Removed the setCrossingChar() method in favor of the setDefaultCrossingChar() method in TableStyle.

Removed the setHorizontalBorderChar() method in favor of the setDefaultCrossingChars() method in TableStyle.

Removed the getHorizontalBorderChar() method in favor of the getBorderChars() method in TableStyle.

Removed the setVerticalBorderChar() method in favor of the setVerticalBorderChars() method in TableStyle.

Removed the getVerticalBorderChar() method in favor of the getBorderChars() method in TableStyle.

The ProcessHelper::run() method takes the command as an array of arguments.

Before:

$processHelper->run($output, 'ls -l');

After:

$processHelper->run($output, array('ls', '-l'));

// alternatively, when a shell wrapper is required
$processHelper->run($output, Process::fromShellCommandline('ls -l'));

Removed support for using the format option of DateType and DateTimeType when the html5 option is enabled.

Using names for buttons that do not start with a letter, a digit, or an underscore leads to an exception.

Using names for buttons that do not contain only letters, digits, underscores, hyphens, and colons leads to an exception.

Using the date_format, date_widget, and time_widget options of the DateTimeType when the widget option is set to single_text is not supported anymore.

The getExtendedType() method was removed from the FormTypeExtensionInterface. It is replaced by the the static getExtendedTypes() method which must return an iterable of extended types.

Before:

class FooTypeExtension extends AbstractTypeExtension
{
    public function getExtendedType()
    {
        return FormType::class;
    }

    // ...
}

After:

class FooTypeExtension extends AbstractTypeExtension
{
    public static function getExtendedTypes(): iterable
    {
        return array(FormType::class);
    }

    // ...
}

The scale option was removed from the IntegerType.

The $scale argument of the IntegerToLocalizedStringTransformer was removed.

Calling FormRenderer::searchAndRenderBlock for fields which were already rendered throws an exception instead of returning empty strings:

Before:

{% for field in fieldsWithPotentialDuplicates %}
   {{ form_widget(field) }}
{% endfor %}

After:

{% for field in fieldsWithPotentialDuplicates if not field.rendered %}
   {{ form_widget(field) }}
{% endfor %}

The regions option was removed from the TimezoneType.

The project dir argument of the constructor of AssetsInstallCommand is required.

Removed support for bundle:controller:action syntax to reference controllers. Use serviceOrFqcn::method instead where serviceOrFqcn is either the service ID when using controllers as services or the FQCN of the controller.

Before:

bundle_controller:
    path: /
    defaults:
        _controller: FrameworkBundle:Redirect:redirect

After:

bundle_controller:
    path: /
    defaults:
        _controller: Symfony\Bundle\FrameworkBundle\Controller\RedirectController::redirectAction

Removed Symfony\Bundle\FrameworkBundle\Controller\ControllerNameParser.

Warming up a router in RouterCacheWarmer that does not implement the WarmableInterface is not supported anymore.

The RequestDataCollector class has been removed. Use the Symfony\Component\HttpKernel\DataCollector\RequestDataCollector class instead.

Removed Symfony\Bundle\FrameworkBundle\Controller\Controller. Use Symfony\Bundle\FrameworkBundle\Controller\AbstractController instead.

Added support for the SameSite attribute for session cookies. It is highly recommended to set this setting (framework.session.cookie_samesite) to lax for increased security against CSRF attacks.

The ContainerAwareCommand class has been removed, use Symfony\Component\Console\Command\Command with dependency injection instead.

The Templating\Helper\TranslatorHelper::transChoice() method has been removed, use the trans() one instead with a %count% parameter.

Removed support for legacy translations directories src/Resources/translations/ and src/Resources/<BundleName>/translations/, use translations/ instead.

Support for the legacy directory structure in translation:update and debug:translation commands has been removed.

Removed the "Psr\SimpleCache\CacheInterface" / "cache.app.simple" service, use "Symfony\Contracts\Cache\CacheInterface" / "cache.app" instead.

Removed the Process::setCommandline() and the PhpProcess::setPhpBinary() methods.

Commands must be defined as arrays when creating a Process instance.

Before:

$process = new Process('ls -l');

After:

$process = new Process(array('ls', '-l'));

// alternatively, when a shell wrapper is required
$process = Process::fromShellCommandline('ls -l');

The Role and SwitchUserRole classes have been removed.

The RoleHierarchyInterface has been removed.

The getReachableRoles() method of the RoleHierarchy class has been removed.

The getRoles() method has been removed from the TokenInterface. It has been replaced by the new getRoleNames() method.

The ContextListener::setLogoutOnUserChange() method has been removed.

The Symfony\Component\Security\Core\User\AdvancedUserInterface has been removed.

The ExpressionVoter::addExpressionLanguageProvider() method has been removed.

The FirewallMapInterface::getListeners() method must return an array of 3 elements, the 3rd one must be either a LogoutListener instance or null.

The AuthenticationTrustResolver constructor arguments have been removed.

A user object that is not an instance of UserInterface cannot be accessed from Security::getUser() anymore and returns null instead.

SimpleAuthenticatorInterface, SimpleFormAuthenticatorInterface, SimplePreAuthenticatorInterface, SimpleAuthenticationProvider, SimpleAuthenticationHandler, SimpleFormAuthenticationListener and SimplePreAuthenticationListener have been removed. Use Guard instead.

The ListenerInterface has been removed, turn your listeners into callables instead.

The Firewall::handleRequest() method has been removed, use Firewall::callListeners() instead.

\Serializable interface has been removed from AbstractToken and AuthenticationException, thus serialize() and unserialize() aren't available. Use getState() and setState() instead.

Before:

public function serialize()
{
    return [$this->myLocalVar, parent::serialize()];
}

public function unserialize($serialized)
{
    [$this->myLocalVar, $parentSerialized] = unserialize($serialized);
    parent::unserialize($parentSerialized);
}

After:

protected function getState(): array
{
    return [$this->myLocalVar, parent::getState()];
}

protected function setState(array $data)
{
    [$this->myLocalVar, $parentData] = $data;
    parent::setState($parentData);
}