`<iterator>`: `std::contiguous_iterator<const volatile int*> == false` because of `volatile`?

[pc125]

static_assert(std::contiguous_iterator<const volatile int*>) fails with this STL, while it works with lib(std)c++. Without the volatile it works everywhere. Who is correct?
I can't see why a pointer to volatile data shouldn't be a valid iterator.

[fsb4000]

Most likely it's a compiler issue. because clang-cl compile the code.

I will try to reduce the code sample.

[miscco]

This is a known issue with MSVCs handling of the ternary operator https://developercommunity.visualstudio.com/t/conditional-operator-errors/876860

It boils down to std::common_reference giving the wrong result for volatile int *

[frederick-vs-ja]

I think this bug happens in the following case:
When I is a cv-unqualified arithmetic or enumeration scalar type (but sometimes pointer types get right results), LRef is cvI&, RRef is cvI&& except for I&&, MSVC erroneously computes decltype(false ? std::declval<LRef>(), std::declval<RRef>()) as I&, while the right result is I.

std::contiguous_iterator<const volatile int*> eventually tests std::common_reference_t<const volatile int&&, const int&> (which is int if correctly computed; but MSVC answers int&), and requires that both const volatile int&& and const int& can be converted to that type. Although the implementation of std::common_reference_t uses something similar (_Returns_exactly in MSVC STL) rather than std::declval.

I guess workaround is available.