feat: allow channels from uncached guilds to be returned from fetch (#6034)

Co-authored-by: Antonio Román <kyradiscord@gmail.com>

src/managers/ChannelManager.js

@@ -19,7 +19,7 @@ class ChannelManager extends CachedManager {
    * @name ChannelManager#cache
    */
 
-  add(data, guild, cache = true) {
+  add(data, guild, cache = true, allowUnknownGuild = false) {
     const existing = this.cache.get(data.id);
     if (existing) {
       if (cache) existing._patch(data);
@@ -30,14 +30,14 @@ class ChannelManager extends CachedManager {
       return existing;
     }
 
-    const channel = Channel.create(this.client, data, guild);
+    const channel = Channel.create(this.client, data, guild, allowUnknownGuild);
 
     if (!channel) {
       this.client.emit(Events.DEBUG, `Failed to find guild, or unknown type for channel ${data.id} ${data.type}`);
       return null;
     }
 
-    if (cache) this.cache.set(channel.id, channel);
+    if (cache && !allowUnknownGuild) this.cache.set(channel.id, channel);
 
     return channel;
   }
@@ -74,10 +74,17 @@ class ChannelManager extends CachedManager {
    * @returns {?Snowflake}
    */
 
+  /**
+   * Options for fetching a channel from discord
+   * @typedef {BaseFetchOptions} FetchChannelOptions
+   * @property {boolean} [allowUnknownGuild=false] Allows the channel to be returned even if the guild is not in cache,
+   * it will not be cached. <warn>Many of the properties and methods on the returned channel will throw errors</warn>
+   */
+
   /**
    * Obtains a channel from Discord, or the channel cache if it's already available.
    * @param {Snowflake} id The channel's id
-   * @param {BaseFetchOptions} [options] Additional options for this fetch
+   * @param {FetchChannelOptions} [options] Additional options for this fetch
    * @returns {Promise<?Channel>}
    * @example
    * // Fetch a channel by its id
@@ -85,14 +92,14 @@ class ChannelManager extends CachedManager {
    *   .then(channel => console.log(channel.name))
    *   .catch(console.error);
    */
-  async fetch(id, { cache = true, force = false } = {}) {
+  async fetch(id, { allowUnknownGuild = false, cache = true, force = false } = {}) {
     if (!force) {
       const existing = this.cache.get(id);
       if (existing && !existing.partial) return existing;
     }
 
     const data = await this.client.api.channels(id).get();
-    return this.add(data, null, cache);
+    return this.add(data, null, cache, allowUnknownGuild);
   }
 }
 

src/managers/GuildChannelManager.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const CachedManager = require('./CachedManager');
+const { Error } = require('../errors');
 const GuildChannel = require('../structures/GuildChannel');
 const PermissionOverwrites = require('../structures/PermissionOverwrites');
 const ThreadChannel = require('../structures/ThreadChannel');
@@ -164,11 +165,17 @@ class GuildChannelManager extends CachedManager {
       if (existing) return existing;
     }
 
-    // We cannot fetch a single guild channel, as of this commit's date, Discord API throws with 404
+    if (id) {
+      const data = await this.client.api.channels(id).get();
+      // Since this is the guild manager, throw if on a different guild
+      if (this.guild.id !== data.guild_id) throw new Error('GUILD_CHANNEL_UNOWNED');
+      return this.client.channels.add(data, this.guild, cache);
+    }
+
     const data = await this.client.api.guilds(this.guild.id).channels.get();
     const channels = new Collection();
     for (const channel of data) channels.set(channel.id, this.client.channels.add(channel, this.guild, cache));
-    return id ? channels.get(id) ?? null : channels;
+    return channels;
   }
 }