Leverages#42149

We need extensive doc on the topic for sure, a whole new chapter.

DebugClassLoader allows patching an app or a lib by going through these steps:

• requiresymfony/error-handler if not already there
• runcomposer install -q --optimize-autoloader
• copy/paste the below script to the root of the app/lib, inpatch-types.php
• run the script withSYMFONY_PATCH_TYPE_DECLARATIONS='force=phpdoc' php patch-types.php

SYMFONY_PATCH_TYPE_DECLARATIONS can be set to:

• 'force=phpdoc' to copy@return annotations from parent classes, to express that the next major version of that lib is going to add a native return types;
• 'force=1' to turn@return annotations into native return types, but only on tests/private/final/internal methods;
• 'force=2' to turn@return annotations into native return types, for all possible methods.

<?phpif (false ===getenv('SYMFONY_PATCH_TYPE_DECLARATIONS')) {echo"Please define the SYMFONY_PATCH_TYPE_DECLARATIONS env var when running this script.\n";exit(1);}$loader =require__DIR__.'/vendor/autoload.php';Symfony\Component\ErrorHandler\DebugClassLoader::enable();foreach ($loader->getClassMap()as$class =>$file) {switch (true) {casefalse !==strpos($file =realpath($file),'/vendor/'):casefalse !==strpos($file,'/src/path-to-exclude/'):// add as many as requiredcontinue2;    }class_exists($class);}Symfony\Component\ErrorHandler\DebugClassLoader::checkClasses();