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

[pinskia at gcc dot gnu.org via Gcc-bugs]

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

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
With a "fixed" source to the new syntax of concepts I get:
<source>: In substitution of 'template<class T>  requires (ToJson<T>) &&
!(Serializable<T>) std::ostream& operator<<(std::ostream&, const T&) [with T =
char]':
<source>:5:86:   required from here
<source>:5:31:   required by the constraints of 'template<class T> concept
Serializable'
<source>:5:46:   in requirements with 'T x', 'std::ostream& os' [with T = char]
<source>:5:46: error: satisfaction of atomic constraint 'requires(T x,
std::ostream& os) {{os << x};} [with T = T]' depends on itself
    5 | template<typename T> concept  Serializable = requires (T x,
std::ostream& os) { { os << x }; };
      |                                             
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




#include <iostream>

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