text: // RUN: %clang_cc1 -std=c++2a -verify %s -fcxx-exceptions -triple=x86_64-linux-gnu
  
  namespace ThreeWayComparison {
    struct A {
      int n;
      constexpr friend int operator<=>(const A &a, const A &b) {
        return a.n < b.n ? -1 : a.n > b.n ? 1 : 0;
      }
    };
    static_assert(A{1} <=> A{2} < 0);
    static_assert(A{2} <=> A{1} > 0);
    static_assert(A{2} <=> A{2} == 0);
  
    // Note: not yet supported.
    static_assert(1 <=> 2 < 0); // expected-error {{invalid operands}}
    static_assert(2 <=> 1 > 0); // expected-error {{invalid operands}}
    static_assert(1 <=> 1 == 0); // expected-error {{invalid operands}}
    constexpr int k = (1 <=> 1, 0);
    // expected-error@-1 {{constexpr variable 'k' must be initialized by a constant expression}}
    // expected-warning@-2 {{three-way comparison result unused}}
  
    constexpr void f() { // expected-error {{constant expression}}
      void(1 <=> 1); // expected-note {{constant expression}}
    }
  
    // TODO: defaulted operator <=>
  }
  