[commands] Fix (Partial)MessageConverter to work with thread messages

discord/threads.py

@@ -23,6 +23,7 @@ DEALINGS IN THE SOFTWARE.
 """
 
 from __future__ import annotations
+
 from typing import Callable, Dict, Iterable, List, Optional, Union, TYPE_CHECKING
 import time
 import asyncio
@@ -48,7 +49,7 @@ if TYPE_CHECKING:
     from .guild import Guild
     from .channel import TextChannel
     from .member import Member
-    from .message import Message
+    from .message import Message, PartialMessage
     from .abc import Snowflake, SnowflakeTime
     from .role import Role
     from .permissions import Permissions
@@ -191,6 +192,7 @@ class Thread(Messageable, Hashable):
             self._unroll_metadata(data['thread_metadata'])
         except KeyError:
             pass
+
     @property
     def type(self) -> ChannelType:
         """:class:`ChannelType`: The channel's Discord type."""
@@ -626,6 +628,29 @@ class Thread(Messageable, Hashable):
         """
         await self._state.http.delete_channel(self.id)
 
+    def get_partial_message(self, message_id: int, /) -> PartialMessage:
+        """Creates a :class:`PartialMessage` from the message ID.
+
+        This is useful if you want to work with a message and only have its ID without
+        doing an unnecessary API call.
+
+        .. versionadded:: 2.0
+
+        Parameters
+        ------------
+        message_id: :class:`int`
+            The message ID to create a partial message for.
+
+        Returns
+        ---------
+        :class:`PartialMessage`
+            The partial message.
+        """
+
+        from .message import PartialMessage
+
+        return PartialMessage(channel=self, id=message_id)
+
     def _add_member(self, member: ThreadMember) -> None:
         self._members[member.id] = member