Implement a least breaking approach to slash commands (#39)

* Most slash command support completed, needs some debugging (and reindent)

* Implement a ctx.send helper for slash commands

* Add group command support

* Add Option converter, fix default optional, fix help command

* Add client.setup and move readying commands to that

* Implement _FakeSlashMessage.from_interaction

* Rename normmal_command to message_command

* Add docs for added params

* Add slash_command_guilds to bot and decos

* Fix merge conflict

* Remove name from commands.Option, wasn't used

* Move slash command processing to BotBase.process_slash_commands

* Create slash_only.py

Basic example for slash commands

* Create slash_and_message.py

Basic example for mixed commands

* Fix slash_command and normal_command bools

* Add some basic error handling for registration

* Fixed converter upload errors

* Fix some logic and make an actual example

* Thanks Safety Jim

* docstrings, *args, and error changes

* Add proper literal support

* Add basic documentation on slash commands

* Fix non-slash command interactions

* Fix ctx.reply in slash command context

* Fix typing on Context.reply

* Fix multiple optional argument sorting

* Update ctx.message docs to mention error instead of warning

* Move slash command creation to BotBase

* Fix code style issues with Black

* Rearrange some stuff and add flag support

* Change some errors and fix interaction.channel fixing

* Fix slash command quoting for *args

Co-authored-by: iDutchy <42503862+iDutchy@users.noreply.github.com>
Co-authored-by: Lint Action <lint-action@samuelmeuli.com>

discord/ext/commands/converter.py

@@ -77,6 +77,7 @@ __all__ = (
     "GuildStickerConverter",
     "clean_content",
     "Greedy",
+    "Option",
     "run_converters",
 )
 
@@ -96,6 +97,8 @@ T_co = TypeVar("T_co", covariant=True)
 CT = TypeVar("CT", bound=discord.abc.GuildChannel)
 TT = TypeVar("TT", bound=discord.Thread)
 
+DT = TypeVar("DT", bound=str)
+
 
 @runtime_checkable
 class Converter(Protocol[T_co]):
@@ -583,7 +586,7 @@ class ThreadConverter(IDConverter[discord.Thread]):
     2. Lookup by mention.
     3. Lookup by name.
 
-    .. versionadded: 2.0
+    .. versionadded:: 2.0
     """
 
     async def convert(self, ctx: Context, argument: str) -> discord.Thread:
@@ -1005,6 +1008,27 @@ class Greedy(List[T]):
         return cls(converter=converter)
 
 
+if TYPE_CHECKING:
+
+    def Option(default: T = inspect.Parameter.empty, *, description: str) -> T:
+        ...
+
+
+else:
+
+    class Option(Generic[T, DT]):
+        description: DT
+        default: Union[T, inspect.Parameter.empty]
+        __slots__ = (
+            "default",
+            "description",
+        )
+
+        def __init__(self, default: T = inspect.Parameter.empty, *, description: DT) -> None:
+            self.description = description
+            self.default = default
+
+
 def _convert_to_bool(argument: str) -> bool:
     lowered = argument.lower()
     if lowered in ("yes", "y", "true", "t", "1", "enable", "on"):