text: // RUN: %clang_cc1 -std=c++2a -x c++ %s -verify
  
  bool r1 = requires () {};
  // expected-error@-1 {{a requires expression must contain at least one requirement}}
  
  bool r2 = requires { requires true; };
  
  bool r3 = requires (int a, ...) { requires true; };
  // expected-error@-1 {{varargs not allowed in requires expression}}
  
  template<typename... T>
  bool r4 = requires (T... ts) { requires true; };
  
  bool r5 = requires (bool c, int d) { c; d; };
  
  bool r6 = requires (bool c, int d) { c; d; } && decltype(d){};
  // expected-error@-1 {{use of undeclared identifier 'd'}}
  
  bool r7 = requires (bool c) { c; (requires (int d) { c; d; }); d; } && decltype(c){} && decltype(d){};
  // expected-error@-1 2{{use of undeclared identifier 'd'}}
  // expected-error@-2 {{use of undeclared identifier 'c'}}
  
  bool r8 = requires (bool, int) { requires true; };
  
  bool r9 = requires (bool a, int a) { requires true; };
  // expected-error@-1 {{redefinition of parameter 'a'}}
  // expected-note@-2 {{previous declaration is here}}
  
  bool r10 = requires (struct new_struct { int x; } s) { requires true; };
  // expected-error@-1 {{'new_struct' cannot be defined in a parameter type}}
  
  bool r11 = requires (int x(1)) { requires true; };
  // expected-error@-1 {{expected parameter declarator}}
  // expected-error@-2 {{expected ')'}}
  // expected-note@-3 {{to match this '('}}
  
  bool r12 = requires (int x = 10) { requires true; };
  // expected-error@-1 {{default arguments not allowed for parameters of a requires expression}}
  
  bool r13 = requires (int f(int)) { requires true; };
  
  bool r14 = requires (int (*f)(int)) { requires true; };
  
  bool r15 = requires (10) { requires true; };
  // expected-error@-1 {{expected parameter declarator}}
  // expected-error@-2 {{expected ')'}} expected-note@-2 {{to match}}
  
  bool r16 = requires (auto x) { requires true; };
  // expected-error@-1 {{'auto' not allowed in requires expression parameter}}
  
  bool r17 = requires (auto [x, y]) { requires true; };
  // expected-error@-1 {{'auto' not allowed in requires expression parameter}}
  // expected-error@-2 {{use of undeclared identifier 'x'}}
  
  using a = int;
  
  bool r18 = requires { typename a; };
  
  bool r19 = requires { typename ::a; };
  
  template<typename T> struct identity { using type = T; };
  
  template<typename T> using identity_t = T;
  
  bool r20 = requires {
      typename identity<int>::type;
      typename identity<int>;
      typename ::identity_t<int>;
  };
  
  struct s { bool operator==(const s&); ~s(); };
  
  bool r21 = requires { typename s::operator==; };
  // expected-error@-1 {{expected an identifier or template-id after '::'}}
  
  bool r22 = requires { typename s::~s; };
  // expected-error@-1 {{expected an identifier or template-id after '::'}}
  
  template<typename T>
  bool r23 = requires { typename identity<T>::temp<T>; };
  // expected-error@-1 {{use 'template' keyword to treat 'temp' as a dependent template name}}
  
  template<typename T>
  bool r24 = requires {
      typename identity<T>::template temp<T>;
      typename identity<T>::template temp; // expected-error{{expected an identifier or template-id after '::'}}
  };
  
  bool r25 = requires { ; };
  // expected-error@-1 {{expected expression}}
  
  bool r26 = requires { {}; };
  // expected-error@-1 {{expected expression}}
  
  bool r27 = requires { { 0 } noexcept; };
  
  bool r28 = requires { { 0 } noexcept noexcept; };
  // expected-error@-1 {{expected '->' before expression type requirement}}
  // expected-error@-2 {{expected concept name with optional arguments}}
  
  template<typename T>
  concept C1 = true;
  
  template<typename T, typename U>
  concept C2 = true;
  
  bool r29 = requires { { 0 } noexcept C1; };
  // expected-error@-1 {{expected '->' before expression type requirement}}
  
  bool r30 = requires { { 0 } noexcept -> C2<int>; };
  
  namespace ns { template<typename T> concept C = true; }
  
  bool r31 = requires { { 0 } noexcept -> ns::C; };
  
  template<typename T>
  T i1 = 0;
  
  bool r32 = requires { requires false, 1; };
  // expected-error@-1 {{expected ';' at end of requirement}}
  
  bool r33 = requires { 0 noexcept; };
  // expected-error@-1 {{'noexcept' can only be used in a compound requirement (with '{' '}' around the expression)}}
  
  bool r34 = requires { 0 int; };
  // expected-error@-1 {{expected ';' at end of requirement}}
  
  bool r35 = requires { requires true };
  // expected-error@-1 {{expected ';' at end of requirement}}
  
  bool r36 = requires (bool b) { requires sizeof(b) == 1; };
  
  void r37(bool b) requires requires { 1 } {}
  // expected-error@-1 {{expected ';' at end of requirement}}
  
  bool r38 = requires { requires { 1; }; };
  // expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
  
  bool r39 = requires { requires () { 1; }; };
  // expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
  
  bool r40 = requires { requires (int i) { i; }; };
  // expected-error@-1 {{requires expression in requirement body; did you intend to place it in a nested requirement? (add another 'requires' before the expression)}}
  
  bool r41 = requires { requires (); };
  // expected-error@-1 {{expected expression}}
  