mute user: Mark as read old messages immediately.

When a user is muted, in the same request,
we mark any existing unreads from that user
as read.

This is done for all types of messages
(PM/huddle/stream) and regardless of whether
the user was mentioned in them.

This will not break the unread count logic
of the web frontend, because that algorithm
decides which messages to mark as read based
only on the pointer location and the whitespace
at the bottom, not on what messages have already
been marked as read.

zerver/lib/actions.py

@@ -5051,6 +5051,46 @@ def do_mark_stream_messages_as_read(
     return count
 
 
+def do_mark_muted_user_messages_as_read(
+    user_profile: UserProfile,
+    muted_user: UserProfile,
+) -> int:
+    messages = UserMessage.objects.filter(
+        user_profile=user_profile, message__sender=muted_user
+    ).extra(where=[UserMessage.where_unread()])
+
+    message_ids = list(messages.values_list("message__id", flat=True))
+
+    count = messages.update(
+        flags=F("flags").bitor(UserMessage.flags.read),
+    )
+
+    event = dict(
+        type="update_message_flags",
+        op="add",
+        operation="add",
+        flag="read",
+        messages=message_ids,
+        all=False,
+    )
+    event_time = timezone_now()
+
+    send_event(user_profile.realm, event, [user_profile.id])
+    do_clear_mobile_push_notifications_for_ids([user_profile.id], message_ids)
+
+    do_increment_logging_stat(
+        user_profile, COUNT_STATS["messages_read::hour"], None, event_time, increment=count
+    )
+    do_increment_logging_stat(
+        user_profile,
+        COUNT_STATS["messages_read_interactions::hour"],
+        None,
+        event_time,
+        increment=min(1, count),
+    )
+    return count
+
+
 def do_update_mobile_push_notification(
     message: Message, prior_mention_user_ids: Set[int], stream_push_user_ids: Set[int]
 ) -> None:
@@ -6515,6 +6555,7 @@ def do_mute_user(
     if date_muted is None:
         date_muted = timezone_now()
     add_user_mute(user_profile, muted_user, date_muted)
+    do_mark_muted_user_messages_as_read(user_profile, muted_user)
     event = dict(type="muted_users", muted_users=get_user_mutes(user_profile))
     send_event(user_profile.realm, event, [user_profile.id])