Fix std::is_pod deprecated in C++20

src/google/protobuf/arena.h

@@ -338,7 +338,7 @@ class PROTOBUF_EXPORT alignas(8) Arena final {
   template <typename T>
   PROTOBUF_ALWAYS_INLINE static T* CreateArray(Arena* arena,
                                                size_t num_elements) {
-    static_assert(std::is_pod<T>::value,
+    static_assert(std::is_standard_layout<T>::value && std::is_trivial<T>::value,
                   "CreateArray requires a trivially constructible type");
     static_assert(std::is_trivially_destructible<T>::value,
                   "CreateArray requires a trivially destructible type");

src/google/protobuf/generated_message_table_driven.h

@@ -206,12 +206,18 @@ struct ParseTable {
 static_assert(sizeof(ParseTableField) <= 16, "ParseTableField is too large");
 // The tables must be composed of POD components to ensure link-time
 // initialization.
-static_assert(std::is_pod<ParseTableField>::value, "");
-static_assert(std::is_pod<AuxillaryParseTableField>::value, "");
-static_assert(std::is_pod<AuxillaryParseTableField::enum_aux>::value, "");
-static_assert(std::is_pod<AuxillaryParseTableField::message_aux>::value, "");
-static_assert(std::is_pod<AuxillaryParseTableField::string_aux>::value, "");
-static_assert(std::is_pod<ParseTable>::value, "");
+static_assert(std::is_standard_layout<ParseTableField>::value, "");
+static_assert(std::is_trivial<ParseTableField>::value, "");
+static_assert(std::is_standard_layout<AuxillaryParseTableField>::value, "");
+static_assert(std::is_trivial<AuxillaryParseTableField>::value, "");
+static_assert(std::is_standard_layout<AuxillaryParseTableField::enum_aux>::value, "");
+static_assert(std::is_trivial<AuxillaryParseTableField::enum_aux>::value, "");
+static_assert(std::is_standard_layout<AuxillaryParseTableField::message_aux>::value, "");
+static_assert(std::is_trivial<AuxillaryParseTableField::message_aux>::value, "");
+static_assert(std::is_standard_layout<AuxillaryParseTableField::string_aux>::value, "");
+static_assert(std::is_trivial<AuxillaryParseTableField::string_aux>::value, "");
+static_assert(std::is_standard_layout<ParseTable>::value, "");
+static_assert(std::is_trivial<ParseTable>::value, "");
 
 // TODO(ckennelly): Consolidate these implementations into a single one, using
 // dynamic dispatch to the appropriate unknown field handler.

src/google/protobuf/generated_message_table_driven_lite.h

@@ -101,7 +101,7 @@ inline ExtensionSet* GetExtensionSet(MessageLite* msg, int64 extension_offset) {
 
 template <typename Type>
 inline Type* AddField(MessageLite* msg, int64 offset) {
-  static_assert(std::is_pod<Type>::value ||
+  static_assert((std::is_standard_layout<Type>::value && std::is_trivial<Type>::value) ||
                     std::is_same<Type, InlinedStringField>::value,
                 "Do not assign");
 
@@ -119,7 +119,7 @@ inline std::string* AddField<std::string>(MessageLite* msg, int64 offset) {
 
 template <typename Type>
 inline void AddField(MessageLite* msg, int64 offset, Type value) {
-  static_assert(std::is_pod<Type>::value,
+  static_assert(std::is_standard_layout<Type>::value && std::is_trivial<Type>::value,
                 "Do not assign");
   *AddField<Type>(msg, offset) = value;
 }
@@ -141,7 +141,7 @@ inline Type* MutableField(MessageLite* msg, uint32* has_bits,
 template <typename Type>
 inline void SetField(MessageLite* msg, uint32* has_bits, uint32 has_bit_index,
                      int64 offset, Type value) {
-  static_assert(std::is_pod<Type>::value,
+  static_assert(std::is_standard_layout<Type>::value && std::is_trivial<Type>::value,
                 "Do not assign");
   *MutableField<Type>(msg, has_bits, has_bit_index, offset) = value;
 }

src/google/protobuf/repeated_field.h

@@ -374,7 +374,7 @@ namespace internal {
 // effectively.
 template <typename Element,
           bool HasTrivialCopy =
-              std::is_pod<Element>::value>
+              std::is_standard_layout<Element>::value && std::is_trivial<Element>::value>
 struct ElementCopier {
   void operator()(Element* to, const Element* from, int array_size);
 };