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From: "dangelog at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/99032] New: GCC accepts attributes on friend declarations
 (not definitions)
Date: Tue, 09 Feb 2021 17:39:09 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99032

            Bug ID: 99032
           Summary: GCC accepts attributes on friend declarations (not
                    definitions)
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dangelog at gmail dot com
  Target Milestone: ---

Hi,

The following code is accepted by GCC 10.2:

  struct S { [[deprecated]] friend void f(); };

No errors and no warnings are generated under -Wall -Wextra -pedantic.

The code is however ill-formed: an attribute cannot appear on a friend=20
declaration which isn't also a definition:

https://eel.is/c++draft/dcl.attr#grammar-5.sentence-3

    If an attribute-specifier-seq appertains to a friend declaration
([class.friend]), that declaration shall be a definition.


For comparison, Clang rejects this, and MSVC accepts it (without warnings).=