Fixup synapse.replication to pass mypy checks (#6667)

synapse/replication/tcp/commands.py

@@ -20,15 +20,16 @@ allowed to be sent by which side.
 
 import logging
 import platform
+from typing import Tuple, Type
 
 if platform.python_implementation() == "PyPy":
     import json
 
     _json_encoder = json.JSONEncoder()
 else:
-    import simplejson as json
+    import simplejson as json  # type: ignore[no-redef]  # noqa: F821
 
-    _json_encoder = json.JSONEncoder(namedtuple_as_object=False)
+    _json_encoder = json.JSONEncoder(namedtuple_as_object=False)  # type: ignore[call-arg]  # noqa: F821
 
 logger = logging.getLogger(__name__)
 
@@ -44,7 +45,7 @@ class Command(object):
     The default implementation creates a command of form `<NAME> <data>`
     """
 
-    NAME = None
+    NAME = None  # type: str
 
     def __init__(self, data):
         self.data = data
@@ -386,25 +387,24 @@ class UserIpCommand(Command):
         )
 
 
+_COMMANDS = (
+    ServerCommand,
+    RdataCommand,
+    PositionCommand,
+    ErrorCommand,
+    PingCommand,
+    NameCommand,
+    ReplicateCommand,
+    UserSyncCommand,
+    FederationAckCommand,
+    SyncCommand,
+    RemovePusherCommand,
+    InvalidateCacheCommand,
+    UserIpCommand,
+)  # type: Tuple[Type[Command], ...]
+
 # Map of command name to command type.
-COMMAND_MAP = {
-    cmd.NAME: cmd
-    for cmd in (
-        ServerCommand,
-        RdataCommand,
-        PositionCommand,
-        ErrorCommand,
-        PingCommand,
-        NameCommand,
-        ReplicateCommand,
-        UserSyncCommand,
-        FederationAckCommand,
-        SyncCommand,
-        RemovePusherCommand,
-        InvalidateCacheCommand,
-        UserIpCommand,
-    )
-}
+COMMAND_MAP = {cmd.NAME: cmd for cmd in _COMMANDS}
 
 # The commands the server is allowed to send
 VALID_SERVER_COMMANDS = (