What does the "key: value" syntax do in composer scripts - php

Question

From compser documentation you can write scripts like so:
{
"scripts": {
"some-event": [
"command1",
"command2",
"command3"
],
}
}
But in Symfony I found a slightly different syntax that instead of a list is using a key:value pair like this:
{
"scripts": {
"auto-scripts": {
"cache:clear": "symfony-cmd",
"assets:install %PUBLIC_DIR%": "symfony-cmd"
},
},
}
How does this syntax work exactly?
Does it redirect commands to another one, adds a dependency between 2 commands or what?

Answer 1

How does this syntax work exactly?
This syntax is undefined in Composer.
To learn more, remove it and then check which component(s) break(s). Then consult the support of that/these component(s) to learn more (and/or leave a comment here).
Does it redirect commands to another one, adds a dependency between 2 commands or what?
As written this is undefined. As far as you're concerned about Composer you can check if it is recognized as a script:
composer run-script --list
You'll likely see that auto-scripts is listed as a script, that is, Composer is recognizing at least the auto-scripts keyword.
You can then execute that script to see how Composer executes it (it is highly recommended you do this and the following in an isolated environment):
composer run-script auto-scripts
To see if a plugin would make a difference, you can also execute it with plugins disabled:
composer --no-plugins run-script auto-scripts
Take care.
And with Composer there is always -vvv.
Some notes on internal Composer configuration file handling: JSON Text files (.json, .lock) in Composer are typically parsed into associative arrays (not stdClass::class objects).
Therefore foreach'ing a script member - which can be a string as well, likely post-processed with an (array) cast - would not care about the key (attribute name), just executing the scripts lines.

Answer 2

This syntax is used by symfony/flex plugin and is only valid under auto-scripts key.
The code in flex looks like this:
$json = new JsonFile(Factory::getComposerFile());
$jsonContents = $json->read();
$executor = new ScriptExecutor($this->composer, $this->io, $this->options);
foreach ($jsonContents['scripts']['auto-scripts'] as $cmd => $type) {
$executor->execute($type, $cmd);
}
With execute being handled using this code:
switch ($type) {
case 'symfony-cmd':
return $this->expandSymfonyCmd($cmd);
case 'php-script':
return $this->expandPhpScript($cmd);
case 'script':
return $cmd;
default:
throw new \InvalidArgumentException();
}