[libc++] Recommit r363692 to implement P0608R3

Re-apply the change which was reverted in r363764 as-is after
breakages being resolved.  Thanks Eric Fiselier for working
hard on this.

See also: https://bugs.llvm.org/show_bug.cgi?id=42330

Differential Revision: https://reviews.llvm.org/D44865

llvm-svn: 363993

libcxx/include/variant

@@ -1098,11 +1098,39 @@ struct __overload<> { void operator()() const; };
 template <class _Tp, class... _Types>
 struct __overload<_Tp, _Types...> : __overload<_Types...> {
   using __overload<_Types...>::operator();
-  __identity<_Tp> operator()(_Tp) const;
+
+  static auto __test(_Tp (&&)[1]) -> __identity<_Tp>;
+
+  template <class _Up>
+  auto operator()(_Tp, _Up&& __t) const
+      -> decltype(__test({ _VSTD::forward<_Up>(__t) }));
 };
 
+template <class _Base, class _Tp>
+struct __overload_bool : _Base {
+  using _Base::operator();
+
+  template <class _Up, class _Ap = __uncvref_t<_Up>>
+  auto operator()(bool, _Up&&) const
+      -> enable_if_t<is_same_v<_Ap, bool>, __identity<_Tp>>;
+};
+
+template <class... _Types>
+struct __overload<bool, _Types...>
+    : __overload_bool<__overload<_Types...>, bool> {};
+template <class... _Types>
+struct __overload<bool const, _Types...>
+    : __overload_bool<__overload<_Types...>, bool const> {};
+template <class... _Types>
+struct __overload<bool volatile, _Types...>
+    : __overload_bool<__overload<_Types...>, bool volatile> {};
+template <class... _Types>
+struct __overload<bool const volatile, _Types...>
+    : __overload_bool<__overload<_Types...>, bool const volatile> {};
+
 template <class _Tp, class... _Types>
-using __best_match_t = typename result_of_t<__overload<_Types...>(_Tp&&)>::type;
+using __best_match_t =
+    typename invoke_result_t<__overload<_Types...>, _Tp, _Tp>::type;
 
 } // __variant_detail
 

libcxx/test/std/utilities/variant/variant.variant/variant.assign/T.pass.cpp

@@ -22,6 +22,7 @@
 #include <string>
 #include <type_traits>
 #include <variant>
+#include <memory>
 
 #include "test_macros.h"
 #include "variant_test_helpers.hpp"
@@ -122,7 +123,7 @@ void test_T_assignment_noexcept() {
 
 void test_T_assignment_sfinae() {
   {
-    using V = std::variant<long, unsigned>;
+    using V = std::variant<long, long long>;
     static_assert(!std::is_assignable<V, int>::value, "ambiguous");
   }
   {
@@ -133,6 +134,31 @@ void test_T_assignment_sfinae() {
     using V = std::variant<std::string, void *>;
     static_assert(!std::is_assignable<V, int>::value, "no matching operator=");
   }
+  {
+    using V = std::variant<std::string, float>;
+    static_assert(!std::is_assignable<V, int>::value, "no matching operator=");
+  }
+  {
+    using V = std::variant<std::unique_ptr<int>, bool>;
+    static_assert(!std::is_assignable<V, std::unique_ptr<char>>::value,
+                  "no explicit bool in operator=");
+    struct X {
+      operator void*();
+    };
+    static_assert(!std::is_assignable<V, X>::value,
+                  "no boolean conversion in operator=");
+    static_assert(!std::is_assignable<V, std::false_type>::value,
+                  "no converted to bool in operator=");
+  }
+  {
+    struct X {};
+    struct Y {
+      operator X();
+    };
+    using V = std::variant<X>;
+    static_assert(std::is_assignable<V, Y>::value,
+                  "regression on user-defined conversions in operator=");
+  }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
     using V = std::variant<int, int &&>;
@@ -161,6 +187,37 @@ void test_T_assignment_basic() {
     assert(v.index() == 1);
     assert(std::get<1>(v) == 43);
   }
+  {
+    std::variant<unsigned, long> v;
+    v = 42;
+    assert(v.index() == 1);
+    assert(std::get<1>(v) == 42);
+    v = 43u;
+    assert(v.index() == 0);
+    assert(std::get<0>(v) == 43);
+  }
+  {
+    std::variant<std::string, bool> v = true;
+    v = "bar";
+    assert(v.index() == 0);
+    assert(std::get<0>(v) == "bar");
+  }
+  {
+    std::variant<bool, std::unique_ptr<int>> v;
+    v = nullptr;
+    assert(v.index() == 1);
+    assert(std::get<1>(v) == nullptr);
+  }
+  {
+    std::variant<bool volatile, int> v = 42;
+    v = false;
+    assert(v.index() == 0);
+    assert(!std::get<0>(v));
+    bool lvt = true;
+    v = lvt;
+    assert(v.index() == 0);
+    assert(std::get<0>(v));
+  }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
     using V = std::variant<int &, int &&, long>;

libcxx/test/std/utilities/variant/variant.variant/variant.assign/conv.fail.cpp

@@ -0,0 +1,52 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// template <class T>
+// variant& operator=(T&&) noexcept(see below);
+
+#include <variant>
+#include <string>
+#include <memory>
+
+int main(int, char**)
+{
+  std::variant<int, int> v1;
+  std::variant<long, long long> v2;
+  std::variant<char> v3;
+  v1 = 1; // expected-error {{no viable overloaded '='}}
+  v2 = 1; // expected-error {{no viable overloaded '='}}
+  v3 = 1; // expected-error {{no viable overloaded '='}}
+
+  std::variant<std::string, float> v4;
+  std::variant<std::string, double> v5;
+  std::variant<std::string, bool> v6;
+  v4 = 1; // expected-error {{no viable overloaded '='}}
+  v5 = 1; // expected-error {{no viable overloaded '='}}
+  v6 = 1; // expected-error {{no viable overloaded '='}}
+
+  std::variant<int, bool> v7;
+  std::variant<int, bool const> v8;
+  std::variant<int, bool volatile> v9;
+  v7 = "meow"; // expected-error {{no viable overloaded '='}}
+  v8 = "meow"; // expected-error {{no viable overloaded '='}}
+  v9 = "meow"; // expected-error {{no viable overloaded '='}}
+
+  std::variant<bool> v10;
+  std::variant<bool> v11;
+  std::variant<bool> v12;
+  v10 = std::true_type(); // expected-error {{no viable overloaded '='}}
+  v11 = std::unique_ptr<char>(); // expected-error {{no viable overloaded '='}}
+  v12 = nullptr; // expected-error {{no viable overloaded '='}}
+}

libcxx/test/std/utilities/variant/variant.variant/variant.ctor/T.pass.cpp

@@ -20,8 +20,8 @@
 #include <string>
 #include <type_traits>
 #include <variant>
+#include <memory>
 
-#include "test_convertible.hpp"
 #include "test_macros.h"
 #include "variant_test_helpers.hpp"
 
@@ -39,6 +39,8 @@ struct NoThrowT {
 
 struct AnyConstructible { template <typename T> AnyConstructible(T&&) {} };
 struct NoConstructible { NoConstructible() = delete; };
+template <class T>
+struct RValueConvertibleFrom { RValueConvertibleFrom(T&&) {} };
 
 void test_T_ctor_noexcept() {
   {
@@ -53,7 +55,7 @@ void test_T_ctor_noexcept() {
 
 void test_T_ctor_sfinae() {
   {
-    using V = std::variant<long, unsigned>;
+    using V = std::variant<long, long long>;
     static_assert(!std::is_constructible<V, int>::value, "ambiguous");
   }
   {
@@ -65,6 +67,32 @@ void test_T_ctor_sfinae() {
     static_assert(!std::is_constructible<V, int>::value,
                   "no matching constructor");
   }
+  {
+    using V = std::variant<std::string, float>;
+    static_assert(!std::is_constructible<V, int>::value,
+                  "no matching constructor");
+  }
+  {
+    using V = std::variant<std::unique_ptr<int>, bool>;
+    static_assert(!std::is_constructible<V, std::unique_ptr<char>>::value,
+                  "no explicit bool in constructor");
+    struct X {
+      operator void*();
+    };
+    static_assert(!std::is_constructible<V, X>::value,
+                  "no boolean conversion in constructor");
+    static_assert(!std::is_constructible<V, std::false_type>::value,
+                  "no converted to bool in constructor");
+  }
+  {
+    struct X {};
+    struct Y {
+      operator X();
+    };
+    using V = std::variant<X>;
+    static_assert(std::is_constructible<V, Y>::value,
+                  "regression on user-defined conversions in constructor");
+  }
   {
     using V = std::variant<AnyConstructible, NoConstructible>;
     static_assert(
@@ -99,6 +127,34 @@ void test_T_ctor_basic() {
     static_assert(v.index() == 1, "");
     static_assert(std::get<1>(v) == 42, "");
   }
+  {
+    constexpr std::variant<unsigned, long> v(42);
+    static_assert(v.index() == 1, "");
+    static_assert(std::get<1>(v) == 42, "");
+  }
+  {
+    std::variant<std::string, bool const> v = "foo";
+    assert(v.index() == 0);
+    assert(std::get<0>(v) == "foo");
+  }
+  {
+    std::variant<bool volatile, std::unique_ptr<int>> v = nullptr;
+    assert(v.index() == 1);
+    assert(std::get<1>(v) == nullptr);
+  }
+  {
+    std::variant<bool volatile const, int> v = true;
+    assert(v.index() == 0);
+    assert(std::get<0>(v));
+  }
+  {
+    std::variant<RValueConvertibleFrom<int>> v1 = 42;
+    assert(v1.index() == 0);
+
+    int x = 42;
+    std::variant<RValueConvertibleFrom<int>, AnyConstructible> v2 = x;
+    assert(v2.index() == 1);
+  }
 #if !defined(TEST_VARIANT_HAS_NO_REFERENCES)
   {
     using V = std::variant<const int &, int &&, long>;

libcxx/test/std/utilities/variant/variant.variant/variant.ctor/conv.fail.cpp

@@ -0,0 +1,39 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// <variant>
+
+// template <class ...Types> class variant;
+
+// template <class T> constexpr variant(T&&) noexcept(see below);
+
+#include <variant>
+#include <string>
+#include <memory>
+
+int main(int, char**)
+{
+  std::variant<int, int> v1 = 1; // expected-error {{no viable conversion}}
+  std::variant<long, long long> v2 = 1; // expected-error {{no viable conversion}}
+  std::variant<char> v3 = 1; // expected-error {{no viable conversion}}
+
+  std::variant<std::string, float> v4 = 1; // expected-error {{no viable conversion}}
+  std::variant<std::string, double> v5 = 1; // expected-error {{no viable conversion}}
+  std::variant<std::string, bool> v6 = 1; // expected-error {{no viable conversion}}
+
+  std::variant<int, bool> v7 = "meow"; // expected-error {{no viable conversion}}
+  std::variant<int, bool const> v8 = "meow"; // expected-error {{no viable conversion}}
+  std::variant<int, bool volatile> v9 = "meow"; // expected-error {{no viable conversion}}
+
+  std::variant<bool> v10 = std::true_type(); // expected-error {{no viable conversion}}
+  std::variant<bool> v11 = std::unique_ptr<char>(); // expected-error {{no viable conversion}}
+  std::variant<bool> v12 = nullptr; // expected-error {{no viable conversion}}
+}

libcxx/www/cxx2a_status.html

@@ -115,7 +115,7 @@
 	<tr><td><a href="https://wg21.link/P0591R4">P0591R4</a></td><td>LWG</td><td>Utility functions to implement uses-allocator construction</td><td>San Diego</td><td><i> </i></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P0595R2">P0595R2</a></td><td>CWG</td><td>P0595R2 std::is_constant_evaluated()</td><td>San Diego</td><td>Complete</td><td>9.0</td></tr>
 	<tr><td><a href="https://wg21.link/P0602R4">P0602R4</a></td><td>LWG</td><td>variant and optional should propagate copy/move triviality</td><td>San Diego</td><td>Complete</td><td>8.0</td></tr>
-	<tr><td><a href="https://wg21.link/P0608R3">P0608R3</a></td><td>LWG</td><td>A sane variant converting constructor</td><td>San Diego</td><td><i> </i></td><td></td></tr>
+	<tr><td><a href="https://wg21.link/P0608R3">P0608R3</a></td><td>LWG</td><td>A sane variant converting constructor</td><td>San Diego</td><td>Complete</td><td>9.0</td></tr>
 	<tr><td><a href="https://wg21.link/P0655R1">P0655R1</a></td><td>LWG</td><td>visit&lt;R&gt;: Explicit Return Type for visit</td><td>San Diego</td><td><i> </i></td><td></td></tr>
 	<tr><td><a href="https://wg21.link/P0771R1">P0771R1</a></td><td>LWG</td><td>std::function move constructor should be noexcept</td><td>San Diego</td><td>Complete</td><td>6.0</td></tr>
 	<tr><td><a href="https://wg21.link/P0896R4">P0896R4</a></td><td>LWG</td><td>The One Ranges Proposal</td><td>San Diego</td><td><i> </i></td><td></td></tr>