[Bug c++/57211] New: wrong line indicated in warning for synthesized method

[Bug c++/57211] New: wrong line indicated in warning for synthesized method

[doko at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57211

             Bug #: 57211
           Summary: wrong line indicated in warning for synthesized method
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: doko@gcc.gnu.org


seen at least in 4.6, 4.7, 4.8 and trunk:

$ g++-4.8 -c -std=c++11 -Wunused-parameter  test.cpp
test.cpp:3:8: warning: unused parameter 'p' [-Wunused-parameter]
 struct A  // line pointed-to by warning
        ^
test.cpp: In function 'int main()':
test.cpp:21:11: note: synthesized method 'A& A::operator=(A&&)' first required
here 
         b = std::move(a);
           ^

$ cat test.cpp 
#include <functional>

struct A  // line pointed-to by warning
{
        struct B
        {
                B& operator=(B&&) { return *this; }
        };

        B f;

        A() = default;
        A& operator=(A&& p) = default;  // where the method is declared
};

int main()
{
        A a;
        A b;

        b = std::move(a);
}

[Bug c++/57211] wrong line indicated in warning for synthesized method

[anthony.foiani at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57211

Anthony Foiani <anthony.foiani at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anthony.foiani at gmail dot com

--- Comment #1 from Anthony Foiani <anthony.foiani at gmail dot com> ---
Created attachment 30117
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30117&action=edit
demonstration code showing problem and workaround

[Bug c++/57211] wrong line indicated in warning for synthesized method

[anthony.foiani at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57211

--- Comment #2 from Anthony Foiani <anthony.foiani at gmail dot com> ---
I'm also seeing this bug, in version 4.7.2.

Instead of trying to fix the line offset, I believe the right thing is to not
emit this warning in this case at all.

The parameter is certainly used, even if the synthesized method uses a
different formal argument name.  (In which case, shouldn't it offer a
corresponding undeclared variable error?)

Put another way: if the method has a signature which can be defaulted, then the
parameter name(s) should be ignored.  (IMHO of course.)

A workaround is to omit the parameter name, but I feel that reduces
readability.  (It also makes some documentation-generating tools sad, e.g.,
doxygen.)

See attached for a version of Matthias's code that shows workaround via macro
flag.

[Bug c++/57211] wrong line indicated in warning for synthesized method

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57211

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2013-05-22
           Assignee|unassigned at gcc dot gnu.org      |paolo.carlini at oracle dot com
   Target Milestone|---                         |4.9.0
     Ever confirmed|0                           |1

[Bug c++/57211] wrong line indicated in warning for synthesized method

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57211

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

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

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> ---
Fixed for 4.9.0.