Hi Rafael, all form options are chainable by design (using the natural parent-child hierarchy and DI registration priority)

For example you can add a global type extension for EnumType, and do this:

$resolver->setDefault('choice_filter', function (Options $options, mixed $previousFilter): string {
    if (is_subclass_of($options['class'], DeprecationAwareInterface::class)) {
        return fn (DeprecationAwareInterface $myEnum) => !$myEnum->isDeprecated();
    }

    // Take default value configured in the base class
    return $previousValue;
});

Does this address your request?

Hi Yonel, nice, I didn't know this! But this only sets a default option, so if a developer defines a choice_filter on the field itself our extension is overwritten. I would like to define a default choice_filter which is always applied first. If it returns true it should step into the field-level choice_filter, if it's defined.

Probably it's somehow possible via DependencyInejction, maybe by decorating DefaultChoiceListFactory and creating a custom FilterChoiceLoaderDecorator, but I'd wish there's a simpler way to do this.

You could use setNormalizer() instead. It allows you to work with the user filter if provided, and then apply your own chaining strategy: default filters + user filters:

$resolver->setNormalizer('choice_filter', function (Options $options, mixed $userFilter) {
    return new CompositeChoiceFilter(...$this->defaultFilters, $userFilter);
});

Being $this->defaultFilters your custom list of filters (e.g. DI-based invokable services), then you can create your own CompositeChoiceFilter and iterate over all filters given.