[Bug c++/57745] New: missing recursive lifetime extension within std::initializer_list

["richard-gccbugzilla at metafoo dot co.uk" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57745

            Bug ID: 57745
           Summary: missing recursive lifetime extension within
                    std::initializer_list
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: richard-gccbugzilla at metafoo dot co.uk

Consider:

#include <iostream>
struct A {
   A() { std::cout << " A()" << std::endl; }
  ~A() { std::cout << "~A()" << std::endl; }
};
struct B {
  const A &a;
  ~B() { std::cout << "~B()" << std::endl; }
};
struct C {
  std::initializer_list<B> b;
  ~C() { std::cout << "~C()" << std::endl; }
};
int main() {
  const C &c = C{ { { A() }, { A() } } };
  std::cout << "-----" << std::endl;
}

This should print:

 A()
 A()
-----
~C()
~B()
~A()
~B()
~A()

... but g++ destroys the two A temporaries at the end of the full-expression.
They are lifetime-extended because they are bound to B::a references in the
aggregate-initialization of the B subobjects of the underlying array of the
initializer_list, which is itself lifetime-extended.