diff --git a/objectivec/GPBMessage_PackagePrivate.h b/objectivec/GPBMessage_PackagePrivate.h
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// This header is private to the ProtobolBuffers library and must NOT be
+// included by any sources outside this library. The contents of this file are
+// subject to change at any time without notice.
+
+#import "GPBMessage.h"
+
+#import <libkern/OSAtomic.h>
+
+#import "GPBBootstrap.h"
+
+typedef struct GPBMessage_Storage {
+  uint32_t _has_storage_[0];
+} GPBMessage_Storage;
+
+typedef struct GPBMessage_Storage *GPBMessage_StoragePtr;
+
+@interface GPBMessage () {
+ @package
+  // NOTE: Because of the +allocWithZone code using NSAllocateObject(),
+  // this structure should ideally always be kept pointer aligned where the
+  // real storage starts is also pointer aligned. The compiler/runtime already
+  // do this, but it may not be documented.
+
+  // A pointer to the actual fields of the subclasses. The actual structure
+  // pointed to by this pointer will depend on the subclass.
+  // All of the actual structures will start the same as
+  // GPBMessage_Storage with _has_storage__ as the first field.
+  // Kept public because static functions need to access it.
+  GPBMessage_StoragePtr messageStorage_;
+
+  // A lock to provide mutual exclusion from internal data that can be modified
+  // by *read* operations such as getters (autocreation of message fields and
+  // message extensions, not setting of values). Used to guarantee thread safety
+  // for concurrent reads on the message.
+  // NOTE: OSSpinLock may seem like a good fit here but Apple engineers have
+  // pointed out that they are vulnerable to live locking on iOS in cases of
+  // priority inversion:
+  //   http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
+  //   https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html
+  dispatch_semaphore_t readOnlySemaphore_;
+}
+
+// Gets an extension value without autocreating the result if not found. (i.e.
+// returns nil if the extension is not set)
+- (id)getExistingExtension:(GPBExtensionDescriptor *)extension;
+
+// Returns an array of GPBExtensionDescriptor* for all the extensions currently
+// in use on the message.  They are sorted by field number.
+- (NSArray *)sortedExtensionsInUse;
+
+// Parses a message of this type from the input and merges it with this
+// message.
+//
+// Warning:  This does not verify that all required fields are present in
+// the input message.
+// Note:  The caller should call
+// -[CodedInputStream checkLastTagWas:] after calling this to
+// verify that the last tag seen was the appropriate end-group tag,
+// or zero for EOF.
+// NOTE: This will throw if there is an error while parsing.
+- (void)mergeFromCodedInputStream:(GPBCodedInputStream *)input
+                extensionRegistry:(GPBExtensionRegistry *)extensionRegistry;
+
+// Parses the next delimited message of this type from the input and merges it
+// with this message.
+- (void)mergeDelimitedFromCodedInputStream:(GPBCodedInputStream *)input
+                         extensionRegistry:
+                             (GPBExtensionRegistry *)extensionRegistry;
+
+- (void)addUnknownMapEntry:(int32_t)fieldNum value:(NSData *)data;
+
+@end
+
+CF_EXTERN_C_BEGIN
+
+// Returns a new instance that was automatically created by |autocreator| for
+// its field |field|.
+GPBMessage *GPBCreateMessageWithAutocreator(Class msgClass,
+                                            GPBMessage *autocreator,
+                                            GPBFieldDescriptor *field)
+    __attribute__((ns_returns_retained));
+
+// Returns whether |message| autocreated this message. This is NO if the message
+// was not autocreated by |message| or if it has been mutated since
+// autocreation.
+BOOL GPBWasMessageAutocreatedBy(GPBMessage *message, GPBMessage *parent);
+
+// Call this when you mutate a message. It will cause the message to become
+// visible to its autocreator.
+void GPBBecomeVisibleToAutocreator(GPBMessage *self);
+
+// Call this when an array/dictionary is mutated so the parent message that
+// autocreated it can react.
+void GPBAutocreatedArrayModified(GPBMessage *self, id array);
+void GPBAutocreatedDictionaryModified(GPBMessage *self, id dictionary);
+
+// Clear the autocreator, if any. Asserts if the autocreator still has an
+// autocreated reference to this message.
+void GPBClearMessageAutocreator(GPBMessage *self);
+
+CF_EXTERN_C_END