llvm-project/clang/test/SemaTemplate/concepts.cpp

// RUN: %clang_cc1 -std=c++20 -verify %s

namespace PR47043 {
  template<typename T> concept True = true;
  template<typename ...T> concept AllTrue1 = True<T>; // expected-error {{expression contains unexpanded parameter pack 'T'}}
  template<typename ...T> concept AllTrue2 = (True<T> && ...);
  static_assert(AllTrue2<int, float, char>);
}

namespace PR47025 {
  template<typename ...T> concept AllAddable1 = requires(T ...t) { (void(t + 1), ...); };
  template<typename ...T> concept AllAddable2 = (requires(T ...t) { (t + 1); } && ...); // expected-error {{requirement contains unexpanded parameter pack 't'}}
  template<typename ...T> concept AllAddable3 = (requires(T t) { (t + 1); } && ...);
  template<typename ...T> concept AllAddable4 = requires(T t) { (t + 1); }; // expected-error {{expression contains unexpanded parameter pack 'T'}}
  template<typename ...T> concept AllAddable5 = requires(T t) { (void(t + 1), ...); }; // expected-error {{does not contain any unexpanded}}
  template<typename ...T> concept AllAddable6 = (requires { (T() + 1); } && ...);
  template<typename ...T> concept AllAddable7 = requires { (T() + 1); }; // expected-error {{expression contains unexpanded parameter pack 'T'}}

  static_assert(AllAddable1<int, float>);
  static_assert(AllAddable3<int, float>);
  static_assert(AllAddable6<int, float>);
  static_assert(!AllAddable1<int, void>);
  static_assert(!AllAddable3<int, void>);
  static_assert(!AllAddable6<int, void>);
}

namespace PR45699 {
  template<class> concept C = true; // expected-note 2{{here}}
  template<class ...Ts> void f1a() requires C<Ts>; // expected-error {{requires clause contains unexpanded parameter pack 'Ts'}}
  template<class ...Ts> requires C<Ts> void f1b(); // expected-error {{requires clause contains unexpanded parameter pack 'Ts'}}
  template<class ...Ts> void f2a() requires (C<Ts> && ...);
  template<class ...Ts> requires (C<Ts> && ...) void f2b();
  template<class ...Ts> void f3a() requires C<Ts...>; // expected-error {{pack expansion used as argument for non-pack parameter of concept}}
  template<class ...Ts> requires C<Ts...> void f3b(); // expected-error {{pack expansion used as argument for non-pack parameter of concept}}
  template<class ...Ts> void f4() {
    ([] () requires C<Ts> {} ()); // expected-error {{expression contains unexpanded parameter pack 'Ts'}}
    ([]<int = 0> requires C<Ts> () {} ()); // FIXME: expected-error {{lambda requires '()' before 'requires' clause}} expected-error 0+{{}}
  }
  template<class ...Ts> void f5() {
    ([] () requires C<Ts> {} (), ...);
    ([]<int = 0> requires C<Ts> () {} (), ...); // FIXME: expected-error {{lambda requires '()' before 'requires' clause}} expected-error 0+{{}}
  }
  void g() {
    f1a();
    f1b(); // FIXME: Bad error recovery. expected-error {{undeclared identifier}}
    f2a();
    f2b();
    f3a();
    f3b(); // FIXME: Bad error recovery. expected-error {{undeclared identifier}}
    f4();
    f5();
  }
}