[Bug libstdc++/84690] std::is_invocable not working for ambiguous calls

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84690

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Vincent Reverdy from comment #0)
> The std::is_invocable type trait from the standard library fails to detect
> that the first call in the main function is ambiguous. The program returns
> 1, 1, 1 instead of 0, 1, 1. This seems to be related to
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84689 and to

Isn't it identical?

The variadic templates in this version seem irrelevant to the bug.

#include <iostream>
#include <type_traits>

// A base class
struct base {void operator()(int){};};

// Two derived classes inheriting from the same base classes
struct derived1: base {
  using base::operator();
};
struct derived2: base {
  using base::operator();
  void operator()(char);
  void operator()(float);
};

// A class inheriting from both derived1 and derived2
struct functor: derived1, derived2 {
    using derived1::operator();
    using derived2::operator();
};

// Main function
int main()
{
    std::cout << std::is_invocable_v<functor, int> << "\n";
    std::cout << std::is_invocable_v<functor, float> << "\n";
    std::cout << std::is_invocable_v<functor, char> << "\n";
}

*** This bug has been marked as a duplicate of bug 84689 ***