gcc/testsuite/g++.dg/cpp2a/concepts-recursive-sat3.C

// { dg-do compile { target c++2a } }

template<typename T>
concept Fooable = requires(T t) { foo(t); };

template<Fooable T>
void foo(T t) { }

void test()
{
  foo(0); // { dg-error "unsatisfied constraints" }
}