Tweak the way plugin attributes are loaded

By using the setdefault method to add plugin parameters to the kwargs
passed to load_from_options() we are unnecessarily calling the getter
function when the value may not be saved.

This has generally not been a problem however if we start doing things
like prompting users for a password in the getter this is an expensive
and disruptive operation for a parameter that may not be stored.

Change-Id: Ic8dc3a425662c4a89372f178b175b8caab44e024

keystoneauth1/loading/base.py

@@ -139,10 +139,10 @@ class BaseLoader(object):
         :returns: An authentication Plugin.
         :rtype: :py:class:`keystoneauth1.plugin.BaseAuthPlugin`
         """
-        for opt in self.get_options():
+        for opt in (o for o in self.get_options() if o.dest not in kwargs):
             val = getter(opt)
             if val is not None:
                 val = opt.type(val)
-            kwargs.setdefault(opt.dest, val)
+            kwargs[opt.dest] = val
 
         return self.load_from_options(**kwargs)

keystoneauth1/tests/unit/loading/test_loading.py

@@ -77,3 +77,26 @@ class LoadingTests(utils.TestCase):
 
         # check that additional kwargs get passed through
         self.assertEqual(val, p['other'])
+
+    def test_loading_getter_with_kwargs(self):
+        called_opts = set()
+
+        vals = {'a-bool': False,
+                'a-float': 99.99}
+
+        def _getter(opt):
+            called_opts.add(opt.name)
+            # return str because oslo.config should convert them back
+            return str(vals[opt.name])
+
+        p = utils.MockLoader().load_from_options_getter(_getter,
+                                                        a_int=66,
+                                                        a_str='another')
+
+        # only the options not passed by kwargs should get passed to getter
+        self.assertEqual(set(('a-bool', 'a-float')), called_opts)
+
+        self.assertEqual(False, p['a_bool'])
+        self.assertEqual(99.99, p['a_float'])
+        self.assertEqual('another', p['a_str'])
+        self.assertEqual(66, p['a_int'])