settings: Add automatically follow and unmute topics policy settings.

This commit adds two user settings, named
* `automatically_follow_topics_policy`
* `automatically_unmute_topics_in_muted_streams_policy`

The settings control the user's preference on which topics they
will automatically 'follow' or 'unmute in muted streams'.

The policies offer four options:
1. Topics I participate in
2. Topics I send a message to
3. Topics I start
4. Never (default)

There is no support for configuring the settings through the UI yet.

api_docs/changelog.md

@@ -20,6 +20,15 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 8.0
 
+**Feature level 214**
+
+* [`PATCH /realm/user_settings_defaults`](/api/update-realm-user-settings-defaults),
+  [`POST /register`](/api/register-queue), [`PATCH /settings`](/api/update-settings):
+  Added two new user settings, `automatically_follow_topics_policy` and
+  `automatically_unmute_topics_in_muted_streams_policy`. The settings control the
+  user's preference on which topics the user will automatically 'follow' and
+  'unmute in muted streams' respectively.
+
 **Feature level 213**
 
 * [`POST /register`](/api/register-queue): Fixed incorrect handling of

tools/linter_lib/custom_check.py

@@ -230,6 +230,9 @@ python_rules = RuleList(
             "good_lines": ["topic_name"],
             "bad_lines": ['subject="foo"', " MAX_SUBJECT_LEN"],
             "exclude": FILES_WITH_LEGACY_SUBJECT,
+            "exclude_line": {
+                ("zerver/lib/message.py", "message__subject__iexact=message.topic_name(),"),
+            },
             "include_only": {
                 "zerver/data_import/",
                 "zerver/lib/",

version.py

@@ -33,7 +33,7 @@ DESKTOP_WARNING_VERSION = "5.9.3"
 # Changes should be accompanied by documentation explaining what the
 # new level means in api_docs/changelog.md, as well as "**Changes**"
 # entries in the endpoint's documentation in `zulip.yaml`.
-API_FEATURE_LEVEL = 213
+API_FEATURE_LEVEL = 214
 
 # Bump the minor PROVISION_VERSION to indicate that folks should provision
 # only when going from an old version of the code to a newer version. Bump

zerver/actions/message_send.py

@@ -30,6 +30,7 @@ from django.utils.translation import override as override_language
 from django_stubs_ext import ValuesQuerySet
 
 from zerver.actions.uploads import do_claim_attachments
+from zerver.actions.user_topics import do_set_user_topic_visibility_policy
 from zerver.lib.addressee import Addressee
 from zerver.lib.alert_words import get_alert_word_automaton
 from zerver.lib.cache import cache_with_key, user_profile_delivery_email_cache_key
@@ -50,7 +51,9 @@ from zerver.lib.message import (
     check_user_group_mention_allowed,
     normalize_body,
     render_markdown,
+    set_visibility_policy_possible,
     truncate_topic,
+    visibility_policy_for_send_message,
     wildcard_mention_allowed,
 )
 from zerver.lib.muted_users import get_muting_users
@@ -180,6 +183,7 @@ class RecipientInfoResult:
     service_bot_tuples: List[Tuple[int, int]]
     all_bot_user_ids: Set[int]
     topic_participant_user_ids: Set[int]
+    sender_muted_stream: Optional[bool]
 
 
 class ActiveUserDict(TypedDict):
@@ -212,6 +216,7 @@ def get_recipient_info(
     stream_wildcard_mention_in_followed_topic_user_ids: Set[int] = set()
     muted_sender_user_ids: Set[int] = get_muting_users(sender_id)
     topic_participant_user_ids: Set[int] = set()
+    sender_muted_stream: Optional[bool] = None
 
     if recipient.type == Recipient.PERSONAL:
         # The sender and recipient may be the same id, so
@@ -275,7 +280,14 @@ def get_recipient_info(
             .order_by("user_profile_id")
         )
 
-        message_to_user_ids = [row["user_profile_id"] for row in subscription_rows]
+        message_to_user_ids = list()
+        for row in subscription_rows:
+            message_to_user_ids.append(row["user_profile_id"])
+            # We store the 'sender_muted_stream' information here to avoid db query at
+            # a later stage when we perform automatically unmute topic in muted stream operation.
+            if row["user_profile_id"] == sender_id:
+                sender_muted_stream = row["is_muted"]
+
         user_id_to_visibility_policy = stream_topic.user_id_to_visibility_policy_dict()
 
         def notification_recipients(setting: str) -> Set[int]:
@@ -466,6 +478,7 @@ def get_recipient_info(
         service_bot_tuples=service_bot_tuples,
         all_bot_user_ids=all_bot_user_ids,
         topic_participant_user_ids=topic_participant_user_ids,
+        sender_muted_stream=sender_muted_stream,
     )
 
 
@@ -642,6 +655,7 @@ def build_message_send_dict(
 
     message_send_dict = SendMessageRequest(
         stream=stream,
+        sender_muted_stream=info.sender_muted_stream,
         local_id=local_id,
         sender_queue_id=sender_queue_id,
         realm=realm,
@@ -896,6 +910,8 @@ def do_send_messages(
 
     # This next loop is responsible for notifying other parts of the
     # Zulip system about the messages we just committed to the database:
+    # * Sender automatically follows or unmutes the topic depending on 'automatically_follow_topics_policy'
+    #   and 'automatically_unmute_topics_in_muted_streams_policy' user settings.
     # * Notifying clients via send_event
     # * Triggering outgoing webhooks via the service event queue.
     # * Updating the `first_message_id` field for streams without any message history.
@@ -910,6 +926,39 @@ def do_send_messages(
             # assert needed because stubs for django are missing
             assert send_request.stream is not None
             realm_id = send_request.stream.realm_id
+            sender = send_request.message.sender
+
+            # Determine and set the visibility_policy depending on 'automatically_follow_topics_policy'
+            # and 'automatically_unmute_topics_in_muted_streams_policy'.
+            if set_visibility_policy_possible(sender, send_request.message) and not (
+                sender.automatically_follow_topics_policy
+                == sender.automatically_unmute_topics_in_muted_streams_policy
+                == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER
+            ):
+                try:
+                    user_topic = UserTopic.objects.get(
+                        user_profile=sender,
+                        stream_id=send_request.stream.id,
+                        topic_name__iexact=send_request.message.topic_name(),
+                    )
+                    visibility_policy = user_topic.visibility_policy
+                except UserTopic.DoesNotExist:
+                    visibility_policy = UserTopic.VisibilityPolicy.INHERIT
+
+                new_visibility_policy = visibility_policy_for_send_message(
+                    sender,
+                    send_request.message,
+                    send_request.stream,
+                    send_request.sender_muted_stream,
+                    visibility_policy,
+                )
+                if new_visibility_policy:
+                    do_set_user_topic_visibility_policy(
+                        user_profile=sender,
+                        stream=send_request.stream,
+                        topic=send_request.message.topic_name(),
+                        visibility_policy=new_visibility_policy,
+                    )
 
         # Deliver events to the real-time push system, as well as
         # enqueuing any additional processing triggered by the message.

zerver/actions/reactions.py

@@ -1,10 +1,18 @@
 from typing import Any, Dict, Optional
 
 from zerver.actions.create_user import create_historical_user_messages
+from zerver.actions.user_topics import do_set_user_topic_visibility_policy
 from zerver.lib.emoji import check_emoji_request, get_emoji_data
 from zerver.lib.exceptions import ReactionExistsError
-from zerver.lib.message import access_message, update_to_dict_cache
+from zerver.lib.message import (
+    access_message,
+    set_visibility_policy_possible,
+    should_change_visibility_policy,
+    update_to_dict_cache,
+    visibility_policy_for_participation,
+)
 from zerver.lib.stream_subscription import subscriber_ids_with_stream_history_access
+from zerver.lib.streams import access_stream_by_id
 from zerver.models import Message, Reaction, Recipient, Stream, UserMessage, UserProfile
 from zerver.tornado.django_api import send_event_on_commit
 
@@ -82,6 +90,32 @@ def do_add_reaction(
 
     reaction.save()
 
+    # Determine and set the visibility_policy depending on 'automatically_follow_topics_policy'
+    # and 'automatically_unmute_topics_in_muted_streams_policy'.
+    if set_visibility_policy_possible(
+        user_profile, message
+    ) and UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION in [
+        user_profile.automatically_follow_topics_policy,
+        user_profile.automatically_unmute_topics_in_muted_streams_policy,
+    ]:
+        stream_id = message.recipient.type_id
+        (stream, sub) = access_stream_by_id(user_profile, stream_id)
+        assert stream is not None
+        if sub:
+            new_visibility_policy = visibility_policy_for_participation(user_profile, sub.is_muted)
+            if new_visibility_policy and should_change_visibility_policy(
+                new_visibility_policy,
+                user_profile,
+                stream_id,
+                topic_name=message.topic_name(),
+            ):
+                do_set_user_topic_visibility_policy(
+                    user_profile=user_profile,
+                    stream=stream,
+                    topic=message.topic_name(),
+                    visibility_policy=new_visibility_policy,
+                )
+
     notify_reaction_update(user_profile, message, reaction, "add")
 
 

zerver/actions/submessage.py

@@ -1,7 +1,14 @@
 from django.utils.translation import gettext as _
 
+from zerver.actions.user_topics import do_set_user_topic_visibility_policy
 from zerver.lib.exceptions import JsonableError
-from zerver.models import Realm, SubMessage, UserMessage
+from zerver.lib.message import (
+    set_visibility_policy_possible,
+    should_change_visibility_policy,
+    visibility_policy_for_participation,
+)
+from zerver.lib.streams import access_stream_by_id
+from zerver.models import Realm, SubMessage, UserMessage, UserProfile
 from zerver.tornado.django_api import send_event_on_commit
 
 
@@ -48,6 +55,33 @@ def do_add_submessage(
     )
     submessage.save()
 
+    # Determine and set the visibility_policy depending on 'automatically_follow_topics_policy'
+    # and 'automatically_unmute_topics_policy'.
+    sender = submessage.sender
+    if set_visibility_policy_possible(
+        sender, submessage.message
+    ) and UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION in [
+        sender.automatically_follow_topics_policy,
+        sender.automatically_unmute_topics_in_muted_streams_policy,
+    ]:
+        stream_id = submessage.message.recipient.type_id
+        (stream, sub) = access_stream_by_id(sender, stream_id)
+        assert stream is not None
+        if sub:
+            new_visibility_policy = visibility_policy_for_participation(sender, sub.is_muted)
+            if new_visibility_policy and should_change_visibility_policy(
+                new_visibility_policy,
+                sender,
+                stream_id,
+                topic_name=submessage.message.topic_name(),
+            ):
+                do_set_user_topic_visibility_policy(
+                    user_profile=sender,
+                    stream=stream,
+                    topic=submessage.message.topic_name(),
+                    visibility_policy=new_visibility_policy,
+                )
+
     event = dict(
         type="submessage",
         msg_type=msg_type,

zerver/lib/message.py

@@ -20,7 +20,7 @@ import ahocorasick
 import orjson
 from django.conf import settings
 from django.db import connection
-from django.db.models import Max, Sum
+from django.db.models import Max, QuerySet, Sum
 from django.utils.timezone import now as timezone_now
 from django.utils.translation import gettext as _
 from django_stubs_ext import ValuesQuerySet
@@ -47,9 +47,15 @@ from zerver.lib.stream_subscription import (
     get_subscribed_stream_recipient_ids_for_user,
     num_subscribers_for_stream_id,
 )
-from zerver.lib.streams import get_web_public_streams_queryset
+from zerver.lib.streams import can_access_stream_history, get_web_public_streams_queryset
 from zerver.lib.timestamp import datetime_to_timestamp
-from zerver.lib.topic import DB_TOPIC_NAME, MESSAGE__TOPIC, TOPIC_LINKS, TOPIC_NAME
+from zerver.lib.topic import (
+    DB_TOPIC_NAME,
+    MESSAGE__TOPIC,
+    TOPIC_LINKS,
+    TOPIC_NAME,
+    messages_for_topic,
+)
 from zerver.lib.types import DisplayRecipientT, EditHistoryEvent, UserDisplayRecipient
 from zerver.lib.url_preview.types import UrlEmbedData
 from zerver.lib.user_groups import is_user_in_group
@@ -147,6 +153,7 @@ class SendMessageRequest:
     message: Message
     rendering_result: MessageRenderingResult
     stream: Optional[Stream]
+    sender_muted_stream: Optional[bool]
     local_id: Optional[str]
     sender_queue_id: Optional[str]
     realm: Realm
@@ -1713,3 +1720,180 @@ def update_to_dict_cache(
 
     cache_set_many(items_for_remote_cache)
     return message_ids
+
+
+def visibility_policy_for_participation(
+    sender: UserProfile,
+    is_stream_muted: Optional[bool],
+) -> Optional[int]:
+    """
+    This function determines the visibility policy to set when a user
+    participates in a topic, depending on the 'automatically_follow_topics_policy'
+    and 'automatically_unmute_topics_in_muted_streams_policy' settings.
+    """
+    if (
+        sender.automatically_follow_topics_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION
+    ):
+        return UserTopic.VisibilityPolicy.FOLLOWED
+
+    if (
+        is_stream_muted
+        and sender.automatically_unmute_topics_in_muted_streams_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION
+    ):
+        return UserTopic.VisibilityPolicy.UNMUTED
+
+    return None
+
+
+def visibility_policy_for_send(
+    sender: UserProfile,
+    is_stream_muted: Optional[bool],
+) -> Optional[int]:
+    if (
+        sender.automatically_follow_topics_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND
+    ):
+        return UserTopic.VisibilityPolicy.FOLLOWED
+
+    if (
+        is_stream_muted
+        and sender.automatically_unmute_topics_in_muted_streams_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND
+    ):
+        return UserTopic.VisibilityPolicy.UNMUTED
+
+    return None
+
+
+def visibility_policy_for_send_message(
+    sender: UserProfile,
+    message: Message,
+    stream: Stream,
+    is_stream_muted: Optional[bool],
+    current_visibility_policy: int,
+) -> Optional[int]:
+    """
+    This function determines the visibility policy to set when a message
+    is sent to a topic, depending on the 'automatically_follow_topics_policy'
+    and 'automatically_unmute_topics_in_muted_streams_policy' settings.
+
+    It returns None when the policies can't make it more visible than the
+    current visibility policy.
+    """
+    # We prioritize 'FOLLOW' over 'UNMUTE' in muted streams.
+    # We need to carefully handle the following two cases:
+    #
+    # 1. When an action qualifies for multiple values. Example:
+    #    - starting a topic is INITIATION, PARTICIPATION as well as SEND
+    #    - sending a non-first message is PARTICIPATION as well as SEND
+    # action | 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+    #  start |    ON_PARTICIPATION / ON_SEND        |                   ON_INITIATION                       |     FOLLOWED
+    #  send  |    ON_SEND / ON_PARTICIPATION        |              ON_PARTICIPATION / ON_SEND               |     FOLLOWED
+    #
+    # 2. When both the policies have the same values.
+    # action | 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+    #  start |         ON_INITIATION                |                   ON_INITIATION                       |     FOLLOWED
+    #  partc |       ON_PARTICIPATION               |                 ON_PARTICIPATION                      |     FOLLOWED
+    #  send  |           ON_SEND                    |                     ON_SEND                           |     FOLLOWED
+    visibility_policy = None
+
+    if current_visibility_policy == UserTopic.VisibilityPolicy.FOLLOWED:
+        return visibility_policy
+
+    visibility_policy_participation = visibility_policy_for_participation(sender, is_stream_muted)
+    visibility_policy_send = visibility_policy_for_send(sender, is_stream_muted)
+
+    if UserTopic.VisibilityPolicy.FOLLOWED in (
+        visibility_policy_participation,
+        visibility_policy_send,
+    ):
+        return UserTopic.VisibilityPolicy.FOLLOWED
+
+    if UserTopic.VisibilityPolicy.UNMUTED in (
+        visibility_policy_participation,
+        visibility_policy_send,
+    ):
+        visibility_policy = UserTopic.VisibilityPolicy.UNMUTED
+
+    # If a topic has a visibility policy set, it can't be the case
+    # of initiation. We return early, thus saving a DB query.
+    if current_visibility_policy != UserTopic.VisibilityPolicy.INHERIT:
+        if visibility_policy and current_visibility_policy == visibility_policy:
+            return None
+        return visibility_policy
+
+    # Now we need to check if the user initiated the topic.
+    old_accessible_messages_in_topic: Union[QuerySet[Message], QuerySet[UserMessage]]
+    if can_access_stream_history(sender, stream):
+        old_accessible_messages_in_topic = messages_for_topic(
+            realm_id=sender.realm_id,
+            stream_recipient_id=message.recipient_id,
+            topic_name=message.topic_name(),
+        ).exclude(id=message.id)
+    else:
+        # We use the user's own message access to avoid leaking information in
+        # private streams with protected history.
+        old_accessible_messages_in_topic = UserMessage.objects.filter(
+            user_profile=sender,
+            message__recipient_id=message.recipient_id,
+            message__subject__iexact=message.topic_name(),
+        ).exclude(message_id=message.id)
+
+    if (
+        sender.automatically_follow_topics_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION
+        and not old_accessible_messages_in_topic.exists()
+    ):
+        return UserTopic.VisibilityPolicy.FOLLOWED
+
+    if (
+        is_stream_muted
+        and sender.automatically_unmute_topics_in_muted_streams_policy
+        == UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION
+        and not old_accessible_messages_in_topic.exists()
+    ):
+        visibility_policy = UserTopic.VisibilityPolicy.UNMUTED
+
+    return visibility_policy
+
+
+def should_change_visibility_policy(
+    new_visibility_policy: int,
+    sender: UserProfile,
+    stream_id: int,
+    topic_name: str,
+) -> bool:
+    try:
+        user_topic = UserTopic.objects.get(
+            user_profile=sender, stream_id=stream_id, topic_name__iexact=topic_name
+        )
+    except UserTopic.DoesNotExist:
+        return True
+    current_visibility_policy = user_topic.visibility_policy
+
+    if new_visibility_policy == current_visibility_policy:
+        return False
+
+    # The intent of these "automatically follow or unmute" policies is that they
+    # can only increase the user's visibility policy for the topic. If a topic is
+    # already FOLLOWED, we don't change the state to UNMUTED due to these policies.
+    if current_visibility_policy == UserTopic.VisibilityPolicy.FOLLOWED:
+        return False
+
+    return True
+
+
+def set_visibility_policy_possible(user_profile: UserProfile, message: Message) -> bool:
+    """If the user can set a visibility policy."""
+    if not message.is_stream_message():
+        return False
+
+    if user_profile.is_bot:
+        return False
+
+    if user_profile.realm != message.get_realm():
+        return False
+
+    return True

zerver/migrations/0476_realmuserdefault_automatically_follow_topics_policy_and_more.py

@@ -0,0 +1,32 @@
+# Generated by Django 4.2.5 on 2023-09-19 10:52
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0475_realm_jitsi_server_url"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="realmuserdefault",
+            name="automatically_follow_topics_policy",
+            field=models.PositiveSmallIntegerField(default=3),
+        ),
+        migrations.AddField(
+            model_name="realmuserdefault",
+            name="automatically_unmute_topics_in_muted_streams_policy",
+            field=models.PositiveSmallIntegerField(default=3),
+        ),
+        migrations.AddField(
+            model_name="userprofile",
+            name="automatically_follow_topics_policy",
+            field=models.PositiveSmallIntegerField(default=3),
+        ),
+        migrations.AddField(
+            model_name="userprofile",
+            name="automatically_unmute_topics_in_muted_streams_policy",
+            field=models.PositiveSmallIntegerField(default=3),
+        ),
+    ]

zerver/migrations/0477_alter_realmuserdefault_automatically_follow_topics_policy_and_more.py

@@ -0,0 +1,32 @@
+# Generated by Django 4.2.5 on 2023-10-02 05:53
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0476_realmuserdefault_automatically_follow_topics_policy_and_more"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="realmuserdefault",
+            name="automatically_follow_topics_policy",
+            field=models.PositiveSmallIntegerField(default=4),
+        ),
+        migrations.AlterField(
+            model_name="realmuserdefault",
+            name="automatically_unmute_topics_in_muted_streams_policy",
+            field=models.PositiveSmallIntegerField(default=4),
+        ),
+        migrations.AlterField(
+            model_name="userprofile",
+            name="automatically_follow_topics_policy",
+            field=models.PositiveSmallIntegerField(default=4),
+        ),
+        migrations.AlterField(
+            model_name="userprofile",
+            name="automatically_unmute_topics_in_muted_streams_policy",
+            field=models.PositiveSmallIntegerField(default=4),
+        ),
+    ]

zerver/models.py

@@ -1642,6 +1642,30 @@ class UserBaseSettings(models.Model):
         default=REALM_NAME_IN_EMAIL_NOTIFICATIONS_POLICY_AUTOMATIC
     )
 
+    # The following two settings control which topics to automatically
+    # 'follow' or 'unmute in a muted stream', respectively.
+    # Follow or unmute a topic automatically on:
+    # - PARTICIPATION: Send a message, React to a message, Participate in a poll or Edit a TO-DO list.
+    # - SEND: Send a message.
+    # - INITIATION: Send the first message in the topic.
+    # - NEVER: Never automatically follow or unmute a topic.
+    AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION = 1
+    AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND = 2
+    AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION = 3
+    AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER = 4
+    AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES = [
+        AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+        AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND,
+        AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+        AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+    ]
+    automatically_follow_topics_policy = models.PositiveSmallIntegerField(
+        default=AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER
+    )
+    automatically_unmute_topics_in_muted_streams_policy = models.PositiveSmallIntegerField(
+        default=AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER
+    )
+
     # Whether or not the user wants to sync their drafts.
     enable_drafts_synchronization = models.BooleanField(default=True)
 
@@ -1737,6 +1761,8 @@ class UserBaseSettings(models.Model):
         enable_followed_topic_push_notifications=bool,
         enable_followed_topic_audible_notifications=bool,
         enable_followed_topic_wildcard_mentions_notify=bool,
+        automatically_follow_topics_policy=int,
+        automatically_unmute_topics_in_muted_streams_policy=int,
     )
 
     notification_setting_types = {

zerver/openapi/zulip.yaml

@@ -10206,6 +10206,44 @@ paths:
               - 2
               - 3
           example: 1
+        - name: automatically_follow_topics_policy
+          in: query
+          description: |
+            Which [topics to follow automatically](/help/mute-a-topic).
+
+            - 1 - Topics the user participates in
+            - 2 - Topics the user sends a message to
+            - 3 - Topics the user starts
+            - 4 - Never
+
+            **Changes**: New in Zulip 8.0 (feature level 214).
+          schema:
+            type: integer
+            enum:
+              - 1
+              - 2
+              - 3
+              - 4
+          example: 1
+        - name: automatically_unmute_topics_in_muted_streams_policy
+          in: query
+          description: |
+            Which [topics to unmute automatically in muted streams](/help/mute-a-topic).
+
+            - 1 - Topics the user participates in
+            - 2 - Topics the user sends a message to
+            - 3 - Topics the user starts
+            - 4 - Never
+
+            **Changes**: New in Zulip 8.0 (feature level 214).
+          schema:
+            type: integer
+            enum:
+              - 1
+              - 2
+              - 3
+              - 4
+          example: 1
         - name: presence_enabled
           in: query
           description: |
@@ -12422,6 +12460,28 @@ paths:
                               **Changes**: New in Zulip 7.0 (feature level 168), replacing the
                               previous `realm_name_in_notifications` boolean;
                               `true` corresponded to `Always`, and `false` to `Never`.
+                          automatically_follow_topics_policy:
+                            type: integer
+                            description: |
+                              Which [topics to follow automatically](/help/mute-a-topic).
+
+                              - 1 - Topics the user participates in
+                              - 2 - Topics the user sends a message to
+                              - 3 - Topics the user starts
+                              - 4 - Never
+
+                              **Changes**: New in Zulip 8.0 (feature level 214).
+                          automatically_unmute_topics_in_muted_streams_policy:
+                            type: integer
+                            description: |
+                              Which [topics to unmute automatically in muted streams](/help/mute-a-topic).
+
+                              - 1 - Topics the user participates in
+                              - 2 - Topics the user sends a message to
+                              - 3 - Topics the user starts
+                              - 4 - Never
+
+                              **Changes**: New in Zulip 8.0 (feature level 214).
                           presence_enabled:
                             type: boolean
                             description: |
@@ -14561,6 +14621,28 @@ paths:
                               **Changes**: New in Zulip 7.0 (feature level 168), replacing the
                               previous `realm_name_in_notifications` boolean;
                               `true` corresponded to `Always`, and `false` to `Never`.
+                          automatically_follow_topics_policy:
+                            type: integer
+                            description: |
+                              Which [topics to follow automatically](/help/mute-a-topic).
+
+                              - 1 - Topics the user participates in
+                              - 2 - Topics the user sends a message to
+                              - 3 - Topics the user starts
+                              - 4 - Never
+
+                              **Changes**: New in Zulip 8.0 (feature level 214).
+                          automatically_unmute_topics_in_muted_streams_policy:
+                            type: integer
+                            description: |
+                              Which [topics to unmute automatically in muted streams](/help/mute-a-topic).
+
+                              - 1 - Topics the user participates in
+                              - 2 - Topics the user sends a message to
+                              - 3 - Topics the user starts
+                              - 4 - Never
+
+                              **Changes**: New in Zulip 8.0 (feature level 214).
                           presence_enabled:
                             type: boolean
                             description: |
@@ -15808,6 +15890,44 @@ paths:
               - 2
               - 3
           example: 1
+        - name: automatically_follow_topics_policy
+          in: query
+          description: |
+            Which [topics to follow automatically](/help/mute-a-topic).
+
+            - 1 - Topics the user participates in
+            - 2 - Topics the user sends a message to
+            - 3 - Topics the user starts
+            - 4 - Never
+
+            **Changes**: New in Zulip 8.0 (feature level 214).
+          schema:
+            type: integer
+            enum:
+              - 1
+              - 2
+              - 3
+              - 4
+          example: 1
+        - name: automatically_unmute_topics_in_muted_streams_policy
+          in: query
+          description: |
+            Which [topics to unmute automatically in muted streams](/help/mute-a-topic).
+
+            - 1 - Topics the user participates in
+            - 2 - Topics the user sends a message to
+            - 3 - Topics the user starts
+            - 4 - Never
+
+            **Changes**: New in Zulip 8.0 (feature level 214).
+          schema:
+            type: integer
+            enum:
+              - 1
+              - 2
+              - 3
+              - 4
+          example: 1
         - name: presence_enabled
           in: query
           description: |

zerver/tests/test_events.py

@@ -535,11 +535,195 @@ class NormalActionsTest(BaseAction):
         )
 
     def test_stream_send_message_events(self) -> None:
-        user_profile = self.example_user("hamlet")
+        hamlet = self.example_user("hamlet")
-        events = self.verify_action(
+        for stream_name in ["Verona", "Denmark", "core team"]:
-            lambda: self.send_stream_message(user_profile, "Verona", "hello"),
+            stream = get_stream(stream_name, hamlet.realm)
-            client_gravatar=False,
+            sub = get_subscription(stream.name, hamlet)
+            do_change_subscription_property(hamlet, sub, stream, "is_muted", True, acting_user=None)
+
+        def verify_events_generated_and_reset_visibility_policy(
+            events: List[Dict[str, Any]], stream_name: str, topic: str
+        ) -> None:
+            # event-type: muted_topics
+            check_muted_topics("events[0]", events[0])
+            # event-type: user_topic
+            check_user_topic("events[1]", events[1])
+
+            if events[2]["type"] == "message":
+                check_message("events[2]", events[2])
+            else:
+                # event-type: reaction
+                check_reaction_add("events[2]", events[2])
+
+            # Reset visibility policy
+            do_set_user_topic_visibility_policy(
+                hamlet,
+                get_stream(stream_name, hamlet.realm),
+                topic,
+                visibility_policy=UserTopic.VisibilityPolicy.INHERIT,
             )
+
+        # Events generated during send message action depends on the 'automatically_follow_topics_policy'
+        # and 'automatically_unmute_topics_in_muted_streams_policy' settings. Here we test all the
+        # possible combinations.
+
+        # action: participation
+        # 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+        #         ON_PARTICIPATION             |                    ON_INITIATION                      |     FOLLOWED
+        #         ON_PARTICIPATION             |                   ON_PARTICIPATION                    |     FOLLOWED
+        #         ON_PARTICIPATION             |                       ON_SEND                         |     FOLLOWED
+        #         ON_PARTICIPATION             |                        NEVER                          |     FOLLOWED
+        message_id = self.send_stream_message(hamlet, "Verona", "hello", "topic")
+        message = Message.objects.get(id=message_id)
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        for setting_value in UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES:
+            do_change_user_setting(
+                user_profile=hamlet,
+                setting_name="automatically_unmute_topics_in_muted_streams_policy",
+                setting_value=setting_value,
+                acting_user=None,
+            )
+            # Three events are generated:
+            # 2 for following the topic and 1 for adding reaction.
+            events = self.verify_action(
+                lambda: do_add_reaction(hamlet, message, "tada", "1f389", "unicode_emoji"),
+                client_gravatar=False,
+                num_events=3,
+            )
+            verify_events_generated_and_reset_visibility_policy(events, "Verona", "topic")
+            do_remove_reaction(hamlet, message, "1f389", "unicode_emoji")
+
+        # action: send
+        # 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+        #                ON_SEND               |                    ON_INITIATION                      |     FOLLOWED
+        #                ON_SEND               |                   ON_PARTICIPATION                    |     FOLLOWED
+        #                ON_SEND               |                       ON_SEND                         |     FOLLOWED
+        #                ON_SEND               |                        NEVER                          |     FOLLOWED
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND,
+            acting_user=None,
+        )
+        for setting_value in UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES:
+            do_change_user_setting(
+                user_profile=hamlet,
+                setting_name="automatically_unmute_topics_in_muted_streams_policy",
+                setting_value=setting_value,
+                acting_user=None,
+            )
+            # Three events are generated:
+            # 2 for following the topic and 1 for the message sent.
+            events = self.verify_action(
+                lambda: self.send_stream_message(hamlet, "Verona", "hello", "topic"),
+                client_gravatar=False,
+                num_events=3,
+            )
+            verify_events_generated_and_reset_visibility_policy(events, "Verona", "topic")
+
+        # action: initiation
+        # 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+        #          ON_INITIATION               |                    ON_INITIATION                      |     FOLLOWED
+        #          ON_INITIATION               |                   ON_PARTICIPATION                    |     FOLLOWED
+        #          ON_INITIATION               |                       ON_SEND                         |     FOLLOWED
+        #          ON_INITIATION               |                        NEVER                          |     FOLLOWED
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+        for index, setting_value in enumerate(
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES
+        ):
+            do_change_user_setting(
+                user_profile=hamlet,
+                setting_name="automatically_unmute_topics_in_muted_streams_policy",
+                setting_value=setting_value,
+                acting_user=None,
+            )
+            # Three events are generated:
+            # 2 for following the topic and 1 for the message sent.
+            send_message = lambda index=index: self.send_stream_message(
+                hamlet, "Denmark", "hello", f"new topic {index}"
+            )
+            events = self.verify_action(
+                send_message,
+                client_gravatar=False,
+                num_events=3,
+            )
+            verify_events_generated_and_reset_visibility_policy(
+                events, "Denmark", f"new topic {index}"
+            )
+
+        # 'automatically_follow_topics_policy' | 'automatically_unmute_topics_in_muted_streams_policy' | visibility_policy
+        #             NEVER                    |                    ON_INITIATION                      |      UNMUTED
+        #             NEVER                    |                  ON_PARTICIPATION                     |      UNMUTED
+        #             NEVER                    |                      ON_SEND                          |      UNMUTED
+        #             NEVER                    |                       NEVER                           |        NA
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
+        for setting_value in [
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND,
+        ]:
+            do_change_user_setting(
+                user_profile=hamlet,
+                setting_name="automatically_unmute_topics_in_muted_streams_policy",
+                setting_value=setting_value,
+                acting_user=None,
+            )
+            # Three events are generated:
+            # 2 for unmuting the topic and 1 for the message sent.
+            events = self.verify_action(
+                lambda: self.send_stream_message(hamlet, "core team", "hello", "topic"),
+                client_gravatar=False,
+                num_events=3,
+            )
+            verify_events_generated_and_reset_visibility_policy(events, "core team", "topic")
+
+        # If current_visibility_policy is already set to the value the policies would set.
+        do_set_user_topic_visibility_policy(
+            hamlet,
+            get_stream("core team", hamlet.realm),
+            "new Topic",
+            visibility_policy=UserTopic.VisibilityPolicy.UNMUTED,
+        )
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_unmute_topics_in_muted_streams_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # 1 event for the message sent
+        events = self.verify_action(
+            lambda: self.send_stream_message(hamlet, "core team", "hello", "new Topic"),
+            client_gravatar=False,
+            num_events=1,
+        )
+
+        do_change_user_setting(
+            user_profile=hamlet,
+            setting_name="automatically_unmute_topics_in_muted_streams_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
+        # Only one message event is generated
+        events = self.verify_action(
+            lambda: self.send_stream_message(hamlet, "core team", "hello"),
+            client_gravatar=True,
+        )
+        # event-type: message
         check_message("events[0]", events[0])
         assert isinstance(events[0]["message"]["avatar_url"], str)
 
@@ -551,7 +735,7 @@ class NormalActionsTest(BaseAction):
         )
 
         events = self.verify_action(
-            lambda: self.send_stream_message(user_profile, "Verona", "hello"),
+            lambda: self.send_stream_message(hamlet, "core team", "hello"),
             client_gravatar=True,
         )
         check_message("events[0]", events[0])
@@ -560,13 +744,9 @@ class NormalActionsTest(BaseAction):
         # Here we add coverage for the case where 'apply_unread_message_event'
         # should be called and unread messages in unmuted or followed topic in
         # muted stream is treated as unmuted stream message, thus added to 'unmuted_stream_msgs'.
-        stream = get_stream("Verona", user_profile.realm)
+        stream = get_stream("Verona", hamlet.realm)
-        sub = get_subscription(stream.name, user_profile)
-        do_change_subscription_property(
-            user_profile, sub, stream, "is_muted", True, acting_user=None
-        )
         do_set_user_topic_visibility_policy(
-            user_profile,
+            hamlet,
             stream,
             "test",
             visibility_policy=UserTopic.VisibilityPolicy.UNMUTED,
@@ -2063,6 +2243,8 @@ class NormalActionsTest(BaseAction):
                 "desktop_icon_count_display",
                 "presence_enabled",
                 "realm_name_in_email_notifications_policy",
+                "automatically_follow_topics_policy",
+                "automatically_unmute_topics_in_muted_streams_policy",
             ]:
                 # These settings are tested in their own tests.
                 continue
@@ -2201,6 +2383,38 @@ class NormalActionsTest(BaseAction):
         check_user_settings_update("events[0]", events[0])
         check_update_global_notifications("events[1]", events[1], 2)
 
+    def test_change_automatically_follow_topics_policy(self) -> None:
+        notification_setting = "automatically_follow_topics_policy"
+
+        for setting_value in UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES:
+            events = self.verify_action(
+                partial(
+                    do_change_user_setting,
+                    self.user_profile,
+                    notification_setting,
+                    setting_value,
+                    acting_user=self.user_profile,
+                ),
+                num_events=1,
+            )
+            check_user_settings_update("events[0]", events[0])
+
+    def test_change_automatically_unmute_topics_in_muted_streams_policy(self) -> None:
+        notification_setting = "automatically_unmute_topics_in_muted_streams_policy"
+
+        for setting_value in UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES:
+            events = self.verify_action(
+                partial(
+                    do_change_user_setting,
+                    self.user_profile,
+                    notification_setting,
+                    setting_value,
+                    acting_user=self.user_profile,
+                ),
+                num_events=1,
+            )
+            check_user_settings_update("events[0]", events[0])
+
     def test_realm_update_org_type(self) -> None:
         realm = self.user_profile.realm
 
@@ -3129,6 +3343,8 @@ class RealmPropertyActionTest(BaseAction):
             email_notifications_batching_period_seconds=[120, 300],
             email_address_visibility=UserProfile.EMAIL_ADDRESS_VISIBILITY_TYPES,
             realm_name_in_email_notifications_policy=UserProfile.REALM_NAME_IN_EMAIL_NOTIFICATIONS_POLICY_CHOICES,
+            automatically_follow_topics_policy=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES,
+            automatically_unmute_topics_in_muted_streams_policy=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES,
         )
 
         vals = test_values.get(name)

zerver/tests/test_message_send.py

@@ -1454,12 +1454,24 @@ class StreamMessagesTest(ZulipTestCase):
         topic_name = "foo"
         content = "whatever"
 
+        # Note: We don't need to assert the db query count for each possible
+        # combination of 'automatically_follow_topics_policy' and 'automatically_unmute_topics_in_muted_streams_policy',
+        # as the query count depends only on the actions, i.e., 'ON_INITIATION',
+        # 'ON_PARTICIPATION', and 'NEVER', and is independent of the final visibility_policy set.
+        # Asserting query count using one of the above-mentioned settings fulfils our purpose.
+
         # To get accurate count of the queries, we should make sure that
         # caches don't come into play. If we count queries while caches are
         # filled, we will get a lower count. Caches are not supposed to be
         # persistent, so our test can also fail if cache is invalidated
         # during the course of the unit test.
         flush_per_request_caches()
+        do_change_user_setting(
+            user_profile=sender,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
         with self.assert_database_query_count(13):
             check_send_stream_message(
                 sender=sender,
@@ -1469,6 +1481,57 @@ class StreamMessagesTest(ZulipTestCase):
                 body=content,
             )
 
+        do_change_user_setting(
+            user_profile=sender,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+        # There will be an increase in the query count of 5 while sending
+        # the first message to a topic.
+        # 5 queries: 1 to check if it is the first message in the topic +
+        # 1 to check if the topic is already followed + 3 to follow the topic.
+        flush_per_request_caches()
+        with self.assert_database_query_count(18):
+            check_send_stream_message(
+                sender=sender,
+                client=sending_client,
+                stream_name=stream_name,
+                topic="new topic",
+                body=content,
+            )
+
+        do_change_user_setting(
+            user_profile=sender,
+            setting_name="automatically_follow_topics_policy",
+            setting_value=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        self.send_stream_message(self.example_user("iago"), stream_name, "Hello", "topic 2")
+        # There will be an increase in the query count of 4 while sending
+        # a message to a topic with visibility policy other than FOLLOWED.
+        # 1 to check if the topic is already followed + 3 queries to follow the topic.
+        flush_per_request_caches()
+        with self.assert_database_query_count(17):
+            check_send_stream_message(
+                sender=sender,
+                client=sending_client,
+                stream_name=stream_name,
+                topic="topic 2",
+                body=content,
+            )
+        # If the topic is already FOLLOWED, there will be an increase in the query
+        # count of 1 to check if the topic is already followed.
+        flush_per_request_caches()
+        with self.assert_database_query_count(14):
+            check_send_stream_message(
+                sender=sender,
+                client=sending_client,
+                stream_name=stream_name,
+                topic="topic 2",
+                body=content,
+            )
+
     def test_stream_message_dict(self) -> None:
         user_profile = self.example_user("iago")
         self.subscribe(user_profile, "Denmark")

zerver/tests/test_realm.py

@@ -1345,6 +1345,8 @@ class RealmAPITest(ZulipTestCase):
             email_notifications_batching_period_seconds=[120, 300],
             email_address_visibility=UserProfile.EMAIL_ADDRESS_VISIBILITY_TYPES,
             realm_name_in_email_notifications_policy=UserProfile.REALM_NAME_IN_EMAIL_NOTIFICATIONS_POLICY_CHOICES,
+            automatically_follow_topics_policy=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES,
+            automatically_unmute_topics_in_muted_streams_policy=UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES,
         )
 
         vals = test_values.get(name)

zerver/tests/test_settings.py

@@ -362,6 +362,8 @@ class ChangeSettingsTest(ZulipTestCase):
             desktop_icon_count_display=2,
             email_address_visibility=3,
             realm_name_in_email_notifications_policy=2,
+            automatically_follow_topics_policy=1,
+            automatically_unmute_topics_in_muted_streams_policy=1,
         )
 
         self.login("hamlet")

zerver/tests/test_user_topics.py

@@ -1,12 +1,16 @@
 from datetime import datetime, timezone
 from typing import Any, Dict, List
 
+import orjson
 import time_machine
 from django.utils.timezone import now as timezone_now
 
+from zerver.actions.reactions import check_add_reaction
+from zerver.actions.user_settings import do_change_user_setting
 from zerver.actions.user_topics import do_set_user_topic_visibility_policy
 from zerver.lib.stream_topic import StreamTopicTarget
 from zerver.lib.test_classes import ZulipTestCase
+from zerver.lib.test_helpers import get_subscription
 from zerver.lib.user_topics import get_topic_mutes, topic_has_visibility_policy
 from zerver.models import UserProfile, UserTopic, get_stream
 
@@ -638,3 +642,895 @@ class UnmutedTopicsTests(ZulipTestCase):
 
         result = self.api_post(user, url, data)
         self.assert_json_error(result, "Invalid stream ID")
+
+
+class AutomaticallyFollowTopicsTests(ZulipTestCase):
+    def test_automatically_follow_topic_on_initiation(self) -> None:
+        hamlet = self.example_user("hamlet")
+        cordelia = self.example_user("cordelia")
+        iago = self.example_user("iago")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # For hamlet & cordelia,
+        # 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION'.
+        for user in [hamlet, cordelia]:
+            do_change_user_setting(
+                user,
+                "automatically_follow_topics_policy",
+                UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+                acting_user=None,
+            )
+        # Hamlet starts a topic. DO automatically follow the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+        # Cordelia sends a message to the topic which hamlet started. DON'T automatically follow the topic.
+        self.send_stream_message(cordelia, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+        # Iago has 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER'.
+        # DON'T automatically follow the topic, even if he starts the topic.
+        do_change_user_setting(
+            iago,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
+        self.send_stream_message(iago, stream_name=stream.name, topic_name="New Topic")
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name="New Topic",
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # When a user sends the first message to a topic with protected history,
+        # the user starts that topic from their perspective. So, the user
+        # should follow the topic if 'automatically_follow_topics_policy' is set
+        # to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION', even if the message
+        # is not the first message in the topic.
+        private_stream = self.make_stream(stream_name="private stream", invite_only=True)
+        self.subscribe(iago, private_stream.name)
+        self.send_stream_message(iago, private_stream.name)
+
+        # Hamlet should automatically follow the topic, even if it already has messages.
+        self.subscribe(hamlet, private_stream.name)
+        self.send_stream_message(hamlet, private_stream.name)
+        stream_topic_target = StreamTopicTarget(
+            stream_id=private_stream.id,
+            topic_name="test",
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_follow_topic_on_send(self) -> None:
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+        self.send_stream_message(aaron, stream.name, "hello", topic_name)
+
+        # For hamlet, 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND'.
+        do_change_user_setting(
+            hamlet,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_follow_topics_policy' NOT set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND'.
+        do_change_user_setting(
+            aaron,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet sends a message. DO automatically follow the topic.
+        # Aaron sends a message. DON'T automatically follow the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_follow_topic_on_participation_send_message(self) -> None:
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+
+        # For hamlet, 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            hamlet,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_follow_topics_policy' NOT set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet sends a message. DO automatically follow the topic.
+        # Aaron sends a message. DON'T automatically follow the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_follow_topic_on_participation_add_reaction(self) -> None:
+        cordelia = self.example_user("cordelia")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+
+        # For cordelia, 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            cordelia,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_follow_topics_policy' NOT set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        message_id = self.send_stream_message(
+            hamlet, stream_name=stream.name, topic_name=topic_name
+        )
+        # Cordelia reacts to a message. DO automatically follow the topic.
+        # Aaron reacts to a message. DON'T automatically follow the topic.
+        check_add_reaction(
+            user_profile=cordelia,
+            message_id=message_id,
+            emoji_name="smile",
+            emoji_code=None,
+            reaction_type=None,
+        )
+        check_add_reaction(
+            user_profile=aaron,
+            message_id=message_id,
+            emoji_name="smile",
+            emoji_code=None,
+            reaction_type=None,
+        )
+
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {cordelia.id})
+
+        # We don't decrease visibility policy
+        sub = get_subscription(stream.name, cordelia)
+        sub.is_muted = True
+        sub.save()
+        do_change_user_setting(
+            cordelia,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
+        do_change_user_setting(
+            cordelia,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        check_add_reaction(
+            user_profile=cordelia,
+            message_id=message_id,
+            emoji_name="plus",
+            emoji_code=None,
+            reaction_type=None,
+        )
+
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {cordelia.id})
+
+        # increase visibility policy
+        do_set_user_topic_visibility_policy(
+            cordelia,
+            stream,
+            topic_name,
+            visibility_policy=UserTopic.VisibilityPolicy.MUTED,
+        )
+        check_add_reaction(
+            user_profile=cordelia,
+            message_id=message_id,
+            emoji_name="heart",
+            emoji_code=None,
+            reaction_type=None,
+        )
+
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {cordelia.id})
+
+        # Add test coverage for 'should_change_visibility_policy' when
+        # new_visibility_policy == current_visibility_policy
+        check_add_reaction(
+            user_profile=cordelia,
+            message_id=message_id,
+            emoji_name="tada",
+            emoji_code=None,
+            reaction_type=None,
+        )
+
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {cordelia.id})
+
+    def test_automatically_follow_topic_on_participation_participate_in_poll(self) -> None:
+        iago = self.example_user("iago")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+
+        # For iago, 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            iago,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_follow_topics_policy' NOT set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet creates a poll.
+        payload = dict(
+            type="stream",
+            to=orjson.dumps(stream.name).decode(),
+            topic=topic_name,
+            content="/poll Preference?\n\nyes\nno",
+        )
+        result = self.api_post(hamlet, "/api/v1/messages", payload)
+        self.assert_json_success(result)
+
+        # Iago participates in the poll. DO automatically follow the topic.
+        # Aaron participates in the poll. DON'T automatically follow the topic.
+        message = self.get_last_message()
+
+        def participate_in_poll(user: UserProfile, data: Dict[str, object]) -> None:
+            content = orjson.dumps(data).decode()
+            payload = dict(
+                message_id=message.id,
+                msg_type="widget",
+                content=content,
+            )
+            result = self.api_post(user, "/api/v1/submessage", payload)
+            self.assert_json_success(result)
+
+        participate_in_poll(iago, dict(type="vote", key="1,1", vote=1))
+        participate_in_poll(aaron, dict(type="new_option", idx=7, option="maybe"))
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {iago.id})
+
+    def test_automatically_follow_topic_on_participation_edit_todo_list(self) -> None:
+        othello = self.example_user("othello")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+
+        # For othello, 'automatically_follow_topics_policy' set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            othello,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_follow_topics_policy' NOT set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_follow_topics_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet creates a todo list.
+        payload = dict(
+            type="stream",
+            to=orjson.dumps(stream.name).decode(),
+            topic=topic_name,
+            content="/todo",
+        )
+        result = self.api_post(hamlet, "/api/v1/messages", payload)
+        self.assert_json_success(result)
+
+        # Othello edits the todo list. DO automatically follow the topic.
+        # Aaron edits the todo list. DON'T automatically follow the topic.
+        message = self.get_last_message()
+
+        def edit_todo_list(user: UserProfile, data: Dict[str, object]) -> None:
+            content = orjson.dumps(data).decode()
+            payload = dict(
+                message_id=message.id,
+                msg_type="widget",
+                content=content,
+            )
+            result = self.api_post(user, "/api/v1/submessage", payload)
+            self.assert_json_success(result)
+
+        edit_todo_list(othello, dict(type="new_task", key=7, task="eat", desc="", completed=False))
+        edit_todo_list(aaron, dict(type="strike", key="5,9"))
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.FOLLOWED
+        )
+        self.assertEqual(user_ids, {othello.id})
+
+
+class AutomaticallyUnmuteTopicsTests(ZulipTestCase):
+    def test_automatically_unmute_topic_on_initiation(self) -> None:
+        hamlet = self.example_user("hamlet")
+        cordelia = self.example_user("cordelia")
+        iago = self.example_user("iago")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+        for user in [hamlet, cordelia, iago]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # For hamlet & cordelia, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION'.
+        for user in [hamlet, cordelia]:
+            do_change_user_setting(
+                user,
+                "automatically_unmute_topics_in_muted_streams_policy",
+                UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+                acting_user=None,
+            )
+        # Hamlet starts a topic. DO automatically unmute the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+        # Cordelia sends a message to the topic which hamlet started. DON'T automatically unmute the topic.
+        self.send_stream_message(cordelia, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+        # Iago has 'automatically_unmute_topics_in_muted_streams_policy' set to
+        # 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER'.
+        # DON'T automatically unmute the topic, even if he starts the topic.
+        do_change_user_setting(
+            iago,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+            acting_user=None,
+        )
+        self.send_stream_message(iago, stream_name=stream.name, topic_name="New Topic")
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name="New Topic",
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # When a user sends the first message to a topic with protected history,
+        # the user starts that topic from their perspective. So, the user
+        # should unmute the topic if 'automatically_unmute_topics_in_muted_streams_policy'
+        # is set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION', even if
+        # the message is not the first message in the topic.
+        private_stream = self.make_stream(stream_name="private stream", invite_only=True)
+        self.subscribe(iago, private_stream.name)
+        self.send_stream_message(iago, private_stream.name)
+
+        # Hamlet should automatically unmute the topic, even if it already has messages.
+        self.subscribe(hamlet, private_stream.name)
+        sub = get_subscription(private_stream.name, hamlet)
+        sub.is_muted = True
+        sub.save()
+        self.send_stream_message(hamlet, private_stream.name)
+        stream_topic_target = StreamTopicTarget(
+            stream_id=private_stream.id,
+            topic_name="test",
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_unmute_topic_on_send(self) -> None:
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+        self.send_stream_message(aaron, stream.name, "hello", topic_name)
+        for user in [hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        # For hamlet, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND'.
+        do_change_user_setting(
+            hamlet,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_unmute_topics_in_muted_streams_policy' NOT
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_SEND'.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet sends a message. DO automatically unmute the topic.
+        # Aaron sends a message. DON'T automatically unmute the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_unmute_topic_on_participation_send_message(self) -> None:
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", hamlet.realm)
+        topic_name = "teST topic"
+        for user in [hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        # For hamlet, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            hamlet,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_unmute_topics_in_muted_streams_policy' NOT
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet sends a message. DO automatically unmute the topic.
+        # Aaron sends a message. DON'T automatically unmute the topic.
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_unmute_topic_on_participation_add_reaction(self) -> None:
+        cordelia = self.example_user("cordelia")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+        for user in [cordelia, hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        # For cordelia, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            cordelia,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_unmute_topics_in_muted_streams_policy' NOT
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        message_id = self.send_stream_message(
+            hamlet, stream_name=stream.name, topic_name=topic_name
+        )
+        # Cordelia reacts to a message. DO automatically unmute the topic.
+        # Aaron reacts to a message. DON'T automatically unmute the topic.
+        check_add_reaction(
+            user_profile=cordelia,
+            message_id=message_id,
+            emoji_name="smile",
+            emoji_code=None,
+            reaction_type=None,
+        )
+        check_add_reaction(
+            user_profile=aaron,
+            message_id=message_id,
+            emoji_name="smile",
+            emoji_code=None,
+            reaction_type=None,
+        )
+
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {cordelia.id})
+
+    def test_automatically_unmute_topic_on_participation_participate_in_poll(self) -> None:
+        iago = self.example_user("iago")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+        for user in [iago, hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        # For iago, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            iago,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_unmute_topics_in_muted_streams_policy' NOT
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet creates a poll.
+        payload = dict(
+            type="stream",
+            to=orjson.dumps(stream.name).decode(),
+            topic=topic_name,
+            content="/poll Preference?\n\nyes\nno",
+        )
+        result = self.api_post(hamlet, "/api/v1/messages", payload)
+        self.assert_json_success(result)
+
+        # Iago participates in the poll. DO automatically unmute the topic.
+        # Aaron participates in the poll. DON'T automatically unmute the topic.
+        message = self.get_last_message()
+
+        def participate_in_poll(user: UserProfile, data: Dict[str, object]) -> None:
+            content = orjson.dumps(data).decode()
+            payload = dict(
+                message_id=message.id,
+                msg_type="widget",
+                content=content,
+            )
+            result = self.api_post(user, "/api/v1/submessage", payload)
+            self.assert_json_success(result)
+
+        participate_in_poll(iago, dict(type="vote", key="1,1", vote=1))
+        participate_in_poll(aaron, dict(type="new_option", idx=7, option="maybe"))
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {iago.id})
+
+    def test_automatically_unmute_topic_on_participation_edit_todo_list(self) -> None:
+        othello = self.example_user("othello")
+        hamlet = self.example_user("hamlet")
+        aaron = self.example_user("aaron")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+        for user in [othello, hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+        # For othello, 'automatically_unmute_topics_in_muted_streams_policy'
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            othello,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        # For aaron, 'automatically_unmute_topics_in_muted_streams_policy' NOT
+        # set to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION'.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # Hamlet creates a todo list.
+        payload = dict(
+            type="stream",
+            to=orjson.dumps(stream.name).decode(),
+            topic=topic_name,
+            content="/todo",
+        )
+        result = self.api_post(hamlet, "/api/v1/messages", payload)
+        self.assert_json_success(result)
+
+        # Othello edits the todo list. DO automatically unmute the topic.
+        # Aaron edits the todo list. DON'T automatically unmute the topic.
+        message = self.get_last_message()
+
+        def edit_todo_list(user: UserProfile, data: Dict[str, object]) -> None:
+            content = orjson.dumps(data).decode()
+            payload = dict(
+                message_id=message.id,
+                msg_type="widget",
+                content=content,
+            )
+            result = self.api_post(user, "/api/v1/submessage", payload)
+            self.assert_json_success(result)
+
+        edit_todo_list(othello, dict(type="new_task", key=7, task="eat", desc="", completed=False))
+        edit_todo_list(aaron, dict(type="strike", key="5,9"))
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {othello.id})
+
+    def test_only_automatically_increase_visibility_policy(self) -> None:
+        aaron = self.example_user("aaron")
+        hamlet = self.example_user("hamlet")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+        for user in [hamlet, aaron]:
+            sub = get_subscription(stream.name, user)
+            sub.is_muted = True
+            sub.save()
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+        # If a topic is already FOLLOWED, we don't change the state to UNMUTED as the
+        # intent of these "automatically follow or unmute" policies is that they can only
+        # increase the user's visibility policy for the topic.
+        do_set_user_topic_visibility_policy(
+            aaron,
+            stream,
+            topic_name,
+            visibility_policy=UserTopic.VisibilityPolicy.FOLLOWED,
+        )
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        # increase visibility from MUTED to UNMUTED
+        topic_name = "new Topic"
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+        do_set_user_topic_visibility_policy(
+            hamlet,
+            stream,
+            topic_name,
+            visibility_policy=UserTopic.VisibilityPolicy.MUTED,
+        )
+        do_change_user_setting(
+            hamlet,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        self.send_stream_message(hamlet, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, {hamlet.id})
+
+    def test_automatically_unmute_policy_unmuted_stream(self) -> None:
+        aaron = self.example_user("aaron")
+        cordelia = self.example_user("cordelia")
+        stream = get_stream("Verona", aaron.realm)
+        topic_name = "teST topic"
+
+        stream_topic_target = StreamTopicTarget(
+            stream_id=stream.id,
+            topic_name=topic_name,
+        )
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+        # The 'automatically_unmute_topics_in_muted_streams_policy' setting has
+        # NO effect in unmuted streams.
+        do_change_user_setting(
+            aaron,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_INITIATION,
+            acting_user=None,
+        )
+        self.send_stream_message(aaron, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())
+
+        do_set_user_topic_visibility_policy(
+            cordelia,
+            stream,
+            topic_name,
+            visibility_policy=UserTopic.VisibilityPolicy.MUTED,
+        )
+        do_change_user_setting(
+            cordelia,
+            "automatically_unmute_topics_in_muted_streams_policy",
+            UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_ON_PARTICIPATION,
+            acting_user=None,
+        )
+        self.send_stream_message(cordelia, stream_name=stream.name, topic_name=topic_name)
+        user_ids = stream_topic_target.user_ids_with_visibility_policy(
+            UserTopic.VisibilityPolicy.UNMUTED
+        )
+        self.assertEqual(user_ids, set())

zerver/tests/test_users.py

@@ -1910,6 +1910,7 @@ class RecipientInfoTest(ZulipTestCase):
             service_bot_tuples=[],
             all_bot_user_ids=set(),
             topic_participant_user_ids=set(),
+            sender_muted_stream=False,
         )
 
         self.assertEqual(info, expected_info)

zerver/views/realm.py

@@ -556,6 +556,14 @@ def update_realm_user_settings_defaults(
         json_validator=check_int_in(UserProfile.REALM_NAME_IN_EMAIL_NOTIFICATIONS_POLICY_CHOICES),
         default=None,
     ),
+    automatically_follow_topics_policy: Optional[int] = REQ(
+        json_validator=check_int_in(UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES),
+        default=None,
+    ),
+    automatically_unmute_topics_in_muted_streams_policy: Optional[int] = REQ(
+        json_validator=check_int_in(UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES),
+        default=None,
+    ),
     presence_enabled: Optional[bool] = REQ(json_validator=check_bool, default=None),
     enter_sends: Optional[bool] = REQ(json_validator=check_bool, default=None),
     enable_drafts_synchronization: Optional[bool] = REQ(json_validator=check_bool, default=None),

zerver/views/user_settings.py

@@ -258,6 +258,14 @@ def json_change_settings(
         json_validator=check_int_in(UserProfile.REALM_NAME_IN_EMAIL_NOTIFICATIONS_POLICY_CHOICES),
         default=None,
     ),
+    automatically_follow_topics_policy: Optional[int] = REQ(
+        json_validator=check_int_in(UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES),
+        default=None,
+    ),
+    automatically_unmute_topics_in_muted_streams_policy: Optional[int] = REQ(
+        json_validator=check_int_in(UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_CHOICES),
+        default=None,
+    ),
     presence_enabled: Optional[bool] = REQ(json_validator=check_bool, default=None),
     enter_sends: Optional[bool] = REQ(json_validator=check_bool, default=None),
     send_private_typing_notifications: Optional[bool] = REQ(

zilencer/management/commands/populate_db.py

@@ -30,6 +30,7 @@ from zerver.actions.realm_linkifiers import do_add_linkifier
 from zerver.actions.scheduled_messages import check_schedule_message
 from zerver.actions.streams import bulk_add_subscriptions
 from zerver.actions.user_groups import create_user_group_in_database
+from zerver.actions.user_settings import do_change_user_setting
 from zerver.actions.users import do_change_user_role
 from zerver.lib.bulk_create import bulk_create_streams
 from zerver.lib.generate_test_data import create_test_data, generate_topics
@@ -825,6 +826,29 @@ class Command(BaseCommand):
             UserProfile.objects.filter(is_bot=False, realm=zulip_realm)
         )
 
+        # As we plan to change the default values for 'automatically_follow_topics_policy' and
+        # 'automatically_unmute_topics_in_muted_streams_policy' in the future, it will lead to
+        # skewing a lot of our tests, which now need to take into account extra events and database queries.
+        #
+        # We explicitly set the values for both settings to 'AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER'
+        # to make the tests independent of the default values.
+        #
+        # We have separate tests to verify events generated, database query counts,
+        # and other important details related to the above-mentioned settings.
+        for user in user_profiles:
+            do_change_user_setting(
+                user,
+                "automatically_follow_topics_policy",
+                UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+                acting_user=None,
+            )
+            do_change_user_setting(
+                user,
+                "automatically_unmute_topics_in_muted_streams_policy",
+                UserProfile.AUTOMATICALLY_CHANGE_VISIBILITY_POLICY_NEVER,
+                acting_user=None,
+            )
+
         # Create a test realm emoji.
         IMAGE_FILE_PATH = static_path("images/test-images/checkbox.png")
         with open(IMAGE_FILE_PATH, "rb") as fp: