[Bug c++/50344] New: friend declaration confused by const qualifier

[Bug c++/50344] New: friend declaration confused by const qualifier

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

             Bug #: 50344
           Summary: friend declaration confused by const qualifier
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: redi@gcc.gnu.org
                CC: jason@gcc.gnu.org


template <typename T> class C
{
   friend T;
   int i;
};

struct S
{
    int f()
    {
       C<const S> c;
       return c.i;
    }
};

This is valid C++11, but fails with:

ac.cc: In member function 'int S::f()':
ac.cc:4:8: error: 'int C<const S>::i' is private
ac.cc:12:17: error: within this context

The problem is that the friend declaration names "const S" so S is not
considered a friend, it works if C<S> is used.  The standard says "If the type
specifier in a friend declaration designates a (possibly cv-qualified) class
type, that class
is declared as a friend"


This bug predates the implementation of the C++0x extended friend rules, as
shown by this example using a non-standard friend declaration supported by G++:

template<typename T> struct identity { typedef T type; };

template <typename T> class C
{
   friend class identity<T>::type;
   int i;
};

struct S
{
    int f()
    {
       C<const S> c;
       return c.i;
    }
};

This works with all versions of G++ is C<S> is used, but not C<const S>

[Bug c++/50344] friend declaration confused by const qualifier

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-09 19:47:42 UTC ---
both testcases are fixed simply by adding this to the top of make_friend_class
in friend.c

  friend_type = cv_unqualified (friend_type);

[Bug c++/50344] friend declaration confused by const qualifier

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-14 21:11:02 UTC ---
So, I guess we only need confirmation that your analysis is correct. Indeed, I
can confirm that the patch, only one line thus not requiring a Copyright
assignment, works for the testcase (however, I didn't fully regression test it
yet).

Jason, can you have a look?

PS: Current Comeau accepts the snippet.

[Bug c++/50344] friend declaration confused by const qualifier

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-14 21:34:35 UTC ---
Passes the testsuite.

[Bug c++/50344] friend declaration confused by const qualifier

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-09-15 10:06:31 UTC ---
Thanks Paolo - I forgot to add a follow-up comment to say I'd tested it

[Bug c++/50344] friend declaration confused by const qualifier

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011-09-21
         AssignedTo|unassigned at gcc dot       |paolo.carlini at oracle dot
                   |gnu.org                     |com
   Target Milestone|---                         |4.7.0
     Ever Confirmed|0                           |1

[Bug c++/50344] friend declaration confused by const qualifier

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

--- Comment #5 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2011-09-22 14:16:33 UTC ---
Author: paolo
Date: Thu Sep 22 14:16:27 2011
New Revision: 179088

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=179088
Log:
/cp
2011-09-22  Jonathan Wakely  <jwakely.gcc@gmail.com>
        Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/50344
    * friend.c (make_friend_class): cv-qualification is ok in a
    friend declaration.

/testsuite
2011-09-22  Jonathan Wakely  <jwakely.gcc@gmail.com>
        Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/50344
    * g++.dg/template/friend52.C: New.

Added:
    trunk/gcc/testsuite/g++.dg/template/friend52.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/friend.c
    trunk/gcc/testsuite/ChangeLog

[Bug c++/50344] friend declaration confused by const qualifier

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50344

Paolo Carlini <paolo.carlini at oracle dot com> changed:

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

--- Comment #6 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-09-22 14:17:54 UTC ---
Done.