[V3] Send meaningful responses on conversion failure (#1817)

* [V3] Send meaningful responses on conversion failures

* Replace existing `discord.ext.commands` imports

Just to be sure

* Better Permissions converter response

redbot/core/checks.py

@@ -1,5 +1,5 @@
 import discord
-from discord.ext import commands
+from redbot.core import commands
 
 
 async def check_overrides(ctx, *, level):

redbot/core/commands/__init__.py

@@ -2,3 +2,4 @@
 from discord.ext.commands import *
 from .commands import *
 from .context import *
+from .errors import *

redbot/core/commands/commands.py

@@ -4,12 +4,20 @@ This module contains extended classes and functions which are intended to
 replace those from the `discord.ext.commands` module.
 """
 import inspect
+from typing import TYPE_CHECKING
 
 from discord.ext import commands
 
+from .errors import ConversionFailure
+from ..i18n import Translator
+
+if TYPE_CHECKING:
+    from .context import Context
 
 __all__ = ["Command", "Group", "command", "group"]
 
+_ = Translator("commands.commands", __file__)
+
 
 class Command(commands.Command):
     """Command class for Red.
@@ -53,7 +61,7 @@ class Command(commands.Command):
         """
         Returns all parent commands of this command.
 
-        This is a list, sorted by the length of :attr:`.qualified_name` from highest to lowest. 
+        This is a list, sorted by the length of :attr:`.qualified_name` from highest to lowest.
         If the command has no parents, this will be an empty list.
         """
         cmd = self.parent
@@ -63,6 +71,37 @@ class Command(commands.Command):
             cmd = cmd.parent
         return sorted(entries, key=lambda x: len(x.qualified_name), reverse=True)
 
+    async def do_conversion(self, ctx: "Context", converter, argument: str):
+        """Convert an argument according to its type annotation.
+
+        Raises
+        ------
+        ConversionFailure
+            If doing the conversion failed.
+
+        Returns
+        -------
+        Any
+            The converted argument.
+
+        """
+        # Let's not worry about all of this junk if it's just a str converter
+        if converter is str:
+            return argument
+
+        try:
+            return await super().do_conversion(ctx, converter, argument)
+        except commands.BadArgument as exc:
+            raise ConversionFailure(converter, argument, *exc.args) from exc
+        except ValueError as exc:
+            # Some common converters need special treatment...
+            if converter in (int, float):
+                message = _('"{argument}" is not a number.').format(argument=argument)
+                raise ConversionFailure(converter, argument, message) from exc
+
+            # We should expose anything which might be a bug in the converter
+            raise exc
+
     def command(self, cls=None, *args, **kwargs):
         """A shortcut decorator that invokes :func:`.command` and adds it to
         the internal command list via :meth:`~.GroupMixin.add_command`.

redbot/core/commands/errors.py

@@ -0,0 +1,13 @@
+"""Errors module for the commands package."""
+from discord.ext import commands
+
+__all__ = ["ConversionFailure"]
+
+
+class ConversionFailure(commands.BadArgument):
+    """Raised when converting an argument fails."""
+
+    def __init__(self, converter, argument: str, *args):
+        self.converter = converter
+        self.argument = argument
+        super().__init__(*args)

redbot/core/events.py

@@ -11,9 +11,8 @@ from pkg_resources import DistributionNotFound
 
 
 import discord
-from discord.ext import commands
 
-from . import __version__
+from . import __version__, commands
 from .data_manager import storage_type
 from .utils.chat_formatting import inline, bordered, pagify, box
 from .utils import fuzzy_command_search
@@ -185,6 +184,11 @@ def init_events(bot, cli_flags):
     async def on_command_error(ctx, error):
         if isinstance(error, commands.MissingRequiredArgument):
             await ctx.send_help()
+        elif isinstance(error, commands.ConversionFailure):
+            if error.args:
+                await ctx.send(error.args[0])
+            else:
+                await ctx.send_help()
         elif isinstance(error, commands.BadArgument):
             await ctx.send_help()
         elif isinstance(error, commands.DisabledCommand):