use stevedore to load extensions

Importing pkg_resources causes the app to scan the entire import path
for all distributions, not just those providing entry points. The
scanner in stevedore will have a cache of the entry point data, making
it significantly faster. This will be especially useful in command
line programs like python-openstackclient.

Change-Id: Ic5eb9401c8ea3bd9624b818e0ffb8dcc13f61559
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

lower-constraints.txt

@@ -92,7 +92,7 @@ Routes==2.3.1
 simplejson==3.5.1
 smmap==0.9.0
 statsd==3.2.1
-stevedore==1.20.0
+stevedore==2.0.1
 tempest==17.1.0
 tenacity==3.2.1
 stestr==2.0.0

novaclient/client.py

@@ -28,7 +28,7 @@ from keystoneauth1 import adapter
 from keystoneauth1 import identity
 from keystoneauth1 import session as ksession
 from oslo_utils import importutils
-import pkg_resources
+import stevedore
 
 import novaclient
 from novaclient import api_versions
@@ -176,12 +176,15 @@ def _discover_via_python_path():
             yield name, module
 
 
-def _discover_via_entry_points():
-    for ep in pkg_resources.iter_entry_points('novaclient.extension'):
-        name = ep.name
-        module = ep.load()
+def _make_discovery_manager():
+    # This function provides a place to mock out the entry point scan
+    return stevedore.ExtensionManager('novaclient.extension')
 
-        yield name, module
+
+def _discover_via_entry_points():
+    mgr = _make_discovery_manager()
+    for extension in mgr:
+        yield extension.name, extension.plugin
 
 
 def _get_client_class_and_version(version):

novaclient/tests/unit/test_discover.py

@@ -17,7 +17,8 @@ import imp
 import inspect
 from unittest import mock
 
-import pkg_resources
+import stevedore
+from stevedore import extension
 
 from novaclient import client
 from novaclient.tests.unit import utils
@@ -27,16 +28,20 @@ class DiscoverTest(utils.TestCase):
 
     def test_discover_via_entry_points(self):
 
-        def mock_iter_entry_points(group):
-            if group == 'novaclient.extension':
-                fake_ep = mock.Mock()
-                fake_ep.name = 'foo'
-                fake_ep.module = imp.new_module('foo')
-                fake_ep.load.return_value = fake_ep.module
-                return [fake_ep]
+        def mock_mgr():
+            fake_ep = mock.Mock()
+            fake_ep.name = 'foo'
+            fake_ep.module = imp.new_module('foo')
+            fake_ep.load.return_value = fake_ep.module
+            fake_ext = extension.Extension(
+                name='foo',
+                entry_point=fake_ep,
+                plugin=fake_ep.module,
+                obj=None,
+            )
+            return stevedore.ExtensionManager.make_test_instance([fake_ext])
 
-        @mock.patch.object(pkg_resources, 'iter_entry_points',
-                           mock_iter_entry_points)
+        @mock.patch.object(client, '_make_discovery_manager', mock_mgr)
         def test():
             for name, module in client._discover_via_entry_points():
                 self.assertEqual('foo', name)

requirements.txt

@@ -9,3 +9,4 @@ oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
 PrettyTable<0.8,>=0.7.2 # BSD
 simplejson>=3.5.1 # MIT
+stevedore>=2.0.1 # Apache-2.0