Adding documentation to CopyFrom and MergeFrom of RepeatedField and RepeatedPtrField.

PiperOrigin-RevId: 652723222

Author: protobuf-github-bot

src/google/protobuf/repeated_field.h

@@ -223,7 +223,12 @@ class RepeatedField final
   void ExtractSubrange(int start, int num, Element* elements);
 
   ABSL_ATTRIBUTE_REINITIALIZES void Clear();
+
+  // Appends the elements from `other` after this instance.
+  // The end result length will be `other.size() + this->size()`.
   void MergeFrom(const RepeatedField& other);
+
+  // Replaces the contents with a copy of the elements from `other`.
   ABSL_ATTRIBUTE_REINITIALIZES void CopyFrom(const RepeatedField& other);
 
   // Replaces the contents with RepeatedField(begin, end).

src/google/protobuf/repeated_ptr_field.h

@@ -1044,7 +1044,12 @@ class RepeatedPtrField final : private internal::RepeatedPtrFieldBase {
   void DeleteSubrange(int start, int num);
 
   ABSL_ATTRIBUTE_REINITIALIZES void Clear();
+
+  // Appends the elements from `other` after this instance.
+  // The end result length will be `other.size() + this->size()`.
   void MergeFrom(const RepeatedPtrField& other);
+
+  // Replaces the contents with a copy of the elements from `other`.
   ABSL_ATTRIBUTE_REINITIALIZES void CopyFrom(const RepeatedPtrField& other);
 
   // Replaces the contents with RepeatedPtrField(begin, end).