Feature: #108508 - PSR-14 events for Fluid components

Description

Three PSR-14 events have been added to influence the processing and rendering of Fluid components that are registered using the new configuration file (see Fluid components integration).

ModifyComponentDefinitionEvent

The \ModifyComponentDefinitionEvent can be used to modify the definition of a component before it's written to the cache. Component definitions must not have any dependencies on runtime information, as they might be used for static analysis or IDE auto-completion. Due to the component definitions cache, this is already enforced, as the registered events are only executed once and not on every request.

Example:

EXT:my_extension/Classes/EventListener/ModifyComponentDefinitionListener.php

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\EventListener;

use TYPO3\CMS\Core\Attribute\AsEventListener;
use TYPO3\CMS\Fluid\Event\ModifyComponentDefinitionEvent;
use TYPO3Fluid\Fluid\Core\Component\ComponentDefinition;
use TYPO3Fluid\Fluid\Core\ViewHelper\ArgumentDefinition;

#[AsEventListener]
final readonly class ModifyComponentDefinitionListener
{
    public function __invoke(ModifyComponentDefinitionEvent $event): void
    {
        // Add required argument to one specific component
        if (
            $event->getNamespace() === 'MyVendor\\MyExtension\\Components' &&
            $event->getComponentDefinition()->getName() === 'myComponent'
        ) {
            $originalDefinition = $event->getComponentDefinition();
            $event->setComponentDefinition(new ComponentDefinition(
                $originalDefinition->getName(),
                [
                    ...$originalDefinition->getArgumentDefinitions(),
                    'myArgument' => new ArgumentDefinition('myArgument', 'string', '', true),
                ],
                $originalDefinition->additionalArgumentsAllowed(),
                $originalDefinition->getAvailableSlots(),
            ));
        }
    }
}

ProvideStaticVariablesToComponentEvent

The \ProvideStaticVariablesToComponentEvent can be used to inject additional static variables into component templates. As with the \ModifyComponentDefinitionEvent, these variables must not have any dependencies on runtime information, as they might be used for static analysis or IDE auto-completion. The \RenderComponentEvent can be used to add variables with runtime dependencies.

Valid use cases for this event might be:

providing static (!) design tokens (colors, icons, ...) to all components in a collection
generating prefix strings based on the component's name

Example:

        EXT:my_extension/Classes/EventListener/ProvideStaticVariablesToComponentListener.php
    

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\EventListener;

use TYPO3\CMS\Core\Attribute\AsEventListener;
use TYPO3\CMS\Fluid\Event\ProvideStaticVariablesToComponentEvent;

#[AsEventListener]
final readonly class ProvideStaticVariablesToComponentListener
{
    public function __invoke(ProvideStaticVariablesToComponentEvent $event): void
    {
        // Provide design tokens to all components in a collection
        if ($event->getComponentCollection()->getNamespace() === 'MyVendor\\MyExtension\\Components') {
            $event->setStaticVariables([
                ...$event->getStaticVariables(),
                'designTokens' => [
                    'color1' => '#abcdef',
                    'color2' => '#123456',
                ],
            ]);
        }
    }
}

RenderComponentEvent

The \RenderComponentEvent can be used to alter or replace the rendering of Fluid components. There are three possible use cases:

fully take over the rendering of components by filling the $renderedContent with $event->setRenderedContent(). The first event that does this skips all following event listeners.
provide additional arguments (= variables in the component template) or slots to the component with $event->setArguments()/$event->setSlots().
execute additional code that doesn't influence the component rendering directly, e. g. adding certain frontend assets to the page automatically.

Example:

EXT:my_extension/Classes/EventListener/RenderComponentListener.php

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\EventListener;

use TYPO3\CMS\Core\Attribute\AsEventListener;
use TYPO3\CMS\Core\Page\AssetCollector;
use TYPO3\CMS\Fluid\Event\RenderComponentEvent;

#[AsEventListener]
final readonly class RenderComponentListener
{
    public function __construct(private AssetCollector $assetCollector) {}

    public function __invoke(RenderComponentEvent $event): void
    {
        // Add bundled components CSS if a component is used on the page
        if ($event->getComponentCollection()->getNamespace() === 'MyVendor\\MyExtension\\Components') {
            $this->assetCollector->addStyleSheet(
                'componentsBundle',
                'EXT:my_extension/Resources/Public/ComponentsBundle.css'
            );
        }
    }
}

Impact

Three new PSR-14 events can be used to influence the processing and rendering of Fluid components.