[commands] Add support for discord.Attachment converters

discord/ext/commands/core.py

@@ -56,7 +56,7 @@ from .errors import *
 from .parameters import Parameter, Signature
 
 if TYPE_CHECKING:
-    from typing_extensions import Concatenate, ParamSpec, Self, TypeGuard
+    from typing_extensions import Concatenate, ParamSpec, Self
 
     from discord.message import Message
 
@@ -237,6 +237,27 @@ class _CaseInsensitiveDict(dict):
         super().__setitem__(k.casefold(), v)
 
 
+class _AttachmentIterator:
+    def __init__(self, data: List[discord.Attachment]):
+        self.data: List[discord.Attachment] = data
+        self.index: int = 0
+
+    def __iter__(self) -> Self:
+        return self
+
+    def __next__(self) -> discord.Attachment:
+        try:
+            value = self.data[self.index]
+        except IndexError:
+            raise StopIteration
+        else:
+            self.index += 1
+            return value
+
+    def is_empty(self) -> bool:
+        return self.index >= len(self.data)
+
+
 class Command(_BaseCommand, Generic[CogT, P, T]):
     r"""A class that implements the protocol for a bot text command.
 
@@ -592,7 +613,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
         finally:
             ctx.bot.dispatch('command_error', ctx, error)
 
-    async def transform(self, ctx: Context[BotT], param: Parameter, /) -> Any:
+    async def transform(self, ctx: Context[BotT], param: Parameter, attachments: _AttachmentIterator, /) -> Any:
         converter = param.converter
         consume_rest_is_special = param.kind == param.KEYWORD_ONLY and not self.rest_is_raw
         view = ctx.view
@@ -601,6 +622,10 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
         # The greedy converter is simple -- it keeps going until it fails in which case,
         # it undos the view ready for the next parameter to use instead
         if isinstance(converter, Greedy):
+            # Special case for Greedy[discord.Attachment] to consume the attachments iterator
+            if converter.converter is discord.Attachment:
+                return list(attachments)
+
             if param.kind in (param.POSITIONAL_OR_KEYWORD, param.POSITIONAL_ONLY):
                 return await self._transform_greedy_pos(ctx, param, param.required, converter.converter)
             elif param.kind == param.VAR_POSITIONAL:
@@ -611,6 +636,20 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
                 # into just X and do the parsing that way.
                 converter = converter.converter
 
+        # Try to detect Optional[discord.Attachment] or discord.Attachment special converter
+        if converter is discord.Attachment:
+            try:
+                return next(attachments)
+            except StopIteration:
+                raise MissingRequiredAttachment(param)
+
+        if self._is_typing_optional(param.annotation) and param.annotation.__args__[0] is discord.Attachment:
+            if attachments.is_empty():
+                # I have no idea who would be doing Optional[discord.Attachment] = 1
+                # but for those cases then 1 should be returned instead of None
+                return None if param.default is param.empty else param.default
+            return next(attachments)
+
         if view.eof:
             if param.kind == param.VAR_POSITIONAL:
                 raise RuntimeError()  # break the loop
@@ -759,6 +798,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
         ctx.kwargs = {}
         args = ctx.args
         kwargs = ctx.kwargs
+        attachments = _AttachmentIterator(ctx.message.attachments)
 
         view = ctx.view
         iterator = iter(self.params.items())
@@ -766,7 +806,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
         for name, param in iterator:
             ctx.current_parameter = param
             if param.kind in (param.POSITIONAL_OR_KEYWORD, param.POSITIONAL_ONLY):
-                transformed = await self.transform(ctx, param)
+                transformed = await self.transform(ctx, param, attachments)
                 args.append(transformed)
             elif param.kind == param.KEYWORD_ONLY:
                 # kwarg only param denotes "consume rest" semantics
@@ -774,14 +814,14 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
                     ctx.current_argument = argument = view.read_rest()
                     kwargs[name] = await run_converters(ctx, param.converter, argument, param)
                 else:
-                    kwargs[name] = await self.transform(ctx, param)
+                    kwargs[name] = await self.transform(ctx, param, attachments)
                 break
             elif param.kind == param.VAR_POSITIONAL:
                 if view.eof and self.require_var_positional:
                     raise MissingRequiredArgument(param)
                 while not view.eof:
                     try:
-                        transformed = await self.transform(ctx, param)
+                        transformed = await self.transform(ctx, param, attachments)
                         args.append(transformed)
                     except RuntimeError:
                         break
@@ -1080,7 +1120,7 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
             return self.help.split('\n', 1)[0]
         return ''
 
-    def _is_typing_optional(self, annotation: Union[T, Optional[T]]) -> TypeGuard[Optional[T]]:
+    def _is_typing_optional(self, annotation: Union[T, Optional[T]]) -> bool:
         return getattr(annotation, '__origin__', None) is Union and type(None) in annotation.__args__  # type: ignore
 
     @property
@@ -1108,6 +1148,17 @@ class Command(_BaseCommand, Generic[CogT, P, T]):
                     annotation = union_args[0]
                     origin = getattr(annotation, '__origin__', None)
 
+            if annotation is discord.Attachment:
+                # For discord.Attachment we need to signal to the user that it's an attachment
+                # It's not exactly pretty but it's enough to differentiate
+                if optional:
+                    result.append(f'[{name} (upload a file)]')
+                elif greedy:
+                    result.append(f'[{name} (upload files)]...')
+                else:
+                    result.append(f'<{name} (upload a file)>')
+                continue
+
             # for typing.Literal[...], typing.Optional[typing.Literal[...]], and Greedy[typing.Literal[...]], the
             # parameter signature is a literal list of it's values
             if origin is Literal:

discord/ext/commands/errors.py

@@ -45,6 +45,7 @@ if TYPE_CHECKING:
 __all__ = (
     'CommandError',
     'MissingRequiredArgument',
+    'MissingRequiredAttachment',
     'BadArgument',
     'PrivateMessageOnly',
     'NoPrivateMessage',
@@ -184,6 +185,25 @@ class MissingRequiredArgument(UserInputError):
         super().__init__(f'{param.name} is a required argument that is missing.')
 
 
+class MissingRequiredAttachment(UserInputError):
+    """Exception raised when parsing a command and a parameter
+    that requires an attachment is not given.
+
+    This inherits from :exc:`UserInputError`
+
+    .. versionadded:: 2.0
+
+    Attributes
+    -----------
+    param: :class:`Parameter`
+        The argument that is missing an attachment.
+    """
+
+    def __init__(self, param: Parameter) -> None:
+        self.param: Parameter = param
+        super().__init__(f'{param.name} is a required argument that is missing an attachment.')
+
+
 class TooManyArguments(UserInputError):
     """Exception raised when the command was passed too many arguments and its
     :attr:`.Command.ignore_extra` attribute was not set to ``True``.

discord/ext/commands/hybrid.py

@@ -186,6 +186,9 @@ def replace_parameters(parameters: Dict[str, Parameter], signature: inspect.Sign
                 # However, in here, it probably makes sense to make it required.
                 # I'm unsure how to allow the user to choose right now.
                 inner = converter.converter
+                if inner is discord.Attachment:
+                    raise TypeError('discord.Attachment with Greedy is not supported in hybrid commands')
+
                 param = param.replace(annotation=make_greedy_transformer(inner, parameter))
             elif is_converter(converter):
                 param = param.replace(annotation=make_converter_transformer(converter))

docs/ext/commands/api.rst

@@ -538,6 +538,9 @@ Exceptions
 .. autoexception:: discord.ext.commands.MissingRequiredArgument
     :members:
 
+.. autoexception:: discord.ext.commands.MissingRequiredAttachment
+    :members:
+
 .. autoexception:: discord.ext.commands.ArgumentParsingError
     :members:
 
@@ -714,6 +717,7 @@ Exception Hierarchy
             - :exc:`~.commands.ConversionError`
             - :exc:`~.commands.UserInputError`
                 - :exc:`~.commands.MissingRequiredArgument`
+                - :exc:`~.commands.MissingRequiredAttachment`
                 - :exc:`~.commands.TooManyArguments`
                 - :exc:`~.commands.BadArgument`
                     - :exc:`~.commands.MessageNotFound`

docs/ext/commands/commands.rst

@@ -639,6 +639,85 @@ This command can be invoked any of the following ways:
     To help aid with some parsing ambiguities, :class:`str`, ``None``, :data:`typing.Optional` and
     :class:`~ext.commands.Greedy` are forbidden as parameters for the :class:`~ext.commands.Greedy` converter.
 
+
+discord.Attachment
+^^^^^^^^^^^^^^^^^^^
+
+.. versionadded:: 2.0
+
+The :class:`discord.Attachment` converter is a special converter that retrieves an attachment from the uploaded attachments on a message. This converter *does not* look at the message content at all and just the uploaded attachments.
+
+Consider the following example:
+
+.. code-block:: python3
+
+    import discord
+
+    @bot.command()
+    async def upload(ctx, attachment: discord.Attachment):
+        await ctx.send(f'You have uploaded <{attachment.url}>')
+
+
+When this command is invoked, the user must directly upload a file for the command body to be executed. When combined with the :data:`typing.Optional` converter, the user does not have to provide an attachment.
+
+.. code-block:: python3
+
+    import typing
+    import discord
+
+    @bot.command()
+    async def upload(ctx, attachment: typing.Optional[discord.Attachment]):
+        if attachment is None:
+            await ctx.send('You did not upload anything!')
+        else:
+            await ctx.send(f'You have uploaded <{attachment.url}>')
+
+
+This also works with multiple attachments:
+
+.. code-block:: python3
+
+    import typing
+    import discord
+
+    @bot.command()
+    async def upload_many(
+        ctx,
+        first: discord.Attachment,
+        second: typing.Optional[discord.Attachment],
+    ):
+        if second is None:
+            files = [first.url]
+        else:
+            files = [first.url, second.url]
+
+        await ctx.send(f'You uploaded: {" ".join(files)}')
+
+
+In this example the user must provide at least one file but the second one is optional.
+
+As a special case, using :class:`~ext.commands.Greedy` will return the remaining attachments in the message, if any.
+
+.. code-block:: python3
+
+    import discord
+    from discord.ext import commands
+
+    @bot.command()
+    async def upload_many(
+        ctx,
+        first: discord.Attachment,
+        remaining: commands.Greedy[discord.Attachment],
+    ):
+        files = [first.url]
+        files.extend(a.url for a in remaining)
+        await ctx.send(f'You uploaded: {" ".join(files)}')
+
+
+Note that using a :class:`discord.Attachment` converter after a :class:`~ext.commands.Greedy` of :class:`discord.Attachment` will always fail since the greedy had already consumed the remaining attachments.
+
+If an attachment is expected but not given, then :exc:`~ext.commands.MissingRequiredAttachment` is raised to the error handlers.
+
 .. _ext_commands_flag_converter:
 
 FlagConverter