Cancel scheduled tasks when cogs unload

When cogs reload, they used new Scheduler instances, which aren't aware
of previously scheduled tasks. This led to duplicate scheduled tasks
when cogs re-scheduled tasks upon initialisation.

Fixes #1080
Fixes BOT-7H

4 files changed, 14 insertions, 1 deletions

diff --git a/bot/cogs/filtering.py b/bot/cogs/filtering.py
index 64afd184d..4ec95ad73 100644
--- a/bot/cogs/filtering.py
+++ b/bot/cogs/filtering.py
@@ -99,6 +99,10 @@ class Filtering(Cog):
 
         self.bot.loop.create_task(self.reschedule_offensive_msg_deletion())
 
+    def cog_unload(self) -> None:
+        """Cancel scheduled tasks."""
+        self.scheduler.cancel_all()
+
     def _get_filterlist_items(self, list_type: str, *, allowed: bool) -> list:
         """Fetch items from the filter_list_cache."""
         return self.bot.filter_list_cache[f"{list_type.upper()}.{allowed}"].keys()
diff --git a/bot/cogs/moderation/scheduler.py b/bot/cogs/moderation/scheduler.py
index 601e238c9..75028d851 100644
--- a/bot/cogs/moderation/scheduler.py
+++ b/bot/cogs/moderation/scheduler.py
@@ -31,6 +31,10 @@ class InfractionScheduler:
 
         self.bot.loop.create_task(self.reschedule_infractions(supported_infractions))
 
+    def cog_unload(self) -> None:
+        """Cancel scheduled tasks."""
+        self.scheduler.cancel_all()
+
     @property
     def mod_log(self) -> ModLog:
         """Get the currently loaded ModLog cog instance."""
diff --git a/bot/cogs/moderation/silence.py b/bot/cogs/moderation/silence.py
index ae4fb7b64..f8a6592bc 100644
--- a/bot/cogs/moderation/silence.py
+++ b/bot/cogs/moderation/silence.py
@@ -152,7 +152,8 @@ class Silence(commands.Cog):
         return False
 
     def cog_unload(self) -> None:
-        """Send alert with silenced channels on unload."""
+        """Send alert with silenced channels and cancel scheduled tasks on unload."""
+        self.scheduler.cancel_all()
         if self.muted_channels:
             channels_string = ''.join(channel.mention for channel in self.muted_channels)
             message = f"<@&{Roles.moderators}> channels left silenced on cog unload: {channels_string}"
diff --git a/bot/cogs/reminders.py b/bot/cogs/reminders.py
index b5998cc0e..670493bcf 100644
--- a/bot/cogs/reminders.py
+++ b/bot/cogs/reminders.py
@@ -37,6 +37,10 @@ class Reminders(Cog):
 
         self.bot.loop.create_task(self.reschedule_reminders())
 
+    def cog_unload(self) -> None:
+        """Cancel scheduled tasks."""
+        self.scheduler.cancel_all()
+
     async def reschedule_reminders(self) -> None:
         """Get all current reminders from the API and reschedule them."""
         await self.bot.wait_until_guild_available()