`Message.channel` is a `DMChannel` in `on_message` for an ephemeral message not sent as a DM

[Harmon758]

Summary

When an ephemeral message is sent, the resulting Message object dispatched to on_message has a channel attribute that is an instance of DMChannel, even if the ephemeral message was not sent as a Direct Message.

Reproduction Steps

• Send an ephemeral message (not as a DM, e.g. in a text channel)
• Check type(message.channel) for the corresponding message in on_message

Expected Results

message.channel should be the proper type (e.g. TextChannel), rather than DMChannel.

Actual Results

message.channel is a DMChannel.

Intents

N/A

System Information

• Python v3.9.5-final
• discord.py v2.0.0-alpha
  • discord.py pkg_resources: v2.0.0a3469+g1e17b7fc
• aiohttp v3.7.4.post0
• system info: Windows 10 10.0.19042

Checklist

• [X] I have searched the open issues for duplicates.
• [X] I have shown the entire traceback, if possible.
• [X] I have removed my token from display, if visible.

Additional Context

This seems to be because Discord's API does not provide guild_id for ephemeral messages for the Message Create event.

When discord.py receives the event, ConnectionState.parse_message_create assigns the channel with ConnectionState._get_guild_channel: https://github.com/Rapptz/discord.py/blob/1e17b7fceaf7173b1666465e639d1bebaa126683/discord/state.py#L509-L511

When the data doesn't have guild_id, ConnectionState._get_guild_channel returns a DMChannel: https://github.com/Rapptz/discord.py/blob/1e17b7fceaf7173b1666465e639d1bebaa126683/discord/state.py#L403-L413

[Rapptz]

Since guild_id isn't provided then the alternative here would be doing an O(n) search for the guild channels to see which one matched which doesn't seem like a good idea.