Propagate AttributeErrors when lazily loading plugins

Previously, if an AttributeError was raised in a plugin's make_client
method, the plugin simply wouldn't be an attribute of the ClientManager,
producing tracebacks like

Traceback (most recent call last):
  File ".../openstackclient/shell.py", line 118, in run
    ret_val = super(OpenStackShell, self).run(argv)

  ...

  File ".../openstackclient/object/v1/container.py", line 150, in take_action
    data = self.app.client_manager.object_store.container_list(
  File ".../openstackclient/common/clientmanager.py", line 66, in __getattr__
    raise AttributeError(name)
AttributeError: object_store

This made writing minimal third-party auth plugins difficult, as it
obliterated the original AttributeError.

Now, AttributeErrors that are raised during plugin initialization will
be re-raised as PluginAttributeErrors, and the original traceback will
be preserved. This gives much more useful information to plugin
developers, as in

Traceback (most recent call last):
  File ".../openstackclient/shell.py", line 118, in run
    ret_val = super(OpenStackShell, self).run(argv)

  ...

  File ".../openstackclient/object/v1/container.py", line 150, in take_action
    data = self.app.client_manager.object_store.container_list(
  File ".../openstackclient/common/clientmanager.py", line 57, in __get__
    err_val, err_tb)
  File ".../openstackclient/common/clientmanager.py", line 51, in __get__
    self._handle = self.factory(instance)
  File ".../openstackclient/object/client.py", line 35, in make_client
    interface=instance._interface,
  File ".../openstackclient/common/clientmanager.py", line 258,
  in get_endpoint_for_service_type
    endpoint = self.auth_ref.service_catalog.url_for(
PluginAttributeError: 'NoneType' object has no attribute 'url_for'

Change-Id: I0eee7eba6eccc6d471a699a381185c4e76da10bd

1 files changed, 9 insertions, 1 deletions

diff --git a/openstackclient/common/clientmanager.py b/openstackclient/common/clientmanager.py
index 6d23b55e..8b0fb921 100644
--- a/openstackclient/common/clientmanager.py
+++ b/openstackclient/common/clientmanager.py
@@ -22,8 +22,10 @@ import sys
 
 from oslo_utils import strutils
 import requests
+import six
 
 from openstackclient.api import auth
+from openstackclient.common import exceptions
 from openstackclient.common import session as osc_session
 from openstackclient.identity import client as identity_client
 
@@ -45,7 +47,13 @@ class ClientCache(object):
     def __get__(self, instance, owner):
         # Tell the ClientManager to login to keystone
         if self._handle is None:
-            self._handle = self.factory(instance)
+            try:
+                self._handle = self.factory(instance)
+            except AttributeError as err:
+                # Make sure the failure propagates. Otherwise, the plugin just
+                # quietly isn't there.
+                new_err = exceptions.PluginAttributeError(err)
+                six.reraise(new_err.__class__, new_err, sys.exc_info()[2])
         return self._handle