Add has_attachment built in check

lightbulb/checks.py

@@ -33,6 +33,7 @@
     "bot_has_guild_permissions",
     "has_permissions",
     "bot_has_permissions",
+    "has_attachment",
     "check",
 ]
 
@@ -234,6 +235,22 @@ async def _bot_has_permissions(ctx: context.Context, *, permissions: hikari.Perm
     return True
 
 
+async def _has_attachment(
+        ctx: context.Context,
+        *,
+        allowed_extensions: typing.Optional[typing.Sequence[str]] = None
+) -> bool:
+    if not ctx.attachments:
+        raise errors.MissingRequiredAttachment("Missing attachment(s) required to run the command")
+
+    if allowed_extensions is not None:
+        for attachment in ctx.attachments:
+            if not any(attachment.filename.endswith(ext) for ext in allowed_extensions):
+                raise errors.MissingRequiredAttachment("Missing attachment(s) required to run the command")
+
+    return True
+
+
 def guild_only() -> typing.Callable[[T_inv], T_inv]:
     """
     A decorator that prevents a command from being used in direct messages.
@@ -484,6 +501,36 @@ def decorate(command: T_inv) -> T_inv:
     return decorate
 
 
+def has_attachment(*extensions: str):
+    """
+    A decorator that prevents the command from being used if the invocation message
+    does not include any attachments.
+
+    Args:
+        *extensions (:obj:`str`): If specified, attachments with a different file extension
+            will cause the check to fail.
+
+    Example:
+
+        .. code-block:: python
+
+            @checks.has_attachment(".yaml", ".json")
+            @bot.command()
+            async def foobar(ctx):
+                print(ctx.attachments[0].filename)
+
+    Note:
+        If ``extensions`` is specified then all attachments must conform to the restriction.
+    """
+
+    def decorate(command: T_inv) -> T_inv:
+        _check_check_decorator_above_commands_decorator(command)
+        command.add_check(functools.partial(_has_attachment, allowed_extensions=extensions if extensions else None))
+        return command
+
+    return decorate
+
+
 def check(check_func: typing.Callable[[context.Context], typing.Coroutine[typing.Any, typing.Any, bool]]):
     """
     A decorator which adds a custom check function to a command. The check function must be a coroutine (async def)

lightbulb/errors.py

@@ -316,6 +316,17 @@ def __init__(self, text: str, permissions: hikari.Permissions) -> None:
         """Permission(s) the bot is missing."""
 
 
+class MissingRequiredAttachment(CheckFailure):
+    """
+    Error raised when the command invocation message is missing an attachment, or an
+    attachment with the correct file extension.
+    """
+
+    def __init__(self, text) -> None:
+        self.text: str = text
+        """The error text."""
+
+
 class CommandInvocationError(CommandError):
     """
     Error raised if an error is encountered during command invocation. This will only be raised