[commands] Fix typing of check/check_any

This changes the type information of check decorators to return a
protocol representing that the decorator leaves the underlying object
unchanged while having a .predicate attribute.

resolves #7949

discord/ext/commands/_types.py

@@ -23,7 +23,7 @@ DEALINGS IN THE SOFTWARE.
 """
 
 
-from typing import Any, Awaitable, Callable, Coroutine, TYPE_CHECKING, TypeVar, Union, Tuple, Optional
+from typing import Any, Awaitable, Callable, Coroutine, TYPE_CHECKING, Protocol, TypeVar, Union, Tuple, Optional
 
 
 T = TypeVar('T')
@@ -51,13 +51,23 @@ MaybeCoro = Union[T, Coro[T]]
 MaybeAwaitable = Union[T, Awaitable[T]]
 
 CogT = TypeVar('CogT', bound='Optional[Cog]')
-Check = Callable[["ContextT"], MaybeCoro[bool]]
+UserCheck = Callable[["ContextT"], MaybeCoro[bool]]
 Hook = Union[Callable[["CogT", "ContextT"], Coro[Any]], Callable[["ContextT"], Coro[Any]]]
 Error = Union[Callable[["CogT", "ContextT", "CommandError"], Coro[Any]], Callable[["ContextT", "CommandError"], Coro[Any]]]
 
 ContextT = TypeVar('ContextT', bound='Context[Any]')
 BotT = TypeVar('BotT', bound=_Bot, covariant=True)
 
+ContextT_co = TypeVar('ContextT_co', bound='Context[Any]', covariant=True)
+
+
+class Check(Protocol[ContextT_co]):
+
+    predicate: Callable[[ContextT_co], Coroutine[Any, Any, bool]]
+
+    def __call__(self, coro_or_commands: T) -> T:
+        ...
+
 
 # This is merely a tag type to avoid circular import issues.
 # Yes, this is a terrible solution but ultimately it is the only solution.

discord/ext/commands/bot.py

@@ -69,7 +69,7 @@ if TYPE_CHECKING:
     from ._types import (
         _Bot,
         BotT,
-        Check,
+        UserCheck,
         CoroFunc,
         ContextT,
         MaybeAwaitableFunc,
@@ -161,8 +161,8 @@ class BotBase(GroupMixin[None]):
         self.extra_events: Dict[str, List[CoroFunc]] = {}
         self.__cogs: Dict[str, Cog] = {}
         self.__extensions: Dict[str, types.ModuleType] = {}
-        self._checks: List[Check] = []
-        self._check_once: List[Check] = []
+        self._checks: List[UserCheck] = []
+        self._check_once: List[UserCheck] = []
         self._before_invoke: Optional[CoroFunc] = None
         self._after_invoke: Optional[CoroFunc] = None
         self._help_command: Optional[HelpCommand] = None
@@ -282,7 +282,7 @@ class BotBase(GroupMixin[None]):
         self.add_check(func)  # type: ignore
         return func
 
-    def add_check(self, func: Check[ContextT], /, *, call_once: bool = False) -> None:
+    def add_check(self, func: UserCheck[ContextT], /, *, call_once: bool = False) -> None:
         """Adds a global check to the bot.
 
         This is the non-decorator interface to :meth:`.check`
@@ -306,7 +306,7 @@ class BotBase(GroupMixin[None]):
         else:
             self._checks.append(func)
 
-    def remove_check(self, func: Check[ContextT], /, *, call_once: bool = False) -> None:
+    def remove_check(self, func: UserCheck[ContextT], /, *, call_once: bool = False) -> None:
         """Removes a global check from the bot.
 
         This function is idempotent and will not raise an exception

discord/ext/commands/core.py

@@ -60,7 +60,7 @@ if TYPE_CHECKING:
 
     from discord.message import Message
 
-    from ._types import BotT, Check, ContextT, Coro, CoroFunc, Error, Hook
+    from ._types import BotT, Check, ContextT, Coro, CoroFunc, Error, Hook, UserCheck
 
 
 __all__ = (
@@ -375,7 +375,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
         except AttributeError:
             checks = kwargs.get('checks', [])
 
-        self.checks: List[Check[ContextT]] = checks
+        self.checks: List[UserCheck[ContextT]] = checks
 
         try:
             cooldown = func.__commands_cooldown__
@@ -447,7 +447,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
 
         self.params: Dict[str, Parameter] = get_signature_parameters(function, globalns)
 
-    def add_check(self, func: Check[ContextT], /) -> None:
+    def add_check(self, func: UserCheck[ContextT], /) -> None:
         """Adds a check to the command.
 
         This is the non-decorator interface to :func:`.check`.
@@ -466,7 +466,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
 
         self.checks.append(func)
 
-    def remove_check(self, func: Check[ContextT], /) -> None:
+    def remove_check(self, func: UserCheck[ContextT], /) -> None:
         """Removes a check from the command.
 
         This function is idempotent and will not raise an exception
@@ -1734,7 +1734,7 @@ def group(
     return command(name=name, cls=cls, **attrs)
 
 
-def check(predicate: Check[ContextT], /) -> Callable[[T], T]:
+def check(predicate: UserCheck[ContextT], /) -> Check[ContextT]:
     r"""A decorator that adds a check to the :class:`.Command` or its
     subclasses. These checks could be accessed via :attr:`.Command.checks`.
 
@@ -1833,7 +1833,7 @@ def check(predicate: Check[ContextT], /) -> Callable[[T], T]:
     return decorator  # type: ignore
 
 
-def check_any(*checks: Check[ContextT]) -> Callable[[T], T]:
+def check_any(*checks: Check[ContextT]) -> Check[ContextT]:
     r"""A :func:`check` that is added that checks if any of the checks passed
     will pass, i.e. using logical OR.
 
@@ -1899,10 +1899,10 @@ def check_any(*checks: Check[ContextT]) -> Callable[[T], T]:
         # if we're here, all checks failed
         raise CheckAnyFailure(unwrapped, errors)
 
-    return check(predicate)
+    return check(predicate)  # type: ignore
 
 
-def has_role(item: Union[int, str], /) -> Callable[[T], T]:
+def has_role(item: Union[int, str], /) -> Check[Any]:
     """A :func:`.check` that is added that checks if the member invoking the
     command has the role specified via the name or ID specified.
 
@@ -2055,7 +2055,7 @@ def bot_has_any_role(*items: int) -> Callable[[T], T]:
     return check(predicate)
 
 
-def has_permissions(**perms: bool) -> Callable[[T], T]:
+def has_permissions(**perms: bool) -> Check[Any]:
     """A :func:`.check` that is added that checks if the member has all of
     the permissions necessary.
 
@@ -2103,7 +2103,7 @@ def has_permissions(**perms: bool) -> Callable[[T], T]:
     return check(predicate)
 
 
-def bot_has_permissions(**perms: bool) -> Callable[[T], T]:
+def bot_has_permissions(**perms: bool) -> Check[Any]:
     """Similar to :func:`.has_permissions` except checks if the bot itself has
     the permissions listed.
 
@@ -2130,7 +2130,7 @@ def bot_has_permissions(**perms: bool) -> Callable[[T], T]:
     return check(predicate)
 
 
-def has_guild_permissions(**perms: bool) -> Callable[[T], T]:
+def has_guild_permissions(**perms: bool) -> Check[Any]:
     """Similar to :func:`.has_permissions`, but operates on guild wide
     permissions instead of the current channel permissions.
 
@@ -2159,7 +2159,7 @@ def has_guild_permissions(**perms: bool) -> Callable[[T], T]:
     return check(predicate)
 
 
-def bot_has_guild_permissions(**perms: bool) -> Callable[[T], T]:
+def bot_has_guild_permissions(**perms: bool) -> Check[Any]:
     """Similar to :func:`.has_guild_permissions`, but checks the bot
     members guild permissions.
 
@@ -2185,7 +2185,7 @@ def bot_has_guild_permissions(**perms: bool) -> Callable[[T], T]:
     return check(predicate)
 
 
-def dm_only() -> Callable[[T], T]:
+def dm_only() -> Check[Any]:
     """A :func:`.check` that indicates this command must only be used in a
     DM context. Only private messages are allowed when
     using the command.
@@ -2204,7 +2204,7 @@ def dm_only() -> Callable[[T], T]:
     return check(predicate)
 
 
-def guild_only() -> Callable[[T], T]:
+def guild_only() -> Check[Any]:
     """A :func:`.check` that indicates this command must only be used in a
     guild context only. Basically, no private messages are allowed when
     using the command.
@@ -2221,7 +2221,7 @@ def guild_only() -> Callable[[T], T]:
     return check(predicate)
 
 
-def is_owner() -> Callable[[T], T]:
+def is_owner() -> Check[Any]:
     """A :func:`.check` that checks if the person invoking this command is the
     owner of the bot.
 
@@ -2239,7 +2239,7 @@ def is_owner() -> Callable[[T], T]:
     return check(predicate)
 
 
-def is_nsfw() -> Callable[[T], T]:
+def is_nsfw() -> Check[Any]:
     """A :func:`.check` that checks if the channel is a NSFW channel.
 
     This check raises a special exception, :exc:`.NSFWChannelRequired`

discord/ext/commands/help.py

@@ -61,7 +61,7 @@ if TYPE_CHECKING:
     from .parameters import Parameter
 
     from ._types import (
-        Check,
+        UserCheck,
         ContextT,
         BotT,
         _Bot,
@@ -377,7 +377,7 @@ class HelpCommand:
         bot.remove_command(self._command_impl.name)
         self._command_impl._eject_cog()
 
-    def add_check(self, func: Check[ContextT], /) -> None:
+    def add_check(self, func: UserCheck[ContextT], /) -> None:
         """
         Adds a check to the help command.
 
@@ -395,7 +395,7 @@ class HelpCommand:
 
         self._command_impl.add_check(func)
 
-    def remove_check(self, func: Check[ContextT], /) -> None:
+    def remove_check(self, func: UserCheck[ContextT], /) -> None:
         """
         Removes a check from the help command.