api: Always return zulip_version/zulip_feature_level.

We no longer make these conditional to simplify writing clients;
there's no cost to including them, and a real cost to not doing so.

templates/zerver/api/changelog.md

@@ -10,6 +10,12 @@ below features are supported.
 
 ## Changes in Zulip 2.2
 
+**Feature level 3**:
+
+* `zulip_version` and `zulip_feature_level` are always returned
+  in `POST /register`; previously they were only returned if `event_types`
+  included `zulip_version`.
+
 **Feature level 2**:
 
 * [`POST /messages/{message_id}/reactions`](/api/add-emoji-reaction):

zerver/lib/events.py

@@ -97,6 +97,10 @@ def fetch_initial_state_data(user_profile: UserProfile,
     else:
         want = set(event_types).__contains__
 
+    # Show the version info unconditionally.
+    state['zulip_version'] = ZULIP_VERSION
+    state['zulip_feature_level'] = API_FEATURE_LEVEL
+
     if want('alert_words'):
         state['alert_words'] = user_alert_words(user_profile)
 
@@ -310,10 +314,6 @@ def fetch_initial_state_data(user_profile: UserProfile,
     if want('user_status'):
         state['user_status'] = get_user_info_dict(realm_id=realm.id)
 
-    if want('zulip_version'):
-        state['zulip_version'] = ZULIP_VERSION
-        state['zulip_feature_level'] = API_FEATURE_LEVEL
-
     return state
 
 def apply_events(state: Dict[str, Any], events: Iterable[Dict[str, Any]],

zerver/openapi/zulip.yaml

@@ -2587,6 +2587,14 @@ paths:
                       type: integer
                       description: |
                         The initial value of `last_event_id` to pass to `GET /api/v1/events`.
+                    zulip_feature_level:
+                      type: integer
+                      description: |
+                        The server's current [Zulip feature level](/api/changelog).
+                    zulip_version:
+                      type: string
+                      description: |
+                        The server's version.
                 - example:
                     {
                         "last_event_id": -1,
@@ -2605,7 +2613,9 @@ paths:
                                 "source_url": "/user_avatars/1/emoji/images/1.png"
                             }
                         },
-                        "result": "success"
+                        "result": "success",
+                        "zulip_feature_level": 2,
+                        "zulip_version": "2.1.0"
                     }
   /server_settings:
     get:

zerver/tests/test_events.py

@@ -3662,7 +3662,6 @@ class FetchQueriesTest(ZulipTestCase):
             update_global_notifications=0,
             update_message_flags=5,
             user_status=1,
-            zulip_version=0,
         )
 
         wanted_event_types = {