Reserves command names (#2977)

* Reserves command names

  - Currently, only reserving ``cancel``
  - This should only impact matching command qualified names
  - This also checks aliases
  - This makes cc and alias use the new module constant with info about
  this
  - Module constant is available for use by 3rd party cogs which may
  dynamically create responses.

* Change misleading var name

* style

* Thanks Flame!

* Handles issues with CC

changelog.d/2973.breaking.rst

@@ -0,0 +1 @@
+Reserves some command names for internal Red use. These are available programatically as ``redbot.core.commands.RESERVED_COMMAND_NAMES``

redbot/cogs/alias/alias.py

@@ -89,8 +89,12 @@ class Alias(commands.Cog):
         return False, None
 
     def is_command(self, alias_name: str) -> bool:
+        """
+        The logic here is that if this returns true, the name shouldnt be used for an alias
+        The function name can be changed when alias is reworked
+        """
         command = self.bot.get_command(alias_name)
-        return command is not None
+        return command is not None or alias_name in commands.RESERVED_COMMAND_NAMES
 
     @staticmethod
     def is_valid_alias_name(alias_name: str) -> bool:

redbot/cogs/customcom/customcom.py

@@ -222,6 +222,9 @@ class CustomCommands(commands.Cog):
 
         Note: This command is interactive.
         """
+        if command in (*self.bot.all_commands, *commands.RESERVED_COMMAND_NAMES):
+            await ctx.send(_("There already exists a bot command with the same name."))
+            return
         responses = await self.commandobj.get_responses(ctx=ctx)
         try:
             await self.commandobj.create(ctx=ctx, command=command, response=responses)
@@ -241,7 +244,7 @@ class CustomCommands(commands.Cog):
         Example:
         - `[p]customcom create simple yourcommand Text you want`
         """
-        if command in self.bot.all_commands:
+        if command in (*self.bot.all_commands, *commands.RESERVED_COMMAND_NAMES):
             await ctx.send(_("There already exists a bot command with the same name."))
             return
         try:

redbot/core/commands/commands.py

@@ -28,8 +28,14 @@ __all__ = [
     "GroupMixin",
     "command",
     "group",
+    "RESERVED_COMMAND_NAMES",
 ]
 
+#: The following names are reserved for various reasons
+RESERVED_COMMAND_NAMES = (
+    "cancel",  # reserved due to use in ``redbot.core.utils.MessagePredicate``
+)
+
 _ = Translator("commands.commands", __file__)
 
 
@@ -155,6 +161,12 @@ class Command(CogCommandMixin, commands.Command):
         super().__init__(*args, **kwargs)
         self._help_override = kwargs.pop("help_override", None)
         self.translator = kwargs.pop("i18n", None)
+        if self.parent is None:
+            for name in (self.name, *self.aliases):
+                if name in RESERVED_COMMAND_NAMES:
+                    raise RuntimeError(
+                        f"The name `{name}` cannot be set as a command name. It is reserved for internal use."
+                    )
 
     def _ensure_assignment_on_copy(self, other):
         super()._ensure_assignment_on_copy(other)