feat(Partials): add DMChannel/MessageReaction#fetch() and PartialTypes.REACTION (#3474)

* add DMChannel#fetch() & Action#getChannel({recipients})

* ref for MessageReaction partial

* typings

* add PartialTypes.REACTION

* accommodate for fully removed reactions

* fix incorrect wording and typo

* typings: MessageReaction#count is nullable

* typings: mark MessageReaction#partial as readonly

Co-Authored-By: Vlad Frangu <kingdgrizzle@gmail.com>

* fix(User): fetch dm channel if cached one is partial

* docs: add missing comma

Co-Authored-By: Antonio Román <kyradiscord@gmail.com>

* fix: accomodate for new reactions

* fix: updating existing/new count on _patch

* docs: typo

* for consistency

Co-authored-by: Vlad Frangu <kingdgrizzle@gmail.com>
Co-authored-by: SpaceEEC <spaceeec@yahoo.com>
Co-authored-by: Antonio Román <kyradiscord@gmail.com>

docs/topics/partials.md

@@ -9,8 +9,8 @@ discard the event. With partials, you're able to receive the event, with a Messa
 Partials are opt-in, and you can enable them in the Client options by specifying [PartialTypes](/#/docs/main/master/typedef/PartialType):
 
 ```js
-// Accept partial messages and DM channels when emitting events
-new Client({ partials: ['MESSAGE', 'CHANNEL'] });
+// Accept partial messages, DM channels, and reactions when emitting events
+new Client({ partials: ['MESSAGE', 'CHANNEL', 'REACTION'] });
 ```
 
 ## Usage & warnings
@@ -45,6 +45,10 @@ client.on('messageReactionAdd', async (reaction, user) => {
   if (reaction.message.partial) await reaction.message.fetch();
   // Now the message has been cached and is fully available:
   console.log(`${reaction.message.author}'s message "${reaction.message.content}" gained a reaction!`);
+  // Fetches and caches the reaction itself, updating resources that were possibly defunct.
+  if (reaction.partial) await reaction.fetch();
+  // Now the reaction is fully available and the properties will be reflected accurately:
+  console.log(`${reaction.count} user(s) have given the same reaction to this message!`);
 });
 ```
 

src/client/actions/Action.js

@@ -36,6 +36,7 @@ class GenericAction {
     return data.channel || this.getPayload({
       id,
       guild_id: data.guild_id,
+      recipients: [data.author || { id: data.user_id }],
     }, this.client.channels, id, PartialTypes.CHANNEL);
   }
 
@@ -52,9 +53,9 @@ class GenericAction {
     const id = data.emoji.id || decodeURIComponent(data.emoji.name);
     return this.getPayload({
       emoji: data.emoji,
-      count: 0,
+      count: message.partial ? null : 0,
       me: user.id === this.client.user.id,
-    }, message.reactions, id, PartialTypes.MESSAGE);
+    }, message.reactions, id, PartialTypes.REACTION);
   }
 
   getMember(data, guild) {

src/client/actions/MessageReactionAdd.js

@@ -2,6 +2,7 @@
 
 const Action = require('./Action');
 const { Events } = require('../../util/Constants');
+const { PartialTypes } = require('../../util/Constants');
 
 /*
 { user_id: 'id',
@@ -26,11 +27,13 @@ class MessageReactionAdd extends Action {
     if (!message) return false;
 
     // Verify reaction
+    if (message.partial && !this.client.options.partials.includes(PartialTypes.REACTION)) return false;
     const reaction = message.reactions.add({
       emoji: data.emoji,
-      count: 0,
+      count: message.partial ? null : 0,
       me: user.id === this.client.user.id,
     });
+    if (!reaction) return false;
     reaction._add(user);
     /**
      * Emitted whenever a reaction is added to a cached message.

src/stores/ReactionStore.js

@@ -50,6 +50,28 @@ class ReactionStore extends DataStore {
     return this.client.api.channels(this.message.channel.id).messages(this.message.id).reactions.delete()
       .then(() => this.message);
   }
+
+  _partial(emoji) {
+    const id = emoji.id || emoji.name;
+    const existing = this.get(id);
+    return !existing || existing.partial;
+  }
+
+  async _fetchReaction(reactionEmoji, cache) {
+    const id = reactionEmoji.id || reactionEmoji.name;
+    const existing = this.get(id);
+    if (!this._partial(reactionEmoji)) return existing;
+    const data = await this.client.api.channels(this.message.channel.id).messages(this.message.id).get();
+    if (!data.reactions || !data.reactions.some(r => (r.emoji.id || r.emoji.name) === id)) {
+      reactionEmoji.reaction._patch({ count: 0 });
+      this.message.reactions.remove(id);
+      return existing;
+    }
+    for (const reaction of data.reactions) {
+      if (this._partial(reaction.emoji)) this.add(reaction, cache);
+    }
+    return existing;
+  }
 }
 
 module.exports = ReactionStore;

src/structures/DMChannel.js

@@ -56,7 +56,15 @@ class DMChannel extends Channel {
    * @readonly
    */
   get partial() {
-    return !this.recipient;
+    return typeof this.lastMessageID === 'undefined';
+  }
+
+  /**
+   * Fetch this DMChannel.
+   * @returns {Promise<DMChannel>}
+   */
+  fetch() {
+    return this.recipient.createDM();
   }
 
   /**

src/structures/MessageReaction.js

@@ -27,12 +27,6 @@ class MessageReaction {
      */
     this.me = data.me;
 
-    /**
-     * The number of people that have given the same reaction
-     * @type {number}
-     */
-    this.count = data.count || 0;
-
     /**
      * The users that have given this reaction, mapped by their ID
      * @type {ReactionUserStore<Snowflake, User>}
@@ -40,6 +34,17 @@ class MessageReaction {
     this.users = new ReactionUserStore(client, undefined, this);
 
     this._emoji = new ReactionEmoji(this, data.emoji);
+
+    this._patch(data);
+  }
+
+  _patch(data) {
+    /**
+     * The number of people that have given the same reaction
+     * @type {?number}
+     */
+    // eslint-disable-next-line eqeqeq
+    if (this.count == undefined) this.count = data.count;
   }
 
   /**
@@ -63,18 +68,36 @@ class MessageReaction {
     return this._emoji;
   }
 
+  /**
+   * Whether or not this reaction is a partial
+   * @type {boolean}
+   * @readonly
+   */
+  get partial() {
+    return this.count === null;
+  }
+
+  /**
+   * Fetch this reaction.
+   * @returns {Promise<MessageReaction>}
+   */
+  fetch() {
+    return this.message.reactions._fetchReaction(this.emoji, true);
+  }
 
   toJSON() {
     return Util.flatten(this, { emoji: 'emojiID', message: 'messageID' });
   }
 
   _add(user) {
+    if (this.partial) return;
     this.users.set(user.id, user);
     if (!this.me || user.id !== this.message.client.user.id || this.count === 0) this.count++;
     if (!this.me) this.me = user.id === this.message.client.user.id;
   }
 
   _remove(user) {
+    if (this.partial) return;
     this.users.delete(user.id);
     if (!this.me || user.id !== this.message.client.user.id) this.count--;
     if (user.id === this.message.client.user.id) this.me = false;

src/structures/User.js

@@ -218,7 +218,7 @@ class User extends Base {
    */
   async createDM() {
     const { dmChannel } = this;
-    if (dmChannel) return dmChannel;
+    if (dmChannel && !dmChannel.partial) return dmChannel;
     const data = await this.client.api.users(this.client.user.id).channels.post({ data: {
       recipient_id: this.id,
     } });

src/util/Constants.js

@@ -294,6 +294,7 @@ exports.ShardEvents = {
  * * CHANNEL (only affects DMChannels)
  * * GUILD_MEMBER
  * * MESSAGE
+ * * REACTION
  * <warn>Partials require you to put checks in place when handling data, read the Partials topic listed in the
  * sidebar for more information.</warn>
  * @typedef {string} PartialType
@@ -303,6 +304,7 @@ exports.PartialTypes = keyMirror([
   'CHANNEL',
   'GUILD_MEMBER',
   'MESSAGE',
+  'REACTION',
 ]);
 
 /**

typings/index.d.ts

@@ -649,6 +649,7 @@ declare module 'discord.js' {
 		public messages: MessageStore;
 		public recipient: User;
 		public readonly partial: false;
+		public fetch(): Promise<DMChannel>;
 	}
 
 	export class Emoji extends Base {
@@ -1100,11 +1101,13 @@ declare module 'discord.js' {
 		constructor(client: Client, data: object, message: Message);
 		private _emoji: GuildEmoji | ReactionEmoji;
 
-		public count: number;
+		public count: number | null;
 		public readonly emoji: GuildEmoji | ReactionEmoji;
 		public me: boolean;
 		public message: Message;
+		public readonly partial: boolean;
 		public users: ReactionUserStore;
+		public fetch(): Promise<MessageReaction>;
 		public toJSON(): object;
 	}
 
@@ -2539,7 +2542,8 @@ declare module 'discord.js' {
 	type PartialTypes = 'USER'
 		| 'CHANNEL'
 		| 'GUILD_MEMBER'
-		| 'MESSAGE';
+		| 'MESSAGE'
+		| 'REACTION';
 
 	type Partialize<T> = {
 		id: string;