[Bug c++/44320] New: ADL names are looked up in namespaces that are only referenced by template arguments

[sstrasser at systemhaus-gruppe dot de]

I believe that the following is a bug. it is accepted by MSVC and comeau.

GCC seems to ADL-lookup names in namespaces that are only used in the template
arguments of the function arguments, for example:

A<otherns::type> a;
adl_func(a); //otherns::adl_func is called

this can cause unintended conflicts with non-function names in "otherns", e.g.
if the ADL function is called "apply" and the argument type happens to be a
template instantiated with a type from namespace boost::mpl, only the fact that
a header containing the type boost::mpl::apply is included can cause a compile
error.

here's a simplified test case that causes a conflict:


namespace mpl{
  class apply{};
  class vector{};
}


template<class T>
void apply(T const &){}

template<class T>
class A{};

int main(){
  A<mpl::vector> a;
  apply(a);
}


-- 
           Summary: ADL names are looked up in namespaces that are only
                    referenced by template arguments
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sstrasser at systemhaus-gruppe dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44320