Change the way callbacks are defined to allow deriving

This should hopefully make these work more consistently as other
functions do.

3 files changed, 45 insertions, 89 deletions

diff --git a/discord/ui/button.py b/discord/ui/button.py
index afc69f7a..8ff4ce74 100644
--- a/discord/ui/button.py
+++ b/discord/ui/button.py
@@ -87,8 +87,6 @@ class Button(Item):
         The emoji of the button, if available.
     """
 
-    __slots__: Tuple[str, ...] = Item.__slots__ + ('_underlying',)
-
     __item_repr_attributes__: Tuple[str, ...] = (
         'style',
         'url',
@@ -192,19 +190,6 @@ class Button(Item):
         else:
             self._underlying.emoji = None
 
-    def copy(self: B) -> B:
-        button = self.__class__(
-            style=self.style,
-            label=self.label,
-            disabled=self.disabled,
-            custom_id=self.custom_id,
-            url=self.url,
-            emoji=self.emoji,
-            group=self.group_id,
-        )
-        button.callback = self.callback
-        return button
-
     @classmethod
     def from_component(cls: Type[B], button: ButtonComponent) -> B:
         return cls(
@@ -239,7 +224,7 @@ def button(
     style: ButtonStyle = ButtonStyle.grey,
     emoji: Optional[Union[str, PartialEmoji]] = None,
     group: Optional[int] = None,
-) -> Callable[[ItemCallbackType], Button]:
+) -> Callable[[ItemCallbackType], ItemCallbackType]:
     """A decorator that attaches a button to a component.
 
     The function being decorated should have three parameters, ``self`` representing
@@ -275,14 +260,22 @@ def button(
         ordering.
     """
 
-    def decorator(func: ItemCallbackType) -> Button:
+    def decorator(func: ItemCallbackType) -> ItemCallbackType:
         nonlocal custom_id
         if not inspect.iscoroutinefunction(func):
             raise TypeError('button function must be a coroutine function')
 
         custom_id = custom_id or os.urandom(32).hex()
-        button = Button(style=style, custom_id=custom_id, url=None, disabled=disabled, label=label, emoji=emoji, group=group)
-        button.callback = func
-        return button
+        func.__discord_ui_model_type__ = Button
+        func.__discord_ui_model_kwargs__ = {
+            'style': style,
+            'custom_id': custom_id,
+            'url': None,
+            'disabled': disabled,
+            'label': label,
+            'emoji': emoji,
+            'group': group,
+        }
+        return func
 
     return decorator
diff --git a/discord/ui/item.py b/discord/ui/item.py
index 7726407e..dc6c91a0 100644
--- a/discord/ui/item.py
+++ b/discord/ui/item.py
@@ -24,8 +24,7 @@ DEALINGS IN THE SOFTWARE.
 
 from __future__ import annotations
 
-from typing import Any, Callable, Coroutine, Dict, Optional, TYPE_CHECKING, Tuple, Type, TypeVar, Union
-import inspect
+from typing import Any, Callable, Coroutine, Dict, Optional, TYPE_CHECKING, Tuple, Type, TypeVar
 
 from ..interactions import Interaction
 
@@ -50,25 +49,15 @@ class Item:
     - :class:`discord.ui.Button`
     """
 
-    __slots__: Tuple[str, ...] = (
-        '_callback',
-        '_pass_view_arg',
-        'group_id',
-    )
-
     __item_repr_attributes__: Tuple[str, ...] = ('group_id',)
 
     def __init__(self):
-        self._callback: Optional[ItemCallbackType] = None
-        self._pass_view_arg = True
+        self._view: Optional[View] = None
         self.group_id: Optional[int] = None
 
     def to_component_dict(self) -> Dict[str, Any]:
         raise NotImplementedError
 
-    def copy(self: I) -> I:
-        raise NotImplementedError
-
     def refresh_state(self, component: Component) -> None:
         return None
 
@@ -88,53 +77,20 @@ class Item:
         return f'<{self.__class__.__name__} {attrs}>'
 
     @property
-    def callback(self) -> Optional[ItemCallbackType]:
-        """Returns the underlying callback associated with this interaction."""
-        return self._callback
-
-    @callback.setter
-    def callback(self, value: Optional[ItemCallbackType]):
-        if value is None:
-            self._callback = None
-            return
-
-        # Check if it's a partial function
-        try:
-            partial = value.func
-        except AttributeError:
-            pass
-        else:
-            if not inspect.iscoroutinefunction(value.func):
-                raise TypeError(f'inner partial function must be a coroutine')
-
-            # Check if the partial is bound
-            try:
-                bound_partial = partial.__self__
-            except AttributeError:
-                pass
-            else:
-                self._pass_view_arg = not hasattr(bound_partial, '__discord_ui_view__')
-
-            self._callback = value
-            return
-
-        try:
-            func_self = value.__self__
-        except AttributeError:
-            pass
-        else:
-            if not isinstance(func_self, Item):
-                raise TypeError(f'callback bound method must be from Item not {func_self!r}')
-            else:
-                value = value.__func__
-
-        if not inspect.iscoroutinefunction(value):
-            raise TypeError(f'callback must be a coroutine not {value!r}')
-
-        self._callback = value
-
-    async def _do_call(self, view: View, interaction: Interaction):
-        if self._pass_view_arg:
-            await self._callback(view, self, interaction)
-        else:
-            await self._callback(self, interaction)  # type: ignore
+    def view(self) -> Optional[View]:
+        """Optional[:class:`View`]: The underlying view for this item."""
+        return self._view
+
+    async def callback(self, interaction: Interaction):
+        """|coro|
+
+        The callback associated with this UI item.
+
+        This can be overriden by subclasses.
+
+        Parameters
+        -----------
+        interaction: :class:`Interaction`
+            The interaction that triggered this UI item.
+        """
+        pass
diff --git a/discord/ui/view.py b/discord/ui/view.py
index 273a45d0..712f787a 100644
--- a/discord/ui/view.py
+++ b/discord/ui/view.py
@@ -31,7 +31,7 @@ import asyncio
 import sys
 import time
 import os
-from .item import Item
+from .item import Item, ItemCallbackType
 from ..enums import ComponentType
 from ..components import (
     Component,
@@ -95,13 +95,13 @@ class View:
     __discord_ui_view__: ClassVar[bool] = True
 
     if TYPE_CHECKING:
-        __view_children_items__: ClassVar[List[Item]]
+        __view_children_items__: ClassVar[List[ItemCallbackType]]
 
     def __init_subclass__(cls) -> None:
-        children: List[Item] = []
+        children: List[ItemCallbackType] = []
         for base in reversed(cls.__mro__):
             for member in base.__dict__.values():
-                if isinstance(member, Item):
+                if hasattr(member, '__discord_ui_model_type__'):
                     children.append(member)
 
         if len(children) > 25:
@@ -111,7 +111,13 @@ class View:
 
     def __init__(self, timeout: Optional[float] = 180.0):
         self.timeout = timeout
-        self.children: List[Item] = [i.copy() for i in self.__view_children_items__]
+        self.children: List[Item] = []
+        for func in self.__view_children_items__:
+            item: Item = func.__discord_ui_model_type__(**func.__discord_ui_model_kwargs__)
+            item.callback = partial(func, self, item)
+            item._view = self
+            self.children.append(item)
+
         self.id = os.urandom(16).hex()
         self._cancel_callback: Optional[Callable[[View], None]] = None
 
@@ -171,11 +177,12 @@ class View:
         if not isinstance(item, Item):
             raise TypeError(f'expected Item not {item.__class__!r}')
 
+        item._view = self
         self.children.append(item)
 
     async def _scheduled_task(self, state: Any, item: Item, interaction: Interaction):
         await state.http.create_interaction_response(interaction.id, interaction.token, type=6)
-        await item._do_call(self, interaction)
+        await item.callback(interaction)
 
     def dispatch(self, state: Any, item: Item, interaction: Interaction):
         asyncio.create_task(self._scheduled_task(state, item, interaction), name=f'discord-ui-view-dispatch-{self.id}')