Deploying Symfony on Heroku - symfony

Question

I'm trying to deploy a Symfony 5.2 on Heroku, I've already configured the Procfile and the required Config Vars such APP_ENV (prod), APP_SECRET and others related to the project.
Procfile:
web: vendor/bin/heroku-php-apache2 public/
composer.json:
{
"type": "project",
"license": "proprietary",
"require": {
"php": "^7.2.5",
"ext-ctype": "*",
"ext-iconv": "*",
"knplabs/knp-paginator-bundle": "^5.2",
"lexik/jwt-authentication-bundle": "^2.8",
"nelmio/cors-bundle": "^2.0",
"sensio/framework-extra-bundle": "^5.5",
"symfony/asset": "5.1.*",
"symfony/console": "5.1.*",
"symfony/dotenv": "5.1.*",
"symfony/flex": "^1.3.1",
"symfony/framework-bundle": "5.1.*",
"symfony/mailer": "5.1.*",
"symfony/orm-pack": "^1.0",
"symfony/security-bundle": "5.1.*",
"symfony/serializer": "5.1.*",
"symfony/yaml": "5.1.*",
"twig/twig": "^3.0"
},
"require-dev": {
"doctrine/doctrine-fixtures-bundle": "^3.3",
"symfony/maker-bundle": "^1.19",
"symfony/profiler-pack": "^1.0"
},
"config": {
"optimize-autoloader": true,
"preferred-install": {
"*": "dist"
},
"sort-packages": true
},
"autoload": {
"psr-4": {
"App\\": "src/"
}
},
"autoload-dev": {
"psr-4": {
"App\\Tests\\": "tests/"
}
},
"replace": {
"paragonie/random_compat": "2.*",
"symfony/polyfill-ctype": "*",
"symfony/polyfill-iconv": "*",
"symfony/polyfill-php72": "*",
"symfony/polyfill-php71": "*",
"symfony/polyfill-php70": "*",
"symfony/polyfill-php56": "*"
},
"scripts": {
"auto-scripts": {
"cache:clear": "symfony-cmd",
"assets:install %PUBLIC_DIR%": "symfony-cmd"
},
"post-install-cmd": [
"#auto-scripts"
],
"post-update-cmd": [
"#auto-scripts"
],
"compile": [
"php bin/console doctrine:migrations:migrate"
]
},
"conflict": {
"symfony/symfony": "*"
},
"extra": {
"symfony": {
"allow-contrib": false,
"require": "5.1.*"
}
}
}
No matter what I do I always end up with an error related to something missing such as:
PHP Fatal error: Uncaught Error: Class 'Symfony\Bundle\TwigBundle\TwigBundle' not found in /tmp/build_271a300c_/vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php:74
My guess is the problem is related with everything ending up in this /tmp/build_271a300c_ folder and when the project is deployed it lost the refereed folder. But I have no idea what to do with this information I appreciate any help.

Answer 1

Solved the problem with, what I think, is nothing more than a workaround.
The deploy process was complaining always about the require-dev dependencies, so I did:
Moved all require-dev to require;
Run composer update to refresh the composer.lock file;
Pushed and tried the deploy again with success.
This solution was take for many people in other issues I read, I'm just describing step-by-step what was done to fix it. Still, I don't think it's the correct fix for this, after all the dev-dependencies shouldn't being installed on prod environment.