New in Symfony 2.8: Final improvements

Added a non-static API for the CssSelector component

Contributed by Christophe Coevoet in #15934

In Symfony 2.7, the CssSelector component exposed a static API to convert the CSS selectors into XPath expressions. In Symfony 2.8, we added a new non-static API:

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// Before
use Symfony\Component\CssSelector\CssSelector;

$expression = CssSelector::toXPath('div.item > h4 > a');

// After
use Symfony\Component\CssSelector\CssSelectorConverter;

$converter = new CssSelectorConverter();
$expression = $converter->toXPath('div.item > h4 > a');

This new API allows to keep a reference to the Converter object and all its internal object graph, which in some situations may be faster than recreating everything whenever you perform a conversion.

Besides, HTML is now selected as the default format. If you are working with XML contents, pass false as the argument of the CssSelectorConverter class:

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// Before
use Symfony\Component\CssSelector\CssSelectorConverter;

$converter = new CssSelectorConverter(false);
$expression = $converter->toXPath('items > item > title');

This component is mostly used by Symfony developers through the DomCrawler component in their tests. In that case, this change doesn't affect you in any way and you don't have to make any additional change.

Added domain exceptions to the Console component

Contributed by Jérôme Tamarelle in #14894

The Console component used generic PHP exceptions such as InvalidArgumentException and LogicException. In Symfony 2.8, to make the component consistent with other parts of the framework, custom exceptions are used.

These "domain exceptions" allow to generate better error messages. For example, when some command wasn't found, in some places we just threw this exception:

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throw new \InvalidArgumentException($message);

Now, we throw this other custom exception which allows to define a series of alternative commands with similar names to the one not found:

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throw new CommandNotFoundException($message, $alternatives);

These are the first custom exceptions defined for the Console component:

• CommandNotFoundException
• ExceptionInterface
• InvalidArgumentException
• InvalidOptionException
• LogicException
• RuntimeException

Added a new ClassCache cache warmer

Contributed by Tugdual Saunier in #16263

In order to improve performance and reduce I/O load, Symfony generates a big classes.php file in the cache with the contents of the most accessed classes. Bundles, including yours, can add new classes to this file through the addClassesToCompile() method.

In Symfony 2.8, we added a new cache warmer that generates this classes.php file. This new warmer removes the known slowness of the first hit to a Symfony application (even when cache has been warmed up). Besides, this feature also allows to make a Symfony application runnable on a read-only filesystem (such as in a Docker container for example).

Allowed to warm up Twig templates in non-standard paths

Contributed by Kevin Bond in #14764

As you may know, Symfony applications can define custom Twig namespaces. Suppose that you're using some third-party library that includes Twig templates that live in vendor/acme/foo-bar/templates. You can refer to those templates as @foo_bar/<template-name> if you define the following configuration:

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# app/config/config.yml
twig:
    # ...
    paths:
        "%kernel.root_dir%/../vendor/acme/foo-bar/templates": foo_bar

In Symfony 2.8, the templates defined under those custom namespaces will be automatically compiled during cache warm up. This will result in a (minor) performance improvement.

Allowed to configure a user checker per firewall

Contributed by Lynn van der Berg in #14721

During the authentication of a user, additional checks might be required to verify if the identified user is allowed to log in. Symfony performs these checks with classes that implement the Symfony\Component\Security\Core\UserCheckerInterface. This interface defines two methods called checkPreAuth() and checkPostAuth() to perform checks before and after user authentication.

In Symfony 2.8, these user checkers became more useful because you can use a custom user checker per firewall thanks to the new user_checker option:

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services:
    app.admin_user_checker:
        class: App\Security\AdminUserChecker
        arguments:
            - "@request_stack"

security:
    firewalls:
        secured_area:
            pattern: ^/admin
            # ...
            user_checker: app.admin_user_checker

Allowed to retrieve the priority of an event listener

Contributed by Fabien Potencier in #16198

One of the most common feature requests for the EventDispatcher component was to add a method to retrieve the priority of the given event listener. In Symfony 2.8 we finally included this method, called getListenerPriority() to the different EventDispatcher implementations.

This will help you figure out which priority is needed to override another event listener without digging in the sources. The first argument of the new method is the event name and the second argument is the listener:

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$eventDispatcher->addListener('post.published', $listener, -10);
$priority = $eventDispatcher->getListenerPriority('post.published', $listener);
// $priority = -10

$priority = $eventDispatcher->getListenerPriority('wrong_event', $listener);
// $priority = null