bug #36103 [DI] fix preloading script generation (nicolas-grekas)

This PR was merged into the 4.4 branch.

Discussion
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[DI] fix preloading script generation

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

(fabbot failure is a false positive)

On master, we should work on being able to preload more classes (esp. all cache-warmup artifacts).

But for 4.4, this is good enough. Submitted as a bug fix because 1. the current code that deals with preloading kinda-works, but only on "dev" mode... and 2. fixing it provides a nice boost!

Small bench on a hello world:
- before: 380 req/s
- after: 580 req/s

That's +50%!

Pro-tip: adding a few `class_exists()` as done in this PR for the classes that are always used in the implementations (e.g. `new Foo()` in the constructor) will help the preload-script generator to work optimally. Without them, it will discover the symbols to preload only if they're found on methods.

Some of those `class_exists()` are mandatory, in relation to anonymous classes and https://bugs.php.net/79349

Commits
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a10fc4da5d [DI] fix preloading script generation

Author: fabpot

Firewall/AnonymousAuthenticationListener.php

@@ -19,6 +19,9 @@
 use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorageInterface;
 use Symfony\Component\Security\Core\Exception\AuthenticationException;
 
+// Help opcache.preload discover always-needed symbols
+class_exists(AnonymousToken::class);
+
 /**
  * AnonymousAuthenticationListener automatically adds a Token if none is
  * already present.

Firewall/LegacyListenerTrait.php

@@ -15,6 +15,9 @@
 use Symfony\Component\HttpKernel\Event\GetResponseEvent;
 use Symfony\Component\HttpKernel\Event\RequestEvent;
 
+// Help opcache.preload discover always-needed symbols
+class_exists(RequestEvent::class);
+
 /**
  * @deprecated
  *