text: // RUN: %clang_cc1 -std=c++2a -fconcepts-ts -x c++ %s -verify
  
  using A = int;
  
  template<typename T, typename U>
  constexpr bool is_same_v = false;
  
  template<typename T>
  constexpr bool is_same_v<T, T> = true;
  
  static_assert(requires { requires true; 0; typename A; { 0 } -> int; });
  static_assert(is_same_v<bool, decltype(requires { requires false; })>);
  
  // Check that requires expr is an unevaluated context.
  struct Y {
    int i;
    static constexpr bool r = requires { i; };
  };
  
  template<typename T> requires requires (T t) {
    requires false; // expected-note{{because 'false' evaluated to false}}
    requires false;
    requires requires {
      requires false;
    };
  }
  struct r1 { };
  
  using r1i = r1<int>;
  // expected-error@-1 {{constraints not satisfied for class template 'r1' [with T = int]}}
  
  template<typename T> requires requires (T t) {
    requires requires {
      requires false; // expected-note{{because 'false' evaluated to false}}
    };
  }
  struct r2 { };
  
  using r2i = r2<int>;
  // expected-error@-1 {{constraints not satisfied for class template 'r2' [with T = int]}}
  
  template<typename T> requires requires (T t) {
    requires requires {
      requires true;
    };
    requires true;
    requires requires {
      requires false; // expected-note{{because 'false' evaluated to false}}
    };
  }
  struct r3 { };
  
  using r3i = r3<int>;
  // expected-error@-1 {{constraints not satisfied for class template 'r3' [with T = int]}}
  
  template<typename T>
  struct S { static const int s = T::value; };
  
  template<typename T> requires requires { T::value; S<T>::s; }
  // expected-note@-1 {{because 'T::value' would be invalid: type 'int' cannot be used prior to '::' because it has no members}}
  struct r4 { };
  
  using r4i = r4<int>;
  // expected-error@-1 {{constraints not satisfied for class template 'r4' [with T = int]}}