defined("Class::CONST") answers false and constant("Class::CONST") fatals in the eval bridge

[Guikingone]

defined("Class::CONST") answers false in the eval bridge, and constant("Class::CONST") fatals, where php resolves both.

Measured

<?php
class K { public const NAME = "k"; }
echo "defined_class_const:", (defined("K::NAME") ? "yes" : "no"), "\n";
echo "constant_class_const:", constant("K::NAME"), "\n";

• php -n 8.5.6 → defined_class_const:yes then constant_class_const:k
• eval bridge → defined_class_const:no, then Fatal error: eval() runtime failed: undefined constant "K::NAME"

Note the two halves fail differently: defined() is a SILENT wrong answer (a guard that should pass never does), constant() is a loud one.

Why it matters

Kernel::checkTrustedHeaders() style code guards with defined(Request::class."::HEADER_X") before configuring trusted headers, and throws InvalidArgumentException when the guard says no — so a false answer turns into a thrown exception several frames away from the cause. EventListener/DebugHandlersListener.php uses the same idiom.

A related case worth covering together, measured separately on this campaign: self::CONST and parent::CONST used inside a CLASS CONSTANT INITIALIZER fail before any code runs.