queue: Fix channel type for TornadoQueueClient.

The BlockingChannel annotations in TornadoQueueClient were flat-out
wrong.  BlockingChannel and Channel have no common base classes.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/queue.py

@@ -4,26 +4,28 @@ import threading
 import time
 from abc import ABCMeta, abstractmethod
 from collections import defaultdict
-from typing import Any, Callable, Dict, List, Mapping, Optional, Set, Union
+from typing import Any, Callable, Dict, Generic, List, Mapping, Optional, Set, TypeVar, Union
 
 import orjson
 import pika
 import pika.adapters.tornado_connection
 from django.conf import settings
 from pika.adapters.blocking_connection import BlockingChannel
+from pika.channel import Channel
 from pika.spec import Basic
 from tornado import ioloop
 
 from zerver.lib.utils import statsd
 
 MAX_REQUEST_RETRIES = 3
-Consumer = Callable[[BlockingChannel, Basic.Deliver, pika.BasicProperties, bytes], None]
+ChannelT = TypeVar("ChannelT", Channel, BlockingChannel)
+Consumer = Callable[[ChannelT, Basic.Deliver, pika.BasicProperties, bytes], None]
 
 # This simple queuing library doesn't expose much of the power of
 # rabbitmq/pika's queuing system; its purpose is to just provide an
 # interface for external files to put things into queues and take them
 # out from bots without having to import pika code all over our codebase.
-class QueueClient(metaclass=ABCMeta):
+class QueueClient(Generic[ChannelT], metaclass=ABCMeta):
     def __init__(
         self,
         # Disable RabbitMQ heartbeats by default because BlockingConnection can't process them
@@ -31,8 +33,8 @@ class QueueClient(metaclass=ABCMeta):
     ) -> None:
         self.log = logging.getLogger("zulip.queue")
         self.queues: Set[str] = set()
-        self.channel: Optional[BlockingChannel] = None
-        self.consumers: Dict[str, Set[Consumer]] = defaultdict(set)
+        self.channel: Optional[ChannelT] = None
+        self.consumers: Dict[str, Set[Consumer[ChannelT]]] = defaultdict(set)
         self.rabbitmq_heartbeat = rabbitmq_heartbeat
         self.is_consuming = False
         self._connect()
@@ -78,7 +80,7 @@ class QueueClient(metaclass=ABCMeta):
     def _generate_ctag(self, queue_name: str) -> str:
         return f"{queue_name}_{str(random.getrandbits(16))}"
 
-    def _reconnect_consumer_callback(self, queue: str, consumer: Consumer) -> None:
+    def _reconnect_consumer_callback(self, queue: str, consumer: Consumer[ChannelT]) -> None:
         self.log.info(f"Queue reconnecting saved consumer {consumer} to queue {queue}")
         self.ensure_queue(
             queue,
@@ -98,11 +100,11 @@ class QueueClient(metaclass=ABCMeta):
         return self.channel is not None
 
     @abstractmethod
-    def ensure_queue(self, queue_name: str, callback: Callable[[BlockingChannel], None]) -> None:
+    def ensure_queue(self, queue_name: str, callback: Callable[[ChannelT], None]) -> None:
         raise NotImplementedError
 
     def publish(self, queue_name: str, body: bytes) -> None:
-        def do_publish(channel: BlockingChannel) -> None:
+        def do_publish(channel: ChannelT) -> None:
             channel.basic_publish(
                 exchange="",
                 routing_key=queue_name,
@@ -126,7 +128,7 @@ class QueueClient(metaclass=ABCMeta):
         self.publish(queue_name, data)
 
 
-class SimpleQueueClient(QueueClient):
+class SimpleQueueClient(QueueClient[BlockingChannel]):
     def _connect(self) -> None:
         start = time.time()
         self.connection = pika.BlockingConnection(self._get_parameters())
@@ -227,7 +229,7 @@ calling _adapter_disconnect, ignoring",
             )
 
 
-class TornadoQueueClient(QueueClient):
+class TornadoQueueClient(QueueClient[Channel]):
     connection: Optional[ExceptionFreeTornadoConnection]
 
     # Based on:
@@ -237,7 +239,7 @@ class TornadoQueueClient(QueueClient):
             # TornadoConnection can process heartbeats, so enable them.
             rabbitmq_heartbeat=None
         )
-        self._on_open_cbs: List[Callable[[BlockingChannel], None]] = []
+        self._on_open_cbs: List[Callable[[Channel], None]] = []
         self._connection_failure_count = 0
 
     def _connect(self) -> None:
@@ -305,7 +307,7 @@ class TornadoQueueClient(QueueClient):
             # Let _on_connection_closed deal with trying again.
             self.log.warning("TornadoQueueClient couldn't open channel: connection already closed")
 
-    def _on_channel_open(self, channel: BlockingChannel) -> None:
+    def _on_channel_open(self, channel: Channel) -> None:
         self.channel = channel
         for callback in self._on_open_cbs:
             callback(channel)
@@ -316,7 +318,7 @@ class TornadoQueueClient(QueueClient):
         if self.connection is not None:
             self.connection.close()
 
-    def ensure_queue(self, queue_name: str, callback: Callable[[BlockingChannel], None]) -> None:
+    def ensure_queue(self, queue_name: str, callback: Callable[[Channel], None]) -> None:
         def finish(frame: Any) -> None:
             assert self.channel is not None
             self.queues.add(queue_name)
@@ -343,7 +345,7 @@ class TornadoQueueClient(QueueClient):
         timeout: Optional[int] = None,
     ) -> None:
         def wrapped_consumer(
-            ch: BlockingChannel,
+            ch: Channel,
             method: Basic.Deliver,
             properties: pika.BasicProperties,
             body: bytes,