[Bug c++/90652] New: Recursive concept leads to segfault

[tobias.bruell at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90652

            Bug ID: 90652
           Summary: Recursive concept leads to segfault
           Product: gcc
           Version: 8.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tobias.bruell at gmail dot com
  Target Milestone: ---

The following program leads to a seg-fault in gcc. Compile with

-Wall -Wextra -std=gnu++2a "-fconcepts"

It works when using "operator << (os, x)" instead of "os << x" in line 4.

-------------------------------------------------------

#include <iostream>

void to_json (std::ostream& os, char c) { os << '"' << c << '"'; }
template<typename T> concept bool Serializable = requires (T x, std::ostream&
os) { { os << x }; };
template<typename T> concept bool ToJson = requires (T x, std::ostream& os) { {
to_json (os, x) }; };

template<typename T>
  requires ToJson<T> && !Serializable<T>
std::ostream& operator << (std::ostream& os, T const& x)
{
  to_json (os, x);
  return os;
}

int main ()
{
  static_assert (Serializable<char>);
  static_assert (ToJson<char>);

  std::cout << 'c';
}