[Bug c++/100596] New: [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[Bug c++/100596] New: [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

            Bug ID: 100596
           Summary: [12 Regression] error: attribute appertains to a
                    friend declaration that is not a definition since
                    r12-786-g149061188c7c6ddf
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jason at gcc dot gnu.org, mpolacek at gcc dot gnu.org
  Target Milestone: ---

Affects multiple packages:

$ cat json.ii
struct final {
  friend __attribute__((visibility)) bool;
};

$ g++ json.ii -c
json.ii:2:3: error: attribute appertains to a friend declaration that is not a
definition
    2 |   friend __attribute__((visibility)) bool;
      |   ^~~~~~

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Target Milestone|---                         |12.0
           Priority|P3                          |P1
   Last reconfirmed|                            |2021-05-14
     Ever confirmed|0                           |1

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Rejecting such code was the point of the patch.  I guess we'll have to either
downgrade to a warning or just not complain about GNU attributes at all.

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
I noticed that in a couple of packages that I have in my testing playground:
https://build.opensuse.org/project/monitor/home:marxin:home:marxin:gcc-periodic-testing-v2

[ 1268s]
/home/abuild/rpmbuild/BUILD/libreoffice-7.1.3.2/workdir/UnpackedTarball/skia/include/core/SkMatrix.h:1579:24:
error: attribute appertains to a friend declaration that is not a definition
[ 1268s]  1579 |     friend SK_API bool operator==(const SkMatrix& a, const
SkMatrix& b);
[ 1268s]       |                        ^~~~~~~~


[   98s] /usr/include/boost/thread/detail/thread.hpp:641:37: error: attribute
appertains to a friend declaration that is not a definition
[   98s]   641 |         friend id BOOST_THREAD_DECL this_thread::get_id()
BOOST_NOEXCEPT;
[   98s]       |                                     ^~~~~~~~~~~


[  279s] /usr/include/qt5/QtCore/qbytearray.h:486:37: error: attribute
appertains to a friend declaration that is not a definition
[  279s]   486 |     friend Q_CORE_EXPORT QByteArray qUncompress(const uchar
*data, int nbytes);
[  279s]       |                                     ^~~~~~~~~~~

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> Rejecting such code was the point of the patch.  I guess we'll have to
> either downgrade to a warning or just not complain about GNU attributes at
> all.

Let's do both.

It occurs to me that attributes on non-definition friends can be useful when
there is no other reachable declaration of the function, as

struct A
{
  __attribute((deprecated)) friend void f(A); // part of A API, definition in
.C
};

int main()
{
  A a;
  f(a); // warning desired
}

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
On it.

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:adcb497bdba499d161d2e5e8de782bdd6f75d62c

commit r12-925-gadcb497bdba499d161d2e5e8de782bdd6f75d62c
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue May 18 16:11:16 2021 -0400

    c++: Relax attribute on friend declaration checking [PR100596]

    It turned out that there are codebases that profusely use GNU attributes
    on friend declarations, so we have to dial back our checking and allow
    them.  And for C++11 attributes let's just warn instead of giving
    errors.

            PR c++/100596

    gcc/cp/ChangeLog:

            * cp-tree.h (any_non_type_attribute_p): Remove.
            * decl.c (grokdeclarator): Turn an error into a warning and only
            warn for standard attributes.
            * decl2.c (any_non_type_attribute_p): Remove.
            * parser.c (cp_parser_elaborated_type_specifier): Turn an error
            into a warning and only warn for standard attributes.
            (cp_parser_member_declaration): Likewise.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/friend7.C: Turn a few dg-warnings into dg-errors.
            Remove dg-errors for GNU attributes.
            * g++.dg/ext/attrib63.C: Remove dg-error.
            * g++.dg/cpp0x/friend8.C: New test.

[Bug c++/100596] [12 Regression] error: attribute appertains to a friend declaration that is not a definition since r12-786-g149061188c7c6ddf

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100596

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Should be fixed, sorry.