Stack overflow when running into C++ union with variadic templates

This bizarre edge case in a library I'm consuming has caused bindgen to segfault. I've simplified it the best I can:

// input.h
template<typename T, typename... U> union Foo {
  Foo<U...> foo;
};

I get no output from bindgen, just a segfault:

$ bindgen input.h -- -x c++
zsh: segmentation fault (core dumped)  bindgen input.h -- -x c++

I know that C++ templates (and especially variadic templates) are beyond the scope of bindgen, but I believe that it would probably be better if it output "Unhandled cursor kind" or something along those lines.

Some other notes for debugging:

• --blacklist-type Foo works, but discovering the type when it's buried deep in a library's header files takes a while (speaking from experience 😉)

• Removing T from the template does not invoke a segfault:

  template<typename... U> union Foo {
    Foo<U...> foo;
  };
  

  Bindgen output

  /* automatically generated by rust-bindgen 0.54.1 */
  
  #[repr(C)]
  pub struct __BindgenUnionField<T>(::std::marker::PhantomData<T>);
  impl<T> __BindgenUnionField<T> {
      #[inline]
      pub const fn new() -> Self {
          __BindgenUnionField(::std::marker::PhantomData)
      }
      #[inline]
      pub unsafe fn as_ref(&self) -> &T {
          ::std::mem::transmute(self)
      }
      #[inline]
      pub unsafe fn as_mut(&mut self) -> &mut T {
          ::std::mem::transmute(self)
      }
  }
  impl<T> ::std::default::Default for __BindgenUnionField<T> {
      #[inline]
      fn default() -> Self {
          Self::new()
      }
  }
  impl<T> ::std::clone::Clone for __BindgenUnionField<T> {
      #[inline]
      fn clone(&self) -> Self {
          Self::new()
      }
  }
  impl<T> ::std::marker::Copy for __BindgenUnionField<T> {}
  impl<T> ::std::fmt::Debug for __BindgenUnionField<T> {
      fn fmt(&self, fmt: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
          fmt.write_str("__BindgenUnionField")
      }
  }
  impl<T> ::std::hash::Hash for __BindgenUnionField<T> {
      fn hash<H: ::std::hash::Hasher>(&self, _state: &mut H) {}
  }
  impl<T> ::std::cmp::PartialEq for __BindgenUnionField<T> {
      fn eq(&self, _other: &__BindgenUnionField<T>) -> bool {
          true
      }
  }
  impl<T> ::std::cmp::Eq for __BindgenUnionField<T> {}
  #[repr(C)]
  pub struct Foo {
      pub foo: __BindgenUnionField<Foo>,
      pub bindgen_union_field: [u8; 0usize],
  }
  

Reproduce the crash with the provided input.h and the bindgen input.h -- -x c++ command, then trace the C++ union and variadic-template handling reached by that invocation. Done means this input no longer segfaults and instead produces a clear unsupported-cursor diagnostic or another graceful result.