We are upgrading our XL C/C++ compiler from V8.0 to V10.1 and found some code that is now giving us an error, even though it compiled under V8.0. Here's a minimal example:

test.h:

#include <iostream>
#include <string>

template <class T>
void f()
{
  std::cout << TEST << std::endl;
}

test.cpp:

#include <string>
#include "test.h"

namespace
{
  std::string TEST = "test";
}

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

Under V10.1, we get the following error:

"test.h", line 7.16: 1540-0274 (S) The name lookup for "TEST" did not find a declaration.
"test.cpp", line 6.15: 1540-1303 (I) "std::string TEST" is not visible.
"test.h", line 5.6: 1540-0700 (I) The previous message was produced while processing "f<int>()".
"test.cpp", line 11.3: 1540-0700 (I) The previous message was produced while processing "main()".

We found a similar difference between g++ 3.3.2 and 4.3.2. I also found in g++, if I move the #include "test.h" to be after the unnamed namespace declaration, the compile error goes away.

So here's my question: what does the Standard say about this? When a template is instantiated, is that instance considered to be declared at the point where the template itself was declared, or is the standard not that clear on this point? I did some looking though the n2461.pdf draft, but didn't really come up with anything definitive.