PHP Warning: Constant already defined when processing multiple sources with __halt_compiler()

[ProgerXP]

Description

Whenever PHP processes more then one __halt_compiler() statement in one session, it emits this cryptic warning:

PHP Warning:  Constant  already defined in ...

Note the empty constant name.

There are several ways to trigger this. Here's one:

# echo '<?php __halt_compiler();' >inc.php
# php -a
php > include('inc.php');
php > include('inc.php');
PHP Warning:  Constant  already defined in /tmp/inc.php on line 1

Here's another:

# php -r "eval('?><?php __halt_compiler();'); eval('?><?php __halt_compiler();');"

PHP Version

PHP 8.4.5 (cli) (built: Mar 12 2025 16:58:15) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.4.5, Copyright (c) Zend Technologies

Operating System

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