The problem is solved by installing a fresh version of Laravel and moving the entire code there.
No, it's not. Cause I deleted PHP 5.6 and installed PHP 7.2 with all required extensions right before Laravel migration. Besides, I wrote before that the tests are working.
Yes, I'm doing it already. Application customizations were fixed in migration process, so I'm mostly moving files now.
No, it seems that the problem is not with service providers. It looks like the problem is occured before config/app.php is loaded. Any more suggestions?
The first four points I made as soon as there was a problem. I think, tomorrow I'll try the option with service providers. Thank you for the idea.
Leordex started a new conversation Laravel Migration From 5.2 To 5.5 - Class Config Does Not Exist
I updated the system step-by-step from 5.2 to 5.5. First, from 5.2 to 5.3, then from 5.3 to 5.4, and finally from 5.4 to 5.5. Unit and integration tests were successful. But when I tried to access the site through the browser, any page gave me error 500. In the log of Laravel there is nothing about it, but the log of Nginx gave me this:
PHP Fatal error: Uncaught ReflectionException: Class config does not exist in /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Container/Container.php:752 Stack trace: #0 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Container/Container.php(752): ReflectionClass->__construct('config') #1 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Container/Container.php(631): Illuminate\Container\Container->build('config') #2 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Container/Container.php(586): Illuminate\Container\Container->resolve('config', Array) #3 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Foundation/Application.php(721): Illuminate\Container\Container->make('config', Array) #4 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Foundation/helpers.php(110): Illuminate\Foundation\Application->make('config', Array) #5 /var/www/agc_club/api/vendor/laravel/framework/src/Illuminate/Foundation/helpers.php(272):
Looks like Laravel can't resolve its config. When I change the git branch back to 5.2 and reinstall the vendors, everything works fine, so it's not enviroment problem.
If someone tells me what I did wrong, I'll be grateful.