Use pkg_resources resolve() and require() instead of load()

setuptools 11.3 deprecated the require flag to load() in favor of two
new methods. If those methods are present, use them instead of calling
load(). If those methods are not present, continue to use load() as
before.

Change-Id: I800eec863e34ba4c7a90153e6ae2bfa953bfddd6
Closes-bug: #1407778

stevedore/extension.py

@@ -175,7 +175,14 @@ class ExtensionManager(object):
 
     def _load_one_plugin(self, ep, invoke_on_load, invoke_args, invoke_kwds,
                          verify_requirements):
-        plugin = ep.load(require=verify_requirements)
+        # NOTE(dhellmann): Using require=False is deprecated in
+        # setuptools 11.3.
+        if hasattr(ep, 'resolve') and hasattr(ep, 'require'):
+            if verify_requirements:
+                ep.require()
+            plugin = ep.resolve()
+        else:
+            plugin = ep.load(require=verify_requirements)
         if invoke_on_load:
             obj = plugin(*invoke_args, **invoke_kwds)
         else:

stevedore/tests/test_extension.py

@@ -169,3 +169,43 @@ class TestCallback(utils.TestCase):
 
         result = em.map_method('get_args_and_data', 42)
         self.assertEqual(set(r[2] for r in result), set([42]))
+
+
+class TestLoadRequirementsNewSetuptools(utils.TestCase):
+    # setuptools 11.3 and later
+
+    def setUp(self):
+        super(TestLoadRequirementsNewSetuptools, self).setUp()
+        self.mock_ep = mock.Mock(spec=['require', 'resolve', 'load', 'name'])
+        self.em = extension.ExtensionManager.make_test_instance([])
+
+    def test_verify_requirements(self):
+        self.em._load_one_plugin(self.mock_ep, False, (), {},
+                                 verify_requirements=True)
+        self.mock_ep.require.assert_called_once_with()
+        self.mock_ep.resolve.assert_called_once_with()
+
+    def test_no_verify_requirements(self):
+        self.em._load_one_plugin(self.mock_ep, False, (), {},
+                                 verify_requirements=False)
+        self.assertEqual(0, self.mock_ep.require.call_count)
+        self.mock_ep.resolve.assert_called_once_with()
+
+
+class TestLoadRequirementsOldSetuptools(utils.TestCase):
+    # Before setuptools 11.3
+
+    def setUp(self):
+        super(TestLoadRequirementsOldSetuptools, self).setUp()
+        self.mock_ep = mock.Mock(spec=['load', 'name'])
+        self.em = extension.ExtensionManager.make_test_instance([])
+
+    def test_verify_requirements(self):
+        self.em._load_one_plugin(self.mock_ep, False, (), {},
+                                 verify_requirements=True)
+        self.mock_ep.load.assert_called_once_with(require=True)
+
+    def test_no_verify_requirements(self):
+        self.em._load_one_plugin(self.mock_ep, False, (), {},
+                                 verify_requirements=False)
+        self.mock_ep.load.assert_called_once_with(require=False)