Clang rejects this:

template<typename T> struct X {
  auto f() { return 0; }
  void g() { f(); }
};

saying:

<stdin>:3:14: error: function 'f' with deduced return type cannot be used before it is defined
  void g() { f(); }
             ^

This isn't right: we should be allowed to reference this function as a member of the current instantiation. We should probably deduce the return type to DependentTy when the template is defined.