Add support for stable code identifier pickling.

cloudpickle/cloudpickle.py

@@ -123,10 +123,18 @@ class CloudPickleConfig:
 
         filepath_interceptor: Used to modify filepaths in `co_filename` and
             function.__globals__['__file__'].
+
+        get_code_object_identifier: Use identifiers derived from code
+            location when pickling dynamic functions (e.g. lambdas). Enabling
+            this setting results in pickled payloads becoming more stable to
+            code changes: when a particular lambda function is slightly
+            modified  but the location of the function in the codebase has not
+            changed, the pickled representation might stay the same.
     """
     id_generator: typing.Optional[callable] = uuid_generator
     skip_reset_dynamic_type_state: bool = False
     filepath_interceptor: typing.Optional[callable]  = None
+    get_code_object_identifier: typing.Optional[callable] = None
 
 DEFAULT_CONFIG = CloudPickleConfig()
 
@@ -569,6 +577,12 @@ def _make_function(code, globals, name, argdefs, closure):
     return types.FunctionType(code, globals, name, argdefs, closure)
 
 
+def _make_function_from_identifier(
+    get_code_from_identifier, code_path, globals, name, argdefs, closure):
+  fcode = get_code_from_identifier(code_path)
+  return _make_function(fcode, globals, name, argdefs, closure)
+
+
 def _make_empty_cell():
     if False:
         # trick the compiler into creating an empty cell in our lambda
@@ -1307,6 +1321,20 @@ class Pickler(pickle.Pickler):
 
     dispatch_table = ChainMap(_dispatch_table, copyreg.dispatch_table)
 
+    def _stable_identifier_function_reduce(self, func):
+        code_path = self.config.get_code_object_identifier(func)
+        if not code_path:
+            return self._dynamic_function_reduce(func)
+        newargs = (code_path, )
+        state = _function_getstate(func)
+        return (
+            _make_function_from_identifier,
+            newargs,
+            state,
+            None,
+            None,
+            _function_setstate)
+
     # function reducers are defined as instance methods of cloudpickle.Pickler
     # objects, as they rely on a cloudpickle.Pickler attribute (globals_ref)
     def _dynamic_function_reduce(self, func):
@@ -1326,6 +1354,8 @@ def _function_reduce(self, obj):
         """
         if _should_pickle_by_reference(obj):
             return NotImplemented
+        elif self.config.get_code_object_identifier is not None:
+            return self._stable_identifier_function_reduce(obj)
         else:
             return self._dynamic_function_reduce(obj)