Howdy Internals, I discovered today (purely on accident) that class_exists($subject) actually parses the "$subect" class in question.
I was attempting to use class_exists(UsesPropertyPromotion::class) to determine if an attribute implementation existed in order to generate a PHP 8 appropriate class - else fall back to generating a PHP 7 appropriate class. For context, this check was being written for Symfony's MakerBundle which generates classes for Symfony projects. Consequently the conditional worked as expected in PHP 8, but in 7 I received a Parse Error. See the bug report https://bugs.php.net/bug.php?id=80938 for additional details. Nikic pointed out the problem (not a bug) is that w/ autoload === true, class_exists will load the class. The purpose of this email is to spark the conversation on a path forward for code bases that must support multiple versions of PHP and still be able to use native PHP functions without having to jump through hoops. It would appear from a userland standpoint that class_exist() is broken / unreliable if it must first be determined if the class being checked is compatible for the PHP version used at runtime. Which brings us to the chicken and the egg... At the very least this could be a "mental note" for RFC's that introduce changes that create BC in unexpected ways in userland. Cheers! Jesse Rushlow
