actions: Send reaction events to subscribers with history access.

Previously, if a user subscribed to a stream with
history_public_to_subscribers, and then was looking at old messages in
the stream, they would not get live-updates for that stream, because
of the structure in how notify_reaction_update only looked at
UserMessage rows (we had a previous workaround involving the
`historical` field in `UserMessage` which had already made it work if
the user themselves added the reaction).

We fix this by including all subscribers with history access in the
set of recipients for update events.

Fixes a bug that was confused with #16942.

zerver/tests/test_reactions.py

@@ -4,6 +4,7 @@ from unittest import mock
 import orjson
 from django.http import HttpResponse
 
+from zerver.lib.actions import do_change_stream_invite_only, do_change_stream_web_public
 from zerver.lib.cache import cache_get, to_dict_cache_key_id
 from zerver.lib.emoji import emoji_name_to_emoji_code
 from zerver.lib.message import extract_message_dict
@@ -479,6 +480,141 @@ class ReactionEventTest(ZulipTestCase):
         self.assertEqual(event["emoji_name"], "smile")
         self.assertEqual(event["message_id"], pm_id)
 
+    def test_reaction_event_scope(self) -> None:
+        iago = self.example_user("iago")
+        hamlet = self.example_user("hamlet")
+        polonius = self.example_user("polonius")
+        reaction_info = {
+            "emoji_name": "smile",
+        }
+
+        # Test `invite_only` streams with `!history_public_to_subscribers` and `!is_web_public`
+        stream = self.make_stream(
+            "test_reactions_stream", invite_only=True, history_public_to_subscribers=False
+        )
+        self.subscribe(iago, stream.name)
+        message_before_id = self.send_stream_message(
+            iago, "test_reactions_stream", "before subscription history private"
+        )
+        self.subscribe(hamlet, stream.name)
+        self.subscribe(polonius, stream.name)
+
+        # Hamlet and Polonius joined after the message was sent, and
+        # so only Iago should receive the event.
+        events: List[Mapping[str, Any]] = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id})
+        remove = self.api_delete(
+            iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+        )
+        self.assert_json_success(remove)
+
+        # Reaction to a Message sent after subscription, should
+        # trigger events for all subscribers (Iago, Hamlet and Polonius).
+        message_after_id = self.send_stream_message(
+            iago, "test_reactions_stream", "after subscription history private"
+        )
+        events = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                iago, f"/api/v1/messages/{message_after_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id, hamlet.id, polonius.id})
+        remove = self.api_delete(
+            iago, f"/api/v1/messages/{message_after_id}/reactions", reaction_info
+        )
+        self.assert_json_success(remove)
+
+        # Make stream history public to subscribers
+        do_change_stream_invite_only(stream, False, history_public_to_subscribers=True)
+        # Since stream history is public to subscribers, reacting to
+        # message_before_id should notify all non-guest subscribers:
+        # Iago and Hamlet.
+        events = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id, hamlet.id})
+        remove = self.api_delete(
+            iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+        )
+        self.assert_json_success(remove)
+
+        # Make stream web_public as well.
+        do_change_stream_web_public(stream, True)
+        # For is_web_public streams, events even on old messages
+        # should go to all subscribers, including guests like polonius.
+        events = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id, hamlet.id, polonius.id})
+        remove = self.api_delete(
+            iago, f"/api/v1/messages/{message_before_id}/reactions", reaction_info
+        )
+        self.assert_json_success(remove)
+
+        # Private message, event should go to both participants.
+        private_message_id = self.send_personal_message(
+            iago,
+            hamlet,
+            "hello to single reciever",
+        )
+        events = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                hamlet, f"/api/v1/messages/{private_message_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id, hamlet.id})
+
+        # Group private message; event should go to all participants.
+        huddle_message_id = self.send_huddle_message(
+            hamlet,
+            [polonius, iago],
+            "hello message to muliple reciever",
+        )
+        events = []
+        with tornado_redirected_to_list(events):
+            result = self.api_post(
+                polonius, f"/api/v1/messages/{huddle_message_id}/reactions", reaction_info
+            )
+        self.assert_json_success(result)
+        self.assert_length(events, 1)
+        event = events[0]["event"]
+        self.assertEqual(event["type"], "reaction")
+        event_user_ids = set(events[0]["users"])
+        self.assertEqual(event_user_ids, {iago.id, hamlet.id, polonius.id})
+
 
 class EmojiReactionBase(ZulipTestCase):
     """Reusable testing functions for emoji reactions tests.  Be careful when