From c7bf7736055c0ae174823d1d2a21fa7a253940d7 Mon Sep 17 00:00:00 2001
From: davewiththenicehat
 <54369722+davewiththenicehat@users.noreply.github.com>
Date: Fri, 16 Apr 2021 10:55:24 -0400
Subject: [PATCH] taskhandler suppress cancel error

Added an errback to handle errors within task handler's deferred instance.
Without this instances of deferred cause a traceback when a deferred is canceled without errback or callback having been called.
This traceback does not end execution, and ultimately would only show to main console.
Reference cancel: https://github.com/twisted/twisted/blob/trunk/src/twisted/internet/defer.py

All evennia unit tests pass.
---
 evennia/scripts/taskhandler.py    | 16 +++++++++++++++-
 evennia/utils/tests/test_utils.py |  8 +++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/evennia/scripts/taskhandler.py b/evennia/scripts/taskhandler.py
index 11ac144a94..3273e27e8a 100644
--- a/evennia/scripts/taskhandler.py
+++ b/evennia/scripts/taskhandler.py
@@ -6,6 +6,7 @@ from datetime import datetime, timedelta
 
 from twisted.internet import reactor
 from twisted.internet.task import deferLater
+from twisted.internet.defer import CancelledError as DefCancelledError
 from evennia.server.models import ServerConfig
 from evennia.utils.logger import log_err
 from evennia.utils.dbserialize import dbserialize, dbunserialize
@@ -13,6 +14,17 @@ from evennia.utils.dbserialize import dbserialize, dbunserialize
 TASK_HANDLER = None
 
 
+def handle_error(*args, **kwargs):
+    """
+    Handle errors withing deferred objects.
+    """
+    for arg in args:
+        # suppress cancel errors
+        if arg.type == DefCancelledError:
+            continue
+        raise arg
+
+
 class TaskHandler(object):
 
     """
@@ -179,7 +191,9 @@ class TaskHandler(object):
             deferLater(self.clock, timedelay, callback, *args, **kwargs)
             return task_id
 
-        return deferLater(self.clock, timedelay, callback, *args, **kwargs)
+        d = deferLater(self.clock, timedelay, callback, *args, **kwargs)
+        d.addErrback(handle_error)
+        return d
 
     def remove(self, task_id):
         """Remove a persistent task without executing it.
diff --git a/evennia/utils/tests/test_utils.py b/evennia/utils/tests/test_utils.py
index ea23601fce..bebea149ce 100644
--- a/evennia/utils/tests/test_utils.py
+++ b/evennia/utils/tests/test_utils.py
@@ -10,7 +10,7 @@ import mock
 
 from django.test import TestCase
 from datetime import datetime
-from twisted.internet import task, reactor
+from twisted.internet import task
 
 from evennia.utils.ansi import ANSIString
 from evennia.utils import utils
@@ -338,3 +338,9 @@ class TestDelay(EvenniaTest):
         _TASK_HANDLER.clock.advance(1)  # make time pass
         self.assertEqual(self.char1.ndb.dummy_var, 'dummy_func ran')
         self.char1.ndb.dummy_var = False
+        # test canceling a deferral.
+        deferal_inst = utils.delay(1, dummy_func, self.char1.dbref)
+        deferal_inst.cancel()
+        _TASK_HANDLER.clock.advance(1)  # make time pass
+        self.assertEqual(self.char1.ndb.dummy_var, False)
+        self.char1.ndb.dummy_var = False