Return read-only collections from @cached methods (#13755)

It's important that collections returned from `@cached` methods are not
modified, otherwise future retrievals from the cache will return the
modified collection.

This applies to the return values from `@cached` methods and the values
inside the dictionaries returned by `@cachedList` methods. It's not
necessary for the dictionaries returned by `@cachedList` methods
themselves to be read-only.

Signed-off-by: Sean Quah <[email protected]>
Co-authored-by: David Robertson <[email protected]>

changelog.d/13755.misc

@@ -0,0 +1 @@
+Re-type hint some collections as read-only.

synapse/app/phone_stats_home.py

@@ -15,7 +15,7 @@
 import math
 import resource
 import sys
-from typing import TYPE_CHECKING, List, Sized, Tuple
+from typing import TYPE_CHECKING, List, Mapping, Sized, Tuple
 
 from prometheus_client import Gauge
 
@@ -194,7 +194,7 @@ def performance_stats_init() -> None:
     @wrap_as_background_process("generate_monthly_active_users")
     async def generate_monthly_active_users() -> None:
         current_mau_count = 0
-        current_mau_count_by_service = {}
+        current_mau_count_by_service: Mapping[str, int] = {}
         reserved_users: Sized = ()
         store = hs.get_datastores().main
         if hs.config.server.limit_usage_by_mau or hs.config.server.mau_stats_only:

synapse/config/room_directory.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Any, List
+from typing import Any, Collection
 
 from matrix_common.regex import glob_to_regex
 
@@ -70,7 +70,7 @@ def is_alias_creation_allowed(self, user_id: str, room_id: str, alias: str) -> b
         return False
 
     def is_publishing_room_allowed(
-        self, user_id: str, room_id: str, aliases: List[str]
+        self, user_id: str, room_id: str, aliases: Collection[str]
     ) -> bool:
         """Checks if the given user is allowed to publish the room
 
@@ -122,7 +122,7 @@ def __init__(self, option_name: str, rule: JsonDict):
         except Exception as e:
             raise ConfigError("Failed to parse glob into regex") from e
 
-    def matches(self, user_id: str, room_id: str, aliases: List[str]) -> bool:
+    def matches(self, user_id: str, room_id: str, aliases: Collection[str]) -> bool:
         """Tests if this rule matches the given user_id, room_id and aliases.
 
         Args:

synapse/events/builder.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
+from typing import TYPE_CHECKING, Any, Collection, Dict, List, Optional, Tuple, Union
 
 import attr
 from signedjson.types import SigningKey
@@ -103,7 +103,7 @@ def is_state(self) -> bool:
 
     async def build(
         self,
-        prev_event_ids: List[str],
+        prev_event_ids: Collection[str],
         auth_event_ids: Optional[List[str]],
         depth: Optional[int] = None,
     ) -> EventBase:
@@ -136,7 +136,7 @@ async def build(
 
         format_version = self.room_version.event_format
         # The types of auth/prev events changes between event versions.
-        prev_events: Union[List[str], List[Tuple[str, Dict[str, str]]]]
+        prev_events: Union[Collection[str], List[Tuple[str, Dict[str, str]]]]
         auth_events: Union[List[str], List[Tuple[str, Dict[str, str]]]]
         if format_version == EventFormatVersions.ROOM_V1_V2:
             auth_events = await self._store.add_event_hashes(auth_event_ids)

synapse/federation/federation_server.py

@@ -23,6 +23,7 @@
     Collection,
     Dict,
     List,
+    Mapping,
     Optional,
     Tuple,
     Union,
@@ -1512,7 +1513,7 @@ async def on_query(self, query_type: str, args: dict) -> JsonDict:
 def _get_event_ids_for_partial_state_join(
     join_event: EventBase,
     prev_state_ids: StateMap[str],
-    summary: Dict[str, MemberSummary],
+    summary: Mapping[str, MemberSummary],
 ) -> Collection[str]:
     """Calculate state to be returned in a partial_state send_join
 

synapse/handlers/directory.py

@@ -14,7 +14,7 @@
 
 import logging
 import string
-from typing import TYPE_CHECKING, Iterable, List, Optional
+from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence
 
 from typing_extensions import Literal
 
@@ -486,7 +486,7 @@ async def edit_published_room_list(
             )
             if canonical_alias:
                 # Ensure we do not mutate room_aliases.
-                room_aliases = room_aliases + [canonical_alias]
+                room_aliases = list(room_aliases) + [canonical_alias]
 
             if not self.config.roomdirectory.is_publishing_room_allowed(
                 user_id, room_id, room_aliases
@@ -529,7 +529,7 @@ async def edit_published_appservice_room_list(
 
     async def get_aliases_for_room(
         self, requester: Requester, room_id: str
-    ) -> List[str]:
+    ) -> Sequence[str]:
         """
         Get a list of the aliases that currently point to this room on this server
         """

synapse/handlers/receipts.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import TYPE_CHECKING, Iterable, List, Optional, Tuple
+from typing import TYPE_CHECKING, Iterable, List, Optional, Sequence, Tuple
 
 from synapse.api.constants import EduTypes, ReceiptTypes
 from synapse.appservice import ApplicationService
@@ -189,7 +189,7 @@ def __init__(self, hs: "HomeServer"):
 
     @staticmethod
     def filter_out_private_receipts(
-        rooms: List[JsonDict], user_id: str
+        rooms: Sequence[JsonDict], user_id: str
     ) -> List[JsonDict]:
         """
         Filters a list of serialized receipts (as returned by /sync and /initialSync)

synapse/handlers/room.py

@@ -1928,6 +1928,6 @@ async def shutdown_room(
         return {
             "kicked_users": kicked_users,
             "failed_to_kick_users": failed_to_kick_users,
-            "local_aliases": aliases_for_room,
+            "local_aliases": list(aliases_for_room),
             "new_room_id": new_room_id,
         }

synapse/handlers/sync.py

@@ -1519,7 +1519,7 @@ async def generate_sync_result(
             one_time_keys_count = await self.store.count_e2e_one_time_keys(
                 user_id, device_id
             )
-            unused_fallback_key_types = (
+            unused_fallback_key_types = list(
                 await self.store.get_e2e_unused_fallback_key_types(user_id, device_id)
             )
 
@@ -2301,7 +2301,7 @@ async def _generate_room_entry(
         sync_result_builder: "SyncResultBuilder",
         room_builder: "RoomSyncResultBuilder",
         ephemeral: List[JsonDict],
-        tags: Optional[Dict[str, Dict[str, Any]]],
+        tags: Optional[Mapping[str, Mapping[str, Any]]],
         account_data: Mapping[str, JsonDict],
         always_include: bool = False,
     ) -> None:

synapse/push/bulk_push_rule_evaluator.py

@@ -22,6 +22,7 @@
     List,
     Mapping,
     Optional,
+    Sequence,
     Set,
     Tuple,
     Union,
@@ -149,7 +150,7 @@ async def _get_rules_for_event(
         # little, we can skip fetching a huge number of push rules in large rooms.
         # This helps make joins and leaves faster.
         if event.type == EventTypes.Member:
-            local_users = []
+            local_users: Sequence[str] = []
             # We never notify a user about their own actions. This is enforced in
             # `_action_for_event_by_user` in the loop over `rules_by_user`, but we
             # do the same check here to avoid unnecessary DB queries.
@@ -184,7 +185,6 @@ async def _get_rules_for_event(
         if event.type == EventTypes.Member and event.membership == Membership.INVITE:
             invited = event.state_key
             if invited and self.hs.is_mine_id(invited) and invited not in local_users:
-                local_users = list(local_users)
                 local_users.append(invited)
 
         if not local_users:

synapse/state/__init__.py

@@ -226,7 +226,7 @@ async def compute_state_after_events(
         return await ret.get_state(self._state_storage_controller, state_filter)
 
     async def get_current_user_ids_in_room(
-        self, room_id: str, latest_event_ids: List[str]
+        self, room_id: str, latest_event_ids: Collection[str]
     ) -> Set[str]:
         """
         Get the users IDs who are currently in a room.

synapse/storage/controllers/state.py

@@ -14,6 +14,7 @@
 import logging
 from typing import (
     TYPE_CHECKING,
+    AbstractSet,
     Any,
     Awaitable,
     Callable,
@@ -23,7 +24,6 @@
     List,
     Mapping,
     Optional,
-    Set,
     Tuple,
 )
 
@@ -527,7 +527,7 @@ async def get_current_state_event(
         )
         return state_map.get(key)
 
-    async def get_current_hosts_in_room(self, room_id: str) -> Set[str]:
+    async def get_current_hosts_in_room(self, room_id: str) -> AbstractSet[str]:
         """Get current hosts in room based on current state.
 
         Blocks until we have full state for the given room. This only happens for rooms
@@ -584,7 +584,7 @@ async def get_current_hosts_in_room_or_partial_state_approximation(
 
     async def get_users_in_room_with_profiles(
         self, room_id: str
-    ) -> Dict[str, ProfileInfo]:
+    ) -> Mapping[str, ProfileInfo]:
         """
         Get the current users in the room with their profiles.
         If the room is currently partial-stated, this will block until the room has

synapse/storage/databases/main/account_data.py

@@ -240,7 +240,7 @@ async def get_global_account_data_by_type_for_user(
     @cached(num_args=2, tree=True)
     async def get_account_data_for_room(
         self, user_id: str, room_id: str
-    ) -> Dict[str, JsonDict]:
+    ) -> Mapping[str, JsonDict]:
         """Get all the client account_data for a user for a room.
 
         Args:

synapse/storage/databases/main/appservice.py

@@ -166,7 +166,7 @@ async def get_app_service_users_in_room(
         room_id: str,
         app_service: "ApplicationService",
         cache_context: _CacheContext,
-    ) -> List[str]:
+    ) -> Sequence[str]:
         """
         Get all users in a room that the appservice controls.
 

synapse/storage/databases/main/devices.py

@@ -21,6 +21,7 @@
     Dict,
     Iterable,
     List,
+    Mapping,
     Optional,
     Set,
     Tuple,
@@ -202,7 +203,9 @@ def _invalidate_caches_for_devices(
     def get_device_stream_token(self) -> int:
         return self._device_list_id_gen.get_current_token()
 
-    async def count_devices_by_users(self, user_ids: Optional[List[str]] = None) -> int:
+    async def count_devices_by_users(
+        self, user_ids: Optional[Collection[str]] = None
+    ) -> int:
         """Retrieve number of all devices of given users.
         Only returns number of devices that are not marked as hidden.
 
@@ -213,7 +216,7 @@ async def count_devices_by_users(self, user_ids: Optional[List[str]] = None) ->
         """
 
         def count_devices_by_users_txn(
-            txn: LoggingTransaction, user_ids: List[str]
+            txn: LoggingTransaction, user_ids: Collection[str]
         ) -> int:
             sql = """
                 SELECT count(*)
@@ -747,7 +750,7 @@ def _add_user_signature_change_txn(
     @cancellable
     async def get_user_devices_from_cache(
         self, user_ids: Set[str], user_and_device_ids: List[Tuple[str, str]]
-    ) -> Tuple[Set[str], Dict[str, Dict[str, JsonDict]]]:
+    ) -> Tuple[Set[str], Dict[str, Mapping[str, JsonDict]]]:
         """Get the devices (and keys if any) for remote users from the cache.
 
         Args:
@@ -775,16 +778,18 @@ async def get_user_devices_from_cache(
         user_ids_not_in_cache = unique_user_ids - user_ids_in_cache
 
         # First fetch all the users which all devices are to be returned.
-        results: Dict[str, Dict[str, JsonDict]] = {}
+        results: Dict[str, Mapping[str, JsonDict]] = {}
         for user_id in user_ids:
             if user_id in user_ids_in_cache:
                 results[user_id] = await self.get_cached_devices_for_user(user_id)
         # Then fetch all device-specific requests, but skip users we've already
         # fetched all devices for.
+        device_specific_results: Dict[str, Dict[str, JsonDict]] = {}
         for user_id, device_id in user_and_device_ids:
             if user_id in user_ids_in_cache and user_id not in user_ids:
                 device = await self._get_cached_user_device(user_id, device_id)
-                results.setdefault(user_id, {})[device_id] = device
+                device_specific_results.setdefault(user_id, {})[device_id] = device
+        results.update(device_specific_results)
 
         set_tag("in_cache", str(results))
         set_tag("not_in_cache", str(user_ids_not_in_cache))
@@ -802,7 +807,7 @@ async def _get_cached_user_device(self, user_id: str, device_id: str) -> JsonDic
         return db_to_json(content)
 
     @cached()
-    async def get_cached_devices_for_user(self, user_id: str) -> Dict[str, JsonDict]:
+    async def get_cached_devices_for_user(self, user_id: str) -> Mapping[str, JsonDict]:
         devices = await self.db_pool.simple_select_list(
             table="device_lists_remote_cache",
             keyvalues={"user_id": user_id},

synapse/storage/databases/main/directory.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import Iterable, List, Optional, Tuple
+from typing import Iterable, List, Optional, Sequence, Tuple
 
 import attr
 
@@ -74,7 +74,7 @@ async def get_room_alias_creator(self, room_alias: str) -> str:
         )
 
     @cached(max_entries=5000)
-    async def get_aliases_for_room(self, room_id: str) -> List[str]:
+    async def get_aliases_for_room(self, room_id: str) -> Sequence[str]:
         return await self.db_pool.simple_select_onecol(
             "room_aliases",
             {"room_id": room_id},