Question on visible scope in template declaration

[Carl Lei]

Hello list,

The following code is rejected by GCC but accepted by Clang:

template <class T>
auto f(T v) -> decltype(g(v));

int g(int) { return 0; }

template <class T>
auto f(T v) -> decltype(g(v))
{
   return g(v) + 1;
}

int main()
{
   return f(0);
}

Error message at http://ideone.com/Vn79Hm.

Basically the problem comes down to which is the visible scope in that 
trailing return type decltype(g(v)), where GCC uses the point of 
declaration but Clang uses the point of definition.  g is a dependent 
name here, and the standard says "template definition context" should be 
used; but I am not very sure about the wording.  I suspect this to be a 
GCC bug, but not sure, so asking here first.

-- 
Carl Lei (XeCycle)
Department of Physics and Astronomy, SJTU