1 files changed, 49 insertions, 3 deletions

diff --git a/src/google/protobuf/arenastring.h b/src/google/protobuf/arenastring.h
index 2b108616..168fc972 100755
--- a/src/google/protobuf/arenastring.h
+++ b/src/google/protobuf/arenastring.h
@@ -99,6 +99,13 @@ struct LIBPROTOBUF_EXPORT ArenaStringPtr {
     if (ptr_ == default_value) {
       return NULL;
     }
+    return ReleaseNonDefault(default_value, arena);
+  }
+
+  // Similar to Release, but ptr_ cannot be the default_value.
+  inline ::std::string* ReleaseNonDefault(
+      const ::std::string* default_value, ::google::protobuf::Arena* arena) {
+    GOOGLE_DCHECK(!IsDefault(default_value));
     ::std::string* released = NULL;
     if (arena != NULL) {
       // ptr_ is owned by the arena.
@@ -164,6 +171,29 @@ struct LIBPROTOBUF_EXPORT ArenaStringPtr {
   GOOGLE_PROTOBUF_ATTRIBUTE_ALWAYS_INLINE void Swap(ArenaStringPtr* other) {
     std::swap(ptr_, other->ptr_);
   }
+  GOOGLE_PROTOBUF_ATTRIBUTE_ALWAYS_INLINE void Swap(
+      ArenaStringPtr* other, const ::std::string* default_value, Arena* arena) {
+#ifndef NDEBUG
+    // For debug builds, we swap the contents of the string, rather than the
+    // string instances themselves.  This invalidates previously taken const
+    // references that are (per our documentation) invalidated by calling Swap()
+    // on the message.
+    //
+    // If both strings are the default_value, swapping is uninteresting.
+    // Otherwise, we use ArenaStringPtr::Mutable() to access the string, to
+    // ensure that we do not try to mutate default_value itself.
+    if (IsDefault(default_value) && other->IsDefault(default_value)) {
+      return;
+    }
+
+    ::std::string* this_ptr = Mutable(default_value, arena);
+    ::std::string* other_ptr = other->Mutable(default_value, arena);
+
+    this_ptr->swap(*other_ptr);
+#else
+    std::swap(ptr_, other->ptr_);
+#endif
+  }
 
   // Frees storage (if not on an arena).
   inline void Destroy(const ::std::string* default_value,
@@ -186,6 +216,15 @@ struct LIBPROTOBUF_EXPORT ArenaStringPtr {
     }
   }
 
+  // Clears content, assuming that the current value is not the empty string
+  // default.
+  inline void ClearNonDefaultToEmpty() {
+    ptr_->clear();
+  }
+  inline void ClearNonDefaultToEmptyNoArena() {
+    ptr_->clear();
+  }
+
   // Clears content, but keeps allocated string if arena != NULL, to avoid the
   // overhead of heap operations. After this returns, the content (as seen by
   // the user) will always be equal to |default_value|.
@@ -253,12 +292,19 @@ struct LIBPROTOBUF_EXPORT ArenaStringPtr {
     if (ptr_ == default_value) {
       return NULL;
     } else {
-      ::std::string* released = ptr_;
-      ptr_ = const_cast< ::std::string* >(default_value);
-      return released;
+      return ReleaseNonDefaultNoArena(default_value);
     }
   }
 
+  inline ::std::string* ReleaseNonDefaultNoArena(
+      const ::std::string* default_value) {
+    GOOGLE_DCHECK(!IsDefault(default_value));
+    ::std::string* released = ptr_;
+    ptr_ = const_cast< ::std::string* >(default_value);
+    return released;
+  }
+
+
   inline void SetAllocatedNoArena(const ::std::string* default_value,
                                   ::std::string* value) {
     if (ptr_ != default_value) {