This code does not compile:

template <class T>
struct Feature {
	friend void AssertFeature0(T *) {}
};

template <class T>
inline void AssertFeature(T *t = 0) { if(t) AssertFeature0(t); }

template <class T>
struct Test : Feature< Test<T> >
{
	int i;
	~Test() { AssertFeature<T>(); }
};

struct Foo : Feature<Foo> { int x; };

void foo()
{
	Test< Test<Foo> > test;
}

----------------------
The problem seems to be in fact that ~Test destructor is instantiated BEFORE
friend is injected and only in the case that templates are nested. Moving
AssertFeature to other method (and instatiating) or reducing test-case to just
"Test<Foo> test;" makes code compile fine.

Comeau C++ testdrive compiles this code without problems.