Fix errors that will occur in python3.11 (#1680)

Apply correct fix for MISSING default

Co-authored-by: BobDotCom <71356958+BobDotCom@users.noreply.github.com>

discord/ext/commands/flags.py

@@ -31,7 +31,7 @@
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any, Iterator, Literal, Pattern, TypeVar, Union
 
-from discord.utils import MISSING, maybe_coroutine, resolve_annotation
+from discord.utils import MISSING, MissingField, maybe_coroutine, resolve_annotation
 
 from .converter import run_converters
 from .errors import (
@@ -81,13 +81,13 @@ class Flag:
         Whether multiple given values overrides the previous value.
     """
 
-    name: str = MISSING
+    name: str = MissingField
     aliases: list[str] = field(default_factory=list)
-    attribute: str = MISSING
-    annotation: Any = MISSING
-    default: Any = MISSING
-    max_args: int = MISSING
-    override: bool = MISSING
+    attribute: str = MissingField
+    annotation: Any = MissingField
+    default: Any = MissingField
+    max_args: int = MissingField
+    override: bool = MissingField
     cast_to_dict: bool = False
 
     @property

discord/utils.py

@@ -38,6 +38,7 @@
 import warnings
 from base64 import b64encode
 from bisect import bisect_left
+from dataclasses import field
 from inspect import isawaitable as _isawaitable
 from inspect import signature as _signature
 from operator import attrgetter
@@ -114,6 +115,11 @@ def __repr__(self) -> str:
 
 
 MISSING: Any = _MissingSentinel()
+# As of 3.11, directly setting a dataclass field to MISSING causes a ValueError. Using
+# field(default=MISSING) produces the same error, but passing a lambda to
+# default_factory produces the same behavior as default=MISSING and does not raise an
+# error.
+MissingField = field(default_factory=lambda: MISSING)
 
 
 class _cached_property: