rewrite: Support crossloading groups.

bot/meta/LionBot.py

@@ -193,3 +193,8 @@ class LionBot(Bot):
                 f"Caught an unknown top-level exception while executing: {cmd_str}",
                 extra={'action': 'BotError', 'with_ctx': True}
             )
+
+    def add_command(self, command):
+        if hasattr(command, '_placeholder_group_'):
+            return
+        super().add_command(command)

bot/meta/LionCog.py

@@ -1,9 +1,31 @@
+from typing import Any
+
 from discord.ext.commands import Cog
+from discord.ext import commands as cmds
 
 
 class LionCog(Cog):
     # A set of other cogs that this cog depends on
     depends_on: set['LionCog'] = set()
+    _placeholder_groups_: set[str]
+
+    def __init_subclass__(cls, **kwargs):
+        super().__init_subclass__(**kwargs)
+
+        cls._placeholder_groups_ = set()
+
+        for base in reversed(cls.__mro__):
+            for elem, value in base.__dict__.items():
+                if isinstance(value, cmds.HybridGroup) and hasattr(value, '_placeholder_group_'):
+                    cls._placeholder_groups_.add(value.name)
+
+    def __new__(cls, *args: Any, **kwargs: Any):
+        # Patch to ensure no placeholder groups are in the command list
+        self = super().__new__(cls)
+        self.__cog_commands__ = [
+            command for command in self.__cog_commands__ if command.name not in cls._placeholder_groups_
+        ]
+        return self
 
     async def _inject(self, bot, *args, **kwargs):
         if self.depends_on:
@@ -11,3 +33,25 @@ class LionCog(Cog):
             raise ValueError(f"Could not load cog '{self.__class__.__name__}', dependencies missing: {not_found}")
 
         return await super()._inject(bot, *args, *kwargs)
+
+    @classmethod
+    def placeholder_group(cls, group: cmds.HybridGroup):
+        group._placeholder_group_ = True
+        return group
+
+    def crossload_group(self, placeholder_group: cmds.HybridGroup, target_group: cmds.HybridGroup):
+        """
+        Crossload a placeholder group's commands into the target group
+        """
+        if not isinstance(placeholder_group, cmds.HybridGroup) or not isinstance(target_group, cmds.HybridGroup):
+            raise ValueError("Placeholder and target groups my be HypridGroups.")
+        if placeholder_group.name not in self._placeholder_groups_:
+            raise ValueError("Placeholder group was not registered! Stopping to avoid duplicates.")
+        if target_group.app_command is None:
+            raise ValueError("Target group has no app_command to crossload into.")
+
+        for command in placeholder_group.commands:
+            placeholder_group.remove_command(command.name)
+            acmd = command.app_command._copy_with(parent=target_group.app_command, binding=self)
+            command.app_command = acmd
+            target_group.add_command(command)