type-requirement.cpp

// RUN: %clang_cc1 -std=c++2a -x c++ %s -verify

using A = int;

template<typename T> using identity_t = T; // expected-note 4{{template is declared here}}}

template<typename T> struct identity { using type = T; };
// expected-note@-1 2{{template is declared here}}

struct C {};

struct D { static int type; }; // expected-note{{referenced member 'type' is declared here}}

// Basic unqualified and global-qualified lookups

static_assert(requires { typename A; typename ::A; });
static_assert(requires { typename identity_t<A>; typename ::identity_t<A>; });
static_assert(!requires { typename identity_t<A, A>; }); // expected-error{{too many template arguments for alias template 'identity_t'}}
static_assert(!requires { typename ::identity_t<A, A>; }); // expected-error{{too many template arguments for alias template 'identity_t'}}
static_assert(requires { typename identity<A>; });
static_assert(!requires { typename identity; });
// expected-error@-1 {{typename specifier refers to class template; argument deduction not allowed here}}
static_assert(!requires { typename ::identity; });
// expected-error@-1 {{typename specifier refers to class template; argument deduction not allowed here}}
static_assert(!requires { typename identity_t; });
// expected-error@-1 {{typename specifier refers to alias template; argument deduction not allowed here}}
static_assert(!requires { typename ::identity_t; });
// expected-error@-1 {{typename specifier refers to alias template; argument deduction not allowed here}}

namespace ns {
  using B = int;
  int C = 0;
  // expected-note@-1 {{referenced 'C' is declared here}}
  static_assert(requires { typename A; typename B; typename ::A; });
  static_assert(!requires { typename ns::A; }); // expected-error{{no type named 'A' in namespace 'ns'}}
  static_assert(!requires { typename ::B; }); // expected-error{{no type named 'B' in the global namespace}}
  static_assert(requires { typename C; });
  // expected-error@-1 {{typename specifier refers to non-type 'C'}}
}

// member type lookups

static_assert(requires { typename identity<int>::type; typename ::identity<int>::type; });
static_assert(!requires { typename identity<int>::typr; }); // expected-error{{no type named 'typr' in 'identity<int>'}}
static_assert(!requires { typename ::identity<int>::typr; }); // expected-error{{no type named 'typr' in 'identity<int>'}}

template<typename T> requires requires { typename T::type; }
// expected-note@-1 {{because 'typename T::type' would be invalid: type 'int' cannot be used prior to '::' because it has no members}}
// expected-note@-2 {{because 'typename T::type' would be invalid: no type named 'type' in 'C'}}
// expected-note@-3 {{because 'typename T::type' would be invalid: typename specifier refers to non-type member 'type' in 'D'}}
// expected-note@-4 {{in instantiation of template class 'invalid<D>' requested here}}
// expected-note@-5 {{in instantiation of requirement here}}
// expected-note@-6 {{while substituting template arguments into constraint expression here}}
// expected-note@-7 {{because 'typename T::type' would be invalid}}
struct r1 {};

using r1i1 = r1<identity<int>>;
using r1i2 = r1<int>; // expected-error{{constraints not satisfied for class template 'r1' [with T = int]}}
using r1i3 = r1<C>; // expected-error{{constraints not satisfied for class template 'r1' [with T = C]}}
using r1i4 = r1<D>; // expected-error{{constraints not satisfied for class template 'r1' [with T = D]}}

template<typename T> struct invalid { typename T::type x; };
// expected-error@-1 {{typename specifier refers to non-type member 'type' in 'D'}}
using r1i5 = r1<invalid<D>>;
// expected-error@-1 {{constraints not satisfied for class template 'r1' [with T = invalid<D>]}}
// expected-note@-2 {{while checking constraint satisfaction for template 'r1<invalid<D>>' required here}}

// mismatching template arguments

template<typename... Ts> requires requires { typename identity<Ts...>; } // expected-note{{because 'typename identity<Ts...>' would be invalid: too many template arguments for class template 'identity'}}
struct r2 {};

using r2i1 = r2<int>;
using r2i2 = r2<void>;
using r2i3 = r2<int, int>; // expected-error{{constraints not satisfied for class template 'r2' [with Ts = <int, int>]}}

namespace ns2 {
  template<typename T, typename U> struct identity {};

  template<typename... Ts> requires requires { typename identity<Ts...>; } // expected-note 2{{because 'typename identity<Ts...>' would be invalid: too few template arguments for class template 'identity'}}
  struct r4 {};

  using r4i1 = r4<int>; // expected-error{{constraints not satisfied for class template 'r4' [with Ts = <int>]}}
}

using r4i2 = ns2::r4<int>; // expected-error{{constraints not satisfied for class template 'r4' [with Ts = <int>]}}

using E = int;
template<typename T> requires requires { typename E<T>; } // expected-error{{expected ';' at end of requirement}}
struct r5v1 {};
template<typename T> requires requires { typename ::E<T>; } // expected-error{{expected ';' at end of requirement}}
struct r5v2 {};

template<typename T> requires (sizeof(T) == 1)
struct chars_only {};

template<typename T> requires requires { typename chars_only<T>; } // expected-note{{because 'typename chars_only<T>' would be invalid: constraints not satisfied for class template 'chars_only' [with T = int]}}
struct r6 {};

using r6i = r6<int>; // expected-error{{constraints not satisfied for class template 'r6' [with T = int]}}

template<typename T> int F = 0; // expected-note 2{{variable template 'F' declared here}}

static_assert(!requires { typename F<int>; });
// expected-error@-1{{template name refers to non-type template 'F'}}
static_assert(!requires { typename ::F<int>; });
// expected-error@-1{{template name refers to non-type template '::F'}}

struct G { template<typename T> static T temp; };

template<typename T> requires requires { typename T::template temp<int>; }
// expected-note@-1{{because 'typename T::template temp<int>' would be invalid: type 'int' cannot be used prior to '::' because it has no members}}
// expected-note@-2{{because 'typename T::template temp<int>' would be invalid: no member named 'temp' in 'D'}}
// expected-note@-3{{because 'typename T::template temp<int>' would be invalid: template name refers to non-type template 'G::template temp'}}
struct r7 {};

using r7i1 = r7<int>; // expected-error{{constraints not satisfied for class template 'r7' [with T = int]}}
using r7i2 = r7<D>; // expected-error{{constraints not satisfied for class template 'r7' [with T = D]}}
using r7i3 = r7<G>; // expected-error{{constraints not satisfied for class template 'r7' [with T = G]}}

template<typename T> struct H;

template<typename T> requires requires { typename H<T>; }
struct r8 {};

using r8i = r8<int>;

template<typename T> struct I { struct incomplete; }; // expected-note{{member is declared here}}

static_assert(!requires { I<int>::incomplete::inner; }); // expected-error{{implicit instantiation of undefined member 'I<int>::incomplete'}}

template<typename T> requires requires { typename I<T>::incomplete::inner; } // expected-note{{because 'typename I<T>::incomplete::inner' would be invalid: implicit instantiation of undefined member 'I<int>::incomplete'}}
struct r9 {};

using r9i = r9<int>; // expected-error{{constraints not satisfied for class template 'r9' [with T = int]}}

namespace ns3 {
  struct X { }; // expected-note 2{{candidate found by name lookup is 'ns3::X'}}
}

struct X { using inner = int; }; // expected-note 2{{candidate found by name lookup is 'X'}}

using namespace ns3;
static_assert(requires { typename X; }); // expected-error{{reference to 'X' is ambiguous}}
static_assert(requires { typename X::inner; }); // expected-error{{reference to 'X' is ambiguous}}
// expected-error@-1{{unknown type name 'inner'}}

// naming a type template specialization in a type requirement does not require
// it to be complete and should not care about partial specializations.

template<typename T>
struct Z;

template<typename T> requires (sizeof(T) >= 1)
struct Z<T> {}; // expected-note{{partial specialization matches [with T = int]}}

template<typename T> requires (sizeof(T) <= 4)
struct Z<T> {}; // expected-note{{partial specialization matches [with T = int]}}

Z<int> x; // expected-error{{ambiguous partial specializations of 'Z<int>'}}

static_assert(requires { typename Z<int>; });

// C++ [expr.prim.req.type] Example
namespace std_example {
  template<typename T, typename T::type = 0> struct S;
  // expected-note@-1 {{because 'typename S<T>' would be invalid: no type named 'type' in 'std_example::has_inner}}
  template<typename T> using Ref = T&; // expected-note{{because 'typename Ref<T>' would be invalid: cannot form a reference to 'void'}}
  template<typename T> concept C1 =
    requires {
      typename T::inner;
      // expected-note@-1 {{because 'typename T::inner' would be invalid: type 'int' cannot be used prior to '::' because it has no members}}
      // expected-note@-2 {{because 'typename T::inner' would be invalid: no type named 'inner' in 'std_example::has_type'}}
    };
  template<typename T> concept C2 = requires { typename S<T>; };
  template<typename T> concept C3 = requires { typename Ref<T>; };

  struct has_inner { using inner = int;};
  struct has_type { using type = int; };
  struct has_inner_and_type { using inner = int; using type = int; };

  static_assert(C1<has_inner_and_type> && C2<has_inner_and_type> && C3<has_inner_and_type>);
  template<C1 T> struct C1_check {};
  // expected-note@-1 {{because 'int' does not satisfy 'C1'}}
  // expected-note@-2 {{because 'std_example::has_type' does not satisfy 'C1'}}
  template<C2 T> struct C2_check {};
  // expected-note@-1 {{because 'std_example::has_inner' does not satisfy 'C2'}}
  template<C3 T> struct C3_check {};
  // expected-note@-1 {{because 'void' does not satisfy 'C3'}}
  using c1 = C1_check<int>; // expected-error{{constraints not satisfied for class template 'C1_check' [with T = int]}}
  using c2 = C1_check<has_type>; // expected-error{{constraints not satisfied for class template 'C1_check' [with T = std_example::has_type]}}
  using c3 = C2_check<has_inner>; // expected-error{{constraints not satisfied for class template 'C2_check' [with T = std_example::has_inner]}}
  using c4 = C3_check<void>; // expected-error{{constraints not satisfied for class template 'C3_check' [with T = void]}}
}

namespace PR48656 {

template <typename T> concept C = requires { requires requires { T::a; }; };
// expected-note@-1 {{because 'T::a' would be invalid: no member named 'a' in 'PR48656::T1'}}

template <C...> struct A {};
// expected-note@-1 {{because 'PR48656::T1' does not satisfy 'C'}}

struct T1 {};
template struct A<T1>; // expected-error {{constraints not satisfied for class template 'A' [with $0 = <PR48656::T1>]}}

struct T2 { static constexpr bool a = false; };
template struct A<T2>;

template <typename T> struct T3 {
  static void m(auto) requires requires { T::fail; } {}
  // expected-note@-1 {{constraints not satisfied}}
  // expected-note@-2 {{type 'int' cannot be used prior to '::'}}
};
template <typename... Args> void t3(Args... args) { (..., T3<int>::m(args)); }
// expected-error@-1 {{no matching function for call to 'm'}}

template void t3<int>(int); // expected-note {{requested here}}

} // namespace PR48656