Currently in symfony 3.3.x parameter kernel.project_dir silently returns kernel_dir if composer.json is not found at all. IMHO it shouldn't be related with composer.json as in prod environment, composer is typically not needed at all, so files could be discarded from build artifacts. So even an error or a warning would be better here compared to option that you can get 2 different paths depending on that you have or not have a 3rd party file.

even cache:clear fails with missing files errors, if project_dir is used without composer.json file

PHP Fatal error:  Uncaught Symfony\Component\Config\Exception\FileLocatorFileNotFoundException: The file "/var/www/releases/20170822132058/app/vendor/willdurand/geocoder/Dumper" does not exist. in /var/www/releases/20170822132058/vendor/symfony/config/FileLocator.php:46
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