Problem with combination of namespaces, templates, and friends

[Martin Staley]

Hello -

I submitted the following code to your online test compilation form
at http://www.codesourcery.com/gcc-compile.html , with C++ specified
as the language, and with no additional compiler flags:

     namespace A {
        template<class T>
        struct thing;
     }

     namespace B {
        template<class T>
        void fun(const A::thing<T> &);
     }

     namespace A {
        template<class T>
        struct thing {
           friend void B::fun<T>(const thing &);
        };
     }

     namespace B {
        template<class T>
        void fun(const A::thing<T> &)
        {
        }
     }

     int main(void) {
        A::thing<int> t;
        B::fun(t);
     }

Here are the output compiler messages:

     /tmp/@31205.1: In instantiation of `A::thing':
     /tmp/@31205.1:26: instantiated from here
     /tmp/@31205.1:14: `fun' was not declared in this scope

With the (slightly older) version of g++ on my machine (g++ -v gives
"gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)"), the
command "g++ bug.cc", where bug.cc contains the above code, gave the
following compiler messages:

     bug.cc:14: declaration of `fun(const ::A::thing<T> &)' not in a
                namespace surrounding `::B'
     bug.cc: In instantiation of `::A::::A::thing<int>':
     bug.cc:26:   instantiated from here
     bug.cc:14: `fun' was not declared in this scope

Am I wrong in believing the above is legal C++?  Incidentally it
compiles with KAI C++ (EDG front-end, which you're probably familiar
with), with all "strict ansi" flags turned on.  That doesn't prove
it's legal, of course, but surely the language doesn't require that
a function be in the same namespace as any class with which it's a
friend...?

I browsed around on http://gcc.gnu.org/ and on the gcc/g++ info pages
but couldn't find any mention of this bug (feature?).

Martin
------------------------------------------------------------------------
Martin Staley                                         (tel) 505-665-4963
T-7, Mathematical Modeling and Analysis               (fax) 505-665-5757
M.S. B-284                                            staley@t7.lanl.gov
Los Alamos National Laboratory
Los Alamos, NM 87544                    http://cnls-www.lanl.gov/~staley
------------------------------------------------------------------------