Memory leak in anonymous function usage on PHP 7.4

[bytestream]

• Laravel Version: 6.18.4
• PHP Version: 7.4.5
• Database Driver & Version:

Description:

Re-opening #30736 with the intention of starting a new discussion based on new information.

Since that issue I have opened a PHP bug report: https://bugs.php.net/bug.php?id=79519

Nikita identified a possible explanation for the increase in PHP 7.4:

PHP 7.4 fixed some issues related to anonymous functions "overwriting" previous anonymous functions in the same file under some circumstances. Unfortunately this also means that this leak is now more pronounced, because this accidental destruction vector no longer exists.

I'm not familiar with Laravel's system, but it can probably be addressed there by making that the includes are memoized.

The fix identified in the previous bug report noted the fix upstream - symfony/symfony#32236. That seems like a very narrow fix to me given the wide spread usage of closures in Laravel.

Is it necessary to re - include routes and factories on every test?

I had a quick play with Eloquent Factory usage and the results were a fairly positive step in the right direction:

    /**
     * Resolved Eloquent factory instance.
     *
     * @var EloquentFactory
     */
    protected static $factory;

    /**
     * Register the Eloquent factory instance in the container.
     *
     * @return void
     */
    protected function registerEloquentFactory()
    {
        $this->app->singleton(FakerGenerator::class, function ($app, $parameters) {
            $locale = $parameters['locale'] ?? $app['config']->get('app.faker_locale', 'en_US');

            if (! isset(static::$fakers[$locale])) {
                static::$fakers[$locale] = FakerFactory::create($locale);
            }

            static::$fakers[$locale]->unique(true);

            return static::$fakers[$locale];
        });

        $this->app->singleton(EloquentFactory::class, function ($app) {
            if (isset(static::$factory)) {
                return static::$factory;
            }

            return static::$factory = EloquentFactory::construct(
                $app->make(FakerGenerator::class),
                $this->app->databasePath('factories')
            );
        });
    }

This cut phpunit memory usage from 3.86 G to 2.6G and my entire test suite still passes but I'm not sure if there's any side effects. I assume similar changes for routes would have a positive effect also.

Welcome to close if you don't intend to fix but your opinion on side effects would be appreciated. This new information should also help others who were reporting high memory usage on the other issue.