Imports are highlighted like the packages do not exist (Symfony 4) - symfony

Question

I'm working on a Symfony 4 project with PhpStorm 2018.1
It has become common for me to see the use declarations highlighted as if they haven't been installed with composer.
The class belongs to a package which is not directly required in your
composer.json. Please add the package into your composer.json.
The following are installed and show in my composer.json file:
stof/doctrine-extensions-bundle
symfony/orm-pack
Am I missing something here or is this a PhpStorm issue?
composer.json
{
"type": "project",
"license": "proprietary",
"platform": {
"php": "7.1"
},
"require": {
"php": "^7.1",
"ext-iconv": "*",
"sensio/framework-extra-bundle": "^5.1",
"stof/doctrine-extensions-bundle": "^1.3",
"symfony/asset": "^4.1",
"symfony/console": "^4.1",
"symfony/expression-language": "^4.1",
"symfony/flex": "^1.0",
"symfony/form": "^4.1",
"symfony/framework-bundle": "^4.1",
"symfony/lts": "^4#dev",
"symfony/maker-bundle": "^1.5",
"symfony/monolog-bundle": "^3.3",
"symfony/orm-pack": "^1.0",
"symfony/process": "^4.1",
"symfony/profiler-pack": "^1.0",
"symfony/security-bundle": "^4.1",
"symfony/security-guard": "^4.1",
"symfony/serializer-pack": "*",
"symfony/swiftmailer-bundle": "^3.1",
"symfony/twig-bundle": "^4.1",
"symfony/validator": "^4.1",
"symfony/var-dumper": "^4.1",
"symfony/web-link": "^4.1",
"symfony/webpack-encore-pack": "^1.0",
"symfony/yaml": "^4.1"
},
"require-dev": {
"doctrine/doctrine-fixtures-bundle": "^3.0",
"symfony/debug-pack": "*",
"symfony/dotenv": "^4.1",
"symfony/test-pack": "^1.0",
"symfony/web-server-bundle": "^4.1"
},
"config": {
"preferred-install": {
"*": "dist"
},
"sort-packages": true
},
"autoload": {
"psr-4": {
"App\\": "src/"
}
},
"autoload-dev": {
"psr-4": {
"App\\Tests\\": "tests/"
}
},
"replace": {
"symfony/polyfill-iconv": "*",
"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"
]
},
"conflict": {
"symfony/symfony": "*"
},
"extra": {
"symfony": {
"allow-contrib": true
}
}
}

Answer 1

What this message is telling you is that the highlighted classes are only available because the packages containing them have been installed as dependencies of some other packages you require (in this case it's probably because of the symfony/orm-pack package). Generally, relying on such transitive dependencies is not something I would do. Though for the Symfony pack that's something acceptable IMO.
If you are still concerned about this message, you can get rid of it by unpacking symfony/orm-pack (see also http://fabien.potencier.org/symfony4-unpack-the-packs.html):
$ composer unpack symfony/orm-pack

Answer 2

Your import path is correct, your composer.json looks good also.
Try to delete the vendor directory then try to launch composer install.
Try to install Symfony Plugin in your PHPStorm.
EDIT
Do you have the line below in your config/bundles.php ?
Doctrine\Bundle\DoctrineBundle\DoctrineBundle::class => ['all' => true],