[Bug c++/64194] [C++14] <unresolved overloaded function type> for function template with auto return

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64194

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Slightly different testcase from PR 69620 which is probably the same issue:

struct function {
  template<typename F>
    function(F);
};

template <typename T1, typename T2>
auto sum(T1 x, T2 y)
{
    return x + y;
}

template <typename T1, typename T2, typename... Targ>
auto sum(T1 x, T2 y, Targ... args)
{
    return sum(x + y, args...);
}

int main()
{
    //(void)sum<int, int, int>;
    function f = sum<int, int, int>;
}

ded.cc: In function 'int main()':
ded.cc:21:18: error: conversion from '<unresolved overloaded function type>' to
non-scalar type 'function' requested
     function f = sum<int, int, int>;
                  ^~~~~~~~~~~~~~~~~~


It works if the function is instantiated first by uncommenting the first line
in main.