<ranges>: filter_view/transform_view::_Iterator_base shadowing

[StephanTLavavej]

filter_view and transform_view have nested _Iterator_base:

STL/stl/inc/ranges

Lines 853 to 864 in 2b4cf99

	class filter_view : public _Cached_position_t<forward_range<_Vw>, _Vw, filter_view<_Vw, _Pr>> {
	// clang-format on
	private:
	/* [[no_unique_address]] */ _Vw _Range{};
	/* [[no_unique_address]] */ _Semiregular_box<_Pr> _Pred{};
	template <class _Traits> // TRANSITION, LWG-3289
	struct _Iterator_base {};
	// clang-format off
	template <class _Traits>
	requires _Has_member_iterator_category<_Traits>
	struct _Iterator_base<_Traits> {

STL/stl/inc/ranges

Lines 1130 to 1144 in 2b4cf99

	class transform_view : public view_interface<transform_view<_Vw, _Fn>> {
	// clang-format on
	private:
	/* [[no_unique_address]] */ _Vw _Range{};
	/* [[no_unique_address]] */ _Semiregular_box<_Fn> _Fun{};
	template <bool _Const>
	class _Sentinel;
	template <class _Traits, class _Base> // TRANSITION, LWG-3289
	struct _Iterator_base {};
	// clang-format off
	template <class _Traits, class _Base>
	requires _Has_member_iterator_category<_Traits>
	struct _Iterator_base<_Traits, _Base> {

This shadows the STL-wide _Iterator_base (which is very important because it powers iterator debugging):

STL/stl/inc/xmemory

Lines 1234 to 1240 in 2b4cf99

	#if _ITERATOR_DEBUG_LEVEL == 0
	using _Container_base = _Container_base0;
	using _Iterator_base = _Iterator_base0;
	#else // _ITERATOR_DEBUG_LEVEL == 0
	using _Container_base = _Container_base12;
	using _Iterator_base = _Iterator_base12;
	#endif // _ITERATOR_DEBUG_LEVEL == 0

I strongly believe that this shadowing is confusing and should be avoided by renaming the nested structs.