TYPO3: how to migrate userFunc TypoScript condition to Symfony Expression Language?

How can I migrate this TypoScript condition to be fully compatible with the Symfony Expression Language for conditions in TYPO3 9.5?

[userFunc = TYPO3\CMS\Core\Utility\ExtensionManagementUtility::isLoaded('fluid_styled_content')]

You'd have to provide your own functions at the moment.

There is a tutorial here: https://usetypo3.com/symfony-expression-language-in-typo3.html

But basically you'd have the file yourext/Configuration/ExpressionLanguage.php with content like:

<?php

return [
    'typoscript' => [
        \Vendor\Yourext\ExpressionLanguage\ConditionProvider::class
    ]
];

This registers a condition provider for the typoscript context.

For adding simple functions you need to set function provider classes to the expressionLanguageProviders of that class.

Which might look like this:

<?php

namespace Vendor\Yourext\ExpressionLanguage;

use TYPO3\CMS\Core\ExpressionLanguage\AbstractProvider;

class ConditionProvider extends AbstractProvider
{
    public function __construct()
    {
        $this->expressionLanguageProviders = [
            UtilitiesConditionFunctionsProvider::class,
            SomeOtherConditionFunctionsProvider::class,
            AThirdConditionFunctionsProvider::class,
        ];
    }
}

(Maybe even set it on the property directly, instead of using the constructor, but that's what I did).

Those function providers need to implement the \Symfony\Component\ExpressionLanguage\ExpressionFunctionProviderInterface interface, which is basically just a getFunctions method that needs to return an array of \Symfony\Component\ExpressionLanguage\ExpressionFunction instances.

My UtilitiesConditionFunctionsProvider looks like this:

<?php

namespace Vendor\Yourext\ExpressionLanguage;

use Symfony\Component\ExpressionLanguage\ExpressionFunction;
use Symfony\Component\ExpressionLanguage\ExpressionFunctionProviderInterface;
use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;

class UtilitiesConditionFunctionsProvider implements ExpressionFunctionProviderInterface
{

    /**
     * @return ExpressionFunction[] An array of Function instances
     */
    public function getFunctions()
    {
        return [
            $this->getIntersectsFunction(),
            $this->getExtensionLoadedFunction(),
        ];
    }

    /**
     * @return ExpressionFunction
     */
    protected function getIntersectsFunction()
    {
        return new ExpressionFunction('intersects', function () {
            // Not implemented, we only use the evaluator
        }, function ($arguments, $left, $right) {
            return count(array_intersect($left, $right)) > 0;
        });
    }

    protected function getExtensionLoadedFunction()
    {
        return new ExpressionFunction('loaded', function () {
            // Not implemented, we only use the evaluator
        }, function ($arguments, $extKey) {
            return ExtensionManagementUtility::isLoaded($extKey);
        });
    }
}

With that it's now possible to use intersects( ... ) and loaded( ... ) in my conditions.