Testcase:


class C;

auto x = []<typename MyC = C>(MyC *p) {
    return p->n;
};

class C {
    int n;
    friend decltype(x);
} c;

int k = x(&c);


This appears to be valid, and Clang, MSVC, and EDG accept, but GCC reports an access error. The templated operator() of the lambda is a member function of a friend of C, so should have access to C::n.