Use six.wraps() for Metrics so decorated methods can be inspected

Previously it was using functools.wraps() to create the decorators.
The problem is that we can't use the
oslo_utils.reflection.get_signature() function to get the correct
signature.

Change it to use six.wraps() which will add the '__wrapped__'
attribute which will be used when calling get_signature() and return
the signature of the decorated function.

Added unit tests to show we are able to see the signature of a wrapped
function.

Closes-Bug: #1746730
Change-Id: I75428e948b64b3b6758d31678a80d158a11c6beb

ironic_lib/metrics.py

@@ -14,7 +14,6 @@
 #    under the License.
 
 import abc
-import functools
 import random
 import time
 
@@ -55,7 +54,7 @@ class Timer(object):
         self._start = None
 
     def __call__(self, f):
-        @functools.wraps(f)
+        @six.wraps(f)
         def wrapped(*args, **kwargs):
             start = _time()
             result = f(*args, **kwargs)
@@ -117,7 +116,7 @@ class Counter(object):
         self.sample_rate = sample_rate
 
     def __call__(self, f):
-        @functools.wraps(f)
+        @six.wraps(f)
         def wrapped(*args, **kwargs):
             self.metrics.send_counter(
                 self.metrics.get_metric_name(self.name),
@@ -164,7 +163,7 @@ class Gauge(object):
         self.name = name
 
     def __call__(self, f):
-        @functools.wraps(f)
+        @six.wraps(f)
         def wrapped(*args, **kwargs):
             result = f(*args, **kwargs)
             self.metrics.send_gauge(self.metrics.get_metric_name(self.name),

ironic_lib/tests/test_metrics.py

@@ -16,17 +16,63 @@
 import types
 
 import mock
+from oslo_utils import reflection
 
 from ironic_lib import metrics as metricslib
+from ironic_lib import metrics_utils
 from ironic_lib.tests import base
 
 
+METRICS = metrics_utils.get_metrics_logger(prefix='foo', backend='noop')
+
+
+@METRICS.timer('testing1')
+def timer_check(run, timer=None):
+    pass
+
+
+@METRICS.counter('testing2')
+def counter_check(run, counter=None):
+    pass
+
+
+@METRICS.gauge('testing2')
+def gauge_check(run, gauge=None):
+    pass
+
+
 class MockedMetricLogger(metricslib.MetricLogger):
     _gauge = mock.Mock(spec_set=types.FunctionType)
     _counter = mock.Mock(spec_set=types.FunctionType)
     _timer = mock.Mock(spec_set=types.FunctionType)
 
 
+class TestMetricReflection(base.IronicLibTestCase):
+    def test_timer_reflection(self):
+        # Ensure our decorator is done correctly (six.wraps) and we can get the
+        # arguments of our decorated function.
+        expected = ['run', 'timer']
+        signature = reflection.get_signature(timer_check)
+        parameters = list(signature.parameters)
+        self.assertEqual(expected, parameters)
+
+    def test_counter_reflection(self):
+        # Ensure our decorator is done correctly (six.wraps) and we can get the
+        # arguments of our decorated function.
+        expected = ['run', 'counter']
+        signature = reflection.get_signature(counter_check)
+        parameters = list(signature.parameters)
+        self.assertEqual(expected, parameters)
+
+    def test_gauge_reflection(self):
+        # Ensure our decorator is done correctly (six.wraps) and we can get the
+        # arguments of our decorated function.
+        expected = ['run', 'gauge']
+        signature = reflection.get_signature(gauge_check)
+        parameters = list(signature.parameters)
+        self.assertEqual(expected, parameters)
+
+
 class TestMetricLogger(base.IronicLibTestCase):
     def setUp(self):
         super(TestMetricLogger, self).setUp()