[Bug c++/67835] New: bug with auto-deduced return type and functions invoked via ADL

[ryan.burn at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67835

            Bug ID: 67835
           Summary: bug with auto-deduced return type and functions
                    invoked via ADL
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ryan.burn at gmail dot com
  Target Milestone: ---

The below code compiles fine with clang and EDG (intel's compiler) but gives
this error with gcc:

t.cpp: In instantiation of ‘auto g(Tag, T) [with Tag = abc::tag; T = abc::A]’:
t.cpp:16:25:   required from here
t.cpp:3:11: error: use of ‘template<class T> auto abc::f(abc::tag, T)’ before
deduction of ‘auto’
   return f(tag, x);
           ^
t.cpp:3:11: error: use of ‘auto abc::f(abc::tag, T) [with T = abc::A]’ before
deduction of ‘auto’

/////////////////////////////////////////////////////////////
template<class Tag, class T>
auto g(Tag tag, T x) {
  return f(tag, x);
}

namespace abc {
struct tag {};

struct A {};

template<class T>
auto f(tag, T x) { return x; }
}

int main() {
  g(abc::tag(), abc::A());
  return 0;
}
/////////////////////////////////////////////////////////////