Skip most service_description for unknown services

When we don't know anything about a service, we can know early
in the process that we're never going to match a supported version.
That means we can just directly and without malice or warnings
return a REST adapter and be done with it.

Change-Id: Ifd4f2fce59c76148807fb7390f68eaae179694c4

openstack/service_description.py

@@ -100,7 +100,19 @@ class ServiceDescription(object):
                 self.service_type,
                 config.get_disabled_reason(self.service_type))
 
-        # First, check to see if we've got config that matches what we
+        # We don't know anything about this service, so the user is
+        # explicitly just using us for a passthrough REST adapter.
+        # Skip all the lower logic.
+        if not self.supported_versions:
+            temp_client = config.get_session_client(
+                self.service_type,
+                allow_version_hack=True,
+            )
+            # trigger EndpointNotFound exception if this is bogus
+            temp_client.get_endpoint()
+            return temp_client
+
+        # Check to see if we've got config that matches what we
         # understand in the SDK.
         version_string = config.get_api_version(self.service_type)
         endpoint_override = config.get_endpoint(self.service_type)
@@ -111,7 +123,7 @@ class ServiceDescription(object):
             version_string = list(self.supported_versions)[0]
 
         proxy_obj = None
-        if endpoint_override and version_string and self.supported_versions:
+        if endpoint_override and version_string:
             # Both endpoint override and version_string are set, we don't
             # need to do discovery - just trust the user.
             proxy_class = self.supported_versions.get(version_string[0])
@@ -129,7 +141,7 @@ class ServiceDescription(object):
                         version=version_string,
                         service_type=self.service_type),
                     category=exceptions.UnsupportedServiceVersion)
-        elif endpoint_override and self.supported_versions:
+        elif endpoint_override:
             temp_adapter = config.get_session_client(
                 self.service_type
             )
@@ -181,7 +193,7 @@ class ServiceDescription(object):
         version_kwargs = {}
         if version_string:
             version_kwargs['version'] = version_string
-        elif self.supported_versions:
+        else:
             supported_versions = sorted([
                 int(f) for f in self.supported_versions])
             version_kwargs['min_version'] = str(supported_versions[0])

openstack/tests/unit/test_connection.py

@@ -15,8 +15,10 @@ import os
 import fixtures
 from keystoneauth1 import session
 import mock
+from testtools import matchers
 
 from openstack import connection
+from openstack import proxy
 import openstack.config
 from openstack.tests.unit import base
 from openstack.tests.unit.fake import fake_service
@@ -145,6 +147,24 @@ class TestConnection(base.TestCase):
         # self.assertEqual('openstack.workflow.v2._proxy',
         #                  conn.workflow.__class__.__module__)
 
+    def test_create_unknown_proxy(self):
+        self.register_uris([
+            self.get_placement_discovery_mock_dict(),
+        ])
+
+        def closure():
+            return self.cloud.placement
+
+        self.assertThat(
+            closure,
+            matchers.Warnings(matchers.HasLength(0)))
+
+        self.assertIsInstance(
+            self.cloud.placement,
+            proxy.Proxy)
+
+        self.assert_calls()
+
     def test_create_connection_version_param_default(self):
         c1 = connection.Connection(cloud='sample-cloud')
         conn = connection.Connection(session=c1.session)