[Bug c++/116366] New: the const specifier is dropped when using member object as template parameter

[niqingliang2003 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116366

            Bug ID: 116366
           Summary: the const specifier is dropped when using member
                    object as template parameter
           Product: gcc
           Version: 14.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: niqingliang2003 at gmail dot com
  Target Milestone: ---

Created attachment 58929
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58929&action=edit
test code

when using member object as template parameter, the const of function parameter
is dropped when deducing function prototype.

error: no matches converting function ‘set_mem’ to type ‘void (struct test::*
const)(int&)’

#include <type_traits>

struct test {
        int x;

        template<auto test::* M>
        using mem_type = decltype(std::declval<test>().*M);

        template<auto test::* M, typename T = mem_type<M>>
        void set_mem(const T& v)
        {
                this->*M = v;
        }
};

static constexpr auto p = &test::set_mem<&test::x>;