[Bug libstdc++/102913] New: variant_construct_single should not remove the const qualifier of Up

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102913

            Bug ID: 102913
           Summary: variant_construct_single should not remove the const
                    qualifier of Up
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

>From https://stackoverflow.com/questions/69696170:

variant#L568:

  template<typename _Tp, typename _Up>
    _GLIBCXX20_CONSTEXPR
    void
    __variant_construct_single(_Tp&& __lhs, _Up&& __rhs_mem)
    {
      using _Type = __remove_cvref_t<_Up>;

This should be using _Type = remove_reference_t<_Up>.

#include <string>
#include <variant>

int main() {
  using var_t = std::variant<const int, const std::string>;
  var_t v;
  var_t v2(v);
}

https://godbolt.org/z/zaov3GxdY