Partials (#3070)

* Remove GroupDMChannels

they sparked no joy

* Start partials for message deletion

* MessageUpdate partials

* Add partials as an opt-in client option

* Add fetch() to Message

* Message.author should never be undefined

* Fix channels being the wrong type

* Allow fetching channels

* Refactor and add reaction add partials

* Reaction remove partials

* Check for emoji first

* fix message fetching

janky

* User partials in audit logs

* refactor overwrite code

* guild member partials

* partials as a whitelist

* document GuildMember#fetch

* fix: check whether a structure is a partial, not whether cache is true

* typings: Updated for latest commit (#3075)

* partials: fix messageUpdate behaviour (now "old" message can be partial)

* partials: add warnings and docs

* partials: add partials to index.yml

* partials: tighten "partial" definitions

* partials: fix embed-only messages counting as partials

src/structures/DMChannel.js

@@ -12,6 +12,8 @@ const MessageStore = require('../stores/MessageStore');
 class DMChannel extends Channel {
   constructor(client, data) {
     super(client, data);
+    // Override the channel type so partials have a known type
+    this.type = 'dm';
     /**
      * A collection containing the messages sent to this channel
      * @type {MessageStore<Snowflake, Message>}
@@ -23,11 +25,13 @@ class DMChannel extends Channel {
   _patch(data) {
     super._patch(data);
 
-    /**
-     * The recipient on the other end of the DM
-     * @type {User}
-     */
-    this.recipient = this.client.users.add(data.recipients[0]);
+    if (data.recipients) {
+      /**
+       * The recipient on the other end of the DM
+       * @type {User}
+       */
+      this.recipient = this.client.users.add(data.recipients[0]);
+    }
 
     /**
      * The ID of the last message in the channel, if one was sent
@@ -42,6 +46,14 @@ class DMChannel extends Channel {
     this.lastPinTimestamp = data.last_pin_timestamp ? new Date(data.last_pin_timestamp).getTime() : null;
   }
 
+  /**
+   * Whether this DMChannel is a partial
+   * @type {boolean}
+   */
+  get partial() {
+    return !this.recipient;
+  }
+
   /**
    * When concatenated with a string, this automatically returns the recipient's mention instead of the
    * DMChannel object.