prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Rename modifier missing from update
  Not sure if this is intentional or not but it would be useful to have the `$rename` operator (or "modifier" for the update method for QuerySet and Document) available.
  
  I'm currently working around it with `exec_js`, like so:
  
  ``` python
  Document.objects.exec_js("""
  function() {
    db[collection].update({}, {$rename: {foo: 'bar'}});
  }""")
  ```
  
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `mongoengine/base/common.py`
  Content:
  ```
  1 from mongoengine.errors import NotRegistered
  2 
  3 __all__ = ('UPDATE_OPERATORS', 'get_document', '_document_registry')
  4 
  5 
  6 UPDATE_OPERATORS = set(['set', 'unset', 'inc', 'dec', 'pop', 'push',
  7                         'push_all', 'pull', 'pull_all', 'add_to_set',
  8                         'set_on_insert', 'min', 'max'])
  9 
  10 
  11 _document_registry = {}
  12 
  13 
  14 def get_document(name):
  15     """Get a document class by name."""
  16     doc = _document_registry.get(name, None)
  17     if not doc:
  18         # Possible old style name
  19         single_end = name.split('.')[-1]
  20         compound_end = '.%s' % single_end
  21         possible_match = [k for k in _document_registry.keys()
  22                           if k.endswith(compound_end) or k == single_end]
  23         if len(possible_match) == 1:
  24             doc = _document_registry.get(possible_match.pop(), None)
  25     if not doc:
  26         raise NotRegistered("""
  27             `%s` has not been registered in the document registry.
  28             Importing the document class automatically registers it, has it
  29             been imported?
  30         """.strip() % name)
  31     return doc
  32
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/mongoengine/base/common.py b/mongoengine/base/common.py
  --- a/mongoengine/base/common.py
  +++ b/mongoengine/base/common.py
  @@ -5,7 +5,7 @@
   
   UPDATE_OPERATORS = set(['set', 'unset', 'inc', 'dec', 'pop', 'push',
                           'push_all', 'pull', 'pull_all', 'add_to_set',
  -                        'set_on_insert', 'min', 'max'])
  +                        'set_on_insert', 'min', 'max', 'rename'])
   
   
   _document_registry = {}
  
verification_info: {"golden_diff": "diff --git a/mongoengine/base/common.py b/mongoengine/base/common.py\n--- a/mongoengine/base/common.py\n+++ b/mongoengine/base/common.py\n@@ -5,7 +5,7 @@\n \n UPDATE_OPERATORS = set(['set', 'unset', 'inc', 'dec', 'pop', 'push',\n                         'push_all', 'pull', 'pull_all', 'add_to_set',\n-                        'set_on_insert', 'min', 'max'])\n+                        'set_on_insert', 'min', 'max', 'rename'])\n \n \n _document_registry = {}\n", "issue": "Rename modifier missing from update\nNot sure if this is intentional or not but it would be useful to have the `$rename` operator (or \"modifier\" for the update method for QuerySet and Document) available.\n\nI'm currently working around it with `exec_js`, like so:\n\n``` python\nDocument.objects.exec_js(\"\"\"\nfunction() {\n  db[collection].update({}, {$rename: {foo: 'bar'}});\n}\"\"\")\n```\n\n", "before_files": [{"content": "from mongoengine.errors import NotRegistered\n\n__all__ = ('UPDATE_OPERATORS', 'get_document', '_document_registry')\n\n\nUPDATE_OPERATORS = set(['set', 'unset', 'inc', 'dec', 'pop', 'push',\n                        'push_all', 'pull', 'pull_all', 'add_to_set',\n                        'set_on_insert', 'min', 'max'])\n\n\n_document_registry = {}\n\n\ndef get_document(name):\n    \"\"\"Get a document class by name.\"\"\"\n    doc = _document_registry.get(name, None)\n    if not doc:\n        # Possible old style name\n        single_end = name.split('.')[-1]\n        compound_end = '.%s' % single_end\n        possible_match = [k for k in _document_registry.keys()\n                          if k.endswith(compound_end) or k == single_end]\n        if len(possible_match) == 1:\n            doc = _document_registry.get(possible_match.pop(), None)\n    if not doc:\n        raise NotRegistered(\"\"\"\n            `%s` has not been registered in the document registry.\n            Importing the document class automatically registers it, has it\n            been imported?\n        \"\"\".strip() % name)\n    return doc\n", "path": "mongoengine/base/common.py"}], "after_files": [{"content": "from mongoengine.errors import NotRegistered\n\n__all__ = ('UPDATE_OPERATORS', 'get_document', '_document_registry')\n\n\nUPDATE_OPERATORS = set(['set', 'unset', 'inc', 'dec', 'pop', 'push',\n                        'push_all', 'pull', 'pull_all', 'add_to_set',\n                        'set_on_insert', 'min', 'max', 'rename'])\n\n\n_document_registry = {}\n\n\ndef get_document(name):\n    \"\"\"Get a document class by name.\"\"\"\n    doc = _document_registry.get(name, None)\n    if not doc:\n        # Possible old style name\n        single_end = name.split('.')[-1]\n        compound_end = '.%s' % single_end\n        possible_match = [k for k in _document_registry.keys()\n                          if k.endswith(compound_end) or k == single_end]\n        if len(possible_match) == 1:\n            doc = _document_registry.get(possible_match.pop(), None)\n    if not doc:\n        raise NotRegistered(\"\"\"\n            `%s` has not been registered in the document registry.\n            Importing the document class automatically registers it, has it\n            been imported?\n        \"\"\".strip() % name)\n    return doc\n", "path": "mongoengine/base/common.py"}]}