Laravel: Unexpected 'readonly' Token Error Likely Due to PHP Version Mismatch

It looks like the error about the unexpected token "readonly" is coming from a PHP version mismatch rather than an outdated PHP library. Laravel 11 requires PHP 8.2 or greater, and the readonly property syntax was introduced in PHP 8.1; however, if the PHP interpreter that runs your web server (or CLI) is older than PHP 8.1, you’ll get that error when a dependency uses the new syntax (as seen in the sebastian/version package).

Here are some steps to help resolve the issue:

1. Verify PHP Versions:
   Although you mentioned PHP v8.4 when using Laravel Herd, it’s a good idea to confirm that both your CLI and web server environment actually point to the correct version. You can check your CLI version by running:

   BASHCopied
   php -v

   Also, check your server’s PHP configuration to ensure it’s using PHP 8.2+.

2. Ensure Composer Uses the Correct PHP Binary:
   Sometimes, your web server and your CLI can be using different versions of PHP. If your CLI is using an older PHP version, you may inadvertently update packages incompatible with the PHP version serving your application. Make sure that the PHP binary your composer uses is PHP 8.2+.

3. Clear Caches and Rebuild Autoloader:
   Occasionally, stale caches or opcache entries might cause unexpected syntax errors. Clear your caches with:

   BASHCopied
   php artisan cache:clear
   php artisan config:clear

   And then rebuild the autoloader:

   BASHCopied
   composer dump-autoload

4. Review Your Composer Dependencies:
   Confirm that your composer.json includes the correct version constraints for Laravel 11 and its dependencies (such as updating laravel/framework to ^11.0, etc.). The Laravel 11 upgrade guide specifies which dependencies should be updated. For example:

   JSONCopied
   "require": {
       "laravel/framework": "^11.0",
       // Other dependencies...
   }

In summary, the error is most likely due to an environment PHP version mismatch. Double-check that every part of your environment is running PHP 8.2 or greater. Once confirmed, run your composer update and clear any caches. This should resolve the syntax error related to the readonly keyword.