect.cc\n@@ -238,9 +238,13 @@ get_reflection (location_t loc, tree t, reflect_kind kind/*=REFLECT_UNDEF*/)\n \tt = dtor;\n }\n \n- /* Look through block scope externs. */\n+ /* Block-scope externs are invalid here as per CWG 3065. */\n if (VAR_OR_FUNCTION_DECL_P (t) && DECL_LOCAL_DECL_P (t))\n- t = DECL_LOCAL_DECL_ALIAS (t);\n+ {\n+ error_at (loc, \"cannot take the reflection of a block-scope extern %qE\",\n+\t\tt);\n+ return error_mark_node;\n+ }\n \n if (t == error_mark_node)\n return error_mark_node;\ndiff --git a/gcc/testsuite/g++.dg/reflect/error13.C b/gcc/testsuite/g++.dg/reflect/error13.C\nnew file mode 100644\nindex 00000000000..8d61b7f192c\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/error13.C\n@@ -0,0 +1,30 @@\n+// PR c++/124756\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection\" }\n+\n+template\n+consteval void\n+f0 ()\n+{\n+ void fun(T);\n+ auto _ = ^^fun; // { dg-error \"cannot take the reflection of a block-scope extern .fun.\" }\n+ extern int arr[3];\n+ auto _ = ^^arr; // { dg-error \"cannot take the reflection of a block-scope extern .arr.\" }\n+ extern int e;\n+ auto _ = ^^e; // { dg-error \"cannot take the reflection of a block-scope extern .e.\" }\n+}\n+\n+consteval {\n+ f0();\n+}\n+\n+consteval void\n+f1 ()\n+{\n+ void fun(int);\n+ auto _ = ^^fun; // { dg-error \"cannot take the reflection of a block-scope extern .fun.\" }\n+ extern int arr[3];\n+ auto _ = ^^arr; // { dg-error \"cannot take the reflection of a block-scope extern .arr.\" }\n+ extern int e;\n+ auto _ = ^^e; // { dg-error \"cannot take the reflection of a block-scope extern .e.\" }\n+}\ndiff --git a/gcc/testsuite/g++.dg/reflect/identifier_of3.C b/gcc/testsuite/g++.dg/reflect/identifier_of3.C\nindex 5383de07dd2..266b43471ae 100644\n--- a/gcc/testsuite/g++.dg/reflect/identifier_of3.C\n+++ b/gcc/testsuite/g++.dg/reflect/identifier_of3.C\n@@ -4,6 +4,7 @@\n // Test std::meta::identifier_of.\n \n #include \n+using namespace std::meta;\n \n void foo (int, int x, int y, int z);\n \n@@ -38,10 +39,10 @@ baz ()\n void foo (int w, int, int v, int z);\n int bar (int, int, int v, int z, int u);\n void qux (int, int x, int y, int z);\n- constexpr auto qux1 = parameters_of (^^qux)[0];\n- constexpr auto qux2 = parameters_of (^^qux)[1];\n- constexpr auto qux3 = parameters_of (^^qux)[2];\n- constexpr auto qux4 = parameters_of (^^qux)[3];\n+ constexpr auto qux1 = parameters_of (^^qux)[0]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux2 = parameters_of (^^qux)[1]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux3 = parameters_of (^^qux)[2]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux4 = parameters_of (^^qux)[3]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n static_assert (!has_identifier (qux1));\n static_assert (identifier_of (qux2) == std::string_view (\"x\"));\n static_assert (identifier_of (qux3) == std::string_view (\"y\"));\n@@ -62,10 +63,10 @@ void\n fred ()\n {\n void qux (int w, int, int v, int z);\n- constexpr auto qux1 = parameters_of (^^qux)[0];\n- constexpr auto qux2 = parameters_of (^^qux)[1];\n- constexpr auto qux3 = parameters_of (^^qux)[2];\n- constexpr auto qux4 = parameters_of (^^qux)[3];\n+ constexpr auto qux1 = parameters_of (^^qux)[0]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux2 = parameters_of (^^qux)[1]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux3 = parameters_of (^^qux)[2]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n+ constexpr auto qux4 = parameters_of (^^qux)[3]; // { dg-error \"cannot take the reflection of a block-scope extern .qux.\" }\n static_assert (identifier_of (qux1) == std::string_view (\"w\"));\n static_assert (identifier_of (qux2) == std::string_view (\"x\"));\n static_assert (!has_identifier (qux3));\ndiff --git a/gcc/testsuite/g++.dg/reflect/pr123612.C b/gcc/testsuite/g++.dg/reflect/pr123612.C\nindex 97da7bbdd0e..0dee4ed4f65 100644\n--- a/gcc/testsuite/g++.dg/reflect/pr123612.C\n+++ b/gcc/testsuite/g++.dg/reflect/pr123612.C\n@@ -3,6 +3,7 @@\n // { dg-additional-options \"-freflection\" }\n \n #include \n+using namespace std::meta;\n \n int a;\n extern int b;\n@@ -12,14 +13,14 @@ consteval auto\n bar ()\n {\n extern int a;\n- return ^^a;\n+ return ^^a;\t// { dg-error \"cannot take the reflection of a block-scope extern .a.\" }\n }\n \n consteval auto\n baz ()\n {\n extern int b;\n- return ^^b;\n+ return ^^b;\t// { dg-error \"cannot take the reflection of a block-scope extern .b.\" }\n }\n \n consteval auto\n@@ -30,10 +31,10 @@ qux ()\n static_assert (has_default_argument (parameters_of (^^foo)[2]));\n {\n extern int foo (int x, int y = 5, int z = 16);\n- static_assert (!has_default_argument (parameters_of (^^foo)[0]));\n- static_assert (has_default_argument (parameters_of (^^foo)[1]));\n- static_assert (has_default_argument (parameters_of (^^foo)[2]));\n- return ^^foo;\n+ static_assert (!has_default_argument (parameters_of (^^foo)[0])); // { dg-error \"cannot take the reflection of a block-scope extern .foo.\" }\n+ static_assert (has_default_argument (parameters_of (^^foo)[1])); // { dg-error \"cannot take the reflection of a block-scope extern .foo.\" }\n+ static_assert (has_default_argument (parameters_of (^^foo)[2])); // { dg-error \"cannot take the reflection of a block-scope extern .foo.\" }\n+ return ^^foo; // { dg-error \"cannot take the reflection of a block-scope extern .foo.\" }\n }\n }\n \n","prefixes":[]}