Allowing formatting non-copyable ranges.

[brevzin]

Fixes #3286

[brevzin]

Some windows build is complaining about noncopyable_range<int> & being non-formattable, but I'm not sure why. Do you know what version "(windows-2019, x64, v140, 14)" corresponds to on compiler-explorer? Could try to repro something there.

[mwinterb]

It's not an exact match, but the general "era" matches "x64 msvc v19.0 (WINE)".

[brevzin]

wat: https://godbolt.org/z/b9TYxqh6s

namespace my {
namespace detail {
    template <typename... > using void_t = void;
}
}

template <typename T>
struct has_mutable_begin_end<
    T, 
    #if 1
    fmt::detail::void_t<
    #else
    my::detail::void_t<
    #endif
        decltype(fmt::detail::range_begin(std::declval<T>()))
        , decltype(fmt::detail::range_end(std::declval<T>()))
        #if 0
        , int
        #endif
        >>
    : std::true_type {};

static_assert(has_mutable_begin_end<noncopyable_range>::value, "");

If I use my::detail::void_t, this works.

If I use fmt::detail::void_t, which is ... the same thing as my::detail::void_t, it fails. Unless I add the extra int at the end, in which case it works?

[vitaut]

Thanks for the PR.