[Bug libstdc++/79226] New: Additional overloads needed for __complex__ types

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79226

            Bug ID: 79226
           Summary: Additional overloads needed for __complex__ types
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This should compile:

#include <complex>
int main()
{
  using namespace std::complex_literals;
  std::real(0.0i);
  std::imag(0.0i);
  std::arg(0.0i);
  std::norm(0.0i);
  std::proj(0.0i);
  std::conj(0.0i);
}

But using -std=gnu++NN the 'i' suffix is the GNU extension that creates
__complex__ double object, instead of the ISO C++ one that creates a
std::complex<double>, and there are no overloads for __complex__ double.

IMHO the GNU extension should be disabled in C++14 and above, because there's a
standardised way to do it (and users can run into similar ambiguities) but
until then we should make the code above DTRT.