chore: Include discord.js in the user agent string (#9267)

* chore: apply user agent string

* fix: enforce even in custom option

* fix: tests

* refactor: simpler way

* docs: add type

* Update packages/discord.js/src/client/BaseClient.js

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

* fix: prioritise `option` type check

* types: `static`

* feat: add runtime check

* docs: update default

* refactor: remove Bun

* Update packages/discord.js/src/client/BaseClient.js

Co-authored-by: Almeida <almeidx@pm.me>

* fix: extra whitespace issues

* refactor: `trimEnd()`

---------

Co-authored-by: Aura Román <kyradiscord@gmail.com>
Co-authored-by: Almeida <almeidx@pm.me>
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/discord.js/src/client/BaseClient.js

@@ -18,6 +18,12 @@ class BaseClient extends EventEmitter {
       throw new DiscordjsTypeError(ErrorCodes.InvalidType, 'options', 'object', true);
     }
 
+    if (options.rest?.userAgentAppendix) {
+      // Merging the default options when a custom user agent appendix is supplied
+      // Replaces the discord.js string. Enforce it.
+      options.rest.userAgentAppendix = `${Options.userAgentAppendix} ${options.rest.userAgentAppendix}`;
+    }
+
     /**
      * The options the client was instantiated with
      * @type {ClientOptions}

packages/discord.js/src/util/Options.js

@@ -1,8 +1,9 @@
 'use strict';
 
 const process = require('node:process');
-const { DefaultRestOptions } = require('@discordjs/rest');
+const { DefaultRestOptions, DefaultUserAgentAppendix } = require('@discordjs/rest');
 const { toSnakeCase } = require('./Transformers');
+const { version } = require('../../package.json');
 
 /**
  * @typedef {Function} CacheFactory
@@ -70,6 +71,14 @@ const { toSnakeCase } = require('./Transformers');
  * Contains various utilities for client options.
  */
 class Options extends null {
+  /**
+   * The default user agent appendix.
+   * @type {string}
+   * @memberof Options
+   * @private
+   */
+  static userAgentAppendix = `discord.js/${version} ${DefaultUserAgentAppendix}`.trimEnd();
+
   /**
    * The default client options.
    * @returns {ClientOptions}
@@ -94,7 +103,10 @@ class Options extends null {
         },
         version: 10,
       },
-      rest: DefaultRestOptions,
+      rest: {
+        ...DefaultRestOptions,
+        userAgentAppendix: this.userAgentAppendix,
+      },
       jsonTransformer: toSnakeCase,
     };
   }