bindgen hangs on c++ header

c++ header

template <typename> struct a;
template <typename, typename, typename, typename, typename, typename, typename, typename, typename, bool> struct b;
template <typename d, typename c, typename f, typename e, typename h, typename g, typename j, typename i, typename l>
struct b<d, c, f, e, h, g, j, i, l, true> {
  using k = a<l>;
  using n = typename k::n;
  using m = typename c ::o;
  m &p(const n &);
};
template <typename d, typename c, typename f, typename e, typename h, typename g, typename j, typename i, typename l>
auto b<d, c, f, e, h, g, j, i, l, true>::p(const n &) -> m & {}

bindgen test-case-5.hpp -- -x c++ hangs.

This hangs bindgen for at least several minutes. The interestingness test I used with creduce was that it would hang it for 2m:30s.

Using RUST_LOG=bindgen on the executable shows that it gets into the codegen phase.

Run bindgen test-case-5.hpp -- -x c++ with RUST_LOG=bindgen and follow the reported codegen phase. Use the provided C++ header as the reproducer; done means bindgen completes instead of hanging, with a regression check for this command.