From 37b845dabc687b1e0d4bc84bf5933db10db641d5 Mon Sep 17 00:00:00 2001
From: David Robertson <davidr@element.io>
Date: Mon, 18 Oct 2021 14:20:04 +0100
Subject: [PATCH] Don't remove local users from dir when the leave their last
 room (#11103)

---
 changelog.d/11103.bugfix              |  1 +
 synapse/handlers/user_directory.py    | 13 ++++---
 tests/handlers/test_user_directory.py | 50 +++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 5 deletions(-)
 create mode 100644 changelog.d/11103.bugfix

diff --git a/changelog.d/11103.bugfix b/changelog.d/11103.bugfix
new file mode 100644
index 000000000..3498f04a4
--- /dev/null
+++ b/changelog.d/11103.bugfix
@@ -0,0 +1 @@
+Fix local users who left all their rooms being removed from the user directory, even if the "search_all_users" config option was enabled.
\ No newline at end of file
diff --git a/synapse/handlers/user_directory.py b/synapse/handlers/user_directory.py
index 99f23ed96..991fee7e5 100644
--- a/synapse/handlers/user_directory.py
+++ b/synapse/handlers/user_directory.py
@@ -415,16 +415,19 @@ class UserDirectoryHandler(StateDeltasHandler):
             room_id: The room ID that user left or stopped being public that
             user_id
         """
-        logger.debug("Removing user %r", user_id)
+        logger.debug("Removing user %r from room %r", user_id, room_id)
 
         # Remove user from sharing tables
         await self.store.remove_user_who_share_room(user_id, room_id)
 
-        # Are they still in any rooms? If not, remove them entirely.
-        rooms_user_is_in = await self.store.get_user_dir_rooms_user_is_in(user_id)
+        # Additionally, if they're a remote user and we're no longer joined
+        # to any rooms they're in, remove them from the user directory.
+        if not self.is_mine_id(user_id):
+            rooms_user_is_in = await self.store.get_user_dir_rooms_user_is_in(user_id)
 
-        if len(rooms_user_is_in) == 0:
-            await self.store.remove_from_user_dir(user_id)
+            if len(rooms_user_is_in) == 0:
+                logger.debug("Removing user %r from directory", user_id)
+                await self.store.remove_from_user_dir(user_id)
 
     async def _handle_possible_remote_profile_change(
         self,
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index e0635c889..b9ad92b97 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -914,6 +914,56 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
             self.hs.get_storage().persistence.persist_event(event, context)
         )
 
+    def test_local_user_leaving_room_remains_in_user_directory(self) -> None:
+        """We've chosen to simplify the user directory's implementation by
+        always including local users. Ensure this invariant is maintained when
+        a local user
+        - leaves a room, and
+        - leaves the last room they're in which is visible to this server.
+
+        This is user-visible if the "search_all_users" config option is on: the
+        local user who left a room would no longer be searchable if this test fails!
+        """
+        alice = self.register_user("alice", "pass")
+        alice_token = self.login(alice, "pass")
+        bob = self.register_user("bob", "pass")
+        bob_token = self.login(bob, "pass")
+
+        # Alice makes two public rooms, which Bob joins.
+        room1 = self.helper.create_room_as(alice, is_public=True, tok=alice_token)
+        room2 = self.helper.create_room_as(alice, is_public=True, tok=alice_token)
+        self.helper.join(room1, bob, tok=bob_token)
+        self.helper.join(room2, bob, tok=bob_token)
+
+        # The user directory tables are updated.
+        users, in_public, in_private = self.get_success(
+            self.user_dir_helper.get_tables()
+        )
+        self.assertEqual(users, {alice, bob})
+        self.assertEqual(
+            in_public, {(alice, room1), (alice, room2), (bob, room1), (bob, room2)}
+        )
+        self.assertEqual(in_private, set())
+
+        # Alice leaves one room. She should still be in the directory.
+        self.helper.leave(room1, alice, tok=alice_token)
+        users, in_public, in_private = self.get_success(
+            self.user_dir_helper.get_tables()
+        )
+        self.assertEqual(users, {alice, bob})
+        self.assertEqual(in_public, {(alice, room2), (bob, room1), (bob, room2)})
+        self.assertEqual(in_private, set())
+
+        # Alice leaves the other. She should still be in the directory.
+        self.helper.leave(room2, alice, tok=alice_token)
+        self.wait_for_background_updates()
+        users, in_public, in_private = self.get_success(
+            self.user_dir_helper.get_tables()
+        )
+        self.assertEqual(users, {alice, bob})
+        self.assertEqual(in_public, {(bob, room1), (bob, room2)})
+        self.assertEqual(in_private, set())
+
 
 class TestUserDirSearchDisabled(unittest.HomeserverTestCase):
     servlets = [