https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93297
--- Comment #8 from John McFarlane <john at mcfarlane dot name> ---
And this input can generate an ICE even with the -std=c++2a switch:
template <class> class a;
template <b> a()->a;
template <2> using c a<int>;
static_assert(c{ }
CL: g++ -v -std=c++2a source.cpp
Online: https://godbolt.org/z/dh9bfc
