[Bug c++/120197] ICE in GCC with decltype(cout << a) in default function parameter leads to recursive diagnostics with -std=c++20

[mcccs at gmx dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120197

mcccs at gmx dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mcccs at gmx dot com

--- Comment #1 from mcccs at gmx dot com ---
Minimized testcase:

struct basic_ostream {int operator<<(auto x);
}; template <typename> bool __derived_from_ios_base;
template <typename _Os, typename>
  requires __derived_from_ios_base<_Os>
using __rvalue_stream_insertion_t = _Os;
template < typename _Ostream, typename _Tp > __rvalue_stream_insertion_t<
_Ostream, _Tp > operator<<(_Ostream ,                                          
              _Tp );
basic_ostream cout;
template < class T > void myFunc(T a, decltype(cout << a) = cout){ }
int main0 {
myFunc(5)
}