Prevent join->join membership transitions changing member count

changelog.d/7977.bugfix

@@ -0,0 +1 @@
+Fix a bug that caused room membership counts to increase when changing per-room profile information. Introduced in Synapse v1.7.2.

synapse/handlers/stats.py

@@ -232,7 +232,7 @@ async def _handle_deltas(self, deltas):
 
                 if membership == prev_membership:
                     pass  # noop
-                if membership == Membership.JOIN:
+                elif membership == Membership.JOIN:
                     room_stats_delta["joined_members"] += 1
                 elif membership == Membership.INVITE:
                     room_stats_delta["invited_members"] += 1

tests/handlers/test_stats.py

@@ -346,6 +346,37 @@ def test_send_message_increments_total_events(self):
 
         self.assertEqual(r1stats_post["total_events"] - r1stats_ante["total_events"], 1)
 
+    def test_updating_profile_information_does_not_increase_joined_members_count(self):
+        """
+        Check that the joined_members count does not increase when a user changes their
+        profile information (which is done by sending another join membership event into
+        the room.
+        """
+        self._perform_background_initial_update()
+
+        # Create a user and room
+        u1 = self.register_user("u1", "pass")
+        u1token = self.login("u1", "pass")
+        r1 = self.helper.create_room_as(u1, tok=u1token)
+
+        # Get the current room stats
+        r1stats_ante = self._get_current_stats("room", r1)
+
+        # Send a profile update into the room
+        new_profile = {"displayname": "bob"}
+        self.helper.change_membership(
+            r1, u1, u1, "join", extra_data=new_profile, tok=u1token
+        )
+
+        # Get the new room stats
+        r1stats_post = self._get_current_stats("room", r1)
+
+        # Ensure that the user count did not changed
+        self.assertEqual(r1stats_post["joined_members"], r1stats_ante["joined_members"])
+        self.assertEqual(
+            r1stats_post["local_users_in_room"], r1stats_ante["local_users_in_room"]
+        )
+
     def test_send_state_event_nonoverwriting(self):
         """
         When we send a non-overwriting state event, it increments total_events AND current_state_events

tests/rest/client/v1/utils.py

@@ -88,7 +88,28 @@ def leave(self, room=None, user=None, expect_code=200, tok=None):
             expect_code=expect_code,
         )
 
-    def change_membership(self, room, src, targ, membership, tok=None, expect_code=200):
+    def change_membership(
+        self,
+        room: str,
+        src: str,
+        targ: str,
+        membership: str,
+        extra_data: dict = {},
+        tok: Optional[str] = None,
+        expect_code: int = 200,
+    ) -> None:
+        """
+        Send a membership state event into a room.
+
+        Args:
+            room: The ID of the room to send to
+            src: The mxid of the event sender
+            targ: The mxid of the event's target. The state key
+            membership: The type of membership event
+            extra_data: Extra information to include in the content of the event
+            tok: The user access token to use
+            expect_code: The expected HTTP response code
+        """
         temp_id = self.auth_user_id
         self.auth_user_id = src
 
@@ -97,6 +118,7 @@ def change_membership(self, room, src, targ, membership, tok=None, expect_code=2
             path = path + "?access_token=%s" % tok
 
         data = {"membership": membership}
+        data.update(extra_data)
 
         request, channel = make_request(
             self.hs.get_reactor(), "PUT", path, json.dumps(data).encode("utf8")