xref: /llvm-project/clang/test/SemaTemplate/deduction.cpp (revision e9e1a72c22181993edf5bd0b660538081c2cdfb5)

// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++17
// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++23

// Template argument deduction with template template parameters.
template<typename T, template<T> class A>
struct X0 {
  static const unsigned value = 0;
};

template<template<int> class A>
struct X0<int, A> {
  static const unsigned value = 1;
};

template<class T>
struct type_identity {
    using type = T;
};

template<class T>
using type_identity_t = typename type_identity<T>::type;

template <typename... T>
struct args_tag {};

template<int> struct X0i;
template<long> struct X0l;
int array_x0a[X0<long, X0l>::value == 0? 1 : -1];
int array_x0b[X0<int, X0i>::value == 1? 1 : -1];

template<typename T, typename U>
struct is_same {
  static const bool value = false;
};

template<typename T>
struct is_same<T, T> {
  static const bool value = true;
};

template<typename T> struct allocator { };
template<typename T, typename Alloc = allocator<T> > struct vector {};

// Fun with meta-lambdas!
struct _1 {};
struct _2 {};

// Replaces all occurrences of _1 with Arg1 and _2 with Arg2 in T.
template<typename T, typename Arg1, typename Arg2>
struct Replace {
  typedef T type;
};

// Replacement of the whole type.
template<typename Arg1, typename Arg2>
struct Replace<_1, Arg1, Arg2> {
  typedef Arg1 type;
};

template<typename Arg1, typename Arg2>
struct Replace<_2, Arg1, Arg2> {
  typedef Arg2 type;
};

// Replacement through cv-qualifiers
template<typename T, typename Arg1, typename Arg2>
struct Replace<const T, Arg1, Arg2> {
  typedef typename Replace<T, Arg1, Arg2>::type const type;
};

// Replacement of templates
template<template<typename> class TT, typename T1, typename Arg1, typename Arg2>
struct Replace<TT<T1>, Arg1, Arg2> {
  typedef TT<typename Replace<T1, Arg1, Arg2>::type> type;
};

template<template<typename, typename> class TT, typename T1, typename T2,
         typename Arg1, typename Arg2>
struct Replace<TT<T1, T2>, Arg1, Arg2> {
  typedef TT<typename Replace<T1, Arg1, Arg2>::type,
             typename Replace<T2, Arg1, Arg2>::type> type;
};

// Just for kicks...
template<template<typename, typename> class TT, typename T1,
         typename Arg1, typename Arg2>
struct Replace<TT<T1, _2>, Arg1, Arg2> {
  typedef TT<typename Replace<T1, Arg1, Arg2>::type, Arg2> type;
};

int array0[is_same<Replace<_1, int, float>::type, int>::value? 1 : -1];
int array1[is_same<Replace<const _1, int, float>::type, const int>::value? 1 : -1];
int array2[is_same<Replace<vector<_1>, int, float>::type, vector<int> >::value? 1 : -1];
int array3[is_same<Replace<vector<const _1>, int, float>::type, vector<const int> >::value? 1 : -1];
int array4[is_same<Replace<vector<int, _2>, double, float>::type, vector<int, float> >::value? 1 : -1];

// PR5911
template <typename T, int N> void f(const T (&a)[N]);
int iarr[] = { 1 };
void test_PR5911() { f(iarr); }

// Must not examine base classes of incomplete type during template argument
// deduction.
namespace PR6257 {
  template <typename T> struct X {
    template <typename U> X(const X<U>& u);
  };
  struct A;
  void f(A& a);
  void f(const X<A>& a);
  void test(A& a) { (void)f(a); }
}

// PR7463
namespace PR7463 {
  const int f ();
  template <typename T_> void g (T_&); // expected-note{{T_ = int}}
  void h (void) { g(f()); } // expected-error{{no matching function for call}}
}

namespace test0 {
  template <class T> void make(const T *(*fn)()); // expected-note {{candidate template ignored: cannot deduce a type for 'T' that would make 'const T' equal 'char'}}
  char *char_maker();
  void test() {
    make(char_maker); // expected-error {{no matching function for call to 'make'}}
  }
}

namespace test1 {
  template<typename T> void foo(const T a[3][3]);
  void test() {
    int a[3][3];
    foo(a);
  }
}

// PR7708
namespace test2 {
  template<typename T> struct Const { typedef void const type; };

  template<typename T> void f(T, typename Const<T>::type*);
  template<typename T> void f(T, void const *);

  void test() {
    void *p = 0;
    f(0, p);
  }
}

namespace test3 {
  struct Foo {
    template <void F(char)> static inline void foo();
  };

  class Bar {
    template<typename T> static inline void wobble(T ch);

  public:
    static void madness() {
      Foo::foo<wobble<char> >();
    }
  };
}

namespace test4 {

template <class> struct a { using b = const float; };
template <class c> using d = typename a<c>::b;

template <class c> void e(d<c> *, c) {}
template void e(const float *, int);

} // namespace test4

namespace test5 {

template <bool, int = 0> class a {};
template <class b> void c(b, b);
template <bool b> void c(a<b>, a<b>);
void d() { c(a<true>(), a<true>()); }

} // namespace test5

namespace test6 {
template <class A1> using A = A1;

template <class F1, class... F2> void f(A<F1>, F1, F2...);
template <class F3> void f(A<F3>, F3);

void g() { f(A<int>{}, int{}); }
} // namespace test6

namespace test7 {
template <class T> void f(T&, T&);
template <class T, unsigned long S> void f(T (&)[S], T (&)[S]);

void g() {
  int i[3], j[3];
  f(i, j);
}
} // namespace test7

namespace test8 {
template <class T> void foo(T);
void test(int a) { // expected-note {{declared here}}
    char n[a]; // expected-warning {{variable length arrays in C++ are a Clang extension}} \
                  expected-note {{function parameter 'a' with unknown value cannot be used in a constant expression}}
    foo(n);
}
} // namespace test8

// Verify that we can deduce enum-typed arguments correctly.
namespace test14 {
  enum E { E0, E1 };
  template <E> struct A {};
  template <E e> void foo(const A<e> &a) {}

  void test() {
    A<E0> a;
    foo(a);
  }
}

namespace PR21536 {
  template<typename ...T> struct X;
  template<typename A, typename ...B> struct S {
    static_assert(sizeof...(B) == 1, "");
    void f() {
      using T = A;
      using T = int;

      using U = X<B...>;
      using U = X<int>;
    }
  };
  template<typename ...T> void f(S<T...>);
  void g() { f(S<int, int>()); }
}

namespace PR19372 {
  template <template<typename...> class C, typename ...Us> struct BindBack {
    template <typename ...Ts> using apply = C<Ts..., Us...>;
  };
  template <typename, typename...> struct Y;
  template <typename ...Ts> using Z = Y<Ts...>;

  using T = BindBack<Z, int>::apply<>;
  using T = Z<int>;

  using U = BindBack<Z, int, int>::apply<char>;
  using U = Z<char, int, int>;

  namespace BetterReduction {
    template<typename ...> struct S;
    template<typename ...A> using X = S<A...>; // expected-note {{parameter}}
    template<typename ...A> using Y = X<A..., A...>;
    template<typename ...A> using Z = X<A..., 1, 2, 3>; // expected-error {{must be a type}}

    using T = Y<int>;
    using T = S<int, int>;
  }
}

namespace PR18645 {
  template<typename F> F Quux(F &&f);
  auto Baz = Quux(Quux<float>);
}

namespace NonDeducedNestedNameSpecifier {
  template<typename T> struct A {
    template<typename U> struct B {
      B(int) {}
    };
  };

  template<typename T> int f(A<T>, typename A<T>::template B<T>);
  int k = f(A<int>(), 0);
}

namespace PR27601_RecursivelyInheritedBaseSpecializationsDeductionAmbiguity {
namespace ns1 {

template<class...> struct B { };
template<class H, class ... Ts> struct B<H, Ts...> : B<> { };
template<class ... Ts> struct D : B<Ts...> { };

template<class T, class ... Ts> void f(B<T, Ts...> &) { }

int main() {
  D<int, char> d;
  f<int>(d);
}
} //end ns1

namespace ns2 {

template <int i, typename... Es> struct tup_impl;

template <int i> struct tup_impl<i> {}; // empty tail

template <int i, typename Head, typename... Tail>
struct tup_impl<i, Head, Tail...> : tup_impl<i + 1, Tail...> {
  using value_type = Head;
  Head head;
};

template <typename... Es> struct tup : tup_impl<0, Es...> {};

template <typename Head, int i, typename... Tail>
Head &get_helper(tup_impl<i, Head, Tail...> &t) {
  return t.head;
}

template <typename Head, int i, typename... Tail>
Head const &get_helper(tup_impl<i, Head, Tail...> const &t) {
  return t.head;
}

int main() {
  tup<int, double, char> t;
  get_helper<double>(t);
  return 0;
}
} // end ns2
}

namespace multiple_deduction_different_type {
  template<typename T, T v> struct X {};
  template<template<typename T, T> class X, typename T, typename U, int N>
    void f(X<T, N>, X<U, N>) {} // expected-note 2{{values of conflicting types}}
  template<template<typename T, T> class X, typename T, typename U, const int *N>
    void g(X<T, N>, X<U, N>) {} // expected-note 0-2{{values of conflicting types}}
  int n;
  void h() {
    f(X<int, 1+1>(), X<unsigned int, 3-1>()); // expected-error {{no matching function}}
    f(X<unsigned int, 1+1>(), X<int, 3-1>()); // expected-error {{no matching function}}
#if __cplusplus > 201402L
    g(X<const int*, &n>(), X<int*, &n + 1 - 1>()); // expected-error {{no matching function}}
    g(X<int*, &n>(), X<const int*, &n + 1 - 1>()); // expected-error {{no matching function}}
#endif
  }

  template<template<typename T, T> class X, typename T, typename U, T N>
    void x(X<T, N>, int(*)[N], X<U, N>) {} // expected-note 1+{{candidate}}
  template<template<typename T, T> class X, typename T, typename U, T N>
    void x(int(*)[N], X<T, N>, X<U, N>) {} // expected-note 1+{{candidate}}
  int arr[3];
  void y() {
    x(X<int, 3>(), &arr, X<int, 3>());
    x(&arr, X<int, 3>(), X<int, 3>());

    x(X<int, 3>(), &arr, X<char, 3>()); // expected-error {{no matching function}}
    x(&arr, X<int, 3>(), X<char, 3>()); // expected-error {{no matching function}}

    x(X<char, 3>(), &arr, X<char, 3>());
    x(&arr, X<char, 3>(), X<char, 3>());
  }
}

namespace nullptr_deduction {
  using nullptr_t = decltype(nullptr);

  template<typename T, T v> struct X {};
  template<typename T, T v> void f(X<T, v>) {
    static_assert(!v, ""); // expected-warning 2{{implicit conversion of nullptr constant to 'bool'}}
  }
  void g() {
    f(X<int*, nullptr>()); // expected-note {{instantiation of}}
    f(X<nullptr_t, nullptr>()); // expected-note {{instantiation of}}
  }

  template<template<typename T, T> class X, typename T, int *P>
    void f0(X<T, P>) {} // expected-note {{deduced non-type template argument does not have the same type as the corresponding template parameter ('std::nullptr_t' vs 'int *')}}
  void h0() {
    f0(X<int*, nullptr>());
    f0(X<nullptr_t, nullptr>()); // expected-error {{no matching function}}
  }

  template<template<typename T, T> class X, typename T, typename U, int *P>
    void f1(X<T, P>, X<U, P>) {} // expected-note 2{{values of conflicting types}}
  void h() {
    f1(X<int*, nullptr>(), X<nullptr_t, nullptr>()); // expected-error {{no matching function}}
    f1(X<nullptr_t, nullptr>(), X<int*, nullptr>()); // expected-error {{no matching function}}
  }

  template<template<typename T, T> class X, typename T, typename U, nullptr_t P>
    void f2(X<T, P>, X<U, P>) {} // expected-note 2{{values of conflicting types}}
  void i() {
    f2(X<int*, nullptr>(), X<nullptr_t, nullptr>()); // expected-error {{no matching function}}
    f2(X<nullptr_t, nullptr>(), X<int*, nullptr>()); // expected-error {{no matching function}}
  }
}

namespace member_pointer {
  struct A { void f(int); };
  template<typename T, void (A::*F)(T)> struct B;
  template<typename T> struct C;
  template<typename T, void (A::*F)(T)> struct C<B<T, F>> {
    C() { A a; T t; (a.*F)(t); }
  };
  C<B<int, &A::f>> c;
}

namespace deduction_substitution_failure {
  template<typename T> struct Fail { typedef typename T::error error; }; // expected-error 2{{prior to '::'}}

  template<typename T, typename U> struct A {};
  template<typename T> struct A<T, typename Fail<T>::error> {}; // expected-note {{instantiation of}}
  A<int, int> ai; // expected-note {{during template argument deduction for class template partial specialization 'A<T, typename Fail<T>::error>' [with T = int]}} expected-note {{in instantiation of template class 'deduction_substitution_failure::A<int, int>'}}

  template<typename T, typename U> int B; // expected-warning 0-1 {{extension}}
  template<typename T> int B<T, typename Fail<T>::error> {}; // expected-note {{instantiation of}}
  int bi = B<char, char>; // expected-note {{during template argument deduction for variable template partial specialization 'B<T, typename Fail<T>::error>' [with T = char]}}
}

namespace deduce_pack_from_argument {
  template <typename... T>
  void separator(args_tag<T...>, T..., int, T...) {}
  template <typename... T>
  void separator_dependent(args_tag<T...>, type_identity_t<T>..., int, type_identity_t<T>...) {}
  template <typename... Y, typename... T>
  void separator_multiple_parameters(args_tag<Y...>, args_tag<T...>, type_identity_t<T>..., int mid, type_identity_t<T>...) {}

  void test_separator() {
    separator(args_tag<int, int>{}, 4, 8, 42, 16, 25);
    separator(args_tag<>{}, 42);
    separator_dependent(args_tag<int, int>{}, 4, 8, 42, 16, 25);
    separator_dependent(args_tag<>{}, 42);
    separator_multiple_parameters(args_tag<const int, const int>{}, args_tag<int, int>{}, 8, 9, 15, 16, 23);
  }

  template <typename... Y, typename... T> void no_separator(args_tag<T...>, T..., T...) {}
  template <typename... Y, typename... T>
  void no_separator_dependent(args_tag<Y...>, args_tag<T...>, type_identity_t<T>..., type_identity_t<T>...) {}

  void test_no_separator() {
    no_separator(args_tag<int, int>{}, 1, 2, 3, 4);
    no_separator(args_tag<>{});
    no_separator_dependent(args_tag<const int, const int>{}, args_tag<int, int>{}, 8, 9, 15, 16);
    no_separator_dependent(args_tag<>{}, args_tag<>{});
  }
}

namespace deduction_after_explicit_pack {
  template<typename ...T, typename U> int *f(T ...t, int &r, U *u) {
    return u;
  }
  template<typename U, typename ...T> int *g(T ...t, int &r, U *u) {
    return u;
  }
  void h(float a, double b, int c) {
    f<float&, double&>(a, b, c, &c); // ok
    g<int, float&, double&>(a, b, c, &c); // ok
  }

  template<class... ExtraArgs>
  int test(ExtraArgs..., unsigned vla_size, const char *input);
  int n = test(0, "");

  template <typename... T> void i(T..., int, T..., ...); // expected-note 5{{deduced packs of different lengths}}
  void j() {
    i(0);
    i(0, 1); // expected-error {{no match}}
    i(0, 1, 2); // expected-error {{no match}}
    i<>(0);
    i<>(0, 1); // expected-error {{no match}}
    i<>(0, 1, 2); // expected-error {{no match}}
    i<int, int>(0, 1, 2, 3, 4);
    i<int, int>(0, 1, 2, 3, 4, 5); // expected-error {{no match}}
  }

  // GCC alarmingly accepts this by deducing T={int} by matching the second
  // parameter against the first argument, then passing the first argument
  // through the first parameter.
  template<typename... T> struct X { X(int); operator int(); };
  template<typename... T> void p(T..., X<T...>, ...); // expected-note {{deduced packs of different lengths for parameter 'T' (<> vs. <int>)}}
  void q() { p(X<int>(0), 0); } // expected-error {{no match}}

  struct A {
    template <typename T> void f(T, void *, int = 0); // expected-note 2{{no known conversion from 'double' to 'void *' for 2nd argument}}
    void f(); // expected-note 2{{requires 0}}

    template <typename T> static void g(T, void *, int = 0); // expected-note 2{{no known conversion from 'double' to 'void *' for 2nd argument}}
    void g(); // expected-note 2{{requires 0}}

    void h() {
      f(1.0, 2.0); // expected-error {{no match}}
      g(1.0, 2.0); // expected-error {{no match}}
    }
  };
  void f(A a) {
    a.f(1.0, 2.0); // expected-error {{no match}}
    a.g(1.0, 2.0); // expected-error {{no match}}
  }
}

namespace overload_vs_pack {
  void f(int);
  void f(float);
  void g(double);

  template<typename ...T> struct X {};
  template<typename ...T> void x(T...);

  template<typename ...T> struct Y { typedef int type(typename T::error...); };
  template<> struct Y<int, float, double> { typedef int type; };

  template<typename ...T> typename Y<T...>::type g1(X<T...>, void (*...fns)(T)); // expected-note {{deduced conflicting types for parameter 'T' (<int, float> vs. <(no value), double>)}}
  template<typename ...T> typename Y<T...>::type g2(void(*)(T...), void (*...fns)(T)); // expected-note {{deduced conflicting types for parameter 'T' (<int, float> vs. <(no value), double>)}}

  template<typename T> int &h1(decltype(g1(X<int, float, T>(), f, f, g)) *p);
  template<typename T> float &h1(...);

  template<typename T> int &h2(decltype(g2(x<int, float, T>, f, f, g)) *p);
  template<typename T> float &h2(...);

  int n1 = g1(X<int, float>(), f, g); // expected-error {{no matching function}}
  int n2 = g2(x<int, float>, f, g); // expected-error {{no matching function}}

  int &a1 = h1<double>(0); // ok, skip deduction for 'f's, deduce matching value from 'g'
  int &a2 = h2<double>(0);

  float &b1 = h1<float>(0); // deduce mismatching value from 'g', so we do not trigger instantiation of Y
  float &b2 = h2<float>(0);

  template<typename ...T> int partial_deduction(void (*...f)(T)); // expected-note {{deduced incomplete pack <(no value), double> for template parameter 'T'}}
  int pd1 = partial_deduction(f, g); // expected-error {{no matching function}}

  template<typename ...T> int partial_deduction_2(void (*...f)(T), ...); // expected-note {{deduced incomplete pack <(no value), double> for template parameter 'T'}}
  int pd2 = partial_deduction_2(f, g); // expected-error {{no matching function}}

  namespace cwg_example {
    void f(char, char);
    void f(int, int);
    void x(int, char);

    template<typename T, typename ...U> void j(void(*)(U...), void (*...fns)(T, U));
    void test() { j(x, f, x); }
  }
}

namespace b29946541 {
  template<typename> class A {};
  template<typename T, typename U, template<typename, typename> class C>
  void f(C<T, U>); // expected-note {{failed template argument deduction}}
  void g(A<int> a) { f(a); } // expected-error {{no match}}
}

namespace deduction_from_empty_list {
  template<int M, int N = 5> void f(int (&&)[N], int (&&)[N]) { // expected-note {{1 vs. 2}}
    static_assert(M == N, "");
  }

  void test() {
    f<5>({}, {});
    f<1>({}, {0});
    f<1>({0}, {});
    f<1>({0}, {0});
    f<1>({0}, {0, 1}); // expected-error {{no matching}}
  }
}

namespace check_extended_pack {
  template<typename T> struct X { typedef int type; };
  template<typename ...T> void f(typename X<T>::type...);
  template<typename T> void f(T, int, int);
  void g() {
    f<int>(0, 0, 0);
  }

  template<int, int*> struct Y {};
  template<int ...N> void g(Y<N...>); // expected-note {{deduced non-type template argument does not have the same type as the corresponding template parameter ('int *' vs 'int')}}
  int n;
  void h() { g<0>(Y<0, &n>()); } // expected-error {{no matching function}}
}

namespace dependent_template_template_param_non_type_param_type {
  template<int N> struct A {
    template<typename V = int, V M = 12, V (*Y)[M], template<V (*v)[M]> class W>
    A(W<Y>);
  };

  int n[12];
  template<int (*)[12]> struct Q {};
  Q<&n> qn;
  A<0> a(qn);
}

namespace dependent_list_deduction {
  template<typename T, T V> void a(const int (&)[V]) {
    static_assert(is_same<T, decltype(sizeof(0))>::value, "");
    static_assert(V == 3, "");
  }
  template<typename T, T V> void b(const T (&)[V]) {
    static_assert(is_same<T, int>::value, "");
    static_assert(V == 3, "");
  }
  template<typename T, T V> void c(const T (&)[V]) {
    static_assert(is_same<T, decltype(sizeof(0))>::value, "");
    static_assert(V == 3, "");
  }
  void d() {
    a({1, 2, 3});
#if __cplusplus <= 201402L
    // expected-error@-2 {{no match}} expected-note@-15 {{couldn't infer template argument 'T'}}
#endif
    b({1, 2, 3});
    c({{}, {}, {}});
#if __cplusplus <= 201402L
    // expected-error@-2 {{no match}} expected-note@-12 {{couldn't infer template argument 'T'}}
#endif
  }

  template<typename ...T> struct X;
  template<int ...T> struct Y;
  template<typename ...T, T ...V> void f(const T (&...p)[V]) {
    static_assert(is_same<X<T...>, X<int, char, char>>::value, "");
    static_assert(is_same<Y<V...>, Y<3, 2, 4>>::value, "");
  }
  template<typename ...T, T ...V> void g(const T (&...p)[V]) {
    static_assert(is_same<X<T...>, X<int, decltype(sizeof(0))>>::value, "");
    static_assert(is_same<Y<V...>, Y<2, 3>>::value, "");
  }
  void h() {
    f({1, 2, 3}, {'a', 'b'}, "foo");
    g({1, 2}, {{}, {}, {}});
#if __cplusplus <= 201402
    // expected-error@-2 {{no match}}
    // expected-note@-9 {{deduced incomplete pack}}
    // We deduce V$1 = (size_t)3, which in C++1z also deduces T$1 = size_t.
#endif
  }
}

namespace designators {
  template<typename T, int N> constexpr int f(T (&&)[N]) { return N; } // expected-note 2{{couldn't infer template argument 'T'}}
  static_assert(f({1, 2, [20] = 3}) == 3, ""); // expected-error {{no matching function}} expected-warning 2{{C99}} expected-note {{}}

  static_assert(f({.a = 1, .b = 2}) == 3, ""); // expected-error {{no matching function}}
}

namespace nested_packs {
  template<typename ...T, typename ...U> void f(T (*...f)(U...)); // expected-note {{deduced packs of different lengths for parameter 'U' (<> vs. <int>)}}
  void g() { f(g); f(g, g); f(g, g, g); }
  void h(int) { f(h); f(h, h); f(h, h, h); }
  void i() { f(g, h); } // expected-error {{no matching function}}

#if __cplusplus >= 201703L
  template<auto ...A> struct Q {};
  template<typename ...T, T ...A, T ...B> void q(Q<A...>, Q<B...>); // #q
  void qt(Q<> q0, Q<1, 2> qii, Q<1, 2, 3> qiii) {
    q(q0, q0);
    q(qii, qii);
    q(qii, qiii); // expected-error {{no match}} expected-note@#q {{deduced packs of different lengths for parameter 'T' (<int, int> vs. <int, int, int>)}}
    q(q0, qiii); // expected-error {{no match}} expected-note@#q {{deduced packs of different lengths for parameter 'T' (<> vs. <int, int, int>)}}
  }
#endif
}

namespace PR44890 {
  template<typename ...Ts>
    struct tuple {};

  template<int I, typename ...Ts>
    int get0(const tuple<Ts...> &t) { return 0; }

  template<typename ...Ts> struct tuple_wrapper : tuple<Ts...> {
    template<int I> int get() { return get0<0, Ts...>(*this); }
  };

  int f() {
    tuple_wrapper<int> w;
    return w.get<0>();
  }
}

namespace merge_size_only_deductions {
#if __cplusplus >= 201703L
  // Based on a testcase by Hubert Tong.
  template<typename ...> struct X {};
  template<auto ...> struct Y {};
  template<typename T> struct id { using Type = T; };

  template<typename ...T, typename T::Type ...V>
    int f(X<char [V] ...>, Y<V ...>, X<T ...>);

  using size_t = __SIZE_TYPE__;
  int a = f(X<char [1], char [2]>(), Y<(size_t)1, (size_t)2>(), X<id<size_t>, id<size_t>>());
  int b = f(X<char [1], char [2]>(), Y<1, 2>(), X<id<int>, id<int>>());
#endif
}

namespace PR49724 {
  struct A;
  template<int A::*> class X {};
  template<int A::*P> void f(X<P>);
  void g(X<nullptr> x) { f(x); }

  template<void (A::*)()> class Y {};
  template<void (A::*P)()> void f(Y<P>);
  void g(Y<nullptr> y) { f(y); }
}

namespace sugared_deduction {
using Int = int;

template <class T, int C> void f1(T(&)[C], T(&)[C+1]);
// expected-note@-1 {{candidate template ignored: deduced type 'int[3]' of 2nd parameter does not match adjusted type 'Int[2]' (aka 'int[2]') of argument [with T = Int, C = 2]}}

void t1() {
  Int a[2], b[2];
  f1(a, b); // expected-error {{no matching function for call to 'f1'}}
}

#if defined(__cpp_concepts)
template <class T> void f2() requires false {}
// expected-note@-1 {{candidate template ignored: constraints not satisfied [with T = Int]}}
// expected-note@-2 {{because 'false' evaluated to false}}

void t2() {
  f2<Int>(); // expected-error {{no matching function for call to 'f2'}}
}
#endif
} // namespace sugared_deduction