Configuration management

Configuration is discovered and loaded at the time of command execution. So, it is not available to be used during the bootstrap phase.

Contexts

Polymer's configuration system discovers and loads contexts provided by Core and it's extensions. The contexts are layered atop one and other, where contexts on top have the highest priority when retrieving a configuration value.

Example

Polymer discovers and loads, in order, the following contexts:

• system
• polymer
• extension_a
• extension_b
• project
• other
• process

The polymer and project contexts both specify the configuration value keyed by my.foo. polymer specifies it as my.foo=bar and project as my.foo=baz.

When the value my.foo is retrieved during runtime, the value baz is returned.

The process context

The process context is a special context that is always included at the top of the context stack. Any configuration that is set during runtime is stored in this context. That means any configuration set during runtime will override contexts with equivalent keys.

Discovering contexts

As the command is about to execute, Polymer initiates configuration compilation by discovering all available contexts, altering them, and finally compiling them, at which point the configuration is ready to be used.

Registered event subscribers can subscribe to the following:

• CollectConfigContextsEvent::class
• AlterConfigContextsEvent::class

For example, in an extension's service provider:

public function register(): void
{
    $container = $this->getContainer();
    $container->addShared('drupalConfigContextProvider', ContextProvidersSubscriber::class)
        ->addArgument(new ResolvableArgument('drupalFileSystem'));
}

public function boot(): void
{
    $container = $this->getContainer();
    $container->extend('eventDispatcher')
        ->addMethodCall('addSubscriber', ['drupalConfigContextProvider']);
}

And in ContextProvidersSubscriber:

public function addContexts(CollectConfigContextsEvent $event): void
{
    try {
        $this->drupalFileSystem->getDrupalRoot();
    } catch (\OutOfBoundsException $e) {
        // If Drupal root is not found, skip adding environment configuration.
        return;
    }
    $site = $event->getInput()->getOption('site');
    $environment = $event->getInput()->getOption('environment');
    $drupalConfig = [];
    $possibleConfigFiles = [];
    if (is_string($site) && in_array($site, $this->drupalFileSystem->getMultisiteDirs())) {
        $sitePath = $this->drupalFileSystem->getDrupalRoot() . '/sites/' . $site;
        $possibleConfigFiles['site'] =  $sitePath . '/polymer.yml';
        if (is_string($environment)) {
            $possibleConfigFiles['site_environment'] = $sitePath . '/' . $environment . '.polymer.yml';
        }
    }
    $possibleConfigFiles = array_filter($possibleConfigFiles, function ($file) {
        return file_exists($file);
    });
    foreach ($possibleConfigFiles as $configId => $file) {
        $loader = new YamlConfigLoader();
        $drupalConfig[$configId] = $loader->load($file)->export();
    }
    $event->addContexts($drupalConfig);
}

public static function getSubscribedEvents(): array
{
    $events = [
        CollectConfigContextsEvent::class => [
            ['addContexts', -1000]
        ],
    ];
    return $events;
}

The above will add the site and site_environment contexts to the configuration.

Tokenized values

Configuration values can be tokenized. For example, a context has foo.bar: ${my.config.key}. Assuming my.config.key can be resolved, foo.bar will be set to the value of my.config.key.