Symfony 4 Composer scripts

Question

I've just installed Symfony 4 project and found this section in composer.json:

"scripts": {
    "auto-scripts": {
        "cache:clear": "symfony-cmd",
        "assets:install %PUBLIC_DIR%": "symfony-cmd"
    },
    "post-install-cmd": [
        "@auto-scripts"
    ],
    "post-update-cmd": [
        "@auto-scripts"
    ],
...

I've found that section auto-scripts is handled somehow differently by the Composer: key is a command to bin/console and value is a command "type" (In this case it's Symfony's). As it is not documented on Composer website, I assume it's not legal definition, but it works, and my question is how the Composer knows how to execute such commands? How Composer knows what is symfony-cmd?

Answer 1

It's as Cerad says. auto-script is parsed by Symfony/Flex and the "right side" of a command:executable pair is processed by this switch-case.

switch ($type) {
    case 'symfony-cmd':
        return $this->expandSymfonyCmd($cmd);
    case 'php-script':
        return $this->expandPhpScript($cmd);
    case 'script':
        return $cmd;

Therefore Composer documentation can not say a word about that as it is Symfony-specific.

Personally don't like the mixing of standard Composer sections with custom ones on the composer.json root level. It simply confuses me and draws me into silent Composer documentation. Also the naming itself, auto-script, should be better. Something less magic and more self-explanatory, like flex-script.