llvm-project/clang/test/SemaCXX/cxx1z-class-template-argument-deduction.cpp

// RUN: %clang_cc1 -std=c++1z -verify %s

namespace std {
  using size_t = decltype(sizeof(0));
  template<typename T> struct initializer_list {
    const T *p;
    size_t n;
    initializer_list();
  };
  // FIXME: This should probably not be necessary.
  template<typename T> initializer_list(initializer_list<T>) -> initializer_list<T>;
}

template<typename T> constexpr bool has_type(...) { return false; }
template<typename T> constexpr bool has_type(T) { return true; }

std::initializer_list il = {1, 2, 3, 4, 5};

template<typename T> struct vector {
  template<typename Iter> vector(Iter, Iter);
  vector(std::initializer_list<T>);
};

template<typename T> vector(std::initializer_list<T>) -> vector<T>;
template<typename Iter> explicit vector(Iter, Iter) -> vector<typename Iter::value_type>;
template<typename T> explicit vector(std::size_t, T) -> vector<T>;

vector v1 = {1, 2, 3, 4};
static_assert(has_type<vector<int>>(v1));

struct iter { typedef char value_type; } it, end;
vector v2(it, end);
static_assert(has_type<vector<char>>(v2));

vector v3(5, 5);
static_assert(has_type<vector<int>>(v3));

vector v4 = {it, end};
static_assert(has_type<vector<iter>>(v4));

vector v5{it, end};
static_assert(has_type<vector<iter>>(v5));

template<typename ...T> struct tuple { tuple(T...); };
template<typename ...T> explicit tuple(T ...t) -> tuple<T...>; // expected-note {{declared}}
// FIXME: Remove
template<typename ...T> tuple(tuple<T...>) -> tuple<T...>;

const int n = 4;
tuple ta = tuple{1, 'a', "foo", n};
static_assert(has_type<tuple<int, char, const char*, int>>(ta));

tuple tb{ta};
static_assert(has_type<tuple<int, char, const char*, int>>(tb));

// FIXME: This should be tuple<tuple<...>>; when the above guide is removed.
tuple tc = {ta};
static_assert(has_type<tuple<int, char, const char*, int>>(tc));

tuple td = {1, 2, 3}; // expected-error {{selected an explicit deduction guide}}
static_assert(has_type<tuple<int, char, const char*, int>>(td));

// FIXME: This is a GCC extension for now; if CWG don't allow this, at least
// add a warning for it.
namespace new_expr {
  tuple<int> *p = new tuple{0};
  tuple<float, float> *q = new tuple(1.0f, 2.0f);
}

namespace ambiguity {
  template<typename T> struct A {};
  A(unsigned short) -> A<int>; // expected-note {{candidate}}
  A(short) -> A<int>; // expected-note {{candidate}}
  A a = 0; // expected-error {{ambiguous deduction for template arguments of 'A'}}

  template<typename T> struct B {};
  template<typename T> B(T(&)(int)) -> B<int>; // expected-note {{candidate function [with T = int]}}
  template<typename T> B(int(&)(T)) -> B<int>; // expected-note {{candidate function [with T = int]}}
  int f(int);
  B b = f; // expected-error {{ambiguous deduction for template arguments of 'B'}}
}

// FIXME: Revisit this once CWG decides if attributes, and [[deprecated]] in
// particular, should be permitted here.
namespace deprecated {
  template<typename T> struct A { A(int); };
  [[deprecated]] A(int) -> A<void>; // expected-note {{marked deprecated here}}
  A a = 0; // expected-warning {{'<deduction guide for A>' is deprecated}}
}

namespace dependent {
  template<template<typename...> typename A> decltype(auto) a = A{1, 2, 3};
  static_assert(has_type<vector<int>>(a<vector>));
  static_assert(has_type<tuple<int, int, int>>(a<tuple>));

  struct B {
    template<typename T> struct X { X(T); };
    X(int) -> X<int>;
    template<typename T> using Y = X<T>; // expected-note {{template}}
  };
  template<typename T> void f() {
    typename T::X tx = 0;
    typename T::Y ty = 0; // expected-error {{alias template 'Y' requires template arguments; argument deduction only allowed for class templates}}
  }
  template void f<B>(); // expected-note {{in instantiation of}}

  template<typename T> struct C { C(T); };
  template<typename T> C(T) -> C<T>;
  template<typename T> void g(T a) {
    C b = 0;
    C c = a;
    using U = decltype(b); // expected-note {{previous}}
    using U = decltype(c); // expected-error {{different types ('C<const char *>' vs 'C<int>')}}
  }
  void h() {
    g(0);
    g("foo"); // expected-note {{instantiation of}}
  }
}

namespace look_into_current_instantiation {
  template<typename U> struct Q {};
  template<typename T> struct A {
    using U = T;
    template<typename> using V = Q<A<T>::U>;
    template<typename W = int> A(V<W>);
  };
  A a = Q<float>(); // ok, can look through class-scope typedefs and alias
                    // templates, and members of the current instantiation
  A<float> &r = a;

  template<typename T> struct B { // expected-note {{could not match 'B<T>' against 'int'}}
    struct X {
      typedef T type;
    };
    B(typename X::type); // expected-note {{couldn't infer template argument 'T'}}
  };
  B b = 0; // expected-error {{no viable}}

  // We should have a substitution failure in the immediate context of
  // deduction when using the C(T, U) constructor (probably; core wording
  // unclear).
  template<typename T> struct C {
    using U = typename T::type;
    C(T, U);
  };

  struct R { R(int); typedef R type; };
  C(...) -> C<R>;

  C c = {1, 2};
}

namespace nondeducible {
  template<typename A, typename B> struct X {};

  template<typename A> // expected-note {{non-deducible template parameter 'A'}}
  X() -> X<A, int>; // expected-error {{deduction guide template contains a template parameter that cannot be deduced}}

  template<typename A> // expected-note {{non-deducible template parameter 'A'}}
  X(typename X<A, int>::type) -> X<A, int>; // expected-error {{deduction guide template contains a template parameter that cannot be deduced}}

  template<typename A = int,
           typename B> // expected-note {{non-deducible template parameter 'B'}}
  X(int) -> X<A, B>; // expected-error {{deduction guide template contains a template parameter that cannot be deduced}}

  template<typename A = int,
           typename ...B>
  X(float) -> X<A, B...>; // ok
}

namespace default_args_from_ctor {
  template <class A> struct S { S(A = 0) {} };
  S s(0);

  template <class A> struct T { template<typename B> T(A = 0, B = 0) {} };
  T t(0, 0);
}

namespace transform_params {
  template<typename T, T N, template<T (*v)[N]> typename U, T (*X)[N]>
  struct A { // expected-note 2{{candidate}}
    template<typename V, V M, V (*Y)[M], template<V (*v)[M]> typename W>
    A(U<X>, W<Y>); // expected-note {{[with V = int, M = 12, Y = &transform_params::n]}}

    static constexpr T v = N;
  };

  int n[12];
  template<int (*)[12]> struct Q {};
  Q<&n> qn;
  // FIXME: The class template argument deduction result here is correct, but
  // we incorrectly fail to deduce arguments for the constructor!
  A a(qn, qn); // expected-error {{no matching constructor for initialization of 'transform_params::A<int, 12, Q, &transform_params::n>'}}
  static_assert(a.v == 12);

  template<typename ...T> struct B {
    template<T ...V> B(const T (&...p)[V]) {
      constexpr int Vs[] = {V...};
      static_assert(Vs[0] == 3 && Vs[1] == 4 && Vs[2] == 4);
    }
    static constexpr int (*p)(T...) = (int(*)(int, char, char))nullptr;
  };
  B b({1, 2, 3}, "foo", {'x', 'y', 'z', 'w'}); // ok

  // This should be accepted once -std=c++1z implies
  // -frelaxed-template-template-args. Without that, a template template
  // parameter 'template<int, int, int> typename' cannot bind to a template
  // template argument 'template<int...> typename'.
  template<typename ...T> struct C { // expected-note {{candidate}}
    template<T ...V, template<T...> typename X>
      C(X<V...>); // expected-note {{substitution failure [with T = <int, int, int>, V = <0, 1, 2>]}}
  };
  template<int...> struct Y {};
  C c(Y<0, 1, 2>{}); // expected-error {{no viable constructor or deduction guide}}

  template<typename ...T> struct D {
    template<T ...V> D(Y<V...>);
  };
  D d(Y<0, 1, 2>{});
}