[Bug c++/103879] error: accessing value of variant::_Copy_ctor_base through a 'const variant' glvalue in a constant expression

[ppalka at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103879

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Reduced C++14 rejects-valid testcase:

struct A {
  int n = 42;
};

struct B : A { };

struct C {
  B b;
};

constexpr int f() {
  C c;
  A& a = static_cast<A&>(c.b);
  B& b = static_cast<B&>(a);
  return b.n;
}

static_assert(f() == 42, "");