Don't pass `nullptr` arena to constructors in `CreateArenaCompatible` when constructing types that use arena offsets.
Note that we can't do this for all arena-constructible types, since user-defined types can be constructed on arenas.
PiperOrigin-RevId: 812352250
diff --git a/src/google/protobuf/arena.h b/src/google/protobuf/arena.h
index 623d076..2246117 100644
--- a/src/google/protobuf/arena.h
+++ b/src/google/protobuf/arena.h
@@ -115,6 +115,15 @@
}
};
+// Returns true if `T` uses arena offsets instead of holding a copy of the arena
+// pointer. This can be deduced if the field's arena representation is not the
+// same as the field itself.
+template <typename T>
+constexpr bool FieldHasArenaOffset() {
+ using ArenaRepT = typename FieldArenaRep<T>::Type;
+ return !std::is_same_v<T, ArenaRepT>;
+}
+
template <typename T>
void arena_delete_object(void* PROTOBUF_NONNULL object) {
delete reinterpret_cast<T*>(object);
@@ -498,9 +507,10 @@
}
static PROTOBUF_ALWAYS_INLINE T* PROTOBUF_NONNULL New() {
- // Repeated pointer fields no longer have an arena constructor, so
- // specialize calling their default constructor.
- if constexpr (std::is_base_of_v<internal::RepeatedPtrFieldBase, T>) {
+ // Fields which use arena offsets don't have constructors that take an
+ // arena pointer. Since the arena is nullptr, it is safe to default
+ // construct the object.
+ if constexpr (internal::FieldHasArenaOffset<T>()) {
return new T();
} else {
return new T(nullptr);
@@ -580,7 +590,11 @@
static_assert(is_arena_constructable<T>::value,
"Can only construct types that are ArenaConstructable");
if (ABSL_PREDICT_FALSE(arena == nullptr)) {
- return new T(nullptr, static_cast<Args&&>(args)...);
+ if constexpr (internal::FieldHasArenaOffset<T>()) {
+ return new T(static_cast<Args&&>(args)...);
+ } else {
+ return new T(nullptr, static_cast<Args&&>(args)...);
+ }
} else {
using ArenaRepT = typename internal::FieldArenaRep<T>::Type;
auto* arena_repr =
