[Bug c++/54058] New: Injected friend functions are not considered when using contextual type info to take a function address

[Bug c++/54058] New: Injected friend functions are not considered when using contextual type info to take a function address

[andy.m.jost at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54058

             Bug #: 54058
           Summary: Injected friend functions are not considered when
                    using contextual type info to take a function address
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: andy.m.jost@gmail.com


Created attachment 27851
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27851
Compiler output

When attempting to take a function address where contextual type info is
needed, injected friend functions are not properly considered.

Here is the source file:

    template<typename Derived> struct Injector
    {
      friend Derived const f(Derived const &) { return Derived(); }
    };

    struct A : Injector<A> {};
    struct B : Injector<B> {};

    int main()
    {
      A const (*fp)(A const &) = &f;
      (void)fp;
    }

The error given is particularly confusing: g++ reports no matching function,
but then proceeds to give a list of candidates that includes an exact match!

test.cpp: In function ‘int main()’:
test.cpp:11:31: error: no matches converting function ‘f’ to type ‘const struct
A (*)(const struct A&)’
test.cpp:3:24: error: candidates are: const A f(const A&)
test.cpp:3:24: error:                 const B f(const B&)

The full output of "g++ -v -save-temps -Wall -Wextra test.cpp" is attached. 
Found with g++ 4.5.2.

[Bug c++/54058] Injected friend functions are not considered when using contextual type info to take a function address

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54058

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-07-20 21:51:30 UTC ---
I think G++ is correct. The injected functions can only be found by ADL and ADL
only applies to function calls, not when taking the address of a function.

[Bug c++/54058] Injected friend functions are not considered when using contextual type info to take a function address

[andy.m.jost at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54058

--- Comment #2 from Andy Jost <andy.m.jost at gmail dot com> 2012-07-21 21:45:30 UTC ---
I think you're right.  Section 14.6.5.2 of the 2nd ed. (2003-10-15) has a
footnote in section 14.6.5.2.  It reads: 131) Friend declarations do not
introduce new names into any scope, either when the template is declared of
when it is instantiated.

Perhaps I just need to provide forward declarations for the friend functions.

[Bug c++/54058] Injected friend functions are not considered when using contextual type info to take a function address

[andy.m.jost at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54058

Andy Jost <andy.m.jost at gmail dot com> changed:

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

--- Comment #3 from Andy Jost <andy.m.jost at gmail dot com> 2012-07-21 21:48:02 UTC ---
Not a bug.