[Cache] PHP7.4 public typed properties cause cache clearing to crash

[tvandervorm]

Symfony version(s) affected: 4.*

Description

Clearing the cache when having a class with a public typed property (available from PHP 7.4) will cause the command to fail with the following error:

In ReflectionClassResource.php line 139:
                              
  [ErrorException]            
  Notice: Undefined index: bar  

Exception trace:
 () at /var/wwww/vendor/symfony/config/Resource/ReflectionClassResource.php:139
 Symfony\Component\Config\Resource\ReflectionClassResource->generateSignature() at /var/wwww/vendor/symfony/config/Resource/ReflectionClassResource.php:113
 Symfony\Component\Config\Resource\ReflectionClassResource->computeHash() at /var/wwww/vendor/symfony/config/Resource/ReflectionClassResource.php:52
 Symfony\Component\Config\Resource\ReflectionClassResource->isFresh() at /var/wwww/vendor/symfony/config/Resource/SelfCheckingResourceChecker.php:34
 Symfony\Component\Config\Resource\SelfCheckingResourceChecker->isFresh() at /var/wwww/vendor/symfony/config/ResourceCheckerConfigCache.php:99
 Symfony\Component\Config\ResourceCheckerConfigCache->isFresh() at /var/wwww/vendor/symfony/config/ConfigCache.php:60
 Symfony\Component\Config\ConfigCache->isFresh() at /var/wwww/vendor/symfony/http-kernel/Kernel.php:486
 Symfony\Component\HttpKernel\Kernel->initializeContainer() at /var/wwww/vendor/symfony/http-kernel/Kernel.php:133
 Symfony\Component\HttpKernel\Kernel->boot() at /var/wwww/vendor/symfony/framework-bundle/Console/Application.php:159
 Symfony\Bundle\FrameworkBundle\Console\Application->registerCommands() at /var/wwww/vendor/symfony/framework-bundle/Console/Application.php:65
 Symfony\Bundle\FrameworkBundle\Console\Application->doRun() at /var/wwww/vendor/symfony/console/Application.php:149
 Symfony\Component\Console\Application->run() at /var/wwww/bin/console:38

Where 'bar' is the name of the property. This is because the assumption is made that a default value is available for each property, which is null by default for untyped properties. However, for a typed property null is no longer a valid value, so it will be undefined instead. Undefined default values are missing from $class->getDefaultProperties(); when doing reflection, hence the 'undefined index' error.

How to reproduce

Generate a class like so:

namespace App;

class Foo {
    public int $bar;
} 

save it in src/Foo.php and run bin/console cache:clear. Requires PHP7.4

Possible Solution

The offending line is this one:

yield print_r($defaults[$p->name], true);

changing it so it accepts missing default values removes the error:

yield print_r($defaults[$p->name] ?? null, true);

Additional context

From the RFC:

Typed properties cannot have a null default value, unless the type is explicitly nullable (?Type). This is in contrast to parameter types, where a null default value automatically implies a nullable type. We consider this to be a legacy behavior, which we do not wish to support for newly introduced syntax.

[nicolas-grekas]

PHP 7.4 is WIP. Would you like to submit a PR to fix this issue?

[ksiatka]

Quick problem solving. (For example if you are upgrading from 3.4 -> 4.0)

Initialize variable with null directly:
public ?int $bar = null;