Dealing with Drupal 9 errors: Symfony\ Component\ DependencyInjection\ Exception\ Service Not Found Exception: The service “pathauto.generator” has a dependent service “token.entity_mapper

A couple of times with websites running on Drupal Version 9.x when I got stuck with below and similar errors:

Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: The service “pathauto.generator” has a dependen
service “token.entity_mapper”… in /vendor/symfony/dependency-injection/Compiler/

All was running well, until I installed a contributed module Taxonomy Views Integrator (TVI) using composer require, ran drush updb, and drush cache:rebuild, when boom! The error…

Here some quick fixes:

1. Update Drupal core to the latest, if not done yet (make sure you have a good backup of both the website files and database which you can restore if anything goes wrong).
   composer update "drupal/*" --with-all-dependencies
drush updatedb
drush cache:rebuild
2. Check your PHP versions if inadvertently or previously set lower than PHP version 8.0
   I had one in instance where my PHP version had been unintentionally set to 7.x. Changing PHP version to 8.x made the error go away.
3. Update your contributed modules to the latest versions; if necessary, to the dev versions of modules that may be causing the error.
   In another case which I experienced, since the error seems to point to instances within pathauto and token modules, I had to re-install both by running composer require commands for the stable versions as recommended by the project module pages.
   In my case:
   composer require ‘drupal/pathauto:^1.11’
   composer require ‘drupal/token:^1.11’
   drush updb
   drush cache:rebuild

Side notes:

While updating contributed modules using composer, another error may appear which seems to prevent the re-installation of the modules:

Installation failed, reverting ./composer.json and ./composer.lock to their original content.
Could not delete …/sites/default/default.settings.php:

To fix the above, run below Linux command (this will temporarily allow the necessary permissions for the D9 modules installation):
chmod u+w sites/default

Then proceed with the re-installation of the modules.

This article and similar troubleshooting articles are also found in iBuild.PH Knowledgebase for Drupal and other CMS https://knowledgebase.ibuild.ph/.

For full Drupal support and managed services in web design and development, you may also reach out to us through our Drupal web development services page at www.ibuild.ph/drupal.

I hope this helps!