STL: `expected<any, T>` and its friends can break container iterator comparison

Describe the bug

The bug reported in GCC Bugzilla #115939 is currently also present in MSVC STL. Iterator comparison is currently broken for all but set containers.

The reason of the bug is that expected<any, T> is so permissive on implicit conversion that operator== for expected can cause ambiguity. Note that while there may be a defect in expected, such ambiguity can also caused by some (misdesigned) user-defined types in C++14 mode.

Command-line test case

Godbolt link

#include <any>
#include <expected>

#include <vector>
#include <forward_list>
#include <deque>
#include <list>
#include <array>
#include <map>
// #include <set> // possibly fine
#include <unordered_map>
// #include <unordered_set> // possibly fine

int main()
{
    {
        std::array<std::expected<std::any, char>, 1> cont{};
        (void)(cont.begin() == cont.end());
    }
    {
        std::vector<std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::forward_list<std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::list<std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::deque<std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }

    {
        std::map<int, std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::multimap<int, std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::unordered_map<int, std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
    {
        std::unordered_multimap<int, std::expected<std::any, char>> cont;
        (void)(cont.begin() == cont.end());
    }
}

Expected behavior

This program compiles and operator== overloads for iterators are selected.

STL version

Microsoft Visual Studio Community 2022
Version 17.11.0 Preview ? (14.41.33923 from Godbolt)

Still present in 17.11.0 Preview 4.0 and ecbc1efa09936f4ef5af529e770a95a29a4290d3.

Additional context

Start by compiling the provided reproducer with , , and the listed container headers, then inspect the iterator operator== overloads involved in the ambiguity. Check the behavior across the containers in the example, including the set cases, and confirm that each comparison compiles with the intended iterator overload selected.