Call `GetArena()` instead of accessing `arena_` directly in `RepeatedPtrFieldBase`.

PiperOrigin-RevId: 805963204

src/google/protobuf/repeated_ptr_field.cc

diff --git a/src/google/protobuf/repeated_ptr_field.cc b/src/google/protobuf/repeated_ptr_field.cc
index 57fd3f5..34fe860 100644
--- a/src/google/protobuf/repeated_ptr_field.cc
+++ b/src/google/protobuf/repeated_ptr_field.cc
@@ -143,7 +143,8 @@
   for (; src < end_assign; ++dst, ++src) {
     (*dst)->assign(**src);
   }
-  if (Arena* const arena = arena_) {
+  Arena* const arena = GetArena();
+  if (arena != nullptr) {
     for (; src < end; ++dst, ++src) {
       *dst = Arena::Create<std::string>(arena, **src);
     }

src/google/protobuf/repeated_ptr_field.h

diff --git a/src/google/protobuf/repeated_ptr_field.h b/src/google/protobuf/repeated_ptr_field.h
index b34959d..cd58358 100644
--- a/src/google/protobuf/repeated_ptr_field.h
+++ b/src/google/protobuf/repeated_ptr_field.h
@@ -168,9 +168,11 @@
 
   ~RepeatedPtrFieldBase() {
 #ifndef NDEBUG
-    // Try to trigger segfault / asan failure in non-opt builds if arena_
-    // lifetime has ended before the destructor.
-    if (arena_) (void)arena_->SpaceAllocated();
+    // Try to trigger segfault / asan failure in non-opt builds if the arena
+    // lifetime has ended before the destructor. Note that `GetArena()` is
+    // not free, but this is debug-only.
+    const Arena* arena = GetArena();
+    if (arena != nullptr) (void)arena->SpaceAllocated();
 #endif
   }
 
@@ -228,7 +230,7 @@
 
     // TODO: arena check is redundant once all `RepeatedPtrField`s
     // with non-null arena are owned by the arena.
-    if (ABSL_PREDICT_FALSE(arena_ != nullptr)) return;
+    if (ABSL_PREDICT_FALSE(GetArena() != nullptr)) return;
 
     using H = CommonHandler<TypeHandler>;
     int n = allocated_size();
@@ -481,7 +483,7 @@
       // this case because otherwise a loop calling AddAllocated() followed by
       // Clear() would leak memory.
       using H = CommonHandler<TypeHandler>;
-      Delete<H>(element_at(current_size_), arena_);
+      Delete<H>(element_at(current_size_), GetArena());
     } else if (current_size_ < allocated_size()) {
       // We have some cleared objects.  We don't care about their order, so we
       // can just move the first one to the end to make space.