Allow ChannelManager#fetch without a guild

[GamingGeek]

Please describe the problem you are having in as much detail as possible:
When using ChannelManager#fetch for a channel that is not cached and is not in any guilds on the current cluster, I get null rather than the channel

Using client.api works fine

Include a reproducible code sample here, if possible:

client.channels.fetch("channelID", false, true) // the channelID likely needs to be a channel accessible to the bot but not accessible to any guilds in the shards of the current process

Further details:

• discord.js version: 12.4.0
• Node.js version: 14.14.0
• Operating system: Ubuntu Server 18.04
• Priority this issue should have – please be realistic and elaborate if possible: Medium

Relevant client options:

• partials: ["REACTION", "MESSAGE", "CHANNEL", "GUILD_MEMBER", "USER"]
• gateway intents: 1607
• other: shardCount is 4 and the shards on the cluster with the issue are [2, 3] whereas the channel in question is on shard 0

• I have also tested the issue on latest master, commit hash: 250c3ae

[NotSugden]

the channel you're trying to fetch is from a guild which is not on the current shard, that seems to be the only explanation for this

discord.js/src/managers/ChannelManager.js

Lines 32 to 35 in 94c9cc2

	if (!channel) {
	this.client.emit(Events.DEBUG, `Failed to find guild, or unknown type for channel ${data.id} ${data.type}`);
	return null;
	}

here is the only way ChannelManager#fetch would return a promise resolving with null

either way there is definetly a problem here, perhaps an error should be thrown if the guild is for another shard, this would have to be for v13 however

[GamingGeek]

@NotSugden It's fetching from the Rest API which is agnostic of shards/clusters meaning it should still work. Using the same method ChannelManager#fetch uses to fetch the channel from the API works as seen in this image so I'm not quite sure what's happening here.

[wasdennnoch]

The issue lies in Channel#create where it only creates a d.js channel instance if the parent guild is known:

discord.js/src/structures/Channel.js

Line 122 in 94c9cc2

if (guild) {

Since this shard is not aware of the guild the channel you're fetching is in, that method will never create a d.js Channel object, since that requires a parent guild object to exist in the current shard's client.
So the issue is not the API call - that works just fine - but the internal structure of Discord.js, in which a GuildChannel always has to have a known parent Guild object.

[GamingGeek]

in which a GuildChannel always has to have a known parent Guild object.

Well that kinda ruins what I was working on. Maybe instead of this being a bug report, it could be a suggestion to make fetching a channel without a guild possible.