shim _resource_extend for neutron-lib

The resource_extend module was rehomed into neutron-lib with commit
https://review.openstack.org/#/c/613431/
This patch shims neutron.db._resource_extend to reference neutron-lib's
implementation allowing consumers to switch over with worrying about
dependency chains. Once all consumers switch over a follow-up patch
will be submitted to remove neutron's _resource_extend module.

NeutronLibImpact

Change-Id: I9ffe91b6dedaf46d679c6a3c4f465f2bfd66e32d

neutron/db/_resource_extend.py

@@ -15,124 +15,13 @@ NOTE: This module shall not be used by external projects. It will be moved
       to neutron-lib in due course, and then it can be used from there.
 """
 
-import collections
-import inspect
+from neutron_lib.db import resource_extend
 
-from neutron_lib.utils import helpers
 
-
-# This dictionary will store methods for extending API resources.
-# Extensions can add their own methods by invoking register_funcs().
-_resource_extend_functions = {
-    # <resource1> : [<func1>, <func2>, ...],
-    # <resource2> : [<func1>, <func2>, ...],
-    # ...
-}
-
-# This dictionary will store @extends decorated methods with a list of
-# resources that each method will extend on class initialization.
-_DECORATED_EXTEND_METHODS = collections.defaultdict(list)
-
-
-def register_funcs(resource, funcs):
-    """Add functions to extend a resource.
-
-    :param resource: A resource collection name.
-    :type resource: str
-
-    :param funcs: A list of functions.
-    :type funcs: list of callable
-
-    These functions take a resource dict and a resource object and
-    update the resource dict with extension data (possibly retrieved
-    from the resource db object).
-        def _extend_foo_with_bar(foo_res, foo_db):
-            foo_res['bar'] = foo_db.bar_info  # example
-            return foo_res
-
-    """
-    funcs = [helpers.make_weak_ref(f) if callable(f) else f
-             for f in funcs]
-    _resource_extend_functions.setdefault(resource, []).extend(funcs)
-
-
-def get_funcs(resource):
-    """Retrieve a list of functions extending a resource.
-
-    :param resource: A resource collection name.
-    :type resource: str
-
-    :return: A list (possibly empty) of functions extending resource.
-    :rtype: list of callable
-
-    """
-    return _resource_extend_functions.get(resource, [])
-
-
-def apply_funcs(resource_type, response, db_object):
-    for func in get_funcs(resource_type):
-        resolved_func = helpers.resolve_ref(func)
-        if resolved_func:
-            resolved_func(response, db_object)
-
-
-def extends(resources):
-    """Use to decorate methods on classes before initialization.
-
-    Any classes that use this must themselves be decorated with the
-    @has_resource_extenders decorator to setup the __new__ method to
-    actually register the instance methods after initialization.
-
-    :param resources: Resource collection names. The decorated method will
-                      be registered with each resource as an extend function.
-    :type resources: list of str
-
-    """
-    def decorator(method):
-        _DECORATED_EXTEND_METHODS[method].extend(resources)
-        return method
-    return decorator
-
-
-def has_resource_extenders(klass):
-    """Decorator to setup __new__ method in classes to extend resources.
-
-    Any method decorated with @extends above is an unbound method on a class.
-    This decorator sets up the class __new__ method to add the bound
-    method to _resource_extend_functions after object instantiation.
-    """
-    orig_new = klass.__new__
-    new_inherited = '__new__' not in klass.__dict__
-
-    @staticmethod
-    def replacement_new(cls, *args, **kwargs):
-        if new_inherited:
-            # class didn't define __new__ so we need to call inherited __new__
-            super_new = super(klass, cls).__new__
-            if super_new is object.__new__:
-                # object.__new__ doesn't accept args nor kwargs
-                instance = super_new(cls)
-            else:
-                instance = super_new(cls, *args, **kwargs)
-        else:
-            instance = orig_new(cls, *args, **kwargs)
-        if getattr(instance, '_DECORATED_METHODS_REGISTERED', False):
-            # Avoid running this logic twice for classes inheriting other
-            # classes with this same decorator. Only one needs to execute
-            # to subscribe all decorated methods.
-            return instance
-        for name, unbound_method in inspect.getmembers(cls):
-            if (not inspect.ismethod(unbound_method) and
-                    not inspect.isfunction(unbound_method)):
-                continue
-            # Handle py27/py34 difference
-            method = getattr(unbound_method, 'im_func', unbound_method)
-            if method not in _DECORATED_EXTEND_METHODS:
-                continue
-            for resource in _DECORATED_EXTEND_METHODS[method]:
-                # Register the bound method for the resourse
-                register_funcs(resource, [method])
-        setattr(instance, '_DECORATED_METHODS_REGISTERED', True)
-        return instance
-    klass.__new__ = replacement_new
-    return klass
+_resource_extend_functions = resource_extend._resource_extend_functions
+_DECORATED_EXTEND_METHODS = resource_extend._DECORATED_EXTEND_METHODS
+register_funcs = resource_extend.register_funcs
+get_funcs = resource_extend.get_funcs
+apply_funcs = resource_extend.apply_funcs
+extends = resource_extend.extends
+has_resource_extenders = resource_extend.has_resource_extenders

neutron/tests/base.py

@@ -46,7 +46,6 @@ from neutron.api.rpc.callbacks.consumer import registry as rpc_consumer_reg
 from neutron.api.rpc.callbacks.producer import registry as rpc_producer_reg
 from neutron.common import config
 from neutron.conf.agent import common as agent_config
-from neutron.db import _resource_extend as resource_extend
 from neutron.db import agentschedulers_db
 from neutron import manager
 from neutron import policy
@@ -205,17 +204,13 @@ class DietTestCase(base.BaseTestCase):
         # six before removing the cleanup callback from here.
         self.addCleanup(mock.patch.stopall)
 
-        self.addCleanup(self.reset_resource_extend_functions)
+        self.useFixture(fixture.DBResourceExtendFixture())
 
         self.addOnException(self.check_for_systemexit)
         self.orig_pid = os.getpid()
 
         tools.reset_random_seed()
 
-    @staticmethod
-    def reset_resource_extend_functions():
-        resource_extend._resource_extend_functions = {}
-
     def addOnException(self, handler):
 
         def safe_handler(*args, **kwargs):