Deprecate legacy way to retrieve neutron usage

neutron 'quota_details' extension was added in Pike to provide
a convenient way to retrieve resource usage in neutron without listing
individual resources. It was added in Pike release and we will have
six releases since then once Ussuri release is shipped. Enough time has
passed to migrate it to the new mechanism, so it is time to deprecate
the legacy way for future cleanup.

Change-Id: Ie0b4613bf9fdcd96481b3bb1139b4fb153bfef83

openstack_dashboard/settings.py

@@ -20,6 +20,7 @@ import glob
 import logging
 import os
 import sys
+import warnings
 
 from django.utils.translation import ugettext_lazy as _
 
@@ -40,6 +41,8 @@ from openstack_dashboard.defaults import *  # noqa: F403,H303
 
 _LOG = logging.getLogger(__name__)
 
+warnings.filterwarnings("default", category=DeprecationWarning)
+
 ROOT_PATH = os.path.dirname(os.path.abspath(__file__))
 
 if ROOT_PATH not in sys.path:

openstack_dashboard/usage/quotas.py

@@ -13,6 +13,7 @@
 from collections import defaultdict
 import itertools
 import logging
+import warnings
 
 from django.utils.translation import ugettext_lazy as _
 
@@ -361,8 +362,14 @@ def _get_neutron_quota_data(request, qs, disabled_quotas, tenant_id):
     return qs
 
 
+# TODO(amotoki): Deprecated in Ussuri. Drop this in Victoria release or later.
 def _get_tenant_network_usages_legacy(request, usages, disabled_quotas,
                                       tenant_id):
+    warnings.warn(
+        "The legacy way to retrieve neutron resource usage is deprecated "
+        "in Ussuri release. Horizon will depend on 'quota_details' "
+        "neutron extension added in Pike release in future.",
+        DeprecationWarning)
     qs = base.QuotaSet()
     _get_neutron_quota_data(request, qs, disabled_quotas, tenant_id)
     for quota in qs:

releasenotes/notes/deprecate-neutron-quota-legacy-144468a1b269cce8.yaml

@@ -0,0 +1,9 @@
+---
+deprecations:
+  - |
+    The legacy way to retrive neutron resource usages is deprecated.
+    In future, horizon will require ``quota_details`` neutron extension.
+    In the legacy way, horizon list all related resources to count resource usage.
+    It is not efficient and ``quota_details`` neutron extension was added
+    to address it. It was implemented in Pike release and the enough migration
+    period has passed, so we deprecate the legacy way.