[commands][types] Type hint commands-ext

discord/ext/commands/_types.py

@@ -22,6 +22,26 @@ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 """
 
+
+from typing import Any, Callable, Coroutine, TYPE_CHECKING, TypeVar, Union
+
+
+if TYPE_CHECKING:
+    from .context import Context
+    from .cog import Cog
+    from .errors import CommandError
+
+T = TypeVar('T')
+
+Coro = Coroutine[Any, Any, T]
+MaybeCoro = Union[T, Coro[T]]
+CoroFunc = Callable[..., Coro[Any]]
+
+Check = Union[Callable[["Cog", "Context[Any]"], MaybeCoro[bool]], Callable[["Context[Any]"], MaybeCoro[bool]]]
+Hook = Union[Callable[["Cog", "Context[Any]"], Coro[Any]], Callable[["Context[Any]"], Coro[Any]]]
+Error = Union[Callable[["Cog", "Context[Any]", "CommandError"], Coro[Any]], Callable[["Context[Any]", "CommandError"], Coro[Any]]]
+
+
 # This is merely a tag type to avoid circular import issues.
 # Yes, this is a terrible solution but ultimately it is the only solution.
 class _BaseCommand:

discord/ext/commands/bot.py

@@ -22,13 +22,18 @@ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 """
 
+from __future__ import annotations
+
+
 import asyncio
 import collections
+import collections.abc
 import inspect
 import importlib.util
 import sys
 import traceback
 import types
+from typing import Any, Callable, Mapping, List, Dict, TYPE_CHECKING, Optional, TypeVar, Type, Union
 
 import discord
 
@@ -39,6 +44,15 @@ from . import errors
 from .help import HelpCommand, DefaultHelpCommand
 from .cog import Cog
 
+if TYPE_CHECKING:
+    import importlib.machinery
+
+    from discord.message import Message
+    from ._types import (
+        Check,
+        CoroFunc,
+    )
+
 __all__ = (
     'when_mentioned',
     'when_mentioned_or',
@@ -46,14 +60,21 @@ __all__ = (
     'AutoShardedBot',
 )
 
-def when_mentioned(bot, msg):
+MISSING: Any = discord.utils.MISSING
+
+T = TypeVar('T')
+CFT = TypeVar('CFT', bound='CoroFunc')
+CXT = TypeVar('CXT', bound='Context')
+
+def when_mentioned(bot: Union[Bot, AutoShardedBot], msg: Message) -> List[str]:
     """A callable that implements a command prefix equivalent to being mentioned.
 
     These are meant to be passed into the :attr:`.Bot.command_prefix` attribute.
     """
-    return [f'<@{bot.user.id}> ', f'<@!{bot.user.id}> ']
+    # bot.user will never be None when this is called
+    return [f'<@{bot.user.id}> ', f'<@!{bot.user.id}> ']  # type: ignore
 
-def when_mentioned_or(*prefixes):
+def when_mentioned_or(*prefixes: str) -> Callable[[Union[Bot, AutoShardedBot], Message], List[str]]:
     """A callable that implements when mentioned or other prefixes provided.
 
     These are meant to be passed into the :attr:`.Bot.command_prefix` attribute.
@@ -89,7 +110,7 @@ def when_mentioned_or(*prefixes):
 
     return inner
 
-def _is_submodule(parent, child):
+def _is_submodule(parent: str, child: str) -> bool:
     return parent == child or child.startswith(parent + ".")
 
 class _DefaultRepr:
@@ -102,10 +123,10 @@ class BotBase(GroupMixin):
     def __init__(self, command_prefix, help_command=_default, description=None, **options):
         super().__init__(**options)
         self.command_prefix = command_prefix
-        self.extra_events = {}
-        self.__cogs = {}
-        self.__extensions = {}
-        self._checks = []
+        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 = []
         self._before_invoke = None
         self._after_invoke = None
@@ -128,13 +149,14 @@ class BotBase(GroupMixin):
 
     # internal helpers
 
-    def dispatch(self, event_name, *args, **kwargs):
-        super().dispatch(event_name, *args, **kwargs)
+    def dispatch(self, event_name: str, *args: Any, **kwargs: Any) -> None:
+        # super() will resolve to Client
+        super().dispatch(event_name, *args, **kwargs)  # type: ignore
         ev = 'on_' + event_name
         for event in self.extra_events.get(ev, []):
-            self._schedule_event(event, ev, *args, **kwargs)
+            self._schedule_event(event, ev, *args, **kwargs)  # type: ignore
 
-    async def close(self):
+    async def close(self) -> None:
         for extension in tuple(self.__extensions):
             try:
                 self.unload_extension(extension)
@@ -147,9 +169,9 @@ class BotBase(GroupMixin):
             except Exception:
                 pass
 
-        await super().close()
+        await super().close()  # type: ignore
 
-    async def on_command_error(self, context, exception):
+    async def on_command_error(self, context: Context, exception: errors.CommandError) -> None:
         """|coro|
 
         The default command error handler provided by the bot.
@@ -175,7 +197,7 @@ class BotBase(GroupMixin):
 
     # global check registration
 
-    def check(self, func):
+    def check(self, func: T) -> T:
         r"""A decorator that adds a global check to the bot.
 
         A global check is similar to a :func:`.check` that is applied
@@ -200,10 +222,11 @@ class BotBase(GroupMixin):
                 return ctx.command.qualified_name in allowed_commands
 
         """
-        self.add_check(func)
+        # T was used instead of Check to ensure the type matches on return
+        self.add_check(func)  # type: ignore
         return func
 
-    def add_check(self, func, *, call_once=False):
+    def add_check(self, func: Check, *, call_once: bool = False) -> None:
         """Adds a global check to the bot.
 
         This is the non-decorator interface to :meth:`.check`
@@ -223,7 +246,7 @@ class BotBase(GroupMixin):
         else:
             self._checks.append(func)
 
-    def remove_check(self, func, *, call_once=False):
+    def remove_check(self, func: Check, *, call_once: bool = False) -> None:
         """Removes a global check from the bot.
 
         This function is idempotent and will not raise an exception
@@ -244,7 +267,7 @@ class BotBase(GroupMixin):
         except ValueError:
             pass
 
-    def check_once(self, func):
+    def check_once(self, func: CFT) -> CFT:
         r"""A decorator that adds a "call once" global check to the bot.
 
         Unlike regular global checks, this one is called only once
@@ -282,15 +305,16 @@ class BotBase(GroupMixin):
         self.add_check(func, call_once=True)
         return func
 
-    async def can_run(self, ctx, *, call_once=False):
+    async def can_run(self, ctx: Context, *, call_once: bool = False) -> bool:
         data = self._check_once if call_once else self._checks
 
         if len(data) == 0:
             return True
 
-        return await discord.utils.async_all(f(ctx) for f in data)
+        # type-checker doesn't distinguish between functions and methods
+        return await discord.utils.async_all(f(ctx) for f in data)  # type: ignore
 
-    async def is_owner(self, user):
+    async def is_owner(self, user: discord.User) -> bool:
         """|coro|
 
         Checks if a :class:`~discord.User` or :class:`~discord.Member` is the owner of
@@ -319,7 +343,8 @@ class BotBase(GroupMixin):
         elif self.owner_ids:
             return user.id in self.owner_ids
         else:
-            app = await self.application_info()
+
+            app = await self.application_info()  # type: ignore
             if app.team:
                 self.owner_ids = ids = {m.id for m in app.team.members}
                 return user.id in ids
@@ -327,7 +352,7 @@ class BotBase(GroupMixin):
                 self.owner_id = owner_id = app.owner.id
                 return user.id == owner_id
 
-    def before_invoke(self, coro):
+    def before_invoke(self, coro: CFT) -> CFT:
         """A decorator that registers a coroutine as a pre-invoke hook.
 
         A pre-invoke hook is called directly before the command is
@@ -359,7 +384,7 @@ class BotBase(GroupMixin):
         self._before_invoke = coro
         return coro
 
-    def after_invoke(self, coro):
+    def after_invoke(self, coro: CFT) -> CFT:
         r"""A decorator that registers a coroutine as a post-invoke hook.
 
         A post-invoke hook is called directly after the command is
@@ -394,14 +419,14 @@ class BotBase(GroupMixin):
 
     # listener registration
 
-    def add_listener(self, func, name=None):
+    def add_listener(self, func: CoroFunc, name: str = MISSING) -> None:
         """The non decorator alternative to :meth:`.listen`.
 
         Parameters
         -----------
         func: :ref:`coroutine <coroutine>`
             The function to call.
-        name: Optional[:class:`str`]
+        name: :class:`str`
             The name of the event to listen for. Defaults to ``func.__name__``.
 
         Example
@@ -416,7 +441,7 @@ class BotBase(GroupMixin):
             bot.add_listener(my_message, 'on_message')
 
         """
-        name = func.__name__ if name is None else name
+        name = func.__name__ if name is MISSING else name
 
         if not asyncio.iscoroutinefunction(func):
             raise TypeError('Listeners must be coroutines')
@@ -426,7 +451,7 @@ class BotBase(GroupMixin):
         else:
             self.extra_events[name] = [func]
 
-    def remove_listener(self, func, name=None):
+    def remove_listener(self, func: CoroFunc, name: str = MISSING) -> None:
         """Removes a listener from the pool of listeners.
 
         Parameters
@@ -438,7 +463,7 @@ class BotBase(GroupMixin):
             ``func.__name__``.
         """
 
-        name = func.__name__ if name is None else name
+        name = func.__name__ if name is MISSING else name
 
         if name in self.extra_events:
             try:
@@ -446,7 +471,7 @@ class BotBase(GroupMixin):
             except ValueError:
                 pass
 
-    def listen(self, name=None):
+    def listen(self, name: str = MISSING) -> Callable[[CFT], CFT]:
         """A decorator that registers another function as an external
         event listener. Basically this allows you to listen to multiple
         events from different places e.g. such as :func:`.on_ready`
@@ -476,7 +501,7 @@ class BotBase(GroupMixin):
             The function being listened to is not a coroutine.
         """
 
-        def decorator(func):
+        def decorator(func: CFT) -> CFT:
             self.add_listener(func, name)
             return func
 
@@ -528,7 +553,7 @@ class BotBase(GroupMixin):
         cog = cog._inject(self)
         self.__cogs[cog_name] = cog
 
-    def get_cog(self, name):
+    def get_cog(self, name: str) -> Optional[Cog]:
         """Gets the cog instance requested.
 
         If the cog is not found, ``None`` is returned instead.
@@ -547,7 +572,7 @@ class BotBase(GroupMixin):
         """
         return self.__cogs.get(name)
 
-    def remove_cog(self, name):
+    def remove_cog(self, name: str) -> Optional[Cog]:
         """Removes a cog from the bot and returns it.
 
         All registered commands and event listeners that the
@@ -578,13 +603,13 @@ class BotBase(GroupMixin):
         return cog
 
     @property
-    def cogs(self):
+    def cogs(self) -> Mapping[str, Cog]:
         """Mapping[:class:`str`, :class:`Cog`]: A read-only mapping of cog name to cog."""
         return types.MappingProxyType(self.__cogs)
 
     # extensions
 
-    def _remove_module_references(self, name):
+    def _remove_module_references(self, name: str) -> None:
         # find all references to the module
         # remove the cogs registered from the module
         for cogname, cog in self.__cogs.copy().items():
@@ -608,7 +633,7 @@ class BotBase(GroupMixin):
             for index in reversed(remove):
                 del event_list[index]
 
-    def _call_module_finalizers(self, lib, key):
+    def _call_module_finalizers(self, lib: types.ModuleType, key: str) -> None:
         try:
             func = getattr(lib, 'teardown')
         except AttributeError:
@@ -626,12 +651,12 @@ class BotBase(GroupMixin):
                 if _is_submodule(name, module):
                     del sys.modules[module]
 
-    def _load_from_module_spec(self, spec, key):
+    def _load_from_module_spec(self, spec: importlib.machinery.ModuleSpec, key: str) -> None:
         # precondition: key not in self.__extensions
         lib = importlib.util.module_from_spec(spec)
         sys.modules[key] = lib
         try:
-            spec.loader.exec_module(lib)
+            spec.loader.exec_module(lib)  # type: ignore
         except Exception as e:
             del sys.modules[key]
             raise errors.ExtensionFailed(key, e) from e
@@ -652,13 +677,13 @@ class BotBase(GroupMixin):
         else:
             self.__extensions[key] = lib
 
-    def _resolve_name(self, name, package):
+    def _resolve_name(self, name: str, package: Optional[str]) -> str:
         try:
             return importlib.util.resolve_name(name, package)
         except ImportError:
             raise errors.ExtensionNotFound(name)
 
-    def load_extension(self, name, *, package=None):
+    def load_extension(self, name: str, *, package: Optional[str] = None) -> None:
         """Loads an extension.
 
         An extension is a python module that contains commands, cogs, or
@@ -705,7 +730,7 @@ class BotBase(GroupMixin):
 
         self._load_from_module_spec(spec, name)
 
-    def unload_extension(self, name, *, package=None):
+    def unload_extension(self, name: str, *, package: Optional[str] = None) -> None:
         """Unloads an extension.
 
         When the extension is unloaded, all commands, listeners, and cogs are
@@ -746,7 +771,7 @@ class BotBase(GroupMixin):
         self._remove_module_references(lib.__name__)
         self._call_module_finalizers(lib, name)
 
-    def reload_extension(self, name, *, package=None):
+    def reload_extension(self, name: str, *, package: Optional[str] = None) -> None:
         """Atomically reloads an extension.
 
         This replaces the extension with the same extension, only refreshed. This is
@@ -802,7 +827,7 @@ class BotBase(GroupMixin):
             # if the load failed, the remnants should have been
             # cleaned from the load_extension function call
             # so let's load it from our old compiled library.
-            lib.setup(self)
+            lib.setup(self)  # type: ignore
             self.__extensions[name] = lib
 
             # revert sys.modules back to normal and raise back to caller
@@ -810,18 +835,18 @@ class BotBase(GroupMixin):
             raise
 
     @property
-    def extensions(self):
+    def extensions(self) -> Mapping[str, types.ModuleType]:
         """Mapping[:class:`str`, :class:`py:types.ModuleType`]: A read-only mapping of extension name to extension."""
         return types.MappingProxyType(self.__extensions)
 
     # help command stuff
 
     @property
-    def help_command(self):
+    def help_command(self) -> Optional[HelpCommand]:
         return self._help_command
 
     @help_command.setter
-    def help_command(self, value):
+    def help_command(self, value: Optional[HelpCommand]) -> None:
         if value is not None:
             if not isinstance(value, HelpCommand):
                 raise TypeError('help_command must be a subclass of HelpCommand')
@@ -837,7 +862,7 @@ class BotBase(GroupMixin):
 
     # command processing
 
-    async def get_prefix(self, message):
+    async def get_prefix(self, message: Message) -> Union[List[str], str]:
         """|coro|
 
         Retrieves the prefix the bot is listening to
@@ -875,7 +900,7 @@ class BotBase(GroupMixin):
 
         return ret
 
-    async def get_context(self, message, *, cls=Context):
+    async def get_context(self, message: Message, *, cls: Type[CXT] = Context) -> CXT:
         r"""|coro|
 
         Returns the invocation context from the message.
@@ -908,7 +933,7 @@ class BotBase(GroupMixin):
         view = StringView(message.content)
         ctx = cls(prefix=None, view=view, bot=self, message=message)
 
-        if message.author.id == self.user.id:
+        if message.author.id == self.user.id:  # type: ignore
             return ctx
 
         prefix = await self.get_prefix(message)
@@ -945,11 +970,12 @@ class BotBase(GroupMixin):
 
         invoker = view.get_word()
         ctx.invoked_with = invoker
-        ctx.prefix = invoked_prefix
+        # type-checker fails to narrow invoked_prefix type.
+        ctx.prefix = invoked_prefix  # type: ignore
         ctx.command = self.all_commands.get(invoker)
         return ctx
 
-    async def invoke(self, ctx):
+    async def invoke(self, ctx: Context) -> None:
         """|coro|
 
         Invokes the command given under the invocation context and
@@ -975,7 +1001,7 @@ class BotBase(GroupMixin):
             exc = errors.CommandNotFound(f'Command "{ctx.invoked_with}" is not found')
             self.dispatch('command_error', ctx, exc)
 
-    async def process_commands(self, message):
+    async def process_commands(self, message: Message) -> None:
         """|coro|
 
         This function processes the commands that have been registered

discord/ext/commands/cog.py

@@ -21,15 +21,30 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 """
+from __future__ import annotations
 
 import inspect
+import discord.utils
+
+from typing import Any, Callable, ClassVar, Dict, Generator, List, Optional, TYPE_CHECKING, Tuple, TypeVar, Type
+
 from ._types import _BaseCommand
 
+if TYPE_CHECKING:
+    from .bot import BotBase
+    from .context import Context
+    from .core import Command
+
 __all__ = (
     'CogMeta',
     'Cog',
 )
 
+CogT = TypeVar('CogT', bound='Cog')
+FuncT = TypeVar('FuncT', bound=Callable[..., Any])
+
+MISSING: Any = discord.utils.MISSING
+
 class CogMeta(type):
     """A metaclass for defining a cog.
 
@@ -89,8 +104,12 @@ class CogMeta(type):
                 async def bar(self, ctx):
                     pass # hidden -> False
     """
+    __cog_name__: str
+    __cog_settings__: Dict[str, Any]
+    __cog_commands__: List[Command]
+    __cog_listeners__: List[Tuple[str, str]]
 
-    def __new__(cls, *args, **kwargs):
+    def __new__(cls: Type[CogMeta], *args: Any, **kwargs: Any) -> CogMeta:
         name, bases, attrs = args
         attrs['__cog_name__'] = kwargs.pop('name', name)
         attrs['__cog_settings__'] = kwargs.pop('command_attrs', {})
@@ -143,14 +162,14 @@ class CogMeta(type):
         new_cls.__cog_listeners__ = listeners_as_list
         return new_cls
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
         super().__init__(*args)
 
     @classmethod
-    def qualified_name(cls):
+    def qualified_name(cls) -> str:
         return cls.__cog_name__
 
-def _cog_special_method(func):
+def _cog_special_method(func: FuncT) -> FuncT:
     func.__cog_special_method__ = None
     return func
 
@@ -164,8 +183,12 @@ class Cog(metaclass=CogMeta):
     When inheriting from this class, the options shown in :class:`CogMeta`
     are equally valid here.
     """
+    __cog_name__: ClassVar[str]
+    __cog_settings__: ClassVar[Dict[str, Any]]
+    __cog_commands__: ClassVar[List[Command]]
+    __cog_listeners__: ClassVar[List[Tuple[str, str]]]
 
-    def __new__(cls, *args, **kwargs):
+    def __new__(cls: Type[CogT], *args: Any, **kwargs: Any) -> CogT:
         # For issue 426, we need to store a copy of the command objects
         # since we modify them to inject `self` to them.
         # To do this, we need to interfere with the Cog creation process.
@@ -173,7 +196,8 @@ class Cog(metaclass=CogMeta):
         cmd_attrs = cls.__cog_settings__
 
         # Either update the command with the cog provided defaults or copy it.
-        self.__cog_commands__ = tuple(c._update_copy(cmd_attrs) for c in cls.__cog_commands__)
+        # r.e type ignore, type-checker complains about overriding a ClassVar
+        self.__cog_commands__ = tuple(c._update_copy(cmd_attrs) for c in cls.__cog_commands__)  # type: ignore
 
         lookup = {
             cmd.qualified_name: cmd
@@ -186,15 +210,15 @@ class Cog(metaclass=CogMeta):
             parent = command.parent
             if parent is not None:
                 # Get the latest parent reference
-                parent = lookup[parent.qualified_name]
+                parent = lookup[parent.qualified_name]  # type: ignore
 
                 # Update our parent's reference to our self
-                parent.remove_command(command.name)
-                parent.add_command(command)
+                parent.remove_command(command.name)  # type: ignore
+                parent.add_command(command)  # type: ignore
 
         return self
 
-    def get_commands(self):
+    def get_commands(self) -> List[Command]:
         r"""
         Returns
         --------
@@ -209,20 +233,20 @@ class Cog(metaclass=CogMeta):
         return [c for c in self.__cog_commands__ if c.parent is None]
 
     @property
-    def qualified_name(self):
+    def qualified_name(self) -> str:
         """:class:`str`: Returns the cog's specified name, not the class name."""
         return self.__cog_name__
 
     @property
-    def description(self):
+    def description(self) -> str:
         """:class:`str`: Returns the cog's description, typically the cleaned docstring."""
         return self.__cog_description__
 
     @description.setter
-    def description(self, description):
+    def description(self, description: str) -> None:
         self.__cog_description__ = description
 
-    def walk_commands(self):
+    def walk_commands(self) -> Generator[Command, None, None]:
         """An iterator that recursively walks through this cog's commands and subcommands.
 
         Yields
@@ -237,7 +261,7 @@ class Cog(metaclass=CogMeta):
                 if isinstance(command, GroupMixin):
                     yield from command.walk_commands()
 
-    def get_listeners(self):
+    def get_listeners(self) -> List[Tuple[str, Callable[..., Any]]]:
         """Returns a :class:`list` of (name, function) listener pairs that are defined in this cog.
 
         Returns
@@ -248,12 +272,12 @@ class Cog(metaclass=CogMeta):
         return [(name, getattr(self, method_name)) for name, method_name in self.__cog_listeners__]
 
     @classmethod
-    def _get_overridden_method(cls, method):
+    def _get_overridden_method(cls, method: FuncT) -> Optional[FuncT]:
         """Return None if the method is not overridden. Otherwise returns the overridden method."""
         return getattr(method.__func__, '__cog_special_method__', method)
 
     @classmethod
-    def listener(cls, name=None):
+    def listener(cls, name: str = MISSING) -> Callable[[FuncT], FuncT]:
         """A decorator that marks a function as a listener.
 
         This is the cog equivalent of :meth:`.Bot.listen`.
@@ -271,10 +295,10 @@ class Cog(metaclass=CogMeta):
             the name.
         """
 
-        if name is not None and not isinstance(name, str):
+        if name is not MISSING and not isinstance(name, str):
             raise TypeError(f'Cog.listener expected str but received {name.__class__.__name__!r} instead.')
 
-        def decorator(func):
+        def decorator(func: FuncT) -> FuncT:
             actual = func
             if isinstance(actual, staticmethod):
                 actual = actual.__func__
@@ -293,7 +317,7 @@ class Cog(metaclass=CogMeta):
             return func
         return decorator
 
-    def has_error_handler(self):
+    def has_error_handler(self) -> bool:
         """:class:`bool`: Checks whether the cog has an error handler.
 
         .. versionadded:: 1.7
@@ -301,7 +325,7 @@ class Cog(metaclass=CogMeta):
         return not hasattr(self.cog_command_error.__func__, '__cog_special_method__')
 
     @_cog_special_method
-    def cog_unload(self):
+    def cog_unload(self) -> None:
         """A special method that is called when the cog gets removed.
 
         This function **cannot** be a coroutine. It must be a regular
@@ -312,7 +336,7 @@ class Cog(metaclass=CogMeta):
         pass
 
     @_cog_special_method
-    def bot_check_once(self, ctx):
+    def bot_check_once(self, ctx: Context) -> bool:
         """A special method that registers as a :meth:`.Bot.check_once`
         check.
 
@@ -322,7 +346,7 @@ class Cog(metaclass=CogMeta):
         return True
 
     @_cog_special_method
-    def bot_check(self, ctx):
+    def bot_check(self, ctx: Context) -> bool:
         """A special method that registers as a :meth:`.Bot.check`
         check.
 
@@ -332,7 +356,7 @@ class Cog(metaclass=CogMeta):
         return True
 
     @_cog_special_method
-    def cog_check(self, ctx):
+    def cog_check(self, ctx: Context) -> bool:
         """A special method that registers as a :func:`~discord.ext.commands.check`
         for every command and subcommand in this cog.
 
@@ -342,7 +366,7 @@ class Cog(metaclass=CogMeta):
         return True
 
     @_cog_special_method
-    async def cog_command_error(self, ctx, error):
+    async def cog_command_error(self, ctx: Context, error: Exception) -> None:
         """A special method that is called whenever an error
         is dispatched inside this cog.
 
@@ -361,7 +385,7 @@ class Cog(metaclass=CogMeta):
         pass
 
     @_cog_special_method
-    async def cog_before_invoke(self, ctx):
+    async def cog_before_invoke(self, ctx: Context) -> None:
         """A special method that acts as a cog local pre-invoke hook.
 
         This is similar to :meth:`.Command.before_invoke`.
@@ -376,7 +400,7 @@ class Cog(metaclass=CogMeta):
         pass
 
     @_cog_special_method
-    async def cog_after_invoke(self, ctx):
+    async def cog_after_invoke(self, ctx: Context) -> None:
         """A special method that acts as a cog local post-invoke hook.
 
         This is similar to :meth:`.Command.after_invoke`.
@@ -390,7 +414,7 @@ class Cog(metaclass=CogMeta):
         """
         pass
 
-    def _inject(self, bot):
+    def _inject(self: CogT, bot: BotBase) -> CogT:
         cls = self.__class__
 
         # realistically, the only thing that can cause loading errors
@@ -425,7 +449,7 @@ class Cog(metaclass=CogMeta):
 
         return self
 
-    def _eject(self, bot):
+    def _eject(self, bot: BotBase) -> None:
         cls = self.__class__
 
         try:

discord/ext/commands/context.py

@@ -21,16 +21,52 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 DEALINGS IN THE SOFTWARE.
 """
+from __future__ import annotations
+
+import inspect
+import re
+
+from typing import Any, Dict, Generic, List, Optional, TYPE_CHECKING, TypeVar, Union
 
 import discord.abc
 import discord.utils
-import re
+
+from discord.message import Message
+
+if TYPE_CHECKING:
+    from typing_extensions import ParamSpec
+
+    from discord.abc import MessageableChannel
+    from discord.guild import Guild
+    from discord.member import Member
+    from discord.state import ConnectionState
+    from discord.user import ClientUser, User
+    from discord.voice_client import VoiceProtocol
+
+    from .bot import Bot, AutoShardedBot
+    from .cog import Cog
+    from .core import Command
+    from .help import HelpCommand
+    from .view import StringView
 
 __all__ = (
     'Context',
 )
 
-class Context(discord.abc.Messageable):
+MISSING: Any = discord.utils.MISSING
+
+
+T = TypeVar('T')
+BotT = TypeVar('BotT', bound="Union[Bot, AutoShardedBot]")
+CogT = TypeVar('CogT', bound="Cog")
+
+if TYPE_CHECKING:
+    P = ParamSpec('P')
+else:
+    P = TypeVar('P')
+
+
+class Context(discord.abc.Messageable, Generic[BotT]):
     r"""Represents the context in which a command is being invoked under.
 
     This class contains a lot of meta data to help you understand more about
@@ -58,11 +94,11 @@ class Context(discord.abc.Messageable):
         This is only of use for within converters.
 
         .. versionadded:: 2.0
-    prefix: :class:`str`
+    prefix: Optional[:class:`str`]
         The prefix that was used to invoke the command.
-    command: :class:`Command`
+    command: Optional[:class:`Command`]
         The command that is being invoked currently.
-    invoked_with: :class:`str`
+    invoked_with: Optional[:class:`str`]
         The command name that triggered this invocation. Useful for finding out
         which alias called the command.
     invoked_parents: List[:class:`str`]
@@ -73,7 +109,7 @@ class Context(discord.abc.Messageable):
 
         .. versionadded:: 1.7
 
-    invoked_subcommand: :class:`Command`
+    invoked_subcommand: Optional[:class:`Command`]
         The subcommand that was invoked.
         If no valid subcommand was invoked then this is equal to ``None``.
     subcommand_passed: Optional[:class:`str`]
@@ -86,23 +122,38 @@ class Context(discord.abc.Messageable):
         or invoked.
     """
 
-    def __init__(self, **attrs):
-        self.message = attrs.pop('message', None)
-        self.bot = attrs.pop('bot', None)
-        self.args = attrs.pop('args', [])
-        self.kwargs = attrs.pop('kwargs', {})
-        self.prefix = attrs.pop('prefix')
-        self.command = attrs.pop('command', None)
-        self.view = attrs.pop('view', None)
-        self.invoked_with = attrs.pop('invoked_with', None)
-        self.invoked_parents = attrs.pop('invoked_parents', [])
-        self.invoked_subcommand = attrs.pop('invoked_subcommand', None)
-        self.subcommand_passed = attrs.pop('subcommand_passed', None)
-        self.command_failed = attrs.pop('command_failed', False)
-        self.current_parameter = attrs.pop('current_parameter', None)
-        self._state = self.message._state
-
-    async def invoke(self, command, /, *args, **kwargs):
+    def __init__(self,
+        *,
+        message: Message,
+        bot: BotT,
+        view: StringView,
+        args: List[Any] = MISSING,
+        kwargs: Dict[str, Any] = MISSING,
+        prefix: Optional[str] = None,
+        command: Optional[Command] = None,
+        invoked_with: Optional[str] = None,
+        invoked_parents: List[str] = MISSING,
+        invoked_subcommand: Optional[Command] = None,
+        subcommand_passed: Optional[str] = None,
+        command_failed: bool = False,
+        current_parameter: Optional[inspect.Parameter] = None,
+    ):
+        self.message: Message = message
+        self.bot: BotT = bot
+        self.args: List[Any] = args or []
+        self.kwargs: Dict[str, Any] = kwargs or {}
+        self.prefix: Optional[str] = prefix
+        self.command: Optional[Command] = command
+        self.view: StringView = view
+        self.invoked_with: Optional[str] = invoked_with
+        self.invoked_parents: List[str] = invoked_parents or []
+        self.invoked_subcommand: Optional[Command] = invoked_subcommand
+        self.subcommand_passed: Optional[str] = subcommand_passed
+        self.command_failed: bool = command_failed
+        self.current_parameter: Optional[inspect.Parameter] = current_parameter
+        self._state: ConnectionState = self.message._state
+
+    async def invoke(self, command: Command[CogT, P, T], /, *args: P.args, **kwargs: P.kwargs) -> T:
         r"""|coro|
 
         Calls a command with the arguments given.
@@ -133,17 +184,9 @@ class Context(discord.abc.Messageable):
         TypeError
             The command argument to invoke is missing.
         """
-        arguments = []
-        if command.cog is not None:
-            arguments.append(command.cog)
-
-        arguments.append(self)
-        arguments.extend(args)
+        return await command(self, *args, **kwargs)
 
-        ret = await command.callback(*arguments, **kwargs)
-        return ret
-
-    async def reinvoke(self, *, call_hooks: bool = False, restart: bool = True):
+    async def reinvoke(self, *, call_hooks: bool = False, restart: bool = True) -> None:
         """|coro|
 
         Calls the command again.
@@ -187,7 +230,7 @@ class Context(discord.abc.Messageable):
 
         if restart:
             to_call = cmd.root_parent or cmd
-            view.index = len(self.prefix)
+            view.index = len(self.prefix or '')
             view.previous = 0
             self.invoked_parents = []
             self.invoked_with = view.get_word() # advance to get the root command
@@ -206,20 +249,23 @@ class Context(discord.abc.Messageable):
             self.subcommand_passed = subcommand_passed
 
     @property
-    def valid(self):
+    def valid(self) -> bool:
         """:class:`bool`: Checks if the invocation context is valid to be invoked with."""
         return self.prefix is not None and self.command is not None
 
-    async def _get_channel(self):
+    async def _get_channel(self) -> discord.abc.Messageable:
         return self.channel
 
     @property
-    def clean_prefix(self):
+    def clean_prefix(self) -> str:
         """:class:`str`: The cleaned up invoke prefix. i.e. mentions are ``@name`` instead of ``<@id>``.
 
         .. versionadded:: 2.0
         """
-        user = self.guild.me if self.guild else self.bot.user
+        if self.prefix is None:
+            return ''
+
+        user = self.me
         # this breaks if the prefix mention is not the bot itself but I
         # consider this to be an *incredibly* strange use case. I'd rather go
         # for this common use case rather than waste performance for the
@@ -228,7 +274,7 @@ class Context(discord.abc.Messageable):
         return pattern.sub("@%s" % user.display_name.replace('\\', r'\\'), self.prefix)
 
     @property
-    def cog(self):
+    def cog(self) -> Optional[Cog]:
         """Optional[:class:`.Cog`]: Returns the cog associated with this context's command. None if it does not exist."""
 
         if self.command is None:
@@ -236,38 +282,39 @@ class Context(discord.abc.Messageable):
         return self.command.cog
 
     @discord.utils.cached_property
-    def guild(self):
+    def guild(self) -> Optional[Guild]:
         """Optional[:class:`.Guild`]: Returns the guild associated with this context's command. None if not available."""
         return self.message.guild
 
     @discord.utils.cached_property
-    def channel(self):
+    def channel(self) -> MessageableChannel:
         """Union[:class:`.abc.Messageable`]: Returns the channel associated with this context's command.
         Shorthand for :attr:`.Message.channel`.
         """
         return self.message.channel
 
     @discord.utils.cached_property
-    def author(self):
+    def author(self) -> Union[User, Member]:
         """Union[:class:`~discord.User`, :class:`.Member`]:
         Returns the author associated with this context's command. Shorthand for :attr:`.Message.author`
         """
         return self.message.author
 
     @discord.utils.cached_property
-    def me(self):
+    def me(self) -> Union[Member, ClientUser]:
         """Union[:class:`.Member`, :class:`.ClientUser`]:
         Similar to :attr:`.Guild.me` except it may return the :class:`.ClientUser` in private message contexts.
         """
-        return self.guild.me if self.guild is not None else self.bot.user
+        # bot.user will never be None at this point.
+        return self.guild.me if self.guild is not None else self.bot.user  # type: ignore
 
     @property
-    def voice_client(self):
+    def voice_client(self) -> Optional[VoiceProtocol]:
         r"""Optional[:class:`.VoiceProtocol`]: A shortcut to :attr:`.Guild.voice_client`\, if applicable."""
         g = self.guild
         return g.voice_client if g else None
 
-    async def send_help(self, *args):
+    async def send_help(self, *args: Any) -> Any:
         """send_help(entity=<bot>)
 
         |coro|
@@ -319,12 +366,12 @@ class Context(discord.abc.Messageable):
                 return None
 
         entity = args[0]
-        if entity is None:
-            return None
-
         if isinstance(entity, str):
             entity = bot.get_cog(entity) or bot.get_command(entity)
 
+        if entity is None:
+            return None
+
         try:
             entity.qualified_name
         except AttributeError:
@@ -348,6 +395,6 @@ class Context(discord.abc.Messageable):
         except CommandError as e:
             await cmd.on_help_command_error(self, e)
 
-    @discord.utils.copy_doc(discord.Message.reply)
-    async def reply(self, content=None, **kwargs):
+    @discord.utils.copy_doc(Message.reply)
+    async def reply(self, content: Optional[str] = None, **kwargs: Any) -> Message:
         return await self.message.reply(content, **kwargs)

discord/ext/commands/help.py

@@ -27,11 +27,17 @@ import copy
 import functools
 import inspect
 import re
+
+from typing import Optional, TYPE_CHECKING
+
 import discord.utils
 
 from .core import Group, Command
 from .errors import CommandError
 
+if TYPE_CHECKING:
+    from .context import Context
+
 __all__ = (
     'Paginator',
     'HelpCommand',
@@ -320,7 +326,7 @@ class HelpCommand:
         self.command_attrs = attrs = options.pop('command_attrs', {})
         attrs.setdefault('name', 'help')
         attrs.setdefault('help', 'Shows this message')
-        self.context = None
+        self.context: Optional[Context] = None
         self._command_impl = _HelpCommandImpl(self, **self.command_attrs)
 
     def copy(self):