Breaking Change: `proto2::Map::value_type` changes to `std::pair<const K, V>`.

PiperOrigin-RevId: 503871374

src/google/protobuf/map.h

@@ -981,42 +981,9 @@ class KeyMapBase : public UntypedMapBase {
 
 }  // namespace internal
 
-#ifdef PROTOBUF_FUTURE_MAP_PAIR_UPGRADE
 // This is the class for Map's internal value_type.
 template <typename Key, typename T>
 using MapPair = std::pair<const Key, T>;
-#else
-// This is the class for Map's internal value_type. Instead of using
-// std::pair as value_type, we use this class which provides us more control of
-// its process of construction and destruction.
-template <typename Key, typename T>
-struct PROTOBUF_ATTRIBUTE_STANDALONE_DEBUG MapPair {
-  using first_type = const Key;
-  using second_type = T;
-
-  MapPair(const Key& other_first, const T& other_second)
-      : first(other_first), second(other_second) {}
-  explicit MapPair(const Key& other_first) : first(other_first), second() {}
-  explicit MapPair(Key&& other_first)
-      : first(std::move(other_first)), second() {}
-  MapPair(const MapPair& other) : first(other.first), second(other.second) {}
-
-  ~MapPair() {}
-
-  // Implicitly convertible to std::pair of compatible types.
-  template <typename T1, typename T2>
-  operator std::pair<T1, T2>() const {  // NOLINT(runtime/explicit)
-    return std::pair<T1, T2>(first, second);
-  }
-
-  const Key first;
-  T second;
-
- private:
-  friend class Arena;
-  friend class Map<Key, T>;
-};
-#endif
 
 // Map is an associative container type used to store protobuf map
 // fields.  Each Map instance may or may not use a different hash function, a

src/google/protobuf/map_test.inc

@@ -813,24 +813,6 @@ TEST_F(MapImplTest, Emplace) {
       m, UnorderedElementsAre(Pair(1, "one"), Pair(2, "two"), Pair(42, "aaa")));
 }
 
-#ifndef PROTOBUF_FUTURE_MAP_PAIR_UPGRADE
-
-TEST_F(MapImplTest, EmplaceKeyOnly) {
-  using ::testing::Pair;
-  using ::testing::UnorderedElementsAre;
-
-  Map<int32_t, std::string> m;
-
-  m.emplace(1);
-  EXPECT_EQ(m.size(), 1);
-
-  const int32_t key = 42;
-  m.emplace(key);
-  EXPECT_THAT(m, UnorderedElementsAre(Pair(1, ""), Pair(42, "")));
-}
-
-#else
-
 TEST_F(MapImplTest, ValueTypeHasMoveConstructor) {
   using vt = typename Map<ConstructorTag, ConstructorTag>::value_type;
   ConstructorTag l, r;
@@ -841,8 +823,6 @@ TEST_F(MapImplTest, ValueTypeHasMoveConstructor) {
   EXPECT_EQ(pair.second.invoked_constructor, ConstructorType::kMove);
 }
 
-#endif  // !PROTOBUF_FUTURE_MAP_PAIR_UPGRADE
-
 TEST_F(MapImplTest, TryEmplaceExisting) {
   Map<int32_t, CountedInstance> m;
 

src/google/protobuf/port_def.inc

@@ -204,10 +204,6 @@ static_assert(PROTOBUF_CPLUSPLUS_MIN(201402L), "Protobuf only supports C++14 and
 
 #ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
 
-// Used to upgrade google::protobuf::MapPair<K, V> to std::pair<const K, V>.
-// Owner: mordberg@
-#define PROTOBUF_FUTURE_MAP_PAIR_UPGRADE 1
-
 // Used to remove the manipulation of cleared elements in RepeatedPtrField.
 // Owner: mkruskal@
 #define PROTOBUF_FUTURE_REMOVE_CLEARED_API 1

src/google/protobuf/port_undef.inc

@@ -117,7 +117,6 @@
 
 #ifdef PROTOBUF_FUTURE_BREAKING_CHANGES
 #undef PROTOBUF_FUTURE_BREAKING_CHANGES
-#undef PROTOBUF_FUTURE_MAP_PAIR_UPGRADE
 #undef PROTOBUF_FUTURE_REMOVE_CLEARED_API
 #endif