[Bug c++/93740] Template base classes parametrized by pointer-to-member are amibiguous

[m.cencora at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93740

--- Comment #3 from m.cencora at gmail dot com ---
Still broken in gcc 10.2 and trunk, also in C++20 mode.

The problem seems to show up only when address of member function (virtual or
not) is passed as template parameter - only then gcc fails during overload
resolution.

For free functions this works fine. 

struct A
{
    void foo();
    void bar();
};

template <int N, auto val>
struct indexed_elem{};

struct A_indexed_member_funcs
  : indexed_elem<0, &A::foo>,
    indexed_elem<1, &A::bar>
{};

template <auto val, int N>
constexpr int index_of(indexed_elem<N, val>)
{
    return N;
}

void foo();
void bar();

struct indexed_free_funcs
  : indexed_elem<0, &foo>,
    indexed_elem<1, &bar>
{};

void test()
{
    // this fails due to gcc claim of ambiguous base classes
    static_assert(index_of<&A::foo>(A_indexed_member_funcs{}) == 0, "");

    // this is ok
    static_assert(index_of<&foo>(indexed_free_funcs{}) == 0, "");
}