[Bug libstdc++/117998] New: : views::counted misses difference casting for contiguous_iterator case

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117998

            Bug ID: 117998
           Summary: <ranges>: views::counted misses difference casting for
                    contiguous_iterator case
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

template<input_or_output_iterator _Iter>
      constexpr auto
      operator() [[nodiscard]] (_Iter __i, iter_difference_t<_Iter> __n) const
      {
        if constexpr (contiguous_iterator<_Iter>)
          return span(std::to_address(__i), __n);


We should static_cast n to type size_t:

https://godbolt.org/z/eM6cWsTeq

#include <ranges>

struct ContiguousIter {
  using iterator_category = std::contiguous_iterator_tag;
  using difference_type = std::ranges::__detail::__max_diff_type;
  using element_type = char;
  element_type& operator*() const;
  ContiguousIter& operator++();
  ContiguousIter operator++(int);
  ContiguousIter& operator--();
  ContiguousIter operator--(int);
  ContiguousIter& operator+=(difference_type);
  ContiguousIter& operator-=(difference_type);
  element_type* operator->() const;
  element_type& operator[](difference_type) const;
  friend ContiguousIter operator+(ContiguousIter, difference_type);
  friend ContiguousIter operator+(difference_type, ContiguousIter);
  friend ContiguousIter operator-(ContiguousIter, difference_type);
  friend difference_type operator-(ContiguousIter, ContiguousIter);
  auto operator<=>(const ContiguousIter&) const = default;
};

int main() {
  ContiguousIter it;
  std::ranges::contiguous_range auto r = std::views::counted(it, 42);
}