[Bug libstdc++/101527] New: The implementation of std::common_iterator::operator== seems to be wrong

[Bug libstdc++/101527] New: The implementation of std::common_iterator::operator== seems to be wrong

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

            Bug ID: 101527
           Summary: The implementation of std::common_iterator::operator==
                    seems to be wrong
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

Libstdc++'s implementation of common_iterator is similar to MSVC-STL, it
defines operator== inside the class and declares template common_iterator class
as a friend. 

But according to the description of [class.friend#10]: "Friendship is neither
inherited nor transitive." this will cause the following valid codes to be
rejected:


  std::common_iterator<int*, std::unreachable_sentinel_t> it1;
  std::common_iterator<const int*, std::unreachable_sentinel_t> it2;
  it1 == it2;


https://godbolt.org/z/15ao981Wb

[Bug libstdc++/101527] The implementation of std::common_iterator::operator== seems to be wrong

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> ---
(In reply to 康桓瑋 from comment #0)
> But according to the description of [class.friend#10]: "Friendship is
> neither inherited nor transitive." this will cause the following valid codes
> to be rejected:

This is the implementation divergence of CWG1699.

[Bug libstdc++/101527] The implementation of std::common_iterator::operator== seems to be wrong

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I find it surprising, but the CWG consensus seems to be that a friend defined
inline in the class body is "a member declaration of the befriended class".

[Bug libstdc++/101527] The implementation of std::common_iterator::operator== seems to be wrong

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

--- Comment #3 from 康桓瑋 <hewillk at gmail dot com> ---
(In reply to Jonathan Wakely from comment #2)
> I find it surprising, but the CWG consensus seems to be that a friend
> defined inline in the class body is "a member declaration of the befriended
> class".

Hey Jonathan, I just found out that std::counted_iterator also has the same
friend access issue.


#include <iterator>

int main() {
  std::counted_iterator<int*> it1;
  std::counted_iterator<const int*> it2;
  return it1 == it2;
}

https://godbolt.org/z/jGT5jhbWz

[Bug libstdc++/101527] The implementation of std::common_iterator and std::counted_iterator's operator== seems to be wrong

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

--- Comment #4 from 康桓瑋 <hewillk at gmail dot com> ---
MSVC has fixed this issue through
https://github.com/microsoft/STL/pull/2066/commits.

[Bug libstdc++/101527] The implementation of std::common_iterator and std::counted_iterator's operator== seems to be wrong

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0
   Last reconfirmed|                            |2022-04-14
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |redi at gcc dot gnu.org

[Bug libstdc++/101527] The implementation of std::common_iterator and std::counted_iterator's operator== seems to be wrong

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.0                        |12.2

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 12.1 is being released, retargeting bugs to GCC 12.2.

[Bug libstdc++/101527] The implementation of std::common_iterator and std::counted_iterator's operator== seems to be wrong

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101527

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|12.3                        |12.4

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 12.3 is being released, retargeting bugs to GCC 12.4.