[Bug libstdc++/106376] New: The implementation of std::pointer_traits seems wrong

["hewillk at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106376

            Bug ID: 106376
           Summary: The implementation of std::pointer_traits seems wrong
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

[pointer.traits.types]: 
using element_type = see below;
Type: Ptr​::​element_­type if the qualified-id Ptr​::​element_­type is valid
and denotes a type ([temp.deduct]); otherwise, T if Ptr is a class template
instantiation of the form SomePointer<T, Args>, where Args is zero or more type
arguments; otherwise, the specialization is *ill-formed*.

So for the following, the instantiation of pointer_traits will be ill-formed,
and static_assert will cause a hard error, just like libc++ and MSVC-STL do.
libstdc++ specifies element_type as a meaningless type, so the static_assert
still   passes.

Although the behavior of libstdc++ is incorrect, but I am not feel good about
this static_assert hard error..

#include <iterator>

struct I {
  using iterator_category = std::contiguous_iterator_tag;
  using difference_type = std::ptrdiff_t;
  using value_type = int;
  value_type& operator*() const;
  I& operator++();
  I operator++(int);
  I& operator--();
  I operator--(int);
  I& operator+=(difference_type);
  I& operator-=(difference_type);
  value_type* operator->() const;
  value_type& operator[](difference_type) const;
  friend I operator+(I, difference_type);
  friend I operator+(difference_type, I);
  friend I operator-(I, difference_type);
  friend difference_type operator-(I, I);
  auto operator<=>(const I&) const = default;
};

static_assert(std::contiguous_iterator<I>);

https://godbolt.org/z/sx763oMn6