UPGRADE FROM 3.x to 4.0

Symfony Framework

The first step to upgrade a Symfony 3.x application to 4.x is to update the file and directory structure of your application:

Symfony 3.x	Symfony 4.x
`app/config/`	`config/`
`app/config/*.yml`	`config/.yaml` and `config/packages/.yaml`
`app/config/parameters.yml.dist`	`config/services.yaml` and `.env.dist`
`app/config/parameters.yml`	`config/services.yaml` and `.env`
`app/Resources/<BundleName>/views/`	`templates/bundles/<BundleName>/`
`app/Resources/`	`src/Resources/`
`app/Resources/assets/`	`assets/`
`app/Resources/translations/`	`translations/`
`app/Resources/views/`	`templates/`
`src/AppBundle/`	`src/`
`var/logs/`	`var/log/`
`web/`	`public/`
`web/app.php`	`public/index.php`
`web/app_dev.php`	`public/index.php`

Then, upgrade the contents of your console script and your front controller:

bin/console: https://github.com/symfony/recipes/blob/master/symfony/console/3.3/bin/console
public/index.php: https://github.com/symfony/recipes/blob/master/symfony/framework-bundle/3.3/public/index.php

Lastly, read the following article to add Symfony Flex to your application and upgrade the configuration files: https://symfony.com/doc/current/setup/flex.html

If you use Symfony components instead of the whole framework, you can find below the upgrading instructions for each individual bundle and component.

ClassLoader

The component has been removed. Use Composer instead.

Config

The protected TreeBuilder::$builder property has been removed.

Console

Setting unknown style options is not supported anymore and throws an exception.

The QuestionHelper::setInputStream() method is removed. Use StreamableInputInterface::setStream() or CommandTester::setInputs() instead.

Before:

$input = new ArrayInput();

$questionHelper->setInputStream($stream);
$questionHelper->ask($input, $output, $question);

After:

$input = new ArrayInput();
$input->setStream($stream);

$questionHelper->ask($input, $output, $question);

Before:

$commandTester = new CommandTester($command);

$stream = fopen('php://memory', 'r+', false);
fputs($stream, "AppBundle\nYes");
rewind($stream);

$command->getHelper('question')->setInputStream($stream);

$commandTester->execute();

After:

$commandTester = new CommandTester($command);

$commandTester->setInputs(array('AppBundle', 'Yes'));

$commandTester->execute();

The console.exception event and the related ConsoleExceptionEvent class have been removed in favor of the console.error event and the ConsoleErrorEvent class.
The SymfonyQuestionHelper::ask default validation has been removed in favor of Question::setValidator.

Debug

The ContextErrorException class has been removed. Use \ErrorException instead.
FlattenException::getTrace() now returns additional type descriptions integer and float.
Support for stacked errors in the ErrorHandler has been removed

DependencyInjection

Definitions and aliases are now private by default in 4.0. You should either use service injection or explicitly define your services as public if you really need to inject the container.

Relying on service auto-registration while autowiring is not supported anymore. Explicitly inject your dependencies or create services whose ids are their fully-qualified class name.

Before:

namespace App\Controller;

use App\Mailer;

class DefaultController
{
    public function __construct(Mailer $mailer) {
        // ...
    }

    // ...
}

services:
    App\Controller\DefaultController:
        autowire: true

After:

// same PHP code

services:
    App\Controller\DefaultController:
        autowire: true

    # or
    # App\Controller\DefaultController:
    #     arguments: { $mailer: "@App\Mailer" }

    App\Mailer:
        autowire: true

Autowiring services based on the types they implement is not supported anymore. It will only look for an alias or a service id that matches a given FQCN. Rename (or alias) your services to their FQCN id to make them autowirable. In 3.4, you can activate this behavior instead of having deprecation messages by setting the following parameter:
```
parameters:
    container.autowiring.strict_mode: true
```
From 4.0, you can remove it as it's the default behavior and the parameter is not handled anymore.
_defaults and _instanceof are now reserved service names in Yaml configurations. Please rename any services with that names.
Non-numeric keys in methods and constructors arguments have never been supported and are now forbidden. Please remove them if you happen to have one.
Service names that start with an underscore are now reserved in Yaml files. Please rename any services with such names.

Autowiring-types have been removed, use aliases instead.

Before:

<service id="annotations.reader" class="Doctrine\Common\Annotations\AnnotationReader" public="false">
    <autowiring-type>Doctrine\Common\Annotations\Reader</autowiring-type>
</service>

After:

<service id="annotations.reader" class="Doctrine\Common\Annotations\AnnotationReader" public="false" />
<service id="Doctrine\Common\Annotations\Reader" alias="annotations.reader" public="false" />

Service identifiers and parameter names are now case sensitive.
The Reference and Alias classes do not make service identifiers lowercase anymore.
Using the PhpDumper with an uncompiled ContainerBuilder is not supported anymore.
Extending the containers generated by PhpDumper is not supported anymore.
The DefinitionDecorator class has been removed. Use the ChildDefinition class instead.
The ResolveDefinitionTemplatesPass class has been removed. Use the ResolveChildDefinitionsPass class instead.
Using unsupported configuration keys in YAML configuration files raises an exception.
Using unsupported options to configure service aliases raises an exception.
Setting or unsetting a service with the Container::set() method is no longer supported. Only synthetic services can be set or unset.
Checking the existence of a private service with the Container::has() method is no longer supported and will return false.
Requesting a private service with the Container::get() method is no longer supported.
The strict attribute in service arguments has been removed. The attribute is ignored since 3.0, so you can simply remove it.
Top-level anonymous services in XML are no longer supported.
The ExtensionCompilerPass has been moved to before-optimization passes with priority -1000.
In 3.4, parameter container.dumper.inline_class_loader was introduced. Unless you're using a custom autoloader, you should enable this parameter. This can drastically improve DX by reducing the time to load classes when the DebugClassLoader is enabled. If you're using FrameworkBundle, this performance improvement will also impact the "dev" environment:
```
parameters:
    container.dumper.inline_class_loader: true
```

DoctrineBridge

The Symfony\Bridge\Doctrine\HttpFoundation\DbalSessionHandler and Symfony\Bridge\Doctrine\HttpFoundation\DbalSessionHandlerSchema have been removed. Use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler instead.

EventDispatcher

The ContainerAwareEventDispatcher class has been removed. Use EventDispatcher with closure factories instead.
The reset() method has been added to TraceableEventDispatcherInterface.

ExpressionLanguage

The ability to pass a ParserCacheInterface instance to the ExpressionLanguage class has been removed. You should use the CacheItemPoolInterface interface instead.

Filesystem

The Symfony\Component\Filesystem\LockHandler has been removed, use the Symfony\Component\Lock\Store\FlockStore class or the Symfony\Component\Lock\Store\FlockStore\SemaphoreStore class directly instead.
Support for passing relative paths to Filesystem::makePathRelative() has been removed.

Finder

The ExceptionInterface has been removed.
The Symfony\Component\Finder\Iterator\FilterIterator class has been removed as it used to fix a bug which existed before version 5.5.23/5.6.7

Form

The values of the FormEvents::* constants have been updated to match the constant names. You should only update your application if you relied on the constant values instead of their names.
The choices_as_values option of the ChoiceType has been removed.
Support for data objects that implements both Traversable and ArrayAccess in ResizeFormListener::preSubmit method has been removed.

Using callable strings as choice options in ChoiceType is not supported anymore in favor of passing PropertyPath instances.

Before:

'choice_value' => new PropertyPath('range'),
'choice_label' => 'strtoupper',

After:

'choice_value' => 'range',
'choice_label' => function ($choice) {
    return strtoupper($choice);
},

Caching of the loaded ChoiceListInterface in the LazyChoiceList has been removed, it must be cached in the ChoiceLoaderInterface implementation instead.
Calling isValid() on a Form instance before submitting it is not supported anymore and raises an exception.

Before:
```
if ($form->isValid()) {
    // ...
}
```
After:
```
if ($form->isSubmitted() && $form->isValid()) {
    // ...
}
```

Using the "choices" option in CountryType, CurrencyType, LanguageType, LocaleType, and TimezoneType without overriding the choice_loader option is now ignored.

Before:

$builder->add('custom_locales', LocaleType::class, array(
    'choices' => $availableLocales,
));

After:

$builder->add('custom_locales', LocaleType::class, array(
    'choices' => $availableLocales,
    'choice_loader' => null,
));
// or
$builder->add('custom_locales', LocaleType::class, array(
    'choice_loader' => new CallbackChoiceLoader(function () {
        return $this->getAvailableLocales();
    }),
));

Removed ChoiceLoaderInterface implementation in TimezoneType. Use the "choice_loader" option instead.

Before:

class MyTimezoneType extends TimezoneType
{
    public function loadChoiceList()
    {
        // override the method
    }
}

After:

class MyTimezoneType extends AbstractType
{
    public function getParent()
    {
        return TimezoneType::class;
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefault('choice_loader', ...); // override the option instead
    }
}

FormRendererInterface::setTheme and FormRendererEngineInterface::setTheme have a new optional argument $useDefaultThemes with a default value set to true.

FrameworkBundle

The session.use_strict_mode option has been removed and strict mode is always enabled.
The validator.mapping.cache.doctrine.apc service has been removed.
The "framework.trusted_proxies" configuration option and the corresponding "kernel.trusted_proxies" parameter have been removed. Use the Request::setTrustedProxies() method in your front controller instead.
The default value of the framework.workflows.[name].type configuration options is now state_machine.
Support for absolute template paths has been removed.
The following form types registered as services have been removed; use their fully-qualified class name instead:
- "form.type.birthday"
- "form.type.checkbox"
- "form.type.collection"
- "form.type.country"
- "form.type.currency"
- "form.type.date"
- "form.type.datetime"
- "form.type.email"
- "form.type.file"
- "form.type.hidden"
- "form.type.integer"
- "form.type.language"
- "form.type.locale"
- "form.type.money"
- "form.type.number"
- "form.type.password"
- "form.type.percent"
- "form.type.radio"
- "form.type.range"
- "form.type.repeated"
- "form.type.search"
- "form.type.textarea"
- "form.type.text"
- "form.type.time"
- "form.type.timezone"
- "form.type.url"
- "form.type.button"
- "form.type.submit"
- "form.type.reset"
The framework.serializer.cache option and the services serializer.mapping.cache.apc and serializer.mapping.cache.doctrine.apc have been removed. APCu should now be automatically used when available.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\CompilerDebugDumpPass has been removed.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddConsoleCommandPass has been removed. Use Symfony\Component\Console\DependencyInjection\AddConsoleCommandPass instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\SerializerPass class has been removed. Use the Symfony\Component\Serializer\DependencyInjection\SerializerPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\FormPass class has been removed. Use the Symfony\Component\Form\DependencyInjection\FormPass class instead.
The Symfony\Bundle\FrameworkBundle\EventListener\SessionListener class has been removed. Use the Symfony\Component\HttpKernel\EventListener\SessionListener class instead.
The Symfony\Bundle\FrameworkBundle\EventListener\TestSessionListener class has been removed. Use the Symfony\Component\HttpKernel\EventListener\TestSessionListener class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\ConfigCachePass class has been removed. Use tagged iterator arguments instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\PropertyInfoPass class has been removed. Use the Symfony\Component\PropertyInfo\DependencyInjection\PropertyInfoPass class instead.
Class parameters related to routing have been removed
- router.options.generator_class
- router.options.generator_base_class
- router.options.generator_dumper_class
- router.options.matcher_class
- router.options.matcher_base_class
- router.options.matcher_dumper_class
- router.options.matcher.cache_class
- router.options.generator.cache_class
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\ControllerArgumentValueResolverPass class has been removed. Use the Symfony\Component\HttpKernel\DependencyInjection\ControllerArgumentValueResolverPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\RoutingResolverPass class has been removed. Use the Symfony\Component\Routing\DependencyInjection\RoutingResolverPass class instead.
The Symfony\Bundle\FrameworkBundle\Translation\Translator constructor now takes the default locale as mandatory 3rd argument.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddValidatorInitializersPass class has been removed. Use the Symfony\Component\Validator\DependencyInjection\AddValidatorInitializersPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddConstraintValidatorsPass class has been removed. Use the Symfony\Component\Validator\DependencyInjection\AddConstraintValidatorsPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\ValidateWorkflowsPass class has been removed. Use the Symfony\Component\Workflow\DependencyInjection\ValidateWorkflowsPass class instead.
Using the KERNEL_DIR environment variable and the automatic guessing based on the phpunit.xml file location have been removed from the KernelTestCase::getKernelClass() method implementation. Set the KERNEL_CLASS environment variable to the fully-qualified class name of your Kernel or override the KernelTestCase::createKernel() or KernelTestCase::getKernelClass() method instead.
The methods KernelTestCase::getPhpUnitXmlDir() and KernelTestCase::getPhpUnitCliConfigArgument() have been removed.
The Symfony\Bundle\FrameworkBundle\Validator\ConstraintValidatorFactory class has been removed. Use Symfony\Component\Validator\ContainerConstraintValidatorFactory instead.
The --no-prefix option of the translation:update command has been removed.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddCacheClearerPass class has been removed. Use tagged iterator arguments instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\AddCacheWarmerPass class has been removed. Use tagged iterator arguments instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\TranslationDumperPass class has been removed. Use the Symfony\Component\Translation\DependencyInjection\TranslationDumperPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\TranslationExtractorPass class has been removed. Use the Symfony\Component\Translation\DependencyInjection\TranslationExtractorPass class instead.
The Symfony\Bundle\FrameworkBundle\DependencyInjection\Compiler\TranslatorPass class has been removed. Use the Symfony\Component\Translation\DependencyInjection\TranslatorPass class instead.
The Symfony\Bundle\FrameworkBundle\Translation\TranslationLoader class has been deprecated and will be removed in 4.0. Use the Symfony\Component\Translation\Reader\TranslationReader class instead.
The translation.loader service has been removed. Use the translation.reader service instead.
AssetsInstallCommand::__construct() now requires an instance of Symfony\Component\Filesystem\Filesystem as first argument.
CacheClearCommand::__construct() now requires an instance of Symfony\Component\HttpKernel\CacheClearer\CacheClearerInterface as first argument.
CachePoolClearCommand::__construct() now requires an instance of Symfony\Component\HttpKernel\CacheClearer\Psr6CacheClearer as first argument.
EventDispatcherDebugCommand::__construct() now requires an instance of Symfony\Component\EventDispatcher\EventDispatcherInterface as first argument.
RouterDebugCommand::__construct() now requires an instance of Symfony\Component\Routing\RouterInterface as first argument.
RouterMatchCommand::__construct() now requires an instance of Symfony\Component\Routing\RouterInterface as first argument.
TranslationDebugCommand::__construct() now requires an instance of Symfony\Component\Translation\TranslatorInterface as first argument.
TranslationUpdateCommand::__construct() now requires an instance of Symfony\Component\Translation\TranslatorInterface as first argument.
The Symfony\Bundle\FrameworkBundle\Translation\PhpExtractor class has been deprecated and will be removed in 4.0. Use the Symfony\Component\Translation\Extractor\PhpExtractor class instead.
The Symfony\Bundle\FrameworkBundle\Translation\PhpStringTokenParser class has been deprecated and will be removed in 4.0. Use the Symfony\Component\Translation\Extractor\PhpStringTokenParser class instead.

HttpFoundation

The Request::setTrustedProxies() method takes a new $trustedHeaderSet argument. See http://symfony.com/doc/current/components/http_foundation/trusting_proxies.html for more info.
The Request::setTrustedHeaderName() and Request::getTrustedHeaderName() methods have been removed.
Extending the following methods of Response is no longer possible (these methods are now final):
- setDate/getDate
- setExpires/getExpires
- setLastModified/getLastModified
- setProtocolVersion/getProtocolVersion
- setStatusCode/getStatusCode
- setCharset/getCharset
- setPrivate/setPublic
- getAge
- getMaxAge/setMaxAge
- setSharedMaxAge
- getTtl/setTtl
- setClientTtl
- getEtag/setEtag
- hasVary/getVary/setVary
- isInvalid/isSuccessful/isRedirection/isClientError/isServerError
- isOk/isForbidden/isNotFound/isRedirect/isEmpty
The ability to check only for cacheable HTTP methods using Request::isMethodSafe() is not supported anymore, use Request::isMethodCacheable() instead.
The Symfony\Component\HttpFoundation\Session\Storage\Handler\WriteCheckSessionHandler class has been removed. Implement SessionUpdateTimestampHandlerInterface or extend AbstractSessionHandler instead.
The Symfony\Component\HttpFoundation\Session\Storage\Handler\NativeSessionHandler and Symfony\Component\HttpFoundation\Session\Storage\Proxy\NativeProxy classes have been removed.
The Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler does not work with the legacy mongo extension anymore. It requires mongodb/mongodb package and ext-mongodb.
The Symfony\Component\HttpFoundation\Session\Storage\Handler\MemcacheSessionHandler class has been removed. Use Symfony\Component\HttpFoundation\Session\Storage\Handler\MemcachedSessionHandler instead.

HttpKernel

Bundle inheritance has been removed.

Relying on convention-based commands discovery is not supported anymore. Use PSR-4 based service discovery instead.

Before:

# app/config/services.yml
services:
    # ...

    # implicit registration of all commands in the `Command` folder

After:

# app/config/services.yml
services:
    # ...

    # explicit commands registration
    AppBundle\Command\:
        resource: '../../src/AppBundle/Command/*'
        tags: ['console.command']

The Extension::addClassesToCompile() and Extension::getClassesToCompile() methods have been removed.
Possibility to pass non-scalar values as URI attributes to the ESI and SSI renderers has been removed. The inline fragment renderer should be used with non-scalar attributes.
The ControllerResolver::getArguments() method has been removed. If you have your own ControllerResolverInterface implementation, you should inject an ArgumentResolverInterface instance.
The DataCollector::varToString() method has been removed in favor of cloneVar().
The Psr6CacheClearer::addPool() method has been removed. Pass an array of pools indexed by name to the constructor instead.
The LazyLoadingFragmentHandler::addRendererService() method has been removed.
The X-Status-Code header method of setting a custom status code in the response when handling exceptions has been removed. There is now a new GetResponseForExceptionEvent::allowCustomResponseCode() method instead, which will tell the Kernel to use the response code set on the event's response object.
The Kernel::getEnvParameters() method has been removed.
The SYMFONY__ environment variables are no longer processed automatically by Symfony. Use the %env()% syntax to get the value of any environment variable from configuration files instead.
The getCacheDir() method of your kernel should not be called while building the container. Use the %kernel.cache_dir% parameter instead. Not doing so may break the cache:clear command.
The Symfony\Component\HttpKernel\Config\EnvParametersResource class has been removed.
The reset() method has been added to Symfony\Component\HttpKernel\DataCollector\DataCollectorInterface.
The clear() method has been added to Symfony\Component\HttpKernel\Log\DebugLoggerInterface.
The ChainCacheClearer::add() method has been removed, inject the list of clearers as a constructor argument instead.
The CacheWarmerAggregate::add() and setWarmers() methods have been removed, inject the list of clearers as a constructor argument instead.
The CacheWarmerAggregate and ChainCacheClearer classes have been made final.

Ldap

The RenameEntryInterface has been removed, and merged with EntryManagerInterface

Process

Passing a not existing working directory to the constructor of the Symfony\Component\Process\Process class is not supported anymore.
The Symfony\Component\Process\ProcessBuilder class has been removed, use the Symfony\Component\Process\Process class directly instead.
The ProcessUtils::escapeArgument() method has been removed, use a command line array or give env vars to the Process::start/run() method instead.
Environment variables are always inherited in sub-processes.
Configuring proc_open() options has been removed.
Configuring Windows and sigchild compatibility is not possible anymore - they are always enabled.
Extending Process::run(), Process::mustRun() and Process::restart() is not supported anymore.
The getEnhanceWindowsCompatibility() and setEnhanceWindowsCompatibility() methods of the Process class have been removed.

Profiler

The profiler.matcher option has been removed.

ProxyManager

The ProxyDumper class has been made final

Security

The RoleInterface has been removed. Extend the Symfony\Component\Security\Core\Role\Role class instead.
The LogoutUrlGenerator::registerListener() method expects a 6th string $context = null argument.
The AccessDecisionManager::setVoters() method has been removed. Pass the voters to the constructor instead.
Support for defining voters that don't implement the VoterInterface has been removed.
Calling ContextListener::setLogoutOnUserChange(false) won't have any effect anymore.
Removed the HTTP digest authentication system. The NonceExpiredException, DigestAuthenticationListener and DigestAuthenticationEntryPoint classes have been removed. Use another authentication system like http_basic instead.
The GuardAuthenticatorInterface interface has been removed. Use AuthenticatorInterface instead.
When extending AbstractGuardAuthenticator getCredentials() cannot return null anymore, return false from supports() if no credentials available instead.

SecurityBundle

The FirewallContext::getContext() method has been removed, use the getListeners() and/or getExceptionListener() method instead.
The FirewallMap::$map and $container properties have been removed.
The UserPasswordEncoderCommand class does not allow null as the first argument anymore.
UserPasswordEncoderCommand does not extend ContainerAwareCommand nor implement ContainerAwareInterface anymore.
InitAclCommand has been removed. Use Symfony\Bundle\AclBundle\Command\InitAclCommand instead
SetAclCommand has been removed. Use Symfony\Bundle\AclBundle\Command\SetAclCommand instead
The firewall option logout_on_user_change is now always true, which will trigger a logout if the user changes between requests.
Removed the HTTP digest authentication system. The HttpDigestFactory class has been removed. Use another authentication system like http_basic instead.
The switch_user.stateless option is now always true if the firewall is stateless.
Not configuring explicitly the provider on a firewall is ambiguous when there is more than one registered provider. The first configured provider is not used anymore and an exception is thrown instead. Explicitly configure the provider to use on your firewalls.

Serializer

The ability to pass a Doctrine Cache instance to the ClassMetadataFactory class has been removed. You should use the CacheClassMetadataFactory class instead.
Not defining the 6th argument $format = null of the AbstractNormalizer::instantiateObject() method when overriding it is not supported anymore.
Extending ChainDecoder, ChainEncoder, ArrayDenormalizer is not supported anymore.

Translation

Removed the backup feature from the file dumper classes.
The default value of the $readerServiceId argument of TranslatorPass::__construct() has been changed to "translation.reader".
Removed Symfony\Component\Translation\Writer\TranslationWriter::writeTranslations, use Symfony\Component\Translation\Writer\TranslationWriter::write instead.
Removed support for passing Symfony\Component\Translation\MessageSelector as a second argument to the Translator::__construct(). You should pass an instance of Symfony\Component\Translation\Formatter\MessageFormatterInterface instead.

TwigBundle

The ContainerAwareRuntimeLoader class has been removed. Use the Twig Twig_ContainerRuntimeLoader class instead.
Removed DebugCommand in favor of Symfony\Bridge\Twig\Command\DebugCommand.
Removed ContainerAwareInterface implementation in Symfony\Bundle\TwigBundle\Command\LintCommand.

TwigBridge

removed the Symfony\Bridge\Twig\Form\TwigRenderer class, use the FormRenderer class from the Form component instead

Removed the possibility to inject the Form TwigRenderer into the FormExtension. Upgrade Twig to ^1.30, inject the Twig_Environment into the TwigRendererEngine and load the TwigRenderer using the Twig_FactoryRuntimeLoader instead.

Before:

use Symfony\Bridge\Twig\Extension\FormExtension;
use Symfony\Bridge\Twig\Form\TwigRenderer;
use Symfony\Bridge\Twig\Form\TwigRendererEngine;

// ...
$rendererEngine = new TwigRendererEngine(array('form_div_layout.html.twig'));
$rendererEngine->setEnvironment($twig);
$twig->addExtension(new FormExtension(new TwigRenderer($rendererEngine, $csrfTokenManager)));

After:

$rendererEngine = new TwigRendererEngine(array('form_div_layout.html.twig'), $twig);
$twig->addRuntimeLoader(new \Twig_FactoryRuntimeLoader(array(
    TwigRenderer::class => function () use ($rendererEngine, $csrfTokenManager) {
        return new TwigRenderer($rendererEngine, $csrfTokenManager);
    },
)));
$twig->addExtension(new FormExtension());

Removed the TwigRendererEngineInterface interface.
The TwigRendererEngine::setEnvironment() method has been removed. Pass the Twig Environment as second argument of the constructor instead.
Removed DebugCommand::set/getTwigEnvironment. Pass an instance of Twig\Environment as first argument of the constructor instead.
Removed LintCommand::set/getTwigEnvironment. Pass an instance of Twig\Environment as first argument of the constructor instead.

Validator

The default value of the strict option of the Choice constraint was changed to true. Using any other value will throw an exception.
The DateTimeValidator::PATTERN constant was removed.

Tests\Constraints\AbstractConstraintValidatorTest has been removed in favor of Test\ConstraintValidatorTestCase.

Before:

// ...
use Symfony\Component\Validator\Tests\Constraints\AbstractConstraintValidatorTest;

class MyCustomValidatorTest extends AbstractConstraintValidatorTest
{
    // ...
}

After:

// ...
use Symfony\Component\Validator\Test\ConstraintValidatorTestCase;

class MyCustomValidatorTest extends ConstraintValidatorTestCase
{
    // ...
}

Setting the checkDNS option of the Url constraint to true is dropped in favor of Url::CHECK_DNS_TYPE_* constants values.

Before:
```
$constraint = new Url(['checkDNS' => true]);
```
After:
```
$constraint = new Url(['checkDNS' => Url::CHECK_DNS_TYPE_ANY]);
```

VarDumper

The VarDumperTestTrait::assertDumpEquals() method expects a 3rd $context = null argument and moves $message = '' argument at 4th position.

Before:

VarDumperTestTrait::assertDumpEquals($dump, $data, $message = '');

After:

VarDumperTestTrait::assertDumpEquals($dump, $data, $filter = 0, $message = '');

The VarDumperTestTrait::assertDumpMatchesFormat() method expects a 3rd $context = null argument and moves $message = '' argument at 4th position.

Before:

VarDumperTestTrait::assertDumpMatchesFormat($dump, $data, $message = '');

After:

VarDumperTestTrait::assertDumpMatchesFormat($dump, $data, $filter = 0, $message = '');

WebProfilerBundle

Removed the getTemplates() method of the TemplateManager class in favor of the getNames() method

Workflow

Removed class name support in WorkflowRegistry::add() as second parameter.

Yaml

Support for the !str tag was removed, use the !!str tag instead.
Starting an unquoted string with a question mark followed by a space throws a ParseException.
Removed support for implicitly parsing non-string mapping keys as strings. Mapping keys that are no strings will result in a ParseException. Use quotes to opt-in for keys to be parsed as strings.

Before:
```
$yaml = <<<YAML
null: null key
true: boolean true
2.0: float key
YAML;

Yaml::parse($yaml);
```
After:
```
$yaml = <<<YAML
"null": null key
"true": boolean true
"2.0": float key
YAML;

Yaml::parse($yaml);
```

Removed the Yaml::PARSE_KEYS_AS_STRINGS flag.

Before:

$yaml = <<<YAML
null: null key
true: boolean true
2.0: float key
YAML;

Yaml::parse($yaml, Yaml::PARSE_KEYS_AS_STRINGS);

After:

$yaml = <<<YAML
"null": null key
"true": boolean true
"2.0": float key
YAML;

Yaml::parse($yaml);

Omitting the key of a mapping is not supported anymore and throws a ParseException.
Mappings with a colon (:) that is not followed by a whitespace are not supported anymore and lead to a ParseException(e.g. foo:bar must be foo: bar).
Starting an unquoted string with % leads to a ParseException.
The Dumper::setIndentation() method was removed. Pass the indentation level to the constructor instead.
Removed support for passing true/false as the second argument to the parse() method to trigger exceptions when an invalid type was passed.

Before:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', true);
```
After:
```
Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE);
```

Removed support for passing true/false as the third argument to the parse() method to toggle object support.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT);

Removed support for passing true/false as the fourth argument to the parse() method to parse objects as maps.

Before:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', false, false, true);

After:

Yaml::parse('{ "foo": "bar", "fiz": "cat" }', Yaml::PARSE_OBJECT_FOR_MAP);

Removed support for passing true/false as the fourth argument to the dump() method to trigger exceptions when an invalid type was passed.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE);

Removed support for passing true/false as the fifth argument to the dump() method to toggle object support.

Before:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, true);

After:

Yaml::dump(array('foo' => new A(), 'bar' => 1), 0, 0, false, Yaml::DUMP_OBJECT);

The !!php/object tag to indicate dumped PHP objects was removed in favor of the !php/object tag.
Duplicate mapping keys lead to a ParseException.
The constructor arguments $offset, $totalNumberOfLines and $skippedLineNumbers of the Parser class were removed.
The behavior of the non-specific tag ! is changed and now forces non-evaluating your values.
The !php/object: tag was removed in favor of the !php/object tag (without the colon).
The !php/const: tag was removed in favor of the !php/const tag (without the colon).

Before:
```
!php/const:PHP_INT_MAX
```
After:
```
!php/const PHP_INT_MAX
```

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UPGRADE-4.0.md

UPGRADE-4.0.md

UPGRADE FROM 3.x to 4.0

Symfony Framework

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Debug

DependencyInjection

DoctrineBridge

EventDispatcher

ExpressionLanguage

Filesystem

Finder

Form

FrameworkBundle

HttpFoundation

HttpKernel

Ldap

Process

Profiler

ProxyManager

Security

SecurityBundle

Serializer

Translation

TwigBundle

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Validator

VarDumper

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Workflow

Yaml

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UPGRADE-4.0.md

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UPGRADE-4.0.md

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UPGRADE FROM 3.x to 4.0

Symfony Framework

ClassLoader

Config

Console

Debug

DependencyInjection

DoctrineBridge

EventDispatcher

ExpressionLanguage

Filesystem

Finder

Form

FrameworkBundle

HttpFoundation

HttpKernel

Ldap

Process

Profiler

ProxyManager

Security

SecurityBundle

Serializer

Translation

TwigBundle

TwigBridge

Validator

VarDumper

WebProfilerBundle

Workflow

Yaml