Fatal error: Uncaught Error: Class 'Magento\Framework\Component\ComponentRegistrar' not found

Question

After Upgrading Magento 2.1.5 to 2.2.6 it's give following error. my magento source code is on subdirectory like www.mysite.com/staging/

/staging/vendor/mailchimp/mc-magento2/registration.php:12 Stack trace: #0

/staging/vendor/composer/autoload_real.php(71): require() #1

/staging/vendor/composer/autoload_real.php(61): composerRequiref4386a435c9f0af056695f7999d4c05d('62008ed0ff26c9a...', '/var/www/vhosts...') #2 #/staging/vendor/autoload.php(7): ComposerAutoloaderInitf4386a435c9f0af056695f7999d4c05d::getLoader() #3

/staging/app/autoload.php(30): include('/var/www/vhosts...') #4

/staging/app/bootstrap.php(30): require_once('/var/www/vhosts...') #5

staging/index.php(22): require('/var/www/vhosts...') #6 {main} thrown in

/staging/vendor/mailchimp/mc-magento2/registration.php on line 12

Answer 1

I don't know what exactly causes this, but composer install may help

Answer 2

As general rule I would delete the content of vendors directory and then

If you are in your local dev: composer update

If you are in some kind of production env where you only pull the repo: composer install