Creation of LTS branch "lts_2019_08_08"20190808

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GitOrigin-RevId: 9ee91d3e430fb33a4590486573792eb0fa146c2d
Change-Id: Ia06e548bc106cc9d136f6c65714be6645317aced

3 files changed, 568 insertions, 30 deletions

diff --git a/absl/types/internal/optional.h b/absl/types/internal/optional.h
new file mode 100644
index 00000000..3c8e7cca
--- /dev/null
+++ b/absl/types/internal/optional.h
@@ -0,0 +1,396 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_TYPES_INTERNAL_OPTIONAL_H_
+#define ABSL_TYPES_INTERNAL_OPTIONAL_H_
+
+#include <functional>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/inline_variable.h"
+#include "absl/memory/memory.h"
+#include "absl/meta/type_traits.h"
+#include "absl/utility/utility.h"
+
+// ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+//
+// Inheriting constructors is supported in GCC 4.8+, Clang 3.3+ and MSVC 2015.
+// __cpp_inheriting_constructors is a predefined macro and a recommended way to
+// check for this language feature, but GCC doesn't support it until 5.0 and
+// Clang doesn't support it until 3.6.
+// Also, MSVC 2015 has a bug: it doesn't inherit the constexpr template
+// constructor. For example, the following code won't work on MSVC 2015 Update3:
+// struct Base {
+//   int t;
+//   template <typename T>
+//   constexpr Base(T t_) : t(t_) {}
+// };
+// struct Foo : Base {
+//   using Base::Base;
+// }
+// constexpr Foo foo(0);  // doesn't work on MSVC 2015
+#if defined(__clang__)
+#if __has_feature(cxx_inheriting_constructors)
+#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1
+#endif
+#elif (defined(__GNUC__) &&                                       \
+       (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ >= 8)) || \
+    (__cpp_inheriting_constructors >= 200802) ||                  \
+    (defined(_MSC_VER) && _MSC_VER >= 1910)
+#define ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS 1
+#endif
+
+namespace absl {
+inline namespace lts_2019_08_08 {
+
+// Forward declaration
+template <typename T>
+class optional;
+
+namespace optional_internal {
+
+// This tag type is used as a constructor parameter type for `nullopt_t`.
+struct init_t {
+  explicit init_t() = default;
+};
+
+struct empty_struct {};
+
+// This class stores the data in optional<T>.
+// It is specialized based on whether T is trivially destructible.
+// This is the specialization for non trivially destructible type.
+template <typename T, bool unused = std::is_trivially_destructible<T>::value>
+class optional_data_dtor_base {
+  struct dummy_type {
+    static_assert(sizeof(T) % sizeof(empty_struct) == 0, "");
+    // Use an array to avoid GCC 6 placement-new warning.
+    empty_struct data[sizeof(T) / sizeof(empty_struct)];
+  };
+
+ protected:
+  // Whether there is data or not.
+  bool engaged_;
+  // Data storage
+  union {
+    dummy_type dummy_;
+    T data_;
+  };
+
+  void destruct() noexcept {
+    if (engaged_) {
+      data_.~T();
+      engaged_ = false;
+    }
+  }
+
+  // dummy_ must be initialized for constexpr constructor.
+  constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {}
+
+  template <typename... Args>
+  constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args)
+      : engaged_(true), data_(absl::forward<Args>(args)...) {}
+
+  ~optional_data_dtor_base() { destruct(); }
+};
+
+// Specialization for trivially destructible type.
+template <typename T>
+class optional_data_dtor_base<T, true> {
+  struct dummy_type {
+    static_assert(sizeof(T) % sizeof(empty_struct) == 0, "");
+    // Use array to avoid GCC 6 placement-new warning.
+    empty_struct data[sizeof(T) / sizeof(empty_struct)];
+  };
+
+ protected:
+  // Whether there is data or not.
+  bool engaged_;
+  // Data storage
+  union {
+    dummy_type dummy_;
+    T data_;
+  };
+  void destruct() noexcept { engaged_ = false; }
+
+  // dummy_ must be initialized for constexpr constructor.
+  constexpr optional_data_dtor_base() noexcept : engaged_(false), dummy_{{}} {}
+
+  template <typename... Args>
+  constexpr explicit optional_data_dtor_base(in_place_t, Args&&... args)
+      : engaged_(true), data_(absl::forward<Args>(args)...) {}
+};
+
+template <typename T>
+class optional_data_base : public optional_data_dtor_base<T> {
+ protected:
+  using base = optional_data_dtor_base<T>;
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using base::base;
+#else
+  optional_data_base() = default;
+
+  template <typename... Args>
+  constexpr explicit optional_data_base(in_place_t t, Args&&... args)
+      : base(t, absl::forward<Args>(args)...) {}
+#endif
+
+  template <typename... Args>
+  void construct(Args&&... args) {
+    // Use dummy_'s address to work around casting cv-qualified T* to void*.
+    ::new (static_cast<void*>(&this->dummy_)) T(std::forward<Args>(args)...);
+    this->engaged_ = true;
+  }
+
+  template <typename U>
+  void assign(U&& u) {
+    if (this->engaged_) {
+      this->data_ = std::forward<U>(u);
+    } else {
+      construct(std::forward<U>(u));
+    }
+  }
+};
+
+// TODO(absl-team): Add another class using
+// std::is_trivially_move_constructible trait when available to match
+// http://cplusplus.github.io/LWG/lwg-defects.html#2900, for types that
+// have trivial move but nontrivial copy.
+// Also, we should be checking is_trivially_copyable here, which is not
+// supported now, so we use is_trivially_* traits instead.
+template <typename T,
+          bool unused = absl::is_trivially_copy_constructible<T>::value&&
+              absl::is_trivially_copy_assignable<typename std::remove_cv<
+                  T>::type>::value&& std::is_trivially_destructible<T>::value>
+class optional_data;
+
+// Trivially copyable types
+template <typename T>
+class optional_data<T, true> : public optional_data_base<T> {
+ protected:
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using optional_data_base<T>::optional_data_base;
+#else
+  optional_data() = default;
+
+  template <typename... Args>
+  constexpr explicit optional_data(in_place_t t, Args&&... args)
+      : optional_data_base<T>(t, absl::forward<Args>(args)...) {}
+#endif
+};
+
+template <typename T>
+class optional_data<T, false> : public optional_data_base<T> {
+ protected:
+#ifdef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+  using optional_data_base<T>::optional_data_base;
+#else
+  template <typename... Args>
+  constexpr explicit optional_data(in_place_t t, Args&&... args)
+      : optional_data_base<T>(t, absl::forward<Args>(args)...) {}
+#endif
+
+  optional_data() = default;
+
+  optional_data(const optional_data& rhs) : optional_data_base<T>() {
+    if (rhs.engaged_) {
+      this->construct(rhs.data_);
+    }
+  }
+
+  optional_data(optional_data&& rhs) noexcept(
+      absl::default_allocator_is_nothrow::value ||
+      std::is_nothrow_move_constructible<T>::value)
+      : optional_data_base<T>() {
+    if (rhs.engaged_) {
+      this->construct(std::move(rhs.data_));
+    }
+  }
+
+  optional_data& operator=(const optional_data& rhs) {
+    if (rhs.engaged_) {
+      this->assign(rhs.data_);
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+
+  optional_data& operator=(optional_data&& rhs) noexcept(
+      std::is_nothrow_move_assignable<T>::value&&
+          std::is_nothrow_move_constructible<T>::value) {
+    if (rhs.engaged_) {
+      this->assign(std::move(rhs.data_));
+    } else {
+      this->destruct();
+    }
+    return *this;
+  }
+};
+
+// Ordered by level of restriction, from low to high.
+// Copyable implies movable.
+enum class copy_traits { copyable = 0, movable = 1, non_movable = 2 };
+
+// Base class for enabling/disabling copy/move constructor.
+template <copy_traits>
+class optional_ctor_base;
+
+template <>
+class optional_ctor_base<copy_traits::copyable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = default;
+  optional_ctor_base(optional_ctor_base&&) = default;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+template <>
+class optional_ctor_base<copy_traits::movable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = delete;
+  optional_ctor_base(optional_ctor_base&&) = default;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+template <>
+class optional_ctor_base<copy_traits::non_movable> {
+ public:
+  constexpr optional_ctor_base() = default;
+  optional_ctor_base(const optional_ctor_base&) = delete;
+  optional_ctor_base(optional_ctor_base&&) = delete;
+  optional_ctor_base& operator=(const optional_ctor_base&) = default;
+  optional_ctor_base& operator=(optional_ctor_base&&) = default;
+};
+
+// Base class for enabling/disabling copy/move assignment.
+template <copy_traits>
+class optional_assign_base;
+
+template <>
+class optional_assign_base<copy_traits::copyable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = default;
+  optional_assign_base& operator=(optional_assign_base&&) = default;
+};
+
+template <>
+class optional_assign_base<copy_traits::movable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = delete;
+  optional_assign_base& operator=(optional_assign_base&&) = default;
+};
+
+template <>
+class optional_assign_base<copy_traits::non_movable> {
+ public:
+  constexpr optional_assign_base() = default;
+  optional_assign_base(const optional_assign_base&) = default;
+  optional_assign_base(optional_assign_base&&) = default;
+  optional_assign_base& operator=(const optional_assign_base&) = delete;
+  optional_assign_base& operator=(optional_assign_base&&) = delete;
+};
+
+template <typename T>
+struct ctor_copy_traits {
+  static constexpr copy_traits traits =
+      std::is_copy_constructible<T>::value
+          ? copy_traits::copyable
+          : std::is_move_constructible<T>::value ? copy_traits::movable
+                                                 : copy_traits::non_movable;
+};
+
+template <typename T>
+struct assign_copy_traits {
+  static constexpr copy_traits traits =
+      absl::is_copy_assignable<T>::value && std::is_copy_constructible<T>::value
+          ? copy_traits::copyable
+          : absl::is_move_assignable<T>::value &&
+                    std::is_move_constructible<T>::value
+                ? copy_traits::movable
+                : copy_traits::non_movable;
+};
+
+// Whether T is constructible or convertible from optional<U>.
+template <typename T, typename U>
+struct is_constructible_convertible_from_optional
+    : std::integral_constant<
+          bool, std::is_constructible<T, optional<U>&>::value ||
+                    std::is_constructible<T, optional<U>&&>::value ||
+                    std::is_constructible<T, const optional<U>&>::value ||
+                    std::is_constructible<T, const optional<U>&&>::value ||
+                    std::is_convertible<optional<U>&, T>::value ||
+                    std::is_convertible<optional<U>&&, T>::value ||
+                    std::is_convertible<const optional<U>&, T>::value ||
+                    std::is_convertible<const optional<U>&&, T>::value> {};
+
+// Whether T is constructible or convertible or assignable from optional<U>.
+template <typename T, typename U>
+struct is_constructible_convertible_assignable_from_optional
+    : std::integral_constant<
+          bool, is_constructible_convertible_from_optional<T, U>::value ||
+                    std::is_assignable<T&, optional<U>&>::value ||
+                    std::is_assignable<T&, optional<U>&&>::value ||
+                    std::is_assignable<T&, const optional<U>&>::value ||
+                    std::is_assignable<T&, const optional<U>&&>::value> {};
+
+// Helper function used by [optional.relops], [optional.comp_with_t],
+// for checking whether an expression is convertible to bool.
+bool convertible_to_bool(bool);
+
+// Base class for std::hash<absl::optional<T>>:
+// If std::hash<std::remove_const_t<T>> is enabled, it provides operator() to
+// compute the hash; Otherwise, it is disabled.
+// Reference N4659 23.14.15 [unord.hash].
+template <typename T, typename = size_t>
+struct optional_hash_base {
+  optional_hash_base() = delete;
+  optional_hash_base(const optional_hash_base&) = delete;
+  optional_hash_base(optional_hash_base&&) = delete;
+  optional_hash_base& operator=(const optional_hash_base&) = delete;
+  optional_hash_base& operator=(optional_hash_base&&) = delete;
+};
+
+template <typename T>
+struct optional_hash_base<T, decltype(std::hash<absl::remove_const_t<T> >()(
+                                 std::declval<absl::remove_const_t<T> >()))> {
+  using argument_type = absl::optional<T>;
+  using result_type = size_t;
+  size_t operator()(const absl::optional<T>& opt) const {
+    absl::type_traits_internal::AssertHashEnabled<absl::remove_const_t<T>>();
+    if (opt) {
+      return std::hash<absl::remove_const_t<T> >()(*opt);
+    } else {
+      return static_cast<size_t>(0x297814aaad196e6dULL);
+    }
+  }
+};
+
+}  // namespace optional_internal
+}  // inline namespace lts_2019_08_08
+}  // namespace absl
+
+#undef ABSL_OPTIONAL_USE_INHERITING_CONSTRUCTORS
+
+#endif  // ABSL_TYPES_INTERNAL_OPTIONAL_H_
diff --git a/absl/types/internal/span.h b/absl/types/internal/span.h
new file mode 100644
index 00000000..873ae160
--- /dev/null
+++ b/absl/types/internal/span.h
@@ -0,0 +1,128 @@
+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_TYPES_INTERNAL_SPAN_H_
+#define ABSL_TYPES_INTERNAL_SPAN_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <string>
+#include <type_traits>
+
+#include "absl/algorithm/algorithm.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+inline namespace lts_2019_08_08 {
+
+namespace span_internal {
+// A constexpr min function
+constexpr size_t Min(size_t a, size_t b) noexcept { return a < b ? a : b; }
+
+// Wrappers for access to container data pointers.
+template <typename C>
+constexpr auto GetDataImpl(C& c, char) noexcept  // NOLINT(runtime/references)
+    -> decltype(c.data()) {
+  return c.data();
+}
+
+// Before C++17, std::string::data returns a const char* in all cases.
+inline char* GetDataImpl(std::string& s,  // NOLINT(runtime/references)
+                         int) noexcept {
+  return &s[0];
+}
+
+template <typename C>
+constexpr auto GetData(C& c) noexcept  // NOLINT(runtime/references)
+    -> decltype(GetDataImpl(c, 0)) {
+  return GetDataImpl(c, 0);
+}
+
+// Detection idioms for size() and data().
+template <typename C>
+using HasSize =
+    std::is_integral<absl::decay_t<decltype(std::declval<C&>().size())>>;
+
+// We want to enable conversion from vector<T*> to Span<const T* const> but
+// disable conversion from vector<Derived> to Span<Base>. Here we use
+// the fact that U** is convertible to Q* const* if and only if Q is the same
+// type or a more cv-qualified version of U.  We also decay the result type of
+// data() to avoid problems with classes which have a member function data()
+// which returns a reference.
+template <typename T, typename C>
+using HasData =
+    std::is_convertible<absl::decay_t<decltype(GetData(std::declval<C&>()))>*,
+                        T* const*>;
+
+// Extracts value type from a Container
+template <typename C>
+struct ElementType {
+  using type = typename absl::remove_reference_t<C>::value_type;
+};
+
+template <typename T, size_t N>
+struct ElementType<T (&)[N]> {
+  using type = T;
+};
+
+template <typename C>
+using ElementT = typename ElementType<C>::type;
+
+template <typename T>
+using EnableIfMutable =
+    typename std::enable_if<!std::is_const<T>::value, int>::type;
+
+template <template <typename> class SpanT, typename T>
+bool EqualImpl(SpanT<T> a, SpanT<T> b) {
+  static_assert(std::is_const<T>::value, "");
+  return absl::equal(a.begin(), a.end(), b.begin(), b.end());
+}
+
+template <template <typename> class SpanT, typename T>
+bool LessThanImpl(SpanT<T> a, SpanT<T> b) {
+  // We can't use value_type since that is remove_cv_t<T>, so we go the long way
+  // around.
+  static_assert(std::is_const<T>::value, "");
+  return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
+}
+
+// The `IsConvertible` classes here are needed because of the
+// `std::is_convertible` bug in libcxx when compiled with GCC. This build
+// configuration is used by Android NDK toolchain. Reference link:
+// https://bugs.llvm.org/show_bug.cgi?id=27538.
+template <typename From, typename To>
+struct IsConvertibleHelper {
+ private:
+  static std::true_type testval(To);
+  static std::false_type testval(...);
+
+ public:
+  using type = decltype(testval(std::declval<From>()));
+};
+
+template <typename From, typename To>
+struct IsConvertible : IsConvertibleHelper<From, To>::type {};
+
+// TODO(zhangxy): replace `IsConvertible` with `std::is_convertible` once the
+// older version of libcxx is not supported.
+template <typename From, typename To>
+using EnableIfConvertibleTo =
+    typename std::enable_if<IsConvertible<From, To>::value>::type;
+}  // namespace span_internal
+}  // inline namespace lts_2019_08_08
+}  // namespace absl
+
+#endif  // ABSL_TYPES_INTERNAL_SPAN_H_
diff --git a/absl/types/internal/variant.h b/absl/types/internal/variant.h
index 875f88e0..4f29f617 100644
--- a/absl/types/internal/variant.h
+++ b/absl/types/internal/variant.h
@@ -4,7 +4,7 @@
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
-//      http://www.apache.org/licenses/LICENSE-2.0
+//      https://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ -15,7 +15,6 @@
 // Implementation details of absl/types/variant.h, pulled into a
 // separate file to avoid cluttering the top of the API header with
 // implementation details.
-//
 
 #ifndef ABSL_TYPES_variant_internal_H_
 #define ABSL_TYPES_variant_internal_H_
@@ -41,7 +40,7 @@
 #if !defined(ABSL_HAVE_STD_VARIANT)
 
 namespace absl {
-inline namespace lts_2018_12_18 {
+inline namespace lts_2019_08_08 {
 
 template <class... Types>
 class variant;
@@ -206,7 +205,7 @@ template <class Op, class... Vs>
 using VisitIndicesResultT = typename VisitIndicesResultImpl<Op, Vs...>::type;
 
 template <class ReturnType, class FunctionObject, class EndIndices,
-          std::size_t... BoundIndices>
+          class BoundIndices>
 struct MakeVisitationMatrix;
 
 template <class ReturnType, class FunctionObject, std::size_t... Indices>
@@ -220,7 +219,7 @@ constexpr ReturnType call_with_indices(FunctionObject&& function) {
 
 template <class ReturnType, class FunctionObject, std::size_t... BoundIndices>
 struct MakeVisitationMatrix<ReturnType, FunctionObject, index_sequence<>,
-                            BoundIndices...> {
+                            index_sequence<BoundIndices...>> {
   using ResultType = ReturnType (*)(FunctionObject&&);
   static constexpr ResultType Run() {
     return &call_with_indices<ReturnType, FunctionObject,
@@ -228,24 +227,34 @@ struct MakeVisitationMatrix<ReturnType, FunctionObject, index_sequence<>,
   }
 };
 
+template <typename Is, std::size_t J>
+struct AppendToIndexSequence;
+
+template <typename Is, std::size_t J>
+using AppendToIndexSequenceT = typename AppendToIndexSequence<Is, J>::type;
+
+template <std::size_t... Is, std::size_t J>
+struct AppendToIndexSequence<index_sequence<Is...>, J> {
+  using type = index_sequence<Is..., J>;
+};
+
 template <class ReturnType, class FunctionObject, class EndIndices,
-          class CurrIndices, std::size_t... BoundIndices>
+          class CurrIndices, class BoundIndices>
 struct MakeVisitationMatrixImpl;
 
-template <class ReturnType, class FunctionObject, std::size_t... EndIndices,
-          std::size_t... CurrIndices, std::size_t... BoundIndices>
-struct MakeVisitationMatrixImpl<
-    ReturnType, FunctionObject, index_sequence<EndIndices...>,
-    index_sequence<CurrIndices...>, BoundIndices...> {
+template <class ReturnType, class FunctionObject, class EndIndices,
+          std::size_t... CurrIndices, class BoundIndices>
+struct MakeVisitationMatrixImpl<ReturnType, FunctionObject, EndIndices,
+                                index_sequence<CurrIndices...>, BoundIndices> {
   using ResultType = SimpleArray<
-      typename MakeVisitationMatrix<ReturnType, FunctionObject,
-                                    index_sequence<EndIndices...>>::ResultType,
+      typename MakeVisitationMatrix<ReturnType, FunctionObject, EndIndices,
+                                    index_sequence<>>::ResultType,
       sizeof...(CurrIndices)>;
 
   static constexpr ResultType Run() {
-    return {{MakeVisitationMatrix<ReturnType, FunctionObject,
-                                  index_sequence<EndIndices...>,
-                                  BoundIndices..., CurrIndices>::Run()...}};
+    return {{MakeVisitationMatrix<
+        ReturnType, FunctionObject, EndIndices,
+        AppendToIndexSequenceT<BoundIndices, CurrIndices>>::Run()...}};
   }
 };
 
@@ -253,10 +262,11 @@ template <class ReturnType, class FunctionObject, std::size_t HeadEndIndex,
           std::size_t... TailEndIndices, std::size_t... BoundIndices>
 struct MakeVisitationMatrix<ReturnType, FunctionObject,
                             index_sequence<HeadEndIndex, TailEndIndices...>,
-                            BoundIndices...>
-    : MakeVisitationMatrixImpl<
-          ReturnType, FunctionObject, index_sequence<TailEndIndices...>,
-          absl::make_index_sequence<HeadEndIndex>, BoundIndices...> {};
+                            index_sequence<BoundIndices...>>
+    : MakeVisitationMatrixImpl<ReturnType, FunctionObject,
+                               index_sequence<TailEndIndices...>,
+                               absl::make_index_sequence<HeadEndIndex>,
+                               index_sequence<BoundIndices...>> {};
 
 struct UnreachableSwitchCase {
   template <class Op>
@@ -425,7 +435,8 @@ struct VisitIndicesFallback {
   static VisitIndicesResultT<Op, SizeT...> Run(Op&& op, SizeT... indices) {
     return AccessSimpleArray(
         MakeVisitationMatrix<VisitIndicesResultT<Op, SizeT...>, Op,
-                             index_sequence<(EndIndices + 1)...>>::Run(),
+                             index_sequence<(EndIndices + 1)...>,
+                             index_sequence<>>::Run(),
         (indices + 1)...)(absl::forward<Op>(op));
   }
 };
@@ -839,8 +850,8 @@ struct ImaginaryFun<variant<H, T...>, I> : ImaginaryFun<variant<T...>, I + 1> {
   // NOTE: const& and && are used instead of by-value due to lack of guaranteed
   // move elision of C++17. This may have other minor differences, but tests
   // pass.
-  static SizeT<I> Run(const H&);
-  static SizeT<I> Run(H&&);
+  static SizeT<I> Run(const H&, SizeT<I>);
+  static SizeT<I> Run(H&&, SizeT<I>);
 };
 
 // The following metafunctions are used in constructor and assignment
@@ -862,7 +873,8 @@ struct ConversionIsPossibleImpl : std::false_type {};
 
 template <class Variant, class T>
 struct ConversionIsPossibleImpl<
-    Variant, T, void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>()))>>
+    Variant, T,
+    void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {}))>>
     : std::true_type {};
 
 template <class Variant, class T>
@@ -870,8 +882,9 @@ struct ConversionIsPossible : ConversionIsPossibleImpl<Variant, T>::type {};
 
 template <class Variant, class T>
 struct IndexOfConstructedType<
-    Variant, T, void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>()))>>
-    : decltype(ImaginaryFun<Variant>::Run(std::declval<T>())) {};
+    Variant, T,
+    void_t<decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {}))>>
+    : decltype(ImaginaryFun<Variant>::Run(std::declval<T>(), {})) {};
 
 template <std::size_t... Is>
 struct ContainsVariantNPos
@@ -1550,8 +1563,8 @@ struct SwapSameIndex {
   variant<Types...>* w;
   template <std::size_t I>
   void operator()(SizeT<I>) const {
-    using std::swap;
-    swap(VariantCoreAccess::Access<I>(*v), VariantCoreAccess::Access<I>(*w));
+    type_traits_internal::Swap(VariantCoreAccess::Access<I>(*v),
+                               VariantCoreAccess::Access<I>(*w));
   }
 
   void operator()(SizeT<variant_npos>) const {}
@@ -1606,11 +1619,12 @@ struct VariantHashVisitor {
 template <typename Variant, typename... Ts>
 struct VariantHashBase<Variant,
                        absl::enable_if_t<absl::conjunction<
-                           type_traits_internal::IsHashEnabled<Ts>...>::value>,
+                           type_traits_internal::IsHashable<Ts>...>::value>,
                        Ts...> {
   using argument_type = Variant;
   using result_type = size_t;
   size_t operator()(const Variant& var) const {
+    type_traits_internal::AssertHashEnabled<Ts...>();
     if (var.valueless_by_exception()) {
       return 239799884;
     }
@@ -1625,7 +1639,7 @@ struct VariantHashBase<Variant,
 };
 
 }  // namespace variant_internal
-}  // inline namespace lts_2018_12_18
+}  // inline namespace lts_2019_08_08
 }  // namespace absl
 
 #endif  // !defined(ABSL_HAVE_STD_VARIANT)