feat(Guild): add fetchBan method (#3726)

* Add error for not resolving ID to fetch ban

* Add Guild#fetchBan

* add missing !

* typings

* lint fixes

* add jsdoc description

src/errors/Messages.js

@@ -71,6 +71,7 @@ const Messages = {
   SPLIT_MAX_LEN: 'Chunk exceeds the max length and contains no split characters.',
 
   BAN_RESOLVE_ID: (ban = false) => `Couldn't resolve the user ID to ${ban ? 'ban' : 'unban'}.`,
+  FETCH_BAN_RESOLVE_ID: 'Couldn\'t resolve the user ID to fetch the ban.',
 
   PRUNE_DAYS_TYPE: 'Days must be a number',
 

src/structures/Guild.js

@@ -554,6 +554,21 @@ class Guild extends Base {
    * @property {?string} reason Reason the user was banned
    */
 
+  /**
+  * Fetches information on a banned user from this guild.
+   * @param {UserResolvable} user The User to fetch the ban info of
+   * @returns {BanInfo}
+   */
+  fetchBan(user) {
+    const id = this.client.users.resolveID(user);
+    if (!id) throw new Error('FETCH_BAN_RESOLVE_ID');
+    return this.client.api.guilds(this.id).bans(id).get()
+      .then(ban => ({
+        reason: ban.reason,
+        user: this.client.users.add(ban.user),
+      }));
+  }
+
   /**
    * Fetches a collection of banned users in this guild.
    * @returns {Promise<Collection<Snowflake, BanInfo>>}

typings/index.d.ts

@@ -733,6 +733,7 @@ declare module 'discord.js' {
 		public equals(guild: Guild): boolean;
 		public fetch(): Promise<Guild>;
 		public fetchAuditLogs(options?: GuildAuditLogsFetchOptions): Promise<GuildAuditLogs>;
+		public fetchBan(user: UserResolvable): Promise<{ user: User, reason: string }>;
 		public fetchBans(): Promise<Collection<Snowflake, { user: User, reason: string }>>;
 		public fetchEmbed(): Promise<GuildEmbedData>;
 		public fetchIntegrations(): Promise<Collection<string, Integration>>;