fix(MessageMentions): add InGuild generic (#8828)

fix(MessageMentions): add InGuild generic

Co-authored-by: Noel <buechler.noel@outlook.com>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/discord.js/typings/index.d.ts

@@ -1859,7 +1859,7 @@ export class Message<InGuild extends boolean = boolean> extends Base {
   public id: Snowflake;
   public interaction: MessageInteraction | null;
   public get member(): GuildMember | null;
-  public mentions: MessageMentions;
+  public mentions: MessageMentions<InGuild>;
   public nonce: string | number | null;
   public get partial(): false;
   public get pinnable(): boolean;
@@ -2018,7 +2018,7 @@ export class MessageFlagsBitField extends BitField<MessageFlagsString> {
   public static resolve(bit?: BitFieldResolvable<MessageFlagsString, number>): number;
 }
 
-export class MessageMentions {
+export class MessageMentions<InGuild extends boolean = boolean> {
   private constructor(
     message: Message,
     users: APIUser[] | Collection<Snowflake, User>,
@@ -2034,9 +2034,9 @@ export class MessageMentions {
   public get channels(): Collection<Snowflake, Channel>;
   public readonly client: Client;
   public everyone: boolean;
-  public readonly guild: Guild;
+  public readonly guild: If<InGuild, Guild>;
   public has(data: UserResolvable | RoleResolvable | ChannelResolvable, options?: MessageMentionsHasOptions): boolean;
-  public get members(): Collection<Snowflake, GuildMember> | null;
+  public get members(): If<InGuild, Collection<Snowflake, GuildMember>>;
   public get parsedUsers(): Collection<Snowflake, User>;
   public repliedUser: User | null;
   public roles: Collection<Snowflake, Role>;

packages/discord.js/typings/index.test-d.ts

@@ -148,6 +148,7 @@ import {
   RoleSelectMenuInteraction,
   ChannelSelectMenuInteraction,
   MentionableSelectMenuInteraction,
+  MessageMentions,
   AutoModerationActionExecution,
   AutoModerationRule,
   AutoModerationRuleManager,
@@ -361,6 +362,10 @@ client.on('messageCreate', async message => {
     expectType<GuildTextBasedChannel>(message.channel);
     expectType<Guild>(message.guild);
     expectType<GuildMember | null>(message.member);
+
+    expectType<MessageMentions<true>>(message.mentions);
+    expectType<Guild>(message.guild);
+    expectType<Collection<Snowflake, GuildMember>>(message.mentions.members);
   }
 
   expectType<TextBasedChannel>(message.channel);
@@ -1460,6 +1465,10 @@ declare const guildChannelManager: GuildChannelManager;
   expectType<null>(message.guild);
   expectType<null>(message.guildId);
   expectType<TextBasedChannel>(message.channel.messages.channel);
+
+  expectType<MessageMentions<false>>(message.mentions);
+  expectType<null>(message.mentions.guild);
+  expectType<null>(message.mentions.members);
 }
 
 declare const guildForumThreadManager: GuildForumThreadManager;