[Bug c++/55924] New: [C++11] Not all copy-assignment operator forms are correctly detected

[Bug c++/55924] New: [C++11] Not all copy-assignment operator forms are correctly detected

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

             Bug #: 55924
           Summary: [C++11] Not all copy-assignment operator forms are
                    correctly detected
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


The following code, compiled with 

-Wall -std=c++11 -pedantic

is rejected by gcc 4.7.2 and gcc 4.8.0 20130106 (experimental):

//----------------
struct mine
{
  mine& operator=(mine rhs) { return *this; }
  mine& operator=(mine&& rhs) noexcept { return *this; }
};

int main()
{
  mine a;
  mine b;
  a = b;
}
//----------------

"In function 'int main()':|
12|error: use of deleted function 'constexpr mine::mine(const mine&)'|
1|note: 'constexpr mine::mine(const mine&)' is implicitly declared as deleted
because 'mine' declares a move constructor or move assignment operator|
3|error:   initializing argument 1 of 'mine& mine::operator=(mine)'|
"

According to 12.8 p17:

"A user-declared copy assignment operator X::operator= is a non-static
non-template member function of class X with exactly one parameter of type X,
X&, const X&, volatile X& or const volatile X&."

and p18:

"If the class definition does not explicitly declare a copy assignment
operator, one is declared implicitly. If the class definition declares a move
constructor or move assignment operator, the implicitly declared copy
assignment operator is defined as deleted;"

Therefore class mine provides a user-declared copy-assignment operator, but gcc
doesn't recognize that.

This code should be accepted.

I reduced the severity, because this kind of code is expected to be a rather
unusual edge-case. Every other form of the copy-assignment operator using
references is correctly detected.

[Bug c++/55924] [C++11] Not all copy-assignment operator forms are correctly detected

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

--- Comment #1 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-09 18:32:26 UTC ---
Remark: The noexcept specifier was added unintentionally and is not relevant to
reproduce the described problem.

[Bug c++/55924] [C++11] Not all copy-assignment operator forms are correctly detected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-01-09
     Ever Confirmed|0                           |1

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-09 18:39:46 UTC ---
Clang thinks you need to add 

  mine() = default;
  mine(const mine&) = default;

for the code to be accepted and I agree, otherwise the operator=(mine)
assignment operator calls the copy constructor which is deleted because of a
user-declared move assignment operator.

[Bug c++/55924] [C++11] Not all copy-assignment operator forms are correctly detected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |UNCONFIRMED
     Ever Confirmed|1                           |0

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-09 18:42:30 UTC ---
Oops, I didn't meant to change this to NEW, sorry

[Bug c++/55924] [C++11] Not all copy-assignment operator forms are correctly detected

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

--- Comment #4 from Daniel Krügler <daniel.kruegler at googlemail dot com> 2013-01-09 18:43:52 UTC ---
Oops I failed to read the error description correctly. The compiler is correct,
so please declare this as INVALID. Sorry for the noise.

[Bug c++/55924] [C++11] Not all copy-assignment operator forms are correctly detected

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55924

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-09 19:04:13 UTC ---
.