Google ref: b/12785605

Test:

template <typename T>
struct AbstractThing {
  virtual ~AbstractThing() { }
  virtual const T* method() const = 0;
};

template <typename T>
struct ConcreteThing : public AbstractThing<T> {
  virtual ~ConcreteThing() { }
  virtual const T* method() const { return 0; }
};

int main()
{
  struct Foo { };

  AbstractThing<Foo>* concrete = new ConcreteThing<Foo>();
  int rc = (concrete->method() == 0) ? 0 : 1;
  delete concrete;
  return rc;
}


Using g++ (GCC) 4.9.0 20140128 (experimental)

g++ -std=c++11 t.cc
t.cc:4:20: error: 'const T* AbstractThing<T>::method() const [with T = main()::Foo]', declared using local type 'const main()::Foo', is used but never defined [-fpermissive]
   virtual const T* method() const = 0;
                    ^

Adding -fpermissive, the executable links and runs fine, so clearly the never-defined method is not *actually* used.