[Bug c++/59975] New: [C++11] Bogus "=?UTF-8?Q?declared=20using=20local=20type=20=E2=80=98?=...=?UTF-8?Q?=E2=80=99?=, is used but never defined"

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59975

            Bug ID: 59975
           Summary: [C++11] Bogus "declared using local type ‘...’, is
                    used but never defined"
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

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.